Quote:
Originally Posted by UnCivic
Since most of my driving is in 5th gear on the highway, in the interest of lowering RPM's at crusing speed to improve fuel economy, has anyone ever tried to increase the final drive ratio by using larger OD tires?
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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.