Smore dat spension tak bout R kaas........
09-20-2002, 10:24 PM
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Smore dat spension tak bout R kaas........
Having fully baked my analysis of the whole JDM vs NA spring rate thing a while back - it wound up like this in case you lost interest before the punchline:
Ok, here's my summary of what some of us have gotten used to referring to as JDM vs NA Spring Rate Question. This is a very general treatment with no specific data or worksheets, beginning from the basics. It will clarify the issues, and resolve the mystery. Everything written is in the context of a real racing driver driving a real racing car on a real race track with the singleminded purpose of going as fast as they can.
1) Assume a static weight distribution of 60% Front and 40% Rear on a car like a G3 Integra prepared for SCCA Club Racing. Because most of us with these chassis' run the similar bars, and because the rear spring motion ratio is better than the front, a given spring rate on the rear produces a higher wheel rate than it does on the front. We can therefore continue for the purpose of discussion to refer to the NA setup as high rear bias and the JDM as high front bias.
2) Under steady state cornering the Front/Rear distribution of lateral force will reflect the static weight distribution and will not change in response to longitudinal acceleration except where the friction circle is overloaded by driver input. This means that the front axle has to do 60% and the rear 40% of the work of cornering (lateral force generation). This along with the stacked workload of the fronts (primary braking and acceleration) is what kills our front tires and has us looking for ways to improve front grip in all modes.
3) What we refer to as the non-linear relationship between vertical force on a tire and the traction it develops is one of our most important tools. Explained simply it's like this: A tire has X grip loaded with A pounds load. That tire has less than 2X grip when loaded with 2A pounds. What this means is that any pair of tires will develop maximum grip as a pair when their load is split 50/50. As the split biases the total grip declines.
4) Acceleration causes weight transfer, visible effects of which are roll under lateral acceleration and pitch (dive or squat) under longitudinal acceleration. Assuming identical acceleration, reduction in roll or pitch resulting from spring or bar changes alone DOES NOT indicate a reduction in weight transfer.
5) Weight transfer is a function of the height of the center of gravity, the track width or wheelbase, and the acceleration. Total weight transfer is reduced by lowering the center of gravity, widening the track, lengthening the wheelbase, or reducing the acceleration. We are not frequently interested in that last option.
6) Under lateral acceleration the end of the car with the highest roll stiffness will transfer the highest percentage of its inside cornerweight to the outside wheel. At any point in time the chassis has ONE roll angle - although our chassis' are not perfectly rigid torsionally, this assumption is necessary. Combined lateral and longitudinal acceleration gives diagonal weight transfer.
7) Our biggest problem in going faster is the problem of UNDERSTEER. We combat this by first maximizing front end grip, and only then sacrificing rear grip to find balance.
8) What we call the friction circle, an application of Mohr's circle, is an analytical tool to explain what we can expect from a contact patch (or the sum of their generated force). Say we can achieve 1g braking, and 1g cornering. We cannot simultaneously achieve both - we'd call such a thing well outside the circle. We can achieve 1g total combined - perhaps 0.7g braking and 0.7g cornering (the square root of 0.7 squared plus 0.7 squared being equal to 1).
9) A front wheel drive car really does literally tow the rear wheels behind it. The front tractive vector of a FWD is generally in the direction of the cars desired heading. The rear tractive vector of a RWD is only so under considerable oversteer (which is the way to go on dirt with virtually any configuration, but not pavement where it will usually mean that the front tires are underworked to the detriment of total grip and maximum speed - sorry drifters.)
10) It might then be relatively straightforward to come to the conclusion that we might want the rear to have the higher roll stiffness. North American cars are typically prepped this way. The correctness of the basic case is unassailable in the most general terms, and corraborated by enormous practical evidence from competition. Smart people do it.
11) It's not necessarily intuitive. Among the encountered superstitions are ideas like "the heavy end gets the heavy springs", and "a car on 4 wheels is working better than one on 3 wheels". Furthermore, there are Japanese DC2's running higher roll stiffness in the front, and, when asked about the difference, Spoon techs say they can't understand why we do the opposite. By reasonable accounts they are not dummies.
12) One of the difficulties we run into with the typical NA setup is available front bump travel. The G3 Integra at NA racing ride heights of 5-5.5 inches has very little shaft travel left (less than 1.3 inches, and even if you had more shaft left, you'd still have upper a-arm interference issues with Skunk arms). We generally wind up as low as we can (at our legal ride height - if any) without bottoming the outside front in the turn in zone and generating massive understeer. In such an event we can either increase ride height (and go slower than we were hoping), or we can increase spring rates to get a total roll resistance that will keep us off the bump stops.
13) Among the few orthodoxies from old books that can be discarded are the particular bounds on Natural Frequency. We've been taught that somewhere not far beyond 2 cycles per second is the limit. Practical examples worldwide suggest that 3cps front and 4cps rear on these cars represent the more useful bounds.
14) Returning to what happens on the track - a rear stiff car will unload the inside rear faster than it unloads the inside front. At some point all of the inside rear weight has been transferred to the outside rear. A rear camber setting is selected so that at the terminal roll angle of the chassis sufficient grip is generated by the outside rear alone. This is typically achieved on our cars at something less than the camber required to generate the maximum potential rear grip. As the outside rear decambers in roll, and converges on its terminal camber, it is generating greater and greater grip - both as the vertical force increases from weight transfer, and as the dynamic camber improves. At the kind of rear spring rates common to both NA and JDM setups, dynamic rear camber change during rear weight transfer in pure roll is approx +1 degree (decambering). In any case the front decambers approx 50% faster than the rear in pure roll while all four wheels are on the ground. Since we rarely have pure roll without pitch effects we should note that the combined effects camber curves are a more complex story that must be examined in cases. Most interesting among these is drop throttle behavior. The rear decambers fast in combined roll and droop. This points to the usefulness from this perspective of high rear spring rates in general as common to both setups. Generally speaking, as we converge on max lateral acceleration we converge on optimal dynamic camber - assuming we're doing our job as a race engineer. In general camber change is not something to be minimized for it's own sake (the chassis performance envelope is a multi-dimensional topography - very little about it can be changed without affecting other perhaps more important factors) - the JDM guys don't do what they do simply to control front dynamic camber.
15)If we suppose a limit imposed by drivability on the rear spring rate (and it's amusing to suppose that a rate change giving less than a tenth of an inch difference in static deflection might be over said limit), there is not much supposition involved in determining that diminishing returns in rear roll stiffness are quickly reached.
