Mileage Discrepancy

[Villager]

I've just travelled from Boston to Winchester, a journey I know to be 188 miles via a given route. However, my GS recorded it as 206 miles. I'm not overly fussed, but I'm curious as to whether this is normal, and what can affect it's accuracy. The only thing I can think of is tyre wear, and mine are probably 2/3 through their lives.

Incidentally, it's the first time I've done sustained motorway speeds since installing my 15t sprocket - it's a much more enjoyable ride, you've got top-end pull that was previously lacking.

[beRto]

I've just travelled from Boston to Winchester, a journey I know to be 188 miles via a given route. However, my GS recorded it as 206 miles. I'm not overly fussed, but I'm curious as to whether this is normal, and what can affect it's accuracy. The only thing I can think of is tyre wear, and mine are probably 2/3 through their lives.

Incidentally, it's the first time I've done sustained motorway speeds since installing my 15t sprocket - it's a much more enjoyable ride, you've got top-end pull that was previously lacking.

Is your front tire the stock size (110/70-17)?

Assuming the "actual" mileage is 188 miles, the 206 mile odometer reading quoted is about 9% high. The speedo is known to read about 10% high. I don't know much about the inner workings of the speedometer/odometer, but I suspect these high readings may be related. 

Maybe bring a GPS with you and run the route over again 

[anthonyd5189]

The odometer is read from the front wheel right?  So the only thing that would effect it then is the size of the front tire.

[surf.seppo]

beRto's got it right. The speedo and odo readings are taken proportionally to you. (The odo basically calculates the integral of velocity, using a fixed proportion to translate it into mileage). GS's are legended to read 10% high, so the mileage bump is about right. This also means that when it looks like you're going 50mph, you're only going 45. Handy to know when you're cruising at speed.

[ohgood]

beRto's got it right. The speedo and odo readings are taken proportionally to you. (The odo basically calculates the integral of velocity, using a fixed proportion to translate it into mileage). GS's are legended to read 10% high, so the mileage bump is about right. This also means that when it looks like you're going 50mph, you're only going 45. Handy to know when you're cruising at speed.

And another nice plus for keeping your money in your pocket. If the speed limit is 55, and you're cruising at 55 indicated, no way you're going to get noticed by the LEO's.

Not to mention you're actually traveling at around 50 mph, which is a pretty efficient speed gas wise.



I've read of some people that correct their electronic speedometers to be exactly correct. I wouldn't want to ride that bike. My truck is spot on, 55 indicated = 55 mph (i've verified with gps) and it's scary to know a slight slip of 5 mph could earn me a $100 ticket

[Chuck]

My GS reads 10% high in speed and distance too.   So when I think I'm getting 55mpg, it's only 50.

[manofthefield]

The odometer is read from the front wheel right?  So the only thing that would effect it then is the size of the front tire.

Yup

[GeeP]

The iron butt people say that all Japanese motorcycles read about 10% high in both speed and distance. 

So for Japanese riders it isn't 1,000 miles in 24 hours, it's 1,100 miles in 24 hours.   

[Janx101]

or possibly 900 miles in 24 hours .. since if they stopped at 1000 ... oh bugger it you know what i mean... i aint gonna be startin no fact war 

[Suzuki Stevo]

Out of all my Zuk's I have found most of my speedo's are around +8% high, while my Odo's are almost spot on (Garmin GPS)

EDIT: Maybe it's time to put the GPS in the map window of my tank bag and check the 500 again?

[twocool]

Out of all my Zuk's I have found most of my speedo's are around +8% high, while my Odo's are almost spot on (Garmin GPS)

EDIT: Maybe it's time to put the GPS in the map window of my tank bag and check the 500 again?

The speedo and the odo are not directly connected to each other.......they work on different principles......so it is posssible to have an error of say 8% on the speedo and be spot on on the odo...(this has been my experience).

You could actually just re-do the speedo dial, and paint on the numbers in the correct places........(8% to the clockwise)

Wrong size tire will mess up both speedo and odo


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[skirecs]

aren't odos geared and the speedos use the magnets

[twocool]

aren't odos geared and the speedos use the magnets

Yep......check this out:
http://www.explainthatstuff.com/how-speedometer-works.html

Shows how they use magnets and "eddy currents" to move the needle against a hair spring.

But again the accuracy, or inaccuracy of the speedo has little to do with the actual mechanism, and everything to do with the placement of the number gradations on the dial. 

The 8% or so error is intentional by the manufacturer.

My old '84 Honda scooter has a "digital" speedo.....worked on a different principle.......was exactly spot on, checked with GPS.........

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[007brendan]

The 8% or so error is intentional by the manufacturer.

Why would they intentionally add error?

[lucifer_mr2]

Because if it reads 1% low and some gets a speeding ticket they might start suing the manufacturer, instead of taking responsibility for their actions.

[sledge]

If you want a mechanical speedo/odo thats as close as possible 100% accurate across its range it will cost you more than some GS5s are worth!! Then you will need to have it regularly calibrated to ensure it stays accurate.

Most countries via their construction and use regulations allow a tolerance of  +10%/-0%. The idea is twofold, it allows manufacturers to produce speedos at a realistic cost without the need for regular checks/calibration and that in use you will never actually be traveling faster than the indicated speed.

[twocool]

If you want a mechanical speedo/odo thats as close as possible 100% accurate across its range it will cost you more than some GS5s are worth!! Then you will need to have it regularly calibrated to ensure it stays accurate.

Most countries via their construction and use regulations allow a tolerance of  +10%/-0%. The idea is twofold, it allows manufacturers to produce speedos at a realistic cost without the need for regular checks/calibration and that in use you will never actually be traveling faster than the indicated speed.

You could just throw on a $100 GPS and get very accurate speed readings.......

"electronic" speedo's, like the one on my '84 scooter are very accurate and not expensive........we've been using them on bicycles for years........you can actually measure your tire "roll out" and program it into the speedo, and you're really accurate....

Even a cheap "mechanical" speedo could be made to be a  lot better than 8% accuracy for no extra cost.......they just don't do it for other reasons..........

The idea of a calibrated speedo is more when you are using it for "legal" reasons.......like for law enforcement.....if it was not calibrated, then the case would not stand up in court.

One could also do a "poor man's " calibration using gps and simply draw some new lines onto the speedo glass, where the "real" speeds are......like 60 mph on the dial would be 55 on the glass, etc.

One of the (many) things I do for a living is calibrate aircraft instruments.....mostly altimeters.......yes a good altimeter is well over $1000 and the calibration is like $250, every two years........Many of these altimeters are upwards of 40 years old, and I seldom find one which is "bad" however.....


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