My bicycle

My Bicycle

by Rainer Pivit

This is my story of a very unusual bicycle and its designers - a bicycle whose handling is still better than other on the market over 10 years after the first ideas and design. I'd like to tell this story, so that others may share these ideas and perhaps keep alive my vision of a comfortable and practical commuter bicycle.

OLF In 1985 we (the bicycle research group at the Oldenburg University) presented the OLF (Oldenburger Lightweight Vehicle), a recumbent tricycle, in a first version without fairing. Vehicles like the OLF were at that time thought of as an alternative form of transport somewhere between automobile and bicycle. Testing told us that the OLF was rather impractical for real traffic conditions. It could not keep pace with cars and we did not feel comfortable with the low position of the driver. We were however convinced of the benefits of using automobile chassis technology. The soft suspension represented enormous progress when compared with normal bikes or even recumbents of the time.

From experience with the OLF we faced two alternatives for for further development. Theses were the MOLF (motorized OLF) and the ZWOLF (two-wheeled [zweirädrige] OLF). The MOLF, with a supplemantary electric motor (of approximately 2 kW [2.7 hp] maximum power) for acceleration, hills, and a speed of up to 70 km/h [43 mph], was never designed in detail or even built. Bringing this ambitious project to realization was beyond the capacity of our small team. At the time, the MOLF idea was contemporary with the development of 'solarmobiles' {with solar cells at home on the garage}.

The ZWOLF, a recumbent bicycle with a suspension like a car, didn't excite the physics department - the university in Oldenburg was not training engineers. It became a private project for Martin Glup and myself. However after first sketches we both decided to abandon the idea of the ZWOLF as a recumbent bicycle. We wanted a bicycle that every cyclist could ride and control immediatelywithout training. So we choose the conventional seating position of a touring bicycle with excellent suspension and better potential for carrying luggage.

The brief we set ourselves resulted in the following design features:

Moulton 60's The 1960's Moulton bicycle served as an initial model with its small wheels and high pressure tires, suspension, broad carriers over the wheels, simple main tube frame with easy step-over, over-all ease of manufacture and associated low-price. Unfortunately the production of this really ingenious bicycle was stopped in 1974.

Moulton 80's The Moulton bicycle of the 80's (AM 7 etc.) with its space frame design was always a high priced product. My personal experiences with my own AM 7 were very divided. It was a great bicycle, but in many ways was still unsatisfactorily - the rear suspension was quite hard, the front suspension had poor friction damping, there were hard impacts at the end of suspension travel, it dived heavily when braking, it had nervous steering-characteristics and an unstable rear carrier. The 17" Moulton tires had too many punctures, were too slippery on wet roads, and were too sensitive on trails and grooves. And on tour it was impossible to get a replacement tire.

We knew that we wanted small wheels that would allow long suspension travel with relatively low carriers. But which tires? Previous experiences ruled out the Moulton tires. We wanted an ETRTO size, commonly available in bicycle shops all over the Western world. The 20"-BMX size seemed a likely choice but was there a high pressure tire? We found a high pressure slick by Avocet, already in use by solar mobiles. However our order with the German importer did not work out.

Coincidentally and in another context, we got in contact with Continental, a German tire manufacturer. We mentioned our problems in finding a small, high pressure tires for a recumbent bicycle. To our surprise Conti had a solution - a special tire in a 16" kid's-bikes size, made from low rolling resistance materials to run at high pressure and for use by the solar-mobiles in the Tour de Sol. Thus we came to our 47-305 tires [16 x 1¾"] around which we built our bicycle!

We sifted through the technical literature on automobile and motorcycle chassis design and decided on a simple rear-wheel swing arm and a leading-link arm for the front fork, similar to earlier designs used by BMW motorcycles. We wanted long suspension travel (12 cm [5"] and more), no brake dive and none of the stiction found with telescopic forks.

From the proposed weight distribution of the bicycle and the resonant frequency of the suspension we could calculate the spring rates for a whole range of loading situations (from a lightly woman without luggage to a heavy man with luggage).

In designing the OLF recumbent tricycle we had decided to use foamed polyurethane as the sole damping medium, as the center of gravity was very low. We were not too worried about wheel bounce on very bad road surfaces. For a bicycle however we needed more suspension damping. However we wanted to avoid friction damping as with the Moulton - we wanted passenger car comfort!

