speedometer

[davehaynes]

changed my wheels a few weeks back and my new ones are slightly smaller so this has put my speedometer out slightly.
what can i do to put it right? any way i can reset it or anything.
thanks.

[meritlover]

you would have to calibrate it again to suit the wheels.
its not so much the rims, but the over all diameter of the tyre. just bear in mind it will be out, or get a friend/lover/collegue to drive at 30 in front of you and you can check or mark your actual speed on the dials.
it is better the wheels are smaller because the car will be slower than it says on the speedo. so you will avoid tickets.

[davehaynes]

how do i go about re calibrating it?

[meritlover]

seriously, if we're talking about the std analogue/mechanical speedo there is no point. you can squeeze the rotors closer to the magnet to make it increase speed or you can bend them away to make it read less, you could re scale your dials or mark on the glass with a sticker, or you could calculate how much of a discrepancy there is and calculate what type of gear you would need on the diff and speedo drive pinion to give you the correct speed for the given wheelsize then have it made up, strip your gearbox and put it in.
you could take it to a dyno and get exact speed on the rollers and use this to check the range and hysteresis of the gauge as well.








or you could live with it.

[Jack]

Bear in mind the standard speedo is stunningly innacurate anyway.

Mine reads 1.4% out (reads 71 @ 70mph, according to two GPS's) and thats with 195/60/R15 tyres, so you can imagine how pants the standard tyres would have been lol

[Philsutton]

Ive noticed that on the corsa when on the rollers that the speed was about right with my speedo, however that is with 195/55/15 tyres lol, so yes as jack said imagine how wrong it would be if I was on the original 13s.

[meritlover]

oh yes, just imagine! lol

[matt_vaughan]

Dam, just put my steelies back on (knackered Alloy tyres...no money)

Better under-speed.