The Steepest Hills

[Morningrider]

As a rainy-day exercise I tried to answer the question: where are the three steepest hills in Thailand, according to Google Earth? My nominations are:

#1: 59% at 19.85063,99.06698 on the 1249 from Nor Lae to Ang Khang. The winner.
#2: 57% at 19.21699,98.03487 on the 5035 Elephant Trail The first-runner up.
#3: 56% at 19.85568,99.05691 on the 1249 from Nor Lae to Ang Khang

These could be the steepest three hills in Thailand, but there may be others that are steeper that my prospecting did not uncover. There are many hills over 40 degrees, and over 30 degrees is routine, but there are very few hills over 50 degrees, let alone almost 60 degrees. I used to have a Willys M38A1 jeep and its maximum rated slope in low-low 4WD mode was only 70 degrees.

Let’s try to perfect the top-three list. You can use Google Earth to plot the elevation profile of a challenging road to measure its steepest slope (plotting more than about ten km at a time reduces the peak grades, probably due to averaging, so you need to check less than 10 km at a time). Enter the start and end coordinates in the Directions boxes, then right click on the resulting route and click on Show Elevation Profile to see the peak and actual grades. If the resulting route isn’t what you expect, then you have to use Google Maps together with Google Earth. Or you can PM the coordinates of a suspected steep hill to me and I’ll help plot. It’s much easier the second time!

This is just the measurement of the grade of one hill and doesn’t indicate how steep the rest of the road is or how difficult the hill climb is considering the surface, curvature, width, and visibility. For that, you can look at the “Steepest Roads” thread.

 

[DavidFL]

Very interesting.
Also worth considering are
1. The Big Dipper switchbacks
2. Singapore Road.
3. The R1149 Doi Tung switchbacks.

 

[Morningrider]

Surprisingly, not even close to the top three:
1. Big Dipper switchbacks, 40%
2. Singapore Road, 35% (they seem steeper because they are so narrow and dangerous)
3. The R1149 Doi Tung switchbacks, 44%

The are all steep roads but as it happens don't contain one really, really steep hill, according to the Google Earth elevation profile. I am not sure how accurate Google Earth is, or their minimum length for a slope calculation, but it probably is more accurate than a consumer-level GPS for elevation.

I checked these before, because my starting point for the Steepest Hills was prospecting in the Steepest Roads list. But there may be a really, really Steep Hill which is not on the Steepest Roads list because there isn't enough of it to count as a road. (For the Steepest Roads I didn't count any road shorter than 5 km.) Maybe around Chiang Dao near the Treehouse. I will have a look tomorrow.

 

[Gregthemagnificent]

Ban Pha Bur switchbacks are steep and ridiculous

 

[Morningrider]

Route 1334 Pha Bur switchbacks, 43% max.
Route from the highway past the Treehouse, Chiang Dao, 44% max.

Printscreens from Google Earth attached.

Google Earth insists on drawing the route in dark blue against the green trees which makes them hard to see.

 

[Morningrider]

Most of the roads on the top half of the "Steepest Roads" list have hills in the low forties. Hills in the thirties are common on narrow back roads, but road signs showing the extreme slopes aren't--they would be everywhere. The much-ballyhooed 3054 is steep but not really steep, but the road is so narrow on the blind switchbacks that you are not going to stay upright if a lorry is coming the other way and you have donkey-box panniers sticking out. Ditto for the Singapore Road.

Unless and until another winner comes to light, we could put up a sign at 19.85063,99.06698, "GT RIDER STEEPEST HILL IN THAILAND," and take a group photo trying to stand up on the 59 degree slope before someone steals the sign or a lorry comes down the hill.

 

[Dodraugen]

Interesting! But I wonder what would be the steepest angle an average motorbike would be able to climb?

I remember riding the R4009(?) off the R108 towards Ban Nong Khiaow-Mae Surin waterfall and the Bua Tong flower field - there were some really steep sections close to the R108, I had to (or felt like I had to) lean my body forward as much as possible just to have some ground contact with the front wheel…..

