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Discussion Starter #1
Alright so I have been checking my fuel milage everytime I fill up and it's been running around 62 MPG, this last time was 62.9 MPG.

My speedometer is off by 10% which I determined with my car GPS.

Does this also mean that my MPG is actually 10% lower and that the odometer count is higher than it should be?

Thank you for the replies.

Jeff
 

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My experiance is based on a 650:

I have corrected my speedometer to be 100% correct by means of a SpeedoHealer.

I use -7.2% correction and my odometer reads 5% to short compared to GPS, so it must have been slightly optimistic before. 2.37% to be exact.

Even before the correction, my fuel mileage meter was pessimistic, now it's more pessimistic.
 

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i figured mine to be 10% high on speedo, and 5% high on odo... absolutely no reason to be off with todays electronics... especially being off by 2 different amounts... uncalled for...
 

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Now there's debate on how accurate GPS is for the odometer, but my odo is off +5% from my GPS. Not sure which one is accurate, but the GPS is generally close to google maps At the end of a route. So I'd say the 400 odo is a bit on the positive side.
 

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Considering the speedo's and odo's all vary from bike to bike in how much they vary from the actual speed or mileage, I wouldn't worry about it. The amounts they are off tends to be overall quite small and of course will vary all the time depending on tyre wear, tyre pressures, temps, weight carried etc etc. Here in the EU speedos must not be more than 10% off at any speed, but most are much more accurate than that. I've used speedo healers and other makes in the past but these did nothing to enhance my ride in any way.

ps. Jeff, my odo under reads slightly with my new rear tyre. On my old worn tyre it over read. So you can see the problem manufacturers face. They do not build in an error as some folks think, it's just physics. So on a recent 300 mile run I actually showed 295 miles on my odo (an error not worth worrying about). However, my onboard computer showed a 4% under read of my mpg so I got better fuel economy than the bike was showing. All taken from gps readings which in themselves are not accurate at this level. Conclusion: this info is not worth a whole pile of beans!
 

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Considering the speedo's and odo's all vary from bike to bike in how much they vary from the actual speed or mileage, I wouldn't worry about it. ...
That was in the age of mechanical speedometers, but odo's were directly mechanically driven, so the only difference was the actual tire's circumference.

Now both are electronically driven, so any error is strictly intentional from the manufacturers' side.

The fault is +10% with new tires, and gets worse as they wear.

Every time I'm out riding, I immensely enjoy that the speed displayed by the huge digital speedometer on the 650's dash is the actual speed within less than ½ kph.

It's such a PITA here in Denmark that recent focus on the revenue-driven speed trap vans have made the clueless drivers drive even slower, never exceeding the posted limit on their +10%+3kph lying speedometers, making speeds of between 68 and 72 kph the norm on wide 80 kph roads, were we used to drive 87 without the Police lifting an eyebrow.
 

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Discussion Starter #8
Well said!!

I am really not concerned about the fuel milage, I am merely curious. I am just one who likes to always know or know the possibilties.

Thanks!!

Jeff


Considering the speedo's and odo's all vary from bike to bike in how much they vary from the actual speed or mileage, I wouldn't worry about it. The amounts they are off tends to be overall quite small and of course will vary all the time depending on tyre wear, tyre pressures, temps, weight carried etc etc. Here in the EU speedos must not be more than 10% off at any speed, but most are much more accurate than that. I've used speedo healers and other makes in the past but these did nothing to enhance my ride in any way.

ps. Jeff, my odo under reads slightly with my new rear tyre. On my old worn tyre it over read. So you can see the problem manufacturers face. They do not build in an error as some folks think, it's just physics. So on a recent 300 mile run I actually showed 295 miles on my odo (an error not worth worrying about). However, my onboard computer showed a 4% under read of my mpg so I got better fuel economy than the bike was showing. All taken from gps readings which in themselves are not accurate at this level. Conclusion: this info is not worth a whole pile of beans!
 

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Been awhile since my 650 CVT went out in Nov 2014. It was a 2007 model..

Speedometer compared to GPS was 10% high with OEM Tire and I think it was 5 or 6% high with Car Tire. But Odometer was close to GPS.

I now have 400 Burgman and it's speedometer was off compared to GPS 10% high with OEM tire and is off 7% high with Car Tire.

I have not checked odometer on the 400 with GPS, but compared to my buddies Valk on our trips - my odometer is off about a mile or 2 in in 100 miles (reads high). So, 1 to 2% high. But, who knows if his is right. ??

