STR in 2012

JasonWatts · **Posted:** Thu Dec 22, 2011 5:24 am

dont forget the 40 is a percentage of the side wall and will change your tire diameter. in the case of the two tires your looking at, I think the 255 is 8 mm or .3 inches bigger. This will up top speed and decrease acceleration. I dont know the formula to get the top speed in X gear or of a website to calculate it. I would imagine the difference the sidewall is going to make will be marginal though and am interested why you would want to pick the 255 over the 245.

I wonder how much of an argument there is for sidewall flex being more.

MarcusMcRae · **Posted:** Thu Dec 22, 2011 8:31 am

Steven Carter wrote:

ignorant STR tire question follows (please be kind)

Seems most people like the RS3 in 255 section width for the 17 x 9 wheel. Checking the tirerack website shows a negligible difference in tread width between 245 (9.1" tread) and 255 (9" tread width). I am not a tire engineer, but why would one opt for a wider section width when tread widths are the same? conceivably one could run 245s on lighter 17 x 8 wheels with the same contact patch, or is that inaccurate?

How far am I out to lunch?

Price is probably the main reason people were running the 255's. They were $121 each and the 245's were like $40-$50 more per tire.

If you want better acceleration try the R1R 245/35. It's an inch shorter than the stock size.

Steven Carter · **Posted:** Thu Dec 22, 2011 9:25 am

double post #1

Steven Carter · **Posted:** Thu Dec 22, 2011 9:25 am

double post

Steven Carter · **Posted:** Thu Dec 22, 2011 9:25 am

JasonWatts wrote:

dont forget the 40 is a percentage of the side wall and will change your tire diameter. in the case of the two tires your looking at, I think the 255 is 8 mm or .3 inches bigger. This will up top speed and decrease acceleration. I dont know the formula to get the top speed in X gear or of a website to calculate it. I would imagine the difference the sidewall is going to make will be marginal though and am interested why you would want to pick the 255 over the 245.

I wonder how much of an argument there is for sidewall flex being more.

Thanks, I'm aware of that. I doubt 10 extra revs per mile will have a huge effect, although the better drivers may complain about hitting rev limit a tad earlier than expected. As for price, the 245s are only $7 more so not a big issue there. Was really curious about whether there was an advantage to be had by running around 16-17 lbs less unsprung weight for the same contact patch, as Kosei makes a 15 lb 17 x 8 wheel, while the "standard" STR wheel, the TR C3, weighs nearly 18ish lbs. The 245 tire is 1 pound lighter, FWIW.

Oh, and 245/40 is the standard rear tire size for an AP2 S2000, the hypothetical car in question... :wink:

Keith Vail · **Posted:** Thu Dec 22, 2011 10:51 am

Steven Carter wrote:

Thanks, I'm aware of that. I doubt 10 extra revs per mile will have a huge effect, although the better drivers may complain about hitting rev limit a tad earlier than expected. As for price, the 245s are only $7 more so not a big issue there. Was really curious about whether there was an advantage to be had by running nearly 20 lbs less unsprung weight for the same contact patch, as Kosei makes a 15 lb 17 x 8 wheel

The 245 on an 8 inch wheel will not be the happiest tire and you would be giving up grip and feedback to the guys running the 255 on the 9 inch wheel. I ran my 255 RS3's on the S2000 on both 8.5 inch width and then 9 inch wide wheels and could feel a difference in how crisp the car was. Being that 17x9's are not expensive and I would take the extra inch of wheel on each corner over saving the couple lbs of rotating mass by going with narrower wheels. This is all IMHO of course.

If you want the 245 you they will be quite happy on the 9 inch wheel or even the 8.5 inch wide wheel. But keep in mind an AP2 on a 245/40/17 will be running out of 2nd gear everywhere on courses like Sanford and Danville, unless you raise the rev-limiter. I speak from experience.

Steven Carter · **Posted:** Thu Dec 22, 2011 11:05 am

Thanks Keith. It's hard for someone without much experience (like me) to know how much emphasis to place on things like weight savings, unsprung mass etc vs grip, "tire happiness" and steering feedback. In a perfect world I could do multiple side-by-side comparisons, but I don't have the $$ to make that happen.

....That GRM article from 2010 still influences me, though, where their STR NC Miata was faster on 245s but (IIRC) lacked some steering feel. It may be entirely different for the S200, however.

DickRasmussen · **Posted:** Thu Dec 22, 2011 11:53 am

As you work through the trade offs of smaller versus larger tires keep in mind whether or not you will be traction limited more often exiting corners with the smaller tires. If so, the "gearing" advantage of shorter tires could be minimal or even negative.

Dick

Steven Carter · **Posted:** Thu Dec 22, 2011 12:19 pm

Dick, that is my problem...the two tires have the same tread width, only differing in section width. So doesn't that mean the contact patch would be the same for a given car when using the "as measured" rim width for each tire?

