I’d like to do it. What’s a very long offroad descent, anyone know?

80 miles .. nice. Col Turini down to Nice can be ~60 miles of descent, just over 2000m of height loss. The Bonette to the valley is also ~60 miles. Best one I’ve ridden is Hehuanshan in Taiwan, 3250m to sea level (~200m climb at 2500m, the rest is all downhill), that’s about 50 miles. Stunning road.

From the top of the Tong La pass in Tibet down into Nepal is pretty close to 50 miles downhill, dropping from just over 5000m down to 500m at the bridge over the the Sun Kosi river at Dolaghat in Nepal.

It’s a long ride down….

Col di Torini is great fun, got some helmet camera footage somewhere of me racing three motorbikes down it (Harley/Indian types rather than sports bikes) They were quick in a straight line but I had them in the corners. Beat two of them 🙂
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Google something like this https://theculturetrip.com/europe/united-kingdom/articles/11-of-the-toughest-climbs-in-cycling-from-around-the-world/ ride the climbs, then come down again,

From the chilean / Bolivian border down to arica there is a 100 mile downhill – from 10 000 ft to sea level. Most of the descent is in 40 miles. When I was there 30 years ago it was mainly a dirt road. Its on my bucket list

Looks like its tarmac now – this is the start point
https://goo.gl/maps/7K6R6DCUkwEWgZUL9

The route in Bolivia along RN3 from Cristo de la Cumbre to Coroico via the infamous Yungas “Road of Death” is quite an amusing ride – drops around 3000m in a distance of about 70km. First part is on decent tarmac, but the last 2/3rd or so is rough track with hairpin bends and some stupendously big drops on the left-hand side. 🙂

The top of the galibier to bourg and beyond must be mainly if not all downhill. So if you don’t worry about the steepness past bourg and onwards.

The route in Bolivia along RN3 from Cristo de la Cumbre to Coroico via the infamous Yungas “Road of Death” is quite an amusing ride – drops around 3000m in a distance of about 70km. First part is on decent tarmac, but the last 2/3rd or so is rough track with hairpin bends and some stupendously big drops on the left-hand side. 🙂

It’s not continuously downhill though. And the short uphill section is extremely hard work on a heavy bike at altitude!

Nice.
I get excited going from the top of Devil’s Dyke to the Brighton Seafront.

Missed the off-road bit, just saw the road bikes in the vid and .. don’t know of anything as long off-road. As above, maybe Nepal, India or similar where dirt roads follow main valley descents in same way as tarmac roads in Europe.