GPS or Speedometer:Which one do I believe?
Club Member
Joined: Nov 2008
Posts: 5,481
Likes: 4
From: Georgia
My 2000 Springer had a certified speedo. Guess that might have been on. 3 mph off doesn't sound too bad. If they are consistently 3 mph off they must be very precision to stand calibration like that.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,897
From: Bedford UK
Its not just your bike speedo that is inaccurate, all vehicles vary and have done since the speedo was invented! There are variations in the accuracy of the speedo itself, also tyre wear to consider.
The speedo on many bikes is driven directly by a wheel. From fitting a new tyre to wearing it down to the wear marks is around a 2 percent difference. Later bikes tend to have gearbox driven speedos, but the same applies. So every vehicle with a speedo and mileometer has that sort of variation as an integral feature. 'Twas ever thus!
They cannot be as accurate as gps, which is using several satellites to monitor your every move....
The speedo on many bikes is driven directly by a wheel. From fitting a new tyre to wearing it down to the wear marks is around a 2 percent difference. Later bikes tend to have gearbox driven speedos, but the same applies. So every vehicle with a speedo and mileometer has that sort of variation as an integral feature. 'Twas ever thus!
They cannot be as accurate as gps, which is using several satellites to monitor your every move....
Outstanding HDF Member
Joined: Jun 2007
Posts: 2,649
Likes: 2
From: x
Once you know that the speedos are off and by how much (mine is 3 over also) I go with the speedometer. Remember that the GPS reading is always a little behind and, if you are in terrain where the satellites are masked, very inaccurate for an up to the second reading. Steady state riding though, the GPS is more accurate.
Outstanding HDF Member
Joined: Mar 2006
Posts: 2,755
Likes: 12
From: Commerce, Mich.
I wish mine were only 3 mph off...on my 2006 Ultra, it was 4-5 miles off at 70 mph, on the 2008, its as much as 6 miles off at 70 mph. On the wifes deluxe, it seems to be close to right...(that or she can't read her speedo...she is always telling me that I am going too slowly, and should move up to speed limit while the GPS says I am slightly above speed limit...)
No matter...I trust the GPS to be accurate, and thats the reading that I use.
No matter...I trust the GPS to be accurate, and thats the reading that I use.
Extreme HDF Member
Joined: Sep 2005
Posts: 11,615
Likes: 50
From: Baton Rouge, LA
You can bet the GPS is right on the money, and the 3mph difference is about the normal error purposefully programmed on all late-model HD's. In the past FLH models had "certified" speedometers that were guaranteed to be within 2%, but no longer. My '96 RK's certified speedo was 1mph slow at 60mph. Almost all speedometers on cars and MC's are fast, some as much as 6%. I have speculated that this is a legal issue to insure that the vehicle is going no more than the indicated speed, even after modifications like larger tires, etc. My '07 SG is 4% fast (showing 62.5mph fast @ a true 60mph) when compared to the GPS as well as checked with mileage markers and a stopwatch.
Last edited by iclick; May 22, 2009 at 10:57 AM.
Grand HDF Member
Joined: Dec 2007
Posts: 4,999
Likes: 55
From: Bay Area
I have the 550, and since I dropped the front gear because of the 103 build, my speedo is 4-6 mph off. 75 is about 68-70, and 110 was 104 on the speedo. The differences are not going to be the same across the entire speedo range at different speeds. Its not like the old cable drives. So you cant say if its 3 mph off its that way across the board. I trust the GPS
Road Warrior
Joined: Oct 2006
Posts: 1,282
Likes: 2
From: Broadview Heights, OH
Absolutely go with the GPS, both of my last Harley's were reading on the optimistic side, whereas in the cars they match the GPS exactly.
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Cruiser
Joined: Jun 2007
Posts: 172
Likes: 0
From:
and my wifes car....subura...same way
Last edited by Trojan63; May 22, 2009 at 12:37 PM. Reason: forgot something