I just picked up 2 sets of used 16" wheels, one of which will be shod with R-compounds for autocross use. I'm trying to decide which set to keep. The first are Borbet, 16x7.5 front, 16x9 rear. These are in nearly new condition and should mount 245/45 tires nicely. The other set are OZ 2 piece, 16x7 front and 16x9 rear, and are rough but (probably) serviceable, but the limited number of 16" tire sizes seems to make this the lesser choice (7" rim is too narrow for my desired 245/45 tire). My car is an '84. Anybody have any experience with either of these combinations?

 

I've used Toyo RA-1's 245/45-16 on all four corners of my 86 951 on 16x7.5j and 16x9j rims, handled great.

 

if it's only for autoX, use the lightest set of the two. 0.5" is really not that much of a difference.

 

If it was me, I would not run the same tire on all fours unless I had the same width rim on all four. They will will behave differently giving you more yaw at one end or the other.

You will need to watch that you do not mix rims on an axle. The spec measurements are on a given rim. If you put the same tire on a narrower rim these will change. You will get more crowning and the tire will not lie as flat. Could be good if you are doing circle track events and need a stagger to help tracking

For either set, a 225x55 should be the largest fitment for the front. Tirerack uses 7's as the spec rim for that size. The actual difference between a 225 and a 245 is not much when you put them sid by side. But you will have a better turn response with the 225. Of the two the 7.5 will give you the best response.

My $.02

 

225's and 245's /255's should work fine for 7.5/9" rims-If you have some understeer you can dial that out w/ tire pressures at the track.

 

I agree. And I think 7.5x16 is too narrow for a 245 width tire. There are plenty of 8Jx16 D-90 or 968 5-spoke rims out there. For cheap.

If you want the same wheel/tire height as stock, the proper size is 225/50-16. I am unsure if they even make a 225-55/16, but they do make a 205-55/16.

Actually, there is a big difference between running 225 front / 245 rear and 245 at all four corners. I've done back to back driving at Lime Rock, and found the 245 x4 to be much better - and the turn in is actually more crisp with the 245's in the front - more rubber = more grip = better turn in. Noticable difference.

-Z-man.

 

Interesting thread.. I've got 8x16 and 9x16 front and rears, and might consider the same size tire all around.

Sbyrne, which r-compound tire were you thinking of going with?

 

I want the 245/45 (vs a 255/50) for the shorter sidewall and to pick up some gearing advantage. Both the Kuhmo Victoracer and the Toyo RA-1 will fit 7.5 up to 9" wide rims, according to the spec sheets I've seen from the manufacturers. I don't need (or want) a massive rear tire to tame my raging NA 143hp. The car balances very nicely on the stock setup (15x7f, 8r Fuchs with 215/60/15s all around), so having the same size tire f / r and using the rim width difference to get a little more rear tire on the pavement seems about right. I'm looking primarily at the Victo's and Toyos as they seem to be a bit more durable and more forgiving than the faster Hoosiers and V710s, and these will be my first R compound tires. My previous autocross cars were 1st gen Dodge Neons prepped to SCCA STS class specs which call for "real" street tires (minimum wear rating of 140). BTW, ivai, what wheels are pictured on your car? They look very much like my OZs.

 

Z-Man, 225/55R16 is a very common tire size, used on Cadillac's and older 3000GTs as well as Mustangs.

Problem with the 16s is that the tires are becoming like dinosaurs.
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Opps, typo on my part. Yes, 225x50.

Good input here.