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Discussion Starter #1
Hi all. Since getting my 650k7 and joining this site I have seen a lot of discussion about the strom speedo being inaccurate. Exactly how bad is it? Does anyone know what the correct speed is at an indicated 80kph, 90kph, and 100kph?

Thanks for your help :)


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I recall that it's about 8% "optimistic"... for example, an indicated 108 is in actuality closer to 100.

IMO, the best fix for this is raceratb's corrected speedo face; it works perfectly and doesn't affect the odometer which is basically accurate as-is.


- Martin
 

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In most parts of the world manufacturers are allowed a +/- 10% error in the speed reading by law. Speed reading will vary due to things like tyre wear, tyre pressure, tyre brand and size and even road conditions which is why the allowance is there as as you would expect it's very difficult for a manufacturer to mass produce a speedo that will be accurate UNDER ALL CIRCUMSTANCES that the vehicle may encounter during it's life span.
Suzuki like many manufacturers err on the side of caution and have speedos that show a faster speed than you are actually travelling. The good thing about this is that it makes it much easier to comply with speed restrictions and if you live in speed camera obsessed places like Victoria (Australia) you have a much better chance of retaining your drivers licence longer.
My speedo is staying as it came from the factory for that reason.
 

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As K1W1 mentioned, or to put his perspective in a different look, the speedo is not necessarily "Off". With the bike sitting straight up (i.e. not leaning in a corner) with properly inflated tires that conform to OEM dimensions the speedometer reads slightly fast. With lower tire pressures, different tire diameters, or more importantly when leaning in a corner, the speedo may be right. When cornering hard you are running on the sides of the tire which have a significantly smaller radius than at the center of the tire. The tire radius also grows at speed slightly due to centrifugal force (watch the rear tires on a top fuel dragster some time). The speedo on my VFR is also slightly optimistic according to my GPS, and about the same amount as my V-Strom.

I posted numbers in a topic somewhere that show GPS speeds every 10 mph from 40 to 90 but I don't know where it is now though. Straight up at 45 mph my speedo is dead on. Straight up at 70 mph it reads about 5 mph high. At 90 mph I think it was about 8 mph high.
 

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When compared to the GPS (Garmin 60C) my DL650K4's speedometer was 8% fast. I installed the corrected speedometer face and it is now right on, at least to 80 mph which is about as fast as I go while comparing GPS to speedometer.
 

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I would be surprised if any of the things you mention make much more than a small (percent or two) difference in the indicated speed reading. The stock speedo setup indicates 8% off on almost every 650. I don't know the error on the 1000 but I expect it would vary more because of the speedo drive being based on the rear tire which experiences more load variation.

If you are seeing GPS readings different in corners I suspect it is the nature of how GPS get the measurements: they measure the distance between two points and derive speed from that.

The GPS speed displayed can be very accurate but you need to understand how it can be inaccurate. I've used GPS units for 5 or 6 years now and have observed some things about them so while the stuff below might not be technically accurate in the description they are how I think of what is going on.

Here's what I've noticed:

-If you are making short turns the GPS will measure the speed from two points on the turn and as a result read a more pessimistic speed. (I think of the line between those points as a "segment".)

-If you are accelerating or decelerating quickly the unit may not "catch up" with the actual speed so that the displayed speed lags behind.

-If you accelerate quickly and then brake hard it may not show the top speed at all, but will tend to show an average speed of a segment.

-If you are traveling very slowly the error of the speed displayed can be higher due to positional error. (Notice on occasion you can get a speed reading when you are sitting still.)

These errors tend to be much less on newer units than on older units that have greater positional accuracy and faster updating.

Your straight up speed differences at 70 and 90 mph show in the area of 7 to 8% error.

..Tom



As K1W1 mentioned, or to put his perspective in a different look, the speedo is not necessarily "Off". With the bike sitting straight up (i.e. not leaning in a corner) with properly inflated tires that conform to OEM dimensions the speedometer reads slightly fast. With lower tire pressures, different tire diameters, or more importantly when leaning in a corner, the speedo may be right. When cornering hard you are running on the sides of the tire which have a significantly smaller radius than at the center of the tire. The tire radius also grows at speed slightly due to centrifugal force (watch the rear tires on a top fuel dragster some time). The speedo on my VFR is also slightly optimistic according to my GPS, and about the same amount as my V-Strom.

I posted numbers in a topic somewhere that show GPS speeds every 10 mph from 40 to 90 but I don't know where it is now though. Straight up at 45 mph my speedo is dead on. Straight up at 70 mph it reads about 5 mph high. At 90 mph I think it was about 8 mph high.
 

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Discussion Starter #7
Thanks

Thanks for the info everyone. This is very good stuff to know. It looks like the general view is that the stock speedo is off by about 8% or so. Since I tend to ride about 10-15 kph above the posted limits in most areas (certainly not all!) I'm actually not doing much more than the posted limits.

