Designing and Building Tandems

The traditional bicycle frame is a simple but inherently strong in design and structure, it is made up of two triangles.

Admitted the front triangle is a triangle with one point cut off to form the head tube, but never-the-less, still strong. (Picture left.)

Now let’s imagine we separate the front and rear triangle and extend the frame to build a tandem to accommodate two riders. We have now weakened the structure considerably, as we now have two triangles and a parallelogram in the center, which would most likely collapse under the weight of the two riders. (Picture above.)

As a simple way to add reinforcement to my tandem frames I liked to add a tube through the center of the frame along a line from the center of the head tube to just above the rear drop out. (Picture above.)

Now we have a structure made up of six triangles. If you ignore the front fork for a moment and treat that as a separate structure. The main frame is like a bridge spanning two points from the head tube to the center or hub of the rear wheel.

This extra tube was made up of an inch and one eighth tube, (The same diameter as the seat and down tubes.) running from the head tube to the front seat tube. Another ran from the front to the rear seat tube, then two separate tubes would run from the rear seat tube to a point just above the rear dropout.

I did this so the right-hand side of these twin tubes would be clear of the chain and sprockets, but apart from that these tubes were added along a straight line from the head tube to the rear hub. Sometimes I would leave out these extra twin stays from the rear seat tube to the hub, but still placed the main center tubes along this same center line.

Paul Swinnerton (Front.) Trevor Gadd (Stoker.) on a track tandem I built, competed in the 1978 World Championships.

It depended on the size of the frame and the combined weight of the two riders. Also considered was the intended use of the tandem. At the bottom of the frame, I placed twin 1 1/8” tubes, side by side between the front and rear bottom brackets. I always felt this option was the lightest and most pleasing to look at, as well as being strong.

Twin bottom tubes

The diagonal center tube was under tension from the weight of the two riders, and by running along a line between the two points of support, it also meant if there was any tendency for the frame to twist, this tube would also have to twist. You can probably appreciate, a tube has a strong resistance to twisting, especially if the twisting forces are applied along its exact length.

However, having said this was the lighter, stronger, better-looking option. It was also the most labor-intensive option, and therefore the more costly option.

Going back to the second line drawing at the top of this page, getting to this initial stage of the frame without the added reinforcement, is relatively easy as many of the standard frame lugs can be used.

But, fitting this extra center tube called for some precise mitering, careful fitting, and fillet brazing, because lugs were not available. A perfectly adequate and practical option was to place smaller diameter lateral tubes, either one pair from the top head-lug to just above the rear dropout.

Or, two set of twin tubes. One from the top head-lug to the rear BB, and another pair from the front seat lug to just above the rear dropout. Again, which option was chosen, depended on the size of the frame and the weight of the riders. This option although heavier, took a lot less time, and therefore brought the cost down.

Twin extensions to the center tube were left off this frame to accommodate fenders (Mudguards.) This was possible becuse it is a smaller frame designed for light touring.

I would like to thank Enrique Asturias who has quite a stable of bikes I built in England, Paris Sport, and California. He owns the green tandem (Above.) built in the UK 1976. He asked why the different configurations and supplied the other pictures to illustrate the variations.

It all came down to cost and what the customer was prepared to pay. They were all adequate and the fact that so many are still around more than forty years since they were built, proves that.

Capillary Action

David R. Ball photo

Capillary Action is one of those laws of physics that most people know exists but don’t think about too much. It is the reason a paper towel or a sponge will soak up water. It is the reason a wick in an oil lamp draws the oil upwards, defying gravity, to the flame where it burns.

However, it is not just soft fibrous materials that have these properties, a clay flower pot or a clay brick will soak up moisture because it is porous. It occurs in any situation where there are tiny gaps or fissures between otherwise solid materials, any liquid will be naturally drawn through that gap.

When a framebuilder is brazing a lugged joint on a bicycle frame, it is capillary action that draws the liquid molten brass through the gap between the tube and the lug. If the tubes are mitered correctly, in other words the end of one tube is cut to precisely fit the curvature of the tube it butts up against, it too leaves another tiny gap between the two separate pieces of metal.

