Internally geared hub for downhill?
Hi Lee,
I have a question for you. I really want to get a speed hub for my downhill race bike.
I am running an external derailleur on my rocky mountain RMX and i was looking at rohloff speed hubs, but they are slightly out of my price range. Could something like a Sram S7 work for downhill racing?
thanks,
wes
Hey Wes,
The rear derailleur is the bane of downhilling. Why does your bike’s most delicate part have to hang down by the rocks and roots? Many smart people have tried to solve this problem, but — aside from the new gearboxes — few solutions have worked better than rear derailleurs.
Disadvantages of internally geared hubs
– Loss of power. External setups are up to 99 percent efficient. Internal hubs are up to about 92 percent efficient. Seven points might seem like a lot, but whey you’re sprinting at 1,000 watts, that’s less than one percent difference at the pedals.
– Weight. Internally geared hubs are heavier than derailleurs and such.
– Cost. A Rohloff is supposed to be awesome, but it costs about $1,200. Wow. The SRAM S7 … $200. OK, that is less than one X.0 rear derailleur. So cost isn’t necessarily a big factor.
– It’s unknown whether the S7 can handle Awesome Power(tm) and the rigors of downhill. But: Most of us mortals don’t make a ton of power, and I’ll guess SRAM tested the heck out of that system.
– Limited rear axle options. 2006 and 2007 RMXes haves a 20mm rear axle. There’s no way the S7’s 10×1 will fit. Older RMXes, I don’t know.
 How about this Madness? Check out The Shaft. |
Advantages of internally geared hubs
– No dangling derailleur. If you ride very tight, very raw trails, your rear derailleur and your hangers are temporary. I spent a three weeks in Whistler when they first opened the Garbanzo, and I trashed three derailleurs in that time. You’re welcome for clearing the trail!
– Quieter. I don’t care how trick your bike is. Chain slap makes any bike feel terrible. An internal hub and properly fitted chain should be silent.
– You can shift without pedaling. This could be a significant time saver. Imagine pedaling all the way to a turn, shifting while you rail, then being in the perfect gear.
Considerations
– Your chain length changes as your RMX goes through its travel. You need a chain tensioner to adjust for this change. You can order a Rohloff DH chain tensioner for about $80. Who knows how that mates to the S7.
This just in: Eric Sovern at Surly Bikes says a Singleator chain tensioner ($40) will probably work.
– Brakes! You don’t want to race DH with the coaster brake S7. The freewheel S7 won’t accept disc brakes. So you’re left with the drum brake model. Will this drum brake handle DH?
– You gotta build a wheel, install a shifter, mess and fiddle and deal with who knows what.
– What about a single speed? Do have have awesome low-end torque? Can you spin like a CR125? Are you a citizen of Pump Track Nation? Pick a gear and do some timed runs. If you’re just as fast without shifting, you know what to do.
Are you ready for some Madness?
Check out The Shaft. My buddy Jon Heim, a genious inventor guy at Stanford, was sick of losing derailleurs at Northstar. Here’s his solution.
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Lee,
That artical is freekin awsome. I cant wait untill there is an affordable alternative to that damn derailure. Can you ask your buddy if he has made any progress on the shaft project.
A Speedhub may cost $1200, but how long do they last? Answer: Rohloff don’t know. One hasn’t ‘worn out’ yet (conditions apply of course). There’s a couple of things that may go wrong but they are rare. A steel ring and a Rohloff chain (the longest wearing chain due to triangular pins hence three points of engagement whereas others have only one) will outlast many drivetrains. In the long run, the Rohloff will be cheaper. There are guys on MTBR that have 20000+ miles on a Speedhub. In comparison, I can’t get 1000 miles from a chain, middle cog and cluster (and $160). Man, I am talking myself into a Speedhub.
Correction: The Rohloff chain pins are pentagonal hence the number of contact points under tension is three.
I think the biggest disadvantage is the unsprung weight. I know a team mechanic who worked for a team that used Speedhubs for one season and they had more flat rear tires and dented rims than before, so they went for a gearbox bike for the next season.
well that really didnt answer my question though lee, i read that artical which was from 2002. 2007-2002 = 5 yrs. in that 5 years has he made any progress?
No, Jon is on to other things. Last I talked to him, he was the lead researcher at Stanford Labs. He was working on artificial muscle tissue.
From our man Stefan:
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Hi Lee
Have you seen the Nuvinci drive train from Fallingbrook Technologies?
http://www.fallbrooktech.com/02_Demo.asp#
It looks good but, I would like to try one.
I run a Saint derailer and it is bomb proof. When I first got it I hit a 3-4″ diamiter tree that had been cut off just a bit higher than my axel, so it caught the derailer full on and stopped the bike dead from like 10 km/hr(aprox., I was flying and in pain for days after) and I got ejected over the bars. I expected to see the derailer hanging or at least pretzeled. To my delight it was intact and diden’t even need an adjustment, since then I try to only run Saint (my bike is almost all Saint). Sorry about the spelling.
Thanks
Stefan
Stefan, at the moment the NuVinci system is aimed at commuters only, not racing and definitely not for the rigours of DH. It is also super heavy (Speedhub = 1.8kg, NuVinci = 4.3kg!). Maybe one day, but not in this decade. But I agree, it looks very good. So simple.
hey thanks a lot lee for your words of wisdom. it really helped me out .
Allright so on internal geared hubs they are cool no derailer but also add weight to your rear wheel bad so why not get a frame with a gear box just a thought you can check nicoli’ s bikes those are sick run a gear box called the g boxx also a company called msc they are the new standard
heres some fitment info on ig rear hubs … dont use a hub with an ‘external’ style shift mechanism , these are gonna get broke off quicker than any deraileur [think old stumyarcher chain & threaded rod lookin stuff]. nexus 7 or 8 spd , alfine 8 spd , or sram 9 spd use a neat & tidy cable mount which sits inside the frame . however , these are all ‘commuter’style hubs and lack the low end gearing for mntbiking …too low of an input gear [think granny gear] will overtorque their internals. they may work for dh chairlift assisted use but their gear ratio jumps are spread rather far apart , too much so for competition use. rohlof hubs have real mnt bike gearing with close even jumps , qr or 10mm axle ,disc brakes, and two different but acceptable methods for cable mounting … also … you will need the chain tensioner unless you have a unified rear end or rigid bike .