Fitting a Schlumpf Mountain Drive into a Milan Velomobile

The first part of this Blog post was also published in the following post: Six Wheels In Germany – October 2016 but I have added more information below.

When I test-rode Millie the Milan Velomobile she had the following gearing:
2 fach Ritzel vorne (2 chainrings front) 64/38
9 fach Ritzel hinten (9 sprockets rear) 13/14/15/16/18/21/25/27/30

This 64-tooth chainring at the front meant that she had lovely high top gears but her lowest gear was rather high to start off on a slope or indeed to climb a hill. Ludwig the seller seemed to have no problem with it but I was concerned for my knees. There was a second smaller chainring at the front but he said he used that only for emergency hill climbing.

Ludwig suggested that he changed the front chainrings for me to a 53 and 43 so that I had more lower gears that worked better for me overall. He said I would be able to pedal up to 50 km/h no problems. So we went ahead with the swap and then I took possession of Millie.

It became clear to me fairly quickly that my low cadence means that I can’t really pedal over 40km/h without wobbling all over the place. My legs just don’t go that fast, and after 100,000km in recumbent trikes and velomobiles in 9 years it isn’t likely to change. I am comfortable in high gears, cruising with medium power. My knees generally are OK with this plan.

I could of course have changed the front chainring for a larger one but then I would have the same problem with starting in low gears. I had already discovered that my weak arm made it extremely difficult to use the grip shift for the front chainring shifter; changing down to the small ring was OK but changing back up again almost impossible. Ludwig suggested I got someone to fit a trigger shifter or bar-end shifter (although that would mean my indicator button would have to move) but I wasn’t sure.

I had been thinking for a little while about a Schlumpf Mountain Drive and decided to do a bit of research on this.

From Wikipedia:

A Schlumpf Drive is a two-speed planetary gear assembly for use on bicycles. It is distinct from other bicycle planetary gear assemblies in that it is located behind the chainring rather than in the rear hub. A push-button on each side of the axle allows the rider to switch between high and low ratios. These are operated by the rider’s heel.

Schlumpf Drives are primarily used as an alternative to multiple chainrings. Four models are currently produced, with differing ratios from pedal revolutions to chainwheel revolutions.

Speed Drive, this allows a 65% increase in the final drive (ratio 1.65).
High Speed Drive, this allows a 150% increase in the final drive (ratio 2.5).
Mountain Drive, this allows a 60% reduction in the final drive (ratio 0.4).
Reha Drive, this also allows a 60% reduction in the final drive (ratio 0.4). However, it is specifically designed for hand-cranked disability vehicles and requires less pressure for shifting.

Schlumpf drives are currently used in some Pashley[3] and Moulton bicycles.

Schlumpf products were initially designed and manufactured in Switzerland. They are now manufactured in Germany by Haberstock Mobility.

It is effectively like switching chainrings at the front to a very small chainring but doesn’t need any cabling.

The Speed Drive and High Speed Drive have their normal mode in low gears and then you can click up to a higher gear but that is using the innards of the drive so a bit lossy. The Mountain Drive is the other way round, the ‘neutral’ gears with direct drive are the high gears but you can knock it down by 2.5x for lower gears if you need them. This sounded very suitable for me!

My local recumbent shop is Liegeradbau Schumacher in Willich. I had visited them several years before and found them to be knowledgeable and with a large amount of stock. I decided to give them a ring and find out if they fitted the Schlumpf – yes they did, so I said I would pop round the next day and have a chat.

I did pop round and we talked about it. It sounded like a great option – until I heard the price. These things are expensive! Especially as I would need shorter cranks (not much room in the nose of Millie) and the larger chainring. The price was just too high for me to justify for some emergency low gears.

We talked a bit more about anything else I might be able to do (new shifters for my existing gear) and then the chap talking to me had a bit of an idea and went to talk to a colleague. It turned out they had a second hand Mountain Drive in stock and they made me a price offer for that, the cranks and chainring and fitting, which was very good and I decided to take them up on it.

They ordered the chainring and pedals and a couple of weeks later we had an appointment for them to do the fitting, hopefully while I waited.

I arrived and met Mr Schumacher (senior) for the first time. We ended up having a lovely time chatting together – the trike world is small and the velomobile world smaller and we had several acquaintances in common. He’s been in the world of recumbents for 30 years so has a vast amount of experience. It was really interesting talking to him.

