Jmac

Hey all,

Question... How come I'm getting an average of 13.5mpg with my new Procomp Extreme All Terrains and with the 315 BFGs I was averaging 14.9mpg.
I've had the speedo recalibrated. Measured myself the revs per mile at 643. One problem I'm having is my tire guy can't get them balanced. Would that cause a loss of economy. I thought going back down to a size closer to stock would yield improved economy. All driving habits are the same. BTW with my stock michelins I was averaging 16.5mpg before going to the 315BFGs

thanks for any input,
Jamie

RonP

I don't know but it might have something to do with rolling resistance and tire design. I just replaced the factory BFG rugged trails with bridgestone dueler revos and the are the same size and e rated and I have lost atleast 1mpg or something else is up and it is just coincidence. the ride is great and the traction is awesome, but man I didn't want to lose any mpg's.
just my .02

90dodge

Jmac,

well tire design will be a diffrence in a big way!! and you are now turning more RPM's at the same speed with a smaller tire. with the 315's your RPM's were lower, meaning less foot on the peddle as well.

i went from a 35-12.50-16 BFG M/T to a 315-75-16 Toyo and picked up almost 3 mpg on the highway. i also went to a less agressive tire, more suted for the road.

hope this helps some, Bob

2Armor

tires weigh different. The heavier spinning mass X4 would require a little more fuel.

omaharam

What everyone else said.
Also, don't assume that they filled the tires to adequate pressure. A lot of these guys think 30-32psi is always the standard - on most of these newer light truck tires it's much much higher. This would kill your mileage. Look at the sidewall and make sure you have them filled to max specs.

HOHN

NO NO NO NO NO!!!

There is PROPER tire pressure and there is ALLOWABLE tire pressure.

The "max" on the sidewall is NOT the ideal pressure for tire wear.

Yes, you will get best MPG at this pressure (rock hard tires-- low rolling resistance), but your tread will prematurely wear out by unevenly wearing out the middle first.

If you don't care about tire wear and brutal ride, then by all means, fill them up until they explode.

Jmac

I agree, I have them as tight as they can go without loosing the edges of the footprint.
Jamie

rammtuff

rec'd pressures are on your door.

4x4not

You area also running at slightly higher RPMs for the same speed now. So take this into consideration. When I went from the stock 245s up to 315s (a BIG difference) my milage stayed about the same. A lot more rolling resistance, BUT my RPMs are down a good 13%. I have 4.10s so I was up there in the RPM range with the stock tiny tires.

omaharam

I've had 3lbs less than max in mine for 30,000+ miles and they are wearing perfectly even. I understand that an overinflated tire can cause excessive wear in the middle, but these trucks are heavy enough to run the pressure and still get good wear. Yes, it rides worse, but at going on $3 a gallon again, I'll bounce around a bit. Also, the narrower the tire, the less it matters. So a 315 will be more prone to center wear slightly overinflated than a 275, and so on.

surfram

I think your revs per mile may be a little high but a more aggressive tire will always have a higher rolling resistence. My speedo is dead on with the pinion factor set at 634 with 285 BFG AT KOs.

surfram

Pressures on the door only apply to the tires that came on the truck.

bekim

I agree. the inflation numbers on the tires are manufacturers suggested numbers, not max pressure. The tire manufacturer knows the ideal operating pressure for their product better than anyone. I get even wear and better mileage at 75 PSI on my "inflate to 80 PSI cold tires".
Cheers
Mike
###
In over 250,000 miles running my tires at 75 PSI(80 PSI cold recommnded on the sidewalls) 6 sets of tires, i've had 2 flat tires and zero other problems. And even wear. Just luck? Not IMHO!!

spro2395

Mike
Do you run 75 psi all the way around with no load in the truck?
Thanks Joe Z