RR98ITR

Have you noticed Ortiz's columns lately? Why is he spending so much time on 3 wheeled vehicles? Kinda make me feel like we're driving interesting and not just silly kaas.

We've had a few ideas make their way thru here lately that take a new or different twist on the 3-wheeled milieu. One that I remember thinking needed a response needed one because it had a peculiar intuitive appeal. Recall the pissing dog thread in which somebody posited that after inside rear liftoff the front axle continues to lose grip and the car increase in understeer. Hence you wanted to apportion front and rear roll stiffness so as to almost but not quite lift the inside rear. So nice how the idea borrows some light from the truth on it's way down the dark path of error.

Does the front axle produce progressively less grip as it continues to have weight transferred across it after the inside rear has lifted? No. So where's the error?

In saying "grip" we're really speaking of potential grip - not developed grip. The two are actually converging. If we're continuing to transfer weight across the front axle it can only be because we continue to increase the total lateral load. If we were truly losing front grip after the inside rear lifted within the context of the coherent intuition we would necessarily plow straight off the first turn we came to.

So the front pair are converging on their terminal or peak load, and so for that matter is that lone rear. And we typically set up a FWD car to have that lone rear hit load saturation Before the front axle pair in pure lateral load - and then we keep the rear behind us by adding enough throttle to shift enough vertical load to attain as optimal as possible balance between front and rear.

Scott, who here would write a long comprehensive disclaimer covering things like static weight distribution, tire sizing bias and proportion to load and horsepower, and all the stuff I'm just going to take for granted those who know anything know to take into account in considering the very general case discussed above...notwithstanding the fact that all logic is rendered moot by sufficiently cool dampers...

solo-x

hrm, good distinction between potential and developed grip. i'm gonna have to mull over this one a bit. good topic and, despite not having cool dampers, worth at least 2 seconds...

nate

descartesfool

Perhaps we need to make a chart like one of these for the 3 wheeler

http://www.neohio-scca.org/com...2.pdf

I have been paying attention to the latest broadcasts of the British Touring Car Championships with that all-conquering orange Honda RSX, and they sure don't spend much time on 3 wheels (nor did they do so in prior seasons) if they're not bumping off the curbs. Something to learn from over the pond perhaps.

RR98ITR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by descartesfool &raquo;</TD></TR><TR><TD CLASS="quote">...Something to learn from over the pond perhaps.
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Perhaps. But note that that car is fuggin stiff...and you can see that the inside rear is about unloaded - it's not going to get very far, the outside front won't let it.

Scott, who figures a car like that has some really cool dampers - with "perfect" droop travel...

Johnny Mac

All this talk about droop and losing two seconds here and there, why don't we talk about falling rate progressive suspension. No, I won't try to derail Scott's thread...I won't....I won't....self repeat after me....I won't.......

RR98ITR

Haha...AS IF...it's totally impossible to derail one of my threads.

Scott, who gets what he deserves every time I try to be serious for a minute...

Johnny Mac

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">Haha...AS IF...it's totally impossible to derail one of my threads.

Scott, who gets what he deserves every time I try to be serious for a minute...</TD></TR></TABLE>

I hear that posting mathematical formulae is a good way.

RR98ITR

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Johnny Mac &raquo;</TD></TR><TR><TD CLASS="quote">

I hear that posting mathematical formulae is a good way. </TD></TR></TABLE>

They bounce right off my forehead.

Scott, who for some reason just had the idea of a burger pop into his head...where'd That come from?

Chris F

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">burger pop</TD></TR></TABLE>

Beefy Coca Cola? Make mine medium rare.

I dunno Scott, all I need to know is written in your signature.

Andrie Hartanto

One thing I notice on the new FWD WC cars, they don't spend much time on 3 wheels either. Realtime's cars and Tripoint came to mind.

azian21485

ortiz is still writing columns? link pleawese?!

descartesfool

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">

But note that that car is fuggin stiff...and you can see that the inside rear is about unloaded - it's not going to get very far, the outside front won't let it.

