In search of the perfect fork blade

When a fork blade comes from the tube manufacturer’s factory, it is straight; the framebuilder bends it to a curve that suits his requirements.

An un-raked road fork blade is oval at the top; the oval section runs parallel for about a third of its length. Then the cross section becomes round and starts to taper gradually to its smallest section at the bottom end.

The fork blade is bent on a curved form that is sometimes made from hard wood. I used one I made myself from two heavy-duty steel fork blades, bent in the desired curve, and brazed together side by side. This made a natural grove between the two blades where the blade would sit as I was bending.

I would slip a short piece of tube over the thin end of the form and the blade I was bending to hold it in place. Then start bending, first by pushing down by hand. The thin end of the blade bends easily, and I would finish off by squeezing it in a vise.

Bicycle tubing is hardened, and it will spring back after bending. Because of this, the form needs to be a greater curve than the finished fork blade will be.

A fork blade is several inches longer than it needs to be. The framebuilder chooses where he will put the bend, and where he will cut to length. For example, if I were making a criterium frame and wanted a very stiff fork, I would cut from the bottom, thin end.

If I were building a touring frame, and wanted a flexible fork for a more comfortable ride, I would cut from the top end and leave the blade thin at the bottom end. The framebuilder creates the perfect fork blade, by selecting the best place to bend the blade, and by choosing how much to cut from either end.

It is rather like a furniture maker choosing where to cut from a piece of wood to achieve the best end product. Once I arrived at the perfect fork blade, it was then an easy matter to repeat the process again and again.

On a John Howard

On a Fuso

And on a Recherche

One exception to this process was the Reynolds 753 fork blades. 753 was heat treated to a degree that the material could not be bent after. These were bent at the factory, then heat treated, and the framebuilder then cut to the required length. You will notice on the 753 Fuso Lux frame (Pictured below.) that the fork bend is a different shape than the ones bent by me. More pictures of this bike can be seen here.

Chainstays and seatstays are also tapered and the same selective cutting to length is employed. In this case, where the cut is made depends a great deal on the size of frame and its end use.

The perfect fork blade is stiff enough to allow precise handling, but with some flex to absorb road shocks. It also looks pleasing to the eye. I have a theory that when something is designed correctly from a functional standpoint, it has a natural aesthetic beauty. This is true of a boat, a bridge, a building, and even a bicycle frame.

The modern trend of building straight forks of course saves the framebuilder a great deal of time and effort. If this look has become acceptable, why should today’s builder go through all the time consuming process I have described here?

The straight blade is angled forward so the same fork rake or offset is achieved and handling would be the same. I can’t comment on the shock absorption qualities because I have never built a frame with a straight fork.

In my view, a great deal is lost aesthetically, so where does that leave my theory about function being linked to aesthetics? On the other hand, is it simply that beauty is in the eye of the beholder?

Down in the Bicycle Forest, something stirred

It can’t be the last day of November; did someone break into my house and steal some days from my calendar?

It used to be there were not enough hours in the day, now this has escalated to not enough days month, or worse not enough months in the year.

Meanwhile there are others in this world who seem to have too much time on their hands; like the people over at The Bicycle Forest. Otherwise, how would they come up with such brilliant concepts like the Treadmill Bike? (Left.)

Now they have this really cool (Or is kewel.) Bike Cad program so you can design your own bike.

And it’s free. Personally, I do not need free stuff to steal more of my time; what I need is more free time, period.

Therefore, I pass it on and let you play with it, as you obviously have more time than I do, otherwise you wouldn’t be reading this blog when you should be working. (If you are not at work, there must be something useful you could be doing.)

Moreover, my design program in my head still works, and mine works at any time so I can multi-task while riding my bike, driving, listening to my wife, etc.

One of the things you can do with Bike Cad is explore “toe overlap.” Judging by the number of times the subject gets Googled, and people arrive here, some are convinced that it is: (a) a design flaw, (b) something bike manufacturers do to save money, or (c) something bike manufacturers do just so people can fall down, then sue their ass.

Some also think this is something new; however, it has been around since the 1970s. Ever since, we stopped building bikes with those horrendous 2 ½ or 3 inches of fork rake. The cure is to go back to those long curved forks, and bikes that handle like a fucking wheelbarrow.