First of all they showed me my new chainring – a real pizza plate!

Apparently when it had arrived Mr Schumacher assumed it was for some super-fit young man, and was clearly a bit surprised to see a middle-aged overweight woman who needed it! But the velomobile’s speed makes all the difference.

Christian Schumacher, his son, would do the fitting and the first plan was to get Millie onto a fork lift so that he could work through the foot hole.

Mr Schumacher Senior and I held Millie steady whilst Christian removed the bottom bracket from the boom. Here it is coming out – and was surprisingly heavy. The Schlumpf Mountain Drive with pedals and chainring actually weighed less.

Millie was lowered back down to the floor whilst Christian fitted the mountain drive to the bottom bracket, which involved some work on the aluminium holder. You can see the bits of metalwork that hold the boom in place on the floor in front of Millie’s nose.

And the view inside – a boom leading to… nothing!

Now Christian spent some time removing the old pedals and bottom bracket and fitting the Schlumpf, which involves some metalwork I believe.

They let me see and test it when he had finished, turning the pedals with one finger and then pressing the button and seeing the speed change.

Christian cleaned up my pedals and fitted them to the cranks, then we were ready to fit the new part into Millie.

Here we all are working on Millie – Christian drew the short straw and had to lie on his back with 28kg of carbon fibre balancing inches from his nose!

And here it is fitted!

We removed the cabling for the front gear changer – another minor weight saving (20 grammes?) – which you could see in the photo above.

Then it was time for a short test ride…

Generally it was great, except my toe was now rubbing against the side of Millie. I had occasionally had this before when really pushing hard but it happened the whole time. It seems that the Mountain Drive pedal area (Q-factor) is wider than the previous chainrings arrangement (Theo at Velomobiel.nl had talked to me on the phone about Mountain Drives and said I needed to have the narrow one; I had asked Schumacher if that was what they had and they said yes, but I do slightly wonder now). Anyway, Christian came to the rescue again with a very simple solution – moving the cleats on my cycling shoes so my feet were more inward.

The second test ride and it was fine, only very occasional brushing of my shoe on Millie’s side, certainly to an acceptable level.

The fitting had taken three hours which was longer than expected but they had clearly done an excellent job and it was interesting to see everything in action. I rode home, very quickly getting used to the new drive and finding the gear changing buttons very simple to operate.

And after a week…

I am enjoying riding with the Mountain Drive.

I am definitely benefitting from the larger chainring. I find it more comfortable to ride at speed. I am able to pull away in first gear most of the time without problems, unless it’s on a slight uphill, at which point I use the Mountain Drive to step down from what is a 4.6 metre gear to a 1.5 metre (that means I travel 4.6 metres along the ground per pedal revolution). Also on some steeper hills I switch into Mountain Drive mode.

As was mentioned by many commentators, the Mountain Drive does give a spongy feel when using the stepped down gears. It is noticeable but as I am only riding in this gear arrangement for a short time it is no problem. Also because of the wide range in gearing it’s quite a big jump back into the higher gears but, again, because you know it’s coming you can adjust accordingly. I like the simplicity of the system and find it easy to do with my heels, even wearing cleats.

With regard to the cleat position, after Christian had adjusted one shoe I obviously had to adjust the other. I then thought about moving the cleats even further and tried that – and found I had unusual foot pain. I suppose after 100,000km with my cleats always on one position the ball of my foot didn’t like the change! So I moved the cleats back to a middle position where my foot only brushes the side of the velomobile when really pushing but the cleats are comfortable.

That spongy feeling…

The above was published on my blog in October and I note that two paragraphs previously I mentioned the gearing feeling a bit spongy – when you first push on the pedals there is a bit of give before you start making progress. I had read about this so expected it, but it seemed to be getting a bit worse over time, as if the rear wheel was slipping. Never mind.

Then in November I did a long ride to Xanten which involved the Mountain Range (small moraine) known as the Sonsbecker Schweiz and as I was trundling my way up there the Mountain Drive was slipping more and more. I had it in the lowest gear but my pedalling was very ineffective – it was as if the back wheel was slipping. Perhaps it was? So I did an experiment and put the parking brake on and tried to pedal. It worked – the pedals went round but the chain didn’t move. Uh oh, something is wrong with the Mountain Drive.