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Fuggin stiff is good in many things. Not sure if that car has reallly cool dampers, but it sure has a cool stick shift. It looks fuggin stiff too! Perhaps "it's a good thing" if the outside front keeps things under control and lets all four tires do the work. And then again maybe those guys have a handle on the front to rear weight bias to keep all four tires on the ground. I looked long and hard at all those BTCC pics to find the one with the inside rear just about to lift-off, but not quite. I also looked long and hard at the video coverage of the races, and if they do some 3 wheeling stuff, it is not for long and not easy to see.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by azian21485 &raquo;</TD></TR><TR><TD CLASS="quote">ortiz is still writing columns? link pleawese?!</TD></TR></TABLE>
http://www.pds.i8.com/Ortiz/Ortiz.htm
http://www.auto-ware.com/ubbth...ebase

j-rho

(Taken at the last BTCC race of the '05 season at Brands Hatch, up at the top of druids)

The BTCC cars generally have the inside rear on the tarmac, and the Halford RSXs (err...Honda Integra Type-R's) more so than most, though even their car did show some air from time to time.

ryan12321

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Andrie &raquo;</TD></TR><TR><TD CLASS="quote">One thing I notice on the new FWD WC cars, they don't spend much time on 3 wheels either. Realtime's cars and Tripoint came to mind.</TD></TR></TABLE>

But also think about how stiff their suspension is. The rear tire might be completely unloaded, yet still on the ground. just because its touching doesn't mean its not unloaded.

Not saying that is whats happening, just what it could be.

solo-x

this thread has brought up a new question for me. similar to scott's original question, why does a car setup to unload the inside rear at low cornering forces exhibit a looser corner entry and transient behavior? lets say the car unloads the inside rear at .5 g's. front grip hasn't been reduced much at all at .5 g's, but rear grip would be the same at .5 g's as it would at 1g since vertical load on the outside rear tire is unchanged as cornering force increases. so why is the car looser at entry in this case? i'm suspicious of static rear camber setting vs. roll angle, but i'm interested to hear what others think.

nate

Black R

methinks scott's thread will progressively progress into progressive rates at a progressive rate.

Jack Black

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x &raquo;</TD></TR><TR><TD CLASS="quote">this thread has brought up a new question for me. similar to scott's original question, why does a car setup to unload the inside rear at low cornering forces exhibit a looser corner entry and transient behavior? lets say the car unloads the inside rear at .5 g's. front grip hasn't been reduced much at all at .5 g's, but rear grip would be the same at .5 g's as it would at 1g since vertical load on the outside rear tire is unchanged as cornering force increases. so why is the car looser at entry in this case? i'm suspicious of static rear camber setting vs. roll angle, but i'm interested to hear what others think.

nate</TD></TR></TABLE>

Regardless of when the inside rear fully unloads, with an increase in rear roll stiffness, more weight transfer will happen sooner, with all the expected effects. I think that's why it's looser even at low cornering loads.

solo-x

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Agent Smith &raquo;</TD></TR><TR><TD CLASS="quote">Regardless of when the inside rear fully unloads, with an increase in rear roll stiffness, more weight transfer will happen sooner, with all the expected effects. I think that's why it's looser even at low cornering loads.
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you missed my distinction. i don't want to regurgitate what the books say. i want to investigate just WHY the car is loose at a low cornering force. developed grip of the front isn't that high, but potential grip is very high. developed grip on the rear is apparently less then developed grip at the front, yet dynamically in all aspects except tire camber to road, it is already at a state that should potentially generate 1g. if we continually add rear roll stiffness, we continually move towards looser at entry (load transfer happens quicker and 100% load transfer happens at lower cornering forces) yet pontential grip of the outside rear remains at roughly 1g. (this is assuming we were already stiff enough that camber gain in ride on the outside rear is negligible and terminal roll angle unchanged.) the case study ignores so many parameters it likely isn't a valid case. i'm rapidly approaching the conclusion that potential grip vs. generated grip is a case of subterfuge directed at Andy. Scott? the jig is up!

nate - is clearly confused today as can be seen by these horrible stream of concious posts

RR98ITR

Nate,

What if you're thinking about this backwards?

Would it help to think instead that there is always a lag in the response from the rear of the car, and that the other thing you're doing with higher rear roll stiffness is Increasing the response to control input of the Front?

Scott, who knows what it's like to have a horrible stream of consciousness...and post it...

Jack Black

I'm sure I don't have near as much experience (in either driving or chassis tuning) as you and Scott, but I'll throw out one personal observation and my interpretation of it and let you chew on it.

