How to measure downforce using damper pots and a DL1
04-24-2006, 06:55 PM
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How to measure downforce using damper pots and a DL1
I have been thinking of ways to measure downforce on the track and thus to evaluate any aero mods. Here is what I am thinking. Downforce can be measured separately front and rear, since the vertical force downwards (or upwards for lift) acts on the front axle line and on the rear axle line. If one knows the ride height vs speed, and the resisting force from the suspension, one can measure downforce at each axle. Then we can also locate the centre of pressure. This just requires knowing ride height and suspension force at the wheel. If one assumes straight line conditions with no wind or bumps, then it might work. We will neglect tire deflection, but we might add it in later.
I would think you first remove the springs and dampers and measure the actual ride height of the body at each axle using a jack along the centreline of the car and record the damper pot readings (this might be a little tricky if dampers are removed). We now make a table and we know front and rear ride height vs. damper pot readings. If the damper pots are perfectly vertical, this would be easier.
We then measure the motion ratio at each wheel so we know the position of the wheel in terms of the position of the spring relative to the body motion to know the force on the tire. This is to get the force at the wheel which we will need to know the downforce. Say a 1/2" movement of the body causes the front springs to compress 1", and that the spring has a constant of 500 lbs/in. Thus each front spring would cause a force of 250 lbs at each front wheel/tire. The total resisting force of the springs is thus 250+250=500 lbs for a 1/2" downward motion of the body due to downforce. We are assuming steady state so there is no damper effect, and no ARB forces. one could just disconnect the ARB's for the test). The same procedure is applied to each axle.
So it seems like some setup to first measure things in the shop and then all we need are the values of the damper pot readings to get downforce by using some math channels. At slow speeds down the straight we have static ride height with static force on the wheels. As speed increases, downforce pushes the car down and we just plot this force vs speed to know what the aero stuff is doing. Sounds easy in principle.
I would think you first remove the springs and dampers and measure the actual ride height of the body at each axle using a jack along the centreline of the car and record the damper pot readings (this might be a little tricky if dampers are removed). We now make a table and we know front and rear ride height vs. damper pot readings. If the damper pots are perfectly vertical, this would be easier.
We then measure the motion ratio at each wheel so we know the position of the wheel in terms of the position of the spring relative to the body motion to know the force on the tire. This is to get the force at the wheel which we will need to know the downforce. Say a 1/2" movement of the body causes the front springs to compress 1", and that the spring has a constant of 500 lbs/in. Thus each front spring would cause a force of 250 lbs at each front wheel/tire. The total resisting force of the springs is thus 250+250=500 lbs for a 1/2" downward motion of the body due to downforce. We are assuming steady state so there is no damper effect, and no ARB forces. one could just disconnect the ARB's for the test). The same procedure is applied to each axle.
So it seems like some setup to first measure things in the shop and then all we need are the values of the damper pot readings to get downforce by using some math channels. At slow speeds down the straight we have static ride height with static force on the wheels. As speed increases, downforce pushes the car down and we just plot this force vs speed to know what the aero stuff is doing. Sounds easy in principle.
04-24-2006, 08:42 PM
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"aero stuff"=? . are you looking at a rear wing setup or a lip and splitter? cannards? i assume you are trying to accomplish results for an aero "package" and not individual pieces since you are using the suspension variables. what car?
04-24-2006, 10:13 PM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nello a. »</TD></TR><TR><TD CLASS="quote">"aero stuff"=? what car?</TD></TR></TABLE> Dude, the guy's not dumb, it's called "abstraction."
The method you've outlined seems very useful in theory. The only practical issue I can think of is the resolution of your damper pot sensors. If your motion ratio isn't extremely advantageous, your springs aren't particularly soft, or you're not generating a lot of downforce, you *might* have trouble getting precise enough readings to generate a meaningful curve. A really, really, really smooth track would also help.
Then again, if you've got decent resolution you might be able to fit a really nice curve to your data.
Good post...
-- Jon
The method you've outlined seems very useful in theory. The only practical issue I can think of is the resolution of your damper pot sensors. If your motion ratio isn't extremely advantageous, your springs aren't particularly soft, or you're not generating a lot of downforce, you *might* have trouble getting precise enough readings to generate a meaningful curve. A really, really, really smooth track would also help.
Then again, if you've got decent resolution you might be able to fit a really nice curve to your data.
Good post...
-- Jon
04-24-2006, 10:43 PM
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Re: How to measure downforce using damper pots and a DL1 (Sterndotstern)
Interesting idea, but I would argue that that is a lot of work to calculate only half of the necessary information to evaluate you aero package. If you want to do some thinking, I would spend time trying to find a way to measure your lift/drag ratio, in my opinion much more useful setting up your car then lift/speed.
I'm saying that based on the assumption that we are looking to create the maximum downforce possible, until the gains we make from the downforce are overshadowed by the amount of drag create by your aero surfaces. The balance of the car can be corrected by suspension settings.
To do this you substitute a section of the mounting arms of your wing with load sensors. Since you know the geometry of your wing mounts relative to your aero surface, you could easily calculate the vector of force on the wing necessary to produce the load data you collected from your sensors. From there, simply break that vector down into its x and y components and you arrive at you lift and drag.
At least thats what I would do...hmmmm, I wonder where I could get some little load sensors?????
I'm saying that based on the assumption that we are looking to create the maximum downforce possible, until the gains we make from the downforce are overshadowed by the amount of drag create by your aero surfaces. The balance of the car can be corrected by suspension settings.
To do this you substitute a section of the mounting arms of your wing with load sensors. Since you know the geometry of your wing mounts relative to your aero surface, you could easily calculate the vector of force on the wing necessary to produce the load data you collected from your sensors. From there, simply break that vector down into its x and y components and you arrive at you lift and drag.
At least thats what I would do...hmmmm, I wonder where I could get some little load sensors?????
04-25-2006, 02:28 AM
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Re: How to measure downforce using damper pots and a DL1 (mikeski38)
The drag part is measured using coast-downs which gives you rolling resistance and aero drag and all you need for that is a log of speed vs time. It could even be done at the same time as the downforce measurement by just lifting off the gas and logging time to decelerate if you have a long enough piece of tarmac. See here for example:https://honda-tech.com/zero...age=4 or on Race Technology's web site:http://www.race-technology.com....html
Many formula cars use force transducers on the pushrods to effectively calculate force at the contact patch, but on my ITR I don't have that luxury. I also don't see how putting a transducer under the wing or splitter could work since it would be hard to know the actual effect at the tire, which is all you care about, that being the point of grip generation, and the basis for using downforce. Any flex in the body between say wing mounting point and axle would negate the precision of the measurement.
I thought up a scheme to get the actual force vs displacement of the suspension directly. One places the car on scales located directly underneath a hefty steel beam (I happen to have such a beam in the middle of my garage). Then one places 2 strong rods with turnbuckles between the beam and the damper mounts. Turn each turnbuckle an equal amount and push the car down towards the scales. Measure actual downward displacement of the body using dial indicators between scales and fender lip above centreline of tire, and record the reading of the suspension pots. Then make a table of the scale reading for force from the scale readings (static and extra from displacement), the measured actual body displacement from the dial indicators and the damper pot reading from a voltmeter or the logger. This takes out the motion ratio calculation and includes the tire deflection, bushing deflection, damper gas pre-load, etc. Repeat for the other axle. On my ITR, all I would have to do is remove the hood and rear hatch I think to locate the vertical "push" rods. A plate to lock them in place using the nuts holding the dampers to the body might be a good idea as the forces would be rather large and might avoid some potential unfortunate "slippage". The scheme might work better with a nice soft set of springs rather than the ones I have in there now, since the comments about pot resolution and actual small displacement are worth taking into consideration.
Many formula cars use force transducers on the pushrods to effectively calculate force at the contact patch, but on my ITR I don't have that luxury. I also don't see how putting a transducer under the wing or splitter could work since it would be hard to know the actual effect at the tire, which is all you care about, that being the point of grip generation, and the basis for using downforce. Any flex in the body between say wing mounting point and axle would negate the precision of the measurement.
