Jump to content

RULE PROPOSAL: Tire size cap


JSG1901

Recommended Posts

Modification to 4. Classification

 

Proposed change

 

Tire size cap:

 

GTS1 - 205

GTS2 - 225

GTS3 - 245

GTS4 - 265

GTS5 - 285

GTSU- Open

 

Moving up to the next bracket affects the power to weight ratio as if running slicks. Example, a GTS3 running a 265 has a power to weight ratio decrease to 12.0, 285 tire 13.0, and so on allowing drivers to still run whatever tire size wanted.

 

Reason

Level the playing field between cars with widebodies / large fenders and cars with stock bodywork.

 

Logic is a 285 R-comp will outperform a 245 slick, but is a "free mod" compared to the increase in grip.

 

Proposed wording

Along the lines of the proposed change.

Link to post
Share on other sites

To set the tire sizes, I'd look at what people are already running and what tires are available. For example, most of use 275s in E46 M3s in GTS/4 with no body modifications. Hoosier doesn't offer a 265 in either 17" or 18" nor does Toyo or Hankook (BFG does), but they all offer 275s. If this goes through, I'd like to see GTS/4 at 275 and GTS/5 at 295 or 305.

Link to post
Share on other sites

I tried proposing this last year, but it went nowhere. Frankly this works on BMWs, but not so much Porsches as they tend to run wider rear tires. Plus this would be a big advantage to any AWD cars.

 

I'd say no.

Link to post
Share on other sites

I believe this proposal grossly overstates the benefit of wider tires. I recently switched my 2700lb GTS3 e36 from 245's to 285's (38lbs/corner to 44lbs/corner). What I have observed is:

 

- No perceptible change in peak grip. This shouldn't be the case according to the theory - maybe the difference is so small I am not able to detect it.

 

- Lost 2mph at the end of the straights (rotating weight, aero drag, rolling resistance). Measured with 10Hz GPS at Thunderhill raceway on different days. Air temperature at the nearest weather station was 92F in both sessions.

 

- Significantly less dropoff in the second half of the race on hot days.

 

On the colder (and the wet!) days, I suspect that the 245's might even be faster. On the hot days the 285 is, I believe, an advantage. But there's absolutely no way that it's worth anywhere near the 38 horsepower which this rule as stated would impose.

Link to post
Share on other sites
I believe this proposal grossly overstates the benefit of wider tires. I recently switched my 2700lb GTS3 e36 from 245's to 285's (38lbs/corner to 44lbs/corner). What I have observed is:

 

- No perceptible change in peak grip. This shouldn't be the case according to the theory - maybe the difference is so small I am not able to detect it.

 

- Lost 2mph at the end of the straights (rotating weight, aero drag, rolling resistance). Measured with 10Hz GPS at Thunderhill raceway on different days. Air temperature at the nearest weather station was 92F in both sessions.

 

- Significantly less dropoff in the second half of the race on hot days.

 

On the colder (and the wet!) days, I suspect that the 245's might even be faster. On the hot days the 285 is, I believe, an advantage. But there's absolutely no way that it's worth anywhere near the 38 horsepower which this rule as stated would impose.

 

I've had similar experiences between 255s and 275s, but would add on track a one is and advantage and track b the other seems to work better. There are tradeoffs between tire sizes and picking the right size for the car/setup/track is part of the fun.

Link to post
Share on other sites
ILIKETODRIVE

Not me but Matt McIntyre (TTB/GTS3 BMW E36) at Nationals in 2010 at MMP was nearly (and consistently) 1 second faster on 245s vs 255s in TTB trim.

Link to post
Share on other sites

The proposed tire rule change is a good idea, but the proposed tire sizes are too narrow.

 

Most competitive cars currently running in these classes have way bigger sizing. I would limit tires based on current cars.

 

Overall not in favor.

Link to post
Share on other sites

Leave tire sizes open. Some of those sizes listed force some models to run a much smaller tire than came standard on their cars from the factory.

 

 

-Scott B.

Link to post
Share on other sites

Absolutely not.

How would you control the difference in tire widths between manufacturers for the same "size" tire?

I switched to BFG R1's this year, and they were almost an inch wider than the Hoosiers. Both were "275's".

Link to post
Share on other sites
Leave tire sizes open. Some of those sizes listed force some models to run a much smaller tire than came standard on their cars from the factory.

 

 

-Scott B.

 

I agree, for instance BMW e46 M3 vs e36 M3. 245's are narrower than factory for the e46. As much I'd like to handcuff you e46's, lol.

Link to post
Share on other sites

This is a bad rule, no caps at all. In addition, if we were going to have a tire cap, the one's suggested are way too narrow. Try adding 30 MM to all of those and the rule would be much more fair.

Link to post
Share on other sites

Bigger isn't always better. You can have too much tire and potentially not get the temperature you need in them. Not saying i'm in favor of limiting tire sizes. Just pointing out why some might experience a fall-off in performance when going wider.

 

That said, i'd be opposed. 245 on a GTS3 911 doesn't even reach the OE tire size of a 993. So a 993 is instantly penalized? Being it's a heavier car than the earlier 911s, that 245 is putting it a disadvantage.

 

Also, a certain size limit may force many to switch wheels at a substantial cost. I know in my case my 17x10 rear wheels would be unfit for a 245 tire, so i'd have to take the penalty or rebuild them (luckily they're 3 pc. wheels) to fit a 245.

 

Leave tire size open. If tire wars are such a concern, mandate a spec tire ........... yeah right. What a firestorm that'd create! Even then, the people that can afford new tires all the time have the upper hand.

 

A lot of people have their cars dialed in to the right tire size and this rule change would throw all of that into a tailspin and require significant setup change. Think about it, a "real" racecar build from the ground up starts with your wheel & tire size and you build around it from there. Change the rules about tires and there goes the foundation.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...