New tyres, different size, more fuel?

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Originally Posted by Rok_Dr

My experience is the same as Tombies, 8-10% low on standard tyres. Current d2a on 245/70s reads basically the same as the GPS unit.

Cheers

Steve

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Interesting

245/70 (D = 29.50) is about 1.9 % above standard issue 235/70 (D = 28.95).

Appear to be at least 2 differing sets of speedo outcomes ex Solihull (Gaudough, larm, Sharkee, Gordo & I pretty close to the mark vs the rest?).

245/75 (D = 30.47) should be about 5.25% over.

My 255/65 (D = 29.05) are 0.35% increase over standard (almost irrelevant).

Just to add here, mine on 255/55-18 stock wheels, is spot on with several different GPS devices.

My 2001 disco on 235/70/16 at 100 km/h on speedo is by numerous gps actually 102 km/h. Variation from intended accuracy by manufacturer as in most instruments can be both ways. Under or over reading.

GPS technology is so helpful but before relying on GPS reading check with another brand or unit. Have had one unit many years ago that was not reliable. :cool: