Good How To Video from RoadKill.
- Thread starter tc1959
- Start date
- Status
Saw it. Good stuff. This is partly why I pay for their service. This is one of many "tech" videos they have and will have.
Or, you could use one of the many online calculators
I do like the whole Roadkill/Hot Rod Garage series
I do like the whole Roadkill/Hot Rod Garage series
It's good to know the actual formula, instead of having to look up a calculator that might be wrong.
How do you know Freiburger is right? Just sayin'...who checks the checker?
I used to use a formula that we were given at BF Goodrich, which used the loaded radius of the tire rather than OD. Was a little more accurate, but not really enough to make a BIG difference.
Last edited:
I've used it.
RPM= mph x rear gear ratio x 336 divided by tire diameter.
So, with my regal, 2.41 gears, TH350 with a 1:1 final gear, and a 195/75/14 tire with a diameter of 25.52 inches, that comes out to 2,379rpm at 75mph. My tach read about 2400-2500rpm at that speed in my regal. And as stated in the video, if you have an OD transmission, on, say a Th200r4, you multiply the rpm (in this case, lets use my 2,379rpm) by the overdrive gear ratio which for a 200r4 is .67. So 2,379 x .67 = 1,593rpm. Math is fun when it's about cars. I sound like a math teacher, but sometimes (especially with cars) it's better to know the formulas for things. Yes with the advent of phones this info, and this video, are just a few taps/clicks away, but it still helps to know.
- Status
