500whp.com

iTrader: (86)

Thanks To:
Roger Kraus Tires Inc.
2896 Grove Way.
Castro Valley, CA 94546

Understeer Corrections:
Push, plowing, front tires slide out first. Usually slight understeer is safer.

How to correct:
Raise front tire pressure
lower rear tire pressure
soften front shocks. Stiffen bump
Stiffen rear shocks
lower front end
raise rear end
widen front track
install shorter front tires
install taller rear tires
install wider front tires
install narrower rear tires
soften front sway bar
stiffen rear sway bar
more front ote out
reduce rear toe in slightly
increase front negative camber
increase postivie caster
soften front springs
stiffen rear springs
may need more front supension travel
install wider front wheels
use softer front springs
stiffen rear springs
may need more front suspension travel
install wider front wheels
use softer front compound if possible
use harder rear compound if possible
remove weight front front of vehicle
add weight to rear of vehicle
drive a different line
use weight transfer to your advantage
high speed. increase front wing downforce
too much front brake

Vehicle is TWITCHY atlimit and hard to keep ahead of in the steering department.

Lower front and rear tire pressures slightly
suspension may be too stiff
shocks may be set to\o firm
tires may be old or hard
vehicle may not have enough suspension travel
vehicel may have a toe problem front or rear
increase negative camber front and rear if possible.

Oversteer Corrections:
Losse, rear tires slide out first
oversteer can be dangerous, especially at high speeds.

Lower front tire pressure
raise rear tire pressure
stiffen front shocks
soften rear shocks
raise front end
lower rear end
reduce rear track
install taller front tires
install shorter rear tires
install narrower front tires
install wider rear tires
stiffen front sway bar
soften rear sway bar
more front toe in
increase rear toe in
reduce front negative camber
reduce positive caster
stiffen front springs
soften rear springs
may need more rear suspension travel
install wider rear wheels
use harder front compound if possible
use softer rear compouond if possible
add weight to front of vehicle
remove weight from rear of vehicle
driver may be going in too deep
driver may be getting on the throttle to early
high speed. increase rear wing downforce
too much rear brake

Vehicle slides and is easy to drive at limit but does not corner to full potential.

Raise front and rear tire pressures slightly
suspension may be too soft
shocks may be too soft
roll center may be too high
lower vehicle
tires may be too hard
widen track front & rear.
widen track front $ rear

evo81

iTrader: (30)

good info.maybe sticky worthy

500whp.com

iTrader: (86)

Yes tire is one of the most important part of tracking!

You can spend 10ks on suspension and run on some ****ty tires, and someone spend 1 k on some R compound, or slicks will rape the other car!

That also goes w/ Cars way too much HP and not enough suspension work, and tires!

FarNorthRacing

I had a quick look through the list, and while everything seems technically correct, real life is Just Not That Simple, especially when dealing with production-based cars.

I'll give you a quick example:

It is very common on production-based cars to have insufficiant camber compensation in roll, especially on cars with McStrut suspensions.

Ideally, as the car rolls into the corner, the outside front (especially) should be kept at the same angle (or a little more negative) relative to the road. If the tire is at -1 degree negative camber at rest, it should be at -1 degree negative camber at full roll. This is "camber compensation"

What commonly happens though is that the suspension rolls along with the sprung mass, at the same rate (or near to it) such that the tire goes increasingly positive in roll. If we assume 1:1 roll change (ie, NO camber compensation) and 2 degrees of roll, then -1 degree static camber will translate into 1 degree POSITIVE camber at full roll - which in turn translates into a loss of grip. If this is the front end of the car (which on production cars is almost always the most heavily loaded end) this will result in terminal understeer.

If you put a larger roll bar or harder springs on this end of the car, you will limit the roll angle. That, in turn, will limit the camber change in roll due to insufficant camber compensation, and reduce the grip lost. The bigger bar will also increase the amount of lateral weight transfer on that end of the car - normally a grip loser - but if the amount of grip GAINED due to better dynamic camber exceeds the amount of grip LOST due to the increased lateral weight transfer, then end result is a GAIN in grip.

So it is entirely possible to put a bigger front sway bar on a car, and REDUCE understeer. Happens all the time.

On McStrut cars, which have really poor camber compensation, it's very common to run a really thick front sway bar and lots of static camber angle. The idea is that 1 tire in it's camber happy place, with 100% of the load on that end placed on it, will produce more grip than two more equally loaded tires in their camber unhappy place. You see this all the time on M3's, Mustangs, the various BTCC cars etc - lots of static camber, and the car carries the inside front wheel out of every corner.

You'd never see a Formula Ford or Formula Atlantic or whatever set up this way, but they don't have to deal with the compromises that a production car does.

Incidently, you might expect that an EVO, being a McStrut front suspension, might benefit from a similar sort of setup as an M3.... except It Ain't That Simple. Unlike an M3, the EVO has it's front and rear tires connected to each other, via three differentials. Those differentials may do Weird Things when one wheel is hiked up in the air like that.....

Incidently, setting up an AWD car - production based or not - is probably one of the most difficult things a race engineer can do. Those diffs connect each end of the car to each other, they crosstalk, and they are often smarter than you. They will often route power around in an unexpected manner and do the exact opposite of what you expect.