So we designed hydraulic shock absorbers based on passenger car criteria. We contacted Stabilus, a German manufacturer of small dampers, who advised us that a hydraulic damper working with such small loads as we had calculated can't be built. Thus we changed our design from a spring and damper working directly at the wheel to a unit mounted at the swing arm and working through the arm's leverage. We also designed a movable suspension mount to adjust for different loads. The front suspension had a small auxiliary fork, connecting the swing arm to the shock absorber mounted in front of the main fork. The result met all our criteria. Stabilus manufactured the hydraulic shock absorbers especially for our bicycle!

We combined our shock absorbers with springs made from Cellasto, a foamed PU material (manufactured by Elastogran). This material has very progressive spring characteristics which saved us adding bump stops to the suspension unit. Foamed PU works by compression of its air spaces like a pneumatic spring. The actual material absorption is quite low - only about 10% on our bicycle.

For the prototype's frame we chose square-section aluminum tubes. Most of the connections were glued and riveted, a technique that we already had used very successfully for building bicycle trailers. The process is quite simple and fast - ideal for prototypes. For aligning frames built this way a sturdy table is good enough. Unlike welding or brazing, nothing will twist or bend and afterwards, no arduous alignment is necessary. Designing was simply done with paper and pencil on a table. Bicycle parts were bought. Floating bushings (Permaglide made by INA) were obtained for the swing arm bearings. For simplificity a cartridge was shrunk into the bottom bracket - we disliked the usual threaded BSA bottom bracket, a standard inherited from the stone age of bicycle design.

Finally after many hours at milling cutter and turning lathe - and some small assistance by the workshop of the university when welding a few spots of the aluminum framework - the bicycle was finished and we could test ride it.

Our dream had become mobile. The suspension was superb - without any brake dive. Due to the high position of the rear swing arm mount there was no bounce with strong acceleration either. The suspension reacted with the drive train over rough surfaces, but we became accustomed to this light foot massage on cobblestone pavements. Only over long undulating surfaces and large spring strokes did this effect in the turning crank set feel a little strange. Although the fork also looked somewhat strange, riding the bicycle was really fantastic.

That is, up to a sudden collapse of the front fork (during a braking?). I suddenly found myself on the ground with a few abrasions and in some disarray. I spent the next few days of nice sunny weather in hospital. Unfortunately this accident happened before we had taken a photo of the finished bicycle. What had gone wrong? We had adequately calculated the strength of the frame, the fork head and the swing arms but we had overlooked the auxiliary fork. It was undersized and there was a serious production defect at the fork head.

Second prototype Well, from errors we learn. The frame was undamaged and some time later we built a new fork. This time the shock absorber was attached on one side directly between front swing arm and the fork making it mechanically stronger. Tests with other bicycles had shown that, despite the resulting asymmetrical weight distribution, steering should still be okay. During test rides the same good suspension characteristics were evident. The steering characteristics were very well controlled, but remained a little bit spongy.

Radical We weren't totally happy with this design. Some time later Marinus Meijers and Marten Gerritsen from Groningen tested our bicycle. They replaced the aluminum fork with a more rigid steel one. This led to improved steering characteristics, but a little bit of asymmetry remained in the handling. The two Dutchmen pursued the idea and through further development it became the Radical Cityflitzer, which today remains in limited production.

Half a year later Martin Glup and I however made a radical new start. We liked the leading-link front swing arm, but not the asymmetry in the fork system. The problem was an alternative location for the front shock absorber. We didn't want it in front of the head tube, with an auxiliary fork (as with the first prototype), because we wanted this space for luggage. Then we asked, why put the front suspension in the fork system at all? Why not the reverse - as with automobile design - integrating suspension into the frame system and then attaching the fork system to it. Motorcycles with Ackermann steering had already been built, but we found the limited steering angle unacceptable. We preferred to stay with a rigid front fork and to put suspension between this and the frame. Thus the rather revolutionary idea of the a leading-link front swing arm as part of the frame, combined with a rigid front fork was born.

How does one then connect the fork with the handlebars? We quickly arrived at the linkage design we later built into the second prototype. A hydraulic steering mechanism would have been more elegant, but keeping costs low and the mechanism reliable we decided against it. We looked at other systems for direct connection of the handlebar system to the front fork but found nothing simpler. Besides another advantage of the indirect linkage steering is that the position of the handlebar is independent of steering geometry and wheel base.

