Street Tire Class 2013

JamesShort · **Posted:** Wed Feb 20, 2013 11:49 am

Steven Carter wrote:

JamesShort wrote:

Jordan Normark wrote:

I was planning on running 225/45/15's on my 8" wheels, but it looks like the 205/50/15's will be available on 2/27. I was thinking the 205's might be a good back-up plan in case the 225's get pushed back, but maybe I should just go with 205's. From what I am reading, it looks like this tire wears very well and tolerates heat since it is designed for both autocross and track. Do you think the bigger is better convention applies here, or should I choose the 205's?

Just a data point. When Ram went from 205/50 Star specs on 6" wheels to 225/45 RS3s on 9" wheels, there was a BIG increase in performance/handling. Not sure if it is was going to a more square setup or the the extra near inch of tire.

Pretty sure it has more to do with 3" of extra wheel width and then secondarily a better ratio of wheel width to tread width. 205s on a 6" wheel is over-tired for street tires.

I agree, but 195s or 205s on 6" wheels is pretty common on OEM cars. But it's a terrible comparison anyway, different wheel size, tire size and tire compound

.

Jordan Normark · **Posted:** Wed Feb 20, 2013 12:23 pm

205's on 8's and 225's on 9's is certainly popular, and everything I have read says 225's on 9's are faster that 225's on 8's since the tire fills out the rim and keeps the sidewall in tension...At least that is how I understand it. Since I already have 8" wheels and have no plans to get 9's, will 225's be faster than 205's for autocross? How wide is too wide for an 8" rim? At what point do diminishing returns become negative returns? As another data point, fast CSP Miata's run 275's on 10" wheels.

BriceJohnson · **Joined:** Thu Apr 13, 2006 7:33 am **Posts:** 2230

for a given wheel size, wider tires are always better, at least to a point far more ridiculous that what you are running, at least thats my view from a stock class autocrosser. SP/SSM cars probably DO react a bit differently, particularly cars that are lacking in power where tire weight is more of an issue, but I think you probably have more than enough power.

As another datapoint, Feinberg ran 275's on 6" wheels for his DS integra in front.

Les Davis · **Joined:** Fri Aug 29, 2003 2:04 pm **Posts:** 2059

I'm personally in the camp where you can't have too much tire as long as your talking about autocross compound tires on a warm/dry day. If its cold or rainy or even snowy, narrower tires could possibly be better depending on the compound. But for your typical autocross situation, wider is always better.

Cash Davidson · **Posted:** Wed Feb 20, 2013 1:15 pm

JamesShort wrote:

RodneyWright wrote:

so my stupid question of the day is I guess we now run "RT" instead of "TIR" for letters this year. I saw a mix of both. Does it matter from a T&S stand point now that this is the same class?

Technically we want to see RT on the cars, however we are going to give a year grace on this. Starting in 2014, TIR will be deprecated.

Did I mis-read Noah in the Heel & Toe? I thought it read that RT would be open to all Stock classes. It left me thinking that RT would be for Stock and TIR for everything else, but that didn't make sense. Sorry, I don't have the newsletter in front of me. This is just me - never bashful about asking a dumb question. :lol:

Anyway, thanks for the clarification, James. :wink:

JamesShort · **Posted:** Wed Feb 20, 2013 1:15 pm

BriceJohnson wrote:

for a given wheel size, wider tires are always better, at least to a point far more ridiculous that what you are running, at least thats my view from a stock class autocrosser. SP/SSM cars probably DO react a bit differently, particularly cars that are lacking in power where tire weight is more of an issue, but I think you probably have more than enough power.

As another datapoint, Feinberg ran 275's on 6" wheels for his DS integra in front.

This applies more to r-comps though, not EPSTs. I mean tons of data already suggests that 195 R1Rs are faster on 7.5" wheels than 225s which is allowed in STC/STS though it might be due to the 195 pixie dust.

I think star specs would probably continue to do well on undersized wheels due to the stiff sidewalls, but not RS3s or Kumho XS for example.

JamesShort · **Posted:** Wed Feb 20, 2013 1:18 pm

Cash Davidson wrote:

JamesShort wrote:

RodneyWright wrote:

so my stupid question of the day is I guess we now run "RT" instead of "TIR" for letters this year. I saw a mix of both. Does it matter from a T&S stand point now that this is the same class?

Technically we want to see RT on the cars, however we are going to give a year grace on this. Starting in 2014, TIR will be deprecated.

Did I mis-read Noah in the Heel & Toe? I thought it read that RT would be open to all Stock classes. It left me thinking that RT would be for Stock and TIR for everything else, but that didn't make sense. Sorry, I don't have the newsletter in front of me. This is just me - never bashful about asking a dumb question. :lol:

Anyway, thanks for the clarification, James. :wink:

RT 2013+ == TIR 2012- except for in RT 2013+ you get your pax discount.

This is slightly different than SCCA in that they have RTF/RTA/RTR which only applies to Stock classes. We are going to all all Stock, SP, M, P cars participate and not split on awd, fwd, rwd.

Matt McGrain · **Posted:** Wed Feb 20, 2013 1:44 pm

JamesShort wrote:

This is slightly different than SCCA in that they have RTF/RTA/RTR which only applies to Stock classes. We are going to all all Stock, SP, M, P cars participate and not split on awd, fwd, rwd.

