1. Home
  2. Jeep and Willys (new and old)
  3. Question: Tire size for 15x8 rims, stock gears, mpg differences

Question: Tire size for 15x8 rims, stock gears, mpg differences

I have a 93 TJ 4.0L, 2.5" body lift, 1" shackle lift, and ax15 trans. Original rims were banged up and looked like crap, got a very good deal on used 15x8 rims.

---Q1 size: For stock gears (I'm assuming 3.11?)should I go for 31 x

10.5's? I have some reservations because a friend said he can't use his 5th gear most of the time on the highway because of the extra intertia from the larger diameter tire with stock gears.

I could go 30 x 9.5 or would 235/75/15's work. My conversion shows it as a 9.25" wide tire so it seems it would work.

---Q2 Appearance: I'm not sure that the lift and smaller tires would look like a freak show or be cosmetically appealing?

---Q3 MPG: Also, what about gas mileage. I recieved feedback that you loose about 1.5mpg per extra inch height over stock? That seems pretty steep, if 225/70/15's are stock for 15x7's at about 28" height, then

31's would be making you loose 4.5mpg if that were true.

I'm not very experienced in the tire issue, only what I've read over the last couple of days. Any help on my 3 questions would be greatly appreciated before I dump some more cash out.

cheers

Reply to
byrsc
Loading thread data ...

Reply to
Bob McClaukin

Reply to
L.W.( ßill ) Hughes III

You really need to figure out what you have. The Jeep in question doesn't exist, the gear ratio doesn't exist and the body lift is really bad news and an odd number for any kit so it likely doesn't exist either.....

????????

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@comcast.net wrote:

Reply to
Mike Romain

Big question is; what do you want to do with the Jeep? Trails? Occasional rocks and fire roads? Sand? Pavement pounder?

chris

90XJ, 92XJ, 83CJ8, 94YJ, 89GW, 86XJ
Reply to
J. C. Duchock

Sorry about the numbers - Jeep is YJ ... not TJ. Probably I'll use in

85% paved road, 15% off road, moderate trails, not too rocky in WV. I think 2.5" suspension, 1" body", 1.5" shackle... it amounts to 4" lift in total.
Reply to
byrsc

Sorry for the confusion- Jeep is YJ ... not TJ. I think 3.73 ( whatever it is it is the original gears) I think 2.5" suspension, 1" body", 1.5" shackle... it amounts to 4" lift in total, not 3". Original owner had as a beach mobile, I'll be more of a hwy driver, some off road, hence the thought of not going for big tires.

Reply to
byrsc

Now you are making sense.

With 'stock' rims and that lift on a YJ you can easily go to 33x10.5 or

33x12.5" tires. 31's will be no issue at all.

The 8" wide rim if it has the correct backspacing will allow up to a

12.5" wide tire. Aftermarket rims are a crap shoot because they could have 'any' backspacing number.

I have the stock 7" tires on my CJ7 and run 33x9.5's with 3.31 gears. My CJ7 runs very well and I get a nice 23 US mpg running at 70 mph loaded. This is also my daily driver.

5th gear, properly called 'overdrive' still has lots of pull, but it puts the engine rpm's in to the 'lug' area so it just drinks gas if I use it. If I totally ignore 5th, my highway rpm at 65 mph is 2300 which is a sweet spot for my engine with tons of punch and good mileage.

My speedometer has been set by GPS for my tires so I know my mileage is 'real' and not misread. You have the 4.0 engine so you won't get as good a mileage as my carb engine, but if you watch the rpm readings, your mileage shouldn't suffer too bad.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

snipped-for-privacy@comcast.net wrote:

Reply to
Mike Romain

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.