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Old 11-15-2011, 10:30 AM   #58 (permalink)
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Join Date: Feb 2008
Location: Virginia, USA
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beamer - '91 bmw 318is
90 day: 32 mpg (US)
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Originally Posted by Frank Lee View Post
This also offers a partial explanation for why my fe DROPPED when I "geared" it down with taller tires- the other part being the effects of the tires themselves on aero and whatnot- but it tells me that were I to keep the original sized tires and gear higher with gears, chances are that would fail to improve fe as well.
No, chances are what caused your truck's fuel economy to drop was that you raised the truck into the air by installing larger tires, the height of a vehicle from the ground has a big effect on fuel economy, engine rpm's in and of itself not as much, smaller tires would likely get you better fuel economy but it would be because it brings your truck closer to the ground, now...

You really shouldn't be running off-size tires, it affects your speedometer in ways which a part of me suspects that you know this and were using the bigger tires as much for this reason and to your advantage, but maybe I'm mistaken, either way you should only run OEM-specific tires.

You want better fuel economy you'll need to lower your truck about an inch, but do it via the suspension, not the tires, if you want to gear it up or down you'll need to address this via either the transmission or the transfer case / differential gear ratio(s).

I'll grant you that bigger tires are much like a different gear ratio, but not really... Bigger tires have effects beyond what meets the eye and the gear ratio is but a side effect, one which again shouldn't be addressed via the tires.

We modify a vehicle 14 different kind of ways, next thing you know there comes a mechanical failure of some kind, ain't going to find a mechanic that wants to work on it when it's been figgerfied that many ways can't anyone figure out what's wrong because nothing works the way it should, see?

Lets do things a proper way, that way when it comes time to troubleshoot, we know where to start.

Peace out

Last edited by 8307c4; 11-15-2011 at 10:39 AM..
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