View Full Version : spedometer error

Ronald Wendt
08-11-2003, 04:27 PM
When I changed rear end gears and tire height, I did the speedometer gear calculation and came up with 19.5. So I bought a 19 gear. The speedometer reads faster than I am going, anywhere from 7 to like 11 mph depending on what gear I am in.

Would going to a 20 tooth gear get me closer to the actual MPH, or just go the opposite way of the 19 tooth gear and read slower than I am going and be off the same amount?



08-11-2003, 04:48 PM
The speedometer should not be off more in a given trans gear, since the reading is taken off the tailshaft and is not affected by the trans gearing.

A speedo gear with more teeth will lower the MPH on the speedometer.

Ronald Wendt
08-12-2003, 10:01 AM
What I did was calculate the MPH based on the engine RPM and the gears I was in. Then tried to eyeball the speedo and tach as I was going down the road and write this down. Then compared the calculated MPH for a given RPM and gear versus what I saw. I know I could be off several MPH and or RPM when looking at the dash. So I certainly could be wrong about different speed differences between different gears.

Do you think With a 20 tooth gear it would read closer to the actual MPH, or be off about the same amount as the 19 gear only the opposite way?



David Neibert
08-12-2003, 01:52 PM
What ratio gears did you install ? Tire height ? Auto or 5 speed ?


08-12-2003, 02:16 PM
Not to but in, but I have a relating question. I switched from 3.31's to 3.27's. Is there a gear available to correct this?
I haven't crunched numbers yet to see how far it change so maybe it isn't worth the trouble if there is one.

Ronald Wendt
08-12-2003, 03:35 PM
I have a 91 with the 5 speed, added 3:27 rear end gears and have 27.1" tires