The Steepest Hills

Morningrider

Ol'Timer
May 19, 2023
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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

56 degrees at 19.85568,99.05691 on the 1249 from Nor Lae to Ang Khang.jpg


57 degrees at 19.21699,98.03487 on the 5035 Elephant Trail.jpg


59 degrees at 19.85063,99.06698 on the 1249 from Nor Lae to Ang Khang.jpg


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.
 
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Morningrider

Ol'Timer
May 19, 2023
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43
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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.
 

Morningrider

Ol'Timer
May 19, 2023
58
43
18
Route 1334 Pha Bur switchbacks, 43% max.
Route from the highway past the Treehouse, Chiang Dao, 44% max.

Printscreens from Google Earth attached.

43 Route 1334 Pha Bur.jpg


44 Chiang Dao Treehouse Road.jpg


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

Ol'Timer
May 19, 2023
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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.

2024-12-14 09.07.04 3054.jpg


2024-12-14 08.10.20 3054.jpg


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.
 
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Dodraugen

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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

Ol'Timer
May 19, 2023
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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:

Mt Bromo.jpg
 
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Morningrider

Ol'Timer
May 19, 2023
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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).

Steepest Hills Summary.jpg


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).

Steepest Hills 64% 19.003346,98.011617 R4009 West Segment.jpg


Steepest Hills 62% 19.850932,99.066882 R1249 NorLae to AngKhang.jpg


Steepest Hills 57% 19.218650,98.032589 R5035 Elephant Trail.jpg
 
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