I had a dream that I rode a regular 10 speed bike down a steep hill and hit 100 mph just by coasting. Could I, a typical bike rider on a “nothing special” bike, survive such a ride?
Only if the bike was perfectly tuned.
Any imbalance or out-of-true in the wheels, and you are going to crash.
That’s a top of the top rider on a top of the top bike.
186 mph is apparently possible in the right conditions. I wouldn’t recommend it…
Flat lake bed, extremely sturdy bike and a tow vehicle to take you up over 100 (and act as a wind break) before turning you loose.
Yeah–can you imagine the gearing? You’d have to get towed to speed. Crashing is not an option–not sure if you’d die of the road rash or the burns from the friction.
I was wondering about the gearing just as I got to @Tride’s post. You can see the gears toward the beginning of the video (0:10 to 0:15), and I thought they looked normal, until I noticed there appear to be two chains and two drive mechanisms. How’s that work?
And using the now illegal (in UCI races) “super tuck”. (With your ass on the top tube and your chest on the bar- very aero, at the expense of control)
[I chicken out @~ 75km/h. To be fair to myself that is on open road, with other cars and cyclists. :) ]
Without the assistance of a tow vehicle the record is 138.8 downhill on snow with a special bike. The record with a normal bike is 116.
The wheel bearings on a bicycle are not going to last long at these speeds, light lubrication and they just aren’t built for the stress. Same with the tires. Even with car tires that are rated ZR (149 mph plus), W (168), and Y (186) you better have new, flawless tires. Once one of these tires has been repaired, like fixed a flat, they are no longer speed rated.
And, even so, at high enough speeds the “nothing special” bike will be increasingly unstable and harder to control to keep from crashing. Better not have to make any turns…
I grew up in West Virginia and you wouldn’t know it to look at me now, but as a teenager I biked a lot and was also on the cross country and track teams. The only hill that you can coast down at 100 mph is a cliff. Going down a very steep West Virginia hill and pedaling as hard as I could got me up to about 60 mph according to the speedometer mounted on the bike (seemed accurate at lower speeds but I had no way to verify how accurate it was). The bike was a “nothing special” 15 speed with no special tuning or particular care to the balancing of the wheels. That was pretty darn fast on a bike, so I knew that I couldn’t make any sudden turns or I would be in a world of hurt, but overall the bike was easy enough to control and I never felt like I was going to crash. The slope decreased quite a bit before I had to make any major turns, so I was down to about 45 mph or so before I had to do anything other than a shallow turn.
That’s compound gearing. The first chain connects a large gear to a small one on the intermediate cogset. The second goes from a large gear on that intermediate set to turn a small one on the rear cogset. It’s basically the same as if they had a really big front gear. Except there’s a limit to how big you can make a bicycle sprocket and not have problems. A compound gear avoids the problems while still getting the extreme gear ratio.
I’ve long wondered about how they got that bike going in the first place, since it’d take an awful lot of muscle to do it. I didn’t realize they towed the bike to get it up to speed.
And then stayed in the little “shed”, completely shielded from the wind.
To me, that makes a complete mockery of “land speed record” on a human powered vehicle.
I dunno–it’s a different class. Like the speed record downhill on snow. To go 184 in any situation takes massive planning and brass ovaries. Pretty cool to me.
I got to 45 kph on my bike once, on a steep downhill, and that was already enough to give me a scare.
So I take it there’s not a stability problem with a normal bike at those speeds, since it’s been done (on snow). That’s what I wondered about after reading the OP.
Back when I was a teenager, circa 1977, I was skateboarding with friends, when some other guys we knew stopped by in their pickup truck. One of the skateboarders held on to the bumper of the truck for a tow, and the truck took off. Everything was fine until the they hit a specific speed, then the skateboard/rider became unstable and it swerved back-and-forth under him a couple of times, extremely quickly, then it was just gone off to one side and the poor skateboarder was left moving at about 25 mph over asphalt with nothing underneath him.
A few years later I learned about control systems and poles moving to the right half-plane when you increase the gain.
I recall the article (Scientific American?) talking about the tests on the salt flats decades ago - basic idea was to put a plastic cage over the bike and rider, hanging from a truck, so that the rider had zero wind resistance. (running coach’s link points to similar testing).
What the article said was that this protection was necessary to test extreme speeds because in normal flat cycling, 35mph to 40mph is top speed because of wind resistance. Considering resistance climbs exponentially with speed, there’s likely a limit to what you can achieve without a protective cover, even on a significant downhill. the Tour de France article does not mention the hill rate; but for the other records, I’ve been on some steep ski hills I was nervous to descend on skis, slowly, in full control.
Also consider the “terminal velocity” for humans, with a 90° slope, is around 120mph. So without a good tailwind, that would be a limiting factor - depending how much tuck you could provide against wind resistance. Planking on the seat may increase your speed, but with a trade-off against life expectancy.
The speed achieved by a human body in free fall is conditioned of two factors, body weight and body orientation. In a stable, belly to earth position, terminal velocity of the human body is about 200 km/h (about 120 mph). A stable, freefly, head down position has a terminal speed of around 240-290 km/h (around 150-180 mph). Further minimizing body drag and streamlining the body position allows the skydiver to reach higher speeds in the vicinity of 480 km/h (300 mph).
My bolding; words to pursue the matter. Thanks for that! 
I got up to 57 mph on a good hill. It feels awfully fast, but I didn’t sense anything that would suddenly change if I’d had a steeper hill.
Agreed, at some speed things could fly apart or become unstable or something. But we really don’t have any evidence that it would happen before 100 or 200 mph.