Anyway, using the odometer and gas consumption - been running 66 MPG since changed belt and went to Dr Pulley Sliders (19GM). MUCH better than old gas mileage.
 

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That was in the age of mechanical speedometers, but odo's were directly mechanically driven, so the only difference was the actual tire's circumference.

Now both are electronically driven, so any error is strictly intentional from the manufacturers' side.

The fault is +10% with new tires, and gets worse as they wear.
Erik, it's actually the other way round. Manufacturers attempt to make the speedo's as accurate as possible when the vehicles and tyres are new, and as the tyres wear the speedo's over read as the wheels turns faster for any given speed the bike is doing. Therefore the speedo's become less accurate. But there is no possibility for example that someone will get a speeding ticket based upon their speedo reading as 60 will actually be less than 60mph as those tyres wear so you are safe from that ticket. As someone who has been involved with engine, car and bike development, I can say for sure, that's how we do it. Whether mechanically driven or electronically driven the outcome is the same. There are also many many other factors (not just tyre wear) that affects how accurate the speedo is at any given time, some of which I mention in my earlier post. Particularly rider weight and tyre pressures, which have a huge effect on wheel circumference and speedo accuracy. All of which the manufacturers have no control over. I'm 175lbs and with me on the bike my speedo is only a tiny bit off by about 2%. But when my buddy rides my 400 who weighs in at a hefty 235lbs, my speedo is way off by around 6% even with the rear tyre inflated to 36psi (the passenger inflation fig). This all figured out by gps readings of course. There is no built in deliberate error by manufacturers, just a whole pile of variables that they have no control over. If we want accurate speedo's then the bikes need to come from the factory with a satellite link to allow gps calibration and in my view is totally unnecessary. Most folks are not bothered by any of this anyway. If anyone is then your system is fine of course.
 

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I don't buy your excuses for the industry going right to the edge of legislation, by referring to production inaccuracies decades ago.
Look at washing machines. The temperature at each setting is precisely as low as the legislation allows.
I worked with air conditioning, where a 10% lack of cooling power is allowed. As a consequence, all effects were quoted 7.5% above actual, because the known variance was 2.5%.
Legislation made by salesmen (liars) for other salesmen (liars)

For normal road-going vehicles, the variables you mention are much less than the 10% allowed and fully exploited by Suzuki and Volkswagen, to name two that I have first-hand knowledge of. The OEM 185/60R14 tire on my car has a circumference of 1814.5 mm when new and only 2.8% less when worn fully bald (8.8 mm less thread) 165/70-R14 has 1.5% more circumference when new than 185/70-R14.
There's no excuse for the manufacturers to make the speedometers show exactly as much to much as the laws allow.

It should be the odd person who puts on knobbies on his road going bike or vice versa's problem that his speedo is off, not the non-modifying majority being punished by grossly optimistic speedometers.

It's a royal PITA when the nitwits block the traffic by never exceeding the posted speed limit on their +10% +3kph intentionally "bragging" speedometers.

The vehicle manufactures should make the speedometers dead-on with new OEM-spec tires and leave it to the owners who put on different tires to correct the speedometer accordingly.

Who doesn't have (access to) a GPS-based speed measuring device these days?
 

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It's such a PITA here in Denmark that recent focus on the revenue-driven speed trap vans have made the clueless drivers drive even slower, never exceeding the posted limit on their +10%+3kph lying speedometers, making speeds of between 68 and 72 kph the norm on wide 80 kph roads, were we used to drive 87 without the Police lifting an eyebrow.
Off topic... Sammy Hagar did a song back in the 80s, "I can't drive 55". And that was MPH. I can't even do 65 mph. 80 kph would drive me insane. And all the tickets you speak of. By God, I'd move.

Come to CA. Weather's great. Very few automated ticket machine (just some red light ones). We have great roads and lane splitting. And the cops don't even look at you if you're at 75 MPH or lower. Heck, you have to be going over 80 Mph for them to spin the lights. Sunday mornings they're always out in force on the freeways. I usually cruise by at 75 and wave. They wave back. Lol. Its nice. :D
 

