Gear change calculation question
Thread Starter
|
Senior User
Joined: Aug 2012
Posts: 126
Likes: 0
From: Oceanside, CA
Gear change calculation question
As far as correcting for oversized tires, how do you calculate what gears you need? My thinking was to take the circumference of the new tire, subtract the circumference of the stock tire, and divide by the stock circumference to get the oversize percentage. Then multiply that by the stock gear to get the new gear. By this example my new tires are 15% larger (31.5 to 33) and that would make my factory 3.73 a 4.30 gear roughly. Does that sound about right?
Logistics Pro
Joined: Nov 2006
Posts: 3,679
Likes: 370
From: Fallon,NV & Bainbridge OH
Why do you want to change gears? If you are going to use your example, that is only 1.5 ", not enough to worry about. I went to 33's and have now gone to 35's and kept my stock 3.73 gears with no issues, and yes I pull trailers and have a truck bed camper so it does not always run empty.
Otherwise use a chart like this.
Engine RPM Calculator
Otherwise use a chart like this.
Engine RPM Calculator
FTE Leadership Emeritus
Joined: Sep 2003
Posts: 12,258
Likes: 767
From: Houston, Texas
(New tire size / Old tire size) x current gear ratio = correct gear ratio to compensate for bigger tires.
In your case:
( 33 / 31.6 ) x 3.73= 3.89 or 4.10 gears.
It almost wouldn't be worth changing gears unless you went to 35s. Then your case would be:
( 34.6 /31.6 ) x 3.73= 4.08 or 4.10 gears like what I have.
After adding 4.10 gears, my speedo was only 5 mph off as opposed to being almost 10 mph off. After some adjusting with the AE, my speedo is dead on again.
In your case:
( 33 / 31.6 ) x 3.73= 3.89 or 4.10 gears.
It almost wouldn't be worth changing gears unless you went to 35s. Then your case would be:
( 34.6 /31.6 ) x 3.73= 4.08 or 4.10 gears like what I have.
After adding 4.10 gears, my speedo was only 5 mph off as opposed to being almost 10 mph off. After some adjusting with the AE, my speedo is dead on again.
Thread
Thread Starter
Forum
Replies
Last Post
