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How to estimate gear ratio? #1003763
05/31/11 03:18 PM
05/31/11 03:18 PM
Joined: Jan 2010
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Santa Barbara, CA
HitIt Offline OP
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Hi there, I'm just trying to estimate the gear ratio in my car so I can start getting together a little deeper gears and suregrip.

When I turn the drive shaft 1.25 times, the axle rotates 1 time. Any way of knowing the gear ratio of this based on those numbers? This is an open 8.75 diff... seems like it could be between a 2.73 or 3.23 when I drive it.

Thanks!


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Re: How to estimate gear ratio? [Re: HitIt] #1003764
05/31/11 03:20 PM
05/31/11 03:20 PM
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If the driveshaft went around 1 1/4 revolutions and just one axle turned 1 revolution, sounds like about a 2.50ish gear ratio.

Re: How to estimate gear ratio? [Re: buildanother] #1003765
05/31/11 03:25 PM
05/31/11 03:25 PM
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Santa Barbara, CA
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thanks buildanother, that's kinda what made me think they could be 2.73s.

will my measurements be off if I didn't prevent the other side from spinning backwards while I counted the one side?


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Re: How to estimate gear ratio? [Re: HitIt] #1003766
05/31/11 03:29 PM
05/31/11 03:29 PM
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Grand Prairie,Texas
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You need to keep the other wheel from turning or you won't get a correct count.

Re: How to estimate gear ratio? [Re: stumpy] #1003767
05/31/11 03:43 PM
05/31/11 03:43 PM
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Santa Barbara, CA
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Got it, thanks. I will try again.


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Re: How to estimate gear ratio? [Re: HitIt] #1003768
05/31/11 04:03 PM
05/31/11 04:03 PM
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Florida
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if it has an inspection cover,you can R&R/change the oil and have a looky see

its stamped on the edge of the ring gear along with the yr and part #

8 3/4 is a little bit of work to pull it just to look though

on my 3.91 it turns 3 7/8 full turns

on a 2.76 gear it will turn 2.75 turn

3.21-3.23 is 3.25 turns

3.55 is 3.5 turns

ect...

make sure your not sliping the spider gears,it will throw it off on the count

Re: How to estimate gear ratio? [Re: scratchnfotraction] #1003769
05/31/11 04:10 PM
05/31/11 04:10 PM
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Santa Barbara, CA
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thanks scratchinfortraction, that is exactly the info I was needing - 2.75 for 2.73 etc.

It's an 8 3/4 so I don't want to pull it apart just for a look. I just want to know about what gears are in it so I can decide on 3.55's or 3.91s.

Gonna try it again today. Thanks!


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Re: How to estimate gear ratio? [Re: HitIt] #1003770
05/31/11 04:44 PM
05/31/11 04:44 PM
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if it turned 1.25 turns on the yoke to make 1 full turn of the axle it would be a 1.something gear ratio

I have only saw a 2.76 as the highest gear ratio with all mine

dont think they make a 1.?? gear

I like 3.55 as the lowest gear for street duty and 3.91 for track duty

3.23 are a little better for mpgs over the 3.55

Last edited by scratchnfotraction; 05/31/11 04:57 PM.
Re: How to estimate gear ratio? [Re: HitIt] #1003771
05/31/11 06:04 PM
05/31/11 06:04 PM
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Lincoln Nebraska
RapidRobert Offline
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1 wheel on the ground. 1 wheel just off the ground. neutral of course. make a mark on the tire at 5 o'clock & turn tire a bit to 6 o'clock to take the backlash out of it. turn tire 2 revolutions (back to 6 o'clock twice) as you count d shaft revolutions. That'll b your exact ratio (ie 3&1/4 turns is 3.23 as Scratch said)


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Re: How to estimate gear ratio? [Re: RapidRobert] #1003772
05/31/11 08:13 PM
05/31/11 08:13 PM
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Posts: 456
Santa Barbara, CA
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Great info guys, thanks very much for the help

Quote:

if it turned 1.25 turns on the yoke to make 1 full turn of the axle it would be a 1.something gear ratio

I have only saw a 2.76 as the highest gear ratio with all mine

dont think they make a 1.?? gear

I like 3.55 as the lowest gear for street duty and 3.91 for track duty

3.23 are a little better for mpgs over the 3.55




Quote:

1 wheel on the ground. 1 wheel just off the ground. neutral of course. make a mark on the tire at 5 o'clock & turn tire a bit to 6 o'clock to take the backlash out of it. turn tire 2 revolutions (back to 6 o'clock twice) as you count d shaft revolutions. That'll b your exact ratio (ie 3&1/4 turns is 3.23 as Scratch said)




very clever dinner. appetizing food fit neatly into interesting round pie.






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