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Author Topic: How accurate is your speedometer?  (Read 2129 times)

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Offline JBMorse

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How accurate is your speedometer?
« on: June 30, 2009, 01:59:56 PM »
I drove by one of those radar-speed limit signs today and it told me I was going 36 MPH.  My speedo said 40.  Just wondering how normal that is on these old gauges.  Anybody know how accurate their gauge is? 
Btw the odometer seems to work fine and the speedo doesn't act crazy at high speeds or anything, so it pretty much works, it's just off by a little!
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Offline Bob Wessner

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Re: How accurate is your speedometer?
« Reply #1 on: June 30, 2009, 02:03:23 PM »
Sounds about right. I think they all read a bit 'low' even our two Honda autos, also checked via GPS. I'm guessing it is done deliberately to avoid getting us into trouble.  ;)
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Offline Duke McDukiedook

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Re: How accurate is your speedometer?
« Reply #2 on: June 30, 2009, 02:03:59 PM »
All these old 750's register higher spedometer speed than their actual speed.
Just figure for the error to get larger as you drive faster.
Someone had a graph that showed the actual speed compared to spedometer speed somewhere on this forum.
 
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Offline grumpy

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Re: How accurate is your speedometer?
« Reply #3 on: June 30, 2009, 02:07:11 PM »
depends on the size of your front tire, too...

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Offline OldSchool_IsCool

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Re: How accurate is your speedometer?
« Reply #4 on: June 30, 2009, 02:11:23 PM »
5 MPH optimistic sounds about right.
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Offline MCRider

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Re: How accurate is your speedometer?
« Reply #5 on: June 30, 2009, 02:13:09 PM »
Quote from: JBMorse on June 30, 2009, 01:59:56 PM
I drove by one of those radar-speed limit signs today and it told me I was going 36 MPH.  My speedo said 40.  Just wondering how normal that is on these old gauges.  Anybody know how accurate their gauge is?  
Btw the odometer seems to work fine and the speedo doesn't act crazy at high speeds or anything, so it pretty much works, it's just off by a little!
A 10% error at 40-60mph is very common, even on modern bikes/vehicles. Should be expected. If you read magazine road tests, Cycle World, Road and Track, etc. they usually publish the speedo error.

Harley's are the worst. High end German stuff (BMW) is best (I think).

That's why people claiming high speeds based on their speedo's can be taken with a grain... of alcohol.
« Last Edit: June 30, 2009, 02:15:44 PM by MCRider »
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Offline flybox1

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Re: How accurate is your speedometer?
« Reply #6 on: June 30, 2009, 02:16:37 PM »
lots of those 'traffic calming' devices around my parts, but I put them to good use  8)
speedo is always +3-5mph over actual.
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Offline Laminar

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Re: How accurate is your speedometer?
« Reply #7 on: June 30, 2009, 02:20:02 PM »
Quote from: flybox1 on June 30, 2009, 02:16:37 PM
lots of those 'traffic calming' devices around my parts, but I put them to good use  8)
speedo is always +3-5mph over actual.
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Offline Inkscars

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Re: How accurate is your speedometer?
« Reply #8 on: June 30, 2009, 02:30:15 PM »
Going "42" on mine is actually 35 or 36.
I was doing "75" on the highway and was told I was hardly breaking 65 though. So mine must be higher the faster I'm going.
So, I guess that said, I'll have to "do" 130 to be in the ton-up club.  :D
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Offline Gordon

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Re: How accurate is your speedometer?
« Reply #9 on: June 30, 2009, 05:02:13 PM »
Quote from: Inkscars on June 30, 2009, 02:30:15 PM
I was doing "75" on the highway and was told I was hardly breaking 65 though. So mine must be higher the faster I'm going.

That's normal.  Speedometers are typically off by a certain percentage, so the faster you're going, the larger the discrepancy. 
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Offline fmctm1sw

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Re: How accurate is your speedometer?
« Reply #10 on: June 30, 2009, 05:15:11 PM »
Mine's not accurate at all but I'm too chicken to try to tear it apart and clean it up.  I've had a "parts" speedo open before an don't want to chance ruining the odometer.  My tach is actually a very good indicator of speed (in 5th gear)...
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Offline Johnny5

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Re: How accurate is your speedometer?
« Reply #11 on: June 30, 2009, 07:29:52 PM »
I drove past one of those radar signs the other day and my speedo is almost spot on. Was only off by 1 mph. I was shocked as this is the first bike I've had where the speedo was this close.

My 06 Vulcan is off by 8% which is normal for motorcycle speedos.
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Offline Dave-and-his-550

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Re: How accurate is your speedometer?
« Reply #12 on: June 30, 2009, 07:56:55 PM »
So if the manual for our bikes say top speed is 115, then really it would be reading somewhere in the 120's on the speedo?
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Offline BobbyR

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Re: How accurate is your speedometer?
« Reply #13 on: June 30, 2009, 08:14:04 PM »
I am sure mine reads low when going fast, which is good. It makes me feel daring.
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