The Real Deal on Speedo Accuracy (Should say INaccuracy)

[QCRider]

Ok, this week was my first week with both my new RX-1 as well as my GPS on a sled. So here's the story.

After a relatively short ride (135 miles on the Odometer) I compared the miles on the GPS to the Odometer, and they were pretty close. 135 on the Odometer, 131 on the GPS. So the difference was about 3%, and I could VERY EASILY write this off to track slip. So let's figure that there is 3% track slip for argument sake. Given this information one would think that the Speedo should also be accurate to within 3% since the speedo and the Odometer get their input from the same place. HOWEVER, this is DEFINITELY not the case. at 112 on the speedo, the GPS read 98.4 MPH. And I held it there for at least 20 seconds so that any delay in GPS reading would be well covered. So the speedo is off by 12.1% or so. No news there. But the real news is that the error is MOSTLY in the speedo display, NOT the track slippage or pickup unit since the Odometer shares the same components at that point.

So just for kicks we ran a test with 3 sleds. 2 RX-1's and a Ski Doo MXZ 600. We all ran down a railroad bed at 70 MPH as indicated on the Speedo, and in fact are speeds were matched in reality as well. The interesting thing is that they were matched at something around 62 MPH on the GPS. So, not only is the RX-1 speedo wrong, but so was the Doo, and to the EXACT same degree.

This absolutely supports my earlier hypothesis that the manufacturers calibrate the speedometers to read high on purpose, while the odometers are actually quite accurate. Think about why they would do this...

1.) It makes people think they are going faster than they really are, so it could be considered a safety measure.

2.) People can always brag about the speeds they see on their speedos and feel better about their sled.

So, no more BS about track slippage please, it is NOT the issue.

 

[impalapower]

No matter how fast I go, it still isn't fast enough.

 

[woodtic]

check it against one that is studded. I ran same test against a polaris and speedo were the same and no slipping . seemed to be off after 95 mph.

 

[QCRider]

Mine has 168 studs. I ran with an RX-1 with 144 and the MXZ600 had 96. The error is there at EVERY speed. As soon as you start to move, the indicated speed is wrong. I checked it all the way up.

 

[jimmie d]

Subtract 10% and you will be close, of all the digital speedos that I have seen Yamaha is the only one off by a wide margin. The old style were always off.

Jim

 

[QCRider]

The Doo was analog and agreed exactly with the digital Yamaha.

 

[LazyBastard]

Do this and I think you'll see more clearly.

Shiny glare ice, spiked track. Run the ice, measure speedo, gps, and the PLACE on the ice where the measurements were made.

Then go back to the ice and measure the LENGTH of the scratch marks.


I bet you $500 that;
(1 - %scratch per pitch) x (speedo) = (gps)

I've actually eyeballed the scratch marks on ice and found them to be about 10 to 15% (except on accel)

 

[QCRider]

Do this and I think you'll see more clearly.

Shiny glare ice, spiked track. Run the ice, measure speedo, gps, and the PLACE on the ice where the measurements were made.

Then go back to the ice and measure the LENGTH of the scratch marks.


I bet you $500 that;
(1 - %scratch per pitch) x (speedo) = (gps)

I've actually eyeballed the scratch marks on ice and found them to be about 10 to 15% (except on accel)

Regardless of whether I BELIEVE you are right or not, the facts do NOT support your argument. IF and I repeat IF track slippage was the issue LB then HOW could the odometer be so much more accurate?

 

[QCRider]

Also LB, I don't doubt that there is slippage on the ice at all. That just means that it would be off by even MORE on ice. I was on hard packed snow. There is a 10% difference between the Speedo and the Odometer. That is a fact, it was that way all three days I rode with it. Not just conditions on one day or anything like that. The two should agree, and they don't.

 

[LazyBastard]

Simple. The odometer is scaled to show more accurately the real distance traveled, so its dropped down by 10%.

Remember that neither the odometer nor speedometer are mechanical. They're going to scale whichever they want to *make the most sense*. It makes no sense to try to show vehicle speed on the speedometer, since there is no way to account for the instantaneous slippage, but statistics can give a real good idea of how much the track slips over long term usage, so the odometer can me made to be reasonably accurate to show real distances traveled.

 

[QCRider]

Oh, and one more thing. We did run up a river for 10 miles at one point that had very little snow on it. Many times we were on bare ice. It made no difference. The speedo was off by the same amount as it was on hard pack.

 

[LazyBastard]

Why would the slippage be higher on ice when you're studded? Hardpack and ice, when you're up at speed and have steel traction, are very similar.

Think about the mountain riders who are paddling through deep fluff all day.

 

[QCRider]

Simple. The odometer is scaled to show more accurately the real distance traveled, so its dropped down by 10%.

Remember that neither the odometer nor speedometer are mechanical. They're going to scale whichever they want to *make the most sense*. It makes no sense to try to show vehicle speed on the speedometer, since there is no way to account for the instantaneous slippage, but statistics can give a real good idea of how much the track slips over long term usage, so the odometer can me made to be reasonably accurate to show real distances traveled.

Whatever LB. So then all manufacturers are aware that all sleds slip at 10% (apparently regardless of whether or not they are studded) and they ALL go to the trouble to subtract 10% from the odometer readings, but LEAVE THE SPEEDO 10% TOO HIGH? Why? Why would they do this?

It would make MUCH more sense to make the speedo read high. Give me a good reason why they would make the odometer accurate by adding a slip factor(which would be nearly impossible to calculate due to the many factors affecting this) yet leave the speedo to read artificially high?

 

[QCRider]

Why would the slippage be higher on ice when you're studded? Hardpack and ice, when you're up at speed and have steel traction, are very similar.

Think about the mountain riders who are paddling through deep fluff all day.

Yes, I agree, THEY have significant track slippage. What I experienced over 3 days was about 3% track slippage.

 

[wolfie]

First, don't waste your time arguing with Dr. Bastard. I'm starting to wonder just what kind of drugs he's on. Secondly, this is old news. At full speed, Yamaha digital speedos have been approximately 14 mph off for several years now. Nothing new here. Two weeks ago, my 127 indicated was 113 on radar, exactly 14 mph.