If I'm right about the difference between the height gains on different route mapping programs being down to the size of the mapping grids then the following should both be true: -
1. On a straight-forward climb such as Cheddar Gorge there should be very little disparity between the systems as there are no up and down undulations for the map to consider - only ups of different gradients.
2. On a moderately hilly ride route there should be considerable variation as the undulations are seen on the 10m grid but not on the 100m one.
So here goes - First; a look at Cheddar Gorge
Taking the start point as the bridge over the River Axe at the foot of the gorge and the top point as the split where the B3371 leaves the B3135...
we get the following stats from Bike Route Toaster...
...and from Ride with GPS we get...
...3.3 miles, 829 feet of ascent and 189 feet of descent. Hang on! Where's that descent? Anyone who's ridden this section of Cheddar Gorge will know that there just isn't the best part of 200 feet of descent on here. There also isn't a significant drop after about 0.8 miles - this is right in the heart of the harder section of the climb. In other words - the mapping is wrong!
If we go ahead with the comparison anyway...
829 feet is the equivalent of 255m - and irrelevant. As the drops aren't there so there has to be 189 fewer feet of ascent than this. This suggests a real height gain of 829 - 189 = 640 feet or 197m. This compares with the BRT height gain of 186m. A difference of 11m; or just about 6% of the BRT figure.
Of course, there arises the question as to whether the 'height drop' suggested by RwGPS is just a one off blip. Another local climb that just goes up is Shipham Road, Cheddar.
Taking the start at the junction with the A371 to the top where the road is just about to descend to the western end of Longbottom...
BRT gives...
where as RwGPS gives...
This time there is no mapped in descent so the figure ought to compare. RwGPS gives a height gain of 463 feet which converts to 142m. This compares with the 133m height gain suggested by BRT, a difference of 9m or just under 7% of the BRT figure. There seems to be some consistency in the way the numbers pan out.
So what of a 'ride' over undulating road. I've kept this very short to allow for comparison of a sort to the climb routes. The chosen ride starts at Sidcot/Winscombe traffic lights, goes through Winscombe out down Barton Road to the Webbington Hotel and then returns via Shute Shelve. Apart from the pull over Shute Shelve this is a flattish, but never flat, run. Ideal...
The figures for BRT say...
where as RwGPS has...
The 519 feet of ascent on RwGPS converts to just about 160m. Compare this with the 99m claimed by BRT and we have a difference of 61m or 62% of the BRT figure.
It seems I may be right. The 6 to 7% differences on the climbs aren't great, but it's not a massive issue. The 62% difference on the short ride does indeed suggest that BRT is missing much of the undulation on the ride and therefore coming up with a smaller figure for total ascent. This fits very well with he theory that BRT is mapping on a 100m grid where as RwGPS is using a 10m one. Whether that's right or not, the disparity is real.
I don't think that we can be giving each other indications of how hard routes are via these mapping sites without agreement of what we are using. Using BRT I've worked on the basis that a comfortable day's ride has an average gradient of 1m of ascent per 100m of horizontal travel; a really hard day about 1.6m. When I've looked at the stats for some of the sportives and seen averages that were in the top end of this or even beyond it I've wondered how anyone (or indeed 1500 anyones) could cope with them. When I've been out on sportives and similar I've found that I cope as well as most, better than many. Those sportives that I've shied away from - were they really that hard, or were their routes just assessed on RwGPS or some equivalent, accentuating their height gains and making them seem excessively hard. Some of each probably. Which leaves me to make one plea...
Will all course setters and reporters, please, indicate which program they have used to assess their route with or, better, provide a course route that we can then plug into our own preferred options so we really know what we're letting ourselves in for.
Rant over!
DP
1. On a straight-forward climb such as Cheddar Gorge there should be very little disparity between the systems as there are no up and down undulations for the map to consider - only ups of different gradients.
2. On a moderately hilly ride route there should be considerable variation as the undulations are seen on the 10m grid but not on the 100m one.
So here goes - First; a look at Cheddar Gorge
Taking the start point as the bridge over the River Axe at the foot of the gorge and the top point as the split where the B3371 leaves the B3135...
we get the following stats from Bike Route Toaster...
...and from Ride with GPS we get...
...3.3 miles, 829 feet of ascent and 189 feet of descent. Hang on! Where's that descent? Anyone who's ridden this section of Cheddar Gorge will know that there just isn't the best part of 200 feet of descent on here. There also isn't a significant drop after about 0.8 miles - this is right in the heart of the harder section of the climb. In other words - the mapping is wrong!
If we go ahead with the comparison anyway...
829 feet is the equivalent of 255m - and irrelevant. As the drops aren't there so there has to be 189 fewer feet of ascent than this. This suggests a real height gain of 829 - 189 = 640 feet or 197m. This compares with the BRT height gain of 186m. A difference of 11m; or just about 6% of the BRT figure.
Of course, there arises the question as to whether the 'height drop' suggested by RwGPS is just a one off blip. Another local climb that just goes up is Shipham Road, Cheddar.
Taking the start at the junction with the A371 to the top where the road is just about to descend to the western end of Longbottom...
BRT gives...
where as RwGPS gives...
This time there is no mapped in descent so the figure ought to compare. RwGPS gives a height gain of 463 feet which converts to 142m. This compares with the 133m height gain suggested by BRT, a difference of 9m or just under 7% of the BRT figure. There seems to be some consistency in the way the numbers pan out.
So what of a 'ride' over undulating road. I've kept this very short to allow for comparison of a sort to the climb routes. The chosen ride starts at Sidcot/Winscombe traffic lights, goes through Winscombe out down Barton Road to the Webbington Hotel and then returns via Shute Shelve. Apart from the pull over Shute Shelve this is a flattish, but never flat, run. Ideal...
The figures for BRT say...
where as RwGPS has...
The 519 feet of ascent on RwGPS converts to just about 160m. Compare this with the 99m claimed by BRT and we have a difference of 61m or 62% of the BRT figure.
It seems I may be right. The 6 to 7% differences on the climbs aren't great, but it's not a massive issue. The 62% difference on the short ride does indeed suggest that BRT is missing much of the undulation on the ride and therefore coming up with a smaller figure for total ascent. This fits very well with he theory that BRT is mapping on a 100m grid where as RwGPS is using a 10m one. Whether that's right or not, the disparity is real.
I don't think that we can be giving each other indications of how hard routes are via these mapping sites without agreement of what we are using. Using BRT I've worked on the basis that a comfortable day's ride has an average gradient of 1m of ascent per 100m of horizontal travel; a really hard day about 1.6m. When I've looked at the stats for some of the sportives and seen averages that were in the top end of this or even beyond it I've wondered how anyone (or indeed 1500 anyones) could cope with them. When I've been out on sportives and similar I've found that I cope as well as most, better than many. Those sportives that I've shied away from - were they really that hard, or were their routes just assessed on RwGPS or some equivalent, accentuating their height gains and making them seem excessively hard. Some of each probably. Which leaves me to make one plea...
Will all course setters and reporters, please, indicate which program they have used to assess their route with or, better, provide a course route that we can then plug into our own preferred options so we really know what we're letting ourselves in for.
Rant over!
DP
Hi David,
ReplyDeleteMe and my partner are travelling from Oxford to the Mendips this weekend for a 60 mile-ish ride incorporating Cheddar Gorge. Would really appreciate some local knowledge of any must-do route suggestions, and more importantly, coffee stop recommendations.
Many Thanks,
Becci