I'm running 31's with 4.56 and have the Chrysler 8.25 rear end with the Trak lock LS. In the front I have a Tru Trac. Have been getting 15 to 16mpg which I keep checking because I do not believe it. Will be going to 33's in the future but for now I am real happy with the upgrade.
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Anyone running 31's and 4.56?
- Thread starter tcm glx
- Start date
Ramsey
NAXJA Forum User
- Location
- Shreveport, LA
did you change your speedo? if not then you are covering less miles than it says and getting worse mileagemtntech said:
i've noticed an increase to about what your getting. i just wonder if it s gonna go down or up once i get 33's
Osprey413
NAXJA Forum User
- Location
- Dallas, TX
Wait wait wait, I thought that with a larger tire size you are actually going faster than the speedo says. Wouldn't that mean that you are covering more ground than the odometer says?
RKBA
NAXJA Member #1012
- Location
- Outer Banks, NC
mtntech said:
Why don't you believe your mileage, are you expecting worse or better? What speedo gear are you running, and have you verified the accuracy?
I am about to have the exact set up you have, but I am keeping the smaller tires.
I did not change the speedo gears, I am using the True Speed from Superlift. Since I have a 97 XJ I wanted the ability to set the speed electronically. It also has a switch with separate setting to run 2 different tire sizes. I just had a friend with a GPS ride along and adjusted it on the go. I was expecting about 13-14 miles per gallon but then I don't race around with a heavy foot.
Ramsey
NAXJA Forum User
- Location
- Shreveport, LA
with a larger tire you are going faster, but once you change to the lower gears you are going slower. i am sure that you can compensate for a bigger tire and be close. but without changing the speedo gear it wont be accurate. i am not 100% on this, so if someone knows correct me about the gears and it reading faster
Ramsey said:
The True Speed from Superlift (and other's) only works on the OBD2 XJ models. The speedo on the transfer case is a electronic sensor that sends it's signal to the ECU and the Speedometer (which is also electronic). The True Speed unit is spliced in the signal wire between the sensor at the transfer case and the ECU / Speedometer. It changes the input signal from the speedo gears into a output that is correct for the ECU / Speedometer.
If you have a mechanical speedometer you have to change the gearing. Even if you have the electronic sensor it is cheaper to change the gearing. But if you can't make up your mind like me on tire sizes the electronic method works for any size.
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