16) At lower ride heights with the production tub configuration, and higher grip levels than can be achieved on typical US DOT race tires, there is no escaping the conclusion that front roll stiffness MUST be increased beyond levels used by NA racers. Some mitigation of this need could be realized by increasing available front wheel travel with a more compact upper a-arm (or modification of the inner fender / tower). If we're going to go faster than a NA car by using stickier rubber and a lower center of gravity, we will be FORCED to increase the front spring rate. The Japanese arrived at their setup the old fashioned way - they found that they went faster. But, if the track is rough, the ride height must go up, the rates down, and the bias rearward again - or else mechanical grip will be sporadic and the car will be undrivable.
17) This illustrates a common problem. One of the big obstacles to understanding this stuff is the haphazard way in which we assimilate new information and practical experience into our knowledge base. We rarely have all the information we need, and many are sufficiently ignorant of the mechanisms as to preclude any real understanding - they match incompatible cause and effect with regularity and are incapable of recognizing contradictions when they inevitably arise. A nice whitewash with "personal preference" masks their confusion.
18) So where does that leave this "argument". I stand by everything I've written to date as it was in the context of our ride heights and conditions, and nobody advocating use of the JDM rate bias made any qualification for conditions. Furthermore nobody made a case for how the JDM rate bias could make any sense - and I certainly provided every provocation for someone to do so. So, only an idiot would now use the JDM setup under typical US conditions, and only an idiot would be stumped by an understeering NA setup at 3 inch ride height, and only an idiot would think that that I'm just a closed minded *******.
19) The special case does not disprove the rule - Physics survives another puny attack - 20 year old books need not be discarded - worship of either NA or JDM tuners is unwarranted - and if you really want to go fast you gotta use your head.
Scott, who hopes you've enjoyed and benefited from this exercise....may I never call YOU an idiot......"I'm ready for my close-up Mr DeMille"......
[Modified by RR98ITR, 10:11 PM 7/21/2002]
This follow up framed some key conclusions too:
Take an ITR with an NA setup (800F/1100R) on DOT tires. It develops enough lateral acceleration such that when trail braking / turning in it unloads the inside rear completely and uses up almost all available outside front shaft travel.
Then increase the lateral acceleration. This might be for a case with grippier tires, or a lower ride height. The lower ride height brings down the cg, but the roll centers move in approx 1:1 relationship on these cars so the overturning moment arm is about the same. The lower cg means lower total lateral weight transfer at the same lateral acceleration, but we do this to go faster - the lateral acceleration will be higher and the weight transfer will be not much lower than before and likely significantly higher. WE NOW HAVE LESS FRONT SHAFT TO DO THE ROUGHLY THE SAME OR GREATER AMOUNT OF WORK WITH. So in the case where we have lower ride height AND grippier tires we have significantly increased TOTAL weight transfer.
If we try to drive that NA car under these new conditions it will be spending alot of time on the outside front bumpstops and understeering since everything is already coming off the inside rear, the increase in total weight transfer must come off the inside front - and go to the outside front in cornering phases prior to runout. This is the key thing to look at: as we increase total weight transfer on a car that already is capable of unloading the inside rear the difference can only come off the inside front. Increasing rear roll stiffness will do nothing to change this fact, and will only unload the inside rear earlier in the cornering sequence - and where rear wheel rates are so high already as to give deflections well under an inch these timing differences will be very slight.
So we are left with having to increase total roll resistance with the only tool left to us - the front roll resistance. The front roll resistance MUST GO UP. For a variety of reasons we would do this with the front spring rates.
And how do we achieve balance now that we've got a spring rate bias that is screwed up in terms of the generally valid FWD rear bias orthodoxy? Rear camber, rear tire size or compound.
Scott, who no matter how many times he reads his post, and no matter how many questions he answers, keeps seeing ways he could have written it up better....
[Modified by RR98ITR, 8:55 AM 7/22/2002]
At this point I didn't think there were any big questions left to work on on this type of chassis. One thing that has nagged at me though is the appropriate thinking with respect to caster, helped along by some of the recent CV problems we've discussed.
I've mentioned now many times (and STILL no response) about the successful pro team I saw running LOW CASTER on a high speed track. I've never gotten a satisfying answer from them about why (beyond "it works better sometimes" - which of course might be an entirely legitimate and honest response).
I mentioned that one of my recent distractions has been Karting and that I enjoyed Steve Smith's Kart Chassis book. In case you don't know Karts, the primary goal of chassis tuning is the control of unloading and lifting of the inside rear. Unlike our application, karts need to do this because the solid driven rear axle would make turning the kart extremely difficult. This lifting is effected by a combination of chassis flex and the dynamic cornerweighting effects of the front end geometry. These effects revealed most clearly in the uncomplicated design of the kart provide instruction for us.
If we examine kingpin inclination (the axis between the upper and lower balljoints in front view), we see that turning the steering wheel pushes the wheel downward equally whether turned left or right. Positive Ackerman (inside wheel turning more than outside) will result in the inside wheel being pushed downward more than the outside wheel.
If we examine positive caster, we see that the outside wheel moves upward and the inside wheel moves downward.
The net effect of the combination of these attributes is increased load on the inside front / outside rear diagonal. On the surface that would appear to suggest a desirable effect with respect to the inside front. But with the inside rear unloading rapidly, it should occur to us that perhaps the primary effect is a raising of the center of gravity - obviously not a good thing. Of course, if we're set up like we like, we're back to a pretty straight wheel soon into the corner, mitigating the effect.
It's possible that more caster gives undesirably more non-linear transients (drivers cope best with linear response). In a magazine currently on the shelfs profiling the Speed World Challenge Volkswagens, Kevin Schrantz is quoted as saying in effect that he found the Volkswagen easier to drive with more confidence than the RTR ITRs. Of course he's very unlikely to go on record at this point comparing the VW's unfavorably to the Acura's, but maybe there's something to his comments, and maybe it's relevant to these considerations.
I recently read an analysis somewhere that concluded that dynamic camber effects from caster were insufficient to warrant the first priority in selecting the caster setting. Since most treatments of caster are concerned with trail and stability, we should note that with our front heavy cars we can get all of that we need from the standard low caster and the typical pneumatic trail effect.
The problem with these questions is that the answers, such as they are, are situational and only to be found for most of us thru on track testing. You can't simply bang out some numbers and get a useful answer.
