Over - reading

fontana · Post by **fontana** » Thu Nov 24, 2016 6:32 pm

I've noticed BMW speedo's are particularly bad for this.
Every one I've had was over - reading.
The worst was a K1100RS which was a reading good 10mph under out from 70mph.
My current car over reads by 2/3moh, and my Yamaha Thunderace is pretty much bang on.
However my R1100RS is a reading a consistent 6mph over from 30mph all the way up.
I'm using GPS to compare, which I assume is the most accurate way of gauging speed.

Al · Post by Al » Thu Nov 24, 2016 6:34 pm

Look on the bright side, you shouldn`t get done for speeding,

fontana · Post by **fontana** » Thu Nov 24, 2016 6:42 pm

Al wrote:Look on the bright side, you shouldn`t get done for speeding,

Eh

If I'm showing a ton on my 1100RS, that's still 94mph
I believe pod would consider that a viable stop

milleplod · Post by **milleplod** » Thu Nov 24, 2016 6:51 pm

fontana wrote:
Al wrote:Look on the bright side, you shouldn`t get done for speeding,
Eh

If I'm showing a ton on my 1100RS, that's still 94mph
I believe pod would consider that a viable stop

Do you do that everywhere then....?

Pete

fontana · Post by **fontana** » Thu Nov 24, 2016 7:09 pm

milleplod wrote:
fontana wrote:
Al wrote:Look on the bright side, you shouldn`t get done for speeding,
Eh

If I'm showing a ton on my 1100RS, that's still 94mph
I believe pod would consider that a viable stop
Do you do that everywhere then....?

Pete

Trying to start an argument again.

milleplod · Post by **milleplod** » Thu Nov 24, 2016 7:23 pm

Do lighten up Fontana! I meant that you might get saved from a ticket at lower speeds, because of your over-reading speedo, that's all.

Pete

fontana · Post by **fontana** » Thu Nov 24, 2016 7:50 pm

milleplod wrote:Do lighten up Fontana! I meant that you might get saved from a ticket at lower speeds, because of your over-reading speedo, that's all.

Pete

Erm
You could have just said that

Herb · Post by **Herb** » Thu Nov 24, 2016 8:00 pm

Speedos are allowed by law to over-read, but not under read. I can't remember if it was law or a guideline, but I seem to remember that max allowable over-read was 7%.

GPS speed is pretty accurate, whereas your speedo has to be designed to allow for different tyres, tread depths, pressures etc, all of which can have a cumulative effect.

10mph at 70 is a lot, but I'm not that surprised. My old Ducati was pretty poor too. Thinking about it, there are probably more variables that could affect the reading on a motorbike, with allowance for tyre sizes, profiles and the fact the effective radius changes as you corner that would have to be designed into a mechanical system.

milleplod · Post by **milleplod** » Thu Nov 24, 2016 8:06 pm

At an indicated 30, my ST is doing an actual 27....as confirmed by a mate with his LTI 20/20!

Pete

fontana · Post by **fontana** » Thu Nov 24, 2016 10:05 pm

Herb wrote:Speedos are allowed by law to over-read, but not under read. I can't remember if it was law or a guideline, but I seem to remember that max allowable over-read was 7%.

GPS speed is pretty accurate, whereas your speedo has to be designed to allow for different tyres, tread depths, pressures etc, all of which can have a cumulative effect.

10mph at 70 is a lot, but I'm not that surprised. My old Ducati was pretty poor too. Thinking about it, there are probably more variables that could affect the reading on a motorbike, with allowance for tyre sizes, profiles and the fact the effective radius changes as you corner that would have to be designed into a mechanical system.

Great answer
Cheers for that

Tapio · Post by **Tapio** » Fri Nov 25, 2016 4:24 pm

Herb wrote:Speedos are allowed by law to over-read, but not under read. I can't remember if it was law or a guideline, but I seem to remember that max allowable over-read was 7%.

In fact, I think there’s a EU law that says that it’s mandatory for speedos to be a little bit on the over-read side of true speed.
Haven’t checked my bikes, but the car I had earlier (M-B E430) showed ca 3 km/h too much regardless of speed. It was clear that it had a built-in over-read feature.

Pete. · Post by **Pete.** » Sat Nov 26, 2016 7:32 pm

Herb wrote:Speedos are allowed by law to over-read, but not under read. I can't remember if it was law or a guideline, but I seem to remember that max allowable over-read was 7%.

It's type-approval - 10% over 0% under. There has to be a tolerance because different tyre profiles/pressures/states of wear means that there will always be a possibility of variation from new. That tolerance can't be 'under' obviously or you could be speeding in the belief that you're observing the law, so they allow for 10% over.

nab 301 · Post by **nab 301** » Sun Nov 27, 2016 7:42 pm

Up to 10% optimistic is average but Enfields seem to be consistently in the 20% optimistic bracket. It always makes me smile when I hear a new Enfield owner suggesting that their pride and joy can "cruise" at 70mph

fontana · Post by **fontana** » Mon Nov 28, 2016 7:54 pm

nab 301 wrote:Up to 10% optimistic is average but Enfields seem to be consistently in the 20% optimistic bracket. It always makes me smile when I hear a new Enfield owner suggesting that their pride and joy can "cruise" at 70mph

I had a K1100RS that was under by 10mph at 70.
It took me a while for the penny to drop.
The old K bikes are quite noisy, and do feel like they're going faster than they actually are.
I couldn't understand why all of a sudden I was spending most of my motorway time in the loser lane being overtaken by pretty much everything.