My 4X4 got thirsty after a Tire change!





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  1. #1
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    Default My 4X4 got thirsty after a Tire change!

    My BFG AT’s really lasted a long time. Maybe too long for my liking. (Over 90k km’s)
    Finally the time came for me to replace them. I have been thinking for quite some time about putting on something a bit bigger – in the range of 33” 8) and decided on the BFG Muds. My thinking (or lack there off) was that if I go bigger in height and give a little on the width, I should not see to big a consumption change……… Boy, was I mistaking! My Jeep went from an ave of 10l/100km to nearly 12l/100km on the open road, and that is at 110km/h
    My old set was AT’s -265 75/16’s. The New set is MT’s 255 85/16’s it cannot be the weight (I think) They should weigh approx. the same with the diffs in width.
    What’s your take? Why is my Jeep suddenly so much more thirsty? (It’s the 2.8 CRD engine)
    Other side effects, I have noticeably experienced a loss of power when off-roading. This I know is due to the change in tyre size and as a result some ratios. That I expected and plan to compensate with a “re-map” for some extra horses and torque. (Will for now stay away from gear ration changes due to “financial” and possibly marital reasons) I see you can get up to 24kw and 112nm extra with a re-map on the diesels.
    I have an extra set of rims. Wondering if i should get a set of "on road" tyres. 33" just looks so much more in perportion. Is there a light weight 33" on the market that will give me my consumption back?
    Last edited by bungykhb; 2014/03/20 at 02:59 PM. Reason: oops
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  2. #2
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    Default

    When you changed the tyrea, did you get a procal and reset the shift points on the auto sorted again? Is it auto?
    Also. Did you correct the speedo to indicate correct speed and distance again. Procal fixes that as well. Speak to Bad Santa from zone offroad.
    Gerhard
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  3. #3
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    Default

    Google for tire size calculator, then you van see the actual circumference of the tyre
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  4. #4
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    Default

    Google 1010tires. According to them, you have gone 4.48% bigger. Your speedo will definitely be out. First check the variance on your speedo and then calculate the fuel consumption. But i can guarantee you that with the bigger tyres, there will be an increase in consumption.
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  5. #5
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  6. #6
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    My Prado says it should get 10.5l/100km..... with the Muddies I have never really seen lower than 12l/100km so on mine it does add the extra bit, and the size increase kills the acceleration so 1st and 2nd gear are so close together you feel like you need a much longer 1st, but you will get used to everyone going past you pulling off at robots, otherwise you pay at the pump!

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  8. #8
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    to put it simply:

    for every revolution of the motor you are now travelling somewhat further.

    so on your odo 100km probably used to be 95km, now it's 105km (or whatever)

    that's most of your difference.

    then, you've increased your gross frontal area by a fair percentage due to the lift, as well as the drag off the bigger tyres.

    you'll probably find you are also trying to keep to (say) 120km/h on the speedo, which used to be 110km/h, and is now a genuine 120km/h, which will use more juice, especially on an aerodynamic brick like a Wrangler.

    plus some extra mechanical drag off the tyres, mud tyre are softer.

    add that lot up, most of your increased consumption is 'in the maths' and the rest, well, what were you hoping for?

    why 255s anyway? bit skinny for a wrangler!!!

    edit: don't remap the diesel motor. just don't.

    resetting the speedo and gear changes etc for the larger tyres is different and highly advised - I don't know what model you have, but the AEV Procal is probably the best tool for the job, but it's not compatible with some CRDs...
    Last edited by Apocalypse; 2014/03/21 at 02:00 PM.

  9. #9
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    Stock on 2013 CRD was: 245/75R17 = 31,5"

    you had : 265/75R16 = 31,6"

    you have: 255/85R16 = 33"

    earlier ones had 255/75R17 as stock, 32"

    the dealership can reprogram you up to 255/75R16 I seem to recall - that would help already with the gearshifts / speedo accuracy...

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