Reminds me of the time I rode up to Mt Bromo in Java-Indonesia. Super steep section, very broken asphalt - people conducting traffic up or down because it was only one way traffic possible due to destroyed road. I was on my loaded Tenere 660 and soon reached the vehicle in front of me travelling at walking pace, impossible to pass due to destroyed road, I couldnt keep riding at so slow speed so I had to stop completely. Braked with front and rear but had a balance problem for a second or two so had to put my right foot to the ground (and thus release the back brake) and backwards I went - faster and faster with front wheel locked until I almost reached the level spot and ended up in the ditch. Scary as f***. I got some bruises and one pannier became quite flat - but it could have went far worse…..

I really wonder how steep that road was and how steep a road its possible to ride with an average motorbike?

 

[Morningrider]

Now you can figure it out. Which route was it? There are several. You can read the start and end coordinates off Google Maps, or mark them on this screenshot with a photo editor:

 

[Morningrider]

I did more experimenting with Google Earth and revised the top three with more accurate calculations. Within the accuracy of the data, the steepest hill in the 4009 moves to first place, with the 1249 a close second and the 5035 (Elephant Trail) in third place. So far I haven’t found any other hills steeper than these three, according to the Google Earth data. There could be others, but hills with 60% grades are mercifully rare.

It turned out that Google’s “Max Slope,” despite being reported with one decimal place, is a rough estimate and can be quite wrong. If the elevation plot is longer than about 9 km, the slopes and the Max Slope are too low because of the algorithm smoothing the slopes. If the elevation plot is shorter than a few km, the Max Slope is too high because of noise in the data points plus rounding error. The Google slope shown at any single point on the elevation plot can have significant noise, with impossible numbers sometimes reported at a single point but also showing up in the “Max Slope).

So to get the most accurate measurement it’s necessary to zoom in on what seems to be the steepest hill, then manually read the horizontal and vertical distances between the bottom and the top of the hill off the chart and calculate the triangle. The longer the hill, the more accurate the measurement because the lower the rounding error (+/- 1 meter of both elevation distance is a lot on a short hill).

 

[Moor66]

Most of the roads on the top half of the "Steepest Roads" list have hills in the low forties. Hills in the thirties are common on narrow back roads, but road signs showing the extreme slopes aren't--they would be everywhere. The much-ballyhooed 3054 is steep but not really steep, but the road is so narrow on the blind switchbacks that you are not going to stay upright if a lorry is coming the other way and you have donkey-box panniers sticking out. Ditto for the Singapore Road.

View attachment 158096

View attachment 158097

Unless and until another winner comes to light, we could put up a sign at 19.85063,99.06698, "GT RIDER STEEPEST HILL IN THAILAND," and take a group photo trying to stand

Most of the roads on the top half of the "Steepest Roads" list have hills in the low forties. Hills in the thirties are common on narrow back roads, but road signs showing the extreme slopes aren't--they would be everywhere. The much-ballyhooed 3054 is steep but not really steep, but the road is so narrow on the blind switchbacks that you are not going to stay upright if a lorry is coming the other way and you have donkey-box panniers sticking out. Ditto for the Singapore Road.

View attachment 158096

View attachment 158097

Unless and until another winner comes to light, we could put up a sign at 19.85063,99.06698, "GT RIDER STEEPEST HILL IN THAILAND," and take a group photo trying to stand up on the 59 degree slope before someone steals the sign or a lorry comes down the hill.

The new percentage signs on 3054 are all wrong, they counted both up and down so we must halve those numbers. The 31% is about 15%. Which is supersteep anyway... I have seen this on one other road too 5 years ago in Nan area

 

[Morningrider]

I remember thinking that the road, heading southbound after that sign, wasn’t very steep! But the signs make a nice photo. That sign is at 17.110510,98.514114. Let’s have a look.

