Post AutoX tire wear; input?

[kz]

why not the 315 30 R18?

I see no reason not to go for the taller 295. In my experience, with the 39 psi the tire is plenty stiff...

they mount so easy I’m tempted to try the 295 on a 9 inch rim just to see what happens. (I probably won’t actually do this)

305s with ET50 wheel and 25 mm slip on spacer are already tight fit, not sure 315 will fit (aside from being pinched on 11" wheel - if I buy anything it'll Apex with ET52mm, definitely not ordering some fancy custom forgelines that I can buy another car for ;-) )

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[TeeLew]

That 305 is really wide for the size according to the Tire Rack specs. It will be hard to keep from killing the outside edges no matter what you did given it is actually pinched on an 11" wide wheel. More camber and a little bit more tire pressure would help.

No, an 11" wheel is the nominal size for a 305.

 

[SteveW]

No, an 11" wheel is the nominal size for a 305.

Look at the tread width for that particular tire: it's 11.5" or pinched on an 11" wheel. Well within the wheel size specs for the tire but not for optimum performance.

 

[JustDSM]

Got a pic of my car rolling the sidewall over..

I think this shows 32psi hot was not nearly enough..

 

[Dana Pants]

yep. More pressure is needed. The photo doesn’t lie.

Also, lol your business face. Mine isn’t much better.

 

[JustDSM]

yep. More pressure is needed. The photo doesn’t lie.

Also, lol your business face. Mine isn’t much better.

I so wanted to blur that out! LOL I was all puckered up!

 

[kz]

Got a pic of my car rolling the sidewall over..

I think this shows 32psi hot was not nearly enough..

Oh yea, this is even worse than mine. The more your drive, more you will be able to feel the sidewall flex - especially with all the mods you have that take rubber bushing compliance out of suspension.

 

[NightmareMoon]

I’ve heard the A052s do need significantly more pressure due to soft sidewalls.

 

[TeeLew]

Look at the tread width for that particular tire: it's 11.5" or pinched on an 11" wheel. Well within the wheel size specs for the tire but not for optimum performance.

Rival 1.5, RE-71R & Sport Cup 2 all specifically state 11" rim for a 305/30-R19. The design range is 10.5-11.5".

 

[Elp_jc]

Tire pressure is definitely low. I'd start with 32 cold, but since Auto-X runs are quick, you might need more, as long as it doesn't get above 36, as mentioned. Your pattern also shows abrupt transitions; try to be smoother. But tight turns are brutal on car tire edges, so you might wear them out on the outside first if, you do that often.

 

[Grintch]

Looks like it wants more camber to me. In my experience you want more camber in autocross than for the road course.

 

[Norm Peterson]

No, an 11" wheel is the nominal size for a 305.

11" is only the width wheel that a 305/30 tire is officially measured on, which is per a tire industry standard guideline. I wouldn't give "measuring width" credit for being anything but a good overall "compromise width" considering ride as well as handling and a few other things. Max- and min-recommended wheel widths aren't exactly hard pass/fail boundaries, either, but that's probably even more tire-size-specific.

The less rigid a tire's carcass is against lateral loads, the more likely it is that there will be some benefit from stretching it out on wheels wider than its "measuring width". Especially for street tire autocross classes where permitted by the rules.


Norm

 

[Grintch]

Problem is the Street classes fix the wheel size but leaves the tire size open. So the standard approach is to put more tire on the stock width wheel.

Though this seems somewhat less extreme with the current crop of Street TW200 tires verses the old Stock class R compounds (which probably had stiffer carcasses).

Using my cars, in HStreet the fast Focus ST guys run 255 tires on 8" wheels (max size recommended 245). While in the old BStock, the fast WRX STI guys ran 275 tires on 8" wheels.

What's the hot FS choice for the Mustang, 285 square ("too wide" for the fronts)?

But as I think Norm has said before, heat build up from tire flex is pretty much a non issue in autocross (and maybe a plus), but important on the track. So you probably would not want to be as aggressive with selecting big tires for the wheel size for track use as autocrossers are.

 

[Dana Pants]

It’s VERY hard to mount a 285 30 re71r on a 9 inch wide wheel and get it to hold air. I saw a whole circus of professionals and amateurs fail. Other brands might be more forgiving but I haven’t tried.

 

[Grintch]

Why would you run 285/30 over a 285/35?

My buddy was running 275/35 & 285/35 on his stock PP, the max recommended sizes for the stock wheel widths with no issues. I would be surprised if going up just one step would be a big problem for autocross (though not much tire selection in 295, and I doubt you would want to run a staggered setup - thus 285 square as my guess at what FS guys use). Significantly easier than 275 on 8" wheels.

Stuffing big tires on small wheels obviously takes more talent (and maybe better equipment) than a run of the mill setup. My local autocross club often has lively forum discussions on which of the local tires shops are best at that sort of thing.

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