I don't believe I know now what I should be running, and some testing next year must be directed toward this question. It should be obvious that these considerations are less important with a high ride height softly sprung car - the displacements from the geometric effects will be much less in proportion to the dynamic operating envelope.
And, oh yeah, without power steering a suitable rationalization for less caster would be that much more interesting.
Scott, who thought some writing might help with the Joneses......
Ok, here's my summary of what some of us have gotten used to referring to as JDM vs NA Spring Rate Question. This is a very general treatment with no specific data or worksheets, beginning from the basics. It will clarify the issues, and resolve the mystery. Everything written is in the context of a real racing driver driving a real racing car on a real race track with the singleminded purpose of going as fast as they can.
1) Assume a static weight distribution of 60% Front and 40% Rear on a car like a G3 Integra prepared for SCCA Club Racing. Because most of us with these chassis' run the similar bars, and because the rear spring motion ratio is better than the front, a given spring rate on the rear produces a higher wheel rate than it does on the front. We can therefore continue for the purpose of discussion to refer to the NA setup as high rear bias and the JDM as high front bias.
2) Under steady state cornering the Front/Rear distribution of lateral force will reflect the static weight distribution and will not change in response to longitudinal acceleration except where the friction circle is overloaded by driver input. This means that the front axle has to do 60% and the rear 40% of the work of cornering (lateral force generation). This along with the stacked workload of the fronts (primary braking and acceleration) is what kills our front tires and has us looking for ways to improve front grip in all modes.
3) What we refer to as the non-linear relationship between vertical force on a tire and the traction it develops is one of our most important tools. Explained simply it's like this: A tire has X grip loaded with A pounds load. That tire has less than 2X grip when loaded with 2A pounds. What this means is that any pair of tires will develop maximum grip as a pair when their load is split 50/50. As the split biases the total grip declines.
4) Acceleration causes weight transfer, visible effects of which are roll under lateral acceleration and pitch (dive or squat) under longitudinal acceleration. Assuming identical acceleration, reduction in roll or pitch resulting from spring or bar changes alone DOES NOT indicate a reduction in weight transfer.
5) Weight transfer is a function of the height of the center of gravity, the track width or wheelbase, and the acceleration. Total weight transfer is reduced by lowering the center of gravity, widening the track, lengthening the wheelbase, or reducing the acceleration. We are not frequently interested in that last option.
6) Under lateral acceleration the end of the car with the highest roll stiffness will transfer the highest percentage of its inside cornerweight to the outside wheel. At any point in time the chassis has ONE roll angle - although our chassis' are not perfectly rigid torsionally, this assumption is necessary. Combined lateral and longitudinal acceleration gives diagonal weight transfer.
7) Our biggest problem in going faster is the problem of UNDERSTEER. We combat this by first maximizing front end grip, and only then sacrificing rear grip to find balance.
8) What we call the friction circle, an application of Mohr's circle, is an analytical tool to explain what we can expect from a contact patch (or the sum of their generated force). Say we can achieve 1g braking, and 1g cornering. We cannot simultaneously achieve both - we'd call such a thing well outside the circle. We can achieve 1g total combined - perhaps 0.7g braking and 0.7g cornering (the square root of 0.7 squared plus 0.7 squared being equal to 1).
9) A front wheel drive car really does literally tow the rear wheels behind it. The front tractive vector of a FWD is generally in the direction of the cars desired heading. The rear tractive vector of a RWD is only so under considerable oversteer (which is the way to go on dirt with virtually any configuration, but not pavement where it will usually mean that the front tires are underworked to the detriment of total grip and maximum speed - sorry drifters.)
10) It might then be relatively straightforward to come to the conclusion that we might want the rear to have the higher roll stiffness. North American cars are typically prepped this way. The correctness of the basic case is unassailable in the most general terms, and corraborated by enormous practical evidence from competition. Smart people do it.
11) It's not necessarily intuitive. Among the encountered superstitions are ideas like "the heavy end gets the heavy springs", and "a car on 4 wheels is working better than one on 3 wheels". Furthermore, there are Japanese DC2's running higher roll stiffness in the front, and, when asked about the difference, Spoon techs say they can't understand why we do the opposite. By reasonable accounts they are not dummies.
12) One of the difficulties we run into with the typical NA setup is available front bump travel. The G3 Integra at NA racing ride heights of 5-5.5 inches has very little shaft travel left (less than 1.3 inches, and even if you had more shaft left, you'd still have upper a-arm interference issues with Skunk arms). We generally wind up as low as we can (at our legal ride height - if any) without bottoming the outside front in the turn in zone and generating massive understeer. In such an event we can either increase ride height (and go slower than we were hoping), or we can increase spring rates to get a total roll resistance that will keep us off the bump stops.
13) Among the few orthodoxies from old books that can be discarded are the particular bounds on Natural Frequency. We've been taught that somewhere not far beyond 2 cycles per second is the limit. Practical examples worldwide suggest that 3cps front and 4cps rear on these cars represent the more useful bounds.
14) Returning to what happens on the track - a rear stiff car will unload the inside rear faster than it unloads the inside front. At some point all of the inside rear weight has been transferred to the outside rear. A rear camber setting is selected so that at the terminal roll angle of the chassis sufficient grip is generated by the outside rear alone. This is typically achieved on our cars at something less than the camber required to generate the maximum potential rear grip. As the outside rear decambers in roll, and converges on its terminal camber, it is generating greater and greater grip - both as the vertical force increases from weight transfer, and as the dynamic camber improves. At the kind of rear spring rates common to both NA and JDM setups, dynamic rear camber change during rear weight transfer in pure roll is approx +1 degree (decambering). In any case the front decambers approx 50% faster than the rear in pure roll while all four wheels are on the ground. Since we rarely have pure roll without pitch effects we should note that the combined effects camber curves are a more complex story that must be examined in cases. Most interesting among these is drop throttle behavior. The rear decambers fast in combined roll and droop. This points to the usefulness from this perspective of high rear spring rates in general as common to both setups. Generally speaking, as we converge on max lateral acceleration we converge on optimal dynamic camber - assuming we're doing our job as a race engineer. In general camber change is not something to be minimized for it's own sake (the chassis performance envelope is a multi-dimensional topography - very little about it can be changed without affecting other perhaps more important factors) - the JDM guys don't do what they do simply to control front dynamic camber.
