Speedometer out 8%?

[SteveO.]

I was reading my manual for my 2011 796 and it mentions the ECU transmits the speed to the display and increases it 8%.  Is it actually reading high or am I misunderstanding it?  Seems weird not to just display the actual speed.  Thanks. ...Steve

[stopintime]

It's supposed to be a safety/legal issue.

They have to make them read higher than actual speed, to allow for changes in readings depending on tire size and behaviour, which varies a little between manufacturers - some tires expand more at high speed than others - a.s.o.

So, to make sure nobody accidently rides/drives too fast (unsafe/illegal) they make them read high.

[Zulu]

They are high, Everytime I pass through those little monitors used by cops that shows your speed on the side of roads, I compare with my bikes speedometer, and my speed displayed on bike is always higher than those cops display.

[Curmudgeon]

The U.S. requirement is something like 3 - 5 MPH @ 60. Would be interesting for someone with a new bike, stock tires and GPS to check the speed with his SatNav and report back.

Here in town we have one of those radar displays, usually parked in a 35 or 45 MPH zone. I seem to recall that mine was close in the 35 MPH range. The programmed error may be less at lower speeds and greater at higher speeds. GPS is the only easy way to confirm.

Any takers? 

[Zulu]

I will try to ride by again tomorrow, but last time I think my speedometer read around 36 and those display was showing 31.. Its on a 2010 696.

[Curmudgeon]

Put some air in your tires!  32.5/36.5 

[SteveO.]

Thanks for the replies.  I thought for sure I was misunderstanding the manual, but it's good to know that it's actually out on my stock bike so I can run a little faster without being over.  Cheers. ...Steve

[WarrenJ]

My 2000 750 works out to about 11% off.  I actually use my GPS as my speedometer.

[sgollapalle]

Stupid regulations.. My theory is they started it with people getting bigger rims on their cars, which would make the speedo read lower than the actual...

At 40mph or lower it will only be over by about 2-3 mph, so you might not notice it. But 8% trickles down to when the speedo shows 100mph, you are only at 92mph

I've checked with the GPS on the car and the cycle, with two different units.. They are pretty close to what the speedo reads.. Again, most units I think only have an accuracy of 100 meters or more, so don't think it is an accurate way to measure speed.

If anyone has a bicycle computer hooked up it should read pretty accurate. (I hope they haven't rigged those too...)

[Curmudgeon]

Stupid regulations.. My theory is they started it with people getting bigger rims on their cars, which would make the speedo read lower than the actual...

The U.S. speedo reg has been around for at least ~ 30 years. No idea when it came in, but for sure speedos read this way in the '70's. Would LOVE to blame it on Joan Claybrook but I'm fairly sure the error existed before the 55 MPH speedometer.  And BOY was that a PITA!!! (It WAS however, dead accurate.)

The practice of this programmed error may have started in Europe, BTW.