Hi guys,

Knowing what a clever bunch you are (angling for the flattery tactic here! )

I have the following calculation I need to solve.

problem:

I have an engine/gearbox with a pre-calibrated speedo sender unit - the host car runs on 16" rims and has a 4.10 final drive diff

I however am running on 15" wheels with a 3.62 diff.

How far out will my speedo be at this point?

I am planning eventually to upgrade the diff - found a place that will sell me a new final drive gear for a 7" Sierra LSD - but a reconditioned unit with Quaife internals and this gear is £1000!!! EEEK! So thats for next year, or maybe the year after.

So what I'm basically saying - is - if I upgrade to 16" rims (advice here as well please on handling effects) -

how far out will the speedo be after upgrading

I'm looking to move to 16" as I think I'll need 225 rears to transmit the power, with 205 fronts. I think the limit on 15"s is 205? (Am I correct in this assumption)

Cheers,

Murray

[Edited on 15/7/07 by muzchap]

play around with this

Wheel size is irrelevant. It's tyre size that is important.

E.g. a 225, 40 X16 tyre is roughly the same circumference as a 205, 50 X 15 tyre.

You might find THIS LINK at least partly useful in your calculation.

Drew

Hi Chris,

Cheers for that - using the standard S2k box.

I could have got the S2k diff - but didn't fancy messing around with driveshafts etc etc - I may do one day - when the budget/time allows

Thanks for the advice about the tyres - that'll save some pennies- I might go 205's on the rear then just to give it a little bit more - I don't think I'm as good a driver as you on those vids of yours!

Murray

Thanks Drew - I'll take a look.

I don't mind the speedo being out - just wondering about the magnitude.

I suppose I can drive around with the TomTom and double check - obviously my key trigger points are:

20mph
30mph
40mph
50mph
60mph
70mph

That should keep me away from the Poleizi!

Cheers,

Murray