Now, thanks to Bike Cad, no one has to take my word for it. They can find out for themselves that toe overlap is unavoidable on smaller size frames. If you happen to find a cure for this non-problem, don’t send it to me, send it to Richard Sachs as I’m sure he would appreciate it.

Seriously, Bike Cad does seem to be something useful that will bring hours of fun. As for me, I have too much fun already, and not enough hours.

Is it time to re-think the derailleur?

One area of the bicycle that seems to be overlooked when it comes to equipment performance is friction; especially in chain drives and derailleur gears.

From an engineering standpoint the derailleur gear is an inefficient system. However, since its invention in France in the 1920s, no one has come up with anything better.

The system of a chain drive running out of alignment on multiple sprockets is not used on any other application except a bicycle as far as I know.

When the chain is not pulling in a straight line, there is extra fiction on the side plates and the bearing pins of the chain. There is also friction on the sides of the teeth on the chainwheel and rear sprocket.

When a chain is in alignment there is only slight friction on the bearing pins as the chain goes around the top portion of the rear sprocket and chainwheel. There is little or no friction on the side plates of the chain.

One thing a person notices the first time they ride a single speed fixed gear bike, is the smoothness of the transmission and the lack of friction. This is because the chain is in alignment, and there are no pulleys the chain has to run around.

The pulleys on the rear derailleur are the other source of friction; there is the friction of the pulleys themselves, and the chain has to go around a constant "S" curve. Turning the links of the chain, first in one direction, the other.

One derailleur popular in the 1930s and 1940s was the Osgear. (Left.) It had chain tensioning arm with a single pulley just under and slightly behind the chainwheel.

This meant the chain ran in the same direction and was not made to go around an "S" curve; there was also one pulley instead of two. At that time freewheels only came in 3 and 4 speed.

The Osgear had its shortcomings; it would not work with a double chainwheel because the tension arm was fixed. However, had it pivoted on a simple ball joint and had sideways movement, it would have aligned itself as the chain switched from one ring to the next.

The other drawback was, the fork that shifted the chain on the rear sprockets was over simplistic and shifting was not that good. Had it been designed like a modern front derailleur it probably would have worked much better.

A modern front derailleur is very efficient in that it will shift the chain over a ten teeth span or more, and once it has shifted the chain it is no longer in contact with the shifter and so causes no friction.

The Osgear had fell out of favor by the 1950s when the French made Simplex and Huret derailleurs appeared; they shifted better, and worked with 5 speed freewheels and double chainwheels. The Simplex and Huret rear derailleur had the chain wrapped around two pulleys in the "S" fashion; the way all modern rear derailleurs are designed today. I do feel the Osgear was a very efficient design that was never fully developed.

Campagnolo’s Cambio Corsa derailleur (Below.) patented in the 1930s but developed in the 1940 was a masterpiece of engineering for its time, but extremely difficult to use. A long lever released the quick-release, the wheel moved forward on a rack built into the frame’s rear dropout thereby loosening the chain. Another lever shifted gear while back-pedaling. At the same time, the wheel moved back tightening the chain, and the quick-release was re-tightened. There were no pulleys to tension the chain, so no friction.


Was the Cambio Corsa developed to its full potential? Has anyone ever experimented with sprockets that slide sideways on the rear hub so the chain is always in alignment? It would not be necessary for the hub to be wider, or the rear wheel dished more; the hub could be large enough for the sprockets to slide inside. Another idea, fixed rear sprockets, and a chainwheel that freewheels, gears could be shifted while coasting.

If the chain is to remain out of alignment, how about a chain with spherical rollers at each joint so it will run out of alignment without the friction of the side plates. I know all these ideas will cost more, but with the price of the top of the line bike what it is today, what is a couple of hundred dollars more for a drive train with less friction that will allow a rider to go faster.

The derailleur gear has remained basically the same for over fifty years; all improvements have been in shifting and the number of gears. Friction is overlooked because you can’t see it; and if everyone is using the same design equipment it is not an issue.

