Internal gear hubs - limitations?

[Count Steer]

As per another thread. I always thought that Sturmey Archer internal gear/planetary hubs were a bit genius and see that now the same sort of thing with eg 7 gears is available for MTBs.
I'm not aware that they've ever been scaled up for bigger/heavier bikes ie motorbikes and wondered why not?
Any ideas? I know that planetary gearing is used in other applications. Just seems odd that it wasn't tried at some time in the transition from bicycle to motorbike. (Unless someone knows that it was).

[Mussels]

When I pulled one apart the gears looked rather fragile, I was replacing broken planetary cogs that only had pedelec power going through them.

[Rockburner]

As per another thread. I always thought that Sturmey Archer internal gear/planetary hubs were a bit genius and see that now the same sort of thing with eg 7 gears is available for MTBs.
I'm not aware that they've ever been scaled up for bigger/heavier bikes ie motorbikes and wondered why not?
Any ideas? I know that planetary gearing is used in other applications. Just seems odd that it wasn't tried at some time in the transition from bicycle to motorbike. (Unless someone knows that it was).

I think they WERE tried, back in the '20s or so.

But, as said, they're tiny little gears and you can only put 'so much' torque through them before they disintegrate.

[The Spin Doctor]

I am sure I read somewhere that a cyclist can produce easily as much torque as a motorcycle - one estimate I saw was 100 Nm - so I'm not sure it's the torque that's the issue... unless pro racers strip Sturmey Archer gears... (but obviously revs only go up to around 120 rpm).

What's the internal friction like? My vague recollection of switching from a 3 speed SA to a 5 speed derailleur was that compared with the 5 speed, going back to the hub gears was like pedalling through treacle.

For a motorcycle, couldn't the rear hub just be increased in diameter and width to accommodate bigger gears? If you look at the size of a drum brake you'd get some extra surface area. And with a motorcycle engine, the friction wouldn't be so much of an issue.

[Mr. Dazzle]

Car automatics use planetary boxes, many EVs have a single speed one too.

My guess would be axial length. Each one can give 3 ratios (4 if you count the whole thing going around as one lump) but at least one of those will be reverse probably. Cars get more ratios by stacking several clusters in a line. Doing so in hub would mean a very 'wide' wheel.

Theyre also usually more expensive that "manual" gearboxes. In cars you could justify the cost both cause the vehcile cost more and cause it made auto boxes possible.

I say "made" cause lots of auto cars now have so called "automated manual transmissions", an oxymoron if ever there was one! Those are laid out like a bike/manual box but have the controls automated for various reasons.

[Le_Fromage_Grande]

I am sure I read somewhere that a cyclist can produce easily as much torque as a motorcycle - one estimate I saw was 100 Nm - so I'm not sure it's the torque that's the issue... unless pro racers strip Sturmey Archer gears... (but obviously revs only go up to around 120 rpm).

What's the internal friction like? My vague recollection of switching from a 3 speed SA to a 5 speed derailleur was that compared with the 5 speed, going back to the hub gears was like pedalling through treacle.

For a motorcycle, couldn't the rear hub just be increased in diameter and width to accommodate bigger gears? If you look at the size of a drum brake you'd get some extra surface area. And with a motorcycle engine, the friction wouldn't be so much of an issue.

Why bother when conventional gearboxes work?

[KungFooBob]

I say "made" cause lots of auto cars now have so called "automated manual transmissions", an oxymoron if ever there was one! Those are laid out like a bike/manual box but have the controls automated for various reasons.

BMW's SMG was a manual box/clutch with a robotic gear change. My wife's 2020 Aygo uses a robotic change too.

[Mr. Dazzle]

I am sure I read somewhere that a cyclist can produce easily as much torque as a motorcycle - one estimate I saw was 100 Nm - so I'm not sure it's the torque that's the issue... unless pro racers strip Sturmey Archer gears... (but obviously revs only go up to around 120 rpm).

