Changed Gears
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Junior User
Joined: Nov 2003
Posts: 89
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From: Louisiana
Changed Gears
I have a c6 tranny, and 9" rear end.
I swapped from 3.00 gears to 3.89 gears.
How do I figure out which speedometer gear to get, so that my speedometer is close to accurate?
Thanks in advance.
I swapped from 3.00 gears to 3.89 gears.
How do I figure out which speedometer gear to get, so that my speedometer is close to accurate?
Thanks in advance.
Senior User
Joined: Jan 2003
Posts: 229
Likes: 0
From: North Carolina
If you have a computer-controlled car, you can have the speedo recalibrated to correct for the new gear change. Otherwise, you can change the speedometer gear. I'm not sure how much this costs but it can't be more than $20. For the gear itself, that is.
Posting Guru
Joined: Dec 1999
Posts: 1,903
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From: Copley, OH
The formula is:
Driven gear teeth = (tire revs/mile x drive gear teeth x final drive ratio) / 1000.
You can count the drive teeth on your tailshaft and can look up your tire revs/mile at www.tirerack.com or your tire manufacturer's web site. For 235/75-15 tires it's about 722 depending on brand and model.
If your speedo was right before, then you can simply count the number of teeth on the existing driven gear and multiply by:
3.89/3.00 = 1.297 and round to the nearest integral value.
Driven gear teeth = (tire revs/mile x drive gear teeth x final drive ratio) / 1000.
You can count the drive teeth on your tailshaft and can look up your tire revs/mile at www.tirerack.com or your tire manufacturer's web site. For 235/75-15 tires it's about 722 depending on brand and model.
If your speedo was right before, then you can simply count the number of teeth on the existing driven gear and multiply by:
3.89/3.00 = 1.297 and round to the nearest integral value.
Senior User
Joined: Jan 2003
Posts: 229
Likes: 0
From: North Carolina
Originally Posted by StrangeRanger
The formula is:
Driven gear teeth = (tire revs/mile x drive gear teeth x final drive ratio) / 1000.
You can count the drive teeth on your tailshaft and can look up your tire revs/mile at www.tirerack.com or your tire manufacturer's web site. For 235/75-15 tires it's about 722 depending on brand and model.
If your speedo was right before, then you can simply count the number of teeth on the existing driven gear and multiply by:
3.89/3.00 = 1.297 and round to the nearest integral value.
Driven gear teeth = (tire revs/mile x drive gear teeth x final drive ratio) / 1000.
You can count the drive teeth on your tailshaft and can look up your tire revs/mile at www.tirerack.com or your tire manufacturer's web site. For 235/75-15 tires it's about 722 depending on brand and model.
If your speedo was right before, then you can simply count the number of teeth on the existing driven gear and multiply by:
3.89/3.00 = 1.297 and round to the nearest integral value.
Yeah, what he said!
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