shaft

I have a 4:10 rear end (auto tranny) and I'm wondering if I upgrade my tires to the 315/70/17 AT BGF, will my gas mileage improve? Any input will be greatly appreciated. Thanks.

tobyw

Doubtful. The substantial increase in rolling resistance will far outweigh the lower cruise RPM's. Now if you were to find a taller, skinny highway tread, you might have a fighting chance...

shaft

[quote author=TWZMYJP link=board=20;threadid=17215;start=0#161296 date=1058505508]<br>Doubtful. The substantial increase in rolling resistance will far outweigh the lower cruise RPM's. Now if you were to find a taller, skinny highway tread, you might have a fighting chance...<br>[/quote]<br><br>TWZMYJP -<br><br>So switching to the 315's will actually decrease the MPG? How did that affect your fuel milage after you went to the 315's? I appeaciate your input.<br>

tobyw

So far, I have put about 1500 miles on with the 315's. I do just about the same types of driving every tankful, so I can honestly say I get a good, equal, and fair evaluation. I figure my rough percentages to be 50% city, 30% highway, and 20% towing. Now towing is obviously a loaded (no pun intended ;D) term, but I'm fairly consistant. It's usually around 5-7000 lbs. Sometimes lighter, sometimes heavier, but it all evens out in the wash. So to answer your question, my pre-315 economy was a stellar 17.76 combined over the first 13,000 miles on the truck. Now sitting at 15,000, my average is down to 16.89. If you like to play with numbers, that means the actual economy after the tires was drastically lower than the 16.89 average, because it's pulling from 17.76 down. I do my calculations by the numbers, not from the computer. And I have made the corrections for odometer changes due to the increased tire diameter, so any way you look at it, it's bad news in the economy department. Keep in mind this is just my experience, and some may have noted an increase in economy. But, I would have a hard time buying into it...

tobyw

Forgot this one: On a recent 300 mile road trip with the 315's, I netted 18.4mpg. On the same trip a few months earlier, with the stock tires, I netted 20.3mpg. Nearly identicle outside conditions (i.e. wind, traffic, temps, etc.). Apples to apples...

shaft

TWZMYJP -<br><br>Excellent explanation and thanks for taking the time. I'm wondering if the dealer will give me a hard time when they see the bigger tires. What do you think? Thanks again.