I don't need a 5-speed, I need the right diff!

[Cannonball Bob]

Knew there was something odd going on...

So, the revs and indicated speed pretty much match and are as expected, however I just got this feeling the car wasn't going as fast as it said it was, so with the aid of a GPSr, sure enough, she's over reading by between 10 and 15% across the entire range.

This means that at a steady 4500rpm she's only doing an embarrassingly lethargic 74-ish mph.

Can someone point me in the direction of the on-line diff/wheel size/speed calculator that I used to have a link for?

And how easy is to swap a diff for a less "hill-climby" one, one that's a little taller to relieve occasional long(er) cruising on motorways. Once the diff is sorted I may then look again at the 5-speed idea.

[DohNut]

 

Try the quaife site or DVA power

[peterg]

or here

[knowley]

MPH calculator here

[Cannonball Bob]

So.....after much burning of midnight oil (see time of posting for an idea), I've come to the conclusion the ratios and final drive are, in fact, correct and the speedo is over-reading a bit, well quite a lot actually.

Still, at least I can stop faffing around now and focus on adding a fifth gear.

[shn7]

If you have the CC electronic speedo have you tried changing the dip switch settings on the back. If you do a search you'll find a link to the caerbont site which has the switch positions define IIRC. I had the same problem and changing the settings has brought the indicated speed much closer to actual (GPS measured) speed.

 

Steve.

Sussex (West) AO

Not forgetting Percy the Polar Bear