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Old 12-12-2013, 02:55 PM   #81 (permalink)
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1 or 2 inch diameter increase, if you can increase the air pressure 20 psi more should still increase mpg. Going from a 30 tall tire to a 36 will usually hurt mpg, but you have to recalibrate the odometer too. I had a 72 Blazer and went from stock 350 w 30 " tall street tires to a 396 and 10" wide 33" tires. Gained 3 mpg.

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Old 12-12-2013, 06:09 PM   #82 (permalink)
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Quote:
Originally Posted by Big Dave View Post
I have talked to hundreds of pickup guys and the trend is very clear:

Bigger diameter wheels/tire = worse MPG.

The reason is straightforward. Unless you run very long legs at the same road speed, you have to accelerate. Not only do you have to accelerate the vehicle, you must first accelerate the wheels/tires before they will accelerate the vehicle.

The polar moment of inertia goes up with the square of the diameter, so if you go from 13 inch wheels to 16 inch wheels the polar moment of inertia increases by 33%. The wheel/tire assemblies act like flywheels.

Look at the high-MPG cars available. Small diameter tires. 13 or 14 inch. No 18 inch wheels on the vehicles with high MPG.

Stay with the factory-sized rubber. They do know what they are doing.
couldn't disagree more!
1. truckers buy bigger tires for looks not mpg...so of course they get worse mpg!!!! ("hey, iwanna fill the wheel well!!!) So that is a false argument.

2. I'm the one who made the comment about truck tires and mpg. My point is this: since 99% of us buy used, there is a greater chance that a truck wont have the factory size (as opposed to cars) So if the purchaser randomly increases the size from what is there, then they may stretch the limits and then get worse mileage.
3. prius 15 inch. 13-14?????? small rims are on SMALL CARS....duh.

4. who here has ever gone from 13 to 16??????? false point.

5. the op is talking about 15 to 16......let's stay topical.

OP, Please look at my post on how to determine your mpg at various speeds and rpms, that is they only way to properly predict success of failure.

rule of thumb...need to up size the tire diameter at least 5% and not more than 10%

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http://ecomodder.com/forum/showthrea...eii-23306.html

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http://ecomodder.com/forum/showthrea...e-10912-2.html

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http://ecomodder.com/forum/showthrea...tml#post247938

Last edited by mcrews; 12-12-2013 at 06:18 PM..
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