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2volvos
Original Poster
449 posts
71 months
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Hi
Fitted a Sigma bike computer to my bike at the weekend. Just a simple non-wireless affair from Decathlon. Over the summer I've been using Mapmyride on my phone, and the standard weekday evening run comes in at 18.61km. Doing it last night the computer comes in at just over 20km. I'm pretty sure I've set the computer right with tyre sizes etc.
Simple question is which one should be more accurate?
Ta
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CoolC
1,900 posts
84 months
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I would expect the GPS one is more accurate.
When we go out on a regular 22 mile loop, my Garmin will say 22 miles, but my mates wireless computer (I forget which make it is) reads 24.5 miles.
Mapping the route on something like MapMyRide also says it's 22 miles.
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donfisher
343 posts
36 months
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I find the normal bike computers are more consistent, especially with constant updates to my Android that seem to mess GPS recording up. On any ride where you lose GPS signal I find they can over read by about 10-15%. In the end I got the wheel size setting on the Cateye to about as right as I could get it and use that in parallel with GPS. On my commute the computer and phone matched 99% of the distance for a year or so then after an update the computer still said 4.7, the phone 5.7. If I look at the map once I’ve uploaded it I’m going through buildings and weaving all over the place.
Also I used to keep the phone in a pocket in my shorts. Now it’s at the top of the rucksack and seems to be closer in line with what I’m doing on the computer.
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Vocal Minority
2,219 posts
22 months
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I have a cateye something or other super simple boggo computer.
It and mapmyride on android correlate to within 2-3% almost invariably.
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2volvos
Original Poster
449 posts
71 months
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Thanks for the quick responses...
"On any ride where you lose GPS signal I find they can over read by about 10-15%"
I think this could be a key aspect as the route does take me out into the country between Worcester and Droitwich - not the ends of the earth I know but coverage could be patchy over the course of a run.
I guess the trick is to keep an eye on them both and see if any consistent pattern energes.
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Vocal Minority
2,219 posts
22 months
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2volvos said: Thanks for the quick responses...
"On any ride where you lose GPS signal I find they can over read by about 10-15%"
I think this could be a key aspect as the route does take me out into the country between Worcester and Droitwich - not the ends of the earth I know but coverage could be patchy over the course of a run.
I guess the trick is to keep an eye on them both and see if any consistent pattern energes. You're my neck of the woods. I ride Malvern - Worcester and occasionally keep going to Droitwich. What route do you take?
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donfisher
343 posts
36 months
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2volvos said: I think this could be a key aspect as the route does take me out into the country between Worcester and Droitwich - not the ends of the earth I know but coverage could be patchy over the course of a run. FWIW I use a HTC and Googles MyTracks. There's a railway bridge with a set of lights infront of it and if I got caught under there for a while then I'm sure it would lose GPS and then mess up the reading a bit. I also found that for a week when my phone randomly deleted it's data settings it was overeading the distance. I'd set off still on wifi - then arrive and pick the wifi back up. The map trace looked right but the distance was 6.5 miles not 4.7 - Maybe some of these mapping apps need to keep the map online to be completely accurate? Perhaps it's losing data signal rather than GPS that's the cause of your difference.
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2volvos
Original Poster
449 posts
71 months
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Vocal Minority said: 2volvos said: Thanks for the quick responses...
"On any ride where you lose GPS signal I find they can over read by about 10-15%"
I think this could be a key aspect as the route does take me out into the country between Worcester and Droitwich - not the ends of the earth I know but coverage could be patchy over the course of a run.
I guess the trick is to keep an eye on them both and see if any consistent pattern energes. You're my neck of the woods. I ride Malvern - Worcester and occasionally keep going to Droitwich. What route do you take? A few routes to choose from around the lanes out of Droitwich in various directions - through Tibberton, Crowle, Hanbury and Oddingly. Sometimes Hadley and Claines (The Mug House adds to the attraction of that run ...). Usually about 45mins to an hour's worth. Nothing intergalactic, but once the kids are in bed not much time for anything too much further.
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CoolC
1,900 posts
84 months
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The problem with calibrating the computer to tyre size is that there seems to be no standard to which all the tyre companies work to.
a 26x2.0 from one manufacturer will be a different size to a 26x2.0 from another, giving a different distance per revolution figure on each.
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yellowjack
1,292 posts
36 months
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One way to confirm your tyre circumference is to:
1) First ensure your tyres are at 'riding' pressure.
2) Make a chalk mark on the bottom centre of your tyre sidewall, and a corresponding mark on the floor
3) Roll the bike forward in a straight line, preferably with your weight on it, until the chalk mark is back at bottom centre
4) Make another corresponding mark on the floor, measure the distance between the 2 marks
This method gives you an accurate measure of the distance covered with each revolution of the wheel, and some cycle computers (certainly older Cateye models) will allow you to stick in the exact measurement in millimetres when you first set them up.
One caveat with this method is that if you change to a different tyre size, or between winter/summer tyres, you should do this every time you change tyres to ensure accuracy. I know that more recent Cateye computers don't let you do the exact measurement thing, but it will allow you to get the nearest figure from the pre-selected list.
If you've forgotten how to set up/calibrate your computer, Cateye let you download the instructions in PDF form from their website.
[You may have gathered that I am a long-term user of Cateye products. Other cycle computers are available]
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daz3210
5,000 posts
110 months
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GPS is pretty accurate, until you lose signal. Then the GPS machine can give you random reports.
Like for instance, on one ride I went through a tunnel under a motorway. Top speed on that ride was reported as 160mph!
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clonmult
7,984 posts
79 months
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Vocal Minority said: I have a cateye something or other super simple boggo computer.
It and mapmyride on android correlate to within 2-3% almost invariably. Similar here - they're pretty darned close, on everything from a couple of miles down the road through to the 50+ mile routes. Just have to ensure that the boggo computer is properly calibrated for your wheel size, otherwise it'll be useless.
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ewenm
24,638 posts
115 months
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yellowjack said: One way to confirm your tyre circumference is to:
1) First ensure your tyres are at 'riding' pressure.
2) Make a chalk mark on the bottom centre of your tyre sidewall, and a corresponding mark on the floor
3) Roll the bike forward in a straight line, preferably with your weight on it, until the chalk mark is back at bottom centre
4) Make another corresponding mark on the floor, measure the distance between the 2 marks
This method gives you an accurate measure of the distance covered with each revolution of the wheel, and some cycle computers (certainly older Cateye models) will allow you to stick in the exact measurement in millimetres when you first set them up.
One caveat with this method is that if you change to a different tyre size, or between winter/summer tyres, you should do this every time you change tyres to ensure accuracy. I know that more recent Cateye computers don't let you do the exact measurement thing, but it will allow you to get the nearest figure from the pre-selected list.
If you've forgotten how to set up/calibrate your computer, Cateye let you download the instructions in PDF form from their website.
[You may have gathered that I am a long-term user of Cateye products. Other cycle computers are available] All of this. Don't trust the pre-set calibrations for your tyre size. Measure it as above and set that (or the nearest you can).
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2volvos
Original Poster
449 posts
71 months
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ewenm said: All of this. Don't trust the pre-set calibrations for your tyre size. Measure it as above and set that (or the nearest you can). Wise words, great mate. Thanks - I'll have a go at that. Similar to Daz's experience, GPS reckoned my top speed last night was 75kph. If only...
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j4ckos mate
367 posts
40 months
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Ive tried loads of different ones for mine,
personally ive found runkeeper the best, it has a cycling setting on it as well
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