Z06Vette.com - Corvette Z06 Forum - Road Race question re: Hoosier Front tires

SuperZ · 10-05-2003, 03:16 PM

I am currently running Pilot Cup sport 295/35/18's on the front and 315/30/18's on the rear for the street. My road race set up is Hoosier 305/30/18's on all 4 corners. Does any one have an opinion regarding using this large of a tire up front without being able to put a larger tire in the rear.

My car is not tubbed so I can not go to the 335/30/18 I have big brakes so I can not use the 17 inch rim on the rear either.

I have not had a lot of seat time in the car I am just trying to get the tire pressure sorted on and suspension settings. However, the turn in does not seem as good as the 295/35/18's when on the street. I know that the car was designed to run a 35 series tire in the front. How much of an effect do you think that the 305 tire is having on the handling positive or negative and what would the likely characteristics be with that set up vs. going smaller with the Hoosier 285/30/18 or the 275/35/18?

What tire pressures do you run with Pilot Cup tires or Hoosier for road racing?

Any Input would be helpful..

LtMash1A · 10-07-2003, 07:37 PM

I run the 305's all around. This is the only track set up, I have ever run so I can't compare it with anything else. I run it because it was John's recommendation from CCW.It is so superior to street tires, I can't imagine a better set up. You could run 315's in the back if you take out your brake ducts. I never bothered to change to a track aligment ( so you are dealing with somebody pretty slack here). After about 6 track days you could really see the wear on the outside edges of the front tires. I just put 4 new ones on and going to get a track alignment tomorrow. I have ordred the Hardbar camber plates but they are back ordered. I'm going with -1.9 on front if I can get it. and -1.5 on the back. I run 34Lbs cold, track/acc handling off. I tape around my wheel wells because the tires stick out a lot. I know this doesn't answere your question but at any rate that's my experience. I love them.
Dave

SuperZ · 10-07-2003, 09:35 PM

Thanks for your input, I will probably go with more negative camber next time I get the car aligned. DJ also feels that the 305 is a superior front tire to the smallers ones so, I guess until I get the car tubbed I will stick with the same set up.

ghoffman · 10-12-2003, 09:09 AM

Guys,
Here is what we use on our T1 '01 ('02 motor) ZO6 for Road Racing, (using our camber plates).

Front Camber -1.8-2.0
Front toe 1/16 toe out

Rear Camber 1.4
Rear toe 1/4 in (total)

This works very well with Hoosiers at 42-44 PSI hot, and is very near T1 lap record times at NHIS and LRP. You run more rear camber, and your straight line grip suffers. Sometimes we will vary the front camber on one side if the track is mostly RH turns, but this is a very fast setup for 90% of the situations and drivers. Beyond this, you need to test for yourself and changes things to suit. A couple of guys (names withheld by request because the parts were not SCCA legal) at the runoffs ran our camber plates and raved about them. We are trying to get approval for next year but if you are not concerned about rules they are the hot setup.
We ran the ZO6 Thursday (10-09-03) at NHIS with this setup at the National "Z" (Nissan) club event and on year old Hoosiers were in the 1:13 range (high 11's is the T1 lap record). We (me) passed every other car there, including an Newman-Sharp GT-3 car driven by Steve Millen. The car was very neutral and was hooked up like it was velcro'ed to the track. BTW, this car has stock brakes with Wilwood "J" pads, very nice, very consistant braking as well.
Cheers,
Gary Hoffman

Subdriver · 10-12-2003, 09:56 AM

I didn't run Hardbar's camber plates this year (if anyone was wondering), because, as Gary said, they aren't legal in T1 yet.
However, I saw them and they are very nice. If I was setting my car up for DE events, I would seriously consider these camber plates.
Basically, they replace the stock concentric bolts with a plate with a hole drilled in it to give you a specific camber setting. You know it isn't going to move on you.
If you bought two sets, one for track and one for street, you could swap them back and forth fairly easily (but would then need to be able to adjust toe in).
I used the GM Performance Parts T1 camber plates for the first time at the runoffs. They give you big time negative camber. More than I would recommend for a car that sees part time street use.

SuperZ,
Pretty sure I answered this question already. Maybe on another forum, or in another section.
In SCCA T1, we run 315/35-17 all around, so running 305s all around will be okay, if not ideal. I'd want more rubber in the rear, but you have constrained yourself by your wheel/brake combo.
Until recently, most T1 drivers were using 275s in front and 315s in the rear which gave tons of static understeer. Moving to a 315 front corrected some of the static understeer, but not all of it.
As Gary said, Hoosiers work well at 42-45 psi hot. Your cold pressures will depend on a lot of variables including: track, ambient temp, camber/toe settings, driver ability, etc.
As a guess, somewhere around 35 front, 32 rear will get you close.
Tirerack has a great section on the hoosier tire:
http://www.tirerack.com/tires/hoosier/hoosier_tips.htm

SuperZ · 10-12-2003, 12:00 PM

It is interesting I experience very little understeer, I have been running the tire pressures in the the reverse stager with the front being 4 lbs higher than the rear is this incorrect. I thought that you would want lower tire pressure in the rear to allow for more traction under power and a higher pressure in the front to keep the side wall stiff and have less tendency for the tire to feel like it is rolling over.

I had been running 39/35 hot temps what characteristics do you think that this will exhibit?

On the tire rack page they recommend lower tire pressure in the rear for a front engine rear wheel drive car?

Subdriver · 10-12-2003, 03:03 PM

SuperZ,
Sorry, I brain dumped.
Higher front, lower rear to start is correct. I fixed my above post.
Guess I was distracted by NFL pre-game.

I do think your hot pressures are too low though. Assuming the same initial conditions, bump up whatever you are using cold by about 5 psi and try that. Should result in 44 front, 40 rear hot. On my car that will still result in a static understeering condition. However, that is safe, and for me, safe is good.
You will find that as you learn to drive harder, you will need lower initial pressures for road racing as you heat the tires up more. If you can't heat the tires up because you don't drive hard enough, there won't be much delta between hot and cold pressures.
I normally see a 10-13 psi delta between hot and cold pressures. Your results may vary.

DPassell · 10-16-2003, 09:44 AM

I have been running Hoosiers305/30/18 front, and 335/30/18 rear on CCW wheels for track events and have been happy with the setup. I have lowered the car 15mm and running -2.0 neg. camber and neutral toe in the front and -1.0 neg. camber and -1/8" toe in rear. Get a very slight amount of rubbing on occasion on inside of rear tires, no problem with brake ducts. I feel a slight amount of push on slow speed tight turns, but overall very neutral with good turn in. I've also found that this much grip is hard on rotors, cracking even VBP two piece heat treated and slotted using Wilwood J pads, but I can late brake with about anybody, even turn 10 at RA. This experienced is based on running five track events at Roebling road and Road Atl. Tires this wide does mean extra taping of the side of the car to protect from flying rock chips, etc. Another neg. is cost, these Hoosiers are about 1200 bucks a set and are good for 3-4 hard driving track weekends, but worth every penny.