edtguy

Hi Experts,

I'm considering replacing my external freewheel gear cluster and derailleur with an internally-geared hub, but first I want to be sure that when the chain pulls forward, the gear engages immediately, as it does on the external freewheel. In other words. if I were to remove the rear wheel from the bike and the chain, grab the freewheel and turn counter-clockwise, it will turn freely, and when I turn clockwise, it will immediately lock, with no travel before it locks. I want to be sure that the internally geared hub performs the same way.

The reason this is important to me, is because this wheel is on my Rowbike 720 sport, not a conventional bicycle. Drive for the gear is from each rowing stroke, not from continuous pedaling (for a visual, see the video on www.rowbike.com), so there are alternating pull and release cycles. I don't want to lose any performance in the stroke due to latency of the gear engaging at the start of the stroke.

Do internally geared hubs hubs perform differently than external gear clusters with respect to this concern, or is this not an issue?

TIA,
Ed

Lossy

My understanding is you will still have a chain and a freewheel outside the hub. When the chain moves the sprocket on the outside it moves the internal gears. However IANABM.

Dan Burkhart 

Of the gearhubs I have here in the shop,(and I have a bunch) the Nexus 8, Alfine 8, Nexus 3 (without coaster brake) and Rohloff all engage forward imediately in any gear. The Sturmey-Archers, both 3 and 8 speed have quite a bit of takeup before engaging, as do the Nexus 3 and 7 speed coaster brake versions. Of course, for the application you have in mind, a coaster brake is out anyway.
I'm thinkin' the Nexus 8 is a good way to go.
Dan Burkhart
www.boomerbicycle.ca

edtguy

Thanks Lossy. I realize that I will still have one external gear driven by the chain, and that I'm only removing the derailleur from the process. What I'm concerned with is when I begin the power stroke, will I immediately feel resistance because the internal gear has engaged, or will there be some travel in the power stroke with no resistance before the gear engages. With a conventional bike this is not a big deal, because after the initial engagement there is continuous pedaling, but for the Rowbike, it is a series of engagements and releases, so it is important for the full stroke to be engaged.

edtguy

Thanks Dan! That takes the Sturmey-Archer (the one I was looking at) out of the running.
Cheers,
Ed

dbg

That is one strange bike. I'd hate to hit a bump or a hole and bottom out that row lever.

Dan Burkhart 

I wish their web site showed the drive mechanism a little more clearly. All I can really see is that, depending on which picture you look at, the top run of the chain appears to be aimed at the bottom of the cogset in some shots and at the top, like you would expect in others. Do you have pictures you could post that would show the mechanism at the cogs?
I'm wondering now if the takeup play on the Sturmey-Archer would really be that significant.
Dan Burkhart
www.boomerbicycle.ca

edtguy

DriveLeft.jpg

DriveRight.jpg

DriveExtended.jpg

Hi Dan,
I've taken a few close-ups to detail the drive mechanism.
The first picture, DriveLeft.jpg, shows the drive mechanism from the left side of the Rowbike. The chain is bolted to the frame and rides over the "Dave" cam at the bottom of the power lever. As the rider pulls back on top of the power lever, the bottom moves forward, pulling the chain over the rear sprocket.

The next picture, DriveRight.jpg, shows the drive mechanism from the right side of the Rowbike. The horizontal length of chain riding over the cam is behind the diagonal length coming from the derailleur. The other end of the chain is attached to a bungee cord that runs through the inside of the power lever from bottom to top and back down. You can see the excess cord tied around the bottom of the power lever. As the rider pulls back on the top of the power lever, pulling the chain over the rear sprocket, more chain is fed out of the power lever as the bungee stretches.

The final picture, DriveExtended.jpg, shows the power lever pulled back, exposing the extended bungee.

By the way, the Rowbike as pictured is set up in a Fluid2 indoor trainer, with 20" wheel adapter, which works nicely.

Hope these pictures help. I haven't moved forward yet on the internal hub, but I do think that any take-up play would be significant, so I would first consider the Nexus 8.

Regards,
Ed

Dan Burkhart 

Thanks for posting the pictures. That is interesting. Can't see any reason why a Nexus wouldn't work with that. You probably need to leave the derailleur in place for extra chain takeup though.
I think I would want to keep a close eye on the integrity of that bungie cord. Having that thing snap at full stroke could be painful, doncha think?
Dan Burkhart
www.boomerbicycle.ca

roughrider504

My Sturmeys dont engage immediately. My Shimano on the other hand, does.

edtguy

I believe I'd be able to eliminate the need for the derailleur by removing a section of chain and re-tensioning the bungee. I'm not worried about the bungee, because in my experience it would be less likely to snap and more likely to gradually lose its elasticity, so I'd replace it when it no longer effectively took up the chain slack. Even if it were to snap, it's inside the power lever, so the result would be little more than the chain falling to the ground. And perhaps the handle bars would slam into my gut, but they don't go near more sensitive areas

Thanks also to roughrider504 for seconding the performance of the Shimano. That's great news.

Dan Burkhart 

Right. It was the attachment point of the bungie that I was thinking about. Anyway, I'll be interested to know how it works out when you get the gearhub installed.
Happy New Year
Dan Burkhart
www.boomerbicycle.ca

geo8rge

The thing to remember about a rowbike is the lower the gear, the more stokes, the more you introduce balance issues as you bounce back and forth. On my rowbike I considered a duel drive to get a lower low, but did not think it was worth the time & $. A gear box might make shifting smoother, but you will still need the derailer. I would make sure the gear range is about the same as the mega range. I think the dual drive has a freehub.

You might email rowbike itself and ask if they have any ideas.