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Incorrect Speedo reading on 1150RT


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Can I get some feedback concerning the accuracy of my Speedo as compared to what others see? I have a 98 1100RTP with the 120MPH Speedo and according to my GPS the Speedo is off by 2 MPH(reads 65 when GPS says 63) which isn't bad in my humble opinion. The same GPS on my 2002 1150RT (has 150MPH Speedo) reads 59-60MPH when the Speedo says 65MPH. I think the difference gets a little wider the faster I go but I wasn't able to document due to traffic. I think a 10% error is rather substantial but wanted to know what others see as normal. The tires on the 1150 are 120/70ZR17 and 170/60ZR17.


I am assuming if you are reading a faster speed than actual that you are also recording more miles on the odometer than you actually ride. Is this true?

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My 1150RT reads about 4-5 mph fast at highway speeds. I understand this is more or less on purpose. I also read that the odometer should read correctly, but I never checked that against the GPS. I guess that would be easy to do.

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Evening HHO


Most 1150RT's do read higher than actual. I had an 02 1150 that showed 109 @ 100 actual. Some are closer some are a bit farther.


As to the odo reading incorrectly?--very possible but as they are linked to the same drive cable-- but the amount of error might not be the same as the speedometer calibration might be farther off than the mechanical odo drive.


Front tire size (actual circumference size) not sidewall marking size is not the same on all tires & amount of wear contribute to speedometer error.


Also the front tire circumference changes as the bike leans into a turn so that can effect spedo & odo accuracy.


Then you have GPS errors due to the GPS truncating the measurement points in curves & basic GPS error when going up & down hills. (on a straight level road a GPS is pretty accurate though)

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very interesting......I guess mine is normal and the comments about a speedo on an authority bike being more accurate seem to be true. I will give the gps a try on a long flat straight road to get an accurate comparison and then I will know for sure. I think the errors are a conspiracy to make us think we are going faster than we are, that the bikes ride better than they actually do at speed, and that we get better gas mileage than we actually do. Marketing at work............

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There's also an old BMW Service bulletin put out to stop dealers from trying to warranty speedos for errors.

The approved error is 10% plus 2.4 %

The odo is correct, but the speedo is intentionally off.

On the RT-P models, the speedo is to be very close to correct as agencies check calibration from time to time. Obviously it's meant to be correct with the Authorities specific tire to the year and model of bike.


Here is a link to the old bulletin. The bulletin was reissued in 1996 or 99 if memory serves but basically says the same thing.



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Morning Tri750


The approved error is 10% plus 2.4 %



I think that is supposed to read 10% plus 2.4mph. At least that is what my BMW bulletin says.

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fun info to know! thanks for the responses. so much for German precision.


Morning HHO


Not so much German precision but mostly US federal speedometer laws & the possibility of variables in front tire circumference variations. (the way BMW sends bikes to US it complies with US speedo laws with most available front tires & avoids fines for not meeting US requirements).



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Hi Harold -

My 1100RT is "optimistic" as well - it's a percentage for sure, and not a MPH number - something like 7-10% above GPS speed is usually what I see.


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thanks everyone for the replies. I guess I will have to remain in the dark about my actual speed as I ride! Now I am terrified that I might get a ticket for going too slow.

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