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MG MGA - Speedo showing a consistent 5 mph high

I'm assuming that is a result of the current tires being smaller than original.

Is there some place one can purchase a conversion gear for the speedo?
T McCarthy

The amount of speedometer error caused by undersized tires would increase as your speed increases. At low speed your speedometer would be off by a small number of mph. At higher speeds your speedometer would be off by more mph. If your speedo is consistently 5 mph high regardless of the speed, it's not caused by undersized tires. Sorry, I can't help with the conversion gear question.
Andy Bounsall

Personally I wouldn't worry about a 5 mph difference. Cable-driven speedos aren't very accurate anyway, and mine wavers by at least 5mph when it is under way. You can get speedos recalibrated fairly easily by an instrument restorer - you would have to do that anyway if you decided to change the rear axle ratio or fit a five speed gearbox. When I had mine done I had to jack up a rear wheel, and record how many times the speedo cable turned when I rotated the rear wheel 25 times. With this info, and the tyre size, the chap who recalibrated the speedo was able to do the job. AB
A Bennett

If its consistently reading 5 mph high across the range it could be that the pointer has moved on its shaft.
Malcolm Asquith

How would you be able to tell 5mph across the entire range unless you had another car along side you you could see the speedo in.

The only upside of all this is if you thought you were doing 100mph when the police pull you over for speeding the ticket would be written for 95mph and not 100mph. This could reduce your fine save you your licence...LOL
DJ Lake

DJ

SAT Nav.

Steve
Steve Gyles

Technology like that in an MGA is cheating...but a very cool solution.

DJ Lake

DJ

Fits in the period (after market) cigarette lighter and sticks on the original windscreen with no modifications!

I used mine to calibrate the speedo throughout its range so I did not run foul of the non-period speed cameras.

Steve
Steve Gyles

DJ,

Despite Steve's modern approach I calculated mine with a stop watch between mile markers on the highway.

I then checked my 30mph speed against one of those remote speed detectors that police put up on roads to tell you what you already knew....you are speeding.
T McCarthy

This thread was discussed between 15/05/2008 and 20/05/2008

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