After much much much study, research, and deliberation, the results of which can be found here (

http://ecomodder.com/forum/showthrea...ling-2813.html ) I have decided to get new wheels and tires. My tires have another 5,000 miles on em, 10,000 if I'm really really lucky.... so.. I will be doing the following:

from 15" wheels to 14" wheels.

Tire size from 195-65-15 to 185-70-14

I used this tire calculation site to calculate the changes in measurements, its not much at all:

http://www.miata.net/garage/tirecalc.html
my odometer would be off by .9% (if it says i'm going 60 MPH i'll be really going 60.5 MPH)

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

195/65-15 5.0in 12.5in 25.0in 78.5in 807 0.0%

185/70-14 5.1in 12.1in 24.2in 76.0in 834 -3.1%

The new tire would be .4 inches or 10 millimeteres narrower, or approx 1.5 inches if you count all tires combined.

I'm going from a GoodYear integrity to BridgeStone B381

This is going from a rolling resistence of 0.00955 to a RR of 0.00615 or a difference of 0.00340 in rolling resistence!

I expect at least 5 more MPG, if not more.

Any thoughts?

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