EVO8LTW

iTrader: (41)

I was just wondering who here has experience with the difference in grip and handling between 275 40 17s and 275 35 18s on track? There is a sizable price difference in the tires and I'm just wondering what that translates to in lap times. I'm confident that the steering response would be better with the 18s and that the "spring rate" of the 17s taller sidewall might be less favorable on an Evo, but I'm looking for real world experience from those who have compared in a road course environment using R compounds.

Thanks!

Bueller

iTrader: (1)

Unless you know an experienced driver who has ran a minimum of 3-4 sets of each size, youre going to have a difficult time getting worthy responses. I havent ran either size, but my choice would be the 18's.

GTLocke13

iTrader: (1)

From a fitment standpoint, the 17s are a pain to get in the wheelwells. You might have the same problems with the 275/35R18's. The popular 18" size is 285/30R18 on 9.5" rims.

xtnct

iTrader: (33)

Depends on the wheels you are using in combination with your tires. If your 18' setup is heavier than the 17' setup you could be adding slight more stiffness but adding unsprung weight which makes more difference than a 10% change in tire profile. But, r-compounds are already made stiff so I really doubt that most people could even tell any difference between a 40 and 30 profile tire.

What is your experience level? And what do you mean by track - racing or just DE's? I would say that unless you are in the highest level in DE's or doing real racing, you would not be able to tell any difference between running the same width with a profile of only 10% on r-compounds.

EVO8LTW

iTrader: (41)

I'm planning to get a time trial license this season and run NASA TT in Group 4/HPDE. So, not w2w, but lap times count.

hokiruu

iTrader: (19)

I don't have any personal experience with this, but if you don't mind I can share what I have read from others' experiences.

285/30/18 is the SM and BSP AutoX competitive standard, and many seem to use this for lapping/road racing as well.
Like GTLocke said, the 275/40/17 are a little trickier to fit. Not impossible, just take certain measures. There is a thread in the Motorsports section about this.
285/30/18 supposedly also provide a little bit of gearing advantage. I assume this means slightly smaller overall diameter than the 275/40/17, but I am not sure and may be wrong about that. If someone knows for sure, please speak up. I am too lazy to look it up right now.

I think the bigger contact patch combined with easier fitment, and more optimal gearing are the main factors that make 285/30/18 a more attractive option to many people. At around $305/tire, the only downside to R Comps in this size compared to 275/40/17s is price.

Oh, and some claim that the 285/30/18 tire itself is lighter than the 275/40/17. Don't know if this is true, but if so, if could be another benefit. Of course this is only a benefit if you are running lightweight 18" wheels, since the same wheel is typically going to be heavier in 18" than 17."

If I do ever step up to R-Comps, I might try the 275 first though, since $1200 for 275/40/17 r comps < $2500 for 285/30/18 r comps and 18x9.5 wheels

Bueller

iTrader: (1)

Gearing is a whole different topic. Anyone who is into road racing, at any level, is pretty aware of the different tire sizes. Although, you have to understand that HPDE's vs a Competition Series like NASA's TT series, is a whole different topic in itself. What works for your average weekend warrior, or even competitive autocrossers, does not always work for someone who wants to run in TT. Why? That is an issue of rules and mod points. Moving on, i havent ran the 285's either, but given what i know, id say that the 285's provide better gearing for autocrossers than road racers. Why? The 285's are shorter than the 275's. And i can think of several places on the tracks i run on where a shorter tire would be a problem. Now, obviously there is some benefit with tread width and what not, but the trade-offs are too demanding to be able to provide reasonable responses. Therefore, without having a good amount of hands-on experience with these different sizes, youre really never going to know.

hokiruu

iTrader: (19)

Good food for thought. Thanks Bueller.