I thought up a scheme to get the actual force vs displacement of the suspension directly. One places the car on scales located directly underneath a hefty steel beam (I happen to have such a beam in the middle of my garage). Then one places 2 strong rods with turnbuckles between the beam and the damper mounts. Turn each turnbuckle an equal amount and push the car down towards the scales. Measure actual downward displacement of the body using dial indicators between scales and fender lip above centreline of tire, and record the reading of the suspension pots. Then make a table of the scale reading for force from the scale readings (static and extra from displacement), the measured actual body displacement from the dial indicators and the damper pot reading from a voltmeter or the logger. This takes out the motion ratio calculation and includes the tire deflection, bushing deflection, damper gas pre-load, etc. Repeat for the other axle. On my ITR, all I would have to do is remove the hood and rear hatch I think to locate the vertical "push" rods. A plate to lock them in place using the nuts holding the dampers to the body might be a good idea as the forces would be rather large and might avoid some potential unfortunate "slippage". The scheme might work better with a nice soft set of springs rather than the ones I have in there now, since the comments about pot resolution and actual small displacement are worth taking into consideration.
04-25-2006, 04:26 AM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
Just a couple notes:
You mentioned tire deflection in your original post. If you're measuring change in damper length, tire deflection should have no impact on the measurements. The damper length should change by the same amount under a given load regardless what the tire does.
Second, do you really care about the actual magnitude of the downforce as much as you care about the front-rear aerodynamic balance and whether a given change increases or decreases downforce? Unless you really need to know that you have 12 lb of rear downforce at 100 mph vs. 13 lb of downforce, I don't think you need to go to such great lengths to calibrate the pots. You should be able to take measurements at low speed and compare that to the high speed measurements to determine the relative amount of downforce generated by different devices or settings.
You mentioned tire deflection in your original post. If you're measuring change in damper length, tire deflection should have no impact on the measurements. The damper length should change by the same amount under a given load regardless what the tire does.
Second, do you really care about the actual magnitude of the downforce as much as you care about the front-rear aerodynamic balance and whether a given change increases or decreases downforce? Unless you really need to know that you have 12 lb of rear downforce at 100 mph vs. 13 lb of downforce, I don't think you need to go to such great lengths to calibrate the pots. You should be able to take measurements at low speed and compare that to the high speed measurements to determine the relative amount of downforce generated by different devices or settings.
04-25-2006, 07:28 AM
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Re: How to measure downforce using damper pots and a DL1 (Jack Black)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jack Black »</TD></TR><TR><TD CLASS="quote">Just a couple notes:
You mentioned tire deflection in your original post. If you're measuring change in damper length, tire deflection should have no impact on the measurements. The damper length should change by the same amount under a given load regardless what the tire does.
</TD></TR></TABLE>
tire deflection WILL affect damper displacement. the tire is another spring in series with the main spring. the actual spring rate at any corner is a composite of the wheel rate of the main spring and the spring rate of the tire. actual spring rate of a corner is less then the wheel rate of the main spring. study the math behind springs in series and dual rate spring setups. it'll make sense then, since i'm pretty sure my explanation only makes perfect sense to me.
You mentioned tire deflection in your original post. If you're measuring change in damper length, tire deflection should have no impact on the measurements. The damper length should change by the same amount under a given load regardless what the tire does.
</TD></TR></TABLE>
tire deflection WILL affect damper displacement. the tire is another spring in series with the main spring. the actual spring rate at any corner is a composite of the wheel rate of the main spring and the spring rate of the tire. actual spring rate of a corner is less then the wheel rate of the main spring. study the math behind springs in series and dual rate spring setups. it'll make sense then, since i'm pretty sure my explanation only makes perfect sense to me.
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04-25-2006, 07:39 AM
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Re: How to measure downforce using damper pots and a DL1 (solo-x)
I'm referring to static damper length. You're right when talking about the response to a dynamic input.
Consider two scenarios: 1 - the car sitting on it's tires, 2 - the car sitting with its wheels off with jackstands under the knuckles. Will the static damper length be the same or different in these two scenarios (ignoring friction)?
