tire size/rpm question

[return to dirt]

i know that changing the final by say a 0.10 will change the rpms by about 100 rpm. is there a formula for figuring rpm change going from say a 75" 235-60/13 to a 86" 255-60/15? the chico track i will be running at can be very rough. cars bottom out going through the ruts. it's also a large 1/4mi compared to my local 1/5mi track. i know the 15s are heavier but if i can go through the corners faster it will be worth it. last year we had cars whos starters and exhausts would break if you got off the bottom. my own pinto started jumping out of gear. by using multifit wheels i can run 15s at one track and then put my 13s back on for my local track without changing gears IF my rpms will be where i need them. thanks.

olin

[Racedad]

86/75=1.147 so you have 14.6% lets say 15% more distance covered per revolution of the wheel.So I suppose you would be turning 15% of say 8000 is about 1200 less rpm on the straights assuming the same speed.

[miniman69]

another way is 1" + or - is about a hundred rpm not a hundred percent but real close quick and easy

[return to dirt]

thanks guys. it looks like in both posts that about 100-110 rpms per inch is what i should expect. that will work out about right.

olin