Taller tires and Gear Ratio, help

[steelskeet]

Hello everyone,

I am trying to figure out my new gear ratio since I changed to 19" wheels and tires on my 02'FE.

I now have 345/30/19 vs the 335/30/18

My previous tire was a PS2 25.9" OD
New tire Hoosier R6 26.8" OD
I have a stock 3.08 rear gear ratio

25.9/26.8 * 3.08 = 2.94 new gear ratio?

Did I do this right? 2.94 I guess that should not be that noticeable?

 

[dave6666]

Your gear ratio is still 3.07:1 with either tire size.

You can calculate your new speeds here at given rpms:

SS %23670 with MM6 manual and GU6 3.42 gears

 

[PhoenixGTS]

The effective difference is 0.20 of gear ratio. For example, if you have 3.73 gears in your Gen II with stock height tires, and you change to Gen III height tires your effectve ratio goes from 3.73 to 3.55. That means if you have stock 3.07 gears and go to the taller rear tires your effective ratio goes down to 2.87 or so. In other words ridiculously tall.

 

[Steve 00RT/10]

Looks like an effective rear end ratio of 2.967. Stock gears are 3.07


Gear Design Equations Formulas Calculator Effective Gear Ratio

Steve

 

[steelskeet]

I think I will drive it this way for awhile, but maybe a set of 3.33 are in my future.

Thanks for the links they were both very useful.

 

[dave6666]

Here's another good calculator. And if you reverse the tire sizes it will tell you what speed on the speedo you should be doing for the correct actual speed.

Offroad Exchange Magazine - Speedometer Correction Factor