MGB Register Forum

Hello troops.

I wish to have the speedometer in my 'B' recalibrated, it over reads by about 6 to 8 %.

I downloaded and completed the template required by the Speedy Cables web site, and am getting ready to pull the instrument and send it off.

However, I am reading some decidedly mixed reviews on them on the various Forums.....(Piston Heads etc, and the like).

Has anybody any experience of Speedycables please?

Thanks in advance.

Ian
Gosh a 1.6mph error at the maximum allowed in Southwark! Can one actually see the difference whilst driving?

Best overreading than under reading.

I am sure a 6 to 8% overread was acceptable when the cars were built. Within the tolerance of tyre wear over the life of the tyre I expect.

Mechanical drive to a mechanical speedo will never give the accuracy of modern electronic systems

I've used them in the past with Ok service

George

Hah! Yes George, not an issue driving around London, but when I venture outside the M25, I would like to be doing 69.99999 mph, not 62 mph.

But seriously though, what you just said echoed Doug Smith's comments when I ran the same question past him.....

I might as well learn to live with it. Funny, I would probably never have known, were it not for my mobile phone's GPS function......

Ian.

Legally, speedos can over-read by 10% but they cannot under-read. So they can indicate 33mph at 30mph but the can't read 27mph when the car is actually doing 30mph. Manufacturers cynically use this to kid people they are getting a faster 0-60 time than the roadtests achieved! My MG6 reads 55mph at a true 50mph. It is also why trucks travel through roadworks faster than the cars, as their speed is taken from the cab tachograph and is very accurate. So, it might be that Speedy Cables can't improve on the 6 - 8% over-reading of your speed.

Tyres will also cause variations, and here it is the tyre revs per mile that is important. The same size tyres (eg 165/14) from different manufacturers may have slightly different revs/mile. There is also a change in the revs/mile as the tyres wear and the diameter decreases. Change the tyre size and you will get an error as well, so the popular 185/70 - 14 used with alloy wheels may not match the 165/80 - 14 of the standard tyre revs/mile.

Additionally don't rely wholly on GPS based systems. These will only give a true speed indication on a level road. On Inclines up or down the true speed will be higher than the indicated speed. However find a straight level piece of road and note how the speed given by a satnav system differs from the speedo reading and adjust your driving accordingly. You will save yourself £78 inc VAT as this is what Speedy Cables charge for a calibration.

Thanks Peter, a very comprehensive comment....