Accuracy of max hill gradients using route mapping software?

[GuyBoden]

What has been your experience of the accuracy of max hill gradients using route mapping software?

 

[figbat]

I have no other reference to gauge it by.

 

[Dogtrousers]

The best thing to do is just use it as your only reference as @figbat says.

How else are you going to measure it?

You could get off your bike and use a spirit level or app. A bit of a faff.

Or you could look down at your GPS at the steepest part. I've tried this but at the steepest bit of a hill I tend to be unable to focus. And anyway, how reliable is the instantaneous GPS readings anyway?

 

[UphillSlowly]

What has been your experience of the accuracy of max hill gradients using route mapping software?

Depends how granular you want to get with your gradients? Is it acceptable to have Max gradient measured over 1m or 10m? Different software can vary quite a lot, but the most accurate, I believe is provided by LIDAR?

 

[Twilkes]

There was (is, I guess) a hill near me that I rode up a lot as a benchmark for how fit I was feeling (and/or what direction the wind was blowing in, let's be fair) and various mapping sites had the max gradient as anything between 18% and 25%. On a day when the wind was against me I actually stopped on the steepest bit to measure the steepness with an app on my phone, and the most I could find was 18%, nothing even close to over 20%. I know this is unscientific and gradient varies a lot when only measuring it using the length of a mobile phone, but even trying to find lumps in the tarmac that might artificially push it up I still could only get to 18%.

So basically pinches of salt all round.

 

[Dogtrousers]

Here's an example. Toy's Hill, first the gradient as predicted by RidewithGPS route planner. Max of 12.8% average of 3.8% (+191m, -14m over 4.8km)

And now as measured by my Garmin E530. Max of 13.7% average of 6.3% (+197m -3m over 4.8km)

So, as you'd expect the route planner is more smoothed out but in general they are pretty close.

 

[Ming the Merciless]

I only see them as a rough guide. Not sure my legs would be able to tell whether 18%, 20%, or 22%. They’d just know it’s steep.

 

[a.twiddler]

I have a feeling that if you plot it as just a few miles which include your selected climb, it might show it as steeper than it would as part of a longer route.

 

[HLaB]

I did a 12.8mile TT at the Weekend and a RWGPS plotted route said the max climb was 5.6% but the garmin recorded 13.2%. It tends to be closer on normal rides perhaps the garmin can't record fast enough a some speeds, at low speeds the garmin tends to be slightly under IIRC.

 

[GuyBoden]

I did a 12.8mile TT at the Weekend and a RWGPS plotted route said the max climb was 5.6% but the garmin recorded 13.2%. It tends to be closer on normal rides perhaps the garmin can't record fast enough a some speeds, at low speeds the garmin tends to be slightly under IIRC.

I find it very disconcerting that if you plot a long route, a stated 10% max gradient could in reality be a 20% max gradient.

 

[Dogtrousers]

I find it very disconcerting that if you plot a long route, a stated 10% max gradient could in reality be a 20% max gradient.

Ive never had that much of a difference.

I find the planner I use is pretty consistent so if there's any sustained distance over, say, 12% it's going to be "bloody steep", with a chance of being "effing steep".

There comes a point where all the different gradients merge into one as I struggle to keep the pedals turning without falling off.

for instance Yorks Hill (site of the Catford CC hill climb) is one of those. I've seen it described as anything between 15 and 22%. Personally I just class it as "aaaaarrgh"

 

[Richard Fairhurst]

I have a feeling that if you plot it as just a few miles which include your selected climb, it might show it as steeper than it would as part of a longer route.

Putting it as a shorter route is more likely to be accurate on some route planners, certainly.

 

[Alex321]

The best thing to do is just use it as your only reference as @figbat says.

How else are you going to measure it?

You could get off your bike and use a spirit level or app. A bit of a faff.

Or you could look down at your GPS at the steepest part. I've tried this but at the steepest bit of a hill I tend to be unable to focus. And anyway, how reliable is the instantaneous GPS readings anyway?

I usually have a GoPro mounted on my handlebars, which includes the Wahoo in the field of vision, so I can look at it afterwards to see what the max gradient was.

Like you, I tend to be unable to really look at it while working that hard.

But I also agree, it isn't necessarily that reliable, and always lags a little, so it will often be showing the steepest gradient just after the road has actually levelled off.

 

[Mr Celine]

I haven't done this segment since I got my Garmin.

I wonder what it will register during the near 800 feet vertical pitch?

 

[Dogtrousers]

I had exactly the same thing at the weekend. I was going up a typical Kent hill which is in a deep chalk cutting. I must have lost signal for a short while. I glanced down at my GPS and it was saying 26%. I thought "it's steep, but it's not that steep". No, the max gradient was not 38.4%

If I look at the same stretch going downhill (where I didn't lose signal) it's actually about 500m long (so I lost 200m when I had no signal) and has a max grade of 21%. It's definitely steep. But not vertical.