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Old 05-19-2008, 03:33 PM   #1
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Stupid question about tire size and FE

I own a 96 Nissan P/U, 4wd that has 30x9.5 tires that are nearly worn out. I have been considering going back to 235/75 R15 tires to see if that will boost my economy a little.

Would going to a 31x10 tire hurt or help my economy right now? I can see economy going down a bit since the tire is going to be heavier but would the taller size reduce RPM's enough to offset that? The reason why I am asking is that I may have a chance to pick up a set of nearly new BFGoodrich all terrain tires at a pretty good price.
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Old 05-19-2008, 04:17 PM   #2
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Increased diameter improves mileage

I understand the desire to save money. These days after paying for fuel there's no money left for anything else.

Energy loss by a tire is equal to the strain energy times the rubber internal friction. You can lower the strain energy, which is proportional to one over ( tire pressure times tire diameter). The internal friction is reduced by buying high-efficiency tires. Unfortunately, the tire manufacturers are being pressured to not publish the efficiency (rolling resistance) of their tires.

If you buy new tires, usually they are backed by a 30-day satisfaction guarantee. Be sure they are (including the balancing?). Then you can try them and see how your mileage changes. Have no qualms about returning poor tires. After all, the manufacturer wasn't bothered about selling them to you.

Ernie Rogers

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Originally Posted by dm1333 View Post
I own a 96 Nissan P/U, 4wd that has 30x9.5 tires that are nearly worn out. I have been considering going back to 235/75 R15 tires to see if that will boost my economy a little.

Would going to a 31x10 tire hurt or help my economy right now? I can see economy going down a bit since the tire is going to be heavier but would the taller size reduce RPM's enough to offset that? The reason why I am asking is that I may have a chance to pick up a set of nearly new BFGoodrich all terrain tires at a pretty good price.
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Old 05-19-2008, 05:27 PM   #3
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A little more information that I should have included

I live on Michigan's Upper Peninsula so a tire that performs well in snow is a must. Everybody I know with that style of BFGoodrich has been happy with the tire because it gives good traction in snow and wears well. If the tire is significantly cheaper used than new (probably less than $200 to buy the tires, pay a shop to mount and balance them, put my old tires on the other truck which is being junked, and get a set of fender flares to mount on my truck) vs. $600 or so new.

My thought right now is to go with the used tires, the extra $400 would go a long way towards offsetting any loss in FE. I'm just curious if anybody has noticed an increase or decrease when going to larger or smaller tires on their truck.

Ernie,
Good post about high efficiency tires but I have to balance that against 130 - 200 inches of snow a year. My mileage goes to crap in the winter anyway because of the winter gas and the need to be in 4wd so much. Tires with better traction may actually help me since I would have to use 4wd a lot less than I did this winter.

Thanks,
Don
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