Having recently been involved with the Adelaide Touring Cyclists it seems some people don't have the distance calibration of their bike computer accurately set.
While it is possible to get within 200m in 50 Km there were people who the calibration was more than 10% out.
If you have a computer with GPS all this just magically happens via satellite.
To get a high degree of accuracy you need to ride a known distance (for instance 1 Km) and then calibrate/recalibrate the computer.
This procedure is outlined on.
Some people struggle with numbers and calibrating instruments.
Some people even have not studied statistics at university.
After all there are all sorts of things that people are very tallented at that have nothing to do with numbers.
I know of an older woman who is computer illiterate but she can make great cake.
Would people be interested in a workshop or assistance calibrating their cycle computer?
There are a few odometer checking points around town.
If you look here you will see where they are.
(yes it is a car website, but sometimes car things are useful)
NOTE the distance on the Greenhill Rd check is 5.64km (as stated in text) not 6.45 as is on the picture!
I've seen the Greenhill Rd pole and never would have guessed how to use it.
Adelaide's suburban main north-south grid roads are 1 mile apart, so allowing for the width of the road, they are 1 mile 1.5 chains apart. That is, 1.640km. (For example, along Greenhill Road, from the centre of Unley Road to the centre of Goodwood Road. Compare this distance to what is actually recorded on your computer, and adjust the wheel circumference setting up or down in the same proportion. Or use a longer distance, using the routing tools in in something like Run Saturday, which allows freehand drawing of routes if required, to find the distance, and compare that with what is actually recorded on your bike computer.
The conversion is to the nearest metre, which is probably not a great deal more imprecise than the original survey, which used a chain with 201 wearing surfaces, and if used incorrectly, could result in large accumulated errors. (100 links, 96@8", 3@6", 1@7" (to allow for a 1" pole) arranged as 24x8, 6, 24x8, 6, 24x8, 6, 24x8, 7.) (The original survey of the Adelaide city was in error by about 2'6" at the corner of South and West Terraces, probably the fault of Light's 2IC, Kingston, who was incompetent.)
Oh dear, poor old Gus.
I started going Metric in the early 1970's. About the only thing I am still "imperial" for is how big are the babies? They be so many kg, but I also like to know how heavy. The reference to, use of, and school instruction in centimetres annoys me no end, as centimetres are not part of the Australian Metric standard. (Just as decimetres, dekametres and hectametres are not.) Also annoying has been the non-availability (until the last couple of weeks) of common-stock Metric nuts and bolts in hardware stores. If one wants BSW, that's what specialty fastener shops are for.
BTW, 60 next Saturday.
Get 5 bikes together, set odo to Zero and hopefully one of you has a GPS odometer.
Ride 5 kms in the same manner and compare reading but be guided by the GPS enhanced ones.
I rode down Upper Sturt road and my mates speedo would read 94km/h, the max I reached was 82km/h, thats a 15% difference and he was just on my wheel.
BTW, his was out as I checked mine against a GPS model many times. All this time he thought he was go so much quicker, even hit 102km/h at one stage, not sure where but I sure as hell was not ever going to better that.
GPS units will give different results to the wheel magnet types in very hilly country
Certainly comparing with a GPS unit gives a good indication of the accuracy on flattish country.
Like a lot of these discussions, you haven't decided what it is you want.
A GPS will not give you an accurate figure for actual distance covered because it doesn't allow for going up and down and probably doesn't cover wobbling from side to side ... and that's before you start considering how accurate the GPS measurements themselves are (and don't tell me 1cm because the thing gives numbers to 1cm).
Measuring yourself against a known bench mark, eg a 1km marked strip, will only give an accurate answer if you stick to a perfectly straight line - you won't.
It is surprisingly easy, even when being careful, to get a 10 % error, when rolling a wheel (or measuring wheel) along a tape laid out in a straight line, so attempting to ride in a straight line or push your bike without a guide line is fraught with errors.
Basically, you are not going to get an 'accurate' answer.
It comes down to what you are trying to achieve and how much effort you're daft enough to go to. For most uses, I would suggest measuring the circumference of your wheel by rolling it along a tape. Enter that number and them compare your results with known distances travelled - no, that doesn't mean your mate's readings, not unless you want to mirror his mistakes. From there it's just a matter of fiddling with the numbers ... if you can be pfaffed doing it.
On my own bikes, as long as they agree to 100m riding to work (sort of), I don't worry about it, and I only worry then because it makes my riding log look untidy if I don't (yes, I'm a numbers nerd).
ex surveyor, ex survey instrument salesman, ex lots of stuff actually but thems the ones that are relevant