have I got this right?

[Cabin_Guy]

I have 2005 TJ with stock (30") tires and 3.73 gears, 4.0 with a 6 speed stick.
I'm thinking of putting 31 inch tires on it, not interested in the costs and issues related to raising it.
will 31's fit ok on a stock TJ Unlimited? Can I go much wider than the stock 9 or 9.5 width?
It's my understanding that a taller tire will hurt my bottom end a bit, lower my top end revs and generally improve milage. Is that right?
I dont do any serious offroading, mostly dirt road, deep snow and highway driving so I think this setup would be good for me.
Does this sound right to you?
Thanks

 

[xt master]

31" tires will fit fine.I have 31" by 10.5" with stock suspension.Only problem I have is at wheel lock when turning left the tires rub some on the control arm.Mine is a 97 TJ.That may have changed on newer Jeeps.If not get after market rims with more back space or get wheel spacers.If you stay with the 9.5" width you will have no problems at all.Honestly if you do not wheel it and do a lot flexing you can get 32" tires under the fenders.

 

[Cabin_Guy]

Great ! thanks for the info !

 

[southtj]

I put 31s on mine before I did the 2 inch lift and noticed no differences. The spedo is right on the money too according to my gps.

 

[Bounty__Hunter]

It may affect your mileage slightly as the overall gearing will be slightly taller, and the engine will be a little lower in the power band. Might not be enough to notice. Mileage may drop slightly.

 

[Cabin_Guy]

drop? I thought taller tires meant the engine would rev less, thereby giving better milage... this stuff makes my head spin

 

[jfrabat]

The engine DOES rev less, but because you are not in the high torque range, it is actually struggling more (thus, it needs more effort, and fuel consumption goes up).

 

[Bounty__Hunter]

A taller gear or larger tires will sometimes help mileage, only if the engine was revving too high initially. In most cases with jeeps, it will cause the engine to lug at lower RPM's more, thus reducing mileage.

 

[xt master]

I find I get better gas mileage if I keep it in the 2000 to 3000 rpm range.MY power curve seems to be around 2200.Only thing not stock is my 31" tires and CAI.ATM I am getting around 17mpg highway and 14mpg city

 

[Cabin_Guy]

ahhh ok, ty for the advise.
I'm used to my Dakota 5 speed v-8, which revs about 1900 at 100km/hr, whereas my jeep revs about 2300 at 100km/hr, so I figured the jeep was reving a little high.

 

[Bounty__Hunter]

A v8 can operate in slightly lower RPM's without lugging, than can a I-6 with less power.

 

[Crazy4diesels]

I have 31's on my 05 TJ with the six speed and 3.07 gears. I find it drives fine most of the time. Reverse is a little too steep in high range off road (No big deal - I just drop it into 4 low if I'm jockeying around much) . Hill starts in first need just a tad bit of clutch slippage to prevent bogging. On the road she is fine. With the six speed you'll have enough gears to play with. I can still use overdrive as long as I'm going faster than 60 MPH and now the Jeep will do 70 very comfortably. I don't really see any differance in gas mileage. Best of luck - John