Street class tires width

[bjinright]

THIS ARTICLE IS ABOUT STREET CLASS ONLY WHERE RIMS/WHEELS ARE SET BY RULES. IF YOU TELL ME ABOUT SOMETHING IN CSP or XP YOU CAN GO TO HELL (respectfully). ALSO IF YOU TELL ME THAT I SHOULD JUST TEST THIS MYSELF AND THAT ALL CARS ARE SPECIAL YOU CAN ALSO GO TO HELL(respectfully) THIS WOULD TAKE YEARS AND TENS OF THOUSANDS OF DOLLARS For any of us.

Been reading soooo many articles about WIDER NOT BEING BETTER lately. Wanted to flesh some things out. Wanted some input from those that are open minded. Just to start here are 2 of the main articles:

https://www.tirerack.com/tires/tests/testDisplay.jsp?ttid=296

and

https://grassrootsmotorsports.com/articles/wheel-width-is-wider-always-better/

also
Problem is they don't talk about air pressure and horsepower and weight. Always something left out.

After reading my 5th article and 12 video, I think I might have come up with something. I believe there is a certain width tire for a given wheel that's faster and its not the max width, but I do think there is a minimum tire width that overrides that having to do with HP/TQ and Weight. For instance:

1mm for every HP/TQ averaged. and Weight of car in lbs /12 is minimum width in mm.

2022 gr86 7.5' wheel 228hp/184tq 2833lbs should be 225 width.
2019 mx5 7' wheel 181hp/151tq 2341lbs should be 195 width but there isnt one and for gearing gotta go up to 225 would a 215 in a 18' wheel work better?
2019 type r 8.5 wheel 315hp/310 3188lbs should be as wide as you can fit starting at 265
2006 330i 8/8.5 255hp/220 3425lbs Looks like a 245 to 255 would work here even though thats big for the wheel should it be a 235?

Look I know this looks crazy but I want some numbers to see if this can be a rule of sorts.

[nickrd10bk]

I think it is crazy. (Respectfully.)

I think there is no good "rule" to any of this.

I think that there is far too much data to gather and too many variables that won't remain static to authenticate any conclusions. As you've said, there are too many different cars, and different compounds are going to affect those chassis differently.
I keep reading the Bridgestone RE71RS is the best tire on the market now. The top cats in A Street last season were ALL running the Yokohama.

Some tires love the "pinch" more than others.

To that end, I think we are unfortunately left to our own anecdote on our respective vehicles. (Which can get expensive.) For example, I think I've purchased the last Falkens for the Corvette, as they never seem to do much past 50 runs, and I can get more usable runs out of the Yokohama. With regard to the Veloster N, I think the Falken really works well with that chassis and power level. I enjoy the responsive steering from the Falken. The Corvette is a bit more sensitive in that regard, and I find it hard to drive as consistently well on the Falken as opposed to the Yokohama.

I pinched the hell out of some tires on the Camaro when I still had it, and I felt the car drove better on the factory width tires. The problem was the factory size tires literally corded within 40 runs, as there wasn't enough rubber to handle the surface temps that car induced on that tire (being heavy, softly sprung, and camber limited).

Now if we look at data, we will see that all of these tires will have identical lateral G. Some tires might have a slight advantage. But, on the surfaces autocross events take place at, I think they're all so close in performance that the driving outweighs ALL of that.

Lateral grip, steering response, compliance, longitudinal grip, and thermal dynamics are all things we should consider on the tires we select, and everyone is going to have their preference on some of those variables. If you love a very responsive tire, you probably aren't going to enjoy an aggressively pinched tire size.

This is why I'm getting away from mixing front and rear tire brands, as I'm effectively engaging in a balancing act, and when the rears are gripping nicely, the front is not in its "window". This can happen with all the same tire brand as well, but I think the tires work together in better harmony when they're all the same brand.

I put very little faith in others feedback on the tires on the market until I get to drive on those tires. I plan to order a set of Bridgestone tires for the Veloster N next, and get my own impressions. I will probably go for the same size we currently are running as there are a few fitment concerns.

Sometimes, you're forced to pinch a crazy tire on your wheel based on what is available. Street class rules really can limit what you CAN run. By your formula, my Camaro should run a 377mm tire. Obviously, in street class, you can't even get a 20" tire in a 315mm width. 295 is the widest I've seen.




With all that being said, I'm not a tire engineer, or a national champion. Don't take my word for law either.

[bjinright]

Yep crazy. Good info though nick. I have noticed for high horsepower cars there is almost no such thing as too wide. You just have to go with what fits.
I think this all started because these videos keep saying put a 205 or 215 on your miata or FRS but no one is doing this. Almost everybody is pinching especially the fast drivers.
my cayman was really fast when I had stock tire sizes and they were YOKOs but I had to switch because I had no camber and they barely made it 30 runs. The next size were crazy big a copy of BS national champ setup.falkens. Fast . . . They felt and looked so weird.

