Tacho precision - Alfa Romeo Forum
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Tacho precision

Hi guys,

Came to 240 km/h on the tacho at more than 6500 rev with my Vee6 (reached the ruptor). Does anybody knows how much this really could be? Does anybody has the convertor table between real and indicated speed ?


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I think a general rule is to allow 10% for speedo inaccuracy but not sure
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Yup + or - 10% only way to tell is with a dyno (I think) or satellite.

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i think 10% is about right,,,ive seen some gadgets you can buy that use GPS for a dash mounted speedo in one of the 'trev mags' might be worth looking at.
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Speedy's right about the accuracy of the tacho's. Best thing to do is work out the speed properly.
RPM of the engine/(60 x diff ratio x gear ratio) gives the speed of the wheel per second.
Multiply this by the wheel circumference (In meters) gives vehicle speed in Meters/second, multiply by 3.6 gives KMH.

Eg 6500rpm, with a 3.9 diff,1.1 gear ratio and wheel radius of 30 cm
6500/(60 x 3.9 x 1.1)=25.252 revs per second
25.252x (2Pi x .30)=47.6 meters/second
47.6 x 3.6 =171.3 KMH
Hope it helps wink

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