15)If we suppose a limit imposed by drivability on the rear spring rate (and it's amusing to suppose that a rate change giving less than a tenth of an inch difference in static deflection might be over said limit), there is not much supposition involved in determining that diminishing returns in rear roll stiffness are quickly reached.
16) At lower ride heights with the production tub configuration, and higher grip levels than can be achieved on typical US DOT race tires, there is no escaping the conclusion that front roll stiffness MUST be increased beyond levels used by NA racers. Some mitigation of this need could be realized by increasing available front wheel travel with a more compact upper a-arm (or modification of the inner fender / tower). If we're going to go faster than a NA car by using stickier rubber and a lower center of gravity, we will be FORCED to increase the front spring rate. The Japanese arrived at their setup the old fashioned way - they found that they went faster. But, if the track is rough, the ride height must go up, the rates down, and the bias rearward again - or else mechanical grip will be sporadic and the car will be undrivable.
17) This illustrates a common problem. One of the big obstacles to understanding this stuff is the haphazard way in which we assimilate new information and practical experience into our knowledge base. We rarely have all the information we need, and many are sufficiently ignorant of the mechanisms as to preclude any real understanding - they match incompatible cause and effect with regularity and are incapable of recognizing contradictions when they inevitably arise. A nice whitewash with "personal preference" masks their confusion.
18) So where does that leave this "argument". I stand by everything I've written to date as it was in the context of our ride heights and conditions, and nobody advocating use of the JDM rate bias made any qualification for conditions. Furthermore nobody made a case for how the JDM rate bias could make any sense - and I certainly provided every provocation for someone to do so. So, only an idiot would now use the JDM setup under typical US conditions, and only an idiot would be stumped by an understeering NA setup at 3 inch ride height, and only an idiot would think that that I'm just a closed minded *******.
19) The special case does not disprove the rule - Physics survives another puny attack - 20 year old books need not be discarded - worship of either NA or JDM tuners is unwarranted - and if you really want to go fast you gotta use your head.
Scott, who hopes you've enjoyed and benefited from this exercise....may I never call YOU an idiot......"I'm ready for my close-up Mr DeMille"......
[Modified by RR98ITR, 10:11 PM 7/21/2002]
This follow up framed some key conclusions too:
Take an ITR with an NA setup (800F/1100R) on DOT tires. It develops enough lateral acceleration such that when trail braking / turning in it unloads the inside rear completely and uses up almost all available outside front shaft travel.
Then increase the lateral acceleration. This might be for a case with grippier tires, or a lower ride height. The lower ride height brings down the cg, but the roll centers move in approx 1:1 relationship on these cars so the overturning moment arm is about the same. The lower cg means lower total lateral weight transfer at the same lateral acceleration, but we do this to go faster - the lateral acceleration will be higher and the weight transfer will be not much lower than before and likely significantly higher. WE NOW HAVE LESS FRONT SHAFT TO DO THE ROUGHLY THE SAME OR GREATER AMOUNT OF WORK WITH. So in the case where we have lower ride height AND grippier tires we have significantly increased TOTAL weight transfer.
If we try to drive that NA car under these new conditions it will be spending alot of time on the outside front bumpstops and understeering since everything is already coming off the inside rear, the increase in total weight transfer must come off the inside front - and go to the outside front in cornering phases prior to runout. This is the key thing to look at: as we increase total weight transfer on a car that already is capable of unloading the inside rear the difference can only come off the inside front. Increasing rear roll stiffness will do nothing to change this fact, and will only unload the inside rear earlier in the cornering sequence - and where rear wheel rates are so high already as to give deflections well under an inch these timing differences will be very slight.
So we are left with having to increase total roll resistance with the only tool left to us - the front roll resistance. The front roll resistance MUST GO UP. For a variety of reasons we would do this with the front spring rates.
And how do we achieve balance now that we've got a spring rate bias that is screwed up in terms of the generally valid FWD rear bias orthodoxy? Rear camber, rear tire size or compound.
Scott, who no matter how many times he reads his post, and no matter how many questions he answers, keeps seeing ways he could have written it up better....
[Modified by RR98ITR, 8:55 AM 7/22/2002]
At this point I didn't think there were any big questions left to work on on this type of chassis. One thing that has nagged at me though is the appropriate thinking with respect to caster, helped along by some of the recent CV problems we've discussed.
I've mentioned now many times (and STILL no response) about the successful pro team I saw running LOW CASTER on a high speed track. I've never gotten a satisfying answer from them about why (beyond "it works better sometimes" - which of course might be an entirely legitimate and honest response).
I mentioned that one of my recent distractions has been Karting and that I enjoyed Steve Smith's Kart Chassis book. In case you don't know Karts, the primary goal of chassis tuning is the control of unloading and lifting of the inside rear. Unlike our application, karts need to do this because the solid driven rear axle would make turning the kart extremely difficult. This lifting is effected by a combination of chassis flex and the dynamic cornerweighting effects of the front end geometry. These effects revealed most clearly in the uncomplicated design of the kart provide instruction for us.
If we examine kingpin inclination (the axis between the upper and lower balljoints in front view), we see that turning the steering wheel pushes the wheel downward equally whether turned left or right. Positive Ackerman (inside wheel turning more than outside) will result in the inside wheel being pushed downward more than the outside wheel.
If we examine positive caster, we see that the outside wheel moves upward and the inside wheel moves downward.
The net effect of the combination of these attributes is increased load on the inside front / outside rear diagonal. On the surface that would appear to suggest a desirable effect with respect to the inside front. But with the inside rear unloading rapidly, it should occur to us that perhaps the primary effect is a raising of the center of gravity - obviously not a good thing. Of course, if we're set up like we like, we're back to a pretty straight wheel soon into the corner, mitigating the effect.
It's possible that more caster gives undesirably more non-linear transients (drivers cope best with linear response). In a magazine currently on the shelfs profiling the Speed World Challenge Volkswagens, Kevin Schrantz is quoted as saying in effect that he found the Volkswagen easier to drive with more confidence than the RTR ITRs. Of course he's very unlikely to go on record at this point comparing the VW's unfavorably to the Acura's, but maybe there's something to his comments, and maybe it's relevant to these considerations.
I recently read an analysis somewhere that concluded that dynamic camber effects from caster were insufficient to warrant the first priority in selecting the caster setting. Since most treatments of caster are concerned with trail and stability, we should note that with our front heavy cars we can get all of that we need from the standard low caster and the typical pneumatic trail effect.