In the short term I had to get up the hill so I switched the Mountain Drive back to its ‘normal’ setting where it’s giving me the high gears and not doing any gearing gadgetry and it worked OK, except that climbing a hill in my lowest gear of the high gears is definitely not fun – it works out at 4.48 metres of travel per revolution. That’s lots! (In my highest gear I get 10.34 metres per pedal revolution, and in my lowest gear with the Mountain Drive active it is 1.79m and in the highest gear but with the Schlumpf 4.14m, so less than the lowest gear without the Schlumpf). In old money my lowest gear without Schlumpf is 56 gear inches, with Schlumpf is 22, highest gear is 129 gear inches and with Schlumpf is 52 gear inches.

In short, riding up a long hill from a stationary start with the lowest gear as 4.48 metres/56 gear inches causes knee pain so I had to be very careful and for the rest of the ride and struggled on a few smaller hills.

I contacted Liegeradbau Schumacher and also asked for some advice from people on the Velomobilforum and it became clear that it was a problem of the Tretlagergehäuse as it is called in German – the bottom bracket in English (I think). This is the tube through which the pedals go. It looks a little bit like this:

The Schlumpf has to be tightened so that a small metal ring with teeth bites into the metal and stops the whole thing rotating under the power of my legs pushing.

Unfortunately the Tretlagergehäuse in the Milan is thinner than that of normal bikes (weight saving I guess) and it was deforming when they tried to tighten it up to the suggested 160 Newtons so only managed 120 Newtons. It seems my ladylike thighs are able overpower this – and once it had started spinning within the tube it quickly stripped the teeth from this metal thingy.

Some people on the Velomobile Forum pointed out instantly my problem – I had the ‘wrong’ Mountain Drive. When using a Schlumpf with a Velomobile you need the version with a torque lever that prevents it from twisting.

The Schlumpf website explains:

Mountain-drive – installation with torque lever (anti-twisting bracket)

There is a very simple way to hold a mountain-drive against the reaction torque. The housing with integrated anti-twisting bracket doesn’t need any modification of the frame at all. The clamp is connected to the rear chainstay. That’s it! No chamfering, not even a high tightening torque is required.

I reported back to Schumacher and they said they were considering their options.

The next day they made their suggestion – that they ordered a new Tretlagergehäuse from the Netherlands to replace the one I have on Millie with a thicker one that can take the Schlumpf. So I agreed to this and they ordered it – from Gerrit Tempelman no less! [Edit – from the comments below I see that Allert Jacobs from Velomobiel.nl made the Tretlagergehäuse, not Tempelman, and it was a special one-off).

How to remove an old Schlumpf when it doesn’t want to be removed

What I had not considered, of course, is that the old Schlumpf would be a right pain to get out.

I had a call from Liegeradbau Schumacher after a couple of weeks (during which I had taken my hill-avoidance route planning to new heights of expertise) to say the new Tretlagergehäuse was ready and we scheduled a time for me to visit to have it changed.

So on a Thursday after work I rode to Liegeradbau. The route there isn’t very nice really, on a quite busy road so I rode on the cycle path – a mistake as I later discovered.

Anyway, as I arrived I was given a biscuit!

and was introduced to my new Tretlagergehäuse.

Very shiny and much, much thicker than the existing one. The tube through which the pedal bracket goes was at least 2.5mm thick instead of the 1.5mm (estimated) thickness of the current one.

Mr Schumacher Senior was still rather surprised I was strong enough to strip the teeth from the cone rings – it just goes to show what Frauenpower can achieve!

Millie was put up on the fork lift and Christian was able to remove the Tretlagergehäuse in just a few minutes.

We went into the workshop and they fixed it all to a bit of square pipe they had hanging around, then used the tool to remove the pedals and attempted to undo the lock ring on one side of the Mountain Drive so it can slide out of the bottom bracket.

Oh dear. The lock ring just spun round. Which of course made sense as that was the problem with the Schlumpf.

First of all they tried to clamp the aluminium of the Tretlagergehäuse with some band thing to do with a car. But that didn’t work.

Then Mr Schumacher said “Plan B” – which was a giant wrench with jaws to hold the Tretlagergehäuse in place so that the Schlumpf within didn’t rotate.

“What is plan C?” I asked. “Is it to kill the customer?” He laughed…

Anyway, plan B using the gripper/wrench thingie was also unsuccessful. They found larger jaws and extended the handles with bits of pipe to get better purchase but still no success, the Schlumpf continued to rotate within the tube as they tried to unscrew the lock ring.

