One for the mathematically gifted.

[jimboalee]

You can be as accurate as you like measuring the circ' of your tyre, but as soon as you ride up or down a hill, is going to be different from a mapped distance.

GPS devices are always 'short'. ??? Who knows,,, what IS the true distance????

AUK rides are always planned 'over distance' by up to 10%.

If your computer says the distance was 100m short, add on another 4 kCals to compensate.

 

[GrasB]

You can be as accurate as you like measuring the circ' of your tyre, but as soon as you ride up or down a hill, is going to be different from a mapped distance.

GPS devices are always 'short'. ??? Who knows,,, what IS the true distance????

AUK rides are always planned 'over distance' by up to 10%.

If your computer says the distance was 100m short, add on another 4 kCals to compensate.

GPS are almost always short as they'll record distances between two points as a straight line, start weaving or go round sharp corners & you quickly lose a noticeable amount of distance. Okay there is some wander but most error is systematic rather than jitter.

 

[Banjo]

dont bother with all that, take your computer off and enjoy riding without the slavery of max speeds, averages, temp etc.

And for your longer rides look up, if you see a ruddy big lump of ground in front of you theres a hill coming up

Yes but is that "ruddy great lump" the last hill on your route or have you miscounted and need to save a bit for the next one?

I find it a phsycological boost to now how far I have gone and at what mileage to expect all the climbs.

I dont have (or want) a gps and find the computer handy for navigating as well.A note like turn right onto minor road 6 miles past such and such village is only usefull if you can measure the miles.

 

[jimboalee]

GPS are almost always short as they'll record distances between two points as a straight line, start weaving or go round sharp corners & you quickly lose a noticeable amount of distance. Okay there is some wander but most error is systematic rather than jitter.

Start weaving or go round sharp corners and the logging sofware recognises a change in direction and records a data point, which makes the history file MORE accurate. But YOU have unnecessarily lengthened your route,,,

Try these for example. -
Get off the bike and carry it up a stairway and the logging shows a 40% hill at 2 mph.
Get off the bike and throw it in the air and the logging shows a 100% incline at 0.0 mph.

In true life reality, lift the bike up a high kerb outside a control point and the logging shows a 60% hill at 1.5 mph.
Do a lot of walking round at the control point and climb a stairs to the loo, and the Garmin will show a lot of 2.5 mph bits followed by a 40% climb, some shaking around when you sit down and then wash your hands, and then a 40% descent back to the cafe.

This, as you would expect, plays havoc with the kCals calculator.

 

[Andy in Sig]

You can be as accurate as you like measuring the circ' of your tyre, but as soon as you ride up or down a hill, is going to be different from a mapped distance.

GPS devices are always 'short'. ??? Who knows,,, what IS the true distance????

AUK rides are always planned 'over distance' by up to 10%.

If your computer says the distance was 100m short, add on another 4 kCals to compensate.

True but if you are interested in the distance you have actually cycled then what you get from the computer is fine. In other words if the shortest distance between two points on a map is 1 mile but by going over a hill you have cycle 1.25 miles, then it is the latter which is the "truer" figure and the map becomes less relevant.

 

[jimboalee]

True but if you are interested in the distance you have actually cycled then what you get from the computer is fine. In other words if the shortest distance between two points on a map is 1 mile but by going over a hill you have cycle 1.25 miles, then it is the latter which is the "truer" figure and the map becomes less relevant.

If the map distances between two villages is 1.00 mile, but your computer records a distance of 1.25 mile because there is a bloody great hill between the villages, this is known as "a country mile".

The question I'd like to ask is,,, "When do you NEED to know the distance of a ride to an accuracy of 100 yds in 100 miles?"

 

[threebikesmcginty]

dont bother with all that, take your computer off and enjoy riding without the slavery of max speeds, averages, temp etc.

And for your longer rides look up, if you see a ruddy big lump of ground in front of you theres a hill coming up

I'm with you and colinj on this too - I just enjoy the riding and the great outdoors!!

 

[GrasB]

Start weaving or go round sharp corners and the logging sofware recognises a change in direction and records a data point, which makes the history file MORE accurate. But YOU have unnecessarily lengthened your route,,,

I was comparing to the true distance traveled v's the GPS distance not mapped distance v's GPS. When you weave & you GPS is sampling every 1s say it'll miss some of the distance you travel so an exaggerated weave from a kerb to kerb turns into a gentle meandering slalom of the cat eyes.

It's interesting when I look at the average speed calculated from wheel diameter v's GPS registered distance. Where I'm pot hole dodging or going quickly around a roundabout corner there's a fairly marked difference between the two but on straight (& it doesn't have to be level!) road there's negligible differences.

