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Old 10-07-2012, 04:11 AM
chris66 chris66 is offline
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Join Date: Jun 2009
Location: Vancouver, BC
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Vehicle: 2009 Ram1500, 5.7L HEMI
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Default larger tires and fuel consumption

Hi Everybody,

I just had new Bilsteins 5100 (front and rear) installed on my 09 RAM 1500 Sport and had the front ones set for the highest position; that gave me about 2.7 lift. I then installed 315/70/17 BFGs All Terrain on 17 Fuel rims (0 offset). The whole setup works beautifully, no rubbing anywhere at all, not even at full lock.
With the new tires, the speedometer is now all messed up. Went to the dealership to get it recalibrated, but unfortunately their software only allows them to select from a drop down menu with the recommended tire sizes; best you can do is pick a combination that comes the closest to your real setup (I am still 4% off from the factory 33 setup; before the recalibration attempt I was 7% off).
The problem is that after changing the tires I have noticed a drastic increase in fuel consumption. I realize the new tires have a higher rolling resistance than the stock ones and are also a bit heavier which of course should affect the fuel consumption. There is also now the speedo inaccuracy which compounds to the final result, but here are the facts:
- Before the tire change I was averaging 18l/100Km (roughly 13mpg) city driving
- After the tire change I average 23l/100Km (about 10.3mpg) in the same driving conditions (almost a 30% increase)
Anyone else experienced similar problems? Do you think this can be blamed on the tire size mismatch? I mean the speedometer is only 4% off but I am seeing an almost 30% increase in fuel consumption. Do you guys have any experience with any of the aftermarket programmers? Are you actually able to accurately recalibrate the speedometer either by being allowed to enter whatever tire size you have or the revs/mile?
Any feedback will be highly appreciated

Thanks
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