The problem with these questions is that the answers, such as they are, are situational and only to be found for most of us thru on track testing. You can't simply bang out some numbers and get a useful answer.
I don't believe I know now what I should be running, and some testing next year must be directed toward this question. It should be obvious that these considerations are less important with a high ride height softly sprung car - the displacements from the geometric effects will be much less in proportion to the dynamic operating envelope.
And, oh yeah, without power steering a suitable rationalization for less caster would be that much more interesting.
Scott, who thought some writing might help with the Joneses......
09-20-2002, 11:37 PM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
I like it. Some things I dont fully understand, but will have to when choosing the best "General" setup for my car next mth. I cant be too specific as I race on many different tracks & the alignment & tire pressures will have to change at each track.
How much experience do you have on track, Scott?? I want to know what has worked for you & what really hasnt through testing at the track. Im really interested to read about how something you changed drastically changed the way your car handles on the track. Im pretty sure you pyro your tires for an even better setup at the track.
Pete
How much experience do you have on track, Scott?? I want to know what has worked for you & what really hasnt through testing at the track. Im really interested to read about how something you changed drastically changed the way your car handles on the track. Im pretty sure you pyro your tires for an even better setup at the track.
Pete
09-21-2002, 12:04 AM
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Re: Smore dat spension tak bout R kaas........ (pest)
Thanks for another insightful and well thought out write up of the dynamics of the handling situations encountered by tracking front drive cars such as ours.
Can't believe I read the whole thing in one sitting, either.
Good luck with the "jonses". Ed
Can't believe I read the whole thing in one sitting, either.
Good luck with the "jonses". Ed
09-21-2002, 07:04 PM
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Re: Smore dat spension tak bout R kaas........ (Zygspeed)
One day I hope to be able to understand 50% of what you wrote. Anyone know enough to help defend or refute this disseration? 
09-23-2002, 09:46 AM
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Re: Smore dat spension tak bout R kaas........ (pest)
Pete,
I've had my ITR since 98 and put about 9000 actual on track miles at Portland, Pacific Raceways and Buttonwillow.
I've driven the car thru four basic development phases: stock, Mugen Lowdown/DOT, Mugen N1 (Soft)/DOT, Mugen N1 (Stiff)/DOT/188whp. I've gone faster each step of the way as both my driving and the cars potential improved. 2002 was my first year of SCCA Regional racing. I ran in RS and won every RS race I entered against competetion that wasn't generally close. I also ran a couple of races in ITE and got my *** handed to me by high horsepower cars.
My best race lap at Portland with the chicane (the CART support race) was faster than Sapp's SVWC TC winning fast lap the previous year, while my qualifying time would've put me 5th on the grid. This is of course an apples to oranges comparison since I was on Hoosiers and they on Toyo T1S's, but then I was down alot of horsepower and Portland is regarded by some as a paved dyno. They're just numbers, but they suggest that I don't suck.
My previous race experience was 6 years of Motocross. I raced CMC and AMA Pro from 79 to 81, and was a decent local pro. That career ended in injury at Saddleback, and I never recovered. I kept racing for two years, and got faster and faster, but I kept reinjuring my knee. I quit one day on a local hilltop practice track, on the ground, in massive pain, crying and pounding the ground ala Mika Hakkinen - I couldn't go on. During that career I learned about racing brutality. I did my share of brake checking, diving under a guy and taking him out, the subtle art of squaring it off in front of somebody and block passing them (I was proud of the front tire rubber on my swingarm and side number plates). I can tell you that I have to work at remembering that I'm in a different world when I'm in the car.
What has worked for me is taking Scott Zellners advice. King Motorsports is a fantastic resource and the price for what you get is exceedingly fair. Go back thru my old posts and you'll find most of what I've done and gone thru. None of the changes I've ever made to the car took me backwards - I always go faster on the next setup (but then I expect to).
I've only done a little bit of tire temp testing since I am my own crew. There's alot to think about with tire temps and it takes alot of time and money to really isolate things. Maybe I'll have more to say about it next year - I've found some infrared packages that might bring real time tire temp capture within my budget.
Scott, who says "you know what caster is right? And so you know what trail is right? So imagine zero caster, and then note that the tire still wants to go straight (though not as much as if there was some caster and trail). A tire typically has a bit of pnuematic trail - a difference between the vertical projection of its center of rotation and the resultant of it's drag)"...something like that....
I've had my ITR since 98 and put about 9000 actual on track miles at Portland, Pacific Raceways and Buttonwillow.
I've driven the car thru four basic development phases: stock, Mugen Lowdown/DOT, Mugen N1 (Soft)/DOT, Mugen N1 (Stiff)/DOT/188whp. I've gone faster each step of the way as both my driving and the cars potential improved. 2002 was my first year of SCCA Regional racing. I ran in RS and won every RS race I entered against competetion that wasn't generally close. I also ran a couple of races in ITE and got my *** handed to me by high horsepower cars.
My best race lap at Portland with the chicane (the CART support race) was faster than Sapp's SVWC TC winning fast lap the previous year, while my qualifying time would've put me 5th on the grid. This is of course an apples to oranges comparison since I was on Hoosiers and they on Toyo T1S's, but then I was down alot of horsepower and Portland is regarded by some as a paved dyno. They're just numbers, but they suggest that I don't suck.
My previous race experience was 6 years of Motocross. I raced CMC and AMA Pro from 79 to 81, and was a decent local pro. That career ended in injury at Saddleback, and I never recovered. I kept racing for two years, and got faster and faster, but I kept reinjuring my knee. I quit one day on a local hilltop practice track, on the ground, in massive pain, crying and pounding the ground ala Mika Hakkinen - I couldn't go on. During that career I learned about racing brutality. I did my share of brake checking, diving under a guy and taking him out, the subtle art of squaring it off in front of somebody and block passing them (I was proud of the front tire rubber on my swingarm and side number plates). I can tell you that I have to work at remembering that I'm in a different world when I'm in the car.
What has worked for me is taking Scott Zellners advice. King Motorsports is a fantastic resource and the price for what you get is exceedingly fair. Go back thru my old posts and you'll find most of what I've done and gone thru. None of the changes I've ever made to the car took me backwards - I always go faster on the next setup (but then I expect to).
