speedometer gear accuracy question.

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Dec 4, 2008 | 08:31 PM

#11

Carlos Pineiro

3rd Gear Member

Joined: Jul 2008

Posts: 958

From: Santa Monica, Calif.

Whoa. Thanks Norm.

CP

Dec 5, 2008 | 08:54 AM

#12

Norm Peterson

6th Gear Member

Joined: Feb 2007

Posts: 7,635

From: state of confusion

Spreadsheet done, sort of.

Norm

Dec 5, 2008 | 10:47 AM

#13

kalli

6th Gear Member

Joined: Oct 2006

Posts: 6,417

From: Cork, Ireland

couldn't delete post. so it's edited

Dec 5, 2008 | 12:38 PM

#14

MBDiagMan

3rd Gear Member

Joined: Aug 2006

Posts: 886

From: North East Texas on the Red River

Yes, with domestic speedometers, 1,000 RPM should read 60MPH and 1,000 revolutions should increment the odometer one mile. European speedometers are calibrated at the speedometer head rather than at the transmission so with those, all bets are off.

So, calculate your driveshaft speed for 60MPH given your rear axle ratio and tire size. Then that can easily be used to calculate the ratio for the speedometer gears that will give 1,000 RPM.