Hi All,

I recently replaced my speedo on my Radian YX600. I can't remember the rpm against the speedo on the old one, but the new one feels like it's over-reading - I can't put my finger on why. The other alternative is that the other one was under-reading.

Anyway, at 6000 rpm in sixth gear, I'm doing an indicated 75 mph. Does that sound about right? I think the chain/sprockets are standard.

On the other hand, it could just be me....

best way to do it is with GPS, even a Satnav will do.

on my DT i have a satnav mount on the handlebars (i kept getting lost...) and my indicated speed from the speedo matches the speed on my satnav

easy way to check

could be the size of your wheels. If standard it should be ok, but then again check that the speedo's not off another model (XJ,FZ, etc) the size of the wheel & speedo drive makes a difference, i think (or am i 2 pissed, lol).

Duh! Forgot about the SatNav - that's how I checked my car.....

I'll get a mount for my TT One.

It's definitely a Radian speedo - they're quite distinctive and different to Xj,FZ etc.

You should expect an error on the speedo of not more than 10%.

You should expect an error on the speedo of not more than 10%.

Nearly every single speedo out there is over estimated, as Yoda has said, anyhting up to 10% is quite normal. There's no real way to be 100% accurate while your riding, you can calculate the speed between two point (Speed= distance/time) over a give piece of ground, but again no use at all!

Despite paying a fortune for a M'cycle speedo, the low cost Bicycle ones are more accurate as long as you setup the wheel circumference right, and don't forget as the tyre wears the circumference decreases, so the speedo becomes less accurate.

GPS is probably the most effective method of speed indication. But,,, it all depands on the GPS, and how often it samples, as these will provide an average speed between two points, if those two points are 100m apart then it's no real use, normaly it is only a few meters so it's not a problem. You also need to know the GPS accuracy (if your unit will tell you), the more off-road bais units (mainly Garmin) will report on thier accuracy typically around 3% so your speed could be either 3% over or under at the extreme. If your unit supports WAAS (EGNOS, I think is the European version - WAAS is a USA definitition but the signal and technology is the same, and your GPS will have an option for WAAS, rather than the other vendors) then you can increase the accuracy as WAAS (Wide Area Augmentation System) is a land based system and not at the will of the US military. WAAS isn't as effective over rough ground though, and loosing the signal is very easy!

So there you have it! I've said this before, we have to ride within the law but Mr Plod has all the correct equipment for accuratly recording our speed, it's not fair, or balanced but that's the way it is. Can you imagine if speedo's reported a slower speed than you are doing ?? the courts would be full of litigations against then from drivers & riders who'd got a ticket!!