I have been reading through the posts on tires sizes and most seem to center around AP2 sizes. Here's the deal...

I bought tires before the 245 were available and wound up with
V710 265/24/16 and 225/50/16 rear last year.

The chief issue was that the 265 were really too large. The narrow rims make the tire crown and while it flattens out some with time, I never felt I was getting as much rubber on the road as a 245 would have provided. In addition, the tires are taller and I know this is affecting gear ratios (and alignment).

The 245 came out about a month later and I vowed to run them in 2010. Ok, 2010 is here, I am ready to buy tires. Now I am seeing threads on square edge/round edge differences. Ok, Square edge looks like the ticket, 245/45's are square, but wait the 225/50's are round AND-- it looks like the 245/45 square edge and 225/50 round edge are virtually the same width

-- so should I run:
245/45's square edge all round (forget about staggering the tires)
- or -
225/50/16 round 245/45/16 square (ignore that they are virtually the same width)
- or -
215/40R16 round 245/45/16 square (and ignore the alignment issues)

I love these pics: 245/45/16 square vs 225/50/16 round

Of course, I could just just run Hoosiers.


I should add this is my DD so I set the alignment up with my street tires. If my track tires are different diameters (tilting the car up or down) the track alignment is effected.

 

This has been the proven route.

 

Get a bigger front bar if you don't already have one. Then buy four 245's.

 

I second Marc and Mark

Especially on the AP1, be very weary of gearing issues. I've posted many times on the utter failure of the 275 hoosier on the AP1 because of the gearing differences compared to the 245 and the already very tall gearing of the AP1 tranny. 245/245 F/R is the way to go for sure. (Multiple seconds faster than a 245/275 F/R).

Compare the overall diameter of the Kumho 265 to the Hoozie 245 and take your pick. The only other combo I would consider is 225 all around, if that got me even shorter gearing in the back. Though I think the 245 is a good balance between gear and tire width and has proven to be fastest nationally.

 

Thanks guys. This is my 4rd season autocrossing. I have a Gendron with the middle weight bar (iupgraded frm Comptech last year) and am installing a set of Penske 8100's this weekend.

 

Cool, and good luck.

With the square setup, don't be surprised to be calling Bill Gendron for the custom hollow bar up front. Though with proper shocks, you may not need that much bar to solve the handling challenges you face.

I'm waiting for my custom-valved double adjustable Koni's to arrive. I'm gonna do a thread on them too.