I made some charts and graphs. You might want to copy this and save it somewhere.
Percentages were rounded, and tires are not always exactly as tall as advertised.
TIre size calculator:
https://tiresize.com/calculator/
Tire Size Differences (in percentages)
| 28” | 31” | 32” | 33” | 34” | 35” |
28” | | .11 | .14 | .18 | .21 | .25 |
31” | | | .03 | .06 | .10 | .13 |
32” | | | | .03 | .06 | .09 |
33” | | | | | .03 | .06 |
34” | | | | | | .03 |
Left hand column is your starting tire size
Upper row is your desired tire size
Numbers underneath represent the change in tire size as a percentage (i.e.: going from a 28” tire size to a 33” tire size represents a .18 or an 18% increase).
Formula is: (larger tire height minus smaller tire height) / smaller tire height = % change. i.e. (33" - 28") divided by 28" = .1785 (or 18%)
Gear Ratio Differences (in percentages)
| 3.07 | 3.55 | 3.73 | 4.10 | 4.56 | 4.88 | 5.13 | 5.38 |
3.07 | | .16 | .21 | .34 | .49 | .59 | .67 | .75 |
3.55 | | | .05 | .15 | .28 | .37 | .46 | .52 |
3.73 | | | | .10 | .22 | .31 | .36 | .44 |
4.10 | | | | | .13 | .19 | .25 | .31 |
4.56 | | | | | | .07 | .13 | .18 |
4.88 | | | | | | | .05 | .10 |
5.13 | | | | | | | | .05 |
Left hand column is your starting gear ratio
Upper row is your desired gear ratio
Numbers underneath represent the change in gear ratio as a percentage (i.e.: going from a 4.10 gear ratio to a 4.88 gear ratio represents a .19 or a 19% increase).
Formula is: (new lower gear ratio minus original gear ratio) / original gear ratio = % change. i.e. (4.88 minus 4.10) divided by 4.10 = .1902 (or 19%)
How to use this information....
So for example… let’s say you have a four-cylinder Jeep TJ with stock 4.10 gears. You have factory 28” tall tires, and you want to go to 33” tires.
Looking at the
tire size differences chart, going across from 28" to 33" would represent an 18% increase in tire size.
Looking at the
gear ratio differences chart, starting with 4.10 and going across, a 4.88 gear ratio would put you at a .19 (19%) increase to essentially compensate for the increase in tire size.
However, going to a 5.13 (.25 or 25% increase over stock 4.10 gears) would only be about another 5% increase over the 4.88 gear ratio, and would help compensate for the additional weight and rolling resistance of the larger tires.
If you come out between two different gear ratios, you're probably better off picking the higher gear ratio (i.e.: if have to choose between 4.56 and 4.88, go with 4.88) to help compensate for the larger tire's added weight, increased rolling resistance, etc.
If you have a six-cylinder TJ, the factory gears may be 3.07 or 3.73. The factory gears in the TJ Rubicon are 4.10 with 31" tires. If you have a non-Rubicon TJ and are wanting to increase your tire size, you
may want to consider using 4.10 gears and 31" tires as your baseline even if you've got 3.07 gears and 28" tires on your Jeep.