Now I'm going to be back in CS but with a z4. And I'm looking for a starting point. Right now it's 235s on 8x18 front and 8.5x18 rear.

[rodhx]

Now I'm going to be back in CS but with a z4. And I'm looking for a starting point. Right now it's 235s

What size wheels on the z4 Bo?

[bjinright]

8x18 front and 8.5x18 rear. Picking 235/40s for fitment and camber issues. But looked at 245/40 they were 2 lbs heavier each.

[rodhx]

8x18 front and 8.5x18 rear. Picking 235/40s for fitment and camber issues. But looked at 245/40 they were 2 lbs heavier each.

I have 8.5s for the IS300 and ran 235 or 245 depending on the tire since tire width sizes are seemingly assigned at random and cannot be compared.

[bjinright]

like an 03 or 06 ?Lexus IS 300 8.5 wheels 215hp/215tq 3255lb. Did you notice the 235 or 245 to feel better or were faster? Did you ever consider the 225? Because of the weight of the car did the tires ever get too hot?

[rodhx]

like an 03 or 06 ?Lexus IS 300 8.5 wheels 215hp/215tq 3255lb. Did you notice the 235 or 245 to feel better or were faster? Did you ever consider the 225? Because of the weight of the car did the tires ever get too hot?

Yes, my blue car and now Zac's bronze one, both 03 IS300s. I ran my car for two years on 7s with 225s. The entire point of the 8.5s, which is the widest you can fit on a 1G IS, was to go wider. I ran 235 Nexens SUR4G because they ran really wide. In 21 I ran 245 Falken 660s. The Kumho 730s I ran last year (and this year) are 255, because those tires run a bit narrow. All were roughly the same actual width so feel or faster was more due to the tire itself, not the size.

Really can't answer that heat question because I ran different tires in the different sizes so no basis for a valid comparison. I feel getting too hot is as much a factor of a specific compound's heat tolerance and multiple drivers. Typical single driver local event? No, never considered heat much of an issue but sprayed if needed. Warm/hot weather two drivers? Yeah, we sprayed them a lot. However that behavior is exactly like I've treated every car/wheel/tire I've ever had so YMMV.

[nickrd10bk]

Yep crazy. Good info though nick. I have noticed for high horsepower cars there is almost no such thing as too wide. You just have to go with what fits.
I think this all started because these videos keep saying put a 205 or 215 on your miata or FRS but no one is doing this. Almost everybody is pinching especially the fast drivers.
my cayman was really fast when I had stock tire sizes and they were YOKOs but I had to switch because I had no camber and they barely made it 30 runs. The next size were crazy big a copy of BS national champ setup.falkens. Fast . . . They felt and looked so weird.

Now I'm going to be back in CS but with a z4. And I'm looking for a starting point. Right now it's 235s on 8x18 front and 8.5x18 rear.

If somebody does really well on ANY tire brand or amount of pinch at a National level event, you WILL see people emulate that tire choice. I remember when Kerry Coughlin beat everyone in E Street at Dixie with a 245 Rival pinched on a 6" wide wheel and everyone showed up to the next event with that SAME setup. Everyone would go on to lose to a fellow on a 225 Falken that next event, and the share price of BFG went up anyway.

[rodhx]

If somebody does really well on ANY tire brand or amount of pinch at a National level event, you WILL see people emulate that tire choice. I remember when Kerry Coughlin beat everyone in E Street at Dixie with a 245 Rival pinched on a 6" wide wheel and everyone showed up to the next event with that SAME setup. Everyone would go on to lose to a fellow on a 225 Falken that next event, and the share price of BFG went up anyway.

autocrossers are the ultimate form of motorsport lemmings!

Rule 1 of watching Dixie results: ignore Dixie results unless you run ALL your events on a site as narrow as an airport runway.

[bjinright]

Gotcha. Well i was looking for another mx5 or gr86 but the prices just have not come down yet. So I picked somthing that was recently moved from bs to cs. I thought this would be fun to run in a class otherwise dominated.

mx5. 180hp. 2341lbs 13lbs/hp. 15.6lbs/tq
Z4 3.0si. 255hp. 3055lbs. 11.9lbs/hp. 13.8lbs/tq

I'm alittle faster t0 60 and we both can make 63 in 2nd with tires. Similar torque curves even though the number are different. I'm way heavier though. But stock suspension in z4 is really really stiff. And i can run more tire. I think its close enough to try. But I can't make it until July.

[rodhx]

Cool! Hit me up if you ever want a tire warmer . I’d like to give that a try.