Just a thought I had.

What would be the top speed if I ever sprinted using one of these?

  • 2
    the top speed depends on the chainring and cog sizes you use, as well as your fitness and abilities – Paul H Sep 9 '20 at 16:29
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    I think a more relevant way to phrase the question might be, how many watts (at some power output) would a gearbox cost me? If I were riding at my functional threshold power, how many mi or km/h would a gearbox cost me? – Weiwen Ng Sep 9 '20 at 18:14
  • Depends what you mean by 'road bike' and for what purpose. Obviously the Pinion systems and various internal hub systems (Rolloff, Shimano Nexus/Alfine) are viable for bicycles in general and are widely used. I believe there is at least one continuously variable system (NuVinci) but I don't know how much up adoption they have. – Argenti Apparatus Sep 9 '20 at 18:18
  • Which question do you want an answer to? "Viable"? Or "Top speed"? Not that either question is particular well-formed. "Viable" depends on numerous factors. There are certainly road bikes with the gearing types you mention. Doesn't that prove they are "viable" in and of themselves? If not, why not? As for "top speed", who knows? What bike frame? Wheels? Tires? Which gearing are you asking about? How much power can you put out? – Peter Duniho Apr 24 at 6:09

Priority Bicycles offers both a Pinion Gearbox Road Bike with a 600% gear range and a CVT Road Bike with a 380% gear range.

I recently purchased the CVT and find it suits my needs. I have on occasion wished for both lower and higher gearing availability but generally I'm not climbing killer hills or trying for speed records.

Sequential gearing (or gear equivalent on the CVT) is very convenient. So too is the ability to shift without pedaling while stopped, although the top and bottom 15% of the CVT requires pedaling.

I can't answer the Top Speed question, it makes me flash to the very old car commercial that specifies top speed as "Down hill in a hurricane". If top speed is an important factor, I would suspect the CVT would not have a range to satisfy you. The Pinion probably would, but it's not inexpensive.

  • 2
    If it helps, track racers ride routinely above 60 km/h on singlespeed bikes. – ojs Apr 23 at 19:30

You could use any of those options, but they will all absorb more of the input energy compared to traditional chain and derailleur gearing. This will reduce your output speed or distance by comparison.

  • Losses within a Rohloff are on the same level as with a derailleur system, so your assertions are not correct in all cases. – cmaster - reinstate monica Apr 23 at 22:40

Just a thought I had What would be the top speed if I ever sprinted using one of these?

The top speed is way over 100 km/h, probably at least 150 km/h.

The process for obtaining such unbelievably high speed is as follows:

  1. You start sprinting
  2. The rear hub fails to withstand the high torque
  3. You fall
  4. A witness calls ambulance
  5. The ambulance arrives, transports you to the hospital, and this is how you obtain the >100 km/h speed

For example, Rohloff speedhub, the 14-speed internal gear hub, supports with standard sized chainring and sprocket only 250 Nm torque at the cranks.

On a road bike, in sprinting position, the handlebar allows you to obtain extra leverage. Maybe 30 kgf of extra force.

The clipless pedals allow you to pull up with the rear pedal and simultaneously push with the front pedal. Maybe 25 kgf + 25 kgf = 50 kgf of extra force.

This is added to your weight. For example, if you weigh 80 kg, it's 80 kgf of force.

So I already see 30 + 25 + 25 + 80 kgf = 160 kgf = 1569 N.

If the crank is 175mm long, this is 0.175 m * 1569 N = 275 Nm, over what the Rohloff speedhub can withstand using standard sized chainring and sprocket.

Rohloff speedhub is not the only one at fault. There are internally geared hubs that suffer from even more severe problems at lower torques, such as the Sturmey Archer 3-speed hub.

  • 3
    It should be noted that Rohloff hubs do not have any safety margin past the specified limit. If you go over it, they explode immediately and violently. Fortunately the 30kg for pulling up on handlebars is completely ludicrous and pulling up 25kg is pretty close, so outside juhist's imagination one should be safe. – ojs Sep 9 '20 at 20:48
  • 1
    In addition to ojs's comment, the point of using an IGH or gearbox is that you do not have to put those 1600N on your cranks. You put out a wattage (= physical power), and the gears turn it into the appropriate torque. Finally, top speeds are typically achieved not by wrenching the cranks, but by crouching low on a descent. You can easily reach 70km/h with this method, without even moving the cranks. Tour de France riders routinely do over 100km/h due to steep descents and extremely low crouching. – cmaster - reinstate monica Apr 24 at 6:00
  • Video or didn't happen. – EarlGrey Apr 26 at 8:46

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