Third prototype For the first time we used a PC to work out the construction by CAD (AutoCAD). With the computer we could better and more exactly consider the movements of the swing arms and debate each millimeter. Finally the new bicycle was ready to ride. Reality was as convincing as the concept. The bike gave a solid and stable ride. The suspension was only slightly less effective than its predecessor due to the increased weight of non-suspended parts. The soft brake diving felt more pleasant than the completely balanced braking forces of the previous prototype.

Because of the steering linkage the rotational axis of the handle bars was flatter than normal. This proved awkward riding one-handed compared with normal bicycles. But otherwise a bull's eye!

After some months test riding I finally booked my long-planned trip to New Zealand. Martin and I decided to build a further two versions of the bicycle prior to my holiday - one for each of us. I wanted to ride mine for 3 months in New Zealand.

During the construction of the new model we improved the angle of the handlebar steering axis and relocated the rear swing arm bearing lower, resulting in more compact rear dropouts. We also installed conventional cantilever brakes and a U-brake rather than the hydraulic brakes which had not always proved convincing on the previous models. We both preferred non-round chain wheels so we designed a special BioPace chain wheel with 72 teeth. A true challenge for my CAD abilities! The university workshop had fun making this mechanical hardware, getting all the data in their CNC milling cutter from our diskette.

Fourth Proto in NZ My bicycle was ready a few days before takeoff. For a rear carrier we made a simple framework of smaller aluminum tubes clipped on to the central rear tube. On the rear carrier I could fit a large 80-litre backpack. In front I had a handlebar bag fixed to the frame for my photo equipment.

The bicycle proved excellent on tour. It was an eye-catcher and a good conversation opener with locals and other tourists. Under heavy loads the suspension characteristics were even better than unloaded. I could glide over speed-bumps quite fast and remain seated, while they turned into ski-jumps for small cars, shaking their passengers badly. Downhill I was faster than unsuspended mountain bikes because my bicycle was easier to handle on rough roads and always had better tire contact.

Once I forgot to fasten my luggage on the carrier, placing the backpack loosely on the rear carrier with my spare tire and food bag on top. I only noticed it at my next stop. Nothing happened - nothing slipped or was wobbly!

The 47 mm [1 ¾"] width of the tires worked well, particularly if I had to escape at full speed from a sheep truck into the grass beside the road. With every other bicycle I would have had serious problems, or at least would have had to get up out of my saddle. Again and again it proved astonishing how much more riding safety this bicycle offered with its soft, well dampened suspension and its broad high pressure tires.

Were there no problems? Well, a few little things. A screw of the rear carrier was lost during the flight. The search for a suitable metric screw in Auckland cost me almost a day. However the rear carrier held without it. And after a long stretch over heavy gravel with high pressures in the tires, a small part of the treads separated from the carcass. One of the screws in the steering linkage worked loose. I also had to readjust the rear cassette hub and had two flats due to glass or thorns. At journey's end the welded joint at the rear end of the front swing arm was a little bit torn. The whole aluminum framework was slightly corroded by the salty air of the west coast. The gear ratio (72 to 13 - 30 with 7 gears) proved a little bit too high, and I had to repeatedly push the bicycle up the hills.

A great advantage was that I did not have 5 or 6 luggage bags to manage as on an ordinary touring bicycle - only a large backpack (which I also could use for hiking), and the handlebar bag. This was much simpler and more pleasant when traveling by train, bus or airplane.

This trip around New Zealand was at the beginning of 1990. More recently I have had to repair the frame due to some fatigue cracks at the seat tube. Otherwise the bicycle has always been my faithful companion.

For Mountain bikers suspension bearings are frequently a topic for annoyance and maintenance work. The bearings of my bicycle - designed as specified by the producer of the bushings - have never been maintained, and even today there is no more play than when new.

Fourth prototype Today I have a lockable plastic box, firmly fastened, on the rear carrier. In this I have my rain clothes, some tools (extremely rarely used) and the battery for the lights. In front I attached (instead of the handle bar bag) a smaller plastic box to provide additional luggage space. In everyday commuting these boxes have performed extraordinarily well. They are very practical and large enough for daily tasks.

With the second bicycle of this design, which Martin Glup still rides today, there has been only a small problem with one of the shock absorbers caused by an assembly error. Otherwise it runs and runs and runs and runs.....