Consider two scenarios: 1 - the car sitting on it's tires, 2 - the car sitting with its wheels off with jackstands under the knuckles. Will the static damper length be the same or different in these two scenarios (ignoring friction)?
04-25-2006, 10:14 PM
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Re: How to measure downforce using damper pots and a DL1 (mikeski38)
This was at sema, don't know how good it works or even if there out yet.
"ARC has released a revolutionary Down Force Meter that mounts sensors between the spoiler and trunk lid so that when you are doing a 150 on the “racetrack” you can see if you are generating adequate down-force to keep the car stable. The really trick part about this setup is that you can actually log your results in real-time as you parade around the track. This will help you fine tune the car to achieve peak performance and optimal track adhesion. The Down Force Meter is going to priced at around $500."
"ARC has released a revolutionary Down Force Meter that mounts sensors between the spoiler and trunk lid so that when you are doing a 150 on the “racetrack” you can see if you are generating adequate down-force to keep the car stable. The really trick part about this setup is that you can actually log your results in real-time as you parade around the track. This will help you fine tune the car to achieve peak performance and optimal track adhesion. The Down Force Meter is going to priced at around $500."
04-26-2006, 03:25 AM
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Re: How to measure downforce using damper pots and a DL1 (ekim952522000)
Such a device might be useful to know what a wing is doing, assuming you could find a way to mount it that makes sense, but it will tell you little about the total downforce or lift on the entire car. You can obviously not know what a device such as an air-dam, a splitter, undertray or diffuser is doing. Nor can you know what effect ride height and rake has on the aero. You could also not know where the center of pressure is to see if your aero package is properly balanced front to rear. If that unit is $500, I would consider money would to be much better spent towards a logger like a DL1 which will calculate drag for you. I think what you need to measure is the force along each axle line, acting on the tires, and I think my scheme might work. It will cost around $1000 for the logger which I have, and another $1000 for 4 damper pots, which I do not yet have. Plus scales which I have, and the big garage beam. I also have some dial indicators for 1" travel which is more than I will ever get from any aero I am going to use. All I would need to fabricate is the damper pot mounts, some heavy duty rods with turnbuckles to push the car down between the scales and the beam, and mounts for the dial indicators. That is going to be some amount of work and expense, so what I am wondering about is how precisely the scheme can work for the likely very low forces and displacements involved. 100 lbs of downforce on the front axle if I could get it is not going to move the suspension much, and one has to figure out a way to separate out the road irregularity noise from the damper displacement. Since I have figured out this scheme myself and not read it in any book, I would be curious if it can actually be done before I try it. While it might work "in theory", will it work "in practice"
04-26-2006, 10:56 AM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
Playing devil's advocate here:
Since you're planning on spending some cash and labor on mocking up your "contraption", one simple way to remove the damper noise caused by road irregularities is to go the extra step and build a wind tunnel.
:D
Since you're planning on spending some cash and labor on mocking up your "contraption", one simple way to remove the damper noise caused by road irregularities is to go the extra step and build a wind tunnel.
:D
04-26-2006, 12:09 PM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
As long as the road is perfectly level and perfectly smooth it'll probably work out just fine. Otherwise you're suspension movements caused by downforce will be mixed with other movements from pavement imperfections and such. Or am I totaly missing the point here?
04-26-2006, 12:54 PM
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Re: How to measure downforce using damper pots and a DL1 (ekim952522000)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ekim952522000 »</TD></TR><TR><TD CLASS="quote">This was at sema, don't know how good it works or even if there out yet.
</TD></TR></TABLE>
That's just a strain gauge/s with a display.
</TD></TR></TABLE>
That's just a strain gauge/s with a display.
04-26-2006, 01:22 PM
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Re: How to measure downforce using damper pots and a DL1 (nonsense)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nonsense »</TD></TR><TR><TD CLASS="quote">As long as the road is perfectly level and perfectly smooth it'll probably work out just fine. Otherwise you're suspension movements caused by downforce will be mixed with other movements from pavement imperfections and such. Or am I totaly missing the point here?
