speedometer accuracy - MVAgusta.net
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post #1 of 11 (permalink) Old 01-26-2007, 03:11 PM Thread Starter
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speedometer accuracy

So, I have been following the "how fast have you gone..." thread, and of course the question about speedometer accuracy comes up.

As it would turn out, the local police (Irvine, CA) have set up a trailer in our neighborhood that has a radar gun and the "Your Speed Is:" sign on it. I've been checking my indicated speed vs that sign for the past week and the two are in complete agreement on my 05 1kS F4. I've tried at various speeds, from 20 up to 55mph, and it's always the same. Right on the money.

I've also check against some other radar signs in some faster zones, up to about 80mph, and again, same results.

I believe that on my particular 1kS, the speedometer is pretty much dead-nuts on.

For reference: I have stock gearing, on a 190/55 Michelin Pilot Power rear.

Curious to see if others have found the same thing.

Alex
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post #2 of 11 (permalink) Old 01-26-2007, 03:15 PM
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i think were people start questioning the speedo integrity is on the upper north side of 100mph. in other words, the land speed record was at 182 or something on the R, but whatever that speed was i know people have posted seeing "indicated" speeds faster than that.
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post #3 of 11 (permalink) Old 01-26-2007, 03:18 PM Thread Starter
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so, the error is non-linear?
really?

i'm not exactly sure how these things work, but my understanding is that it's a pulse counter driven by a hall-effect sensor which is mounted to a wheel on the output shaft of the transmission. is that not right?

what nonlinearity effects would come from such a system? other than say tire slippage and distortion?

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Originally Posted by style_one
i think were people start questioning the speedo integrity is on the upper north side of 100mph.
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post #4 of 11 (permalink) Old 01-26-2007, 03:33 PM
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Quote:
Originally Posted by altoon
i'm not exactly sure how these things work, but my understanding is that it's a pulse counter driven by a hall-effect sensor which is mounted to a wheel on the output shaft of the transmission. is that not right?

Yes that's it, 12 tooth??. You'll remove the toothed wheel when swapping countershaft sprockets. Sensor is mounted to the sprocket cover.

JamesC

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post #5 of 11 (permalink) Old 01-26-2007, 03:34 PM
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my gsxr1000k5 speedo was a lot happier than my 1000r at 100 miles an hour my mv said 90 compared to the gsxr my ducati was the same so much for the honourable japs
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post #6 of 11 (permalink) Old 01-26-2007, 04:06 PM
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Sometimes I have to doubt the accurancy of those "Your speed is" machines. By the Rose Bowl, Pasadena PD set one up and at time it says your speed is 40mph when my car's speed is saying 25mph and based on a visual, there's no way I'm doing 40mph.
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post #7 of 11 (permalink) Old 01-26-2007, 04:43 PM Thread Starter
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Allan - I have also wondered how often, if at all, those radar guns are calibrated. However, I have been checking against a couple of different ones, and doubt that they are both off by exactly the same amount of error.
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post #8 of 11 (permalink) Old 01-26-2007, 06:02 PM
 
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I have an 04 brutale that shows about 15% slow, while on group rides others hit 100mph and I never show more than 80. Before someone asks, yes I am pacing with them.
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post #9 of 11 (permalink) Old 01-26-2007, 06:55 PM
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my '07 910R.....
one of the most ACCURATE bike speedos i've seen

40 on bike = 38.8 (GPS-verified)
60 on bike = 58.2

120 on bike = 116.9 on the GPS

pretty darn good, i'd say



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post #10 of 11 (permalink) Old 01-26-2007, 07:05 PM
 
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Two point to make:

Radar gun accuracy is affected by the angle of approach. In other words, unless the radar beam is pointed perfectly head on, inaccuracy results. The more acute the angle, the higher the discrepancy (it will read slower than actual speed).

At high speeds the rear tire is running a constant slip. If the speedo is reading rear wheel RPM it will be inaccurate at high speed. The higher the speed, the greater the amount of slip due to wind resistance. Picture taking a snowplow and trying to push a huge lead block across a parking lot. Wind resistance is the lead block and your motorcycle is the snow plow. Years ago there were tests done at Daytona measuring front wheel speed VS rear wheel speed and the results were astounding. rear wheel was indicating more than 10mph difference (higher) than front wheel due to slippage.
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