The slope, southbound, runs 811m downhill. Loading it into Google Earth shows the elevation change to be 134m over 811m, so the grade is 16.5% +/- 0.1%, a very accurate number, which is a little more than half the 31% grade shown on the sign (which would be 15.5%).

My guess is not that their grade-six math (slope = rise / run * 100%) is wrong, but that they used an inclinometer to measure the steepest (worst-case) part of the slope between the top and the bottom of the whole hill. According to Google Earth, the steepest part of the 811m grade starts about 280m south of the sign, and the grade over that 20m is 32% +/- 4%. The second-steepest part of the hill starts about 690m after the sign, and the grade over that 35m is 29% +/- 2%. So the maximum slope of that 811m grade reported on the sign happens to be roughly double the mean grade.

There are at least two 20m-long parts of that 800m hill that are about a 31% grade. There are also parts of the hill that are flat and parts that rise before going down again. The signs are misleading and are right or wrong, depending on what it is you want to measure. If I have a lorry with a heavy load, I want to know the average grade to the bottom of the hill before my brakes catch fire, not the peak of the short ups and downs, so the sign is wrong. If I am a cyclist I want to know whether I have the gears and thighs to make it up the hill, so the sign (if there was the same sign at the bottom of the hill) would be right. Ditto if I am a biker looking for steep hills. But who cares about cyclists and bikers? It’s overloaded lorries that matter, so yes the signs are wrong. The number on the sign is accurate but it measures the wrong thing.

Over the whole 3054, the steepest hill I could find is a 50% +/- 6% grade at 17.096008,98.512894 (14m rise over 28m) according to Google Earth, extremely steep, but much less steep than the rare 60%+ hills on R4009 and R1249.

 

[Morningrider]

Malga Palazzo Scanuppia, a private road in the Dolomites, is said to be the steepest road in Europe. If this is true, then Europe's steepest hill, with a 38% maximum slope, doesn’t come close to the steepest hills of Thailand, at about 60% slope, or even the steepest hill on the 3054 at about a 50% slope.

 

[Morningrider]

I was curious how the hill signage would look if Thailand followed first-world regulations, such as Canada’s. The overall grade of the hill, from top to bottom, would be calculated after manually identifying and removing all segments that are less than 6% grade, which would increase the overall average. So the present sign at the top of that “31%” grade hill on the 3054 would say 16% to 18%, and the present 31% sign would be moved about 280m down the hill to the point where that 31% segment actually starts.

Every segment of the hill exceeding a 15% grade and longer than 60m (there are plenty) would need another sign. And more signs for every segment between 6% and 15%, depending on the segment length (as per chart in the attachment). There would be a forest of signs on our favorite roads! Following first-world signage rules would be completely impractical because the roads are so steep, so steep that they could not be gazetted as public roads in Canada.

 

[DavidFL]

Maybe R4032 Thoed Thai - Mae Mo needs to be considered?

 

[Morningrider]

I had a look on Google Earth and my most recent GPS track, 2022 (when I took the interesting photo at the north end of the town, riding south).

The steepest single hill on it is about 35% grade, a little over half as steep as the two steepest hills discovered so far (65%).

The whole 12 km road from the town to the top is about 8% average grade, making it a little over half as steep as the steepest roads so far (15%). The grade divided by the speed is 15, making it about half as difficult as the most difficult steepest roads (30). On the steepest roads list so far, it comes in about the thirty-fifth place (see bold).

 

[Dodraugen]

And how would the R4010 Na Muen to (almost) Phrae be? It certainly had some damn steep parts…

 

[Morningrider]

The steepest hill I can find on that route on Google Earth is 39% +/- 1% over 57 meters at 18.191389,100.473890. Very steep but not in the fearful fifties.

The 38 km Route 4010 to Na Muen sits on the steepest roads list (see attachment in previous message) at #37, just below the 4032 Ban Thoed Thai road, with about the same average grade but slightly lower grade/speed (the route difficulty must be a bit lower because the speed is higher).

 

[Morningrider]

Time for coffee: