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I have an idea and I'm wondering if it's feasible.

For an upcoming recumbent cargo touring build, I wonder if I could say use an 8-speed hub gear connected directly to an identical 8-speed hub gear, or three hub gears 4*4*4, to get logically 64 gears.

What sorts of problems might there be? I don't have any particular parts in mind regarding ratios, but does anyone do this?

Are there any good examples of how to do a high number of gears right?

The whole point of this would be to be able to drive the bike up anything from a long ridiculous 30% grade at walking pace to an easy 100km/h on a straightaway with fairing. Is that feasible using a large number of gears?

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It's fairly common on bents and hand cycles to have a multi-speed hub combined with a derailleur setup. I've not seen multiple multi-speed hubs, but don't know why it wouldn't be possible. – Daniel R Hicks Feb 20 '14 at 23:34

The HP Velotechnik Scorpion is available with three front chain rings, three-gear internal hub, 8-speed rear derailleur setup. This has the additional advantage that you can shift while stopped, e.g. after emergency stops or similar.

I found it rather tedious to keep the overview over which gear I'm currently in. My Velomobiel Quest has triple front, 9-speed rear derailleur and that covers enough ground for me. Walking pace is not a problem and I spin out at about 70km/h, which is already pretty hard to keep up, even with race fairing.

Depending on where you live, riding 70km/h is already pretty dangerous taking into account that trikes cannot brake too well because the rear wheel will lift off pretty quickly.

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re braking -- my design is a quad with front-wheel-drive and rear brakes. But that's not the point of this OP -- it's just about whether it can work to use a series of two or three hub gears. – themirror Feb 19 '14 at 18:03
Then yes, it can work ;) – arne Feb 21 '14 at 6:42

You will likely be using at least one of the hubs outside of its maximum torque specification when riding in a low gear.

Here's a random thread about a guy breaking a NuVinci by overtorquing it with a gas motor assist:

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But if the bike is human-powered, and the gear range is similar to a derailleur bike, the torque would be likewise similar. Of course, both the your guy and the OP want to have a lower low gear, but the OP didn't express a desire for motor assist. – Daniel R Hicks Feb 20 '14 at 23:42
If the output of one hub is fed into the second hub, there'd be a ton of torque going into that second hub when pushing a big heavy bike up a hill. – Alan Gerber Feb 21 '14 at 17:26
No more than a gorilla driving the same load up the same hill. There's easily a 5:1 variation in the force different bikers can/will generate, and hard to say where the OP is on the gorilla scale. – Daniel R Hicks Feb 21 '14 at 17:36

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