Speedometer accuracy
Road Captain
Joined: Jul 2009
Posts: 583
Likes: 2
From: Eaton, OH
There are a number of companies that make little electronic boxes that go between the speedometer sender unit and the speedometer itself. You can put in a correction factor on the box like -5% to correct your speedometer.
Road Master
Joined: Apr 2009
Posts: 875
Likes: 1
From: Rochester, NY
If you go fast enough eventually the law will let you know how close it it. As posted, GPS, road radar, and I disagree with those that say they aren't accurate... they are calibrated, and a measured mile on the highway in 1 minute at 60 mph will tell you what you need to know.
Road Master
Joined: Oct 2009
Posts: 1,074
Likes: 1
From: Baltimore, MD
I find it interesting to note that tires with the same nominal size may be a different size. Going from brand to brand can make a difference, possibly more difference than the accuracy of the speedometer unit itself. I've never personally come across a situation where changing tire size could not have been a factor. But it depends on where speedometer cable goes to. Yamaha FZX700 takes speed at the front wheel, so, obviously changing rear size would not effect speedometer reading (would effect RPM's at certain speeds.) However, most machines take it at the transmission, where rear tire would change speedometer readings. This is from observations, not meant to sound like I'm an expert.
Stellar HDF Member
Joined: Jul 2009
Posts: 2,476
Likes: 193
From: Las Vegas, NV
My 09 Ultra is off. According to my GPS it fluctuates about 3 to 5 MPH. My brother and I ride together most of the time; his 09 BMW R1200RT is much closer; maybe one or two MPH off. At the end of the day riding the same trip our mileage is off; my Ultra always says we went further than his BMW.
Ultimate HDF Member
Joined: Sep 2005
Posts: 8,641
Likes: 26
From: Ozark Country
Most of the Harleys have a Hall Effect electronic speedo sensor that gets it's reading off of 4th gear in the tranny.
So I would assume that going with a non-standard rear tire diameter would also have an impact on the speedometer reading.
But then again, you know what they say about assuming anything.
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