Speedo error..?

[James.Burton]

Since picking up my '96 VXi 4 years ago, the speedo has been under reading by almost 25%.

I had thought this may be down to somebody replacing the final drive with a 3.14 or something like that.

However I realised that in 3rd I hit the rev limiter around 150kmph. From tech specs sheets that's 6800 rpm (the needle of the rev counter waggles so wildly when accelerating you can't read it). Doing some maths with 559mm diameter ZZS tyres, and assuming standard ratios in the gearbox, the standard 3.92 final drive would max out at 145kmph. Close enough given wheel diameter changes with speed, pressure, temperature.

Further checking at my best estimates of a constant 4000rpm, and GPS speedo readings in 1st, 2nd, 3rd, 4th it would seem to confirm standard final drive. So I assume the gearbox and final drive are standard.

BUT the speedo is still under reading by almost 25%. Does anybody have a clue how can that be?

[Alastair B]

Assuming you have a Type 9 gearbox then a good place to start is the speedo drive gear which is a small replaceable component with different colours and ratios, also you could look to get a modified speedo angle drive with a custom ratio to adjust, check the archives with a google search there is lots on this topic.

[JonT]

Mine wasn't that far out, but it was a good 10-15% out (although not so much on the milometer, which I found even more odd). Discovered the gearbox connection was also weeping slightly, so in the end binned the lot, fitted blanking plugs in the gearbox and an electric Racetech speedo driven off the front brake disc bolts. Bonus is that it's very easily recalibrated if I change to a different tyre/wheel size with different rolling radius.

The gearbox pinion drive seals were horribly worn so it wasn't surprising it was leaking. Although the cogs can be changed, I was told mine was as close to accurate as it could be made to be anyway.

[Jonathan Kay]

Private Message sent.

[James.Burton]

Thanks to all for the tipps. I'm getting a better understanding, of what's going on in the gearbox and final drive. Not quite figured out the speedo yet, but having fun in the process.  :)