</TD></TR></TABLE>
The data will have to be processed quite a bit to get useful numbers from it. It will have to be smoothed quite a bit to remove the suspension movement caused by bumps, and the overall motion of the chassis due to lateral and longitudinal acceleration will also have to be factored out.
Honestly, I'm not sure this can be done using damper length. Consider a G3 Integra with 1000 lb/in rear springs. Adding 100 lb of downforce at the rear axle will only compress the shock by an additional 0.0625 inches. Here, check my calculations:
f = force at wheel (assumed to be force at axle / 2)
k = wheel rate
d = wheel motion
K = spring rate
D = spring motion
M = motion ration as (wheel/spring)
f = k*d
k = K/M^2
d = D*M
f = (K/M^2)*(D*M) = K*D/M
D = f*M/K = 50 * 1.35 / 1000 = 0.0675
That seems like it could very well be within the range of uncertainty caused by friction. I haven't figured out a test to quantify the uncertainty due to friction yet.
Because of the uncertainty caused by friction in the suspension, it would seem to me that it would be much more accurate to use force rather than motion. Maybe use strain guages on the shock or something like those wing pads pictured above between the upper shock mount and the chassis.
</TD></TR></TABLE>
The data will have to be processed quite a bit to get useful numbers from it. It will have to be smoothed quite a bit to remove the suspension movement caused by bumps, and the overall motion of the chassis due to lateral and longitudinal acceleration will also have to be factored out.
Honestly, I'm not sure this can be done using damper length. Consider a G3 Integra with 1000 lb/in rear springs. Adding 100 lb of downforce at the rear axle will only compress the shock by an additional 0.0625 inches. Here, check my calculations:
f = force at wheel (assumed to be force at axle / 2)
k = wheel rate
d = wheel motion
K = spring rate
D = spring motion
M = motion ration as (wheel/spring)
f = k*d
k = K/M^2
d = D*M
f = (K/M^2)*(D*M) = K*D/M
D = f*M/K = 50 * 1.35 / 1000 = 0.0675
That seems like it could very well be within the range of uncertainty caused by friction. I haven't figured out a test to quantify the uncertainty due to friction yet.
Because of the uncertainty caused by friction in the suspension, it would seem to me that it would be much more accurate to use force rather than motion. Maybe use strain guages on the shock or something like those wing pads pictured above between the upper shock mount and the chassis.
04-26-2006, 04:21 PM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
What is a DL1?
I made this contraption to measure shock movements on my type r, at the time it was the fastest cheapest B&B data modual they sold, $150, serial. Now they have a USB modual that is faster, it's $260.
http://www.bb-elec.com/product...l=742
Here's the modual I have, wow! it's half the price I paid only three years ago!
http://www.bb-elec.com/product...il=40
I made this contraption to measure shock movements on my type r, at the time it was the fastest cheapest B&B data modual they sold, $150, serial. Now they have a USB modual that is faster, it's $260.
http://www.bb-elec.com/product...l=742
Here's the modual I have, wow! it's half the price I paid only three years ago!
http://www.bb-elec.com/product...il=40
04-27-2006, 12:09 PM
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Re: How to measure downforce using damper pots and a DL1 (rallybird)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rallybird »</TD></TR><TR><TD CLASS="quote">What is a DL1?</TD></TR></TABLE>
See here: http://www.race-technology.com....html
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jack Black »</TD></TR><TR><TD CLASS="quote">
The data will have to be processed quite a bit to get useful numbers from it. It will have to be smoothed quite a bit to remove the suspension movement caused by bumps, and the overall motion of the chassis due to lateral and longitudinal acceleration will also have to be factored out.
Honestly, I'm not sure this can be done using damper length. ...
...Because of the uncertainty caused by friction in the suspension, it would seem to me that it would be much more accurate to use force rather than motion. Maybe use strain gauges on the shock or something like those wing pads pictured above between the upper shock mount and the chassis.