I've only done a little bit of tire temp testing since I am my own crew. There's alot to think about with tire temps and it takes alot of time and money to really isolate things. Maybe I'll have more to say about it next year - I've found some infrared packages that might bring real time tire temp capture within my budget.
Scott, who says "you know what caster is right? And so you know what trail is right? So imagine zero caster, and then note that the tire still wants to go straight (though not as much as if there was some caster and trail). A tire typically has a bit of pnuematic trail - a difference between the vertical projection of its center of rotation and the resultant of it's drag)"...something like that....
03-06-2003, 11:44 AM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
I figure that this belongs most appropriately here. Some of the local technical racers in my area have started getting together once per month for a dinner / tech meeting. This is the response that I sent to the participants following the first meeting the other night.
One of the "subjects" discussed was the following text from one of my bulletin board posts:
***Quote from Part-3 of my Spension Thread*****
I've mentioned now many times (and STILL no response) about the successful pro team I saw running LOW CASTER on a high speed track. I've never gotten a satisfying answer from them about why (beyond "it works better sometimes" - which of course might be an entirely legitimate and honest response).
I mentioned that one of my recent distractions has been Karting and that I enjoyed Steve Smith's Kart Chassis book. In case you don't know Karts, the primary goal of chassis tuning is the control of unloading and lifting of the inside rear. Unlike our application, karts need to do this because the solid driven rear axle would make turning the kart extremely difficult. This lifting is effected by a combination of chassis flex and the dynamic cornerweighting effects of the front end geometry. These effects revealed most clearly in the uncomplicated design of the kart provide instruction for us.
If we examine kingpin inclination (the axis between the upper and lower balljoints in front view), we see that turning the steering wheel pushes the wheel downward equally whether turned left or right. Positive Ackerman (inside wheel turning more than outside) will result in the inside wheel being pushed downward more than the outside wheel.
If we examine positive caster, we see that the outside wheel moves upward and the inside wheel moves downward.
The net effect of the combination of these attributes is increased load on the inside front / outside rear diagonal. On the surface that would appear to suggest a desirable effect with respect to the inside front. But with the inside rear unloading rapidly, it should occur to us that perhaps the primary effect is a raising of the center of gravity - obviously not a good thing. Of course, if we're set up like we like, we're back to a pretty straight wheel soon into the corner, mitigating the effect.
It's possible that more caster gives undesirably more non-linear transients (drivers cope best with linear response). In a magazine currently on the shelfs profiling the Speed World Challenge Volkswagens, Kevin Schrantz is quoted as saying in effect that he found the Volkswagen easier to drive with more confidence than the RTR ITRs. Of course he's very unlikely to go on record at this point comparing the VW's unfavorably to the Acura's, but maybe there's something to his comments, and maybe it's relevant to these considerations.
I recently read an analysis somewhere that concluded that dynamic camber effects from caster were insufficient to warrant the first priority in selecting the caster setting. Since most treatments of caster are concerned with trail and stability, we should note that with our front heavy cars we can get all of that we need from the standard low caster and the typical pneumatic trail effect.
***End Quote of Part 3 of Spension Thread***
Dave said that when he puts his Golf on the scales and turns the wheels, the outside front reads heavier - a counterexample that's hard to argue with.
Chris likewise said that he "didn't buy" my analysis.
Naturally, knowing I'm right and that my analysis is sound, I had to think about what's happening on Dave's scales.
Two things occur to me:
1) Karts have lots of scrub radius (contact patch outboard of steering axis intersection with the ground plane) - That's why a kart does what I said it does.
2) A race car with minimal scrub radius (or negative scrub radius) can behave very differently.
3) In conjunction with (2) above, static negative camber will have an effect.
Note that the camber effects of KPI are induced Positive on both the Outside and Inside wheels.
Note that the camber effects of Caster are induced Negative on the Outside wheel and induced Positive on the Inside wheel.
Note that the combined effect of KPI and Caster are indeterminate in the general case on the outside wheel, but Positive on the Inside wheel - this is why Dave's Golf does what it does on the scales. What the actual dynamic weight jacking is during actual turn in on Dave's Golf is unclear to me at this time - it will require more thought.
I will try to work up a description that ties all this up more neatly, and present it at the next meeting.
All of us were interested in why Ferrari (only?) are running the outboard end of the front suspension pushrods to the upright. Is it merely for structural reasons - simplifying LCA load and construction (no doubt it does do that). Is it for some dynamic turn in weight jacking? This last point suggests a possible relevance to the discussion above.
I hope that you will all decide that this monthly meeting is interesting enough to continue having - I think it is, but then I have alot to learn and it helps to have people kick my crutches out from under me.
The other issues I'm going to spend some time on are the role of roll center height. Above ground we keep roll centers fairly low to minimize jacking forces. Alot of our Honda's wind up with roll centers below ground giving negative jacking forces - a good thing in my estimation.
Strut cars like the new RSX offer additional challenges. Below ground roll centers, if they are even possible, might be associated with decreased negative camber gain, and that might be much more important than minor amounts of jacking force. My friends Golf with pushrod front end and dummy strut has 20 degrees of kingpin to get a decent camber curve - and maybe 9 degrees of caster. Formula cars - modern Fords in particular appear to run below ground roll centers; F1 cars are harder to figure out - it's possible they might have high wheel instant centers outside the track and roll centers well below ground and let static negative camber do it all.
Scott, who when he gets some time will have to play games with Mitchell to see if that makes any sense....
[Modified by RR98ITR, 1:05 PM 3/6/2003]
One of the "subjects" discussed was the following text from one of my bulletin board posts:
***Quote from Part-3 of my Spension Thread*****
I've mentioned now many times (and STILL no response) about the successful pro team I saw running LOW CASTER on a high speed track. I've never gotten a satisfying answer from them about why (beyond "it works better sometimes" - which of course might be an entirely legitimate and honest response).
I mentioned that one of my recent distractions has been Karting and that I enjoyed Steve Smith's Kart Chassis book. In case you don't know Karts, the primary goal of chassis tuning is the control of unloading and lifting of the inside rear. Unlike our application, karts need to do this because the solid driven rear axle would make turning the kart extremely difficult. This lifting is effected by a combination of chassis flex and the dynamic cornerweighting effects of the front end geometry. These effects revealed most clearly in the uncomplicated design of the kart provide instruction for us.
If we examine kingpin inclination (the axis between the upper and lower balljoints in front view), we see that turning the steering wheel pushes the wheel downward equally whether turned left or right. Positive Ackerman (inside wheel turning more than outside) will result in the inside wheel being pushed downward more than the outside wheel.
