Well now, I have about 100 miles on the new bike and hence the new 3 speed hub. My thoughts so far:
Having 3 gears is quite nice. I have a 36 tooth ring up front and a 16 tooth in the back, so that may be a little steep for some people. I like it because I wanted to be in the middle gear the majority of the time, because as I understand it the middle gear is direct drive. Therefore, the middle gear should not suck up any power via mechanical losses.
Speaking of efficiency, the only other IGH I have had experience with is the Nexus 7. And that thing totally sucked. It was very heavy, and it felt like it sucked all the power away when you tried to go. This 3 speed is unlike that old 7 speed, and that is a good thing. The hub is still heavy, but when I stand up and mash on the pedals the bike moves. I can't notice any real losses of efficiency, I'm sure they are there, but I can't tell.
This is the only 3 speed hub that you can get that is 32 hole, at least that I have seen. The SRAM i-motion is only 36 hole, and the S-A as well. The Nexus 3 speed is also the lightest, listed at under 1000 grams whereas the i-motion and the S-A are a little heavier. I found the prices to be similiar between the disc versions of the Nexus and Sram hubs(~ $100), but if I recall the S-A disc hub was around $130. Its also black, I don't like the bling bling chrome.
I have found that when shifting you really need to let off the power, it does not like to shift under a load at all. I have had only one missed shift and that was when I was in traffic trying to really move, so I was putting the power down and it balked while shifting between 2 and 3. The grip shifter is backwards for my taste as well. I works like the shifter for the front derailleur, in that you twist forward for an easier gear. I'm slowly getting used to that, but I would prefer the opposite.
The shifting mechanism, meaning the bellcrank thing that is bolted to the hub, is lame in my opinion. I bolts to the axle nut and operates a pushrod that goes into the hub. It kinda sticks out and it is just waiting for something to smack it and break it. Also I imagine that the part will have clearance issues for many bike frames. I had to take a dremel tool and grind away almost all of the plastic on the housing so that it could fit on the axle nut. My frame has sliding dropouts so the axle sits very close to the frame, which is no problem if you had a QR. But simply tightening the bolts for the axle is sorta troublesome because the only place to get a wrench is from the bottom. I carry a 15mm socket and ratchet in case I need to take the wheel off. So, unless your frame has wide open dropouts where the axle nuts are out in the open and not recessed behind a flange of sorts, be prepared to dremel the bell crank in order for it to fit on the axle nut.
Speaking of taking the wheel off, that will be a pain as well. Because you will have to undo the bell crank from the axle, and make sure you keep track of the pushrod that goes into the hub. It may just be me being a baby, but that is just more stuff to deal with when changing a flat. Plus the shifter may come out of adjustment when taking it off, it shouldn't, but it might.
The chainline on mine was really off. The rear cog mounts very inboard it seems, and so I had to fiddle with the spacers on my BB. Doing that made the chainring hit the chainstays, so I had to expirement with spacers until I got the cranks as close to inboard as possible. That would not be a problem if I were using a smaller ring that the 36 tooth one I have on there now. I also had to mount the front ring on the inboard side in order to get the chain straight. It seems like Shimano took the effort to make it disc compatable, but did nothing about making the chainline better for MTB's. Also the hub uses a centerlock rotor, so in order to get a 6 bolt rotor on there you need an adaptor.
I am happy witht the hub so far. Most of the issues I have had have been with mounting the thing on my bike and getting everything to line up. That was kinda a pain in the bum. But now that everything is all setup I rather like it. The only drawback to the hub is the weight and shifting under power, but not much you can do there. That seems to be par for the course with IGH's. It is really nice to have the small selection of gears in case you get lazy, that is of course coming from a SS rider. People used to 27 gears may find it lacking. Of course I haven't enough miles on it to judge reliability, or how it will stand up to occasional light off roading (its my commuter bike) So if you are thinking about trying the IGH thing for cheap, I would reccommend the Nexus hub.
If you have any questions about specifics of the hub or how it rides please ask me. Kyle
I cannot post pictures yet because I have only 8 posts. Pictures soon mkay...
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Thread: Nexus 3 speed hub review