</TD></TR></TABLE>
I agree with you on the scale of displacements one gets. That is why one would be wise to change out the springs for ones in the 250 lb range to increase the displacement by 4 times. I am wondering if anyone sees anything wrong with the principle of the scheme I have outlined. While I agree that a direct force measurement would be better, I am not sure it can be done in the range of the $1000 I was thinking of spending on damper pots from these guys:http://www.activesensors.com/
I have seen some very slick strain gauge arrangements on the top of damper shafts used by high end pro teams, but I am sure the price is out of my league, as is building my own wind tunnel (unless I scale it down a little and use some ABS plumbing pipe and a hair dryer to make it, but then the Reynolds number will kill me). I was just hoping to come up with something a little more ghetto that I can just hook up to my DL1. I have never seen any write up on what I am describing, so perhaps it is not possible in practice, but it might be worth a try. I can use the damper pots to get suspension info as well, so they would serve more than one purpose.
Then there is the issue of signal processing. Does one filter out the data to remove high frequencies (road irregularities) and take the difference between low speed and high speed runs down a straight section of road?
See here: http://www.race-technology.com....html
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jack Black »</TD></TR><TR><TD CLASS="quote">
The data will have to be processed quite a bit to get useful numbers from it. It will have to be smoothed quite a bit to remove the suspension movement caused by bumps, and the overall motion of the chassis due to lateral and longitudinal acceleration will also have to be factored out.
Honestly, I'm not sure this can be done using damper length. ...
...Because of the uncertainty caused by friction in the suspension, it would seem to me that it would be much more accurate to use force rather than motion. Maybe use strain gauges on the shock or something like those wing pads pictured above between the upper shock mount and the chassis.
</TD></TR></TABLE>
I agree with you on the scale of displacements one gets. That is why one would be wise to change out the springs for ones in the 250 lb range to increase the displacement by 4 times. I am wondering if anyone sees anything wrong with the principle of the scheme I have outlined. While I agree that a direct force measurement would be better, I am not sure it can be done in the range of the $1000 I was thinking of spending on damper pots from these guys:http://www.activesensors.com/
I have seen some very slick strain gauge arrangements on the top of damper shafts used by high end pro teams, but I am sure the price is out of my league, as is building my own wind tunnel (unless I scale it down a little and use some ABS plumbing pipe and a hair dryer to make it, but then the Reynolds number will kill me). I was just hoping to come up with something a little more ghetto that I can just hook up to my DL1. I have never seen any write up on what I am describing, so perhaps it is not possible in practice, but it might be worth a try. I can use the damper pots to get suspension info as well, so they would serve more than one purpose.
Then there is the issue of signal processing. Does one filter out the data to remove high frequencies (road irregularities) and take the difference between low speed and high speed runs down a straight section of road?
04-27-2006, 12:16 PM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
In case anyone wants to know pricing for damper pots, here is a response I got recently from activesensors:
"Hello Claude,
Thank you for your enquiry for linear sensors. We recommend the CLS1322 model for suspension measurement. They are more robust than the CLS095.
The prices are:
CLS1322-100mm @ $185.00 each.
CLS1322-125mm @ $195.00 each.
CLS1322--150mm @ $205.00 each.
Delivery from stock.
Can I ask you a question? Where did you hear about us?
best regards
Chris Smith."
"Hello Claude,
Thank you for your enquiry for linear sensors. We recommend the CLS1322 model for suspension measurement. They are more robust than the CLS095.
The prices are:
CLS1322-100mm @ $185.00 each.
CLS1322-125mm @ $195.00 each.
CLS1322--150mm @ $205.00 each.
Delivery from stock.
Can I ask you a question? Where did you hear about us?
best regards
Chris Smith."
04-27-2006, 12:28 PM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
What are you really going to get out of all this? So you'll know how much downforce part A makes compared to part B. After spending $1000 on the sensors and all the time you'll spend setting it up and testing, then crunching the data you could have tried all the configurations at the track comparing lap times. $1000 will buy you at least 6 days of track testing.
Slower is bad, faster is good. Pretty easy to figure out, especially if you already use a DL1.
Slower is bad, faster is good. Pretty easy to figure out, especially if you already use a DL1.
04-28-2006, 02:58 AM
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Re: How to measure downforce using damper pots and a DL1 (nonsense)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nonsense »</TD></TR><TR><TD CLASS="quote">$1000 will buy you at least 6 days of track testing.
