tomfpurves Posted June 2, 2015 Report Share Posted June 2, 2015 My 3a has a standard axle and 4A engine and box with overdrive.The car is fitted with Firestone F560 165 15 tyres. If I am doing a constant 25 or 30 mph on a regularity rally what should the rev counter read in direct 3rd and direct top.The rev counter is accurate...the speedo less so. Quote Link to post Share on other sites
stillp Posted June 2, 2015 Report Share Posted June 2, 2015 Depends on which diff ratio you have. Have you tried comparing the speedo reading with the speed indication on a satnav? By the way, how do you know the rev counter is accurate? Pete Quote Link to post Share on other sites
tomfpurves Posted June 2, 2015 Author Report Share Posted June 2, 2015 The rev counter has been checked twice and each time using different instruments and on each occasion it was within 100 rpm at 5000 revs.The dif ratio is to the best of my knowledge standard TR3A Quote Link to post Share on other sites
Marc R Posted June 2, 2015 Report Share Posted June 2, 2015 Hi tomfpurves, Did you know this tool, http://www.mintylamb.co.uk/gearspeed/ The TR3 is not mentionned, nevertheless you can change (and play with) all the parameters (Gearbox,OD, Diff, Tyre, Units... Regards Quote Link to post Share on other sites
tomfpurves Posted June 2, 2015 Author Report Share Posted June 2, 2015 Dear Marc That is very helpful . Merci. Tom Quote Link to post Share on other sites
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