The molten brass will also be drawn between this gap to actually braze one tube to the other inside the lug. The final result is a strong joint, but one that spreads the stresses over an area.

When joining metal, in this case steel tubing, there is a need for the tubing and the finished joint to be of somewhat equal strength. If the joint is much stronger than the tube, the tube may fail adjacent to the joint. Conversely, if the joint is weaker than the tubes, the joint will fail.

The above picture is me brazing the main triangle of a frame together. In particular, I am brazing the head lugs. I am using an oxy-acetylene torch as my heat source. I used a fairy small but very hot flame, which allowed me to pin-point the heat where it was needed.

Metal when heated becomes red hot. A dark cherry red first. This is the temperature silver solder melts. I used brass for all brazing of the main joints so this melted at an orange red color. Temperature was controlled by constantly moving the torch on and off the part I was working on, and the color of the hot metal was my temperature guide.

In my right hand is the brazing torch, and a small hammer. I am not actually using the hammer, although at first glance it might appear that I am. It is just there in readiness should I need it. In my left hand is the brass filler rod. I am heating the top head lug and the top tube, and when it reaches the desired temperature, I feed in the brass.

As I feed in the brass, I watch for it to flow through the lug to appear on the head tube. You will notice the head tube extends beyond the head lugs by an inch or so. When the lug is full of brass, (I know it is because I saw the brass flow from one side to the other.) I flow out all the lug edges and any surplus brass is flowed out on the head tube where it extends beyond the lug.

This will later be cut off as scrap. Working in this fashion there is very little excess brass to clean up after. There is a similar situation at the seat lug where the seat tube is left sticking through the seat lug, to be cut off later. Again, excess brass is flowed out onto the scrap portion.

Brazing different thicknesses of steel together can create a problem. For example, the front and rear drop outs. These are of course much thicker than the tube it is slotted into, and if you come in with the flame at the point you need to braze, the tube will almost immediately glow red hot, whereas the drop out itself is still relatively cold.

The trick is to heat the dropout away from the tube, wait for it to turn red, then move towards the tube, which will quickly glow red to match the pre-heated drop out. When the first drop of brass melts and forms a bridge across the two separate parts, it magically becomes one piece of metal and all glows evenly at the desired orange-red color.

One cannot see how much brass is flowing inside the tube where the tang of the dropout reaches beyond the slot, unlike the lugged joint where the framebuilder can see the brass flow from one edge of a lug to the other. However, the builder gets a feel for how much filler rod is going into the joint to know whether it is full or not.

Finally, what is that little hammer for? Well, lugs usually come in standard angles of 73 degrees. But not every frame I built was those exact same angles. So when I assembled the frame and pulled the lugs to the desired angle it left a little gap on one side.

As soon as the lug was heated it relieved any stress, but there was still a little gap to contend with. A quick switch of hands, moving the brazing torch to my left hand, keeping the joint heated and a quick tap-tap with the little hammer in my right hand closed the gap in the lug. Then switching back to as I was, I continued brazing. No loss of heat or time while I searched for my little hammer.

A little refined blacksmithing if you like.

The Golden Age

There is a period in recent history known as the Golden Age of Cycling, during the late 1940s after WWII and into the 1950s. In countries like Italy, France, Belgium and Switzerland, professional cyclists were the super stars of their day.

It is the period that the Eroica event celibates, and tries to recapture. It was the era when I started cycling, and I remember what a joy it was to ride a bike in England back then. In the UK there was a lot less motorized traffic, and people were in less of a hurry.

We could always ride two abreast anywhere, and it was unlikely there was opposing traffic when a car needed to pass a couple of cyclists, or even a bunch of twenty or more.

There was no honking of car horns or screaming abuse, most people had grown up riding a bike to school, or probably their first job was delivering groceries on a bike, so they could relate. There was coexistence on the roads.

It has occurred to me recently that this era was not just the Golden Age of Cycling, but it was the Golden Age, period.

For a few brief years there was peace and prosperity, the world economy was booming as everyone rebuilt after the war. There were plenty of hard manual labor jobs available, where a person could work physically hard. Jobs for people of all levels of education.

