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Aftermarket speedo error

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Joined: Thu Oct 18, 2007 1:19 am

Aftermarket speedo error


Post by ArizonaMike » Tue Aug 15, 2006 1:20 pm

I did the highway side-by-side speedo comparison with a car and learned when going 60, my aftermarket speedo reads 55. Does this mean it will read 5 mph slower all through the range or will this difference
change? (It's hard to do the side-by side test at slower speeds than high way since two vehicles in one lane are illegal at slower speeds/roads.) I ask as I'm trying to determine my true mpg. Thanks in advance for any help.


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Re: Aftermarket speedo error


Post by Billy » Wed Aug 16, 2006 6:02 am


Forget side-by-side for slow readings...
Just inform your *chase car* driver before he follows you, that at 20- 30- 40- 50- 60 mph you will raise your hand at each speed, as you reach them. Have chase car driver check his speedo at every interval, & carefully scratch down his speed (each time)....later compare notes..
Do remember; that a taller tire will slow the mph, slightly, + a low-profile tire will make speedo read faster than accurate..

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Location: Michigan, USA

Re: Aftermarket speedo error


Post by 57pan » Wed Aug 16, 2006 4:06 pm

If you have a gps you can use that to check your speedo.

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Re: Aftermarket speedo error


Post by kell » Wed Aug 16, 2006 11:12 pm

To answer the question you actually asked, no it won't have a 5 mph error all through the range. Assuming your highway test was accurate, add one eleventh to the speedo reading, or 9%.
55 + 9% = 60mph.
33 + 9% = 36mph.

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Re: Aftermarket speedo error


Post by Toymaster » Thu Aug 17, 2006 1:34 pm

I find it easiest to take it out on an 'interstate' highway with mile markers run off 10 miles, etc [or 20, or any amount really, just that 10 is easiest] then compare it w/the odometer reading, and compute the % deviation..
And yes, it would be a % diff for speedo, not a MPH diff..

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Re: Aftermarket speedo error


Post by ArizonaMike » Fri Aug 18, 2006 5:07 pm

Thanks to all who responded to my speedo error. It appears that the odometer registers miles plus or minus, depending on the bike's speed. In other words, it states a different distance travelled when going the
same distance at 40mph and at 60mpg. This makes computing for maintenance and determining mpg somewhat harder. I know I'm not getting 58 mpg, probably closer to 48-50, going no faster than 55 mph.

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