The way you guys categorized it is the best way based on the amount of folks running RT and it should be a fun year watching everyone battle it out: let every class into RT except the ST* classes (b/c their pax is already predetermined based on streets of course). :thumbsup:

I read an interesting point yesterday on another forum that Andy Hollis tested an AP2 with 7" front wheels, and found that the car got slower running anything larger than a 215 section width street tire. Funny, because I know a guy that thought 235 Star Spec's would be perfect on stock front wheels last year. :lol:

The rule of thumb seems to be for r-comps to get as much race tire as you can that doesn't kill the gearing and on streets not to let the section width get too out of hand compared to wheel width.

Jordan Normark · **Posted:** Wed Feb 20, 2013 2:01 pm

So wider is better, except when it's not. Either way, I can't imagine there is that much of a difference between 225's and 205's on an 8" wheel on my car. It does not feel underpowered or sluggish with the wider tires.

Ryan Holton · **Posted:** Wed Feb 20, 2013 3:32 pm

From reading what Andy Hollis has shared, with street tire, its best to stay within a .5" spread tread width to wheel width.

I know it was.night and day on my old 240 with 245's on 9" vs 8"

Matt McGrain · **Posted:** Wed Feb 20, 2013 3:51 pm

Ryan Holton wrote:

I know it was.night and day on my old 240 with 245's on 9" vs 8"

Sounds like the experience I had driving Jeremy's car with 9" wheels versus the stock size running 255's. Much more confident under throttle with less sidewall squirm, especially through the faster sections.

Jordan Normark · **Posted:** Wed Feb 20, 2013 4:33 pm

Ok, So I stumbled across this from Andy Hollis from his Facebook page. It's interesting to note that Tirerack does not list tread width for the Rival yet.

Quote:

Optimal wheel size

Many folks entering the ST category are refugees from Stock looking to make some performance upgrades to their car and/or reduce their tire budget. Unfortunately, they carry with them some baggage on concepts that may work well in Stock, but not in ST. One of these is optimal wheel/tire fitment.

Since Stock limits you to the OE wheel sizing, astute competitors have learned how to stuff increasingly wider tires onto those skinny rims. And tire makers have been happy to make wider and wider tires, likewise charging more and more money. But, is wider better? In Stock, the answer is often "yes". The sidewalls on these DOT-approved "Not for Highway Use" R-comps are super stiff and allow for "overtiring" much in the way that a cantilever style slick works to get around wheel width limitations for formula cars.

In ST, drivers in most classes have limits on both wheel width and tire section width, both of which are much wider than OE. The tendency is to cram the widest legal tire on the widest legal rim that will fit and go for it. But that is not always the optimal solution, as street tires do not have the same super-stiff sidewalls as do the best R-comps. Sometimes it makes sense to run a narrower tire for a given rim fitment. From the testing we've done, we find that a good rule of thumb is that the optimal rim is the same size (rounded up to the nearest half-inch or so) as the tread width (not section width!). So a 205/50-15 tire with a typical tread width of 7.5" is best on 7.5" rim. An 8" rim will work, too, but it will be majorly stretched on a 9. Likewise, it will lose some performance on a 7, and will lose a LOT going down to a 6 or 6.5. Similarly, a 225/45-15 with an 8.2" tread width works best on at least an 8.5" rim and loses a fair bit on a 7.5".

A practical example of this is in STC, STF and STS where the rim limitation of 7.5" keeps the 195/50-15 Toyo R1R at the top despite it not being the widest allowed tire size. The 225/45-15 R-S3 mounted on that same 7.5" rim is not quite as fast. But put that same R-S3 on an 8 and it comes alive. And it's even better on something a bit bigger. So in STR, where wider rims are allowed, the common 225 R-S3 on 9's is a faster combo than the 195 R1R on a 7.5 (assuming nominal weather). And putting the 195 on an 8 or wider does nothing to enhance performance and close the gap.

JohnByers · **Posted:** Wed Feb 20, 2013 6:30 pm

My BFG Rivals came in today

Steven Carter · **Posted:** Thu Feb 21, 2013 9:42 am

Two more points on the "widerr not always faster for street tires" discussion. 2010 GRM tire testing on the MX-5 showed 245s faster than 255s. More recently, Jon Lugod (2012 STR Nats champ) determined that 235 R1R(not pixie dust size) was faster than 255 StarSpec. Certainly, the "widest Hoosier possible" theory is valid for Stock classes, but doesn't necessarily translate to street tire classes.

Chuck Branscomb · **Posted:** Thu Feb 21, 2013 9:57 am

Everything I can gather supports what Steve and others have said about street tires. Even with some R-comps, you have to be careful with tire stuffing. Peter Calhoun (who is the motorsports manager for BFG/Michelin North America) cautioned against doing extreme attempts with the BFG R1 and R1S saying that "The recommended rim width for the 285/30-18 BFG R1 or R1-S is 10-11". You will be able to squeeze it onto a 1" narrower rim, but to go 2" narrower down to an 8" would seriously compromise the performance and structural integrity of the tire."

The R1 has very stiff sidewalls similar to the Kumho V710 (my opinion from using both of them years ago) whereas the Hoosier A6 has a much, much different sidewall design (which of course is why something like a 295/30 A6 will mount right up to an 8" wheel when a V710 or R1 in the same size will *not* make you happy trying to do the same, and in many case you can't get it to air up once you get it on the rim without extreme measures). Peter says doing stuff like this with the R1/R1S will compromise the structural integrity of the tire. Of course if it is somehow faster by a 0.1 sec on a 30 sec course, and it doesn't blow up, the serious autocrosser would take that chance. However, taking that tire to a road course and running 140+mph is probably not a great idea.

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