Schlumpf Mountain Drive, and a NuVinci 360, on a mountain tandem?
I have a new Fandango, it's our first tandem, we love it BUT it is clear that we need lower gears to make some climbs. Having ridden a Schlumpf unicycle hub and being familiar with other amazing innovations that come from Mr. Schlumpf's imagination, I was interested in seeing if I could get rid of my 44/33/22 and replace it with a Mountain Drive.
The Mountain Drive is 1:1 in high gear (fixed) and reduces the effective gearing by a factor of 2.5 : 1 when shifted, so a 44t chain ring is reduced to a 17.6t, which is quite a bit lower than our 22t.
It's pricey, I'm not even sure if it'll fit the frame, but if it worked I would have a great gearing range overall, lower effective gearing, and I could junk the front deraileur and two chain rings
So then, to bump things further, what about using the Mountain Drive in conjunction with a NuVinci? Schlumpf does not recommend their drive with a Rohloff due to excessive torque in low gear, but the Trike folks are already using the Mountain Drive and Nuvinci in combination and it appears to be working fine.
I wonder about the torque issues with the NuVinci, like the Rohloff it is sensitive to low end torque, though it's design parameters indicate it is quite a bit stronger than a Rohloff.
Anyone have experience on a tandem with either of these products?
Re: Schlumpf Mountain Drive, and a NuVinci 360, on a mountain tandem?
Sounds really cool, but... complicated. Wouldn't it be easier to use a larger cassette? We use a Shimano 11-36 and with a 22t front, provides a low enough gear. Just a thought.
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Changing our largest cog (34) to a 36 would help, but not that much, two teeth in back is like one tooth in front, so a minimal change at best. I'm lookin for stump pulling gears!
Dropping four teeth in front with the Schlumpf Mountain Drive would be like going from a 34 to a 42.
The two systems together would provide almost double the range of a Rohloff, and then go to two chainrings on front and the range is truly amazing. Of course there is a weight penalty, but overall the complexity and reliability is better, at least in theory.
The hub would be the least expensive and easiest mod, just build a wheel and try it out. If it is less than adequate, I can sell it or put it on my son's 29er.
One of the things that intrigue me about a NuVinci is the seamless shifting and the "dampened" feel in high torque situations, this would make low speed maneuvering and sudden speed changes much easier to manage/compensate for.
But changing to a 36 would be easier and a lot cheaper
Not sure what cranks you are running. If the bike was MTBTandems.com built, it may have Middleburn cranks. Get your hands on a 5 arm 58 / 94 spider for the stoker and run a 20t front. Next would be to find some matching single bike cranks that were micro drive and run square tapers and helicoil the stoker cranks for the pedals. These cranks too would be 5 arm 58 /94 BCD.
This could get you to a 20 in front and 36 rear, that is pretty low. Enough for us to be more concerned about needing to run a DID motorcycle chain.
Reps! We don't need no stickin' reps!
A 20 x 36 would be a big enough difference, didn't know a 20t was an option, so let me look into that.
We have the Truvativ cranks, so I don't know that a 20t is available...
Truvative I doubt it. You need not ancient, but vintage 5 bolt 58mm inner chainring style cranks.
Middleburn does show an available spider in that size.
Reps! We don't need no stickin' reps!
MTB Tandem Nut
IIRC, the Schlumpf is tandem-rated only in the road overdrive version, not the mountain drive, unless they've changed something.
The cranks you have will not accommodate a CD spider, but there are, I believe 20T Ti or stainless rings available for 64BCD cranks from Action Tec. I know we've ordered them in for customers before.
I saw that 20t for sale in a couple places. Any idea if it will have chain rub issues?
So what's your opinion on the Schlumpf cranks and or Nuvinci hub?
You'll want the N171 and not the N360 Nuvinci. Much more durable. Holding up fine so far on my 960w electric cargo bike.
That appears to be true, but Fallbrook hasn't posted max torque ratings for the N360, only the N171 (130 Nm/96 lb-ft).
You'll want the N171 and not the N360 Nuvinci. Much more durable. Holding up fine so far on my 960w electric cargo bike
Technically the hub is not tandem rated (voids warranty), but it should be strong enough, some trike riders are already using them for touring while pulling a trailer.
I'd have to undergear it considerabley to make it work for off road use, at least low enough to be comparable with our current 22/34 gearing.
But it's probably not team weight (comparable to loaded cargo bike) that is going to be the issue. It'll be team torque output that will kill a hub. That's also not going to be helped by undergearing it. I think most of us would be surprised what sort of torque loads are put down through a tandem in granny up a steep hill...
You'd want to have conversations with people from both companies. Not that you're concerned with warranty service (and you'll probably have to repeat that to them a few times), but I'd be hesitant about spending the money creating this thing only to have it fail.
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