ED9man

has your friend ever even tried to drive fast around a corner his overweight understeering pig, i have no idea why you would be wishing for more rear grip after trying that even once

RED_90TEG

dont talk to ur friend anymore. problem solved. and dont make posts like this in ht.

solo-x

I wouldn't go _that_ far. I thought the post evolved into a pretty decent exchange of ideas.

Stinkycheezmonky

Yeah, I agree there too. Some interesting stuff came up out of the original ridiculousness.

L8apex

I like to think of it as track time for the ol' noggin.

meb58

The point isn't more rear grip, it's more rear roll stiffness...which increases when making the rear track wider. Initial turn-in oversteer increases with an increase in steady state rear grip...which leads to high speed stability or high speed understeer...the perfect balance you should seek on a road course...an increase in initial turn-in oversteer is also very helpful in autoX...all perfectly exploitable physics.

Wacked2882

I'm having issues with accepting that wider rear track width will increase entry oversteer. Wider track widths decrease TLLTD - so the rear is going to transfer less load across its axle pair and increase grip. In my experience, going to a wider front track width greatly increase the transient response of the car and increased entry oversteer - but with very little effect on midcorner grip.

As already mentioned - spacers and lower offset wheels will change the wheel rate of any double wishbone suspension as well. Going to a wider rear track will decrease the wheel rate.


Also - I think the "more rear roll stiffness = oversteer" argument might need some clarification. I agree with it to a point, but only under the assumption that you are close to the peak of the bell curve and are already near "optimal roll stiffness". If the car is too soft in the rear, going stiffer may increase rear grip and induce understeer in certain phases of a corner.

meb58

I should clarify that wheel rates are assumed to remain the same...so no loss in motion ratio with SLA or multi-link rear.

My experience with a wider front track is exactly the opposite of yours...although my last track car used a Mac Strut front end - JCW Mini. Since motion ratio is nearly 1:1 the wider track provided more front roll resistance and increased understeer. For an SLA setup you have to adjust wheel rate to achieve tha same result, I should think.

Regarding TLLTD...if we increase roll resistance over a given axle it must distribute weight to the other axle. I think the argument may be with a type of suspension design rather than roll resistance...all else equal - wheel rate/bar rates - a wider rear track should induce more oversteer...conversly, making the front track more narrow - in a simplified way - is the same thing.

...when you write bell curve are you refering tire saturation? i know you wrote roll stiffness...just tryin to understand your question/statement.

EDIT: Wacked2882...I've been thinking about this all day...I don't think we can apply TLLTD to track width in the same way we do swaybars, as an example. Although I cannot give you a concrete reason I am having some trouble...a few random thoughts...increasing track width in many cases raises roll center height and as such will cause the tires to load up faster - initial turn-in oversteer...this is typically enough to be helpful and not a hinderance. Increasing track width increases the potential work a set of tires can perform. If roll is resisited with a larger swaybar, lateral traction loss over the rear axle/tires increases. But there is a difference between laterla traction loss via a big rear bar and making the rear track wider - assuming this adds to more roll resistance - because the tires can actualy perform more work...saturation thrshold is higher...or the peak in the sin wave or bell curve is higher...tires have completely saturated when they reverse sin.

I think this is a very interesting subject and one we ought to figure out because there are a few potential tuning tools here that affect handling in perhaps not so subtle ways...

ED9man

I run 225 front 195 back on my autocross CRX. koni sports with 500f/600r and a sway bar. The car has no problem picking up the inside rear but even with the stagger but I still have to overinflate the rear tires to reduce the contact patch and get the balance I want. I think no matter how your suspension is set you just dont need more tire back there because there is no weight back there. A loose car is a fast car in my opinion.

meb58

I understand your comment now...and I agree, loose is good on an autox course...not sure I would like that at a 130 mph in a faster sweeper on a road course though. But I understand.

Wacked2882

My experience is in a Mac Strut car as well - 91 Sentra SE-R.


When I speak of bell curve - I'm referencing a generic X/Y graph where grip is on the Y axis and Roll Stiffness would be on the X axis.

solo-x

Could this possibly be due to the front of the car needing more roll stiffness combined with the fact that it's a tricycle in steady state? (assuming this was your ST Civic and not the STR S2K)

I truly think we're well into hair splitting territory here. Hasn't stopped me from playing around with spacers on the rear of the R though.

meb58

I left a message with a man who designs suspension systems for a living...

I'm left thinking that a larger rear bar and a wider rear track have related but different outcomes. Lets assume for now that motion ratio have been corrected.

