Live data from Hacker News

The world's fastest human-powered vehicle tops 85 mph

engadget.com

61–70 of 112 posts

Re: The world's fastest human-powered vehicle tops 85 mph

#61
post #2

The video ends with a brief second where the cyclist explains what prevented even higher speed. I make out: "too much vibration...", "knees rubbing...", "unable to continue increasing power output". Would love to hear more about this.

Here's the current video of them actually beating the record: https://www.youtube.com/watch?v=33clAZoaLWs

Re: The world's fastest human-powered vehicle tops 85 mph

#63

Earlier quoted context omitted.

I would imagine that power to weight ratio is more important than just the power. Also the smaller the cyclist, the smaller they can build the aerodynamic shell, thus reducing drag.

Actually, on a flat surface with a constant speed or acceleration, weight matters much, much less than frontal area. Weight comes into play much more when many quick accelerations or elevation gains come into play. Because frontal area doesn't increase proportionally with weight, I would argue that power output should be the primary concern and that typically increases substantially with weight. For evidence of this,…

Was wondering the same since, this is about top speed and not about acceleration the weight shouldn't matter much at all, since it has no direct influence on the air resistance.

Would be interested in knowing, if a human powered vehicle on steel rails with steel wheels with the same air resistance could be faster than this just due to the lower rolling resistance.

Re: The world's fastest human-powered vehicle tops 85 mph

#64

So my question is now: In terms of aerodynamics, what aren't they doing? Some commentators have noted that the shape of this bike is just about as good as it can get. The rider/engine is also not going to see any vast improvements. So rather than this become a pure athletic event, where can engineers look for improvements? Will they have to start dealing with boundary layer issues? Will the next generation of bike be…

Maybe the road surface? I'm assuming an actual highway has some friction that could be sacrificed perhaps? Not sure what the cutoff is there before too little traction becomes problematic? Just spitballing here, I have no idea how most of this stuff works.

Related to road surface, are properties of the tires used. The goal is to optimize for rolling resistance. On a long brevet, different tires can shave hours off your time.

Since their requirements for durability are much lower (i.e. they don't need to get days or months of use), they could optimize for tires that are just durable enough for the event and have minimal rolling resistance.

Suspension losses are another area where power is lost. I'm curious if it is possible to perform these tests in a velodrome where gains from better tires suspension would be minimal.

Also check out motor-paced records, where the current record is 166.9mph by Fred Rompelberg.

https://en.wikipedia.org/wiki/Cycling_records#History_of_mot...

http://mammajammaride.org/wp-content/uploads/2014/08/Fred.jp... http://fredrompelberg.com/upload/images/site/Wereldrecord_fi...

This is worth a read on the surface of the Bonneville salt flats: http://saltflats.com/traction.html

Re: The world's fastest human-powered vehicle tops 85 mph

#65

So my question is now: In terms of aerodynamics, what aren't they doing? Some commentators have noted that the shape of this bike is just about as good as it can get. The rider/engine is also not going to see any vast improvements. So rather than this become a pure athletic event, where can engineers look for improvements? Will they have to start dealing with boundary layer issues? Will the next generation of bike be…

Dimples on golf balls help in inducing turbulence, not the other way. Turbulence in this case reduces drag significantly. This is a well known counter intuitive result in flu mech.

Re: The world's fastest human-powered vehicle tops 85 mph

#66
post #52

Earlier quoted context omitted.

It stretches the concept of "human powered". Why not just pedal while stationary to charge a battery (take as long as you like), and then ride the course with no additional expenditure of effort.

Because then you would be bringing additional stored energy into the competition (beyond what's in your body)?

Well, the course is a 5mile run up to a 200m speed trap. So if you allow batteries/motors, you could just sit stationary somewhere in that 5 miles pedalling for a while, and then use electrical acceleration to get up to speed for the trap. You're not bringing any additional energy, but its clearly not in the spirit of the challenge.

Re: The world's fastest human-powered vehicle tops 85 mph

#67

Earlier quoted context omitted.

You could really probably optimize for the 200m speed zone. As long as you can get to your top speed before it, you dont need to fly through the 5 mile zone. Better to save energy for an explosive finish. Track cyclists sometimes do a "flying 200m." The record is 9.347 seconds which is 47.86 mph. Thats on a non aero bike with drop handle bars. It would be very interesting to see them in a perfectly aero recumbant bik…

Absolutely. Being trained for such short intervals, I wonder how much their power output would drop in the final 200m after that 5 mile buildup. In any case, there has to be some optimal cyclist build for this event. I suspect it's probably somewhere between a time trialist and a pure sprinter.

Would it be within the rules to include a power capturing mechanism like a flywheel or spring that can be unleashed at the end? That would change the game to maximizing total energy output over the 5 miles, and make the whole section count.

Re: The world's fastest human-powered vehicle tops 85 mph

#69
I was gonna say this makes me realized just how aerodynamically inefficient a regular bike is, but then I found out that the world record of cycling on flat surface is actually 83.13 mph [0], which is actually pretty close to this. Assuming the rider is also top notch, I guess the benefit from optimizations done on aero isn't much larger than the weight added.

[0] https://en.wikipedia.org/wiki/Cycling_records

Re: The world's fastest human-powered vehicle tops 85 mph

#70
post #69

I was gonna say this makes me realized just how aerodynamically inefficient a regular bike is, but then I found out that the world record of cycling on flat surface is actually 83.13 mph [0], which is actually pretty close to this. Assuming the rider is also top notch, I guess the benefit from optimizations done on aero isn't much larger than the weight added. [0] https://en.wikipedia.org/wiki/Cycling_records

wikiepedia doesn't check it's own references.

The speed is for a human powered vehicle (fully fared). Edit: All the flat records in the section you're referencing are for hpvs, not tradition bicycles, as a look at the pages of the riders will show.

See: https://en.wikipedia.org/wiki/Sebastiaan_Bowier https://en.wikipedia.org/wiki/Barbara_Buatois

Post reply on HN