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Erik, it doesn't matter that you don't 'buy it'. That's just how it is I assure you. Manufacturers don't build in the error. It's the laws of physics and variables that do that. It wasn't me referring to 'production inaccuracies' from year's ago, it was you in your earlier post. You also don't seem to understand the issues that manufacturers face regarding the designing of a speedo that is completely accurate. It's not possible unless the bike is using a gps based speedo correction device which will add to the cost of the new bike. What most bike manufacturers do (car systems are designed to work the same way) is design the speed sensing system to operate with the average rider weight onboard and hope that the rider also runs the correct pressures in his or her tyres. This gives quite good accuracy and fit the bill for most folks. Furthermore, tyre wear creeping in over time adds to the problem. But it's only part of the issue. It's the weight the bike is carrying too that dictates what the wheel circumference is and this factor has even more effect than tyre pressures. Other things like ambient temperature and the tyre temps also will cause a speedo variance and some other factors too. So you see Erik it's not possible to make the speedo completely accurate for everyone without using a gps system to constantly recalibrate, which frankly is overkill and not required. That's why some folks say their speedo is 10% off, but other report that theirs is only 2% off and others may be anywhere in between. It can be different for everyone due to all those variables we have been speaking about. I would add that comparing issues with dishwasher operating temps and speedo inaccuracies have absolutely nothing in common as the dishwasher thing is down to manufacturers, speedo inaccuracy is down to physics and all the variables that the manufacturer has no control over. It's an interesting topic though.
 

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All the things you mention do not warrant the speedo showing 10% to much with new OEM tires.
+5% with worn-out tires would cover all the scenarios you list.
The guys fitting different tires should be left to clear out their own mess, so should people under- or over inflating the tires.

What happens above the speed limit of 130 kph or above is irrelevant, the speedo should be accurate in the range where we want to go as fast as possible without getting a speeding ticket.

If anyone is claiming his non-mechanical Suzuki Burgman speedometer being only 2% optimistic, he is either using a larger tire or not using a GPS for reference.

I come to think of the Japanese company signing a contract with an American company, where 2% defective parts were acceptable.
The Japanese asked if the Americans wanted them to pack the defective items separately.

The ONLY reason for the speedometers to be intentionally that far off is to please the customers with their vehicles having a higher top speed than listed and for making people drive slower.
Those stupid ideas should have been killed 20 years ago, when GPS became affordable.
 

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Sorrry Erik but you are way off with your assertions. But that's ok, we live in the free west! Many folk believe what you do. I can tell you however, the weight the bike carries is one of the most influential factors, along with tyre pressures and tyre wear. You don't have to take my word for it. It's something you can probably test yourself with a gps if you do it right. Note how the inaccuracy of your speedo increases with a passenger and luggage. Use a Tom Tom gps or something like that and it won't lie. In manufacturing engine testing on pre-production bikes it's important we get real time speedo readings to match our dyno output graphs. Our more sophisticated dyno's show speed vs power/torque/revs and a whole bunch of other stuff. We use a speedo healer to correct for inaccuracies before a run and it's very noticeable how the speedo varies between riders due to their weights being different. We factor in temperatures etc etc so that's not a problem. My B400 speedo is only off by 2% with my new rear tyre and that's been checked with my gps but previously with my worn tyre it was off much more (6%). My weight allows for that level of accuracy but someone else may not obtain that 2% due to different rider weight. You must also remember that speedo inaccuracies tend to be overall much more on scooters and maxi scooters due to smaller wheels. They rotate a lot more than bigger bike wheels for any given mile ridden increasing any inaccuracy. Again, that's just laws of physics and cannot be corrected by the manufacturers due to the variables we all suffer on our bikes. I will just say that manufacturers do allow for a small over read at 30mph to be sure owners will not get a ticket. That's just sensible. And we are only talking about 1-3mph. Even without that error, error would still be there. The laws of physics will do the rest at all other speeds. Also it's worth remembering that gps is not totally accurate at some times either and can be off by at least 2% in our testing and sometimes, although not often 7%. It all depends on where you are in the world, how many satallites are up and one or two other factors. Like I said it's an interesting subject with much misinformation surrounding it and much nonsense talked about it.
 

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From your wall of text.

The speedometer should not be optimistic to save us from ourselves, it only leads to some people always going "x-over" on the speedo, because they know it is optimistic, while others either think the speedo is accurate, or that the posted speed limit means that your speedometer, regardless of how optimistic it is, should never show more than the posted speed.

Secondly, on your 400, with analog scale, you can't read the exact speed anyway, while I on my 650 with cruise control can compare a direct number "85" with the GPS display and confirm that they agree within less than a digit, in the way that they rarely differ by 1 kph for more than a short while.

Let the speedo be 1% pessimistic with new tires, inflated to the limit, and a very light rider, and we might creep up to 10% optimistic with under-inflated worn out tires, riding 2 fatties up with lots of luggage.
Starting up with 10% optimistic and getting worse as you go is just wrong.

