Does sidewall height affect performance? 40 vs 45 series. Recommendations?

[Nicks67GTO]

I'm going to be in the market for tires this fall/spring for the 67' GTO. I was running around a faster auto X course last weekend on the Nitto555's and the car felt almost out of control in a lot of the turns. It was much more pronounced than the lower speed course I ran a few weeks back though I got that feeling a little bit then too. Lots of pushing and not responding well to what I was telling it to do. It just didn't want to stick and go. I did a little research and find that the Nitto555's I have are a great street tire, maybe not so much an auto x performer.

Anyhow I like a taller tire for looks on this car. IMO it just plain looks better with a large car to have a tall sidewall to fill up the wheel wells. Now with that said i'm wondering how much it affects performance to stay with the 45 series tires as opposed to dropping down to the much more common 40 series tires. I'm looking at 245/18's in the front and 275/18's in the rear. Matching 245/45/18 and 275/45/18's are almost non existent in a performance tire. I found them in a 220 treadwear Pirelli P Zero and that's about it...

http://www.tirerack.com/tires/tires....omCompare1=yes

So my questions are...

-Does sidewall height between a 40 and 45 series tire affect performance in any kind of major way? I understand there is a bit more deflection but is it really a huge deal breaker?



-If you needed a 245/18 and a 275/18 to perform well, what tires would you be going with?

[Twentyover]

Can't help you with the tire question, but getting a couple "Stick You Bitch" Stickers from Mary Pozzi way help- maybe not your times, but certainly your attitude.

[rrelco]

I have been running the falken Aznis 285 40 18 and had very good auto x numbers. it also depends on the track layout a short twisty coarse i run 25-30 rear tire pressure and a fast layout i run 32-36 rear pressure.

ps...i have the stick you bitch stickers and they don't really help!!!!

[Paul Huryk]

The 245-40-18 or 275-35-18 is a "normal" 25.75" tall tire - OEM on many years of GM cars up to the most recent ones. These are two of the most popular sizes in 18" - for good reason, they fit many cars.

When you look at series "45, 40, 35", it is easy to get confused - unless you know the sidewall height, which is more important. In the case of the tires above, there is a total of about 7.75" of total sidewall (not including the 1" or so for the bead).

Looks aside, the 245-40-18, 275-35-18, and 315-30-18 all offer a near-perfect sidewall height for a 25.75" tire - no too small that you kill the wheels on every bump and not so tall the sidewalls roll over in turns.

The one area I would look into seriously is increasing your front tire width - 245/275 is going to understeer mechanically. If you can get a 255 up front (or wider), it will only help.