speedo gear
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Elder User
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speedo gear
currently running 215/75r15 (factory tires) w/ c6 and 2.75 gears
wanting to change to 3.50-3.55 gear and 235/75r15 tires...
the question is what speedo gear do i have, and which one do i need?
wanting to change to 3.50-3.55 gear and 235/75r15 tires...
the question is what speedo gear do i have, and which one do i need?
Posting Guru
Joined: Jun 2002
Posts: 2,091
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From: Suffolk, VA USA
What is unknown is the size of the drive gear...that's the gear that the speedometer driven gear (the one at the end of the speedometer cable that you can easily change) rides on. Generally there are two drive gears, 7 or 8 teeth. The 7 tooth drive gear is more common with an automatic transmission, but given the 215 tire size and 2.75 gearing the math says that a 7 tooth drive gear would require a 15 tooth driven gear, which may exist, but I've never seen one. So I'm going to assume an 8 tooth drive gear which would mean you have either a 16 (maroon) or 17 (white) tooth gear installed (the math says 16.51). You can verify this very easily but pulling the gear...it takes about 30 seconds to do). If the assumption is correct, you'll need a 21 tooth (purple) gear with the new 235 tires and 3.55 gears. If by some rare chance your drive gear does turn out to be 7 teeth, the new setup will require an 18 tooth (gray) gear.
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Elder User
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thank you very much for the answer..you said you used a formula to come up with this, by chance would you mind sharing so that for some reason i change tire size i can know what to buy without having to ask?
Thanks, Rob
Thanks, Rob
Methanoholic
Joined: Mar 2009
Posts: 6,442
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From: Maine (NorCal Native)
You can do it here: FTE Calculators
I prefer: TCIAuto.com
The best thing you can do for yourself is pull the current driven gear and see what it is, the driven gear will give you a good indication of what the drive gear is.
They make a 6 tooth drive gear as well..
-Enjoy
fh : )_~
I prefer: TCIAuto.com
The best thing you can do for yourself is pull the current driven gear and see what it is, the driven gear will give you a good indication of what the drive gear is.
They make a 6 tooth drive gear as well..
-Enjoy
fh : )_~
Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
Basic formula for new gear with tire change is:
Old Tire Diameter (inches) x Old Gear (# of teeth) / New Tire Diameter (inches) = New Gear (# of teeth)
To add in a rear end gear change:
Solution from above (# of teeth) / Old Ratio x New Ratio = New Gear (# of teeth)
Old Tire Diameter (inches) x Old Gear (# of teeth) / New Tire Diameter (inches) = New Gear (# of teeth)
To add in a rear end gear change:
Solution from above (# of teeth) / Old Ratio x New Ratio = New Gear (# of teeth)
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