The most spectacular accidents can and will happen when you touch the rear wheel of the guy before you with your front wheel while trying to stay close behind.
My link roll is mounted between two horizontal rods extending from the rear wheel hub. With a diameter of a few inches, it has a surface of polished or chrome steel or any other material with very low friction.
Now when you are catching up with the fast cyclist before you, don't worry about too close contact with his/her bike. Just keep spinning and enjoy the ride. And don't forget to mount the device to your own bike as well to become a pacemaker for the lesser endowed citizenry.
Cf. motor-paced racing where a similar device is mounted to the pace making motorbike. Make it lightweight and compulsory.-- Toto Anders, Dec 03 2014 Sketch http://CoSketch.com/Saved/pV1SHCh2A poor sketch of this. [scad mientist, Dec 03 2014] Having been spectacularly accidented by a guy who thought he was being cute cutting in front of me I can see some potential applications for this.-- normzone, Dec 03 2014 WTAGIPBAN. On a bike idea no less.-- MechE, Dec 03 2014 How is this different from the chromium-plated mudguards which every bicycle is already fitted with?-- pocmloc, Dec 03 2014 I think, translated into British English, that's "Mount a roller behind the rear wheel.."?-- not_morrison_rm, Dec 03 2014 //How is this different from the chromium-plated mudguards which every bicycle is already fitted with?//
Because it spins when the other bike's wheel makes contact with it. I'm not clear from the post whether it is supposed to ride against your rear wheel (so that it is already at speed, but would be an annoyance the rest of the time) or is simply free-wheeling, but either way, there would be no tendency for the rear bicycle to try to climb the front, resulting in a much safer bike-bike interaction.-- MechE, Dec 03 2014 // WTAGIPBAN. On a bike ... // *WTAGIPBAN yourself*, you bloody ... oh, it's a compliment. Thank you.
// I think, translated into British English, that's "Mount a roller behind the rear wheel.."? // Yes of course. Further translation help welcome, english not being my first language.
// ...whether it is supposed to ride against your rear wheel... // No it's not. This would not eliminate the potential danger in touching the spinning roller which would be driven by the rear wheel of the bike in front.-- Toto Anders, Dec 03 2014 I just discovered Cosketch which seems like a nice platform to use for sketching ideas for the Halfbakery so I decided to try it out. See link. [Toto] feel free to delete the link if you don't like it or if you create a better one.
Of course according to their terms of service, there's no guarantee on how long the sketch will remain visible...-- scad mientist, Dec 03 2014 On viewing [scad mientist's] sketch it becomes clear that the rigidity of the apparatus and the lack thereof might pose a problem. What may definitively not happen is that the roller touches the rear wheel. Therefore either the horizontal rod has to be quite rigid and heavy, or it has to be integrated in a triangular framework - maybe into a pannier? Or extend the frame tubes going to the rear hub so that they connect at the mounting axis for the roller.-- Toto Anders, Dec 04 2014 //...for the lesser endowed citizenry// - how do you know this? - they might not be wearing lycra-- hippo, Dec 04 2014 // they might not be wearing lycra // The muscular endowment shows in their speed. That of the corpus cavernosum - well, that's another story.-- Toto Anders, Dec 04 2014 Hi [Toto]. Are you new here or just an [Alterother]? Welcome anyway.-- xandram, Dec 04 2014 I don't think the roller contacting the rear wheel would actually be that much of a problem. The reason wheel/wheel contact is so bad is because the wheels are moving in opposite directions at the point of contact. The rear bike tries to climb the wheel and the front bike tries to tip backwards. If the roller is in between, the points of contact will be in the same direction.
And since the surface speeds of the bikes are very similar (this won't help in a high speed differential contact), the points of contact with the roller should be at similar speeds.-- MechE, Dec 04 2014 t'sgood-- 2 fries shy of a happy meal, Dec 04 2014 If you had a set of rollers attached to your rear wheel, such that the roller 'exposed' to the rear was geared down slightly and going slightly slower than might be expected but in the 'right' direction, then any touch by a bike following too closely would have the effect of sapping power from that bike and increasing your speed slightly and decreasing their speed.-- hippo, Dec 04 2014 // roller 'exposed' to the rear was geared down slightly and going slightly slower than might be expected but in the 'right' direction//
To do this you just need a slightly smaller rear wheel than their front wheel. Just another reason my 26 x 1 3/8" wheels win in a world dominated by 700c. Now, i just have to figure out how to make it do more than 10mph.-- bs0u0155, Dec 04 2014 No, you'd need a slightly larger rear wheel than their front wheel to ensure that the roller was rotating slower than expected and would then be sped up by a touch of their front wheel. I think that's right, anyway. It's quite a hard thing to imagine.-- hippo, Dec 04 2014 The wheels don't matter. If the bikes are at the same speed, the outer (contact) surface of the wheels are at the same speed. You would need a pulley or wheel and axle to get the required mechanical advantage, which means at least 3 rollers involved in order to get the mechanical advantage and the rotation both correct.-- MechE, Dec 04 2014 Yup, had to work entirely through the maths to convince myself... a 2068 mm circumference tire moving at 10 mph is revolving at 2.16 revolutions per second and a 2200mm circumference tire is revolving (proportionally) more slowly at 2.03. You multiply them up and you get the same ground speed in metres per second (4.47).
I think some kind of viscous coupling is the way to go, to steal torque in a less jerky way.-- bs0u0155, Dec 04 2014 The discussion somehow steers in a wrong direction. The main advantage would be aerodynamic coupling of two bikes. No need for further help or stealing advantage from or for the front or rear driver.
Just came back from a 100 km (de)tour without any pace-making help in sight but with lots of time to ponder.
