OK, OK. There's a standard bar in Paris and a more accurate definition based on wavelengths of light emanating from Krypton. So we know how big a metre is. Or do we?
Earlier this year I did the Shropshire Hills sportive. Now I got quite a bit wrong; bad breakfast, probably not really fit enough after the crash etc and I found it a bit of a struggle. Having said all of which, it seemed to be more of a struggle than the comparatively easy stats on the route said it would be even given those conditions. I therefore took some solace in the fact that Mike's Strava app suggested that the height gain was about half as much again as the route setters suggested. When I got home I plugged it into Bike Route Toaster - which agreed with the course setter. At the time I wrote this off as inaccuracy in the strava app, but I now realise there's much more to it.
This Saturday I went off for a training ride round Somerset. I missed a turn going through Wells and ended up going out to Shepton Mallet. Nice run, but I didn't know the stats on the route so when I got back I put the route into 'toaster'. The map and profile are below...
So, a pretty typical 40 bit mile mendip cycling route involving going over the top once. Total ascent, as shown by the snippet below, 574m.
Now toaster is a useful website. It does the whole mapping and analysis thing very well. But it doesn't do gradients. I'd been quite surprised on the route by the long hill up from not far out of Wells to above Shepton Mallet. Good training for the Exmoor Beast next week perhaps. I've recently discovered 'Ride With GPR' which does do gradients, so I put the route into that as well - see below.
...67km (which equates to 41.5 miles) and 520m of ascent. It seems that the various websites have broad agreement on the length of a kilometre and/or mile, the worst spread that can be argued is a 2% range. The metre, on the other hand, seems to show little standardisation. How can the same route possibly be measured as having anything from 520m of ascent to 878?
I have a theory. Someone out there may even know if I'm right. I think it's down to the level of precision in the mapping. My guess is that Bike Route Toaster and Bike Map are looking at the altitude of the road less often than Ride With GPS does. If BRT and BM are looking every 100m then they won't see all the small undulations of the road. If RWGPS is looking every 10m then it would. I know it's possible to 'see' with GPS on a 10m grid - we used to be able to do that in geophysics 30 years ago. I don't know what the resolution is these days but I'd be surprised to find that it's much worse than 0.5m - if you pay enough.
Does it matter? Yes, I think it does. Next week I'm doing the Exmoor Beast which I entered when I found, much to my surprise, that it had a total height gain of rather less than an event in Gloucestershire that I was intending to do. But has it? I don't know. I know the figures that the two 'advertising sites' gave but I don't know if they're comparable. If the organisers in Gloucestershire used an altitude assessment based on 10m mapping and those doing the Exmoor Beast used a 100m grid then the results won't match up. It's even quite likely that if they'd chosen their mapping tools the other way round then I would have been getting soaked in Gloucestershire today! Unless there is a standardised system for analysing height gains on routes then we won't really know what we're signing up for. The only other solution would be for the event organisers to publish their actual routes well in advance so that we can all put them into our own preferred analysis tool and see what we're up against. Somehow I don't see that happening.
What does this tell us? Firstly, we can't trust the height gain data that we read for anything except a continuous climb with no undulations, certainly not for any 'ride'. Secondly, for our own purposes we have to pick an analysis tool and stick with it so that we compare the rides we do in our own heads. Trouble is, I rather think I should switch to a 10m resolution tool from the 100m one I think I'm using at present as only then will I be able to make sense of why some days seem so much harder than the hills on the road suggest they should be. Oh yes, I need to remember to eat properly before I go out as well.
DP
Earlier this year I did the Shropshire Hills sportive. Now I got quite a bit wrong; bad breakfast, probably not really fit enough after the crash etc and I found it a bit of a struggle. Having said all of which, it seemed to be more of a struggle than the comparatively easy stats on the route said it would be even given those conditions. I therefore took some solace in the fact that Mike's Strava app suggested that the height gain was about half as much again as the route setters suggested. When I got home I plugged it into Bike Route Toaster - which agreed with the course setter. At the time I wrote this off as inaccuracy in the strava app, but I now realise there's much more to it.
This Saturday I went off for a training ride round Somerset. I missed a turn going through Wells and ended up going out to Shepton Mallet. Nice run, but I didn't know the stats on the route so when I got back I put the route into 'toaster'. The map and profile are below...
So, a pretty typical 40 bit mile mendip cycling route involving going over the top once. Total ascent, as shown by the snippet below, 574m.
Now toaster is a useful website. It does the whole mapping and analysis thing very well. But it doesn't do gradients. I'd been quite surprised on the route by the long hill up from not far out of Wells to above Shepton Mallet. Good training for the Exmoor Beast next week perhaps. I've recently discovered 'Ride With GPR' which does do gradients, so I put the route into that as well - see below.
Now, if you look closely at the cross section on the bottom of the snippet you'll see that Ride With GPR gives the route at 42.3 miles with 2854 feet of ascent. Toaster provides a pretty close match on the distance travelled. After translation from kilometres it comes up with 42.05 miles. Both figures tally reasonably well with the data from my bike computer which gave 42.8 miles. However...
The height information is in major disagreement. Toaster, as I said, gave a height gain of 574m. After conversion from feet to metres (divide by 3.25 if you don't know) Ride With GPR gives 878m. Surely they can't both be right?
Another mapping and analysis app that I've discovered recently is Bikemap.net. I like the idea that it can link up with an app called Bike Navi on my phone and thus, in theory, turn into a route guide while I'm out on the bike. I decided I'd plug the route into that to see which, if either, it agreed with. The result is below...
...67km (which equates to 41.5 miles) and 520m of ascent. It seems that the various websites have broad agreement on the length of a kilometre and/or mile, the worst spread that can be argued is a 2% range. The metre, on the other hand, seems to show little standardisation. How can the same route possibly be measured as having anything from 520m of ascent to 878?
I have a theory. Someone out there may even know if I'm right. I think it's down to the level of precision in the mapping. My guess is that Bike Route Toaster and Bike Map are looking at the altitude of the road less often than Ride With GPS does. If BRT and BM are looking every 100m then they won't see all the small undulations of the road. If RWGPS is looking every 10m then it would. I know it's possible to 'see' with GPS on a 10m grid - we used to be able to do that in geophysics 30 years ago. I don't know what the resolution is these days but I'd be surprised to find that it's much worse than 0.5m - if you pay enough.
Does it matter? Yes, I think it does. Next week I'm doing the Exmoor Beast which I entered when I found, much to my surprise, that it had a total height gain of rather less than an event in Gloucestershire that I was intending to do. But has it? I don't know. I know the figures that the two 'advertising sites' gave but I don't know if they're comparable. If the organisers in Gloucestershire used an altitude assessment based on 10m mapping and those doing the Exmoor Beast used a 100m grid then the results won't match up. It's even quite likely that if they'd chosen their mapping tools the other way round then I would have been getting soaked in Gloucestershire today! Unless there is a standardised system for analysing height gains on routes then we won't really know what we're signing up for. The only other solution would be for the event organisers to publish their actual routes well in advance so that we can all put them into our own preferred analysis tool and see what we're up against. Somehow I don't see that happening.
What does this tell us? Firstly, we can't trust the height gain data that we read for anything except a continuous climb with no undulations, certainly not for any 'ride'. Secondly, for our own purposes we have to pick an analysis tool and stick with it so that we compare the rides we do in our own heads. Trouble is, I rather think I should switch to a 10m resolution tool from the 100m one I think I'm using at present as only then will I be able to make sense of why some days seem so much harder than the hills on the road suggest they should be. Oh yes, I need to remember to eat properly before I go out as well.
DP
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