Spec E30 wheels from 949 Racing.

[DSP74]

That's pretty narrow to reap the benefits of the 275, IMO. Consider that up until recently, the fast FSP guy were using 225/45-13s mounted to 13x9s....

I've mounted the 275/35-15 onto 15x8s, and the effective width was not much greater than that of my 225/55-15 radial rains. Very disappointing. My times were pretty much in line with those attainable with 245/45-16s with that setup, BTW. Things are better with the much wider width.

Unfortunately, the only way to objectively ascertain whether the 9" width is actually enough for a 2500-2700 lb E30 would be back-to-back tests. Unfortunately, that is rarely feasible (unless you're as insane as Alex S...). Honestly, I think my car was fastest with 285/30-18s, even though my setup weighed nearly 25 lbs *per corner* more than my current setup.

I agree the 8.5" wheels are too narrow. But that tire on a 9" wheel really doesn't look to be giving up much of anything as far as width is concerned. Maybe a little in the way of sidewall stiffness. Given the way the rear of the car is normally sprung, I'd think giving up some sidewall stiffness back there would be benificial.

But the only way to tell is to try it.



Quick question garrick, how much does your car weigh?

[DSP74]

Honestly, I think my car was fastest with 285/30-18s, even though my setup weighed nearly 25 lbs *per corner* more than my current setup.

As I pointed out in the spring rate thread I'm no engineer, and I certainly beleive that the car doesn't always perform as an engineered example should.
But HOW? You lost weight, and quite a bit of it. And it was unsprung. You lost rotating weight, so acceleration and braking should have been alot better considering the lighter weight and smaller diameter. You lowered the car without ever having to touch anything as far as ride height is concerned.
You should be at a more favorable suspension geometry point at a given ride height with the shorter tire.

Just wondering that's all. Did you do back to back tests on comparable rubber-ie fresh rubber in both sizes?

[E30 Racer]

As I pointed out in the spring rate thread I'm no engineer, and I certainly beleive that the car doesn't always perform as an engineered example should.
But HOW? You lost weight, and quite a bit of it. And it was unsprung. You lost rotating weight, so acceleration and braking should have been alot better considering the lighter weight and smaller diameter. You lowered the car without ever having to touch anything as far as ride height is concerned.
You should be at a more favorable suspension geometry point at a given ride height with the shorter tire.

Just wondering that's all. Did you do back to back tests on comparable rubber-ie fresh rubber in both sizes?

Let's just say things don't always play out the way you think they should. If you look at specs alone, one may even be compelled to argue 275/285s are too wide to be effective <shrug>. For example, consider Tunnel's old website. For along time, he was committed to running 245s all the way around. That all ended when he began losing to 285-equipped cars.

[E30 Racer]

Quick question garrick, how much does your car weigh?

About 100 lbs more than it should. : )

[DSP74]

About 100 lbs more than it should. : )

Nice one. So about 2475-2525;)

[DSP74]

Let's just say things don't always play out the way you think they should. If you look at specs alone, one may even be compelled to argue 275/285s are too wide to be effective <shrug>. For example, consider Tunnel's old website. For along time, he was committed to running 245s all the way around. That all ended when he began losing to 285-equipped cars.

Yeah and that was when Bob was in ESP too.

New tires aren't A3SO3 Hoosiers.

[E30 Racer]

Yeah and that was when Bob was in ESP too.

New tires aren't A3SO3 Hoosiers.

Not exactly, better do some more homework. : ) The 285 hasn't been around *that* long. Anyway, I'm sure you get my point. Bench racing will only get you so far. If you're truly committed to your tuning perspective, hop in the car, log some seat time, and let your results speak for themselves.

See you in Toledo/Peru?

[DSP74]

Not exactly, better do some more homework. : ) See you in Toledo/Peru?

Um no not quite. But next year yes.

[DSP74]

Not exactly, better do some more homework. : ) The 285 hasn't been around *that* long. Anyway, I'm sure you get my point. Bench racing will only get you so far. If you're truly committed to your tuning perspective, hop in the car, log some seat time, and let your results speak for themselves.

See you in Toledo/Peru?

Yeah exactly. Bob was in ESP, on 245's. Supposedly to keep the tires warm by using a smaller size. He gets moved to BSP runs a year and then is on 285's and swaps to a 3.2. Funny how there were things left to make that car faster, despite being "well prepped" when in ESP. (note all due respect to Bob, great guy, fast, well prepped cars etc,etc.)

Your right bench racing will only get me so far. But I'm not going to be out there until next season as I've got more important things to tend to first. Anytime your willing to come to Peru though, by all means do. I'll be there plenty next year. (and Toledo)

[DSP74]

I forgot to mention that the Edge DSP car that Sias is driving is on 305's now. I don't want to hear any BS about tires to large won't heat up.
I had to spray my 315 710's in 70-ish degree weather and one driver.

[alex]

I had to spray my 315 710's in 70-ish degree weather and one driver.

On what car?

[DSP74]

On what car?

A much different one. 3400lb ESP Camaro. But the tires were constantly hot, and the car worked much better with cool tires.