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how to calculate average gradient of a hill
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11-06-2012 04:30PM#1
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You need a gps to get gradient.
The only way to work it out is if you know the distance cycled and the height gained.
Ride with gps, or strava might be able to give you the answer also.
..........or a bike computer with an altimeter
Try Ciclosport, they have models that do gradients or have an altimeter.
I got lucky with my model, it was on sale on bike24.com and for €110 I got:
bike computer with altimeter/speed/temperature/cadence/heart-rate-monitor/power,
and it can be all uploaded to the PC for (ahem cough "expert") analysis.
Example of a cheap Ciclosport.
Websites that could help you:
www.osi.ie
www.ridewithgps.com
www.strava.com
http://bikeroutetoaster.com
www.mapmyride.com0 -
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Recreational GPS is unreliable for altitude, BX19 is correct that map and ruler is the best way!
Altimeters (non GPS) are unreliable also, as they are air pressure dependent, and should be regularly checked against map for accurate altitude fixes based on position.
Map and compass is not a difficult skill, but not needed for road cycling. I do use map and and compass for reccy on new terrain, with GPS as back up only.
Yep, GPS units are totally useless for any accurate altitude fix. The unit itself has to do a load of math on the fly with several factors (google reference ellipsoid for the nerdy explanation) and any interference can throw the height way off. And if you go under a few trees on a wet day? Forget about it. If your only available GPS sats are on your horizon? Your altitude is going to be wildly off. Phones with built in GPS fall into this category.
The Edge 500 afaik has a barometric altimeter which is accurate enough but is air pressure dependent which can throw it off by a fair amount. I've not a clue how to adjust it. Usually in aircraft etc, it can be adjusted for the air pressure on the day. If you listen to the sea area forecast you can hear it been read out - eg. Belmullet, North-Northwest, 12 Knots, Fair, 26 Miles, 1008, Rising Slowly. The 1008 is the air pressure in Hectopascals. That's what's it dependent on.
OS map. Old reliable.
If you don't have them you can use the http://maps.osi.ie/publicviewer and zoom into the 1:20,000 scale and screengrab what you need and print it out.
See what years of mapping does to you?
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Scuba_Scoper wrote: »--- ..-. -.-- --- .-. ... .
I didn't know they allowed foul language like that on the boards !!! 0 -
Yep, GPS units are totally useless for any accurate altitude fix. The unit itself has to do a load of math on the fly with several factors (google reference ellipsoid for the nerdy explanation) and any interference can throw the height way off. And if you go under a few trees on a wet day? Forget about it. If your only available GPS sats are on your horizon? Your altitude is going to be wildly off. Phones with built in GPS fall into this category.
The Edge 500 afaik has a barometric altimeter which is accurate enough but is air pressure dependent which can throw it off by a fair amount. I've not a clue how to adjust it. Usually in aircraft etc, it can be adjusted for the air pressure on the day. If you listen to the sea area forecast you can hear it been read out - eg. Belmullet, North-Northwest, 12 Knots, Fair, 26 Miles, 1008, Rising Slowly. The 1008 is the air pressure in Hectopascals. That's what's it dependent on.
OS map. Old reliable.
If you don't have them you can use the http://maps.osi.ie/publicviewer and zoom into the 1:20,000 scale and screengrab what you need and print it out.
See what years of mapping does to you?
You can set altitude reference points on your Garmin, like your front door for instance, so it gets an accurate barometric reading at the start of a ride based off you factual altitude.0 -
You can set altitude reference points on your Garmin, like your front door for instance, so it gets an accurate barometric reading at the start of a ride based off you factual altitude.
Now I know. You would have to do that every ride when the weather is different though for it to be dead accurate.
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Recreational GPS is unreliable for altitude, BX19 is correct that map and ruler is the best way!
Altimeters (non GPS) are unreliable also, as they are air pressure dependent, and should be regularly checked against map for accurate altitude fixes based on position.
Map and compass is not a difficult skill, but not needed for road cycling. I do use map and and compass for reccy on new terrain, with GPS as back up only.
What he said, but also...
If you don't have the OSI maps to hand, you can explore them free on-line by clicking the explore map tab on www.osi.ie (direct linking doesn't work well). This will give you something like the following;
The grid interval (horizontal and vertical blue lines) is 1km, and the contour interval is 10m. The contour at the bottom of ballinagee (the Wall) is 170m and 240m at the top. The plan distance is 625m. The mean gradient as a percentage is 100*(Height difference/plan distance) = 100*((240-170)/625) = 11.2%, though as anyone who has cycled up the wall will tell you the steepest gradient is way more severe than the mean gradient in parts. If you carry out the same exercise at the two contours closest together you see they're 100m apart which yields a 20% gradient for than section. There are very few roads in Ireland that go over this gradient for anything other than a short distance, other than the likes of roads up to masts like Kippure and Mt Leinster. When scaling gradients from contours a rule of thumb is that the accuracy is plus or minus half the contour interval, so using pairs of contours over short distances is not going to be accurate.
OSi used to have a leisure mapping digital product called TrailMaster which I still use but the coverage is patchy in parts. Most of the other free on-line maps with elevation are based on the SRTM data set, though there are others. The OSi data is still the most accurate data that's readily available.0 -
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You can set altitude reference points on your Garmin, like your front door for instance, so it gets an accurate barometric reading at the start of a ride based off you factual altitude.
If your garmin is on as you leave the house, it'll get an altitude reading and will automatically recalibrate so you don't need to do anything. Dunno if you have to start it recording for this to work or if it just needs to be on.Now I know. You would have to do that every ride when the weather is different though for it to be dead accurate.
I wonder does the garmin use multiple readings at reference points to adjust the data in between. So, if you leave the house at 1008hPa and return 3 hours later at 1012hPa, does it adjust the intermediate values to fit? Incidentally, that pressure change equates to 40m of altitude.You may be ok starting out doing a recalib at a known spot height for example, but that does not mean a constant as a change in pressure over the course of the trip will result in errors.
Just having a look at the data for Dublin Airport, the average annual pressure change over 3 hours is 1.1hPa (or 11m) while the average annual max pressure change over 3 hours is about 12.0hPa (or 120m). Highest ever 3-hour change was 18.5hPa (or 185m) on 12th Nov 1991 in the midst of a howling gale (so you probably weren't out on the bike at the time)...0 -
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Morrisseeee wrote: »Slightly off topic but the OSI maps are good for searching for roads that have potential for climbing, ie. I found Shanrahan Hill and many other steep hills this way. The trick is to find a road that has a load of black lines accross it !!
I've done the same a fair bit, though exploratory trips down lesser used L-roads can lead you onto some very dodgy surfaces. The hill beside the church at Clara vale comes to mind, along with the backroad to ballinagee, and these are practically highways by comparison to some of the smaller Cork and Kerry roads where the term L-road means 'was mostly paved at some time in the past' 0 -
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underNope, gradient is the distance you travel in plan over the height you gain. See http://www.mathsisfun.com/gradient.html 0 -
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Source: me
Those are interesting slopes/curves, I wonder how you could measure the gradient of them?*
*Welcome to your Groundhog Day thread0 -
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there you go. 
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