A rear swaybar reduces lateral traction over the rear axle - I am not distinguishing between inside or outside wheel here. As the torque tube twists it transfers weight over the inside front wheel until which point it begins to left the inside rear wheel off the ground...and its contribution to transfer begins to fall off - but it is still working.

Increasing rear track does something different...it contribution to roll resistance is in the form of leverage with repsect to the RC or roll axis and the center of gravity - the wheel are spread farther apart and can perform more work - again, assuming motion ratio has been corrected. And again, RC height should increase in just about every application if rear track width is increased and this helps load the tire more quickly initially. Steady state grip should be higher across both tires - in difference to a larger rear bar.

The real question, and I cannot answer it, does an increase in rear track aid load transfer or weight distribution? Wacked2882, you wrote that is does not and I can for sure see this but...it must if it increases roll ressistance...but I don't know why. I sized my rear bars to give me as much inside front wheel traction as possible...but I wonder if a wider track helped or made my task harder...I am second guess myself...

Okay, thought you were looking at a sin graph/wave. got it

EDIT: a wider rear track will allow you to use a bigger swaybar and hence more TLLTD If that is the net affect then all is good...I simply cannot remember...I don't do this for a living.

Darkonian

I would say, going wider front and rear equally is the key but only to an extent. after while you start to run into issues.

beanbag

I don't understand your question. What does "aid" mean?

meb58

Aid = help.

If a wider rear track increases only rear roll resistance than it contributes to load transfer...has to - if my caveat is considered - motion ratio is unchange.

I also beleive that an even larger rear bar - relative comment - is possible after increasing rear track width and this potentially increases load transfer - even if the same bushing and endlink positions are used.

Wacked2882

It was on the SE-R. I never messed with spacers on the Civic - just ride height and rear alignment.

That car was so top heavy that it would still tricycle a bit with 500lb springs and a 30mm solid front bar.

beanbag

In your context, it is not clear what "aid" or "help" means. Does smoking "aid" lung cancer? IOW, what did you want the increased rear track to do for load transfer or weight distribution?

I thought about it a little bit, and came up with the following conclusion-
Assuming that a car has no rear camber curve (so that adding track doesn't change motion ratio) and comparing the case of a reference car vs a car with rear spacers, then:

For the same lateral g's, the front axle weight distribution will be more even on the car with rear spacers, in all cases. This is because rear roll resistance has increased.

For the rear axle weight distribution, it depends. In the extreme cases, if the rear end is much much heavier, then the car with spacers will have a more even weight distribution due to the usual weight transfer = g's / track equation.

If the front end is much much heavier, then the rear weight distribution will get more uneven if you add rear spacers because the front end of the car is going to tilt the rear end over no matter what, so increasing the roll resistance is only going to increase the weight disparity.

Then there is some middle range when adding rear spacers doesn't affect rear weight distribution. The front weight still get more even, and in the rear, the weight evening effects of extra track and the weight un-evening effects of increasing the roll resistance cancel out.

STN_Pat

this thread is mind blowing

meb58

Better load distribution = more grip. I had to balance changes made up front where 62% of the mass sits...the final setup on my JCW mini was a front track 20mm wider than rear - because that's where the weight is. I should clarify, and I do make a distinction, that setting up a car for a road course like Lime rock or Watkins Glen is much different than an AutoX course...I'm sure most of us understand why.

beanbag, I have to digest some of this...but I'm not sure about the 5th paragraph...if we increase rear roll resistance load transfer to the inside front tire must increase...

Also, regard motion ration and wider tracks...you may find that wheel rate do not have be brought back to pre-widen track rates.

And, I cannot find where I wrote aid anymore...but it's early...and I never smoked

beanbag

I think we are mostly in agreement. When you say "load transfer to the front must increase", that is the same as me saying the "front weights get more even". (Paragraph 3)

I can rewrite the 5th paragraph as follows:

If the front end is much much heavier, then the rear weight distribution will get more uneven if you add rear spacers because the front end of the car is going to tilt the rear end over no matter what. Then the higher rear roll resistance is only going to make the rear weights more uneven for the same amount of chassis tilt.

Arsenal

I remember putting 215 on the front, and 205 on the rear in the old Integra, and well high speed driving was quite a bit different! Very twitchy in corners.

meb58

...except, and my thinking may be flawed, if the track up front is wider than the rear there is less load transfer up front. This is the missing piece I think...I haven't gone back to read any of my replies. In my case front track width is 20mm wider than rear track- 10mm per wheel wider...and 54mm wider than stock - total left and right.

kili

I think if your friends intent is to use torque steer to power out, then wider rear tires might be useful. just let'em be and see what happens.

beanbag

There is nothing special if the front track is wider than the rear or vise verse. Everything is based on a change you make compared to its former state.