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Monday
May222017

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 diameter section at the bottom end.

The fork blade is bent cold 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. This acted as a collar to hold it in place. Then I'd 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

On a Recherché

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.

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?

 

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Reader Comments (10)

I have bikes with both curved and straight steel forks. As far as shock absorption goes, they're pretty much the same. The other thing is that straight forks are built without a fork crown but with fork blades brazed/welded directly to the steerer tube. This is probably a cost saving measure but also, the holes on the crown to take the blades would have to be angled forward, which they're not normally.

May 23, 2017 | Unregistered CommenterYoav

In my opinion the straight forks, along with sloped top tubes, are the ugliest features of modern bikes.

May 23, 2017 | Unregistered CommenterJohn B

Shown above is a mid size John Howard frame (56) a large Fuso (62) and a small Recherche. (51) Each has the handlebar stem set at roughly the same height above the headset. The stem length, and the amount of seat post showing is proportionate to the frame size. There is a balanced overall look to each of these bikes.

These bikes were built in 18 different sizes, one centimeter increments. It is difficult to achieve a balanced look for all size bikes with today's limited range of frame sizes.

Back in the day of level top tubes, "Handlebar drop" never entered the equation because if you had the correct size frame it was automatic.

Dave .

May 23, 2017 | Registered CommenterDave Moulton

The shortest distance between two points is a straight line. While this may be true in most geometrical situations, it is not always aesthetically pleasing. Enter the straight fork.

Curved fork blades are considered by most to be Old Fashioned. This has nothing to do with function, but only form. Same with sloping top tubes. Sure, any of these designs can be Functional, and possess Form, but it convinces no one they are also beautiful.

Form is merely the shape something takes. It can go along with function, but not always. So when someone sees a curved fork, being rare today, or even a level top tube, they ‘form’ an opinion. That opinion can take the ‘shape’ of derision or mocking, or maybe, rarely, recalling days of yore, when traditions held meaning, and it took years to become a good rider.

And maybe that is the most important function a curved fork can have: To evoke fond memories to those that have them. Ironically, it has nothing to do with function.

May 23, 2017 | Unregistered CommenterSteve

I am with you John, The straight unicrown forks are butt ugly.
I am not fully opposed to sloping top tubes, but the enormous head tubes being used these days are a looks killer. If you are doing all trail work maybe an oversized headset is helpful, but not on a road bike.

May 23, 2017 | Unregistered Commenteredstainless

In my experience with 90s mountain bikes curved forks are more comfortable than straight forks.

May 23, 2017 | Unregistered CommenterRich

Didn't some builders use fork blades for chainstays?

May 24, 2017 | Unregistered CommenterSteve

I find flaws with conclusions comparing curved forks to straight forks. And this view also supports the beauty of the bike. Call it Relativity.

If I have one bike with a straight fork, one with a curved fork, what is my reference point? Say it’s the saddle I sit on. One is a Brooks B17 and the other a padded WTB. I will be gripping the bars, one carbon the other aluminum, one round section the other Ergo-shaped, one covered with thick Lizard Skin the other Benotto Plastic. My feet will also give me feedback, one crankset AL the other Carbon, pedals are Crank Brothers the other platform SPD’s. All give different feedback, therefore how the bike feels.
Wheels play more of a part in how a bike feels and handles, and the spokes and pattern used, the rim material and width and depth, the width of my tires, sewup vs clincher vs tubeless, tire pressure, tread pattern and even hub flange height will all contribute to how it rolls over rough and smooth terrain.

Oh, let’s throw in the rider; one a muscular GP champion, the other a skinny US Cycling Masters racer. Both have unique perspectives on same bike. Thus the dilemma for accurate data. The data will be as varied as saddle height is among pros. There can be no established reference point, and that mimics life. And forget about measuring instruments, they don’t work in cycling.

Support for this thinking: Alexi Grewal in the 1984 Olympic Road Race. He road his “whippy” Pinarello, refusing the custom “Murrays” supplied to the rest of the road team. It all came down to a climber out-sprinting Bauer on a bike that wasn’t a sprinting bike.
First time US medaled since 1912.

I guess we ride what we have, marketing be damned. And that is the heart of cycling.

May 24, 2017 | Unregistered CommenterSteve

I don't think the beauty of a fork can be considered without the rest of the picture.

Modern straight forks can look great when they have deep blades and extend down below a wide headtube, and are paired with an aluminum or carbon frame.
The front edge of the fork doesn't need to be angled forward very much in order to achieve moderate offset, so only the back edge of the blades departs obviously from the headtube as it heads forward toward the dropout, which looks fine and complements the frame's non-square angles. It still looks basically like the fork is coming down from the headtube, and it fits well with the other oversized tubes on the frame.

Modern steel bikes with straight fork blades have a problem. The fork blades need to be narrow in order to look correct as they flow down from a narrow headtube. But if straight blades are narrow, then even the front edge of the fork blades needs to angle obviously forward from the headtube angle in order to create the desired offset. (Or the forks could be offset from the steering axis at the crown, which would also create a visual disconnect with the headtube).

I think the mostly-straight-ish fork on my 2016 Emonda ALR looks great, and the curved vintage steel fork on my 1983 Miyata 710 looks great. If you swapped them, though, they'd both look ridiculous and terrible.

May 25, 2017 | Unregistered CommenterHTupolev

I still find the curved fork to be the most aesthetically pleasing.......... In the world of curved forks that which is essentially a constant radius pleases my eye the most. That typically combined with flat crown, to a lesser extent slight sloping crown. Unicrown............, in a word, yuck! The whole bend thing has changed a bit over decades but as long as the right amount of trail is achieved we're good to go.....................

ps: Did I say that lugged steel of classic geometry is the only way to go....., Campagnolo included? I don't think I did. Well, it is. Still. Always.

June 2, 2017 | Unregistered CommenterJohn

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