Speedo vs GPS
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
No. The speedo is dependent on the rear wheel, except older bikes that may have a front wheel cable-drive speedo. When a rear tyre is new it has about 3/8" tread and is typically just over 25" in diameter. If we wear the tread down to zero, the diameter changes by 3%. The speedo is only accurate to between zero and 5%, so adding those together the scope for error with a speedo is quite a lot. 'Twas ever thus - blame gps for revealing the ugly truth!
If you want better accuracy, use a gps.
If you want better accuracy, use a gps.
Road Master
Joined: Apr 2008
Posts: 983
Likes: 4
From: Indiana
Several tuners can do this.
TTS and Powervision are 2
But be stay away from the plug in calibrators on any bike with a cruise control of 6th gear light unless you want to loose these functions I found this out the hard way with the Dakota Digital Electronic Speedometer Adjustment Module at the time I bought it they did not have the warning about it affecting the cruise. As noted at the bottom of this link.
http://www.dakotadigital.com/index.c...rod/prd238.htm
TTS and Powervision are 2
But be stay away from the plug in calibrators on any bike with a cruise control of 6th gear light unless you want to loose these functions I found this out the hard way with the Dakota Digital Electronic Speedometer Adjustment Module at the time I bought it they did not have the warning about it affecting the cruise. As noted at the bottom of this link.
http://www.dakotadigital.com/index.c...rod/prd238.htm
Outstanding HDF Member
Joined: Jul 2007
Posts: 2,241
Likes: 7
From: Daytona, Fla.
For the OP, there are a few add-on units that claim to adjust speedometers. Their accuracy is suspect. The ThunderMax Auto Tune I have in my FLTR has corrected that speedo. Power Vision will do the same. A really good tuner that will correct spedometer inaccuracy is a great thing.
Harley could do it, but won't. It's an algorithm in the CPU that interprets speed from the transmission. Correcting that algorithm corrects the signal to the speedo.
Road Warrior
Joined: Mar 2011
Posts: 1,456
Likes: 132
From: Deep South, Louisiana
And I have had several trucks that were under at times, over at times, way over at times, and now dead accurate. How because I changed tire size from the factory size. Bigger the tire like big ole mud grips will put you way faster than what the speedometer is showing. When they had cables you could change the gear but I never did just learned how far off and lived with it. I now usually go just one size up and it will be accurate with my GPS. Remember this is with a new vehicle and new tires, tire inflated to proper pressure, with no worn componets for 2 mph off. If you dont believe me contact your vehicle manufacturer just like I did for a court case.
Last edited by K Melancon; Jan 13, 2013 at 08:15 AM.
Advanced
Joined: Jan 2013
Posts: 98
Likes: 0
From: Greensboro
The wife and I went on a 200 mile ride today so I thought this would be a perfect time to try out the new GPS mount. While riding I looked down and compared my speedo verses the GPS and at 80mph on the speedo, my GPS was reading 75mph! I thought WOW that is pretty far off. Is this normal?
Advanced
Joined: Jan 2013
Posts: 98
Likes: 0
From: Greensboro
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Road Master
Joined: Oct 2007
Posts: 925
Likes: 56
From: Memphis, TN via NoVA
I've verified my speed against stationary radar and then compared to GPS reading. My speedo ('12 FLHX) is 2 mph faster than the radar and 3 mph faster than what GPS tells me. On my SUperGlide Custom, the speedo is 4 mph faster than radar and 3 faster than the same GPS. Go figure huh?
Road Warrior
Joined: May 2012
Posts: 1,988
Likes: 17
From: Between Fort Worth and Wichita Falls Texas
I actually don't mind it showing high. I go mainly by sound when cruising down the highway and when it purrs I'm doing about 72 according to speedo and that keeps me from getting tickets. 2500 rpms seems to get me the best fuel mileage and that's around 72mph. Works for me.