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chris66 10-07-2012 03:11 AM

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


Excoastie 10-07-2012 06:56 AM

I think a significant portion of your fuel economy drop was a result of the tires. The rest you can blame on the non calibration..

I also don't think that you can equate a 4% difference in tire size to a 30% difference in fuel mileage. It's like comparing apples and oranges. Two separate animals.

I believe most programers will allow you to adjust for tire size. I'm not sure how they do it, but I've been told by several different people that it can be done, plus you're able to tweak a few things in the computer to add some more go to the truck

good luck


huntergreen 10-20-2012 10:46 PM

dealer cn calibrate a wide variety of tire sizes on jeeps, should be able to fix you right up. larger tires will eat up some mpg and power. no way to figure your mpg as your odometer is now off. maybe a gps will let you figure correct mpg.

Gantman 10-20-2012 11:33 PM

Yes, you hit it on the head. Bigger tires equals more weight the axle has to move as well as bigger air resistance at highway speeds. Your truck is probably bogging due to miscalibration between tire diameter, speed sensor, and transmission shifts. Aerodynamics plays a big part in fuel economy when lifting or widening the physical stance of any truck. It is a choice most of us live with when the cool lookin factor is more important.

06RamPA 11-01-2012 06:12 PM

Yeah I have the same problem. I went with a 315/70/17 tire also, mud tire in fact, and I'm getting around 11-ish mpgs, and I'm usually pretty light on the gas pedal too!

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