Pedaling at 128km/h

[Donhou] had a dream. To create a road bike capable of reaching 100mph (160km/h).

He damn well near did it too. The goal of this project wasn’t to set a land speed record, but more of an experiment in design, and building a really fast bike that still looks like a bicycle. In case you’re wondering though, the land speed record is currently set at 167mph by [Fred Rompelberg] who was drafting behind a dragster on the Salt Flats of Bonneville.

The bike features custom everything; a welded lightweight frame using Columbus Max tubing (to help with speed wobbles), super low handlebars for aerodynamics, and a massive 104 tooth chainring which almost scrapes the ground as you pedal. Even the rims and tires are unique — regular bicycle wheels just aren’t designed to go that fast.

We aren’t even bike nuts, but we thoroughly enjoyed the awesome 9-minute documentary on this project. Check it out after the break.

40 thoughts on “Pedaling at 128km/h

  1. Can a Zephyr go 100mph? (c:

    He could get Sir Chris Hoy to ride the bike. I’d bet he can go 100mph without drafting a dragster. (c;

    Anyhow, awesome project.

    1. It’s physically impossible to ride a bike 100 mph.

      Suppose you need 250 Watts to sustain 25 mph which is a fairly ordinary figure for a human cyclist on an average bike. Double that twice and you get 100 mph, and with each doubling you need eight times the power, so that’s 250 W x 8 x 8 = 16 kilowatts (~12 HP).

      What that tells you is, a bicycle could be made mad fast with a smallish engine, and no matter how doped up you are or what the gear ratio is, you are never getting to 100 mph on your muscle power alone. Even a fit person can only sustain a couple kilowatts for a couple seconds, because you run out of oxygen.

      If people had birds’ lungs, we could do a couple seconds more and then overheat because the human metabolism + mechanical efficiency only totals to about 24% so for a 2 kW output you’re heating your body at 6 1/3 kW and assuming you have the specific heat capacity of 75 kilos of water, you would start to overheat in 49 seconds and drop dead at 3½ minutes from a blood clot in your brain.

      1. And that was actually the plot of some old movie where a man got irradiated by some sort of space thingy and gained the power of ultra-fast metabolism. His problem was that if he continued to use it for more than a couple minutes, his head would boil out.

      2. You are forgetting about drafting. The main energy sink on the biker is air resistance. Without a car to draft, you are right, the human body just isn’t capable of putting out that much power, even for a second. However, with a car to draft, the car is in effect taking most of the drag load onto itself, and therefore you can go much faster since you are in effect sitting in a pool of still air. I do doubt his relatively low tech bike, because he was only able to get up to 102 on a set of rollers, and I imagine the real world drag loads would be worth at least 2 mph. I haven’t seen the 167 mph bike, but I bet it is considerably more high tech (for instance a two chain gear reduction to eliminate that ridiculous 104 tooth sprocket). I would guess that some sort of aero system would be necessary to improve the aerodynamics of the bike and rider.

        1. But the whole point is that drafting is cheating. The rolling resistance of a well built bicycle on a good road at 100 mph is nothing. With good tires, no more than about 120 Watts. Any slob, even children would be able to maintain 100 mph pretty much until they get bored if the air resistance was completely removed.

          It’s no longer a “can you do it” question. Of course you can. It’s just a matter of doing it.

  2. “the land speed record is currently set at 167mph by [Fred Rompelberg] who was drafting behind a dragster on the Salt Flats of Bonneville.”

    Come on now, that can’t count. At that speed, I wouldn’t be surprised if the dragster was practically dragging the bicycle along in a vacuum…

    1. Yup, in my opinion that should be categorized as high speed bicycle dragging or something. It can’t be compared to a cyclist reaching that speed on his own strength. I have a good bicycle and I like to thing I’m in good shape, but I only reached 48km/h a few times when I wanted to test my limit and believe me that is pretty fast and pretty hard to reach for normal bike riders like me. As for reaching 128km/h, that’s really freakin’ fast – respect for the courage and ambition.

    1. That’s probably because of the bicycle, my old single gear bike from 1950 gets very wobbly above 23km/h on asphalt. The thing is even though my news bicycles handle paved roads better that old one is still marvelous at low speed and on bumpy gravel roads.

    2. When I was a kid I used to run my 10-speed down hills at over 40 MPH. It was fast enough that I could barely see (wind in my eyes) but the bike was stable and I was too stupid to know better than to keep doing it.

  3. Nice video and project – but that whole “drafting” thing just takes the accomplishment down several notches for me. It’s a bike, pedal it, not get sucked along by a motor powered “shed”.

