speedo

[nicko]

hi,i have installed good speedo cable,but it reads at least 10mph faster than what im doing,i have a FE with 132 grey motor ,is there a different type for 138's which might cause the problem?
cheers Nicko

[robbzfc58]

g'day nicko     speedo cable wont make a difference but tyre size will.....smaller the tyres  the faster the speedo
or the diff ratio will do it too
        cheers trev

[nicko]

the diff is stock as car revs high on hi way at 60mph and it has 75series tyres.maybe speedo is stuffed?

[Jodstar]

My FC wagon revs high so i can only asume that
ute's and wagons are geared down. I have been
thinking of changing my diff center for better economy.
Does anybody have any ideas on good ratios ,as i have
been told models up to HR will fit? ??? ??? ???

[nicko]

yes thats what im planning to do soon,the 3.55 ratio centre is the suggested best all round ratio for a stock grey.

[Burnsy]

Just changed to 3.55 on my EK with 138 and hydramatic.  I have only driven it 2km as the brakes are still being fine tuned but it definitly seems to drive better than the old 3.89.  Centre was from a HR.

Would be interested to hear from anyone who has had their speedo recalibrated to read correctly after changing diffs (using original box that does not allow for simply changing the plasic coloured cog on the end of the cable).

[RET]

Nicko,

Your tyres are the most likely culprit, although it could possibly be your speedo as well.  75 series tyres are way too small for stock drive-line.  At 60mph it will be revving its head off.  Remember that these things were originally calibrated for "balloon" cross-ply tyres.

85 series tyres will give you a much closer speedo reading if you keep the stock diff, but you would probably find highway cruising much more comfortable with a 3.55 diff.

cheers
RET

[sgo]

This calculator may be of help when looking for the right size tyre for speedo error?
http://www.miata.net/garage/tirecalc.html