IGH’s for 170mm Fat Bikes?

10 11 2011

Salsa Ti Mukluk with 170mm rear dropout spacing...

Wide tires/rims mean that in order to use a derailleur at the back end of a Fat Bike you need to either offset the drivetrain to the right [ie. Surly Pugsley & Moonlander] or use a very wide 170mm rear hub [ie. Fatback & Salsa Mukluk]. To me the obvious solution for a bike that will be used in the snow/sand/mud is an IGH where the shifting is internal and not exposed to the elements which also means the chain doesn’t have to move side to side so clearance with the tire is not as much of a problem.

Offset Fat Bikes like the Pugsley use a 135mm dropout spacing so an IGH works just fine. However, bikes like the Mukluk shown above that use a 170mm dropout spacing don’t allow for an IGH since nobody is making 170mm IGHs.

Salsa 170mm to 135mm adapter...

Salsa and Fatback are offering adapters that reduce the rear spacing of their frames from 170mm to a standard MTB 135mm. That gives you the option to use an IGH and if you want to run a 170mm derailleur hub you can do that as well.

170mm to 135mm Salsa adapter...

Fatback is talking about offering a 170mm frame with sliding dropouts. Currently their adapter will only work with the aluminum Fatback frames. Those frames are available without sliding dropouts, but they are prototyping an aluminum sliding dropout Fatback. I’m not sure when that will be available.

A few notes:

  • from what I can tell you’ll have to use an IGH that accepts a QR [ie. Rohloff @ $1600] to use a 170mm to 135mm adapter. I also have to confirm that OEM2 torque support/Monkey Bone setup would work with the adapter.
  • all IGHs require some method to resist rotation of the shell under high pedal loads [Rohloff uses a torque arm, Alfine uses non-turn washers, etc..] I haven’t seen anyone make this work with the Salsa adapter yet. It might be feasible, but it could be a deal breaker if not so it’s worth noting the uncertainty.
  • the chainline of an IGH needs to be straight and lined up with the single ring up front. I know that the 17.5mm Pugs offset is no problem, the Moonlander uses 28mm offset [I’m not sure how easy it is to get a good chainline there] and with the Salsa adapter you’d have an offset of 35mm which may be a significant issue as you don’t have that many ultra wide BB/crank choices.
  • 9:zero:7 offers frames in 135mm and 170mm dropout spacing and has confirmed that a 135mm AL fat bike with sliding dropouts is on the menu for next season
  • so if you want to use a bolt on IGH [ie. Alfine 8 or 11] you’ll need to stick with a 135mm dropout Fat Bike
  • so your options for an Alfine’d Fat Bike without using a chain tensioner are Surly’s which use 135mm horizontal dropouts
  • you can use an Alfine in a 135mm 9:zero:7 frame with a tensioner

Taken together I don’t think a 170mm wide fatbike and an IGH make much sense. You lose so much of the benefits and there are so many hassles unknowns that if you really want an IGH in a fatbike you should stick to a 135mm offset build.



15 responses

10 11 2011
Rob E. Loomis

Get out of my head. Or stay in there and keep doing my research for me. I was pondering this exact issue the other day. I have a weakness for Surly, but I didn’t want that to blind me to other options, especially because I could see the appeal of a lighter, aluminum frame on a bike that’s going to do more climbing and off road. But I also prefer an IGH in just about any situation, especially, as you say, messier environments. Also, while a chain tensioner is fine on my Long Haul Trucker, if your bike is going to be spending a good amount of time off road, then I see a lot of merit in keeping the drive train as simple as possible, and that means horizontal dropouts.

I’ve only just started looking into this, but I was finding the same thing that you’re saying: If I want to prioritize IGH compatibility and a derrailler/tensioner-free drive train, Surly is still the only game in town. Or a Fatback with an adapter and a Rohloff, but I’ve pretty much discounted Rohloff as an option due to expense and to the fact that I’m still in love with my Nuvinci, mostly.