Many Thanks


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Agreed on all points above about GPS speed accuracy. But...I've always heard (and assumed) that if you're traveling in a straight line at a consistent speed along a flat road in the open, your GPS speed readings are pretty darn accurate!

I'm torn...part of me would love to get the corrected speedo face...but a part of me likes having the speedo read high. (Plus over the years I've embedded a 5mph "transposition factor" into my head, sort of like transposing music into another key while playing!)

Scott
 

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GPS readings are typically very good. A short glitch will pop up. My trip log right now says my maximum speed during the period was 151mph. Last year, I believe Stromette broke the sound barrier.
 

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Yes.. in a straight line at constant speed they are incredibly accurate. They are pretty good in most other circumstances but the nature of them means that errors can creep in.

My other hobby is flying an Ultralight Aircraft. (A "Trike" for those that care about these things) I generally download the track from my flights and save them on my computer. (Ok, I am a bit nerdy but there are reasons I do this.) You can look at the track afterwards and check out exactly where you have gone, your speed, your altitude, etc. I usually fly at about 1000 feet above the ground and sometimes a lot lower when there is something interesting to see (deer, wolves etc.) I have seen on some of the tracks that my altitude jumped from 1000 ft (above ground level) to 50,000 feet or some other incredible number and then right back down again. The same thing with the occasional speed jump to supersonic or whatever. There have been some cases where the GPS might think you are miles from your location temporarily.

Now most of those glitches were with my older Garmin eMap, but I think there have been a few on the Garmin 60Cx as well.

..Tom

Agreed on all points above about GPS speed accuracy. But...I've always heard (and assumed) that if you're traveling in a straight line at a consistent speed along a flat road in the open, your GPS speed readings are pretty darn accurate!

I'm torn...part of me would love to get the corrected speedo face...but a part of me likes having the speedo read high. (Plus over the years I've embedded a 5mph "transposition factor" into my head, sort of like transposing music into another key while playing!)

Scott
 

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In most parts of the world manufacturers are allowed a +/- 10% error in the speed reading by law.QUOTE]

That is not true. Manufacturers are allowed to be up to 10% optimistic, but never can they read slower than you are actually travelling. Coppers use speedos that are "certified". Which means they are pretty darn accurate.
 

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I would be surprised if any of the things you mention make much more than a small (percent or two) difference in the indicated speed reading. The stock speedo setup indicates 8% off on almost every 650. I don't know the error on the 1000 but I expect it would vary more because of the speedo drive being based on the rear tire which experiences more load variation.
All good points ... but let's quantify this one:

The spedometer pickup on the DL650 is on the front wheel, and the front
tire is a 110/80VR-19.

A 110/80VR-19 tire will have a diameter of 22.464"
Circumfreence = PI x D = 70.573"

Assume low pressure, wear, riding on the edges reduces
the RADIUS by 1" (worst case scenario in other words):
Diameter = 20.464"
Circumference = 64.289"

Difference = 8.9%

Maybe an inch off the radius is too much, I'm not sure, but manufacturers will have to consider worst-case to keep themselves (and us for that matter) legal.

-If you are making short turns the GPS will measure the speed from two points on the turn and as a result read a more pessimistic speed. (I think of the line between those points as a "segment".)
Technically, just FYI, that segment is called a "Chord". I ran a survey crew for years, and one of the things I learned very quickly was how to calculate curve data ;)

Again, all very good points, Tom, and I agree completely with what you said.

Another thing to consider when talking about GPS devices is that they will frequently show differing values for the same circumstances at different times. The satellites are not in geosynchronous orbits (they don't stay over the same point of the Earth all the time) so the odds of catching the exact same geometric solution at any given point at different times are huge. Additionally, since the devices are actually measuring the time it takes a signal to go from the satellite to the device, they are very much dependant on atmospheric conditions, reflections from nearby buildings, tree cover, lack of satellites, satellite error, timing error, etc. The bottom line is that if you measure a GPS point (or speed) at one spot today and again at the same spot tomorrow and you may get differing values.

High accuracy GPS devices use either RTK (Real-Time Kinematic) or Post Processing or both to get their accuracy. Hobby-grade devices such as we use use neither RTK or post processing, they only use real-time from the satellites since accuracy is not a real issue. Our "Mapping Grade" GPS at work (Trimble GeoXH with an external antenna) will usually give a post processed horizontal error of about 1/2 foot. Some survey grade devices using RTK and post processing can provide centimeter horizontal accuracy.

One final bit of advice: Vertical accuracy on GPS devices is usually 2 to 5 times the horizontal accuracy. If your GPS shows 10 feet of horizontal accuracy you can usually expect 20 to 50 feet of vertical error. My Garmin 2820 is normally pretty close but I've seen my Garmin ETrex Legend C going up and down while it was sitting on my desk.
 

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If you install a Speedohealer, the correction for the DL650 is 7.7%. I had a speedohealer on my '05 DL650 and that 7.7% correction was verified with both a Garmin 2610 and Zumo 550.

Granted that we aren't talking about lab-grade accuracy here, but it's at least as close as police radar.
 
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