What size tires for 17x9 wheels?

So I've traditionally run 275-40-17 tires on my 17x9 wheels for my time trial car. I'm not constrained by any rules, I can run any size I want without penalty or gain.

I always ran the 275's thinking they were the largest I could fit and I'd get the best traction (421rwhp and about the same in torque) and handling.

Lately I've been wondering if I'd actually get better handling etc by going down to a 255-40-17 tire. Perhaps the actual contact patch wouldn't be all that different than the 275's I've been running...

Thoughts?

I tend to go with a 1" rule of thumb - tire shouldn't be more than 1/2" over on each side. Can it be done - sure and many will tell you it's just fine, they don't notice a bulge or feel it rolling over. With variations in tires/wheels this gets a big maybe. I've heard people say 315s will work. 275 is the max size listed for some rim manufacturers. By my thinking a 255 is the optimal fit, but if a 275 has been working for you...

I actually had 245/40 on that setup under my ms3. They were the old z1 *spec and they were just under square. 255 woulda been perfect. They stuck like glue, but breakaway wasn't very progressive. From what ive been told, if grip is the only goal, more because more.

Yeah but there has to be a point of diminishing returns. 275 is the largest I can fit on the front and I want to run a square setup so I can rotate them.

So basically it's stick with the 275's or try a set of 255's. I'm probably going to buy a set of Toyo RR's this coming spring...

I used to race a Mustang and I used the 17X9 Cobra R wheels. I used 245, 255, & 275 section tires on these rims and the best balance were the 255's. The 275's did give me a bit more traction if used in the rear but they seemed to wear a bit more on the edges due to roll over. On the street I would have no problem with 275's but the crisper response of the 255's on track won me over. They also wore more evenly with less edge wear then the 275's.

Also you need to look at the tire specs of each brand/model tire your looking at using. Two tires with the same size, for example 255/40X17 may vary in section width, tread width, and diameter. I've found Hoosiers tend to be wider in tread width then most other brands of tires, size for size. But I have seen other brands run wider then others as well.

It's worth doing your homework on what the "actual" section width of your tires is rather than going by the 275 yada yada. There is a huge difference across tires in actual width. I've seen as much as 20mm difference across tires. The 205's under the rabbit actually measure out more like 220.

Aside from that I abide by the 1" rule mentioned by oldtin as well.

I had 255 star specs on my 17x9s, they were fantastic.

I'd lean toward a 255, but its probably a toss up on the track.

I ran 245s on mine on my S2k.

I believe GRM did a test comparing 245s to 255s both on 17x9s and the 245s were faster. That was specifically for the STR miata though.

Something I didn't consider in my first post but the cars weight has an impact on what tire size your choose. A light car may indeed handle better overall on 245's vrs 255 or 275 tires since they won't be over loaded by a light car compared to something like a Fox Mustang.

Car weighs 3250lbs with me in it. I want to run Toyo RR's...