If we examine positive caster, we see that the outside wheel moves upward and the inside wheel moves downward.
The net effect of the combination of these attributes is increased load on the inside front / outside rear diagonal. On the surface that would appear to suggest a desirable effect with respect to the inside front. But with the inside rear unloading rapidly, it should occur to us that perhaps the primary effect is a raising of the center of gravity - obviously not a good thing. Of course, if we're set up like we like, we're back to a pretty straight wheel soon into the corner, mitigating the effect.
It's possible that more caster gives undesirably more non-linear transients (drivers cope best with linear response). In a magazine currently on the shelfs profiling the Speed World Challenge Volkswagens, Kevin Schrantz is quoted as saying in effect that he found the Volkswagen easier to drive with more confidence than the RTR ITRs. Of course he's very unlikely to go on record at this point comparing the VW's unfavorably to the Acura's, but maybe there's something to his comments, and maybe it's relevant to these considerations.
I recently read an analysis somewhere that concluded that dynamic camber effects from caster were insufficient to warrant the first priority in selecting the caster setting. Since most treatments of caster are concerned with trail and stability, we should note that with our front heavy cars we can get all of that we need from the standard low caster and the typical pneumatic trail effect.
***End Quote of Part 3 of Spension Thread***
Dave said that when he puts his Golf on the scales and turns the wheels, the outside front reads heavier - a counterexample that's hard to argue with.
Chris likewise said that he "didn't buy" my analysis.
Naturally, knowing I'm right and that my analysis is sound, I had to think about what's happening on Dave's scales.
Two things occur to me:
1) Karts have lots of scrub radius (contact patch outboard of steering axis intersection with the ground plane) - That's why a kart does what I said it does.
2) A race car with minimal scrub radius (or negative scrub radius) can behave very differently.
3) In conjunction with (2) above, static negative camber will have an effect.
Note that the camber effects of KPI are induced Positive on both the Outside and Inside wheels.
Note that the camber effects of Caster are induced Negative on the Outside wheel and induced Positive on the Inside wheel.
Note that the combined effect of KPI and Caster are indeterminate in the general case on the outside wheel, but Positive on the Inside wheel - this is why Dave's Golf does what it does on the scales. What the actual dynamic weight jacking is during actual turn in on Dave's Golf is unclear to me at this time - it will require more thought.
I will try to work up a description that ties all this up more neatly, and present it at the next meeting.
All of us were interested in why Ferrari (only?) are running the outboard end of the front suspension pushrods to the upright. Is it merely for structural reasons - simplifying LCA load and construction (no doubt it does do that). Is it for some dynamic turn in weight jacking? This last point suggests a possible relevance to the discussion above.
I hope that you will all decide that this monthly meeting is interesting enough to continue having - I think it is, but then I have alot to learn and it helps to have people kick my crutches out from under me.
Strut cars like the new RSX offer additional challenges. Below ground roll centers, if they are even possible, might be associated with decreased negative camber gain, and that might be much more important than minor amounts of jacking force. My friends Golf with pushrod front end and dummy strut has 20 degrees of kingpin to get a decent camber curve - and maybe 9 degrees of caster. Formula cars - modern Fords in particular appear to run below ground roll centers; F1 cars are harder to figure out - it's possible they might have high wheel instant centers outside the track and roll centers well below ground and let static negative camber do it all.
Scott, who when he gets some time will have to play games with Mitchell to see if that makes any sense....
[Modified by RR98ITR, 1:05 PM 3/6/2003]
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03-06-2003, 12:31 PM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
i'm drooling over the prospect of your analysis of roll centers. any way to tell how roll center relation to cg affects rate of lateral weight transfer? or is it too difficult to calculate/a useless value in respect to tuning??
nate
[Modified by solo-x, 2:09 AM 3/7/2003]
nate
[Modified by solo-x, 2:09 AM 3/7/2003]
03-06-2003, 05:04 PM
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Re: Smore dat spension tak bout R kaas........ (solo-x)
Take an ITR with an NA setup (800F/1100R) on DOT tires. It develops enough lateral acceleration such that when trail braking / turning in it unloads the inside rear completely and uses up almost all available outside front shaft travel.
Then increase the lateral acceleration. This might be for a case with grippier tires, or a lower ride height. The lower ride height brings down the cg, but the roll centers move in approx 1:1 relationship on these cars so the overturning moment arm is about the same. The lower cg means lower total lateral weight transfer at the same lateral acceleration, but we do this to go faster - the lateral acceleration will be higher and the weight transfer will be not much lower than before and likely significantly higher. WE NOW HAVE LESS FRONT SHAFT TO DO THE ROUGHLY THE SAME OR GREATER AMOUNT OF WORK WITH. So in the case where we have lower ride height AND grippier tires we have significantly increased TOTAL weight transfer.
If we try to drive that NA car under these new conditions it will be spending alot of time on the outside front bumpstops and understeering since everything is already coming off the inside rear, the increase in total weight transfer must come off the inside front - and go to the outside front in cornering phases prior to runout. This is the key thing to look at: as we increase total weight transfer on a car that already is capable of unloading the inside rear the difference can only come off the inside front. Increasing rear roll stiffness will do nothing to change this fact, and will only unload the inside rear earlier in the cornering sequence - and where rear wheel rates are so high already as to give deflections well under an inch these timing differences will be very slight.
So we are left with having to increase total roll resistance with the only tool left to us - the front roll resistance. The front roll resistance MUST GO UP. For a variety of reasons we would do this with the front spring rates.
And how do we achieve balance now that we've got a spring rate bias that is screwed up in terms of the generally valid FWD rear bias orthodoxy? Rear camber, rear tire size or compound.
Scott, who no matter how many times he reads his post, and no matter how many questions he answers, keeps seeing ways he could have written it up better....
Then increase the lateral acceleration. This might be for a case with grippier tires, or a lower ride height. The lower ride height brings down the cg, but the roll centers move in approx 1:1 relationship on these cars so the overturning moment arm is about the same. The lower cg means lower total lateral weight transfer at the same lateral acceleration, but we do this to go faster - the lateral acceleration will be higher and the weight transfer will be not much lower than before and likely significantly higher. WE NOW HAVE LESS FRONT SHAFT TO DO THE ROUGHLY THE SAME OR GREATER AMOUNT OF WORK WITH. So in the case where we have lower ride height AND grippier tires we have significantly increased TOTAL weight transfer.