    1. Yah, but that’s what “legit” (UCI) cycling is all about… drafting. Well, that and all the doping. This is about the only way a wedgie (appropriate, though some would argue derogatory, term for a conventional bike) can stack up to a recumbent bike (much more comfortable, faster, better rider visibility, superior in every way… outlawed by UCI in 1934).

      Awesome build. I’d like to see the hipsters on their fixies try using *that* chainring around town.

  4. All he needs is a bigger front gear, he’s still got a bit a bit of ground clearance.

    I wonder if he’s every gotten his trouser leg caught in that thing.

  5. So i’ve always wondered why aren’t more bicycles sold with gear ratios similar to this? When I was a kid I had a 21 speed and I rarely used most of the gears. And now that I drive around, it does get rather annoying when I’m stuck behind a cyclist who is incapable of going the speed limit.

    1. The speed of a cyclist doesn’t have much to do with gear ratios; it’s all in the leg strength. When I ride, I start off in low gears (better acceleration) and work my way up.

      My bike tops out at about 18mph, limited by my leg strength, not the gear ratio. In the higher gears, I lose cadence on hills. (I output the most power pedalling in the 50-70rpm range.)

      I know it’s frustrating to get stuck behind bikes moving slowly. It’s as annoying to be a cyclist with cars zipping past you. Bike lanes and such would be great, but are really rare in America.

        1. They want to have the final gear ratio with minimum possible parts to maintain efficiency. All the derailleurs etc. cause extra friction.

    2. Now that I bike around, it does get rather annoying when I’ve got some jerk behind me who thinks that the speed limit isn’t the LIMIT but what he’s ENTITLED to drive at and feels justified to act out his rage by endangering my life or honking or screaming profanities or racing his engine because he’s overcompensating.

      1. Vehicles going at different speeds on the same roadway is a safety hazard. Lobby for bicycle lanes instead of complaining when people complain that you’re blocking the road and wasting everyone’s time.

  6. Pedaling in a low pressure zone with no wind resistance is cheating. It’s an impressive feat but we will never have a person pedaling at 100mph without a car in front of them, the human body can not put out enough power to sustain much above 50 even with an aerodynamic shell around them.

    Sam Whittingham holds the record for the fastest average speed for an hours worth of road riding: 58 mph and this was on perfectly flat road with a special aero shell. he did get close to 85 once, but this was on a recumbant where you can convert a lot more huan power to motion than the traditional style bike.

    1. It’s lame cheating to drive in the low pressure “suction” zone behind a car that is customized to increase the low pressure zone behind it.

      I guess that it is possible to aerodynamically “attach” a bike to a car by designing the car as the first part of a drop shaped low drag body and the bike as the second part of this body, and then braking the bike so that there remains a low pressure gap between them (according to Bernoulli’s principle, fast airspeed around the greatest circumference of aerodynamic body causes low pressure).

      If the brakes are electronically controlled by e.g. a ultrasound distance detector so the second vehicle will never run into the first one, then the second part is a separate vehicle that is powered by the aerodynamic drag of the first

    2. > we will never have a person pedaling at 100mph without a car in front of them

      CHALLENGE!

      > the human body can not put out enough power to sustain much above 50 even with an aerodynamic shell around them.

      i think you underestimate just how far people can push their bodies or the brilliance of engineers. just look at how far olympians go and the “crazy” stuff engineers come up with that works.

      1. A person can physically put out 2000 Watts of power for a brief moment, so the drag force at 100 mph should be no more than 45 Newtons.

        That means the CdA of the bike and rider has to be less than 0.04

        In comparison, an upright bike with an average rider with dropped handlebars has a CdA ~ 0.32 which is 8 times more drag than what can be sustained. The lowest measured CdA for an athletic cyclist on an uncovered recumbent bicycle that I can find is 0.153 which is still about 4 times too much drag.

        Shell Eco-marathon vehicles go down as far as 0.02 but they hardly have any space to spare for a cyclist and pedals.

  7. Anyone else notice at 5:57 when he says they couldn’t hear each other the driver has earphones in? I don’t know why that caught my eye.

    Awesome work, I would like to see the acceleration when the cyclist is not behind a vehicle.

  8. So the real question is……If the bike and the “draft inducing” car were on a treadmill…well, you see where I’m going with that. ;)

    1. Or just put the bike on the trailer and say “look at me, I’m riding a bike at a bazillion miles per hour” (or put the bike on a pallet and the pallet in the cargo hold of a jet plane).

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