When are tires too wide......

[DocWalt]

Terry, autocross doesn't have the same air and rotational drag concerns of high speed track use, you know that

My lap times dropped ~10 seconds, but my point was that rolling drag & aero drag will eventually cause issues. I changed the entire suspension setup and went from -1 degree of camber up front to -3 and changed to better dampers, etc etc. Lots of other factors there

Counter Space Garage tested sticky 225s vs sticky 245s and for lower power levels on a high average speed track 225s were faster. I'm not privy to *how* they tested, but that's the info they presented.

FWIW Shenandoah circuit isn't a high speed track, somewhere like VIR I'd likely have been setting the same lap times on sticky 225s versus sticky 245s just due to drag. If I'm giving up 1 mph apex speed with narrower tires but making speed up the entire back straight then the math likely works out to a wash eventually.

Also, I think the other comments here about just slapping wider tires on with doing no other setup work is likely why the ZL1 on OP's post went slower. Balance change, everything too soft, etc etc. The ZL1 has enough power to not care much about that extra bit of rubber width causing drag. It's not a 200hp 4 banger, haha.

 

[racer47]

My lap times dropped ~10 seconds, but ...

But what? You gained 10 secs with tires and you're still arguing in favor of bigger is not better.

I don't get it. I never knew there would ever be a debate like this. Its crazy. I'm 100% with Fair on this. I'm running 315 A7s only because I don't want to cut fenders. My car is not a race car. Its a play car and not built to fit any set of rules. If 335s would fit, thats what I would have.

The rolling resistance increase between a 275 and 315 is trivial. Can you all of a sudden not push your car around because you put bigger tires on it? Tire aero drag is real on Indy cars and F1 not on a Mustang, Vette or BRZ.

 

[DocWalt]

But what? You gained 10 secs with tires and you're still arguing in favor of big is not better.

I don't get it. I never knew there would ever be a debate like this. Its crazy. I'm 100% with Fair on this. I'm running 315 A7s only because I don't want to cut fenders. My car is not a race car. Its a play car and not built to fit any set of rules. If 335s would fit, thats what I would have.

The rolling resistance increase between a 275 and 315 is trivial. Can you all of a sudden not push your car around because you put bigger tires on it? Tire aero drag is real on Indy cars and F1 not on a Mustang, Vette or BRZ.

I gained 10 seconds by changing tire compound (if you've driven the crappy stock BRZ tires you'd understand why RE-71Rs are better even if I went narrower...) and entirely changing the car setup. Not by going wider... The difference would be much smaller if I had sticky tires on my car in the first place, maybe to the point where I'd have been faster at the end of the straights than with the wider tires even with higher apex speeds.

*shrug* I was just making a point. No need for you two to jump on me that it doesn't matter because it clearly does matter at some point. Relevant for many hundreds of horsepower, maybe not.

 

[racer47]

Didn't mean to come off harsh. Also didn't catch the detail on stock vs sticky tires, was focused on the size thing.

But the only real limit is what you can make fit. More rubber is faster. Supermodifieds are another good example.

 

[DocWalt]

If you have enough power to push the tires, wider is always faster (assuming you change the setup to match). How about we all agree on that?

I wasn't disagreeing, just being hard headed about a point that's probably not relevant to anyone on this forum and certainly not to the ZL1 in OP's question, lol

Also, I checked data, it was more like 5 or 6 seconds, not 10. Not sure where that came from, my apologies.

 

[302BOB]

5 or 6 second lap time improvement is HUGE!.....

 

[DocWalt]

5 or 6 second lap time improvement is HUGE!.....

I take it you haven't subjected yourself to tracking a "sports car" on Prius low rolling resistance tires? It's amusing at best.

 

[302BOB]

Sorry for the insult...Most others consider a 1 or 2 second improvement to be happy about.

 

[DocWalt]

Sorry for the insult...Most others consider a 1 or 2 second improvement to be happy about.

Trust me, no offense taken! The stock BRZ tires are terrible. A monkey could find seconds with a tire change on that car, even in the same size tire

 

[ArizonaBOSS]

I'm with @Fair and @racer47 on this one--run as much tire as you can fit (unless limited by classing rules). This needs to be thought of in the respect of Tire Contact Patch to Vehicle Weight as much as Vehicle Power to Weight is considered.