My car is set up relatively tight compared to a lot of people (450f, 400r, 22mm r arb, -2* r camber). Even so, if I enter a high speed turn without at least a little throttle applied after turn-in, the rear end is coming around.

What if our cars are tuned in such a way that there is no such thing as a stable steady-state condition? What if they are tuned to be dynamically unstable (in the oversteer direction) above a certain speed (or turning rate, maybe?), and the only to create a stable state is to use throttle to transfer weight to the rear? I suspect that this is the case and what stiffening the rear does is lower the speed at which the transition to dynamic instability occurs (and the magnitude of the instability past that point).

Smurf BNMS

These pics are more to provide counter examples than anything...
Also, I remember Tri-Point frequently smoking inside rears while trailbraking. They even had a puncture do to excessive inside rear locking at Laguna Seca. Obviously if the tire is smoking there is still some normal force on it, but either way, it's very nearly unloaded in order to be locked on a FWD car running a high front brake bias.

I think that the reason the inside rear tire is not lifted as much has more to do with controlling camber in the front (higher front roll stiffness). Meaning the ability to run less negative camber, and thus maximize avaliable braking traction. I'm not saying that this is the only reason, but it cannot be neglected, imo. In nearly all of these photos, the cars are braking or at least negatively accelerating and not in a pure roll, when a tire is lifted off the ground (except kerb riding). After talking with Eric Curran's crew chief, he didn't say why they used high front roll stiffness, but he did say that they needed 3000lbs/in, a huge bar, and high canister pressures in the rear to get the balance back. I know this is subject to motion ratios of the car, but at least is shows that both the front and back of touring cars are getting much stiffer. I'm not offering a solution, just speculating on setup trends...















I just found these photos on the web, saved them to my hd, then reposted them. Only the last three are mine...

solo-x

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RR98ITR &raquo;</TD></TR><TR><TD CLASS="quote">Nate,

What if you're thinking about this backwards?

Would it help to think instead that there is always a lag in the response from the rear of the car, and that the other thing you're doing with higher rear roll stiffness is Increasing the response to control input of the Front?

Scott, who knows what it's like to have a horrible stream of consciousness...and post it...</TD></TR></TABLE>

ya got me. a very easily could be thinking about it backwards. wouldn't be the first time. a response time effect would make sense, but i think static rear camber and outside rear tire slip angle play a bigger role. anyway, there is a reason i purchased a DL1, and it's not so i can play around on my computer more. i keep getting the feeling that this thread is just another way of asking if the chicken came before the egg or vice versa though.

imo, the only advantage to unloading the inside rear at lower then max cornering force is an improvement in how early you can get on the throttle coming off a corner. i suppose if you can do that without letting your cg height go up or without having to sacrifice mid-corner balance for entry stability it's all good. for an autocross car you have to worry about having a package that is both stable enough to aggressively drive a slalom while at the same time being loose enough to turn well in tight radius corners. i was unable to accomplish both of those goals by throwing a lot of rear roll stiffness at the car. once i started to free the car up mid-corner with camber, toe, tire size, tire pressure, etc. i ended up with a package that was way too loose at entry. i didn't accomplish both stable in transient and loose in steady state until i got the inside rear tire down. maybe ortiz is talking about the same thing? a car that is sufficiently free in steady state while lifting the tire at low cornering forces will be too loose at entry. tune the car for entry and now it's too tight steady state and gets progressively tighter as roll angle/cornering force increases after wheel lift off.

once i get my DL1 i do plan on spending a couple days on a skidpad to see if my current setup is giving anything up steady state and off over a more rearward biased setup. it's a backburner project though, so when and if it happens is still up in the air.

nate - isn't sure if anyone is even reading this anymore. isn't sure if HE is even reading it anymore...

solo-x

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Smurf BNMS &raquo;</TD></TR><TR><TD CLASS="quote">These pics are more to provide counter examples than anything...
Also, I remember Tri-Point frequently smoking inside rears while trailbraking. They even had a puncture do to excessive inside rear locking at Laguna Seca. Obviously if the tire is smoking there is still some normal force on it, but either way, it's very nearly unloaded in order to be locked on a FWD car running a high front brake bias.