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

I really doubt tire size/wheel size is going to make much difference in our times, since we're not winning national championships or anything.

But anyway, I got the 17x8 Enkei RPF1's, which are 15.? lbs each, and I plan to run my old 235/45 Dunlops in front and get some new 245/45 Dunlops for the rear, based on how much the rear end was sliding around at Danville. Once I wear out the fronts, I'll decide what to replace them with, but it will probably be 225 or 235 Dunlops.

Forgot to mention the 17x9's are almost the same weight as the 17x8's. But they're a lot more expensive.

MarcusMcRae · **Posted:** Thu Dec 22, 2011 1:22 pm

Kevin Allen wrote:

I really doubt tire size/wheel size is going to make much difference in our times, since we're not winning national championships or anything.

But anyway, I got the 17x8 Enkei RPF1's, which are 15.? lbs each, and I plan to run my old 235/45 Dunlops in front and get some new 245/45 Dunlops for the rear, based on how much the rear end was sliding around at Danville. Once I wear out the fronts, I'll decide what to replace them with, but it will probably be 225 or 235 Dunlops.

Forgot to mention the 17x9's are almost the same weight as the 17x8's. But they're a lot more expensive.

Are you sure want a 45 series sidewall? That's a pretty tall tire.

Be carefull with your tire width too. With the offset of your wheels you might get the rubz.

FWIW I will not be getting another set of the RS-3's.

DickRasmussen · **Posted:** Thu Dec 22, 2011 1:28 pm

Steven Carter wrote:

Dick, that is my problem...the two tires have the same tread width, only differing in section width. So doesn't that mean the contact patch would be the same for a given car when using the "as measured" rim width for each tire?

Steve,

I really don't know. However, from a little bit of personal experience and some observations from others over the decades a couple of considerations all of which assume the same size wheel and identical compound tires:

1) Will the wider tire hurt steering response time in transitions (i.e. what works for open track may not work for autox slaloms)?
2) Will the wider tire have trouble getting up to the needed temp for max grip and/or will the narrower tire be more likely to overheat?
3) Is the cost difference enough that the lower cost of the narrower tires will allow more competitive runs?
4) Generally a wider tire will have more grip . . . within reason so will you be able to use the grip where it counts?
5) Will the wider tire fit in your trunk, tire trailer, etc. :sing:

As Kevin says, will we even be able to tell the difference?

Vincent Keene · **Posted:** Thu Dec 22, 2011 1:31 pm

DickRasmussen wrote:

Steven Carter wrote:

Dick, that is my problem...the two tires have the same tread width, only differing in section width. So doesn't that mean the contact patch would be the same for a given car when using the "as measured" rim width for each tire?

Steve,

I really don't know. However, from a little bit of personal experience and some observations from others over the decades a couple of considerations all of which assume the same size wheel and identical compound tires:

1) Will the wider tire hurt steering response time in transitions (i.e. what works for open track may not work for autox slaloms)?
2) Will the wider tire have trouble getting up to the needed temp for max grip and/or will the narrower tire be more likely to overheat?
3) Is the cost difference enough that the lower cost of the narrower tires will allow more competitive runs?
4) Generally a wider tire will have more grip . . . within reason so will you be able to use the grip where it counts?
5) Will the wider tire fit in your trunk, tire trailer, etc. :sing:

As Kevin says, will we even be able to tell the difference?

Wow, did all of you turn into James overnight?

Since the nut behind the wheel is the biggest variable here, me thinks you might be overthinking this...just a tad.

Steven Carter · **Posted:** Thu Dec 22, 2011 1:40 pm

DickRasmussen wrote:

[As Kevin says, will we even be able to tell the difference?

As a driver, probably not... :shock:

I am simply trying to avoid paying for two sets of wheels, so doing all the thinking (at no cost) before purchasing usually helps me out by avoiding costly missteps. Some like to follow the herd/forum mentality and do what everyone else does, which is fine for them. For me, I enjoy learning about why Autocross setups work the way they do, as well why certain attitudes exist about what works and what doesn't. If it makes sense to me, then I'll follow along too.

Matt McGrain · **Posted:** Thu Dec 22, 2011 2:16 pm

MarcusMcRae wrote:

FWIW I will not be getting another set of the RS-3's.

Do tell why sir. They seem like a steal compared to the Specs and 140 versus 200. Are they teh suck?

Having run 6" and 7" wheels for most of my autocrosses, a 9" wheel up front on any Honda other that one fully prepped like Jinx's still seems really foreign to me and sounds like you better have a ziplock bag with plenty of fenderliner clips. I now know it's the norm though for STR.

Isn't it true you sort of see diminishing transitional grip if you do run too large of a section width on a street tire compared to rim width unlike R-comps? I'm not saying a 9" wheel wouldn't be happy, just thinking about a 255 on a stock 7.5" AP1 wheel for example.

VK, auto-x is over for the year so all we can do now is geek out until we start making the schedule for next year. :lol:

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