Topic: 550K Speedometer Error Measured

[CoachDoc]

For no particular reason I decided to measure the accuracy of the stock speedo on my stock '74 550. It was always clear to me that the MPH readings were optimistic! but how much so? I velcroed my Garmin to the tank and off I went. I found a consistent error of 4 mph, from 20 to 90 indicated, and as I suspected the speedo consistently overstated the mpg. My front wheel is stock, and I'm running the stock front tire 3.25x19 with very little wear.  I think the same was true for most cycle as well as automotive speedos of that era. My newer bikes are usually right on the money.

[seanbarney41]

hmmm, very interesting, thanks for posting.  This may explain why MJStone always rides so slow on the relay rally, but swears his 500's speedo is nearly perfectly accurate according to his gps.  I don't know what kind of gps he has.  Maybe he will be along at some point to comment.

[Airborne 82nd]

Well I don't have a gps or Garmin Hell I don't have a cell phone. But I do live in a small town and know the local leos and they have all that stuff and it is calibrated every year along with the speedometers in the cars. So I get him to go down the nearest four lane and light me up at 45 55 60 70 and I am off 10mph above what he is reading. This is on a 78 750K stock wheel & tire. That is why every one is flying by me all the time.  I can do the ton in a heart beat and don't worry so much about speeding tickets when out of town

[Jayelwin]

I've never seen an accurate speedo. My vstar has more of a sliding scale. Instead of a fixed amount of mph under its more like consistently 10%. Never tested my 750.


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[flatlander]

yes 10% under seems about right for my stock 550, also. i often ride with a gps and usually when it shows about 120kph the speedo is around 130. with the gps at 155kph the speedo shows an optimistic 170.

[Kenzo1979]

Passed one of those "your speed" signals on the highway.  My stock '74 550 read 65mph, signal read 60mph.  Seems to have the same percentage of error.