Hmmmm.

The original plan was that I would be able to keep the old Tretlagergehäuse in case I ever put the old chainrings back on but it was now very marked by the teeth of the grippers. There were a few scratches on the Schlumpf chainring holder too.

I tentatively asked if we were now onto Plan C, kill the customer, but Mr Schumacher said it was Plan B part 2 – to cut away at a bit of the Tretlagergehäuse to hopefully allow the Schlumpf to be gripped more strongly.

Christian got out his circular saw and ear defenders and we retreated to a safe distance.

Stage 1 was cutting a ring around the Tretlagergehäuse.

A bit more cutting was needed…

Then he was able to remove some pieces of the aluminium. Here is the view from both sides.

However, this did not solve the problem. The pesky lock ring (next to where they have cut away the metal) still could not be loosened, the entire item inside rotated.

The Tretlagergehäuse was clearly ruined so I suggested Plan B part 3 (in preference to Plan C), cutting away the entire Tretlagergehäuse. This was clearly the only option. So Christian got his circular saw out again.

First section… You can see the marks of the toothed grippers on the part of the Gehäuse that butts against the black disc of the Schlumpf where the chainring is fitted.

And from the other side. You can see how thin the aluminium is – about 1.5mm we thought.

And finally – Schlumpf is removed!!!

Success!!!

The cone ring from within was interesting – its teeth had be worn away so it was almost smooth. It was clear why it was not able to withstand the torque from my pedalling.

Here is the old Gehäuse next to the new one.

Fitting the Schlumpf to the new Tretlagergehäuse was the work of 5 minutes, and they managed to tighten it to more than 160 Newtons – this one would not be rotating!

Christian fitted it back into Millie fairly quickly and we were ready for a test ride. Except I had a quick look at her tail – flat rear tyre! Fortunately it was in a warm place with an air compressor to pump up the tyre so the rear wheel extraction and tyre change didn’t take long at all (I am getting better at it!) The old tyre had some very bad sidewall damage so was retired there and then. I have since fitted a Schwalbe Marathon on the back – it’s wider and slower but at least has some puncture protection. That’s two rear punctures I’ve had in 2000km, fortunately both times under cover with suitable tools and track pumps. I wouldn’t like to have to change a rear tyre in the dark, rain and cold.

After the new tyre was fitted I did a short test ride and thought initially that it was still not right, but it turns out this is just the normal sponginess of the Schlumpf, plus a lot of slack in the chainline getting taken up when I put a lot of torque through.

I rode off home again with the old Tretlagergehäuse as a bit of modern art, periodically testing the Schlumpf and all seemed well. I have since ridden 300km with it including a significant hill and all is working well. I do notice the sponginess when using the Mountain Drive gearing, but when in the higher gears it is as if nothing was there. The gear change is easy with my heel and it’s great to have this emergency step-down gear.

I am also very happy with Liegeradbau Schumacher’s help with this. It is unfortunate that it was the wrong type of Mountain Drive but none of us knew that and the problem was solved. It took a lot of time for Schumacher (probably they worked on Millie for 6 hours in total) but they were always friendly and helpful. They said I should pop in whenever I’m passing, but preferably not if Millie has a problem…

Riding with the Schlumpf

For Velomobiles I think the Schlumpf Mountain Drive is an excellent option. It allows the rider to have a large chainring which is useful for the high speeds a Velomobile can attain. It’s lightweight and doesn’t add much drag at all to the pedalling (someone said 1-2 watts). No cabling is a bonus as working in the nose of the Velomobile is no fun at all. Being able to change gear when stationery is really useful, and having such a wide range of gears is extremely helpful.

A couple of other friends with Velomobiles are considering the Mountain Drive. I think more would take it up if it wasn’t such an expensive option (it costs at least 600 Euros, with new chainrings and pedals and fitting this amount can get close to 1000 Euros very quickly), but I think for me and my special requirements it was worth it (although I paid about half of that amount because it was second hand). It’s something I can recommend, with the few disadvantages in mind (hard to fit yourself without the right tools, wider than the normal pedals it replaced which means my feet are closer to the sides of the Velomobile, has to have oil injected in once per year which will involve grovelling on the floor under the Velomobile, and the mega faff if like me you fit the wrong one) but these are small in comparison to the advantage of convenient gearing without cables.