GT3 Nut

What front tire size is better for the 997 GT3/RS on 18" wheels:
245/40-18 or 245/35-18?
I have tried the 245/40-18 on my "old" 997 GT3 and it seemed to be fine. But it seems like most people are saying to use the 245/35-18 size.
What is the consensus here based on real world experience?
Thanks.

eclou

I use 245/35/18 and 315/30/18 Hoosier R6's. They keep the rolling diameter ratio F:R the same as stock

GT3 Nut

Okay, but the difference in size is:
245/35 = 24.4" tall
315/30 = 25.6" tall
Difference of 1.2"
Ratio of 1 to 1.04 ??

245/40 = 25.3" tall
315/30 = 25.6" tall
Difference of 0.3"
Ratio of 1 to 1.01 ??

Stock MPSC:
235/35-19 = 25.5" tall
305/30-19 = 26.3" tall
Difference of 0.8"
Ratio of 1 to 1.03 ??

Either way the difference is not exact right?
So is one really better than the other?

I just ordered a set of 245/40 so I hope it doesn't matter.
Thanks for the help.

GT3 Nut

Would using the 245/40 actually change the brake bias slightly - more rear?
The 245/40 would be rotating less than the 245/35 so would this make the ABS think the rear needs to slow down more?
Does that make any sense?

doc2s

245/35/18 are 24.7" according to hoosier website (tirerack has them listed as 24.4"). this makes the ratio 1.03 same as stock.

TraqGear

Preferably a D cup. But a full C will do.

GT3 Nut

Thanks.
I just called tirerack and was able to switch my order to the 245/35-18's.

NJ-GT

Matt,

You should use the 245/35R18. I use a 285/30R18 instead of the 275/35R18 for the same reasons. The turn in is crisp with the lower profile tire, and the braking is more linear.

The 245/35R18 -315/30R18 combination keeps a similar ratio to the stock 997 GT3 sizes, but the car height decreases without affecting the stock suspension geometry. Assuming the same compound and construction as the stock tires, your lap times will be faster (lower center of gravity). However, the R6 are faster tires than the MPSC, so you should see even faster lap times.

eclou

A good source if you can find them are Hoosier VRL 305 scrubs. Find a dealer that does track support and they might have a pile of tires used in Viper qualifying laps. I pick up the 305/30/18 VRL's which are the same as R6's, and have the exact same height as the 315/30/18. They will usually sell for perhaps $70 ea and have near full tread

GT3 Nut

Thanks for the info.
By the way, if you can get a 285 in the front what are you using in the rear? What kind of tires?

GT3 Nut

I would love to find tires that cheap. But I don't know of any dealer near here that does track support.

eclou

Try Viper Club of America - they might list some sponsors that provide trackside support in your area

NJ-GT

Hoosier A6

285/30R18 on 10"
335/30R18 on 12"

The 335 fits really well in my narrow body 996.

GT3 Nut

I bet that thing sticks like glue in an autocross!!!
Sweet!