speedometer/odometer question

[weeman]

Am I right to assume that if my speedometer is 3% inaccurate then the odometer is inaccurate by the same degree?

I'm trying to work out my mpg after the IOM weekend and want to make sure that I'm using the correct info.

TIA

 

Be lucky!!

 

Martin

[Sheds Moderator]

Yes.

[Garth]

Not necessarily! My speed compared to my satnav varies by about 5% whereas my odometer readings vary about 40%! Am still trying to figure it all out. One year old standard gear on a Sigma 125

[Domus]

On mine, 150 Sigma, speed is quite accurate however the odometer only registers 7 miles for every 10 the sat nav covers. Nick at Caterham Midlands suggests I get the sensor closer. I am not convinced.

[Lambretta]

The mechanism for recording these on traditional speedo's is different. The Odometer is typically connected directly to the cable through gears whereas the speedo uses other means such as rotating magnets/discs.

 

The above is based on knowlege from when Dodo's where a future concept for the Pterodactyl so who knows how they work now.

[Fil M]

If its any help my speedo is all over the place for first quarter mile but the odometer trips around steadily so they seem seperate. Perhaps we could all do a tally from Wickham on Friday to see how all the cars compare ... that might give a good idea Martin.

 

Fil

[lavena]

As has been said - it depends. MY speedo/odometer use the same sensor on the rear axle - a toothed disc and sensor. For this set up the sensor may not always see each tooth on the disc and therefore under-reads. But....

 

The speedo - which is a needle - damps out the missing teeth and under reads but because it damps it out you can miss the impact of a single missed tooth.

 

The odometer - numeric - seems to count the pulses from seeing each tooth.

 

So - I had calibrated my speedo to match the GPS but the odometer was still under-reading by around 20%.

 

Fix was relatively simple - move the sensor even closer to the toothed disc (ensuring it doesn't catch). You can tell if it sees each tooth by rotating the wheel - an LED lights up on the sensor.

[JetSepter]

My speedo, now some two months and - supposedly - 2100 miles old, is really no more than a cheerleader these days, ie rather than give me information, it waves around a lot to encourage me. Thanks be for the Garmin. In general, when it works, it is 5 mph faster than the GPS. When it quits entirely, as it does from time to time - no doubt when its needle gets tired from all that waving - the odometer gives up too. Till now, I had not thought to check the odometer reading against the GPS. But it's likely to be the sensor, eh, rather than a fault in the speedo head? I must take it back to the factory - but why can't they get it right from the start? Never had the problem with the Wolwo (or any other car that I have had, come to that).