265 Width Tires in STX Autocross
 

Anyone using 265/35R18 tires on a 18x9 wheel? It seems that would be allowed under the current rules. I've seen some debates on 245 vs 255 on 17s, but nothing about 265 on 18s. I know a number of track drivers us 265 on 18x9.5.

Downsides:
-weight
-0.6" larger in diameter than 245s on 17s
-cost

Upsides:
-more grip?

No twins in the trophies at nats on 18s.

Not that you couldn't trophy on 18s, I just think you're increasing your consumables cost and also making it harder to trophy on 90% of courses. The gearing penalty is so much larger than the extra width you gain.

Aside from increased weight, you're looking at a overall diameter increase of .5" which translates to a numerically lower final drive gear on the rear end. While that means you can go faster, you'll lose RPM and usually you'll lose quickness because you'll likely be lower in the power band than you would with 245's.

I know this because I did the same but with 255/40/17's and I've been able to validate that it definitely hurts on a bigger track and it definitely seemed to be a detriment in Solo.

So, anything you might gain in grip, you lose in weight and gear reduction in my opinion.

Bad idea. Turn-in will be insanely sloppy, acceleration will be down, and you will rarely find a course where you can make up for the performance difference with increased grip.

I know that several people tested this a few years back. I don't know the results of any of those tests, but I know that people didn't gravitate towards the 265's.

245/40/17 or 245/45/17 are tried and true. If 18's worked with 265's, everyone would be running them and they aren't.


More weight when you more to 18's. This isn't a super heavy car that you 'need' a 265+ on. Consumables go up too with tires with 18's.

If you can find the right tire in a 265/30-18 then it might be worth a try but I've never found anything like that period. At least you would be at the correct diameter so you weren't hurting yourself on gearing but you would still get the impact of the added weight from both the wheel and tire.

949 Racing's Blub is running 265s which is what make me think of them. I know their car is not quite STX, but it is close. They seem to have a lot of knowledge and experience and don't pick parts "just because".
They also mentioned that for their new wheels they are making specifically for track they are doing 18s first due to racing needs.

There is also mention of a 4.67 FD in that thread. So that probably helps them get away with a taller tire.

Because brakes. Bigger wheels mean bigger brakes which makes sense for track lapping, a lot of 17's, including 6ULs don't clear the bigger calipers that are out there.

I don't think it's a terrible idea, it's not like 18s are awful, they'll get you Street cred. And realistically 17s are going to be less and less popular as the years go on, you'll be ahead of the curve on that.

My reason for moving to 18s on my next set. Wheels are consumables at the track (they wear down and end up bending or craking with heat and offtrack excursions). Its getting harder and harder to get good wheels in 17x9.5 or 17x10, and even 17x9 there are a couple of choices but not many. But 18x10 and even 18x11 is so much easier to find.

They also have 10" wide wheels which will help the tire be more effective. There are diminishing returns to putting wider tires on the width size wheels. 245 is starting to nose over the peak of the curve on a 9" wheel for 200tw.