With new Kumhos & 250# rear springs, once again I'll be going out onto an AX course driving a "new" car (which I haven't learned to drive yet). Someday the mods & changes will stop (right?).

I know that driving style, car setup, etc. all affect tire pressures, but, for those of you that are experienced with Kumho Victoracers, what air pressures have you found to work for our cars (go in a higher or lower direction)?

The Kumho instructions aren't real clear. They give a 35-40# pressure range and then go on to say if your car is light & well balanced, you may want to use LOWER settings. Do they mean 35# instead of 40#? Or do they mean to go LOWER than 35# - like maybe 30-32#????

The 250# springs, finally, seem to be helping the car to rotate nicely in turns. Anymore rotation could easily end up becoming 180 degrees of rotation.

I ran 26-28 psi cold in the Vracers.....then didn't let it go over 30.

Sure, someday the mods & changes will stop.....does that make feel better?

I'm with JP on this too.. but my experience is not on autox... only on tracks...

I ran 225 victoracers and 250 rear springs..
on a race track we would usually run around 26-28 range.... couldn't get grip out of them over 30lbs...

usually same pressure front and rear... sometimes I'd end up with 1lb extra in the rear.. but more likely than not the same...


of course I don't know how that applies to autox
brant

Joseph, Bring them to Hallett next weekend and run with me. I'm doing the novice DE thing. Should be a blast.

Curt

Wow! Inflation pressure of 28 pounds?

Hey, you guys aren't playing a joke on me are ya?

I was going to start a 40 and keep dropping down to the low 30's.

OK, remember, this is your fault. This pic has seen the rounds, but they are V racers with 26/28 f-r.

I've had a bit of experience running heavy cars.. and we used to use 34lbs and up on a 944 turbo.. (3000lbs)

but on a 914, I really do go 28

try a bit higher and work down and see..

brant

I bet if you had more air in them tyres they wouldn't be jumpin' up like that.

Okay. You guys have convinced me. I just dropped them down from 35# to 28# & I'm going out and hittin' some off ramps.

Will report back. Hopefully.

Dang. Started drizzling when I pulled out of the carport.

Guess it will have to wait til tomorrow.

JP, looking at your outside tires it looks like you must be running the widest rims recommended for your particular tire size. Is this an advantage over running the narrowest rim recommended?

I think it just looks that way because he's pulling about .9 G's.

-Ben M.

Those are 7 inch rims. 205s on front, 225s on rear.
Did I mention that them tiars roll under some?.....however, the scrub marks are right at the tips of the arrows.....which is gud....I think Those are the best indicator of proper pressure.....I think

Tiar pressure is a black art......I think .....which is why I'm not too adament bout anything.

Not kidding, same exact experience here on the Kumhos (Victo and Ecsta). The common wisdom with Hoosiers is 38-40 hot but the Kumhos do not stick at those pressures. I was clued into this by Tyson Schmidt from TRE down here in LA who has been tearing up some incredible times at our local tracks...he found 26-28 (or maybe even less) is where the Kumhos like to be.

Well, I just returned from playing with various air pressures and hitting multiple off ramps (L & R handers), and all I can say is WOW! I think I've found my tire!

You guys are sooo right. I set them at 28# and on my "test" ramps they did not exhibit the slipperiness they did at 35#. In fact, I went back to 35 and then 32# just to be clear about what I was feeling. They would just simply start slipping before you could reach the same threshold obtainable at 28#. I didn't bother with 30 and just went back again to 28#. There is so much grip there I actually started getting concerned about my engine oil pressure!

I now have another question. I plan on running tomorrow's AX at the 28# setting. Kumho says which ever end of the car slips, to add air to make it stop slipping. But with this lower setting, it seems that this would not be true - instead it would seem that adding air could make it worse.

Let's say it's understeering and I'm running 28# F&R. It would seem I need to add 2-3# to the rear tires to create less grip at the rear, which would in turn reduce the understeer (slip up front). Does this sound like a correct assessment for Kumhos at these lower pressures?

I ran 26 in front, but.....this is somethin' your gonna have to fool with. Big handling ills can't be cured by tire pressure alone....just little ones....I think

Anyhew, 26/28 front to rear is safe...kinda..., so rather than raise the rear pressure, drop the front.
Go lower than 26 and your on your own.

I'm beginning to think that tiar manufacture's pressure ratings don't take into account a 2000 lb car cause most everything else weighs considerably more. I have seen a few vauge references to dropping psi based on a 3000 lb car.....X amount of drop per X amount of weight.

A tire temp gauge is still your best tool.....I think

With the 250# springs, I "think" I'm down to small handling ills (discounting the driver).

Your 26F & 28R suggestion makes sense. I know you were looking for more rotation with your car also. At least now I know where to go tomorrow if I want to get the rear a little looser: 26F & 28R.

I will take my temp gauge & St. Christopher (temp gauge may need some help).


Hey Curt, I'd love to go to Hallett but have another AX the same weekend. Another time.

Thats great info.



According to what I know, Running the widest rim is the best. Because If I put 225's on my 7 in rims I get maybe half an inch less of tire than if they where on my dads 9in rims. The wider wheel allows the tire to run its maximum potential. If it where a smaller rim, the tire would roll more and there would not be as much tire on the ground.


I think thats correct.. lol, Im learing.

Andrew

I think your right, Andrew.
I'd run 8s if they'd fit. I need some more

I may have to do some "body work" as well. I'm running 225s on 8's in the rear. With these Kumhos I can just barely squeeze my little pinkie between the tire and fender. When I hit a dip, sometimes they chirp.

I have lotso clearance in front......note the cone damage to the rocker.

Ze problem lies here.
Those are the S04 Hoosiers. Note the canteliver effect at the bead.