Schlumpf drive 2-speed chainset

This weird thing pops up now and again, but it’s hard to find people riding them for mtb

I’ve always liked the idea of using one for a simple dinglespeed, but I wonder how they would cope with mtb (XC that is) and how they would feel with a reasonable amount of torque going through them (running them dinglespeed would still mean a lot of single-speed-like low-candence gurning)

So, is anyone using a Schlumpf drive for proper offroad riding, or better still as a dinglespeed?

Not really answering the question, but anyone remember that setup that someone did with a clever arrangement of freewheels and a tensioner, which meant that if you pedalled forwards you were in one gear, and if you pedalled backwards you were in another gear?

Retro-direct is the thing. Early 1900s.

The double freewheel thing is often referred to as “retrodirect”.

I’ve also wondered the same about Schlumpf drives. I’m in the early stages of a full Sus singlespeed frame design and have been wondering if I should incorporate one as an option.

I’m using an idler shaft design and would ideally like something like a lightweight 3 SPD version of the original effigear gearbox / high forward pivot.

I used to have a Sturmey Archer S2C – a two-speed hub kick shift coaster brake rear hub.

Back-pedal a bit to change gear; back-pedal a lot to brake.
Used it on the utility – which was previously a single-speed.
Bloody nightmare – was always in the wrong gear at roundabouts.

The Schlumpf uses a crank centre shift button that you kick with your heel. Not sure how well that works in off road reality….

Back to the Schlumpf drive, I was tempted to up gear a small wheeled bike, but the thing that put me off (other than the cost) was that you had to chamfer your bottom bracket shell to fit one.

@Aidy no need anymore, they do a version with a torque arm that attaches to the chainstay, similar to one of the Rohloff mounting options. The chainset doesn’t thread into the frame though, it just sits on the threads, which I intuitively feel isn’t good for them (although I really have no idea)

@mick_r for the riding I had in mind that’d be fine. You’d just give it a kick before an significant hill and again at the top, and consider it a singlespeed for anything else

Not sure about the Schlumpf, but I remember the SRAM Hammerschmidt had the lower gear being the draggy one. I forget the technicalities now, but I read about it and it put me off. Something about the direct drive being the higher gear, so when you wanted to climb you had to contend with a load of drag. Not sure which end of the gears is the direct ratio for Schlumpf.

The Schlumpf mtn drive version is direct drive and then low gear is 2.5:1. To be honest that is the way most semi-reformed singlespeeders will want – normal direct drive 52” ish ”SS” and then a granny gear for winching up stuff. At that kind of crawl, a bit of drag won’t be an issue.

I’d be more interested about how direct / locked solid the 1:1 feels and how well sealed it is.

The Hammerschmidt was the opposite – 1:1 direct with a very small chainring, and then geared up for higher speed – so you get the gearing losses at the same time as fighting wind resistance which increases at the square of speed.

I quite like the idea of the 27t no-spider chainring option, but slightly worried about how high the chain tension forces are getting compared to a similar ratio using a big cassette.

The Schlumpf uses a crank centre shift button that you kick with your heel. Not sure how well that works in off road reality….

It’s not like a geared bike it’s a single speed with two ratios. You might only switch modes a few times a ride. Use the higher gear on road to get out to the trails and then switch for the off road. Like a flip-flop hub but easier.

I’d be more interested about how direct / locked solid the 1:1 feels and how well sealed it is.

@mick_r same here, that’s what I’m most interested in and I’ve not been able to find any people’s feedback on that

@Rickos from what little info I could find the Schlumpf isn’t particularly draggy, while I’ve heard loads of people complaining about the Hammerschmidt

Drag with the Schlumpf apparently varies with the model. I think I read that:

The mountain drive is the most efficient (that has a 1:1 ratio then a step down to 40% of that)

The speed drive a little less so but still ok (1:1 ratio with a step up to 165%)

The high speed drive quite draggy (1:1 with a step up to 250%)

Might be worth asking Ben at Kinetics if he knows of one that could be demo’d – he seems to be one of the few UK places listing it.

Mol – I’m fully aware of how the heel shift would get used as an occasional range change. I’m more concerned if it gets accidentally caught during bumpy stuff or only half shifts and pops out unexpectedly or damages the internal gears.

Weight is the other thing. Looks like the middle bit is 900g, so that needs to be compared to a square taper BB and spider. Then cranks and chainring are on top of that.