which is more accurate..

[sickboyblue]

cycle computer or map my ride phone app? Went out to test the new computer this morning but still used map my ride as well. Turns out they measured different distances, mmr measured about 1/4 mile more than my computer. Both gave the same average and top speeds. Probably just because mmr relies on gps. but i'm hoping i've not set my comp up incorrectly.

 

[ColinJ]

If your computer was set up perfectly then it should be slightly more accurate than the GPS since it counts every revolution of your wheels, whereas the GPS will often be sampling your position reading less often than that.

How long was your ride? A 1/4 mile difference in 3 miles is significant but that difference over 50 miles would only be 0.5%.

I've never bothered about that degree of inaccuracy. I did away with my bike computer since it seemed redundant once I bought my GPS. The distance reading that gives is very close to the distance that my mapping software gives for the same route.

 

[sickboyblue]

The ride was only 4 miles (ish). I reckon it could be as you said, a kind of lag on the gps. I'll see if the difference is any bigger on a longer ride.

 

[Fab Foodie]

Yiou know what? It really doesn't matter.

 

[snorri]

Yiou know what? It really doesn't matter.

It matters a lot if you're a nerd or geek

 

[Scoosh]

The cycle computer will record virtually every turn of the wheel, whereas the gps will only record movement above a certain minimum distance, AFAIK.

Gps systems only have an accuracy of - what - 1 metre (tops), while the cycle computer is recording every time the wee magnet passes the sender unit.

I'd go with the cycle computer distance ...

 

[AndyPeace]

As above, the cycle computer will be more accurate, provided it is set up with your wheel diameter. This is why Gps units, like Garmin, can be used with speed sensors. However, to track your progress either will work as long as you stick to one. I'd go with the bigger number

 

[neil_merseyside]

A bike with front and rear wheel cycle computer combo will give different distances on any ride, mostly due to the front wheel wobbling and the rear cutting turns, let's not mention different ends acting differently under load (search mickf on CTC forum for data) and returning different rev counts on the same road depending if it's up or down.
Bit anal whichever you go with, someone else will have gone faster or further - unless you hold the World Record!

 

[Fab Foodie]

It matters a lot if you're a nerd or geek

I'm sure help is available.....

 

[AndyPeace]

A bike with front and rear wheel cycle computer combo will give different distances on any ride, mostly due to the front wheel wobbling and the rear cutting turns, let's not mention different ends acting differently under load (search mickf on CTC forum for data) and returning different rev counts on the same road depending if it's up or down.
Bit anal whichever you go with, someone else will have gone faster or further - unless you hold the World Record!

I don't doubt your right, but the inaccuracies on either are still small enough not to matter. I searched mickf, but came up with no results, any chance of a direct link to the data

 

[MaxInc]

GPS data on a mobile phone can be inacurate over short distances. The way the software works is by reading GPS coordinates at set intervals sometimes as far apart as 5 seconds (to preserve battery) and estimating the speed and distance between several readouts by various formulas. The difference could come from corners when a datapoint comes from on direction of travel and the following point is in a different direction. The GPS doesn't know when you turned, at which speed, radius or weather you cut the corner or not, so it will make a calculated guess. GPS accurancy on a mobile phone in itself is pretty low, peraps 10m but sometime depending on the position of the phone on the pocket or backpack, obstacles such as tall buildings or trees could be 50m or more.

More data points (longer distances) will provide more accurate results.

If accuracy as well as data logging and mapping are important and you own an iPhone 4S or 5, you can try the Wahoo Fitness Cycling Speed and Candence sensor which will add more data to the algorithm and get you those precise numbers. If you are really geeky, you can even get the heart rate monitor sensor to track your fitness levels with every ride too.

 

[Ern1e]

I had a simular differnce between the comp on my bike and the one on the wife's (both same make of comp) set both up as per instructions but always got two slightly dif reading after the same ride's,it turns out that the numbers supplied by the makers are an average. so I was advised to put a chalk mark on the floor with the valve at the bottom then push bike forwards 1 revolution mark on floor when valve at bottom the measure the distance between in millimeters i.e. 2407 this is then the rolling circumference for that tyre per revolution which you then enter this in the comp.Much to my surprise the difference between the two tyres was 15mm ok not a lot on 1 rev but over a mile it will add up and so dose the inaccuracy,hope this helps you out a little.
Ernie.

 

[GrasB]

Gps systems only have an accuracy of - what - 1 metre (tops), while the cycle computer is recording every time the wee magnet passes the sender unit.

There is 2 types of accuracy. One is absolute accuracy the other is relative. A good GPS system is going to hit some kind of brick wall of absolute accuracy at 1m or so, typically it's closer to 5m. However it's relative accuracy (that is the position between two sample points) can be much higher. I have access to a £6000 GPS unit which has an absolute accuracy is no better than my Garmin Edge 500. However it has a relative position accuracy of 5cm, something my Garmin can't get close to.

 

[neil_merseyside]

I don't doubt your right, but the inaccuracies on either are still small enough not to matter. I searched mickf, but came up with no results, any chance of a direct link to the data

'Mick F' and revolutions did it, several pages...

http://forum.ctc.org.uk/viewtopic.php?f=5&t=56788&hilit=revolutions

 

[Davidc]

At that level take a look at the computer set up (especially accuracy of circumference measurement).

there will always be a difference. The normal sampling interval for GPS is 1 second, but can be set longer on some systems to save power, and the distance is made up of a lot of straight lines between sampling points, whereas wheels are in contact with the ground most of the time, most GPS systems seem to measure distance as if they were at an assumed sea level, computers measure the road surface distance, and so on.

As FF says, it doesn't matter at all for real cycling.

Bring back the Lucas Cyclometer!