avizandum

I run in a street tire class for AutoX. If I go 20 cm wider front and rear with the same tires, will I notice an appreciable difference. (Issue of most importance is improving understeer)

UstaB-GS549

20 cm !!!!!!!!!!!!!!!!!!!!!!! Like 275 to 475?

You must mean 20mm.

Feel the difference? Depends on how sensitive your posterior is. I went from 275 fronts to 315 and could feel the difference.

Adding 20mm to both ends should not change balance.

avizandum

Yes, mm! More precisely, will I (potentially) be faster?

hemipanter

What happen is that you will transfer some 20 pound less to the outside wheels during 1g cornering. Ok, this makes for better friction numbers, but I doubt that you will notice it.
Goran

avizandum

I won't get better traction with wider tires / bigger contact patch?

hemipanter

I probabley misunderstod you here.
As you mentioned the same tires I thought you meant wider track width. Wider tires will give better grip, not only from having larger, but also from the altred shape, of the contact patch. The wheel should be matched to the tires used. However, the contact patch will not grow according to the width of the tire since the contact area is partly following load and inflation pressure. A wider but shorter contact patch will produce less cornering slipp area, but for straight line acceleration, and braking, it is more the gain in area that is important.
Goran

avizandum

Mostly looking for less undetsteer. Cornering slip area is Greek to me...

hemipanter

Do you have any out of corner accleleration grip problems?
Goran

gkull

Alignment settings give you the ability to use your whole tire. Tire compound, air pressure, and age is more important than additional width.

IMO - get a tire temp gauge and set up your car first.

avizandum

A bit of oversteer - nothing excessive or that I can't control with a little restraint. I'm happy with the car as is. I've had two alignments and have played with temps and am getting close to what I believe is optimal. I'm just thinking more grip = more fun and I don't mind spending a little money. I'm trying to stay away from switching to Rs on event days for convenience...

gkull

IMO - The problem with max performance AA A Z rated street tires is that they have too many tread grooves for rain. Like my street tires are 315 rears - 20-30% for the air gaps. It makes them have less traction than something like a 245 width slick.

Some guys use toyo's and Nitto DOT tires for a whole race season. I use up hoosier r's in 6-9 sessions. But a few weeks ago my fellow racing buddy did not make an event with me. I cut down a rear slick in the first 10 minutes of practice. All this prep and I didn't have my buddy with our spares in his trailer. I in the SCCA points so I needed to run.

So I threw on my Rear street tires. I completely destroyed my rear 315's in qualifying and the race. I might add with a loss of 6-8 seconds a lap.

So you are money ahead to get near treadless tires. They last longer and work much better