Plus one tire sizing effect on mpg?

[some_other_dave]

Originally Posted by 93Cobra#2771

The pariticular upsize I have chosen is within .2% of the oem size tire. That is, if my memory is correct. I'm posting from my phone and too lazy to look at the miata tire size calculator.

Tire calculators will only give you a very general notion of a tire's actual diameter or circumference. The sidewall numbers are "general guidelines" only, and the exact size of a 205/60-16 tire (for instance) varies from manufacturer to manufacturer.

If you can, check on the Tire Rack website (or similar resource) to find the actual published diameter for that specific make and model of tire--or the revs/mile figure, which is roughly equivalent. Compare to whatever you are "used" to having on the car, or to the OEM tires if you can find the specs.

In general, you will lose a little bit of MPG going to a wider tire. It may very well not be enough to notice, though.

-soD

[CapriRacer]

Originally Posted by 93Cobra#2771

Capri - wouldn't deflection me less due to the shorter and stiffer sidewall?

Well, I fudged a little.

What actually happens is that the PERCENT deflection remains the same because "everything else was equal" and that would include the sidewall stiffness (if you grant that we are talking percent stiffness due to the shorter sidewall)

But that doesn't change the basic premise.

[93Cobra#2771]

Well, after all my research and such, I ended up having to go back with the stock 14" rim. As I mentioned, the tires were pretty worn. Noticed a hopping in the right rear. Pulled the tire, and tread was beginning to separate from the carcass/casing. In other words, you don't drive on a tire doing that, or you may see sever destruction of tire. So, I had to get tires today, and guess which size they had in stock.

The 185/55/15 was also a bit of an odd size, and about $25/tire more than the stock size. Guess I'll just do some moon wheel covers instead.