In the beginning we both had planned to develop the bicycle for large scale production. It seems likely that such production would not be able to utilize a glued and riveted frame. Would customers have the courage to ride such an unusual design? We haven't managed series production yet. There is still a very long way to go. We also wanted to build a successor that could be folded. For a long time we have not been able to find a convincing solution for this and so our commitment to the project has diminished.

Martin still rides his bicycle but has moved to a totally different industry. I have continued working professionally with bicycles and was for a few years at a bicycle manufacturer, the Fahrradmanufaktur in Bremen. Inspired by my bicycle there, a research and development project, named "city bicycle", was started. Based on my ideas for the suspension, a bicycle was developed with much more attention to aesthetics.

Design studies led to use of 20" wheels with suitable high pressure tires of medium width being developed by Schwalbe/Swallow and Vredestein. The frame construction was shaped like a star with a central area consisting of magnesium casting. This was inspired by a frame design from Bridgestone, in which the tubes were assembled by casting around them instead of using sockets and brazing.

The integrated carrier contained a luggage drawer for the usual odds including rain clothes. Several suitcases could be fixed by quick-locking mechanisms and a child seat was planned for the rear carrier too.

Prototype Fahrradmanufaktur Prototypes of the city bicycle called "ATAER city" were shown at the IFMA 1992 bicycle show. Subsequently however the "city bicycle" project ran down at Fahrradmanufaktur and the planned series production never started. Considerable development was still needed to put the prototypes shown at the fair into production.

After this I moved to a larger bicycle company. There I sometimes had opportunities to ride other bicycles with suspension, in particular mountain bikes. However a hard suspension, which is appropriate for a downhill bike, is not suitable for commuter riding on bad roads and cycle tracks. A really comfortable suspension is what is needed for ordinary bicycle life. After test riding these MTBs it was always a special pleasure to ride home on my own bicycle with its soft suspension. I still have not found a bicycle with ordinary riding position that is more comfortable than mine.

I subsequently left the bicycle industry and embarked on new vocational directions. I sometimes find I want to continue to work on my next bicycle. However I am now too spoiled by the high end 3D-CAD at my last workplace to go on working with pencil and paper. Also, the most terrific ideas for our bicycle always arose from the dialog between myself and Martin. At the moment, I don't have an appropriate partner or team to work with. But perhaps someone who's reading this text may like to continue this project with me or independently.

I would like to summarize the most important advantages of my bicycle:

More than 10 years have passed since this bicycle was first developed. What has the bicycle industry offered us as new one? MTBs with suspension, a lot of telescopic forks, unisex commuter bicycles with low step-through (well done - more of these), and some commuter bicycles with suspension and telescopic front forks. There has been some limited progress. But where can we see the use of real chassis engineering?

We need to abandon "trial and error " in favor of scientific engineering methods in chassis design. And why are the wheels still so gigantic? Smaller wheels are lighter, more stable and accelerate faster. Bicycles with small wheels offer more luggage possibilities and are more compact for storage. They have slightly higher rolling resistance but this is more than compensated by low rolling resistance tires and suspension.

Dear bicycle manufacturer, please - find a little more courage. You can build better and more comfortable bicycles. It is possible! Do you want your own unique profile, or do you want to continue to build commuter bicycles in the 21st century which, from a few meters away, look just like those from 100 years ago?

And you, dear bicycle salesmen - give some new ideas a chance. Support new bicycle concepts, ask for them from manufacturers and sell to your customers the dream of floating over bad roads. The dream of a comfortable and practical bicycle that they will want to use every day.

Everyone together - let's ride into the future on such marvelously comfortable and practical bicycles!


About the author:
Rainer Pivit is a physicist and operates in Bielefeld as a independent consultant, coach and trainer with the emphasis on project management and innovation processes.

Many thanks to Sam Powrie from Adelaide, Australia, who helped me with the translation.




Moulton 60's
Moulton bicycle of the 60's

Moulton 80's
Moulton bicycle of the 80's

Second prototype
Second prototype

Radical Cityflitzer
Radical Cityflitzer

Third prototype
Third prototype

Vierter Proto in Neuseeland
Fourth prototype in New Zealand

Fourth prototype
Fourth prototype as commuter bicycle

Proto der Fahrradmanufaktur
Prototype of the Fahrradmanufaktur

Copyright of the pictures:

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Rainer Pivit
Marktstr. 29a
D-33602 Bielefeld
Tel.: +49 521 201 80 81
Fax: +49 521 201 80 66

by Rainer Pivit, 03/2001