Also I wonder if there’s any benefit and/or drawback to the adapter approach. If you know starting out that you plan to use a 135 hub, then my thought would be to not even look at 170-spaced bikes. Perhaps there are no drawbacks to the adapter approach, but in my mind, simpler is better, and 135 mm-spaced frame mated to a 135 mm-spaced hub is the simplest.

10 11 2011

@Rob – the only proven IGH fat bike without tensioner is a Surly Pug or ML. The weight difference between the frames vs. a Fatback is about 1lb. You can save over 1lb per wheel compared to the stock Pugs rims by going with a lighter cut out version…more if you run a tubless setup.

The main benefit to a 170mm setup is choice amongst fat wheelsets. If you don’t want/need that then it offers limited benefits.

Having said that if you want AL frame without tensioner you are buying a Fatback AL with sliding dropouts WHEN they are available – may not be until late 2012 they aren’t even testing the prototypes quite yet.

If you want an IGH fatbike now I would buy a Pugs frame/fork or a complete and just rebuild the rear wheel with an IGH. Ride it for this season and then next winter when you have an AL option you’ll have the info if it’s worth it to swap.

Pugs sell pretty well or you can swap everything over and just sell the frame/fork. Heck you can even keep the fork and just sell the frame.

10 11 2011
Rob E. Loomis

Well, my fat bike purchase is still in the dreaming phase right now. Perhaps it will be late 2012 before we get to a purchasing phase. But your point of the small size of the weight difference is well taken. I’m just trying to not get into my LHT build trap, in which, at every component choice, I decided the weight differences were negligible and, as a result, usually ended up with the heavier option. I didn’t really think it mattered until I decided to experiment with a lighter tire and noticed serious improvements. Then I decided that maybe ignoring weight issues was perhaps a mistake. But, to be fair, my tire experience may well have as much or more to do with a more supple casing than with weight differences.

10 11 2011

“But, to be fair, my tire experience may well have as much or more to do with a more supple casing than with weight differences.”

+100 – although stiff tires tend to be heavier than the same size tire that’s more supple.

10 11 2011

Realistically with a fat bike unless you want to get crazy obsessive the weight will be in the wheels. Use light rims, think about tubless and get reasonable hubs – although I wouldn’t worry too much about the later.

An IGH will be heavier than a derailleur, but may be worth the weight penalty.

Beyond that you can start carbonizing the fork, seatpost, bars, cranks, etc…not sure it it’s worth it.

10 11 2011
Val Garou

I’m kind of allergic to the idea of a tensioner. It seems to give up a significant percentage of the IGH’s benefit. Not all of it, surely, but a very real chunk of it.

10 11 2011
Rob E. Loomis

“I’m kind of allergic to the idea of a tensioner. It seems to give up a significant percentage of the IGH’s benefit. Not all of it, surely, but a very real chunk of it.”

I agree that being able to do without a tensioner is far simpler and far preferable, mostly, but I’ve made the tensioner on my Trucker very functional. It lets me move easily between two front chainrings. Originally I thought I’d get good use out of a front derailer, but in reality the hub has such a wide range that I shift rarely, so the derailer came off, but the double chainrings remained. For riding around town, the big chainring is in use, but when loaded up, touring or otherwise, I just push the chain over to the small ring. I try to imagine this process without a tensioner, which would involve shortening/lengthening the chain every time, and suddenly I’m not so concerned that my trucker has vertical dropouts.

Add to that the fact that my trucker has been on the stand, waiting for a part delivery, for a week, and I’ve been riding my wife’s 24 speed, and I find that I am very intolerant of the shifting. All the conveniences of riding with an IGH become very apparent when you suddenly don’t have one. And while a tensioner might be a drawback on some very specific types of terrain (but not a huge drawback given that most mountain bikes have a similar, chain-pulling derailer), the other drawbacks are all in the building process, which is a one-time thing. Unless you spend as much time building your bike as you do riding it, most of the drawbacks fade away when you hit the road.

As for wheel weight: I guess I’ve already chose as my preferred gearing system the heaviest hub in production, so, again, I guess that makes a 1 pound difference in frame weight pretty much a non-issue.

