Last post on Sep 19, 2011 at 12:38 PM
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Jeep Wrangler, Jeep Wrangler Unlimited, Jeep Scrambler, Jeep CJ-5, Jeep CJ-7, Tires, Wheels, SUV
#107 of 226 Jeep Wrangler Gear Ratio Changes with bigger Tires
Sep 18, 2008 (3:22 pm)
I just bought a used 2003 Wrangler X....I'm a newbie to these multi-faceted man mobiles....for now. In anycase, my current tire size is the stock 215 75R15, and I'm thinking of upgrading to 31x10.5x15 without lift. Does anyone know what else needs to be done to ensure a smooth ride? I've heard the gear ratio will change and there is something we can do about that (a sensor in the transmission needs to be changed), but no one seems to know exactly what - - not even the JEEP Dealer!! Please elaborate if you know.....Thanks.
#108 of 226 Re: Jeep Wrangler Gear Ratio Changes with bigger Tires [relgnarwpeej]
Sep 19, 2008 (5:12 am)
31's won't be that big of a deal. 30's were available options from the dealer. Your gear ratio will not change, but your performance may be slightly impacted.
There is a speedometer gear you can change out. It is based on your tire size and your differential gearing. Likely you have 3.73 gearing in your differential. There are several speedometer gear charts/applications on the web that will tell you what you need. Generally, with a 1" change, it won't be a big deal as far as accuracy.
I'm not sure what the stock tooth count is for a 3.73-geared TJ. Your invoice/build sheet will tell your stock gearing (assuming it hasn't been changed).
As a comparison, I have an SE geared at 4.10 stock. I was on 30's and the speedo was off (geared for 28" tires). I regeared to 4.88 and added 33's. My speedo gear is actually more accurate than it was with the 30's.
#109 of 226 Re: Jeep Wrangler Gear Ratio Changes with bigger Tires [erickpl]
Sep 20, 2008 (12:59 pm)
When you say "regeared", do you mean just changing out the speedometer gear? Or is there some way to re-calibrate the speedometer to meet the demand of the bigger tires?
By the way, where can I purchase a speedometer gear?
#110 of 226 Re: Jeep Wrangler Gear Ratio Changes with bigger Tires [relgnarwpeej]
Sep 22, 2008 (5:05 am)
Regearing can take place in the differentials. THAT regearing will affect the perceived power. 3.73 gearing and bigger tires will make your Jeep feel slow and underpowered.
Another regear can take place in the speedometer gearing attached to the transfer case. THAT regearing will not affect power. All that does is make your speedometer reflect correct speed. It works in conjunction with your differential gearing and tire size to ensure proper speed and odometer readings.
Usually you can get speedometer gears from the dealer from $15 to 30, depending on the number of teeth you need for your tire/gear setup. Given that you only have 31's on there right now, the effects of the larger tire size on power and speedometer accuracy would be minimal. If you have a handheld GPS, drive with it and see how your speed is on the GPS vs the speedo. Save the $$ if you can.
Just a note, Rubicons use a different speedometer sensor and it is NOT a gear. It is electronically set and a bit more complicated to do.
Here is a writeup for changing the speedometer gear yourself. It is VERY easy.
#112 of 226 tire pressure monitoring
Oct 03, 2008 (7:29 am)
we just bought our first jeep a 2008 wrangler and the stamped steel wheels have to go so my question is if i change wheels will i have a low pressure light staying on? thats not really acceptable how have other owners dealt with the problem. the people at the dealership dont really seem too helpful. they really dont seem to want us changing anything.
Oct 05, 2008 (10:14 am)
Will 33" tires fit on a stock '06 Wrangler?
Oct 06, 2008 (9:51 am)
So i take it no one has chenged the wheels on a Wrangler with the tire pressure monitoring yet!
#116 of 226 Re: tire pressure monitoring [jlehman]
Oct 06, 2008 (11:56 am)
Probably need to drill holes in the wheels to fit a TPMS or they just get moved from one wheel to another.