Monday, May 25, 2009 at 22:28
I think its agreed that going to larger tyres will increase your
fuel consumption but maybe not as much as you expect.
Yes your acceleration will be slower, you will need to drop back a gear earlier, the vehicle will be slightly higher resulting in more drag, but when crusing, the rpm of your engine should be closer to its most efficient speed. i.e. the point of maximum torque. Most cars even in top gear cruise above that rpm @ 100km/h so a larger diameter tyre is like having a higher 5th (or 6th) gear.
On a flat level road, with good pressure in the tyres, a reasonable
fuel consumption can be acheived. There is probably more difference between the final drive ratio of a manual than of an auto. An auto generally has a much higher top gear resulting in a lower rpm @ 100km/h.
Also when making comparisons, users are often going from road tyres to larger AT or MT's. A larger road tyre would give a better
fuel consumption difference indication, which has probably never really been documented.
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