Which MPH is acurate - GPS or Speedo?

From a "LOCAL LEO" Been riding Hondas since my first 1979 Goldwing, Every speedometer on every honda since then has read faster than true speed. On average when the bike says 65MPH my radar gun has shown 60 to 61 mph. More recently (current bike 2006 ST1300) Got 59 reading. I purchased the speedo healer and calibrated it using my Zumo. Then compared it with my newest radar gun. SPOT on! BUT now my odometer is off substantially. I actually cover more miles than bike shows now.
 
I hope it IS the GPS! I've only recently ridden with one and it's surprising that my natural thresholds (I.e. 35mph in a 30 zone) are pretty much spot on for the more accurate demands of the Institute of Advanced Riding coaching to ride 'progressively'.

Reading through this gives me full confidence.

So, how many miles has Shadowfax really done showing 90,000 this week, are the servicing intervals too frequent, and will Joe still give us our 50,000 award at 95,400?!!
 
Thanks, Jon. (Sigh). I was silently hoping that, when the sad day arrives, I could tell some hapless sap, "sure, he's showing 250,000 miles but we all know it's closer to 80!" ;)
 
GPS speedos are accurate, but they lag at times. I have a Sigma bicycle speedo mounted on my shelf next the the V1 remote. It continuously updates and is within 1 mph of the gps speedo. When the V1 goes off I can see both the V1 and my speed with this setup with a single glance. You can see it here:

http://koczarski.com/ST1300/Sigma/Sigma.htm
 
If Honda can make a precise speedo for the POPO version, why do we get the POS version? Since the error/difference increases as the speed increases, it's very difficult to figure your actual speed, very annoying. Bad Honda :mad1:
 
illzoni said:
The motorcycle manufacturers CAN make an accurate speedometer, they simply CHOOSE not to.

Why do I say this?
Because the odometers are spot on. They've purposefully inserted the speedometer error.
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Why would they do it intensionally? :confused: To what gain?
 
Ah, similar to the way Yamaha would make their RPMs read too high, to make it look like they had an even more incredible red line. I favor theory two but it's still not as good as theory three which is... Honda Execs secretly get Speedohealer stock options.:D
 
EASt said:
I am bumping this thread.

The reason? When my Sumo 550 reads 65mph, my ST will read 70. There's always been a 5mph difference between the two at highway speeds. I figured everyone had that, and I figured it was Honda's Speedo at fault.

However, I flipped my Official ST-Owners Calendar to August today. I looked at the picture of Indypup's ST1300 cockpit that's pictured. His Sumo 550 and his Speedo indicate the exact same number of 61mph.

So... I'm just sayin'...
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Wow, I can't believe I was only going 61... :D

And yes I have a "speedohealer" installed. ;)
 
I set my Speedohealer for -6.9% per advice from a member here and my speedometer now matches exactly my Zumo and the speedometer check mileposts sometimes along the freeway. Readings do change a bit because of tire wear. When I'm doing 130 on worn tires, there are certain inaccuracies :)

John
 
Blue One said:
I have not read the majority of the responses, but really, this is a question that should not even be asked.

The answer is too obvious. GPS
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I agree that GPS can be more accurate. But the answer isn't that obvious. I would never agree that the question shouldn't be asked though !
I expounded a lot in post #51, so I won't repeat that, but in summary:

A small percentage of speedos will be very accurate.
Some will be slightly out (manufacturing tolerances). All will err (more or less) with a higher reading on the speedo than the actual speed.
The GPS calculates the speed very accurately, providing it can get a good fix, and providing the software isn't guessing your position at the time.
All GPS devices tell you how fast you have just been going, not how fast you are going. Accelerate hard, under tree cover or in built up areas and the often the GPS will be wrong.

The trick is to know when your GPS is likely to be giving you an incorrect reading. The rest of the time you can probably trust it.
 
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I think you mean a higher reading than actual as is required in the UK..... so if your speedo reads 30, you are probably doing 28..... if it were the other way around you would be doing 32 instead of the actual 30....

My ST1100, which of course reads the speed from the drive on the front wheel as opposed to an electronic pick off on the gearbox, read fairly accurately, being only at most 1-3mph out at higher speeds...... at around 60mph indicated on the bike the Satnag will often read 59.....
 
Firstpeke said:
I think you mean a higher reading than actual ....
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Yes, that's what I meant ! Thanks for that. I think I'll go back and correct it. As I was writing, I'd got a picture in my head of statistical Normal (Bell) curves and sampling populations and performing a left shift so that the majority of the population were travelling slower than the indicated speed. You can't really expect me to use the correct words as well !
 
With ALL Hondas being 7-10% fast on the speedos, the difference not surprising. My ST11's speedo is 7mph fast at any given speed checked against GPS.
 
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