Ok so here's my question:
What tire width would grip better for the Autocross?
(On a 17x9in rim)
Would a 255/40r17 or 275/40r17 grip better?

I was told that a tire closer to the ideal width for a 9in rim would grip better than a slightly bluged tire.
That person claimed a 255 fits perfectly on a 9in rim and a 275 would have a bit of bulging.
Therefore the 255 would be more optimal.
But I can't seem to find any info refuting or supporting that.
Thoughts?

 

Choose the better rubber. You can buy a much better tire in a 255 width than you can in a 275 width. That trumps any further discussion about wheel fitment.

 

1. Cover tires in rubber cement
2. Appreciate increased grip
3. ???
4. Profit !

 

For autocross, your primary concern should be treadwear and rubber quality. Depending upon your class, there will be one or two "go-to" tires that all the top guys use. Check your rules and search some SCCA forums.

If you're SCCA, 17x9" wheels will put you out of stock and into either ESP or CAM-T. Being competitive in either will be a big uphill battle unless your thirdgen is heavily modified and you're an experienced driver, but getting the best tire is one of the most important steps.

I'm on 17x9s with 275/40/17 BFG Comp-2 Summer Tires, Treadwear 340. They're a great spirited street tire. But for autocross, they're lacking. I'd be better off with something in the 200 treadwear range. My car is primarily a weekend street driver, so I went with 275s for regular roads plus aesthetics. If you're main concern is autocross times, pick the best available tire (and recognize it may be a bad street tire - treadwear 200 won't last long, and slicks can't be used on the street).

If you're really concerned with looks, though, the 255s look too narrow on the 17x9s.

 

While a 255 width might be the optimal size for a 9" wheel, the additional 20mm of tire per corner will probably give better grip in an autocross situation. This is assuming the same tire in both 255 and 275 section widths - not all tires are created equal by any means.

A 275 on a 9" wheel is not going to bulge much - certainly not like the 315 someone stuck on a 9" wheel in another thread here. Typically you would run a 9.5" or 10" wheel with a 275 width tire.

 

Thx for the responses.
I'm racing in the novice class right now.
Unfortunately, I have suspension components with ends similar to Heim joints.
(Umi calls em something else)
That alone would put me in a class I'm not competitive in.
But I did manage to beat two 6th gen SS 1le camaros last time.

 

If you are just starting out, just run whatever you have. I started on 10 yr old tires that were as hard as rocks...... but it taught me car control

I then bought the biggest RS3's I could get in 17" and ran those for the following year.

Then I got autocross smart and just bought a miata.....

I have since left autocross and now do road racing with the SCCA in their spec miata class...... talk about a fast way to throw money out the window!

the point is to have fun and to get faster every event. Once you find yourself running the same times consistently, then you start spending money on rubber, or other mods as you see fit.

btw, do you have a wonderbar? If not, spend the money on that to save your steering box and the frame from cracking.

 

I have a wonderbar and inner and outer SFC.
and i'm trying to fabricate a 6AL4V Titanium strut tower brace.

Probably the best AutoX mod I did was rebuild the steering and got a ReadHead steering Box.
stock boxes are basically trash after 25+ years of use.