One the plus side, that makes it very hard to really screw up - setups that would have a Corvette or Viper passing itself on every corner exit an EVO will just deal with. On the down side, it is VERY difficult to determine if your snazzy new setup change actually improved anything.

A typical AWD setup moment is the one where I softened the rear sway bar (in an attempt to tame down a slightly too active rear end) and picked up FRONT grip as well. WTF??

So while the rules of thumb are a good starting point, be ready for almost every single one of them to work backwards at some point.

DG

DaWorstPlaya

iTrader: (31)

Its always a pleasure reading you posts FarNorthRacing .... intelligent and insightful ...
Except I don't quite understand how lowering the front and raising the rear will decrease understeer (from the original poster) .... if you did that wouldn't the weight bias be Front and wouldn't that lead to understeer?
Go

500whp.com

iTrader: (86)

good write up DG

For most evo drivers they will not be able to do 80% of the things up there.

In general, what people can do is tire pressure, sway bars, damping adjustments!

If you are hard core then you can start doing all the other corrections!

hi_nrg_fizzix

Good stuff and thanks for the insight DG. I had my alignment done at Roger Kraus Racing. These guys do quality work at reasonable rates. I highly recommend them if you are in the Bay Area.

FarNorthRacing

Well, that's another problem with rules of thumb... what PHASE of the corner are we talking about?

There are, at a minimum, 3 phases to a corner - entry, midphase, and exit. It is entirely possible (and in fact, totally normal) for the oversteer/understeer balance to be different in all three of them. It is not at all unusual on a FWD or AWD car to have corner-entry oversteer leading into midphase slight understeer into strong exit understeer.

And if you want, you can break down entry into two phases as well - "initial turn in" and "sprung mass moving" and get slight understeer into medium oversteer into slight oversteer into mild understeer (that's my car, actually - as long as the tires aren't dead, in which case it's medium understeer into strong oversteer into medium oversteer into strong understeer )

And of course we need to differentiate between low speed and high speed (aero) corners....

DG

TexasRS

Oversteer Corrections:
Lower front tire pressure
raise rear tire pressure

Lower front tire pressure
raise rear tire pressure The article recommends increasing rear tire pressure and decreasing front in order to decrease overstear....but, in order to increase rear stability at high speeds, I was under the impression that a decrease in rear tire pressure is in order, is that correct? (I would think that doing something to decrease overstear would decrease rear stability at high speeds, or not?)

500whp.com

iTrader: (86)

I totally agree with you that in entry you will most likely have understeer, and exit oversteer. But if one is more than another in any kinda extreme there are things that you can do to help fix it.

These are recommendations that people can do at the track, but not everyone will be able to most!

FarNorthRacing

It is next to impossible to get power-on, corner-exit oversteer in an AWD car with a 50/50 split centre diff.

For a discussion as to why, see http://autox.dsm.org/diffs.html

DG

00R101

Here's a classic misunderstanding. All this lower/raise pressure should be suffixed with "from optimal grip pressure"

Given a specific set of suspension, temperature, pavement parameters any tire has an optimimum pressure. Any pressure above or below will reduce grip.

In my ITR running Hoosier A3S04s, for example, if the rear end is tight I can loosen it up at corner entry by changing my normal pressure from 42 to 34 or I can loosen it up at corner entry by raising the pressure to 50. I find that lowering the pressure gives me more controllable results during mid-corner and exit than raising. My point here is that 42 tends to produce the best grip at the end any change reduces grip.

Overall I found that list just about worthless.

regards,
alan

Kayaalp

iTrader: (1)

Exactly! The problem with these "cheat sheets" for chassis tuning is that they assume the suspension is already set up perfectly (or near perfectly).

If you have insufficient negative camber (as most of us do) and stock ride height (as many of us do), then you can't just follow the rules. As DG correctly points out, increasing front stiffness can overcome the ill effects of excessive body roll and insufficient negative camber and actually lead to a paradoxical improvement in front grip.

The bottom line is to set the car up in a sensible way then pay very close attention to tires to help guide you. Your tire pressures, tire temps, and especially wear patterns can tell you a LOT about how you can maximize grip at each corner.

Emre

DaWorstPlaya

iTrader: (31)

Makes sense ... as you enter a corner you are usually braking and thus experience dive, more weight shift to the front. Mid corner, ideally, you would be neutral on the throttle and weight shifting to the sides and on corner exit you would accelerate, causing squat more weight to the rear .....

Aluma

ummm, I have a gripe with the toe out to solve understeer....as I recall, more toe out in front gives you quicker turn in, but loses its effect in the middle and exit of the turn. While the opposite occurs the less toe out you have...more grip in the middle and exit of the turn.

Y'all should get some pro level R/C 4wd touring cars and mess with the settings at a track. You'd be surprised as to how complex getting a good 4wd setup can be...They have more settings than our cars do...caster, camber, toe, antisquat, bumpsteer, shock position, spring rates, shock oil, tires, wheelbase, rideheight, corner weighting, geesh...and theirs Still more like the diff tightness or diff preference, gearing, motor...etc...etc...etc...