Speedo Accuracy
Road Master
Joined: Nov 2006
Posts: 1,227
Likes: 3
From: Central Illinois
The speedo program on Dynojet 250i's are certified. You can have it put on a Dyno and verify. It reads actual drum speed/distance then calculates. We usually check while a bike is on there and they are all within a coule mile an hour of actual.
Tourer
Joined: Mar 2008
Posts: 435
Likes: 2
From: Alberta, Canada
The speedo on my '08 Road King says I'm going 4 mph (~5 kph) faster than I am according to my GPS. Funny thing is, it's out the same amount regardless of my speed.
I took the bike to the stealer for the first service (I wanted them to do the first service) and asked them to also correct the error, but they somehow forgot to do it. My arguement is - the bike is mileing out before it's time. In fact the slower I ride the quicker it is mileing out. Sounds goofy, doesn't it?
I have since taken my bike on several long rides (More than 3000 miles each) and compared the odometer to the GPS. Both the GPS and the odometer are always within a few miles of each other at the end of the ride. It's only the speedo that's out, the odometer is quite accurate.
Up until now I always thought speedos and odometers were based on the same calculated values using RPM, wheel diameter, etc. Apparently that isn't true.
I took the bike to the stealer for the first service (I wanted them to do the first service) and asked them to also correct the error, but they somehow forgot to do it. My arguement is - the bike is mileing out before it's time. In fact the slower I ride the quicker it is mileing out. Sounds goofy, doesn't it?
I have since taken my bike on several long rides (More than 3000 miles each) and compared the odometer to the GPS. Both the GPS and the odometer are always within a few miles of each other at the end of the ride. It's only the speedo that's out, the odometer is quite accurate.
Up until now I always thought speedos and odometers were based on the same calculated values using RPM, wheel diameter, etc. Apparently that isn't true.
Road Captain
Joined: Feb 2006
Posts: 739
Likes: 3
From the TTS Master Tune VSS Calculator:
I got caught in a bad storm, the next day speedo reads wrong, I know I'm going about 60, but speedo shows 35. the speedo shows no sign of water damage (not foggy) I was in really heavy rain approx. 20 mins. 2000 roadglide.
Banned
Joined: Jul 2009
Posts: 216
Likes: 0
Whoa, zombie thread.....
Anyway, cubesteak, that's gotta be a bit of corrosion with a contact point for the wires leading to your speedo. The bike getting wet is one thing, but storms tend to kick up a little bit of extra grime and crud that works its way onto contacts. I'd look at disconnecting, cleaning, applying dielectric grease and reconnecting the wires at the speedo (and wherever those connect to next). Disconnect the battery first, ya know, for safety and to reduce/eliminate the risk of accidentally shorting out your speedo (costly replacement).
Anyway, cubesteak, that's gotta be a bit of corrosion with a contact point for the wires leading to your speedo. The bike getting wet is one thing, but storms tend to kick up a little bit of extra grime and crud that works its way onto contacts. I'd look at disconnecting, cleaning, applying dielectric grease and reconnecting the wires at the speedo (and wherever those connect to next). Disconnect the battery first, ya know, for safety and to reduce/eliminate the risk of accidentally shorting out your speedo (costly replacement).
Road Master
Joined: Sep 2010
Posts: 752
Likes: 23
From: Acton, CA
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Road Captain
Joined: Apr 2009
Posts: 537
Likes: 0
From: Columbus, Ohio
Tested my Magellan GPS with both my RK and my Chevy Silverado.
At 70 mph my truck speedo and GPS both indicated 70 mph- perfect match.
Ran the test all the way down to 35 mph and the same results.
At 70 mph on the King speedo the GPS showed 67 mph. Consistently 3 mph off through all the speeds I compared.
I mentally adjust when riding and setting my cruise accordingly.
At 70 mph my truck speedo and GPS both indicated 70 mph- perfect match.
Ran the test all the way down to 35 mph and the same results.
At 70 mph on the King speedo the GPS showed 67 mph. Consistently 3 mph off through all the speeds I compared.
I mentally adjust when riding and setting my cruise accordingly.
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