Tire Talk

[shatto]

Tire Talk
My baby Tundra has the stock; 265/70R/16 tires on the stock 16" rims.
I deduced that a larger diameter tire would go further per rotation and, working backward to the engine turning fewer RPM's, that ought to translate to better gas mileage.

So far so good.
Today, I dropped in and talked with an expert.
He said I could put on a: 265/75R/16.

He said Toyo not only cost less they lasted longer than the Michelin LTX MS

Okay, so here are my questions:
1. Since it has been 50 years since I studied Geometry, how do I calculate the abovementioned? and
2. Has anyone experienced Toyo's, Michelins, etc. and MPG differences?
__________________
2006 Tundra replaced a
98 Dakota 3.9 automatic, long bed.
Retired with broken A/C, July 2008.
623,000 miles.
On original engine and transmission, using Amsoil by-pass filters and lubrication.

+Everybody knows something you don't know.
+Truth does not need to be 'balanced' and it ain't caused by voting or consensus or polls or yelling louder or silencing someone.
+Artists prove truth can be in forms you don't understand.

[Gatorman76]

Originally Posted by shatto

Tire Talk
My baby Tundra has the stock; 265/70R/16 tires on the stock 16" rims.
I deduced that a larger diameter tire would go further per rotation and, working backward to the engine turning fewer RPM's, that ought to translate to better gas mileage.

So far so good.
Today, I dropped in and talked with an expert.
He said I could put on a: 265/75R/16.

He said Toyo not only cost less they lasted longer than the Michelin LTX MS

Okay, so here are my questions:
1. Since it has been 50 years since I studied Geometry, how do I calculate the abovementioned? and
2. Has anyone experienced Toyo's, Michelins, etc. and MPG differences?
__________________
2006 Tundra replaced a
98 Dakota 3.9 automatic, long bed.
Retired with broken A/C, July 2008.
623,000 miles.
On original engine and transmission, using Amsoil by-pass filters and lubrication.

+Everybody knows something you don't know.
+Truth does not need to be 'balanced' and it ain't caused by voting or consensus or polls or yelling louder or silencing someone.
+Artists prove truth can be in forms you don't understand.

OK. You don't get something for nothing. Larger diameter=larger circumference. Remember Pi * D? So you will roll farther with each tire revolution but it will take more work. Increased weight & rolling resistance of a larger tire can offset mpg gains from increased travel per revolution. The change also affects gearing, slightly. A taller tire gives an effective "higher" gear ratio. For example, if you move from a 265/70/16 & a 3.91 rear gear, changing to a 265/75/16 gives you an effective gear of 3.78. That's the percentage difference in tire circumference times the gear ratio. Better for highway but worse for towing, acceleration, or city. The change in tires will throw your odometer & speedometer off by the same percentage. Speedo will read low & odometer will record fewer than actual miles traveled. Or, you might get better highway mpg's at the expense of stop & go mpg's. Go to Tire Rack & check the "specs" on a similar tire. They will give you the overall diameter & revolutions per mile. I know the Michelin is one of the longest lasting tires. I do not know much about Toyos. From my own experience, going to a wider tire decreases mpg's. Keeping the same width and going a little taller has only a minor effect, if any.