The S2000 STR prep resource thread is now 174 pages long and is no longer a resource.

I felt that STR prep could be broken down into 4 distinct threads:
AP1 STR Autocross prep
AP2 STR Autocross prep
AP1 Track prep
AP2 Track prep

While there is some information that applies to 2,3 or even all 4 of those catagories, given the 174 size page size of the STR prep thread, it seems obvious to me that STR information needs to be broken down some how.

 

I ordered 4 TR Motorsports C3 17X9 +62 wheels from Tire Rack.

Originally, I had ordered 255/40 Dunlap StarSpecs, but, changed the order to 245/40 Dunlap StarSpecs.
I still have the opportunity to change back to the 255s, but, wanted feedback on my rational for going with the 245s.

I read a lot about how beneficial wider tires are to grip or not. The one consistent theme was that wider tires dissipate heat better. This impacted the manufactures ability to use softer stickier rubber, which also benefited from a wider area resisting tangential forces.

So, why 245s for Autocross.
Given the shorter runs and the ability for the tires to cool between runs the heat dissipation is not as great an issue for an Autocross Car as it would be for a Track Car.
The 245/40s have a smaller diameter than the 255/40s, which equates to more torque delivered to the contact patch.
The 245/40s are 2 pounds lighter per tire than the 255/40s, this means less unsprung weight, and less inertia to overcome.
The 255/40 Dunlap StarSpecs produce some rubbing on non-rolled fenders with standard suspensions.
I was buying the wheels and tires as an Autocross only set-up. If I find I made the wrong choice, I can wait for them to wear out and get 255s, or if they are really bad I can use them as summer rears on my OEM summer rims.

Comments?

 

Get the 255s. Width is king when it comes to lateral grip and autox is 85% lateral grip.

 

My opinion: I doubt it will matter much. The difference in width is miniscule, and there are pros and cons of both. 245s will give you less weight and better response and better fender clearance and are sometimes slightly cheaper, 255s will give you better heat dissipation and more lateral grip. Personally I'm sticking with 255s but it really doesn't matter. The people I've talked to that have tried both seem to confirm this.

BTW, I disagree with the need to split into AP1 and AP2 - they're really very similar in all respects other than very few. I do agree that the thread needs to be summarized or something and started over. I honestly think STR should get it's own forum and then we could just post individual threads about stuff. But whatever, it works (use the search within the thread function). I remember when I first read that thread from start to finish and I think it was like 80 pages at the time - that took a while. Most of the stuff has been rehashed though so you could probably read the second half and get most of the information out.

 

I am currently on 245 RS-3's due to them being out of 255's... so far I am noticing they heat up quicker, and transition better. I think I notice a slight acceleration bump but that honestly could be placebo. There also seems to be a very marginal decrease in absolute grip. My times seem to be about the same but I only have 1, 9 run, event on them so it may be a little too soon to tell for sure. note this is on an AP1

 

Thanks, that's the kind of information I'm looking for.

I don't think your imagining the increased torque.

 

TTMartin, keep in mind that Glagola is an SCCA National Champion. I'd listen to him. That being said, unless you're a very good driver it's not going to matter at all. It's like a 20-handicap golfer talking about which driver is the best when he's shanking the ball all over the place.

 

Another thing I forgot to mention... I find the 245 RS3 to have about the same grip and feel as the 255 Dunlop D1SS I used to have, but not as good in the wet and handle heat better. (I have had D1ss in 255, and RS3 in 255 and 245)

 

Thanks for the prospective and I do appreciate his and your feedback. The more learn about suspension tuning, the more I realize how many people on the internet are just parroting snippets of what they’ve read, which may or may not apply to a complete set up. Knowing his stature helps me put the appropriate weight to his comments.

As for the metaphor, it might closers to the 20 handicap golfer talking about what are the best balls, as once the balls are all lost, he'll have the chance to buy new ones.

If I get the 245s in a year I'll be buying new tires, and if I've gotten my fenders rolled and/or am comfortable the extra diameter and extra width of the 255s won’t cause rubbing I can always buy some then. I'm happy with where I am driving, but, I definitely have room for improvement.

 

After todays event I'm convinced that the 245's are faster on low grip lots (might be that they heat up quicker)... I was almost a full second faster than the people that I am normally within .2 seconds +/-... this on a 45-50 second course. I am getting more even tire wear and temps too...

Jury is still out on grippy surfaces. But I think part of the reason I am getting these results is alignment, my -2.8f/-2.2r camber was heating up the outsides of the 255's much more than the insides, I get better tire temps with the 245's and running more reasonable pressures (low-mid 32-34's psi instead of 38-40psi)

I also like the feel of the car a little better with the 245's but I think I would run 255's at a large concrete course such as nationals because I don't think the 245's would have the heating advantage and I think that on a grippy surface the slight increase in lateral grip would outweigh the better response and transitions.

today seemed to support my observation that the 245 kooks feel like they perform very similarly to the 255 dunlops I had but with better heat resistance and better performance on less grippy lots, yet not as much wet grip.