Quote:
Originally Posted by daqcivic
I haven't experimented with different diameters, but I can tell you a tire with significantly greater diameter will probably also have a higher tread width, which will eat up some of the efficiency you save with lower RPMs (as will the greater rotational losses already mentioned). I've noticed with my 195 (vs. 175 stock) tires I get noticeably reduced coasting distance, indicating that just 20mm adds significant rolling resistance.
To me the cost/benefit ratio doesn't make it worthwhile, as you could probably make up the same improvement with other (cheaper) strategies such as slowing down and doing simple aero mods.
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I totally agree with this. With 185/65-14's I'd get 34 to 40 mpg. With 205/45-16's I'd be lucky to get 34 mpg.
I still haven't gotten around to trying 195/65-14's yet though... Actually, I've been thinking about a setup with 195/55-16 on a set of 16x6 rims. That's ~4% over stock diameter. The problem has been finding a set of cheap 16x6's to experiment with!