Gradient Question

Bloggsie · 26-03-2015 2:41pm #1

Hows it going,

I have serious doubts over a gradient percetange shown by strava on my last spin. To those of you who know Bond Bridge(over canal & train track) heading towards the Rathcoffey Road on the way out of Maynooth(R148), the gradient was shown as 24%, that cannot be right!

Your comments please!

colm_gti · 26-03-2015 2:48pm

Were you pulling a wheelie as you went over the bridge?

Bloggsie · 26-03-2015 2:54pm

no, i was blowing out my A**e as it was my 1st spin since September, all the gym work does not make up for out on the road!

Charlie69 · 26-03-2015 3:08pm

I wouldn't trust strava tbh, there's huge discrepancy between elevation readings on my garmin compared to a couple of my friends also.

Luxman · 26-03-2015 3:19pm

Did you cross check with the garmin as you ascended? I have a speed bump (very small and short drag)on the way out of my village and strava has it as a cat 4 climbðŸ˜œðŸ˜႒

smacl · 26-03-2015 3:37pm

Bloggsie wrote: »

Hows it going,

I have serious doubts over a gradient percetange shown by strava on my last spin. To those of you who know Bond Bridge(over canal & train track) heading towards the Rathcoffey Road on the way out of Maynooth(R148), the gradient was shown as 24%, that cannot be right!

Your comments please!

Depends on the underlying elevation model being used, typically SRTM for Google Earth and OpenStreetmaps. Not much use for gradient over short distances. Better solution is to look at the Ordnance survey contour maps for the area, measure the distance on the road between two contours, and divide by the contour interval to get the gradient. e.g. if the contour interval 10m and the horizontal road distance between two contour lines is 50m the gradient is 10:50 = 1:5 = 1/5 = 0.2 = 20%. Not many 24% public roads locally AFAIK, maybe short sections of Kilmashogue / Wall / Devils Elbow.

07Lapierre · 26-03-2015 3:38pm

If you can cycle up the hill in the big chainring its a Cat 4

If you have to cycle in the small chainring its a Cat 3

If you have to cycle in the small chainring and you keep looking for a lower gear, it's a Cat 2

If you have to cycle in the small chainring and you can't breathe ... It's a wall!

Ryath · 26-03-2015 3:48pm

Charlie69 wrote: »

I wouldn't trust strava tbh, there's huge discrepancy between elevation readings on my garmin compared to a couple of my friends also.

Are you sure? Little known fact Ballinasloe is 124m bellow sea level and I once averaged 35.2kph on the Cat3 through it

Don't know why I can't do it in A4 races!

https://www.strava.com/segments/2412021

mcgratheoin · 26-03-2015 4:51pm

Bloggsie wrote: »

Hows it going,

I have serious doubts over a gradient percetange shown by strava on my last spin. To those of you who know Bond Bridge(over canal & train track) heading towards the Rathcoffey Road on the way out of Maynooth(R148), the gradient was shown as 24%, that cannot be right!

Your comments please!

Was it the gradient from your spin or was it the gradient listed on a segment. The segment gradients depend on the accuracy of the creator's GPS, hence you get some ridiculous segments like Ryath linked to. If you check out the KOM spin from that segment you'll see that the altitudes don't match up at all. I would like to see Strava have an option where a segment like that can be flagged and re-generated based off either some form of average or off SRTM. You may also notice weird elevation changes if you stop and start your GPS while taking a break, usually due to pressure changes.

Wishbone Ash · 26-03-2015 6:46pm

mcgratheoin wrote: »

... You may also notice weird elevation changes if you stop and start your GPS while taking a break, usually due to pressure changes.

Ah, that explains why I have to correct the elevation on a regular ride to Dublin City Centre and back. When I park up in Drury Street for a few hours and then resume the ride, the elevation profile looks like I fell off a cliff half way through the ride!

Cookie_Monster · 26-03-2015 9:46pm

gradient is done by temp and pressure rather than GPS so can be affected even if it starts raining during a cycle with the pressure change...

crosstownk · 26-03-2015 10:03pm

Cookie_Monster wrote: »

gradient is done by temp and pressure rather than GPS so can be affected even if it starts raining during a cycle with the pressure change...

That depends. Not all Garmins have a barometer (Edge 200 for example). Some just use a plot reference much like a phone app.

That said, my Edge 200 can sometimes indicate that I've climbed up to 60m in my first 0.2Km. Elevation correction usually sorts this out when I upload after the spin.

Bloggsie · 27-03-2015 2:05pm

mcgratheoin wrote: »

Was it the gradient from your spin or was it the gradient listed on a segment. The segment gradients depend on the accuracy of the creator's GPS, hence you get some ridiculous segments like Ryath linked to. If you check out the KOM spin from that segment you'll see that the altitudes don't match up at all. I would like to see Strava have an option where a segment like that can be flagged and re-generated based off either some form of average or off SRTM. You may also notice weird elevation changes if you stop and start your GPS while taking a break, usually due to pressure changes.

it was just that segement, 0.5 km 24.0 %. it is short & Im generally bushed by the time I go over it & it feels like Im on alpine stage of the tour. I have the app on my phone, i assume that its not all that accurate!

27-03-2015 2:18pm

GPS can do elevation but cheap ones tend to do it badly. I'm sure Strava take barometric and other data into account due to the variations in the data between different devices.

Gradient Question

Comments