Over the years life has become easier and easier, but easy does not necessarily go hand in hand with the quality of life.

Have we reached a point where our quality of life is now at a standstill or even in reverse?

At one point in ancient history people had to chase animals with a stick in order to eat and survive, life was extremely hard and there was much suffering.

The problem as I see it is that it took tens of thousands, if not millions of years to get from killing animals with a stick, to tying a rock on the end of the stick to make a simple tool.

Now in just the last two or three hundred years, technology has exploded and continues to develop at an ever increasing and alarming rate of speed.

Meanwhile our DNA, our bodies have not caught up with technology. We are still programmed to chase animals with a stick. We no longer have to work physically hard in order to eat, the result is we exercise too little, and eat too much.

Our children are unable to follow their basic instinct, and are constantly told, "Don't run." Watch any baby animal at play and it involves chasing each other, training for later life when they are either chasing or running away from other animals.

When I was a child our games too consisted of chasing each other, I remember I pretty much ran everywhere, two miles to school and back. Running was effortless, it seemed my feet hardly touched the ground. 

I loved to climb trees, sitting at the top of an eighty foot tree, looking out over the canopy of a wooded area, is an experience I will never forget. Squirrels and birds would come and sit close to me. I cannot remember the last time I witnessed a kid in a tree.

It is a shame children and young adults cannot experience adventure. When I was fourteen I went touring on my bike with a school friend. We rode all over England, we slept in a tent, or stayed at Youth Hostels for very little money.

Maybe the reason video games are so popular is because it satisfies a need for adventure, along with a primitive instinct to chase something.

The problem is only virtual adventure, all in the mind and there is no physical effort associated with it. Real adventure prepares one for the real world. It involves physical activity, and interaction with real people.

One answer for a young person would be to take a job like construction work that is hard physical labor or take up a sport so the exercise and training has an end purpose.

The problem is some are so stressed working to maintain a “comfortable” life style, they just want to relax after a hard day at the office, and lead a sedentary life.

If we are honest, we don’t work hard anymore, not physically hard that is. Our minds work hard, multitasking, trying to cram a million things into our day. We rush here, rush there. We end each day mentally exhausted, rather than physically exhausted.

Physical exhaustion means sleeping soundly at the end of the day, whereas mental exhaustion means stress and the likelihood of being unable to sleep.

Governments are not going to change things for us, it is up to each individual to decide on his/her own lifestyle. “Less is more” is a worn-out cliché I know, but learning to live simply on less, rather than trying to make more, is worth considering.

Question: What are you doing to make your life better? Not necessarily more prosperous, or easier, but a better quality of life

Remembering Paul Carbutt

Paul Carbutt 1976

Much has been written about Paul Carbutt since his untimely passing on May 1st. 2004 at the relatively young age of 53. He is often remembered most for his record-breaking ride from Land’s End to John ‘O Groats 1979, although his career achievements were many and varied. However, I have never shared my personal memories of Paul.

As an amateur he represented Great Britain in the 1976 Olympics. He rode a bike I had built for him, which helped me gain recognition as a framebuilder. I built him one frame in 1975, which he rode in the Tour of Britain. (Milk Race.) I built another in 1976, which he again he rode the Milk Race, and the Olympics as part of the Team Time Trial event.

That frame pictured above, as I remember was painted a metallic gunmetal grey, with bright yellow panels where the decals were placed. There were strict rules back in the 1970s, regarding amateur status. I could not advertise the fact that Paul was riding one of my bikes, but by displaying the name prominently on both the seat and down tubes, increased the chance of the name showing up in press photos.

Paul Carbutt number 2, in the 1975 Tour of Britain

I remember asking him what size frame he rode. “I don’t know, you tell me.” Was his answer. Again, going by memory, I built him a 21 inch frame. (53 cm.) Another story I heard after the Olympics, Paul arrived in Montreal, Canada, with one green brake cable housing, and the other blue. It was all he had at the time, and it didn’t matter to him, the bike would go just as fast with odd color cable housing.