I have never experienced any fluctuations in the GPS vs. road speed measured through the tire, and also never any disagreement between up to 3 simultaneously running GPS's in my car.

When you say "in our testing" I think you have a horse in this race, on the manufacturer's side, who are interested in skewing the facts, by fooling the consumers into thinking that their vehicles' go faster and use less fuel at a given speed than actual.
Cheating on the scales, in other words.
 

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Your wheel circumference also reduces when you go round bends or lean into a crosswind

The discrepancy is for margin of error.
There are agreed regulations that require vehicle speedos to made so they cannot show a lower speed than actual (along with position of lights and all kinds of annoyances to the designer - component type approval, whole vehicle type approval and "construction and use" regs)

No conspiracy, just physics and legislation

There are speedos that are accurate.
They are used in testing and data collection and have to be certified with frequent and expensive testing to keep them that way - no motorist would put up with that level of effort.

GPS is not an accurate way to measure speed
 

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BS
The discrepancy is CMY for the manufacturers.

As to GPS being inaccurate, I have driven endless hours with cruise control on German Autobahns, and there has never been any difference in where the speedometer needle was at a certain speed indicated on the GPS.

Drop your sorry excuses. The speedo can and should be dead on with new OEM tires, half-full tank and only the driver.
It's always the drivers responsibility not to exceed the speed limit, and those who put on non-standard tires must make their own arrangement to know their true speed, it should not be the rest of us being forced to correct the displayed speed some way or another.
 

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Erik, in case you hadn't noticed, new tyres often do produce the most accurate reading. I've never seen a bike or car that produces anywhere near a 10% off reading with new tyres. You will see that I do say that in my earlier posts. Anyone putting on non standard tyres is none of my concern or the manufacturers. They are on their own. I don't work and have never worked for a manufacturer, just an engine design and development firm and I've teched as a master for Honda and Nissan franchises too. We as an engine design and development firm in turn were hired by some manufacturers to develop new engines and sometimes that entailed starting from scratch with a completely new design. This also involved considerable travel (by bike whenever I could) to get to our offices overseas. In some parts of Asia where we had workshops for blueprinting and repairs to our engines the gps signal was not as reliable as many might think. This leads to some inaccuracies and these inaccuracies can be a major concern for development firms like ours (I actually retired early last year). I used to ride up to 55,000 miles per year on intercontinental runs (used my GSX1400 and my 1000 Vstrom for that) so I noticed inaccuracies more than most. They are not frequent or big most of the time but they do exist as many will tell you. Lots of reasons for that. No sorry excuses or the BS you accuse me of.

ps. Bluebottle is right about the legislation concerning the speedo margin or error that has to be complied with.
 

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Hmm, this has been a topic of debate for many years.

Many vehicles do have variances.

On one extreme we have my wife's Lexus LS which is 100% accurate (speedo and odo) when compared against the GPS. The fact that the vehicle has laser (vehicle sensing) cruise control suggests that the greatest degree of accuracy is required in order to maintain given distances from other vehicles.

On bikes, the worst I had was a Bandit 1200 - 14% optimistic fresh off the factory floor using standard tyres.

I do not believe that either passenger weight, or tyre wear is a major factor in speedo inaccuracy - do the sums (I have) and you will discover that at most it will be 1-2%, which is nothing compared with the ~ 10% standard optimism on most motorcycles. As a matter of fact that 1-2% is equal to the standard optimism built into the odometer.

The simple fact that the odometer is accurate to a much higher percentage than the speedo tells us very clearly that the manufacturers are simply "painting the lines and numbers in the wrong place (or 10% to the left of where they should be).

There is no excuse for this on standard road going vehicles. As you mention Erik, the manufacturers either want us to believe the bike is going a lot faster than it is (e.g. Honda claiming their Blackbird was the first bike capable of 300kmh when 300kmh on the speedo is only 265kmhh actual) or they see themselves as supporting some form of nanny state by misleading us to travel more slowly (safely) than we otherwise would.

Ultimately, I have no quibble with what the manufacturers are doing now that (in the age of GPS) we know what they are doing (personally I also knew this quite a few years earlier as from the late '90s I would always fit bicycle computers to my bikes) . There is no point banging our heads against brick walls either, trying to get the manufacturers to change - they won't.

It is what it is, we know how to workaround it if we are not happy, let's leave it at that.
 
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