How about moving the apparatus to the front wheel -? It is mainly in the interest of the rear rider to get close to their pace-maker, so they should bring the equipment, too. Could be an integral part of a low-rider front pannier, or just a standalone contraption, bolted to the hub axis. It could even serve to hold a mudgard reaching a quarter circle more to the front than the standard.-- Toto Anders, Dec 04 2014 Yeah, discussions here do that, you get used to it.
The front wheel thing makes some sense from a responsibility stand point, but it's going to be harder to mount. With the rear wheel, you can clamp to the chain- stays, which tend to be geometrically consistent, and most bikes have them. so the mount is a simple tube.
On the front, you don't have that line, so you're going to need a more elaborate frame that bolts to the pannier/mud guard mounts. However, since a lot of racing bikes (the type most often ridden in pace lines) don't have these mounts, your'e also going to need a version that clamps to the fork, in multiple spots, and then you're going to need adjustment to correct for different rakes and tube shapes.-- MechE, Dec 04 2014 //and the front bike tries to tip backwards// bollocks.-- pocmloc, Dec 04 2014 I didn't mean to say it actually does tip backwards, just that that's the direction of force involved. It's going to tend to present as a rear wheel skid, possibly with a sideways element depending on the exact contact.-- MechE, Dec 04 2014 Any number of ways to make the initial 'two wheels hitting each other' less bumpy, storing the energy in a spring or bungee cord.
Imagines possibly 30 bicycles, nose to tail, cycling around in a ring. Given the aerodynamic advantages, it might be possible to achieve something near the speed of sound.-- not_morrison_rm, Dec 04 2014 //it might be possible to achieve something near the speed of sound.//
Or not. Rolling resistance scales approximately linearly with speed (constant with distance traveled), and is equal to air resistance for most riders somewhere around 12mph. Wind resistance goes up as the square of speed. Therefore double the speed equals 4x the force for wind resistance. So that 24mph cyclist can maybe make 60mph.
The record individual time trial (no drafting) for a cyclist is 34mph, which means ~8x the power input.
108mph theoretical max. This is probably a realistic, since the peak for a human powered vehicle (fully faired recumbent) is 86mph right now, and those are highly streamlined.-- MechE, Dec 05 2014 Ah. While trying to work out if it would be possible with sulphur hexafloride (it's not) I just decided to give up.
But then I remembered the bicycle Ouroboros would function best in a large vacuum chamber anyway, so cutting down air resistance and pushing the local speed of sound down to about zero.-- not_morrison_rm, Dec 05 2014 // ... the bicycle Ouroboros ... // I couldn't help thinking of the scene in "Day of the Oprichnik" where a group of russian pretorians form a circle by each penetrating his colleague while being penetrated by another one. I swear this isn't what I had in mind when devising my bike train.-- Toto Anders, Dec 05 2014 Truly one learns something new every day....-- not_morrison_rm, Dec 05 2014 //108mph theoretical max.//
Are you allowed a high altitude plain and 100% oxygen to breath?-- bs0u0155, Dec 05 2014 That was based on zero wind resistance, so you won't do much better than that with regard to altitude.
The base speed I used was based on the current time trial record for short (3 mile) time trial records. I realized I missed a category there, and the record for the flying (rolling start) 200 meter sprint time trial is about 47 mph. (I'm using time trials because they are unpaced/solo, so no drafting to improve wind resistance. That allows a baseline using my 12mph number above.) That's probably about as close to an instantaneous peak as you can get (it's less than 10 seconds).
That might push the limit up towards 200 mph with no wind resistance over very short distances. And obviously, if an athlete can beat that record, they could improve proportionally, so, for instance, riding in a pure oxygen atmosphere would probably help.
Also this assumes a typical bike. If the bike was lightened below UCI limits, that would help a small bit (not much, even the lightest elite athletes weigh many multiples of their bikes already). It might also be possible to lower rolling resistance, but bikes are pretty good in that regard, and most of the ultra low friction approaches come at a serious weight penalty (e.g. air bearings).
In summary, I consider it extremely unlikely that human powered vehicles will ever break 250mph (even without wind resistance, say on a treadmill, and even with performance enhancing drugs), and the speed of sound at the peak of Everest is still in excess of 650mph.
Of course, as [not] points out, if you ride an a vacuum (with a breath mask, say), any speed is exceeding the speed of sound, but I'm going to say that's outside of the intent of the original statement. Also, you still be hard pressed to exceed the speed of sound in your riding surface (as low as 88mph in soft rubber, but soft rubber = much higher rolling resistance).-- MechE, Dec 05 2014 If we can figure out how to make dogs cycle, their VO2 max is about 4 fold higher than a person, add oxygen, and a ball to chase-- bs0u0155, Dec 05 2014 " Yeah, discussions here do that, you get used to it ".
So I need a dog, a ball, and an oxygen tank on my bike? I mean, who can afford an oxygen atmosphere? Let's not even use the s word.-- normzone, Dec 05 2014 There is no force tipping the bicycle backwards. At most, there is a force retarding the rotation of the rear wheel, so I say again bollox. And I do think that this whole friction thing is massively over-rated. I think interference with steering and consequent loss of balance is a much more pressing issue here, and so a third time I utter my opinion, bollox.-- pocmloc, Dec 05 2014 If you stop a wheel dead, the object attached to it will tend to attempt to continue the rotation. for the rear wheel, that is an up and over tip.
And no speed would inherently cause you to lose balance, so the only theoretical restriction on speed (in a vacuum) is rolling resistance.
[Notation] Really not sure. Probably more in the tires, so going to something like solid tires or even metal contact might improve the numbers, as long as you had a perfectly smooth floor, and enough traction that you didn't lose the ability to steer enough to maintain balance.-- MechE, Dec 05 2014 random, halfbakery