245 vs 225 on 8 inch wheel with RE71R
 

Getting a second set of wheel/tires for autocross. I've read a lot of posts and starting to see cross-eyed, so any help would be appreciated.

Currently running 245/40/17 PS4S on 17x8 +35 wheel. This was always just a daily setup that would be enough to get me back into autocross after 15+ years off. I'll be purchasing a set of 17x8 +35 RPF1's with RE71R's just for the autocross days and maybe a track day a couple of times a year.

I feel like that I might be getting a little rollover on the 245 PS4S's that I've run on 3 autocross days. I know that's at the upper limit for that width of rim (although I've seen bigger). I'm wondering if the sidewall on the RE71R might deal with the 245/40 a little better or should I step down to 225/45?

I know there are other setup options, but I'd like to stick with the 17x8 +35. I have another 12mm of clearance to the front strut to dial in just a bit more camber (currently about -1.5). With 17x9, I'd have to lose the camber for clearance. Not interested in coilovers or camber plates or other stuff like that for now. My car has always been a compromise for daily and weekend fun. I'm not hardcore or trying to win any trophies, just trying to improve the driver and have fun.

I have a '18 w/ PP dropped on Eibach Pro's. SPC Camber bolts and LCA's. Also have the JRSC C30. So bottom line 245/40/17 or 225/45/17 on 17x8 with RE71R's?

225
RE71R's aren't Hoosiers

Neither are bad options. The 245 will be a little faster.

Firsthand experience trumps theory, but from what I’ve read on Motoiq.com, they recommend that the tire’s actual tread width be within 0.5” of wheel width. So, you can check to see the width of you 245s and compare. With that said, most people who autocross or track their cars seem to prefer a 225 on an 8” wide wheel.


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I have not run that tire. But, here is my experience with MPSS in 225 and 245 on 8" and 9" wide wheels.

I ran 245's on 8" wide wheels. The steering went all mushy, I hated it. I removed them and installed 225's. The steering was much better. I then bought 9"wide wheel and installed the 245's. The steering with 245 +9" wheels feels very similar to 8" wide wheels and 225's.

So far, great feedback, thanks. I've been leaning toward the 225 and it's starting to look like that might be the best option. I appreciate the real world experiences. I don't have much to compare, but I can see the the 245's I'm running now might have a little more roll onto the sidewall than I would like. I just wasn't sure if the RE71R's would be any different. The 245's look good and don't look "too" pinched, if at all. That's great for the daily, but I'd rather the better performance for the weekend days.

The RE71R will be significantly better about that.

I've ran street class and tested tires in a few different cars and the wider tire ALWAYS tested faster. My most comparable personal experience was running a S2000 CR in AS. We ran a 225 on a 7.5 for a while, then the 245 repeatedly tested faster by a few tenths. I want to say that some people were running the 245's on the stock 7's when the twins at/near the top of CS.

Thanks, that's what I'm wondering. Obviously, different tires behave differently, so generalizations don't always apply. While my PS4S might not be as good at that size, it may be just right for the RE71R.

The real answer is that I'm probably not good enough driver to notice, but I'd like to at least start with a setup that'll let me reach my potential.

Per TireRack, the minimum recommended clearance between the spring perch and the wheel/tires is 3mm, so you’ve got plenty of room for more camber, but keep in mind that the tire will rub before the wheel. I’d go 225 personally and up the camber. I think Pedders top hats are a good option that may be worth looking into for your application.



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.Thanks. Yep, I looked at Pedders. I think that's an option as well, especially if I went up to 17x9. Just don't think I'm ready for that yet. Like you said, I have some room for more camber right now. And that is the 245 tire that is setting that clearance right now. Should have just little bit more with a 225.

Running 245's on my 17x8 rims. No issues so far. Stock dampers and rce yellows with crash bolts up front and lca in rear. Less the 2 degrees of camber up front. Offset is 40 and I have a 3mm spacer up front and rear. Front brake clearance and rear just because poke [emoji16]

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Ahh, it’s the 40 offset and the spacers that’s are saving ya the extra clearance. How much you got with that setup?


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Doesn't exactly answer the question, but for reference with my current setup 17x8 +35 245/40/17 and about -1.5 deg camber I get around 12-13 mm clearance. So take away 5mm for the +40 offset, add back in 3mm for the spacer, and subtract for the extra camber. Might be around 5mm, I'm guessing.

For autocross, more tire is always faster time. "Feeling" be dammed, even if the car is a boat, more tire = more grip = faster times. For track where speed actually matters this isnt always the case. There's always a balance of tire size to wheel size and this balance provides better times than just oversizing the tire as much as possible. (said balance changes depending on a lot of factors, there isnt a "one size fits all" type of solution here).