Kindaslow

Just like Sesame Street, which one of these does not belong!

They just put up a new sign that lists the steepest hill in my area at 10%. However, the hill on the other side of the valley, that is not as steep had a 12% sign for a couple of years and is a much easier hill. According to my Garmin, the steeper hill is about 14-15% and the other hill is mostly 10, with a little bit at 12.

Do they just guess? Turn their heads to the side, shut one eye a bit, lick their finger to check the wind and give it a guess?

Does not matter much, since I am stuck with both on my commute, but it just seems so strange.

Don't know if this is a rant or just some head scratching....

fthomas

You just can't trust those guys with a Theodolite any longer!

Kindaslow

They have always looked shady to me!

fthomas

+1

Rowan

I wouldn't trust your Garmin (I wouldn't trust a Garmin at all, for anything, but that's just me). But it's not just Garmin. Anything I put on Strava also comes up with much much steeper inclines than reality. Like one hill shows 25% when I wouldn't rate it much more than 15%.

Signs also give averages for the climb from the start to finish.

corrado33

Why not just take a level and a protractor and measure each hill a few times on the way up? (I don't know what the actual tool used to measure hill grade is.)

Also, most GPS devices are terrible at elevation. They use maps after the fact to correct their elevation, which are often wrong.

gregf83 

Most Garmins use a barometer for elevation and it works quite well but it's a 'noisy' signal. Easy to smooth out for display during or after a ride but a problem if you're looking for instantaneous slope. If you smooth the elevation too much before calculating grade the grade displayed will be delayed and the rider will perceive it as being incorrect. It's very difficult to have an accurate real-time display of grade. I don't bother looking at it.

Kindaslow

Some old people do not know how to have a little fun....

And, my guess is that the Garmin is not likely to overestimate the hill on one side of the valley and underestimate the one on the other side (about 1.5 miles apart) repeatedly.

Now, how about those guys and their lasers, they would be much more trustworthy if the had protractors!

Retro Grouch 

I've got the cheapie Garmin. It gives me an "altitude gain" figure for every ride. It's accurate enough to use for bragging to my son but I wouldn't count on it for any thing else.

corrado33

I don't know if I'd say "most," but I come from the running world, and a lot of the watches don't have barometers over there. My watch, however, does. I find the elevation to be perfectly accurate over a loop to within a few feet. Barometers ARE affected by weather, so if the weather changes during your run/ride, the elevation will be a few feet off when you finish.

OldsCOOL

My Strava (iphone app, only) shows that our steep hills are 4% and two of the many many hills we have show 10%. Gross undercalculating. Maybe I need the premium version.

rck

Don't feel badly, I ride to a town NE from here and on an out and back its 17 miles going but coming back its only 15 at least according to the signs.

Biker395 

My understanding is that today's Garmins use both barometric pressure and GPS to estimate elevation and grade (the earlier ones used only GPS). And I think they are reasonably accurate. My VDO cyclometer uses only barometric pressure, and I'm really surprised it's as accurate as it is.

stardognine

I've noticed that the wind affects my mileage, nearly as much as signs. One thing's for sure, they didn't use the same tape measure, in every state, county, and town. There are miles, and then there are "manly" miles, I guess.

Oldguyonoldbike

I'm pretty sure all the hills around where I live suddenly get steeper as soon as I start climbing.

DiabloScott

I don't know about the signage, but what the engineers do is look at maps that have elevation lines on them - so calculating percent grade is much simpler and faster than calculating in degrees or something. So if the surveying is off, the slope calc will be off as well.

My Strava android app is remarkably consistent from ride to ride and I have hundreds of mountain rides that are literally identical. Sometimes it puts me in the ditch or something for one datum, but it always seems to work out.

Once in a while it puts me at the bottom of the river instead of the bridge I'm really on... that makes for a funky graph.

bobwysiwyg

This thread got me curious. I use Strava (Android on a Samsung Galaxy S6). After some research I discovered it has both GPS and barometric capability for elevation. I've compared results against topographical maps of my routes and it is very accurate though I don't know which capability is doing it. As for lateral location, that too is very accurate. There is one long hill here from the river up to Skyline High School. The first 150 ft has to equate to 30 ft of elevation. Damn near wipes me out. Any way, at the 150 ft mark there flat area to accommodate a side road intersect. Last time I went up it, I did a tight little circle to catch my breath, maybe 8-10 ft, before continuing up the rest of the way. That little loop is clearly visible on the post ride map. Certainly accurate enough for me.

Daspydyr 

Does it really matter, if YOU can climb it, how steep could it be?


hahahhaha

mrodgers

I love when my RWGPS tells me I climbed 2300 miles in 24 miles on the dead flat Allegheny River trail. Almost 100 ft per mile because of the 2 dang tunnels going through the mountains and the app recording me going over the mountains.

John E

... and it is uphill both ways for you, as well.

Rowan

Yep. I climbed a mountain recently that was at 1240-metres (approx, but close enough). RWGPS, Strava and whatnot all had the total climbing at some ridiculous amount such as 1800 metres. Trust me, there weren't 560 metres of other climbing involved in essentially was a straight-up ride.

Oh, and the other beauty to behold is the start-finish elevations when starting-finishing from exactly the same spot, which always seem to be between 20 and 80 metres out of whack. Did the earth move for me?!

I learnt in a surveying class that GPS is not as accurate as certain people would have everyone believe in calculating inclines.

It might make someone feel good to poke fun at road engineers and those with degrees, but revisions go on all the time. If you want accurate, do as I do, make up a measurer (one-metre length of aluminium angle bar, a small spirit level attached, and a tape measure), go out and measure the incline yourself.

Stick69

Just look at the quad map and divide the elevation difference by the horizontal distance to get the average grade. You will quickly see that the average depends on where you begin and end you measurements. The vertical curves often begin and end with a spiral which will effect the average if you include them.

Some of the MapMyRide type sites have topo lines so you can map the distance between the lowest and highest line on the hill and compute the grade between the contour lines, if you are so inclined. (Ha, engineer and Dad humor all in one)

berner

That is what I did. I was curious about two hills where I ride. I was guessing fir first hill was about a 12% grade and the second about an 18% grade. I went out with my measuring device and found the first hill to be 8% maximum and the second was 11%. The first hill is a healthy climb I look forward to and the second is serious.