When I was working with British Cycling I obviously saw some of these numbers. People like Jason Kenny can just about get to 2000W and 500Nm. Wiggins et al sustain just under 500W for a few minutes.

So yeah, a mere mortal would be able to do 100Nm no problem. You'd get more than that with by standing on one pedal if you're reasonably friendly with pies.

Edit: As for stripping gears....the big guys snap chains! They also find the tyres slip on the rims and the frames distort so much the wheels rub on the stays.

[Mr. Dazzle]

I say "made" cause lots of auto cars now have so called "automated manual transmissions", an oxymoron if ever there was one! Those are laid out like a bike/manual box but have the controls automated for various reasons.

BMW's SMG was a manual box/clutch with a robotic gear change. My wife's 2020 Aygo uses a robotic change too.

Anything with a twin clutch flappy paddle box is an automated manual, rather than a traditional epicyclic slush box.

[KungFooBob]

The SMG and the wife's car are not dual clutch jobbies tho'

They're exactly the same as a manual car, but the gears are changed by computer controlled solenoids rather than a linkage connected to a gear stick.

[Mr. Dazzle]

Sorry...should have been more specific.

Anything with dual clutch will be an AMT. Lots of single clutch AMTs also exist...SMG, Alfa Selespeed, Ferrari F1, original AM Vanquishes, Maseratis....etc. etc. However all of the twin clutch ones are AMT.

It does indeed work just like a three pedal car. Hence the slightly contradictory name.

[Count Steer]

Well, I've done some swotting and I'm still puzzled. There's no real reason planetary/epicyclic gears should be fragile unless perhaps they're overcomplicated for increasing ratios. They're supposed to deal with torque very well. They're more inefficient than deraillieurs but you wouldn't put those on a motorbike. They'll increase unsprung weight but that probably wasn't the big issue in the 20s/30s. Accessibility/maintenance may be an issue. It just seems a bit curious.

[Mr. Dazzle]

They're just physically bigger, heavier and more complicated if you want multiple ratios and automated shifting.

[The Spin Doctor]

I am sure I read somewhere that a cyclist can produce easily as much torque as a motorcycle - one estimate I saw was 100 Nm - so I'm not sure it's the torque that's the issue... unless pro racers strip Sturmey Archer gears... (but obviously revs only go up to around 120 rpm).

What's the internal friction like? My vague recollection of switching from a 3 speed SA to a 5 speed derailleur was that compared with the 5 speed, going back to the hub gears was like pedalling through treacle.

For a motorcycle, couldn't the rear hub just be increased in diameter and width to accommodate bigger gears? If you look at the size of a drum brake you'd get some extra surface area. And with a motorcycle engine, the friction wouldn't be so much of an issue.

Why bother when conventional gearboxes work?

Intellectual curiosity really... but maybe there could be applications for 'small capacity' electric bikes in the near future, where a simple hub gearbox overcomes the RPM limitation on the motor. Probably simpler than building a 'unit' electric motor / gearbox combo, or trying to tie the motor to an external gearbox tucked in the frame behind it.

[Mr. Dazzle]

Most EV motors already have an planetary gear on them some even have twin speeds.

I suspect higher performance motors would take precedence over added gears in future, but its always a balance.

[The Spin Doctor]

Most EV motors already have an planetary gear on them some even have twin speeds.

I suspect higher performance motors would take precedence over added gears in future, but its always a balance.

Once you get to the +200cc market I suspect you're right... but right now, the bulk of leccie bikes are the equivalent of 50cc - 200 cc petrol engines. So the weight penalty of an unsprung hub gear isn't nearly so much of an issue.

[Mr. Dazzle]

You just don't need it though. Anything small won't have enough power for the rpm limit to be an issue anyway.

[Count Steer]

You just don't need it though. Anything small won't have enough power for the rpm limit to be an issue anyway.

EMTBs have 'small engines' and you can get them with hub gears. I suppose they have the advantage of not being vulnerable to rocks etc.

[Mr. Dazzle]

They have bugger all power and torque compared to an EV too though. About 1/3 of a BHP.