Rainy Day Suspension Basics... Understanding understeer.

[exwestracer]

To some extent, you can do that, at least with a setup that's way off to begin with. But as you get into diminishing returns, no additional amount of rear roll stiffness can make an undersized front tire gain grip that it never had to begin with.

I *think* you'd have less room between the push caused by insufficient basic front tire grip and going way loose from too much throttle on corner exit.


Norm

Good point as always, Norm.

And, as a general rule; if we have a problem at the front (lack of grip), we need to FIX it at the front (find more grip) rather than giving up rear traction. Balance adjustments with bars are supposed to be very minute tweaks, not crutches...

[Norm Peterson]

Never heard of those types of understeer - the first one sounds like you could call it "You're driving it wrong understeer" - which isn't really the car's fault.

There are quite a few effects that when you add them all together give you something that you collectively call either "understeer" or "oversteer" depending on what the end sum total is. You might have heard of "understeer budget", which sums the effects happening at the front, the effects happening at the rear, and finds a difference value that can be either + or -. It's convenient to identify each of these effects by what causes them (i.e. weight distribution, bushing and bracket compliances, roll camber, roll steer/toe steer, etc.), and at the OE level where they have actual numbers for all these things it gives some direction for how to proceed with the suspension tuning.

When I look out at the bevy of P-T cars, most have typical nose-heavy static weight distribution (something like 57% front), but with rear tires that are 50-90mm wider than the fronts. To me, that common pitfall contributes to chronic understeer more than anything else.

Even with good geometry and appropriate alignment settings, fitting your competition car to that sort of appearance-based formula is definitely leaving something on the table.

Not so long ago, one of the FWD GM cars was actually produced with front tires one size larger than the rear tires. That wasn't by accident or by the benefit of oversight by the bean-counters and management . . .


Norm

[diesel25lrs]

Negative camber by itself isn't that bad on tires. I have tens of thousands of street miles on cars with over 2 degrees static negative camber, and experienced pretty even wear once some auto-x/track time was mixed in. It's when you combine measurable toe values with that camber, that you start to chew them up on the street. Keep toe at zero (which is fine for most performance applications) and a ton of negative camber won't kill you.

If the front end is redesigned properly the ride height doesn't have to go up any with wider tires, which can be just as short as the narrower ones.

With the amount of $ being spent on some of these builds, with full-on aftermarket subframes and whatnot, it boggles my mind that people aren't working harder to get more front tire under their rides, many of which are carrying 1000+lbs/corner up front. When getting around corners matters, the greatest geometry in the world with skinny tires will be no match for a ho-hum but well-executed suspension blessed with wide tires.

Jason,
I'm just trying to educate myself as it's all pretty new to me buy why 0 on the toe? I know that my recommended toe is 3/16. Also-would you say that -1.5* would be a good setup for street and occasional autoX as far as tire wear is concerned?

[Bryce]

If you run zero toe or even toe out your turn in will be quicker.

Also your toe spec will affect ackermann.