Gernby

iTrader: (1)

I've been working on an Excel chart to show the difference between stock gearing on an IS350 with OEM tire sizes versus lower profile tires. Below is a graph of the forward thrust of an OEM 255/40-18 which has a 26.1" outer diameter compared to a 245/35-18 Hoosier R6 which has a 24.4" outer diameter. The resulting difference in total gearing to the ground is about a 6.5% reduction.

The green zones are where the lower profile tire produces more thrust, and the red zones are where the OEM tire produces more thrust (due to staying in the lower gear longer). When comparing the difference in area between the curves, the circled zones pretty much cancel themselves out. This means that if you are starting at 0 MPH, the advantage of the lower gearing in 1st gear with the lower profile tire will never be overcome by the higher profile tire. Basically, from a standing start, the lower profile tire will win every time, but a race from 30 to 95, the higher profile tire will probably win every time.

BTW, I generated this graph using lobuxracer's gearing spreadsheet in combination with my dyno results. Since my dyno test didn't go below 3700 RPMs, I just interpolated those.

CWS

So, are you going to get some, and try to better that 13.251?

Gernby

iTrader: (1)

I already have the tires mounted up, and ready to go for this Saturday.

t0e

iTrader: (1)

Good Luck! :d

Irishman06

I'm wondering if your R6s will get warm enough to get full traction off the line on a drag run. The A6s are the auto-x spec, aren't they? They'll work better in a "cold tire" application.

Gernby

iTrader: (1)

The A6 is the autocross compound, and I'm sure it would be better than the R6 when it's cold. However, I don't plan to autocross, and the A6 wouldn't be a good road course tire.

al503

lightweight 18"s (say 18lbs v. the stocker's 25?lbs) might also knock off a tenth.