Speedometer ´error´

[Petrus]

Yes, another one.

Yes, used the search engine.

As all I get are a older hence a new thread.

Flogging the bike down the local pass the speedometer read 195 km/h.

I know the speedomete by law reads fast with quite bit of margin to compensate for variables.
Also the bike is limited to 180 km/h.

My comment is the rear tyre being bias ply. This means the diameter is subject to increase under centrifugal forces. Meaning that if the software instructions are a linear % (+5 km/h or so), then at top speed the speedometer is more accurate than at 100 km/h
Stands to reason as otherwise 180 km/h plus 10% plus 5 km/h would be 203 km/h indicated.

Btw this is only half serious as top speed speedo accuracy is a bit of a moot subject on a large cruiser

 

[Ischa]

It can always get worse. My speedometer didnt properly reference and was therefore around 40km/u off. (Due to a bad battery)

 

[fbomb.garage]

My speedo is 10 percent out. Which I think is more "outright wrong" than simply "margin" That would make your 195 top a more realistic 176. Try it again with a gps speedo app on your phone?

 

[Petrus]

I will for súre thunder down one of the empty highways one day just to try and see how far the the needle on the speedometer climbs up.
I will trý install an app on the handy and gps the speed although the real top speed is not of much interest to me other than a nice to know.
What doés spark my interest is the app potentiallial registerimh bothe the speedo ´error´ and the tyre growth.

First need the weather to dry and meanwhile find/install an app

 

[Shawn Bedser]

I also tried to top end mine but at 190 km/h on the speedo I started wondering if it was going to be worth the effort and backed off, suspect that it would reach 200 though giving a 180 km/h top end.

 

[Petrus]

tried mine with gps backup and it dialed power back at indicated 195, 185-187 on gps.

 

[Cu Dubh]

My speedo is 10 percent out. Which I think is more "outright wrong" than simply "margin" That would make your 195 top a more realistic 176. Try it again with a gps speedo app on your phone?

My '02 1150GS has always had the 10% speedo 'error'. IIRC from long long ago discussions on the AdvRider forum, this was/is common with BMW's, possibly even the cars. There were some who considered that this may be a corporate choice, for some reason.
Others who are more current on this may chime in with more up-to-date knowledge.

 

[Petrus]

in ye olde days, the speeometers had a % of deviation because of the way the drive worked. With the advent of electronic speedos, the input from the sensor could be given basically any readout profile. As such most modern speedometers have no % error, but a rather constant margin of deviation. How much deviation is a function of law x marketing.

 

[bdalameda]

There is never a perfectly accurate speedometer as there is tire wear to consider. Some manufacturers build in a slight offset to compensate for wear. As the tire wears down the speed reading will increase slightly as the tire is slightly smaller and has to rotate faster for any given actual speed. It seems to me many manufacturers offset this far too much.