Gear ratio
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From: emerson ga
Gear ratio
By the sticker on my door jam i have the H9 differental and 3.55 gears. I need to find out what ratio i need to get if im looking to drop my rpms when i am going 40 mph i am running almost 2300 rpms and it is a 4 speed with a granny. please help
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Your trans would have a 1:1 4th gear.
With 29 inch tires, (stock height) 3.55s and a 1:1 gear, you should be turning 1645 rpm at 40 mph.
At 55 mph with that combo, you would turn 2262--
You would need 4.88s to turn 2261 at 40, close to your claimed 2300. 55 would then be 3110
If you have a T19, all synchro 4 speed with granny first, your 3rd gear is 1.79, which would result in 2945 rpm at 40.
If you have a NP435, 3rd would be 1.66 or 1.74, for 2731 or 2863 at 40.
Something is wrong here--is there a tag down on the axle? If so, post those numbers. What trans do you have? What size tire? Are we really talking 40mph?
Once we figure this out, if you are still geared too short, you can either convert to a 5 speed, or change the axle, but let's get a correct base line figure to start. BTW, what tach are you using to check rpm to mph? And does your speedo read correctly?
With 29 inch tires, (stock height) 3.55s and a 1:1 gear, you should be turning 1645 rpm at 40 mph.
At 55 mph with that combo, you would turn 2262--
You would need 4.88s to turn 2261 at 40, close to your claimed 2300. 55 would then be 3110
If you have a T19, all synchro 4 speed with granny first, your 3rd gear is 1.79, which would result in 2945 rpm at 40.
If you have a NP435, 3rd would be 1.66 or 1.74, for 2731 or 2863 at 40.
Something is wrong here--is there a tag down on the axle? If so, post those numbers. What trans do you have? What size tire? Are we really talking 40mph?
Once we figure this out, if you are still geared too short, you can either convert to a 5 speed, or change the axle, but let's get a correct base line figure to start. BTW, what tach are you using to check rpm to mph? And does your speedo read correctly?
Last edited by 85e150; Mar 3, 2009 at 01:59 AM. Reason: Speed question
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