Re: Speedometer Accuracy

["Steve Makohin" <wateredg@xxxxxxxxxxxx>]

Gregory Appling <gappling@xxxxxxxxxxxxxx> wrote:

> The bike in question: 2002 R1150r
>
> Does anyone know how accurate the speedometers for the R1150r's are? I'm 
> currently trying to figure out if my speedometer is way off or if my GPS 
> units is just so cheap that it's not even close.
>
> Yesterday while running down the highway my speedometer read 92mph, my GPS 
> read 81.7mph and my girlfriends SUV (following closely) was somewhere 
> around 85mph.
>
> Just wondering if this is normal or time to take it in to be checked 
> (still under warranty).

Speedometers are a crap shoot, and not just those on BMW bikes. They tend to 
register on the high side of actual speed, the logic being that they won't 
be to blame for a driver going north of a posted speed limit. Their 
inaccuracy is also not necessarily linear, meaning that a speedo may be 5% 
optimistic at 40 mph, but 10% optimistic at 130 mph. Variances may also 
differ between units of the same model -- ride with a twin of your bike at 
exactly the same speed, and the two speedos may register a few mph 
difference from each other. Further speed inaccuracy may be introduced 
between models of tires, through tire wear, and due to variances of tire 
pressure.  Knowing that these variances exist, and that speedo error is not 
necessarily linear, realize that your odometer is not necessarily accurate 
either, but that's a different matter.

So what does this all mean? Don't sweat that your speedometer does not 
perform with the accuracy of a fine Swiss watch, because it was not designed 
to. If you are still concerned, or you are a real stickler for accuracy, 
report this to your BMW dealer, and ask for an "accurate" speedo, or in the 
very least, ask to see a written document from BMW that states their 
acceptable tolerances for speedometer error. I have read (though I don't 
remember where, and I would not take this statement as gospel truth) that 
BMW allows for up to 13% inaccuracy in their speedometers.

- -Steve Makohin
 '01 R1100S/ABS
 Oakville, Ontario, Canada 

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