As for your example let me throw this one at you. On the 38% stairs with a nice wide smooth piece of metal for wheeling the bikes up & down if I wheel the bike up/down them I get +/-0.1m the correct length every time via GPS where as the wheel sensor always over reads by 0.5m or so (I'd hazard a guess if I actually rode on them the wheel sensor would be bang on).

What I do for my average speed is a crude GPS + wheel distance over 2 as I'm fairly certain that the wheel reading is going to read high rather than low.

 

[Davidc]

I was perfectly happy with a mechanical cyclometer! No battery, it just sat there working. I'd still be completely happy with a distance only device.

Cyclometers were available for all common wheel sizes, and despite not having any fine circumference setting I always got agreement with maps within better than a mile in a hundred (i.e. better than 1%) which is fine for almost any purpose.

On a car there's often 10mm diference in wheel diameter between a new and a worn out tyre, so 30mm in circumference. We don't recalibrate the odometer and speedometer for that.

 

[jimboalee]

I was comparing to the true distance traveled v's the GPS distance not mapped distance v's GPS. When you weave & you GPS is sampling every 1s say it'll miss some of the distance you travel so an exaggerated weave from a kerb to kerb turns into a gentle meandering slalom of the cat eyes.

It's interesting when I look at the average speed calculated from wheel diameter v's GPS registered distance. Where I'm pot hole dodging or going quickly around a roundabout corner there's a fairly marked difference between the two but on straight (& it doesn't have to be level!) road there's negligible differences.

As for your example let me throw this one at you. On the 38% stairs with a nice wide smooth piece of metal for wheeling the bikes up & down if I wheel the bike up/down them I get +/-0.1m the correct length every time via GPS where as the wheel sensor always over reads by 0.5m or so (I'd hazard a guess if I actually rode on them the wheel sensor would be bang on).

What I do for my average speed is a crude GPS + wheel distance over 2 as I'm fairly certain that the wheel reading is going to read high rather than low.

Toggle your Garmin to "Smart Recording" and your 'missing mileage' problem will be over.

 

[jimboalee]

On some Audaxes where I am unfamiliar with the area, I have 'Distance to Destination' displayed.

I'm not bothered if it miscalcs by 100yds. When it shows 0.25 miles, I get the 'Coffee and buns' urge, and weariness leaves my body.

 

[GrasB]

Toggle your Garmin to "Smart Recording" and your 'missing mileage' problem will be over.

Actually mine uses nothing but "Smart Recording" & it still gets it wrong The problem is the sample time it takes to work out the direction is to large. Ignore the satellite/gps miss-sync here it you can see the road & my line will be on-nigh the same for both times I turn right coming from the south east. Okay I've not lost much but do that for every sweeping corner & it adds up quickly.

 

[jimboalee]

I don't understand the 'hang up' with distance measurement.

Most bike rides are for a purpose. Work, Audax, visiting friends etc. Only race training rides are pre planned and should be well over the race distance anyway.

So the distance must be ridden. Home to work may be a nominal 10 miles by ViaMichelin, OS, bikely, mapmyride etc. If one is concerned about being late, depart home five minutes earlier. If one is concerned about calories, it will be a handfull, 25 at the most will be the deficiency.

If it's an Audax you're entering, the distance is pre-planned by the organiser and is always more than the distance stamped on the medal. The nominal distance will be published, so aim to be a little faster than theory. About 1% faster and you will get your medal.

IF, and its a big IF, 250m error in 200 km causes you to collapse on the roadside with mental and physical exhaustion, maybe you should question your abilities rather than the accuracy of your distance measuring equipment.

 

[MacB]

I use the trip distance on my computer, in conjunction with printed routes, as a poor mans GPS. This is only on new routes and quite often involves stopping to make notes. I don't wear a watch either so the clock function can be handy.

Barring that I tend towards the ColinJ view now, my computer only goes on for long rides and training, where I want to record some stats. I no longer record any of my local trips and don't bother putting the computer on. It's rather liberating and I'm not sure I'll be replacing batteries on the comps when they run out.

 

[jimboalee]

Another amusing feature on Garmin is the 'ETA at Destination'.

With a route loaded and the device toggled to 'Bicycle', the Garmin estimates the arrival time at the route's end.

Name the destination with a 3 Letter abbreviation and the planned time of arrival, e.g. SOA 07:25 ( Stratford on Avon 07:25 ) or STW 09:10 ( Stow on the Wold 09:10 ) and you will be able to judge whether you will be on schedule.

It just so happens Garmin estimates the average speed of a bicycle as 12.5 mph. [A 27 mile trip home from work is estimated to take 2 hrs 10 mins.] This is the speed I aim to achieve on Audax rides, so I use it happily.

I break AUK rides into several sections and take a leisurely ride round the countryside.