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914World.com _ 914World Garage _ Tire diameter to gear ratio calculation

Posted by: nine14cats Oct 30 2003, 10:50 AM

Does anyone have a spreadsheet that includes tire diameters to gear ratio calculations? I'm trying to figure out gearing changes to my car.

Example: I am currently running ~23" diameter slick on the back with a 901 gearbox. If I changed to a 24" or a 25", I'd like to know what approx speed change per gear would be. I have upcoming tire testing which includes different diameters and I wanted to have a preliminary idea.

Just being lazy....I was hoping someone on the board had already done the work and I could steal it....

Thanks,

Bill

Posted by: Air_Cooled_Nut Oct 30 2003, 10:54 AM

You ARE lucky because I created an Excel spreadsheet way back for the 5-speed conversion I put in my Squareback I wanted to change the gearing and all my toodling came up with this:

Zipped download (dial-up): http://www.icbm.org/erkson/personal/gearing.zip
Raw download (DSL, cable, T1, etc.): http://www.icbm.org/erkson/personal/gearing-analyzer.xls

Posted by: nine14cats Oct 30 2003, 12:04 PM

Hi Toby,

WOW I've got a winner!

Now I just have to sit down and enter some values....

Thanks a bunch!

Bill

Posted by: Brad Roberts Oct 30 2003, 01:15 PM

Bill..

we have a *secret* area on this site where we have some questionable software.

http://www.914world.com/downloads/

My gear chart has the 901 ratios and shows a RPM graph.

B