Gear Ratio Calculation
Thread Starter
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Logistics Pro
Joined: Oct 2002
Posts: 4,489
Likes: 5
From: Valley Center, CA
Gear Ratio Calculation
OK, I think I'm doing it right, but I need somebody to check my math. We checked the rotations on two rearends. With the left tire jacked off the ground I counted tire revolutions vs drive shaft revolutions:
10 tire revolutions with 19.5 drive shaft revolutions = 3.90 gears???
19.5 / 10 = 1.95 x 2 = 3.90
and
10 tire revolutions with 16.5 drive shaft revolutions = 3.30 gears???
16.5 / 10 = 1.65 x 2 = 3.30
Is this correct or am I all goofed up? Thanks, Jag
10 tire revolutions with 19.5 drive shaft revolutions = 3.90 gears???
19.5 / 10 = 1.95 x 2 = 3.90
and
10 tire revolutions with 16.5 drive shaft revolutions = 3.30 gears???
16.5 / 10 = 1.65 x 2 = 3.30
Is this correct or am I all goofed up? Thanks, Jag
Senior User
Joined: Oct 2006
Posts: 299
Likes: 0
From: Topeka, KS
Think you're right. I always thought of it by going around twice as many times with the tire which would be the equivalent of both wheels going around once. So if you went 10 times around, you'd divide by 5 instead of 10. The same as multiplying your answer by two.
Bottom line, despite goofy explanation, I think you're right.
Bottom line, despite goofy explanation, I think you're right.
Postmaster
Joined: Apr 2004
Posts: 3,005
Likes: 2
From: Santa Clarita
Jag, not sure why you do the 10 revolutions? I usually raise the rear end off the ground. Make one complete revolution with the wheel tire and count the revolutions of the drive shaft (I usually mark the U joint) If the drive shaft turns 3 complete with the one revolution of the tire, that's 3.00. If the drive shaft is less than 3, say 2 3/4, you probably have 2.70 or so. Slightly more than 4 turns, 4.11. This method has given me a very close idea of what my gearing is if not exact. Best way and accurate way is to count the ring pinion and divide the numbers such as 45 teeth on the ring and 13 on the pinion. 45 divided by 13= 3.46 or 3.50 gears. Hope this helps.
Thread Starter
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Logistics Pro
Joined: Oct 2002
Posts: 4,489
Likes: 5
From: Valley Center, CA
Thanks for the input everybody. Now, all I have to do is find some new 3.30 gears. Do they still make gears for the old mid-fifties Dana/Spicer? Jag
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Postmaster
Joined: Apr 2004
Posts: 3,005
Likes: 2
From: Santa Clarita
They should Jag, there's two guys I use for rear ends, both excellent references.
Ramjet Rear Ends, 9075 Glenoaks, Blvd, Sun Valley, CA. 818-768-7786
Hooper's Rear end exchange, 12201 Branford st. Sun Valley, CA 818-899-2515
These guys both know their stuff. If you contact Ramjet, ask for Don (owner) or Eddie( head guy)
Ramjet Rear Ends, 9075 Glenoaks, Blvd, Sun Valley, CA. 818-768-7786
Hooper's Rear end exchange, 12201 Branford st. Sun Valley, CA 818-899-2515
These guys both know their stuff. If you contact Ramjet, ask for Don (owner) or Eddie( head guy)
Last edited by imlowr2; May 14, 2007 at 11:29 AM.
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