In some of my recent posts I have waxed nostalgic and longed for simpler times. I am not against change if it benefits the bicycle and the cyclist. Many changes I see benefit the manufacturer, and then sold to the consumer after the fact.

I am just throwing out a few off the wall ideas that may or may not be practical, but would it hurt one of the manufacturers to put a little money into some research and development to find out just how much of the rider’s energy is wasted overcoming friction?

Lugs

A bike store owner told me recently told me of a young customer in his store looking at a 1980s vintage steel bike that was in for a service. He pointed to the lugs and asked the store owner, “What are these for?”

I find it amazing that a method of building bicycles can be around for over a 100 years, and become lost to a new generation in ten years or so.

Since the bicycle’s invention in the late 1800s the traditional way to join steel tubes to make a bicycle frame was by melting brass into a lugged joint. Similar in a way to a plumber joining copper pipe by sliding the pipe into a pipefitting, heating, and filling the joint with solder.

Brazing, as it is known, done at a higher temperature and the resulting joint is much stronger. Early lugs were in fact pipefittings; these were heavy steel sand castings, cut square at the edges, and machined on the inside to fit the tube.

As steel tubing for bicycles became thinner and lighter, it was found the tube would sometimes break at the edge of the lug. This was because the lug was far stronger than the tube.

In any structure, if you make a joint far stronger than the parent material, the material will fail during stress, immediately adjacent to the joint. Framebuilders started filing the lugs thinner to bring the strength closer to that of the tube. For the same reason, they also started cutting the lugs into fancy shapes to eliminate the square edge of the lug.


By the 1950s the cutting and filing of lugs became the way a framebuilder would express his art and individuality. Hetchins (Left.) were one of the first to take this art to extremes.

By the 1960s and 1970s, fancy lugwork became too costly and lugs stamped from sheet steel and welded, became available. The top picture is a set of pressed steel lugs that I prepared during the 1970s, with some custom shaping a cutout work.

By the 1980s “Investment” cast lugs became available. A method developed for the aircraft industry, investment casting was achieved by first hand making a lug. From this “pattern” lug a simple plaster mould was made.

A lug made of wax was cast in the plaster mold; this in turn was coated in a ceramic material and fired in an oven. The firing hardened the ceramic coating and at the same time melted the wax from inside, leaving a void the perfect shape of a lug.

Molten steel was poured into the mold, and when cooled the ceramic mold had to be broken to remove the finished lug, hence the name, “Investment” casting. An expensive process, but the finished lug was near perfect, the tubes fit with no machining required; very little filing required from the framebuilder. Lugs, bottom bracket shells, and fork crowns are made this way.

Traditionally frames were never welded. Not because welding was not strong enough but rather the heat required to weld weakened the parent material adjacent to the weld. By the 1980s welding technology had advanced to where it could have been used to build lightweight frames. However, at the time customers, connoisseurs of the lugged frame would not accept it.

This changed during the “death” of the road bike in the early 1990s. Mountain bike manufactures could get away with the quicker and cheaper welding process, because the MTB was new and there were not the old standards, and traditions to break down. There was a whole new generation who grew up with welded BMX bikes.

When the road bike was reborn, sadly, for some of us it was an ugly bastard. Its gene pool contaminated by MTB and BMX, the beauty, style and class bred out of it. A well, that is I suppose the price we pay for progress.

Stayers

[Picture from Cycling News.]

My last article on Fork Rake and Trail brought an email with the question:

“Why does bike designed for Motor Pace Racing have the fork raked backwards. Is it to increase trail?”

The Stayer bike as it is called, has a smaller front wheel, a steeper head angle, and reverse fork; all designed to get the rider closer to the motorcycle that is pacing him. There is a roller mounted behind the pace machine, set at a regulation distance. It is up to the rider to get as close to that roller as he can for maximum drafting effect.



If you look at the drawing on the left, you can visualize that a smaller wheel means less trail, a steeper head angle also means less trail, but the reverse fork increases trail to compensate. A stayer bike may have a little more trail than the average track bike, but not an excessive amount.

Another reason to have the fork reversed is that occasionally the rider will bump the roller on the back of the motorcycle. If he does the roller will spin and the fork will flex easier in the direction it is raked or bent, thus absorbing these slight bumps.