10 11 2011

Thanks so much for peoples answers to my question recently about using the Pugs as my only mountain bike. I like the idea of the Pugs+Alfine 11 and had two questions…

1) Is there much experience/opinion/review regarding the Alfine 11 and mountain biking? Googling doesn’t seem to turn up many details.

2) Anyone care to venture an opinion on the cost of a Pugs built up from a frame-set with an Alfine 11 vs buying a complete Pugs and having the rear wheel rebuilt with the Alfine? Seems like I’d come out ahead rebuilding the wheel if the other parts on the complete bike were acceptable to me.

10 11 2011

@Bryan – some people are having a problem with their Alfine 11’s in MTBs…Alfine 8’s seem to be more robust, but the 11 is new and I expect Shimano is going to sort them out.

I have an early edition Alfine 11 I bought last fall and haven’t used yet. I’ll be trying in my next fatbike wheel set *fingers crossed*.

My suggestion would be to buy a complete Pugs and ride it as is. Give Shimano another year to sort out the Alfne 11 and buy one next spring if it sounds positive.

Here is a good source for MTB IGH info:


If you want an IGH now and want to be on the safe side consider an Alfine 8.

10 11 2011

@Val – for a touring/city bike I don’t think a tensioner is a problem. I don’t think you’d notice a power loss, they require virtually no maintenance and they are far more robust then a derailleur so they can take some knocks. On a MTB or fat bike – where you can rip something off the frame or subject it to sand/saltwater I’d be less enthusiastic. Having said that look at all the folks running derailleurs on their fat bikes. If that works than a tensioner is no problem.

A chain drive IGH without tensioner does look quite slick.

10 11 2011
Rob E.

I know when I built up my LHT, I knew from the get-go that I wanted a different set-up than the Complete. The IGH not only meant a new rear wheel, but it changed the chain line enough that I needed a new bottom bracket. Running a tripple up front was unneccessary, so I wanted a new crank with a compact double. Stock shifters would have been useless with the IGH, plus I wanted a different handlebar set. Add to that the dynamo hub I wanted to add, and I’m not sure what part of the complete bike that I would have kept.
Vic’s comment is good that if you want to wait and make sure the Alfine 11 is up to the task, you can ride the complete while you wait. But if you think you want to put an IGH in from the beginning, it’s worth looking at all the stuff you will end up changing as a result. Chain line probably won’t be an issue because the Pugsley is already set up to push the chain line to the limit. But think if there’s anything else you want to change. You can probably flip most of the parts on eBay or swap them out in trade at the shop, but at some it ends up being more trouble then it’s worth. If the hub is coming later, or if the hub is the only swap you want to make, a complete bike probably makes sense, but with every part you replace, it makes less sense. And if you were going to rebuild the wheel, I’d check out the going rate for a fat bike wheel on eBay. Might make more sense to build an all new wheel and sell the old one.

11 11 2011

Even with an adaptor an Alfine IGH rear wheel would still need to be built offset to fit a 170mm rear end, as the cog still needs to be all the way to the right side. I don’t think that makes a huge difference in terms of strength though. The part I’ve struggled with is how one would get access to the rear nut on the left side as this would presumably be in the recess of the adaptor, unless the axle were changed to something longer to move the nut and washer to the outside left.

So, has anyone successfully changed out the Alfine rear axle to a longer version pulled this off yet? 🙂

11 11 2011

@Sean – to use an IGH with those adapters you’d be limited to one that uses a QR like a Rohloff.

11 11 2011

@Sean – even with a Rohloff we’ll only know for sure about any downfalls with a particular 170mm to 135mm adapter & IGH setup once somebody tries it and reports back.

fatbikes.com are working on a version of their 135mm 907 that will use sliding rear dropouts. I’ll look for that next season and keep it on my list of candidates.

3 07 2015

There is also Sturmey Archer that make a 170mm OLD 3 speed hub (disc or band brake). Originally built for fat wheeled cruisers. But it’s difficult to find.

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