Some interesting points....Yes GPS does have some limitations and weak points..

Fortunately for me, I don't often go thru tunnels, other than really short ones.....I don't ride in the big city, and the mountains around here are not too tall....

So for me the GPS works wonderfully..........

The only issue I find is that it takes the GPS some time to initially lock on to the satellites....especially if the unit has been shut down for a couple of days.......

I see why GPS is so useful for nautical or aviation as there are no obstructions to the sky....

I can see that a hub sensor, which is calibrated an be extremely accurate...THis is what our MC speedo is....Really the only problem with the GS500 speedo is that the numbers are printed on the dial in the wrong places....

I remember reading old car magazines...they always had a bicycle wheel apparatus bolted to the rear bumper to give accurate road test data..... can be extremely accurate in a wide variety of conditions.........

What about "inertial sensors" this is the big deal in aircraft now...the AHARS..also used in robotics...

You have solid state "gyros" and accelerometers......in a tiny package...

Cookie

Quote from: BrianRC on June 03, 2013, 10:47:25 PM
I would love to add my two cents here as a road rally competitor (in cars) I have seen a huge difference in the various speed measurement instruments available. I drive an older car that uses a mechanical cable driven input from the gearbox and it is fairly accurate..up to 35mph, after that you start to get slippage of the gears  (spinning on the input shafts) on the inside of the speedometer. Some are better than others but they all have a deviation.

The international standard regarding how much vehicle speeds can be off was put into effect in the late 80's if I remember correctly (65 on my 1983 car speedo is closer to 70 actual) so I missed out on that by a few years. GPS is accurate speed and distance wise only if you are traveling in a fairly straight line without any quick direction changes (switchbacks anyone?  , those can alter readings by a few 10ths of a mile and momentarily throw speed readings. GPS also suffers from line of sight signal reception issues, if you are in the mountains and there are no satellites directly above, you loose signal accuracy and it starts to guess on your speed and direction based on last known direction and speed; or it cuts out entirely. 

I use a purpose made rally computer that reads pulses off the hub of an un-driven wheel of my car and they display speed to a 10th and distance down to the 100th of a mile (or km if you like). It still can be thrown off by wheel slip of course but it is the answer to GPS inaccuracy and can easily be tuned for different wheel and tire sizes. 
I think for all intents and purposes a dedicated Gps more than fits the average riders needs.

My Acewell uses a pickup strapped to the left fork leg and a magnetic bolt replacing one of the disc bolts to trigger it, so the resolution is pretty good and it's programmed with the diameter of the front tyre so you can get nice and accurate.



I added 10 or 15mm to the diameter when programming it so that it would over read a little.

http://www.speedotuner.com/install.html

Here's somebody's solution....funny though...one of the calibration methods is to use a GPS!

You can use time over distance too...very accurate...

Cookie

Sure........We've been using magnetic pick ups on bicycles for many years....We do a roll-out test to get accurate tire circumference and simply program the unit...

Cookie

Quote from: peteGS on June 04, 2013, 05:10:09 AM
My Acewell uses a pickup strapped to the left fork leg and a magnetic bolt replacing one of the disc bolts to trigger it, so the resolution is pretty good and it's programmed with the diameter of the front tyre so you can get nice and accurate.



I added 10 or 15mm to the diameter when programming it so that it would over read a little.

Yup, nothing new to that principal!

I just marked the tyre and floor with some tape and rolled it forward three different times and split the difference for my circumference measurement 

Easy!

Apparently on the Honda VFR, the speedo is out by 10% but the odo is accurate. Maybe the manufacturers are trying to give us a bit of breathing space in terms of speeding fines 

Pretty much. Good feature though. Means we keep our licences to figh another day

The GS500 is also pretty accurate on the odo.....I figure 8% off on the speedo ...

I think the philosophy is twofold....

1) to keep the speedo on the conservitive side to prevent speeding tickets
2) the speedo boasts a higher than real speed...so we can boast on how fast we go.....

But let's get real...who's kidding who?

I mean I know there is a 8 to 10% error...so I just go 10% faster

Also when I have the GPS fitted and it give accurate speed...well the speed IS accurate...if I'm over the limit...well, I AM speeding...simple as that........

It's like I know people who set their clocks 10 min fast so they are not late for meetings and stuff....

dooouuuughhhhh!


Cookie

only 10% faster?!! c'mon own up!! ... we wont tell!! 

Quote from: sledge on June 02, 2013, 11:54:33 PM
Yep......over indicating by about 10%

Don't worry about it, they all do it 

yep 10% on average.

Those replacement digital displays do almost everything my expensive rally computer does except for being able to adjust and calibrate them on the fly, even the magnetic sensor is pretty much the same (I just use a proximity sensor which is more durable but not quite as sensitive as the magnetic hall-effect sensors)

Twocool, I think I remember hearing about those inertial sensors being used in black box recorders and from a bit of reading the good 'ol wikipedia when integrated with gps an other inputs they can be pretty damn precise. If we could get that in a small handheld gps that would be pretty damn cool!