speedo calibration

[spanners]

anyone know an easy way to calibrate the speedo drive or if you could change the drive gear on a reliant g'box to get correct speed reading when running 14 inch wheels on reliant rear axle

[toad]

yep tis dead easy follow yer mate up the road at a set speed then remark ya speedo!

[spanners]

yeh thanks for that  but i'm looking for something more high tech maybe a g/box from a commercial tachograph drive cable

[Manky Monkey]

Give Speedy Cables a ring. Their link's in the Links for commercial purposes bit of the forum.
They use exactly that -a modified tacho drive. They'll send you a photocopied slip of paper with an equation on it -a few measurements they require, (rolling circumference of the tyre, number of times your gearbox speedo cable output revolves to number of turns of the wheel etc). You enter the measurements in the equation & send it back to them with the details of length of speedo cable you need & it's fittings. In a week or so they send you a shiny new cable with a matchbox sized recalibration unit fitted in-line in it. It contains a couple of cogs & by mixing & matching them, they can speed up or slow down the cable so that your speedo reads correctly.
I was going to fit one on my Reliant trike but went for a front wheel driven one instead. The recalibration thingy costs 45 quid. They also do 90 degree angled drives for 35 quid. 

[spanners]

tanks a lot thats just the job cheers