Bicycle Mechanics - Few questions on internal gear hubs.

Just need some clarity.

1. can they take punishment? Like out of the seat mashing uphill in a hurry. Are they durable?
2. What's with shifting? Can I shift the gear hub on the fly? (while pedaling)
3. Are there any other limitations like gear range or anything else?
4. What is the failure mode. Do they fail to a predetermined gear or just rotate freely?
5. Maintenance, anything I should know?

Cheers

CE

1. can they take punishment? Like out of the seat mashing uphill in a hurry. Are they durable?

Old Shimano 3-speeds were known to break, but the current generations (as well as many older generations too) have good records of durability.
Not saying that a track sprinter wouldn't be able to create havoc at an all-out effort, but for regular use there isn't much to worry about.
The Rohloff comes with recommendations regarding chainwheel/sprocket sizes in order to limit the available torque, so maybe not the stuff to use if you're in the habit of breaking stuff that others are fine with.



2. What's with shifting? Can I shift the gear hub on the fly? (while pedaling)
All I've tried have required that you ease off on the pedals very briefly to get the "new" gear to go in, but I haven't tried them all.



3. Are there any other limitations like gear range or anything else?

Gear range usually is limited, if compared to a bike with a triple crank. But unless you're in mountainous regions you can usually get the coverage you need from an IGH.
3-speeds have fairly big steps, so they're not the best choice if you're used to the tight gearing of a road hub.
Sheldon Brown has a nice gear calculator (http://sheldonbrown.com/gears/) that lets you compare what you've got with what the IGH's can give you.

And, as stated, there can be chainwheel/sprocket restrictions in order to limit available torque.



4. What is the failure mode. Do they fail to a predetermined gear or just rotate freely?
IME the gears will fail one by one, by refusing to engage. Usually you'll have some gear(s) left to limp home with.



5. Maintenance, anything I should know?

On the whole, they don't need much maintenance. Not that a disassembly, clean and relube is going to hurt them, but adding some oil and repacking the main bearings every odd year will usually go a long way.
Most important is probably not to ride the bike unless the gears go in clean. With a half-baked engagement the risk of shearing/grinding teeth off the gears increases significantly.

Old Shimano 3-speeds were known to break, but the current generations (as well as many older generations too) have good records of durability.
Not saying that a track sprinter wouldn't be able to create havoc at an all-out effort, but for regular use there isn't much to worry about.
The Rohloff comes with recommendations regarding chainwheel/sprocket sizes in order to limit the available torque, so maybe not the stuff to use if you're in the habit of breaking stuff that others are fine with.


All I've tried have required that you ease off on the pedals very briefly to get the "new" gear to go in, but I haven't tried them all.



Gear range usually is limited, if compared to a bike with a triple crank. But unless you're in mountainous regions you can usually get the coverage you need from an IGH.
3-speeds have fairly big steps, so they're not the best choice if you're used to the tight gearing of a road hub.
Sheldon Brown has a nice gear calculator (http://sheldonbrown.com/gears/) that lets you compare what you've got with what the IGH's can give you.

And, as stated, there can be chainwheel/sprocket restrictions in order to limit available torque.


IME the gears will fail one by one, by refusing to engage. Usually you'll have some gear(s) left to limp home with.



On the whole, they don't need much maintenance. Not that a disassembly, clean and relube is going to hurt them, but adding some oil and repacking the main bearings every odd year will usually go a long way.
Most important is probably not to ride the bike unless the gears go in clean. With a half-baked engagement the risk of shearing/grinding teeth off the gears increases significantly.

Rohloff is highly durable, I know one local ride leader that has over 25,000 miles on his.
The Rohloff doesn't require backing off on the pedalling as other internal gear hubs and also has a broader range-but you pay for that in a higher price tag and with greater weight.

SRAMs seem to fail by getting stuck in overdrive.

check out this site;

Internal Gear Hubs (http://hubstripping.wordpress.com/internal-gear-hub-review/)

As far as the gearing goes, my 48x19 Shimano Nexus-8 redband has a wider range than a 20-speed road bike but not quite as wide as something with a triple. It's pretty close to 34x50 compact crank with 12-27 on the cassette.

I've done a couple of imperial centuries and a dozen metrics through rolling hills. I've mashed up and sprinted down hills. Everything breaks and there is only so much gearing down you can do before you break even the most durable hub so don't expect to put a 26 chainring on it with a 23 cog and start a stump-pulling service. If you look at the hub's own gearing and plot out a chainring/cog combo that matches the derailleur gearing you want to emulate, you'll be fine. Note that the same chainring/cog combo is going to give you different results with the Nexus, SRAM, and Rohloff hubs because each is geared differently inside. Sheldon's calculator is really helpful.