Speedometer vs GPS...

[Bike #12_imp]

This is the first bike I've owned where the speedometer is accurate. 70 mph on the CB speedo also reads 70 mph via GPS. 70 mph showed~ 4000 rpms on the tachometer. According to this gearing/speed calculator I've used for years...

The Colorado Sportbike Club - Speed Calculator

My CB will do 70.2 mph at 3650 rpms. So my tach reads ~350 rpms fast. Not sure if this discrepancy will hold true at lower or higher speeds. I'll keep checking.

All the data needed for use of the calculator is in the manual.

 

[Cormanus]

Thanks for that info, Bike #12. I need to check my speedo again. I thought it wasn't reading the same as the GPS.

 

[the Ferret]

My 13 matched the gps. Haven't checked the 14, just assumed it's good too.

 

[CIP57_imp]

This is the first bike I've owned where the speedometer is accurate. 70 mph on the CB speedo also reads 70 mph via GPS. 70 mph showed~ 4000 rpms on the tachometer. According to this gearing/speed calculator I've used for years...

The Colorado Sportbike Club - Speed Calculator

My CB will do 70.2 mph at 3650 rpms. So my tach reads ~350 rpms fast. Not sure if this discrepancy will hold true at lower or higher speeds. I'll keep checking.

All the data needed for use of the calculator is in the manual.

The tach reads 500+ on top so 9000 is actually 8500

 

[Papa Weeley_imp]

Very cool info, thanks.
I just always assume that bike speedos are all over the place. :dodgy:
Nice to know that I can actually rely on this one!

 

[rboe]

Can you imagine the guys that think this speedo is off and race like crazy? I didn't think it was that accurate. I'm not a big speeder, but........ it coulda happened to me.

 

[DAC]

Good to hear it's accurate. Most aren't. The viffer was off by 9%.

 

[the Ferret]

Good to hear it's accurate. Most aren't. The viffer was off by 9%.

About the same with the ST .

 

[flynrider]

In the days of mechanical speedos, there were half a dozen variables that could affect the accuracy (and usually did). The electronic setup on our CB11s is simple by comparison. x number of pulses over y seconds = z mph. It's either dead accurate or obviously broken.

Last year I took my '13 out with the GPS and the only difference I saw was during acceleration/deceleration (probably a lag due to differences in processing time). Even then the difference was only +/- 2 mph and it stabilized quickly. At 95 mph on the bike speedo, my GPS said 94.6 mph. Not bad.

 

[Rocky_imp]

My CB900F is slow by nearly 10kph at highway speeds according to my GPS. My Bonneville is only slow by 2-3kph at highway speeds.
Just so I'll know, I'll fit the Garmin to the CB one of these days and check the speed.
It's probably fine (as related above) but I would still like to know for my own peace of mind.

 

[AzBob_imp]

In the days of mechanical speedos, there were half a dozen variables that could affect the accuracy (and usually did). The electronic setup on our CB11s is simple by comparison. x number of pulses over y seconds = z mph. It's either dead accurate or obviously broken.

Last year I took my '13 out with the GPS and the only difference I saw was during acceleration/deceleration (probably a lag due to differences in processing time). Even then the difference was only +/- 2 mph and it stabilized quickly. At 95 mph on the bike speedo, my GPS said 94.6 mph. Not bad.

Electronics doesn't explain it. Just about every modern super sport bike's speedometer is _WAY_ off. My CBR is off by about 5%.

 

[flynrider]

In the days of mechanical speedos, there were half a dozen variables that could affect the accuracy (and usually did). The electronic setup on our CB11s is simple by comparison. x number of pulses over y seconds = z mph. It's either dead accurate or obviously broken.

Last year I took my '13 out with the GPS and the only difference I saw was during acceleration/deceleration (probably a lag due to differences in processing time). Even then the difference was only +/- 2 mph and it stabilized quickly. At 95 mph on the bike speedo, my GPS said 94.6 mph. Not bad.

Electronics doesn't explain it. Just about every modern super sport bike's speedometer is _WAY_ off. My CBR is off by about 5%.

Hmmm. I wasn't aware of that. The mechanicals have several points throughout the system that can introduce errors (cable, magnet, cup, etc...). Hard to figure why a full electronic system would be off. Basically, if the Hall effect sensor at the wheel is working properly, the rest is just math.

 

[DAC]

A funny thing about speedo errors sometimes is that the odometer can still be right. Like I said, the VFR had a speedo error of 9% but the odo was right on. Out of curiosity one time I google mapped the distance of a ride I did against the odo and they were within a mile. (This was about a 180 mile ride.) Weird. Makes me feel like the error was intentional.