If we try to drive that NA car under these new conditions it will be spending alot of time on the outside front bumpstops and understeering since everything is already coming off the inside rear, the increase in total weight transfer must come off the inside front - and go to the outside front in cornering phases prior to runout. This is the key thing to look at: as we increase total weight transfer on a car that already is capable of unloading the inside rear the difference can only come off the inside front. Increasing rear roll stiffness will do nothing to change this fact, and will only unload the inside rear earlier in the cornering sequence - and where rear wheel rates are so high already as to give deflections well under an inch these timing differences will be very slight.
So we are left with having to increase total roll resistance with the only tool left to us - the front roll resistance. The front roll resistance MUST GO UP. For a variety of reasons we would do this with the front spring rates.
And how do we achieve balance now that we've got a spring rate bias that is screwed up in terms of the generally valid FWD rear bias orthodoxy? Rear camber, rear tire size or compound.
Scott, who no matter how many times he reads his post, and no matter how many questions he answers, keeps seeing ways he could have written it up better....
nate
03-06-2003, 05:37 PM
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Re: Smore dat spension tak bout R kaas........ (solo-x)
"They're just numbers, but they suggest that I don't suck."
Well, maybe not in this context.
Fear the Frog!!!
Wheeeeeeeee!!!!
Well, maybe not in this context.
Fear the Frog!!!
Wheeeeeeeee!!!!
07-26-2003, 09:56 AM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
I think something that isn't mentioned frequently is, since FWD means so much work at done at the front end, to really make the car go fast, ultimately you have to setup the car to be very aggressively. In the past Racecar Engineering has done several pieces interviewing BTCC drivers and discuss some of the car setup principles. The drivers is a very important part of the performance equation. And his driving style can dictate the setup changes a lot. You can have two drivers with different driving style and different setup achieving nearly identicle lap times.
07-26-2003, 11:08 PM
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Re: Smore dat spension tak bout R kaas........ (tinkerbell)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tinkerbell »</TD></TR><TR><TD CLASS="quote">what is "pneumatic trail effect"
thanks,
t..</TD></TR></TABLE>
http://216.239.53.104/search?q...UTF-8
This helped me.
thanks,
t..</TD></TR></TABLE>
http://216.239.53.104/search?q...UTF-8
This helped me.
03-18-2006, 09:16 PM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote »</TD></TR><TR><TD CLASS="quote">(the square root of 0.7 squared plus 0.7 squared being equal to 1).</TD></TR></TABLE>
So you're saying that the square root of .49 (which is .7) plus .49 is equal to 1? Because it doesn't.
Or are you saying that .7 squared plus .7 squared equals 1? Because it does.
Did you word your math wrong and that's why I'm having a hard time following along?
btw: BACK FROM THE DEAD! Great post so far... I'm half way done reading and 1/4 way done comprehending.
So you're saying that the square root of .49 (which is .7) plus .49 is equal to 1? Because it doesn't.
Or are you saying that .7 squared plus .7 squared equals 1? Because it does.
Did you word your math wrong and that's why I'm having a hard time following along?
btw: BACK FROM THE DEAD! Great post so far... I'm half way done reading and 1/4 way done comprehending.
03-18-2006, 09:43 PM
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Re: Smore dat spension tak bout R kaas........ (rice_classic)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rice_classic »</TD></TR><TR><TD CLASS="quote">
So you're saying that the square root of .49 (which is .7) plus .49 is equal to 1? Because it doesn't.
Or are you saying that .7 squared plus .7 squared equals 1? Because it does.
</TD></TR></TABLE>
Pythagorean theorem.
a^2 + b^2 = c^2
(the square root of 0.7 squared plus 0.7 squared being equal to 1).
Scott was getting at (a^2 + b^2) ^ 0.5 = c
with c = 1 or the radius of your friction circle, and a = b, then a = b = 0.5^0.5 or .71 something.
So you're saying that the square root of .49 (which is .7) plus .49 is equal to 1? Because it doesn't.
Or are you saying that .7 squared plus .7 squared equals 1? Because it does.
</TD></TR></TABLE>
Pythagorean theorem.
a^2 + b^2 = c^2
(the square root of 0.7 squared plus 0.7 squared being equal to 1).
Scott was getting at (a^2 + b^2) ^ 0.5 = c
with c = 1 or the radius of your friction circle, and a = b, then a = b = 0.5^0.5 or .71 something.
03-20-2006, 09:52 AM
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Re: Smore dat spension tak bout R kaas........ (RR98ITR)
Wow, there went my entire lunch break. 
Weight transfer, huh? I've made it a habit of correcting myself (and others) by using "load transfer" instead. I know its a nitpicky thing, but am I correct?
Weight transfer, huh? I've made it a habit of correcting myself (and others) by using "load transfer" instead. I know its a nitpicky thing, but am I correct?
03-20-2006, 07:31 PM
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Re: Smore dat spension tak bout R kaas........ (PIC Performance)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by PIC Performance »</TD></TR><TR><TD CLASS="quote">Wow, there went my entire lunch break.
Weight transfer, huh? I've made it a habit of correcting myself (and others) by using "load transfer" instead. I know its a nitpicky thing, but am I correct?</TD></TR></TABLE>
IMO...
If you define "weight" as the force the earth applies to an object... then most of your "downforce" on an ITA/HC car is from purely weight, when driving on a flat surface. That's not all of it, since you may be cresting a hill, or using a banked turn, or have some significant aero downforce.
Since you're really moving the tire loading, and that tire loading isn't a pure function of weight... well... I guess "load transfer" is more accurate. I'm still going to say "weight transfer", since it's pretty obvious we're not talking about mass transfer.
-Chris, not Scott.
Weight transfer, huh? I've made it a habit of correcting myself (and others) by using "load transfer" instead. I know its a nitpicky thing, but am I correct?</TD></TR></TABLE>
IMO...
If you define "weight" as the force the earth applies to an object... then most of your "downforce" on an ITA/HC car is from purely weight, when driving on a flat surface. That's not all of it, since you may be cresting a hill, or using a banked turn, or have some significant aero downforce.
Since you're really moving the tire loading, and that tire loading isn't a pure function of weight... well... I guess "load transfer" is more accurate. I'm still going to say "weight transfer", since it's pretty obvious we're not talking about mass transfer.
-Chris, not Scott.
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