Is regearing necessary?

[TWDJ]

Originally my YJ was equipped with 205x75/15 tires and the previous owner replaced those with 235x75/15. The 205 were ~27" in diameter while the 235 is ~29".

Now, I am wanting to go with 31x10.5/15. That works out to an overall increase of ~15% in diameter from that which was OE. Is this too much without regearing?

Thanks for the assist.

 

[Joopin]

With a difference that small I don't think you will have to regear. You will loose a little bit of your top end and a little power, but nothing drastic. Maybe this chart will help you decide... http://www.4lo.com/calc/geartable.htm

 

[TWDJ]

For the day-to-day I was figuring the oversize tires would be roughly akin to a 15% overdrive, and that would be about right for that kind of application. This Jeep does not spend much time around town. The freeway is 1 mile from my house so miles would be freeway and off-road. My concern was whether it would affect off-road performance to any great degree?

The 2.72 low range becomes, in effect, 2.31. The cost of having the differentials regeared vs. a 4.0:1 TeraFlex unit is roughly the same and I was just looking to see if that may need to be done at some point.

Rockcrawling is not part of the plan, but there are trails in the Class 5 and 6 that I'd like to tackle.

 

[raptor_pilot]

I didnt regear my YJ when i put 31"s on it. You def loose top end and gas milieage but its not severe enough to warrant doing it ASAP. I have no problem living with it.

 

[harletaz]

I had run my YJ with a 6cyl and auto for a while with 33's and the stock gear ratio was 3.07..

it ran good... i finally replaced the those axles with axles that have 3.73's..

 

[Snitty]

I have 33 inchers and still stock 3.07... I don't have any problems

 

[Junkpile]

My TJ has the 999 transmission, 3.07:1 gearing, and 31" tires. While it's not exactly a rocket, it's really no slower than it was. Offroad it acts the same as well, but slightly taller gearing often helps with my type of wheeling, so results may vary on that one. The gearing is too tall to begin with, but the lack of overdrive somewhat dictates that it be that way for a daily driver.