Of course, it drove the rest of the team crazy, and the cables were replaced before the event, but it showed Paul’s carefree attitude. The bike was necessary equipment needed to race. Function mattered, aesthetics, not so much.

Paul Carbutt in the 1975 Tour of Britain

A week or so after he returned home from the Olympics, Paul made a special trip to my shop to thank me in person for my support in supplying him with a frame. He brought with him several large black and white professional quality photos of him and the bikes I built, some of which I show here. He also brought an assortment of Olympic pins that he had collected from other Olympic athletes.

As I have mentioned Paul Carbutt and other top international class riders, seen riding my frames, resulted in a tremendous boost in sales. It should have been me thanking him. But this was his nature, and the way I remember him. Just a kind and loving person, who cared about the feelings of others.

I knew Paul Carbutt at least two or three years before I began my framebilding business. Riding in the same time-trial events in the West Midlands area of the UK. He probably didn’t know my name at the time, but would recognize and remember me, and always have a friendly word. He would often catch and pass me during the event, and again always have something sociable and pleasant to say.

I remember Paul Carbutt, I remember the other British riders. We entered into very casual agreements that were to our mutual benefit. The lesson I learned and pass on now, is this.

As you embark on a career, be it a profession, or as an athlete or artist. Be nice to everyone, whether they can help you or not. You may meet again, you may not. They may be able to help you, they may not. They will at least remember you and remember your name and will do so long after you have passed. Just as I remember Paul Carbutt.

The gift that keeps on giving

When I was building frames in Southern California in the 1980s, I could not foresee there would be a future with the Internet and social media.

Therefore, as I built frames and stamped a serial number on them, sent them off to the bicycle dealer, unless those frames came back for repair or a repaint, I never expected to see them, or hear about them again.

There was never a second thought that I might be corresponding people about these very same frames thirty or even forty years down the road. Who could even imagine what the future will hold that many years ahead?

When I stop and think about what has happened, I am both amazed and at the same time humbled that I find myself spending much of my time corresponding with people, either directly, or though this blog and social media.

My online presence started in 2003, ten years after I left the bike business. I had written a novel, Prodigal Child, and created a website to promote the book. People started to write to me asking, “Are you the Dave Moulton who used to build bikes?”

People started sending pictures of their bikes, and I opened a bicycle section on the book website to post these pictures. This bike section grew, and I found myself somewhat “Dragged” back into the bike thing.

Two years later in 2005 I began this “Bike Blog.” Three years on in 2008 I quit writing for reasons I outlined in this post, “The Party’s Over.” The post received 88 comments, probably my highest score ever. It was mostly an outpouring of kindness, and thanks for what I had written.

Quitting was a huge mistake. I lost a huge following, one that I will probably never see again. Six months later I was back when a group of bike enthusiasts, (Some of which I had never met.) got together and presented me with a “Tribute Bike.”

I was so touched that I had to at least write about it. Once more I was “Dragged” back, but this time with a new resolve never to quit again.

It is still difficult to come up with fresh and interesting stuff each week, but I look on it as exercise for my brain, which as I age, is just as important as physical exercise.

When I started out building bike frames, I was trying to build a better bike for myself. I achieved that goal, then set about building frames across the entire range of sizes, even though I could never test ride most of the larger sizes myself.

However, feedback from people who rode my bikes told me I was on the right track. I often went against what was fashionable and stuck with what I believed was right.

I remember turning down an order for 10 track frames in 1975. The order was from the Canadian Olympic Team. It was lucrative and would have carried a lot of prestige.

The problem was the team coach, sent drawings for each frame and insisted I build to the exact specs. I could have built the frames and took the money, but I would have hated it knowing that I could have built something better.

The same happened when I resumed building custom frames in California in 1982, some thought “Custom” meant building to their specs. I always said “No.” Had I built the frame, and they later sold it, it had my name on it, and it was my reputation at stake.

I went for consistency, every frame I built will ride, handle, go around corners, and feel stable on fast descents. People constantly tell me, “This is my favorite bike, my go to ride.”

And that for me is the gift that keeps on giving.