</TD></TR></TABLE>
I do a lot of track days. You and I must be driving at different venues. Here is a typical track day budget at Watkins Glen for me:
Description QTY Cost Ext-Cost Days-of-use Cost per day
Hoosiers 4 $194.00 $776.00 10 $77.60
Tire shipping 1 $60.00 $60.00 10 $6.00
Tire mounting 4 $20.00 $80.00 10 $8.00
XP10 F w rotors 1 $163.00 $163.00 4 $40.75
XP10 R w rotors 1 $129.00 $129.00 6 $21.50
Pads/rotors ship 1 $20.00 $20.00 6 $3.33
Seneca Lodge 2 $80.00 $160.00 2 $80.00
Trackmasters 2 $260.00 $520.00 2 $260.00
Sunoco 94 to Track 26 $3.50 $91.00 2 $45.50
Sunoco 94 at Track 20 $3.50 $70.00 1 $70.00
That works out to $91.60 for tires, $65.58 for brakes, $80 for hotel, $260 for track fees, $115.60 for fuel, per track day.
Total Cost per Track day $612.68
(I should never add those numbers up!!!!)
That is assuming I don't include cost for any food, wear items on car, breakdowns or consider the cost per year/per track day of any new parts added to the car.
$1000 per 6 track days: I wish!
</TD></TR></TABLE>
I do a lot of track days. You and I must be driving at different venues. Here is a typical track day budget at Watkins Glen for me:
Description QTY Cost Ext-Cost Days-of-use Cost per day
Hoosiers 4 $194.00 $776.00 10 $77.60
Tire shipping 1 $60.00 $60.00 10 $6.00
Tire mounting 4 $20.00 $80.00 10 $8.00
XP10 F w rotors 1 $163.00 $163.00 4 $40.75
XP10 R w rotors 1 $129.00 $129.00 6 $21.50
Pads/rotors ship 1 $20.00 $20.00 6 $3.33
Seneca Lodge 2 $80.00 $160.00 2 $80.00
Trackmasters 2 $260.00 $520.00 2 $260.00
Sunoco 94 to Track 26 $3.50 $91.00 2 $45.50
Sunoco 94 at Track 20 $3.50 $70.00 1 $70.00
That works out to $91.60 for tires, $65.58 for brakes, $80 for hotel, $260 for track fees, $115.60 for fuel, per track day.
Total Cost per Track day $612.68
(I should never add those numbers up!!!!)
That is assuming I don't include cost for any food, wear items on car, breakdowns or consider the cost per year/per track day of any new parts added to the car.
$1000 per 6 track days: I wish!
04-28-2006, 04:33 AM
#20
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool »</TD></TR><TR><TD CLASS="quote">Then there is the issue of signal processing. Does one filter out the data to remove high frequencies (road irregularities) and take the difference between low speed and high speed runs down a straight section of road?</TD></TR></TABLE>
That would be the simplest way to do it. Extract some constant-speed sections of at least a few seconds, and average that to get the suspension position at that speed.
You can get an idea of how reliable the data is by computing the average suspension position for many different sections at each of your target speeds. There are various statistical methods you can use to determine if the data is significant (I've happily forgotten most of them by now). As a first cut, I would compute the standard deviation of the positions at each speed; if the mean of the position at high speed is within the standard deviation of the position at low speed, the data is probably not reliable.
That would be the simplest way to do it. Extract some constant-speed sections of at least a few seconds, and average that to get the suspension position at that speed.
You can get an idea of how reliable the data is by computing the average suspension position for many different sections at each of your target speeds. There are various statistical methods you can use to determine if the data is significant (I've happily forgotten most of them by now). As a first cut, I would compute the standard deviation of the positions at each speed; if the mean of the position at high speed is within the standard deviation of the position at low speed, the data is probably not reliable.
05-02-2006, 03:23 AM
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Re: How to measure downforce using damper pots and a DL1 (descartesfool)
who said anyone was dumb professor? could this data already exist and the right engineer just needs to be found ? i guess not.
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Vracer111
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