R888 tire fitment question

I have 18x8 and 18x10 wheels. I have a stock '03 996 C2. I am planning to move up to R888 for my autocrossing. Our autocrossing is done on a rough asphault parking lot with significant elevation changes, with course length usually around a mile and averaging around 70 seconds. On most days, I am in 2nd most of the time, with 2 or 3 shifts to 3rd. There are usually corners varying from sweepers to hairpins in every course, and there is always at least one slalom. The other local autocrossers that have made the jump to tires with better than 140 treadwear have nearly unanimously recommended the Toyo R888 for our venue and my car setup. So... The tire size option I am considering is 245/40/18 in front, 295/30/18 in rear. Both of these tire sizes list my rim size as the minimum width, and the diameters are within tolerance for my PSM/ABS (25.7 front, 25.1 rear). Has anyone run these sizes with these tires, and can you confirm fitment before I purchase?

I have not personally run that tire size, but we are planning on running 245 fronts and 285 rears for 996 Spec Racing. Koni Challenge cars run 245/275's, but these are on 17 inch rims. Cup cars run very close to 245/285, so there must be something special with that size stagger. Make sure that the sidewall of the 245 and 295 are similar and intended to be used on that end of the car. This does make a difference. You should contact Toyo for more info. If you wanted to save some $$$ you could by Nitto NT-01's from Discount Tire. These are basically a Toyo RA-1 tread compound with an R888 style tread design. Remember, that to optimize the tire, you will also need to run seriously increased camber values.

R-888 are pretty wide and personally I wouldn't run 295s on a 10 inch rim. I herd Z214 from hankook were pretty good for autocrossing.

CWay27 is correct. The tires run wider than the old RA-1's did and the 295 is pretty stuffed on a 10" rim. I ran 255/295 this season (I have 8.5" fronts) and it was great on the car BUT I had to play with rear pressures a bit to compensate for the shape distortion of the rear tire because it was on such a narrow wheel. I'm either going to try to find 11' rears or go down to 245/285 for my next set as I feel like I was carrying around extra weight in the rear with no additional contact patch over the 285. Not to mention I'm pretty sure the 245/285 have the same rolling diameter. The 255/295 also both have 25.1 as the diameter but the 255 would have the same "too big" issue on an 8' front" Andy

Some guys here reported that 245/40/18 front tires cause rubbing and that 245/35/18 is a better fit. I run 235/40/18 with no issue on an 8 inch wheel combined with 275/35/18 rears on a 10 inch wheel. I like my Falken Azenis RT-615 for combined street/DE driving.

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Without any suspension mods, the 245/40-18 and 295/30-18 should fit on your car without rubbing. And 295 is the biggest you would ever reasonably go on a 10" rim. BTW, I had to roll my fenders with my 245/40-18 (suspension upgrades, dropped car, and 7mm spacers) - but they DID fit. However, I've recently switched back to 245/35 up front for more consistent rolling diameters (285/30 rears). -td

So, it sounds like I might be better served to drop to 235/40 front, and 285/30 rear? That would be only slightly over-stuffed in front, and 'natural' width for the rear. I believe the rolling diameters are (barely) within tolerance, 25.5" and 24.8" (0.7" difference, or 2.8%). Remember, I'm not talking about generic tires, I'm talking specifically about the R888. The comment above about overstuffing the R888 being counter-productive was excellent, thank you, Andy.

Here's a picture of the 295 on the 10. Like I said with pressure adjustments they work but I'm really not sure I got any benefit from the 295 over the 285. I simply ran them because I got a killer deal on the 295's that I bought second hand off of someone after they didn't fit his car. 245/285 for me next season though.