I think that the reason the inside rear tire is not lifted as much has more to do with controlling camber in the front (higher front roll stiffness). Meaning the ability to run less negative camber, and thus maximize avaliable braking traction. I'm not saying that this is the only reason, but it cannot be neglected, imo. In nearly all of these photos, the cars are braking or at least negatively accelerating and not in a pure roll, when a tire is lifted off the ground (except kerb riding). After talking with Eric Curran's crew chief, he didn't say why they used high front roll stiffness, but he did say that they needed 3000lbs/in, a huge bar, and high canister pressures in the rear to get the balance back. I know this is subject to motion ratios of the car, but at least is shows that both the front and back of touring cars are getting much stiffer. I'm not offering a solution, just speculating on setup trends...
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getting a front heavy car to not lift the inside rear in combined dive and roll is VERY tough. on street tires in the rain, my setup will lift an inside rear in combined dive and roll. and one of those cars was on two wheels, so it doesn't count!

Andy Hollis

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by solo-x &raquo;</TD></TR><TR><TD CLASS="quote">

you missed my distinction. i don't want to regurgitate what the books say. i want to investigate just WHY the car is loose at a low cornering force. developed grip of the front isn't that high, but potential grip is very high. developed grip on the rear is apparently less then developed grip at the front, yet dynamically in all aspects except tire camber to road, it is already at a state that should potentially generate 1g. if we continually add rear roll stiffness, we continually move towards looser at entry (load transfer happens quicker and 100% load transfer happens at lower cornering forces) yet pontential grip of the outside rear remains at roughly 1g. (this is assuming we were already stiff enough that camber gain in ride on the outside rear is negligible and terminal roll angle unchanged.) the case study ignores so many parameters it likely isn't a valid case. i'm rapidly approaching the conclusion that potential grip vs. generated grip is a case of subterfuge directed at Andy. Scott? the jig is up!

nate - is clearly confused today as can be seen by these horrible stream of concious posts</TD></TR></TABLE>

Thought: "Loose" doesn't mean that the rear has actually let go. It means that the slip angle of the rear tires is larger than that of the fronts. If you move roll stiffness more to the rear, the outside rear tire is getting more weight than the outside front...right up until there is no more weight on the inside rear to transfer outwards.

Let's do an example. Say 60/40 car at 2000 lbs total, and even side-to-side. So that's 1200/800, or 600/400 for each corner. And let's say we have roll stiffness biased to the back in the extreme...say at a 1:4 ratio (big *** rear bar).

Now, we start pulling moderate g's and 500 lbs of total weight transfer to the outside. 100 of that goes across the front, and 400 goes across the rear. Now you have your dynamic outside weights at 700/800. The outside rear tire is now working harder than the outside front, thus running at a larger slip angle. That's the definition of oversteer. And you aren't over the limit at either end, yet.

Or am I missing the point?

--Andy

solo-x

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Andy Hollis &raquo;</TD></TR><TR><TD CLASS="quote">Thought: "Loose" doesn't mean that the rear has actually let go. It means that the slip angle of the rear tires is larger than that of the fronts. If you move roll stiffness more to the rear, the outside rear tire is getting more weight than the outside front...right up until there is no more weight on the inside rear to transfer outwards.

Let's do an example. Say 60/40 car at 2000 lbs total, and even side-to-side. So that's 1200/800, or 600/400 for each corner. And let's say we have roll stiffness biased to the back in the extreme...say at a 1:4 ratio (big *** rear bar).

Now, we start pulling moderate g's and 500 lbs of total weight transfer to the outside. 100 of that goes across the front, and 400 goes across the rear. Now you have your dynamic outside weights at 700/800. The outside rear tire is now working harder than the outside front, thus running at a larger slip angle. That's the definition of oversteer. And you aren't over the limit at either end, yet.

Or am I missing the point?

--Andy
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i don't know if there was a point. i was overlooking slip angle and a whole slew of other things. i keep posting because this thread topic interests me but there is very little analytical content beyond "so and so lifts, so and so doesn't". i don't feel like i'm actually contributing much though, beyond bumping a thread without being excruciatingly obvious. i've got that whole "on the verge of THE breakthrough" feeling though it's more likely one of those "ah crap, i was close, but left out this one little thing..." sort of breakthroughs. thinking out loud sometimes helps me put many random thoughts into order and "solve" them. other times it serves as a way to have others "check my work". i'm willing to sound like an idiot every now and again if that motivates someone wiser then i to straighten me out. so where is johnny mac and gspeedr??

nate - thinks discovering you didn't actually know something you thought you knew is fun, but only sometimes