how big of a dent will bigger tires cause in my gas mileage?

[blue_kjR417]

right now I have Goodyear Fortera's 235/70/16 and I average about 17mpg, I plan to throw on a 2" spacer lift at some point and upsize to some 245/75/16 BFG All Terrain T/A KO's. How big of a dent will this put in my gas mileage?

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[J-Thompson]

not much
my wife has 245/75 R16 MTR's on the KJ and get about 15 city and 19-21 highway depending on how much of a rush I am in

now you said you were thinking spacer lift
I would think other wise if I were you
here is why
labor for a suspension replacement or a spacer lift is about the same
the OE struts on a KJ are only good for about 30-40K at best ,got 32K out of hers
if you are any where near 30K a spacer lift will be a complete waste of money
keeping in mind that labor does not matter 1 way or the other now
the spacer kit will hit you about $175 to buy and you will need longer rear shocks
that means that if you are close to 30K you should buy new struts ,dont pay for labor twice
so struts are a wash ,shocks are needed either way
that only leaves the cost of coils
if you shop around you can get OME coils for around $130 a pair ,IIRC
that puts you at less than $100 more for a full coil lift

Just my .02

 

[blue_kjR417]

thanks for the advice i'm new to the kj ownership so i'm still in the researching stage...

 

[coloradored]

on that same note dose any one know how you correct there speedometer after that larger tire (245/70/16) is added or is it not needed?

 

[tbaldridge]

I'm running 245/70/16 with steel wheels and its hardley noticeable regarding the gas mileage.
As far as the speedo...in my opinion, not worth the trouble with a 245/70/16. just keep in mind that you will be traveling around 1mph slower.

 

[J-Thompson]

on that same note dose any one know how you correct there speedometer after that larger tire (245/70/16) is added or is it not needed?

I would not bother with that small of a change
if you want to know get a GPS and compare it

I know that the one in the KJ is way off
we are going almost 10% faster than what the speedo reads ,compared to 2 GPS units
70=77 +/- a little
know that and you are good
I do 65 in a 70 and have yet to get a ticket

 

[blue_kjR417]

my kj is still stock and i compared it to my gps and i was actually going about 2mph slower than what the speedo was reading

 

[coloradored]

the last jeep i built up was an MJ (Comanche) i did 225/75/15 or something like that, to a 31/10.50/15 and it was off 10mph at 65. so the change that im doing now is close 215/75/16 to a 245/70/16 so i thought i would be at least 7or8mph at 65. but the MJ was a mechanical system compared to a electronic system so all i had to do is re-gear the speedometer, what would i do with the KJs electronic system, would i need to go to the dealer?

 

[tjkj2002]

the last jeep i built up was an MJ (Comanche) i did 225/75/15 or something like that, to a 31/10.50/15 and it was off 10mph at 65. so the change that im doing now is close 215/75/16 to a 245/70/16 so i thought i would be at least 7or8mph at 65. but the MJ was a mechanical system compared to a electronic system so all i had to do is re-gear the speedometer, what would i do with the KJs electronic system, would i need to go to the dealer?

Yes a trip to the dealer is required for the speedo relcalibration.Some years of KJ's can not be calibrated with non-stock sized tires,some can.Getting the speedo recalibrated is very important since that speed sensor affects the transmission shifting and how mush gas you use via the PCM/TCM.

 

[coloradored]

Yes a trip to the dealer is required for the speedo relcalibration.Some years of KJ's can not be calibrated with non-stock sized tires,some can.Getting the speedo recalibrated is very important since that speed sensor affects the transmission shifting and how mush gas you use via the PCM/TCM.

how would i know if i could get my jeep relcalibrated or not? what years cant or can
mines an 04 is that safe?

 

[jsc7002]

I lost about 1-1.5 mpg and I also went from stock wheels to steelies