TheSamba.com :: View topic - Tire Size vs Speed, RPM's, Diameter...etc. Calculator

Wed Apr 07, 2010 7:46 pm

I haven't seen this posted before...pretty cool tool.

http://www.syncro.ca/tiresize/

Wed Apr 07, 2010 10:45 pm

That's cool. I would like to see one that converts mpg for different sized tires.

Thu Apr 08, 2010 10:12 am

members.shaw.ca/vwdiesel/VanagonTransRatios.xls
Here's another one
If the link doesn't work just search for vanagon tranny calculator

Thu Apr 08, 2010 10:23 am

Ok, so what am I doing wrong with that, I logged in, 215/75/15 at 4000rpm and I get 94mph, I think I am really close to 70mph.
I used the 4.09 auto tranny on the scale.

Thu Apr 08, 2010 12:07 pm

Two things.
First the program makes huge error calculating from the input tire size.
Second, you need to change the .85 to your gear ratio. I think you want 1.00?

Mark

Beygon wrote: Ok, so what am I doing wrong with that, I logged in, 215/75/15 at 4000rpm and I get 94mph, I think I am really close to 70mph.
I used the 4.09 auto tranny on the scale.

Thu Apr 08, 2010 12:41 pm

OK Mark, that brought it down to 80, I guess I should get out of the slow lane.

How's Mex?

Thu Apr 08, 2010 12:57 pm

Baja is good this year. Going again next month. More people should give it a try.

If you look at the tire company specs for 215/75/15 tires you will find they list rev/mile around 750-760. That lame program calculates it from the nominal size to be 721 rev/mile, WAY OFF from real tires that size. Click on the tire diameter box to see how bad it is. If you know what the true rev/mile is of your tire you can experiment with putting smaller sizes in until the program calculates a close rev/mile to your known value. 205/70/15 for example gives 759.

Then use that size for the rest of the playing around below there. Not an accurate tool, but some people don't mind I guess.

Mark

Beygon wrote: OK Mark, that brought it down to 80, I guess I should get out of the slow lane.

How's Mex?