ThrottleJunkie

I was reading on some other forums that guys with Jeeps running 35's and 37's were only getting like 9-10 mpg? Is that true? If so, that would kinda ruin the high I had when looking into a Jeep. Still getting one though.

wayoflife

True? Yes and No. Did they happen to mention if they regeared to the proper ratio for the tires they're running? This will make a difference in your MPG. But, there's really no way to prevent MPG loss of some sort especially when you're pushing big fat tires and all the extra armor, bumpers, etc that most built Jeeps tend to have.

ThrottleJunkie

so, forgive me if this is a noob question, but the higher the gear ratio the better or worse the mileage?

wayoflife

Please, there's really nothing to forgive here. To answer your question, every tire size pretty much has a specific gear ratio that should accompany it for optimal performance. Typically, if you're running something like 33" tires, you should be running 4.56 gears and with 35's, you should be running 4.88 gears. When you're run incorrect gears, your engine will end up working too hard or not hard enough depending on what you want it to be doing. Does that make sense?

ThrottleJunkie

Yeah, makes perfect sense. Why make it work harder than it has to?

SpudRacer

My 95' XJ got about 20mpg when I got it in 02'. I replaced the 27" tires with 31" Super Swamper Thornbirds, replaced the gears with 4.10s, then added new (HEAVY) Bullet-Proof bumpers, a Warn 9500ti winch on the front, heavy duty rock bars, a Garvin roof rack, CB radio, Hi-lift Jack, 31" full size spare on the back.

When all was said and done, I averaged 10-12mpg when driving it out to NC from CA. Around town, I see about 6-8mpg. Of course, I am not a light foot and my tires spin more often than they should. I was trying to burn them up faster so I could replace then with 33" tires. Now the title's on the chopping block to be sold once I get a build date on my 4-door Rubi. So much for my plan...

TOM
Bryson City, NC

ThrottleJunkie

That's quite a difference. But gas prices have come down so maybe it won't be as bad stopping at the pump every other day.

Bad Dawg

Hi, new guy here. We are thinking of coming over to the "Dark Side" and getting a new Rubi Unlimited. We are long time Land Cruiser owners and race our highly modified FJ 40.
I noticed that the Rubi's come with 4:10 gears and all the others come with 3:21 gears. From my past experiance in other rigs, besides Jeeps, automatics usually have a lower first gear than a manual. My thought here is that the milage on the Rubi's with the 4:10's should be worse than the Sahara with the 3:21's with the same size tires. Then I would think that if we went with taller tires it would bring the Rubi's milage up to about where the Sahara's is with the "smaller" 32's. Of course it depends on tire tread design and such (MT's vs. AT's). Does that make sence?

wayoflife

Hey Bad Dawg, welcome to JK-Forum.com! Regarding your post, I should point out that the 4.10's are an option that can also be had on both the X and Sahara Unlimited models. As far as everything else goes, yes, technically a slight bump in tire size should give you better MPG on the highway but it has been my experience that it hurts your MPG in stop and go driving conditions or when climbing hills.

BTW, I love FJ40's and hope you're not getting rid of yours

Bad Dawg

Had the 40 up for sale a few weeks ago but got my wife back into the racers seat and decided to keep it. Here is a shot of it cleaned up: