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Discussion Starter · #1 ·
I have always figured that my bike, a VN 900LT, was like everyone else's in terms of the actual speed verses the speedometer. From most of the posts I've read about this issue, most people report, through GPS, and trailing friends on other bikes, etc, that the 900s run about 5 miles below the speedometer.

I happened upon a police radar machine today, while out for a ride. I noticed as I passed that I was about 2 miles off, moving at around 40 mph, the reading was 38.

Now I thought that was odd, so I went around the block and double checked to make sure I was not reading incorrectly. It was dead on again at 38, me going 40.

I did it again, this time me going 45. The reading was 43. I did it again this time at 50. The reading was 48.

It seems that my bike is off by 2 mph off at every speed I tested her at. I went for one last test run, and this time I punched it, and took her up to 65 mph, and sure enough the radar machine was showing 63 when I went past.

Can anyone tell us if these radar machines are acurate? If so, what is the percentage they are acurate with in?

D
 

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Live Long & Prosper
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The radar systems are usually calibrated and fairly accurate. Your bike would be an oddity if it has a fixed 2MPH offset rather than a percent-of-speed error. Based on what I've tested and on what others have stated it appears that most speedometers are in the range of 8%-10% off, indicating a higher than true speed.
 

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Discussion Starter · #3 ·
The radar systems are usually calibrated and fairly accurate. Your bike would be an oddity if it has a fixed 2MPH offset rather than a percent-of-speed error. Based on what I've tested and on what others have stated it appears that most speedometers are in the range of 8%-10% off, indicating a higher than true speed.
My thoughts exactly. I wonder if when I took the bike in for service, to get a new ECU installed, if it's possible that the new ECU corrected the mph error. Either way, I'm very pleased that it's working, and will do some other tests. I will also update the thread when I've dome that.

D
 

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I would NOT believe the radar... especially since you keep "testing" on the same one. Living in CA., I come across these radar indicators all the time and I find them very inconsistent. If you want to fix your speedo (or get it much closer to accuracy) get the replacement pulley from Scootworks.
 

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Discussion Starter · #6 ·
The biggest problem with them is figuring out if you're the one it's reading.
This is true, but I was the only one on the road. I'm gonna go out tomorrow and follow my wife in her car. That's how we checked it before, but I'm telling you, when they changed that ECU, it became a different bike.

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Discussion Starter · #8 ·
What do you mean "... it became a diffrent bike."
The best way I can explain it, is it just runs better. Not that it ran bad before. I had trouble when I was in 3rd gear with the throttle sticking, and she would stall out every now and then when I was coming to a stop.

When I was in the twisties, the 3rg gear throttle sticking was a real problem. Now it shifts better, doesn't stall out when I stop, and seems to have more power. When I'm in the twisties, she handles so much smoother.

The other thing I changed other than the ECU, was the air psi in the tires. The manual calls for 28 28 or something like that, and the tires side wall calls for 40 40. Turns out the manual is wrong.

D
 

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The radar systems are usually calibrated and fairly accurate. Your bike would be an oddity if it has a fixed 2MPH offset rather than a percent-of-speed error. Based on what I've tested and on what others have stated it appears that most speedometers are in the range of 8%-10% off, indicating a higher than true speed.
Police radar systems used for enforcement are calibrated and accurate (checked every morning), but the roadside warning signs aren't attended to that regularly.

On the way back from Calico last month leading a large group, the radar signs on the right lane consistently were 5mph below my indicated speed.

I thought my Speedo Healer had taken a dump, so as soon as I got home I hooked up the GPS and went for a ride.
Nope... GPS (Nuvi 660) and speedo were accurate up to 80mph.
Came back home, mounted up my wife's GPS (Streetpilot 2610)... same thing.
Other radar signs have also been consistent with my indicated readings.


If you were off 2mph at 40, that would indicate an error of about 5%
At a 5% error, you won't see a difference between 40, 45, and maybe even 50 (at 50 a 5% error is only 2.5mph).

However, I would suspect that the unit was indeed out of calibration... and MAYBE even calibrated on the high side intentionally in an attempt to slow people down. Traffic engineers do all kinds of tricks to slow traffic when they are preparing to run a speed survey. If they calibrated it "high" anywhere near 5%, then at 40-50mph, it would put it's indication within 2.5 mph of your reading even if your speedo were actually reading 10% fast.
If it was indeed exactly 2mph off at any speed (any chance you can safely test it at 75?), then I think it is indeed calibrated high.

It really is hard to gauge speedo accuracy at slow speeds. The error is amplified by higher speeds.

OTOH, your speedo MAY actually be only 5% off, which would be unusual, but not unheard of. If you've gone up to a 200 rear tire, or installed the Scootworks pulley, that will affect your calibration (in the right direction).
 

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The third gear problem your talking about sounds like the ECU problem that is well documented on these Kawa forums and the Delphi 900 and Vulcan group. I'm glad you got it fixed, it should have been warranty

I have not heard anyone say that the ECU does any calculations on the speedometer error. Doesn't mean it doesn't though. I would imagine though with the small difference in speed that you were going you would have really noticed the difference.

IF your bike was showing 50 and you were doing 48, and really, it's a big dial, That's a 4% error. At 40 you would log 38.4 on the radar unit. So it seems its rounding down correctly. At 100 you would indicate 96 and I think you owe it to all of us to blow through that trap tomorrow and verify for us.

Best thing to do though is to beg, borrow, steal or heck, pay for a GPS and check your speed with that on a flat chunk of ground. IT takes a small period for the GPS to settle down, but the newer ones are faster and if you can hold your speed in one place and watch the GPS you should be able to get your correct speed.

With it only being 4% off I really don't know if I'd worry much about it. Mine was 10% off and that's pretty standard. But with the scootworks pulley I'm showing 80 at 80 so I don't worry about it now.

I don't know why I have this mental block, but I got tired of thinking, It shows 78, so I'm only doing 70. Course the bigger problem with that is there is NO 78 on the gauge, your inferring 78 between teh 75 and 80 marks. Frustrating.
 

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Vicrory is Mine
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My stock speedometer is exactly 10% off, so I use my Zumo as a speedometer. I hope to get the scootworks pulley this month.
 

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according to the cop I talked to about them once they aren't calibrated and never accurate. His words "they are a piece of sh1t"
Calibration is easy too... A roadside unit I was working with, when calibrated prior to shipment... just hold a tuning fork in front of it and it would read 55 (I've forgotten the pitch).
 

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Calibration is easy too... A roadside unit I was working with, when calibrated prior to shipment... just hold a tuning fork in front of it and it would read 55 (I've forgotten the pitch).
Are those roadside ones Doppler?
The gun I use for baseball is accurate to 1% when calibrated properly
 

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Discussion Starter · #15 ·
I Just got back from testing the speed against a car. The bike is almost 8% to 10% off at different speeds. I took it up to 80 on the last run waited for my buddy to get right next to me, put my hand up so we could each note the speed, and he was doing about 74 mph, and I was doing 80 mph.

I went passed the place were the radar machine was, but they moved it. There is one a few streets over, but I can't be sure it's the same one, and it's on a street that has a 35 mph limit, so I can't get any speed going to check it.

That's it, I have to get to work, but I never thought those machines were that far off. Go figure.

D
 

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I come upon these machines from time to time and they have all consistantly measured my machine about 5 MPH below the speedo reading. This has occurred at various speeds ranging from 25 (speedo reading of 30) up to 55 (speedo reading 60).
 

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That's it, I have to get to work, but I never thought those machines were that far off. Go figure.
To determine speed limits, the engineering department must do a speed survey every so often. The speed limit is determined by taking the 80th percentile, and then the engineer has the discretion to adjust up or down by 10mph.

I've listened in on conversations when residents complain about people speeding through a 35 zone and requesting it be lowered. The engineer would coordinate with the PD to do very heavy enforcement for a 2-week period, then they vacate the street for 1 week, then the speed survey is done.
A week after everyone has been getting tickets or being told by friends "they mean it", NOBODY goes 36.
Bingo... 80th percentile comes back between 30 and 35 and the engineer can legally drop the limit to 25 or 30.

If a speed survey has not been done OR if the speed limit is outside of the current 80th percentile, the limit can be declared invalid... a lot of tickets are won this way (laws in your state may vary).

Sticking a miscalibrated radar sign out could be a part of one of these games.
 

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Are those roadside ones Doppler?
The gun I use for baseball is accurate to 1% when calibrated properly
This was close to 10 years ago, but I would assume they are still using the same technology, given that it has to have a pretty wide field.
Lazer wouldn't work very well for multiple lanes.

When calibrated, they are quite accurate, but even temperature can cause electronics to drift... moreso consumer grade than PD grade.
 
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