 

[Busdriver]

Speed on the straight doesn't tell you everything. Assuming I haven't totally screwed up the kinematics I learned back in the day here goes:

Starting at 22.3 (50mph) and 26.8 m/s (60mph) coming off the turn and an average acceleration of 3m/s^2 (half a G) an 800m straight will take 16.8 seconds to cover with the slower corner exit speed vs 15.8 seconds for the faster case. Speed after that 800m will be 162.8 on the slower exit vs 166.2 for the faster exit.

 

[smallblock]

Take this for what it’s worth.... as a casual weekend warrior... running, god forbid yellow Konis on Eibach Sport Springs.... I have gone from stock 255 Pirellis, to 285 pirelli corsa Systems, to 285 R-S3’s, to 285 Contis, to Pirelli 305 DS slicks. Tire width and stickiness are the single biggest differentiator in my experience with my S197. (aside from seat time) If I could fit a 385 pirelli slick with my Koni’s and eibach springs I’m sure I would improve times in spite of my resistance to a quality set-up.... guaranteed.

 

[Mad Hatter]

All true.... but even a 305 is narrow for our cars..... I am hoping to go to 315 asap. But looks like going to a massive 335 needs to have the corresponding suspension goodies.... Will find out this Saturday how I do against the Camaro with my puny 295's!!

 

[blacksheep-1]

Quote:
"Again, I don't see an obvious limit even on "under powered cars". In SCCA autocross the tiniest cars are going faster with ever wider tires (275-295mm Hoosiers on 1.6L Miata Street Prepared cars, 315-335mm Hoosiers on 3.0L DSP BMWs, etc). The track guys are more reluctant to test these wider tires because "conventional wisdom" talks them out of it so often. Shame."

This where I would disagree, autocross, in reality, has little to do with track performance. Most autocrosses are extremely limited with a 70 mph maximum mandated by insurance companies, that makes them all mostly, "point and shoot" propositions, the other thing is that autocross tires never...never come up to a decent operating temperature, they basically act like qualifying tires,( lots of pressure early on and limited length). tires play a far more important roll in autocross than a road course because, since the car is almost always in some form of transition, you can never have enough tire.
I would submit that a miata with 335 stuffed on it would be right at home on an autocross, but after 3 laps on on a road course, it would be like pulling and anchor around.
I do agree with the statement that wider tires require a rethink on the suspension, especially shocks, it seems a wider tire translates much more ..."information, loads..whatever" to the shock , making a coil over mandatory.
We're going to find out on the auto-x mustang, I've sourced some 14 inch wide .45 durometer tires for that

 

[modernbeat]

Well Blacksheep, on our Mustang we've found, through testing, that in both autocross AND on track that we got faster with more tire every time.

 

[blacksheep-1]

Well, autocross doesn't translate directly to the road course, and, apparently your mustang is heavy and has enough HP to overcome a fat tire, I doubt the same could be said for my 100hp MG midget I used to race

 

[modernbeat]

Today, I'd still run a larger tire (largest that will fit within the rules) on a 100hp car. We still do that. It's called a Miata and it's even lighter than that MG, so it's an even more difficult car to "get heat" in. If there are heat issues with the larger tire, then you change the compound. The larger tires give us better consistency, and better life, even in the extremely soft compounds. And it's not just about the "power". They also brake harder and corner harder, allowing us higher corner exit speeds and longer time on the gas, which is even MORE important when you have a 100hp car.

 

[Grant 302]

If there are heat issues with the larger tire, then you change the compound.

I'd like to see an example/comparison where *that* proves to be faster on track.

 

[smittytx]

Well' I guess the only thing I can say about my Toyo RR 275s is they are cheaper

 

[blacksheep-1]

Didn't mean to come off harsh. Also didn't catch the detail on stock vs sticky tires, was focused on the size thing.

But the only real limit is what you can make fit. More rubber is faster. Supermodifieds are another good example.

View attachment 3635

Since most of the supers run articulating wings, that's not a great example, but point taken.

Sorry modernbeat, nothing is lighter than an MG Midget with the exception of a box of Kleenex.
At some point out there, there will be an edge, whether it's a kart, or formula car or a sedan, at some point a fat, sticky tire can very well become the point of diminishing returns.
If you were to take that miata, and run 14 inch , 45 durometer tires on it, (or whatever) fire it into a corner without lifting, ever, the car is probably too tight.