Alloy Wheels Relation to Speedo

[twim]

What is the relationship between an increased wheel size and the effect it has on the Speedo (not giving correct readings)?

I ask as I have an SR (1.3) with 15 Inch wheels and was wondering if there was a way of re-calibrating the Speedo to give correct speed readings? One way I was considering was to re-label the Speedo according to the speed of another vehicle.

Can I have anyone's comments or suggestions.

Thanks

twim

[burgessovsalford]

YEAH I THINK IT WILL DO SOMEHTING TO YOUR SPEEDO, BUT PROB NOT ALOT ON 15" WHEELS.

THERES WEBPAGE ABOUT THIS, WHICH ACTUALLY CALCULATES THIS OUT FOR U... CANT FINK WOT ITS CALLED THO???

SOMEONE WILL KNOW IT ON HERE??? ITS A NOVA WEBSITE ASWELL...

[Dicko]

not worth it as nova clocks read high anyways byt putting slightly bigger wheels on it is probably correct upto about 70mph, then it will still read higher lol.
if u have 45 profile tyres on its almost the same as having 14" wheels with 65 profile so i wouldnt worry!!

[twim]

The problem is that its about 15mph off all the way round the clock! what else cud it be other than the wheels its not jerky so its not the gearbox conection!

[ade]

you can try these (not the one that was on here ages ago though)
http://www.miata.net/garage/tirecalc.html

http://www.geocities.com/lrc_act/4wdstuff/tyre.htm

top buzz says this -

http://www.knighta.f9.co.uk/info/wheels_tyres/wheels_tyres.htm

and for those that are paranoid try this (dunno if it works on a nova)

http://www.blackrobotics.com/desc.htm

Ade
:wink:

[Dicko]

15mph off all the way round the clock!

well that makes no sense, unless ur needle has been bent round or something lol. so it reads 15mph when ur stoped.
they are usualy a little out at 30-40, a bit more at 70, then way out at 90+

[twim]

Its the fact that the needle climbs too fast. it will shoot to about 20 when am clearly doing about 10!

[mikeoxford]

if youve changed your closk (fitted a dial kit or etc) u may have refitted the needles incorrectly

if not maybe you just need a new set of clocks as these sound shot......?

[ade]

get a m8 to pace you in an unmodded car with a mobile - and when he hits 70 mark the speed on the glass with a pen or summut. Then just adjust the clocks based on the amount being out, then take for another spin and keep adjusting them till right.

or summut like that!

Ade

[Nova-Boy]

You can send the dimentions of your wheel and final drive away to a company (cant think what they are called at the min) and they will will produce a gearbox to fit inline with your speedo cable to sort out incorrect readings.

Does anyone find they gain top end but loose acceleration having bigger/wider tyres on??

My 1.2 strains a bit more now i have gone up from very thin 13"s to 195 15"s. :cry:

[twim]

How do i adjust the clocks though??? is there like a screw i can turn?
It has the mark one lockwood dials on if that helps??? I have replaced the needle as it was resting at about 10 mph but the problem is still there.

Thanks

Twim