Recommend me tire widths track use

[aftermath]

I have a 84 944. Many 951 parts pushing 400hp at the crank. I have 255 17's on the car now. Im lacking grip ( but they were street tires ) mostly a touch of understeer, but lack of grip overall. My tire sponsor is getting me some Nitto NT01 for next season. These Nittos are a touch wider than what I have. So I either have to 1) remove the spacer, or shave it down in the rear to fit or 2) change the rear rim, that opens the door for a 275 or maybe a 315 will fit. In the front I currently rub on the air ducts when at a full lock ( Ive been meaning to find another route for the air ducts ). So I can go 255 front and 275 rear. Or should I try to go wider? Sticking with the rims I have is the cheapest option ( 9 inches wide ). But I could save these rims for rolling the car around. I dont think I have the early offsets as the car has so many parts swapped out by the previous owner, Im not really sure.

[looneybin]

if you are already having understeer issues, adding more rubber to the rear will only make things worse.
BTW, how are you getting 400 HP from an NA?

[pontifex4]

Judging from that guy's facial expression, I'm guessing it has an SBC.

I'm not sure you'll need to go wider than 9" wheels. I think you should try them with a new compound, first.

[racer]

Do you have 255s all around currently or only on the rear?

Lots of ways to combat understeer, but generally speaking, a bit of understeer on the track is preferred to too much oversteer.

I am guessing you are running 225/235 front and 255 rear? I'd go with a 245 front and maybe a 275 rear. You don't mention too much about your current suspension set up, what's adjustable and whats not etc. that might help to know.

[aftermath]

It has a LS1 with some upgrades .

Yes I have 255 on all 4 corners. I don't think I can fit more up front without a wide body fender kit. The understeer might just be from lack of overall grip because of crappy tires. Car is easy to drive, can go to fast into the corners and I wish it would turn in better, cant get on the gas and can easily kick out or spin the rears. Ive been getting better at squeezing the pedals.

All the 951's that Ive raced against have much wider tires than I have.

The problem I have if I use the 9 inch rims that I have is that the Nitto width wont fit in the rear. I have already ground down the inner rear fenders a bit as I was shaving off the lettering on outside of the tires. The tires fit for the previous owner but tire temps said to much rear camber so we took a bit out. I think he cranked up the camber to fit the tires. The Nittos are 1/4 inch wider and I don't have room in the back, unless I remove the rear spacers or get them shaved down a bit or change the rim. The reason for wanting a bit more rubber in the back is I have trouble getting the power down. The recommended rim width for the 275 is a 9.5 inch rim but the 9 could be used. Budget option is to use the rims I have. But I can go 255 front and 255 rear or I could go 255 front and 275 rear. Either way I have to do something with the rear spacer. I would love to run 275/315 but I dont know if a 275 can fit inthe front.

A friend of mine is a suspension guru. We have fiddled and now have very even tire temps from when I first got the car. Got the car turning in about the best we can after we removed some toe out in the front. Im beating the BMW's now so we must be doing something right. I think they will reclasify me once I get onto R compound tires.

Front coil overs, bigger rear torsion bars from stock. Adjustable big sway bars. 951 brakes, 951 trans axle. Front shocks are adjustable, rears are not.

Get to start all over with R compound now.

[Lemming]

275 on all corners will work, that's what I run on my track car and it works very well. Are you running early or late control arms in the front? I have early on mine and can still run 25mm spacers to maximize width. Late arms should work without spacers.

In the rear I am running 15mm spacers on a late hub offset with no problem. What size is the spacer that you are running?

My setup is with Hoosier R6's in 275/40-17.

[aftermath]

My friends 275 on a 10 inch rim fit on the back. So I will use my 9 inch rim and reduce the size of the spacer ( his rim has a different offset ). This will result in my needing about a 5mm spacer from the 25mm one I have now. Not sure if I should lengthen the studs. In the front his tire touched the coil overs, but I think I will be ok with my applicaition and worst case need some small spacers in the front. So looks like 275 on a 4 corners. I ordered 2 tires, will mount one and measure for spacers just in case I need to go with the second pair at 255. The 275 are a touch taller than the 255 and I didnt really want that, but decided I would be better off with the wider tires.