Percentage of grade - gotta love these hills!

[RolliePollie]

Does anyone have a feeling about how accurately Map My Ride calculates hill grade percentages? I don't have GPS so I can't cross check. I just mapped some of the hills on my local route and I'm kind of surprised by what it came up with.

My most hated hill came out to 20% grade () at the bottom, flattening out to between 15% and 17% as the climb continues. My heart rate really kicks up on that hill, so I assumed it was a pretty good percentage grade. Another steep section came out to 19% and several other hills calculated at between 12% and 15%. If these are accurate, then I know why I need my granny gear!

[Gowest]

I have to think those percentage of grades are too high. Even when I calibrate my Garmin it tends to read a few percentage points high.

Reason I say this is that 20% is a wall and here you will be in your granny out of the saddle and trying like heck to not pull up your front wheel and tip over. Most recreational cyclists cannot ride this grade.

Sustained grades of 15% are believable and can be ridden, but again I would think you would be out of your saddle alot.

Just my experiences from living in the mountains.

[Mr. Bloom]

This is an ongoing debate, but I'll share my experience:

In our area, we have Boltinghouse Hill. In comparing my Garmin result and MapMyRide result using distinct landmarks as reference points, I get exactly the same result...and this is a grade that peaks at 23% and average 18%.

So, I'm accepting each one as offering an accurate frame of reference despite some potential imprecision.

ETA: It just occurred to me that I could check the county GIS system for Monroe County Indiana which offers contour lines in the GIS maps. My previous measurement for the hill in a prior post was 181 feet and in checking GIS, I see there are 18 10foot contour lines between my reference points on the GIS map.

So, I think you're good to go on the hills.

Although, you may find that they both give erroneous results on bridges - where they seem to reflect the elevation of "terra firma" rather than the bridge/roadway...I found that when riding over a bridge at Orange Beach Al, that the Garmin registered elevation of 80', but the mapping software reflected it as 25 feet BELOW sea level (which is why I was on a bridge!)

[Crankin]

I routinely ride several short, steep hills that are 18-20% in places. I am in my granniest of granny, but I am not standing. So, I don't think you can say most recreational cyclists can't do this. It's all what you are used to. My driveway has a spot that is 15% and my street has some 10-12% grades. Believe me, I am not a racer, etc., just someone who lives around hills.
Now, while I can handle this, I don't like long climbs, i.e. mountains that go on forever, even if they are less steep. And the only time I got off my bike and walked was a sustained 18-22% grade for about a mile. I rode about 1/4 of it.
I have also found that my DH's Garmin estimates the grade as about the same as any other method we have used.

[mudmucker]

Just as a note, most of these "12-18%" grades that are encountered here in MA points east, are only sustained anywhere from 200 to 900 feet of horizontal (* generally mostly), maybe a little more in some circumstances, where the grades either drop to flat or changes to gently rolling topography thereafter and so there is much time for recovery. So yes these are quite do-able. And yes, I ride the same hills as Crankin on occasion and these are some of the ones I'm talking about. Most of the time, there may be 2 or 3 of the "steep sessions" but they occur within a short 1/4 mile stretch where again, the topography levels out to half that grade and less but there is still an incline maybe for a mile or so or not. Many times I look down at my Garmin, and the 13 or 15% only lasts a few seconds, or that amount of time it takes for the unit to register a few times and then it drops down a bit. Furthermore I have seen the Garmin register unlikely high spikes when I look at the data afterwards so don't take the max reading as gospel.

I am a GIS analyst and work with contours and USGS data and have had to take contour measurements in the field in my younger days. Most contour data used in county/state GIS offices come from USGS digital terrain models (the same contour lines you see on the topo maps) with vertical accuracies of several feet (can't remember exactly and it is a range so we don't know). Not only that, depending on the number of data points, the contours are interpolated so we are only good as the number of datapoints, the method of measurement and the interpolation method, all of which may have varying degrees of inaccuracy at any given location in the US. If you are looking for absolute data vs trend. So the answer to RolliePollie is these mapping sites are using USGS data that is standard and overall very good, but even some areas may have a "degree" of inaccuracy due to the aforementioned concepts. These surveys were done in the 1940's-70's with only slight updates in small areas - just as a note, in some county/states that can afford it, more accurate LIDAR data has been flown and I would trust that more but I don't believe the mapping sites are using this yet because there is not full coverage of the US. I still wonder about correlating Garmin measurements against places like MapMyRide but it's inconsistent - accurate in some areas, not in others. The same with the mapping sites - might be accurate in some places, or in the ballpark within 1 or several percentage numbers.

[Mr. Bloom]

Thanks mud - it's good to have authoritative feedback offered.

For the record on standing - I generally don't stand on the steepest hills unless I'm racing the clock...

[Grasshoppergirl]

I see you are riding those hills here in the Sierra Foothills which is my backyard too. I'd say those percentages are accurate. Those old mining roads are steep. My computer that gave the %grade just gave out, but many of our local favorites would give a reading of 16% for a short distance and anything more than that I'm standing up and too far over to see it. Many of our club rides out of Plymouth, Sutter Creek, and Ione have options for these climbs. So, yea - you're climbing - good work!

The profiles are posted for many of the popular(famous?) routes at www.stocktonbikeclub.org. Maybe yours is there?