1

I have been looking at getting an internal gear hub wheel for my commuter. I currently ride a fixie and I find myself wanting a lower gear at stop lights and a higher gear in straight aways. Basically I want two speeds: fast and something comfortable from a stand still while I get to fast. I would hate to end up adding a derailleur so I'm very interested in internal gears.

I have ridden several bikes with Nexus hubs and I'm generally underwhelmed with the gear ratio. I was researching hubs and found the Brompton Wide Ratio Hub (3-speed) which has a gear ratio of ~246% (according to Wikipedia and JohnSAllen) which is significantly higher than other 3-speed hubs. Normally the BWR on a Brompton bike would be paired with a 2-speed rear derailleur, which makes the ratio go to ~305%. But I don't care about that. I want the hub.

I can find the BWR for sale online, but as far as I can tell nobody has put one on anything other than a Brompton 20-inch wheel. That seems like such a waste. So I'm wondering whether it would be insane/impossible to build up a full size 700c wheel with the BWR hub for use on my converted road bike commuter.

  • 1
    Should be nothing preventing you from building the wheel. Whether it will fit the bike is something I can't guess. – Daniel R Hicks Aug 21 at 0:33
  • It's not a silly idea, but you'll want to know what the actual hub ratios are, so you can work out what sprocket and chainring sizes you'll need to get the gear-inch values you want. I could not find the ratios with a basic google search. – Argenti Apparatus Aug 21 at 1:07
  • 1
    You can get decent SRAM 7 speed IGHs pretty cheap second-hand (last time I paid 25 Euros!). They have a ratio of about 300% and are definitely suited for an adult commuter in constant stop-and-go usage. Don't worry about having to skip over many gears when you accelerate, the SRAM can definitely switch from first gear to fourth gear directly with a single click. That's unlike a deraileur which would need to move the chain physically across all the cogs in between. The IGH switches the gears virtually instantly, even when going directly from lowest to highest gear. – cmaster Aug 22 at 21:35
  • Thanks @cmaster, I'll try finding a 5 or 7 speed IGH to test out. I don't like the added weight which I was aiming for a 3-speed that weights under a kilo. – PatchCR Aug 23 at 15:35
2

It is possible and I wouldn't call it insane, but I would advise against doing so.

As Adam mentioned before, the hub is narrower than standard. Washers might not work well due to the shifting mechanism, but I'm not sure about that. Also, the wheel will be a little weaker to side impacts due to lower dish - not a problem for tiny Brompton wheels, but a 700C might suffer.

The bigger problem would be the gearing - Brompton has tiny wheels, so the chainring is large with a low torque going through the fast-spinning hub. A regular bike would need a smaller chainring, placing an unusually high load on the hub, which I'm not sure it would manage well.

While you'd be hard-pressed to find a different 3-speed hub with such range, I'd recommend Sturmey-Archer. Their 5-speed hubs are close to the same range and give much nicer gearing. There is a reason the wide-range is only recommended for the 6-speed Bromptons.

  • I'd like to understand more about the gearing problem here. It sounds like a larger cog than normal would be desirable to reduce torque on the hub. That would give the bike a lower overall gearing but that might be just fine if the top gear is adequate. Since you bring it up, what I'm most concerned about is how to tell if the hub would manage well under the higher load. Would I need to baby it just to prevent it from breaking on every ride or would it simply reduce the usable lifespan by some fraction. – PatchCR Aug 23 at 15:45
  • The difference between chainring and sprocket multiplies your speed but divides your torque—you gear down when climbing a hill to apply more torque. So, for example, if you've got a 39/13, that divides your torque by 3. Bromptons typically have an exaggerated difference between chainring and sprocket to make up for the small drive wheel, so the torque divider is greater; you'd be using something less exaggerated on a conventional bike, so the torque divider would be smaller, exposing the hub to more torque. – Adam Rice Aug 24 at 0:01
5

A Brompton rear hub has a non-standard over-locknut distance of 111 mm, I think. A single-speed bike probably has 120 mm. So you'd need to cold-set the frame.

Sturmey-Archer (which I believe makes the Brompton hub) also makes a 5-speed hub that has about the range you want, although from what I can tell, the OLD on that is longer than your rear triangle's spacing. So again, you'd need to cold-set the frame, although less violently. Their other 3-speeds should fit 120-mm rear spacing.

  • 2
    Going from 111 to 120mm could be done with washers. 4.5mm per side should be feasible. – Carel Aug 21 at 18:06
  • Perhaps, assuming the axle has sufficient excess length. Anyhow, something the OP should take into consideration. – Adam Rice Aug 21 at 19:36
0

You could use washers outside the hub locknuts to make up the narrower hub, as long as the axle is long enough. You could just squeeze the dropouts (I've seen it done with tiedowns!) or a combination of squeeze and washers-- not ideal, though, for sure. If you just squeeze the dropouts in 4.5mm on each side, the frame might deform asymmetrically, the dropouts won't remain parallel and you'll be riding slightly sideways!

A bigger issue is: How does a Brompton hub address the hub torsion / control cable hanger issue? You might need frame fittings. Or coaster-brake-ish chainstay strap.

For an internally-geared hub I'd go with a Sturmey-archer or Shimano that is designed for a bike with horizontal dropouts (I'm assuming that's what is on your track bike?) instead of trying to make an oddball hub fit.

Another issue is that building the wheel around the hub would be spendy unless you DIY... but if you're asking this question you're probably not going to build your own wheel :)

Go to your LBS, tell them what you're trying to do, and have them order a 700c wheel with a Sturmey or Nexus. You can change the cog on it, although that won't do anything for the STEPS between gears, which seem to bother you.

  • Thanks. While I'm admittedly very new to the bike repair/build scene I would almost certainly be doing this by myself as a spare project. Mainly because I suspect by LBS wouldn't build the wheel for reasons stated in other answers. – PatchCR Aug 23 at 15:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.