Aero Time Trial Fork

Before I post about the 400k brevet I did this past weekend, I better do one  about some of the work I have been doing around the workshop.

This last project was quite interesting, and it really pushed my design skills, craftsmanship, and ability to meet very tight deadlines to a whole new level.

I was approached by Russ “Big Daddy” Walker, a top level racer from Shreveport, LA, to build a very aerodynamic time trial fork to replace the carbon fiber one that the frame came with. He needed the bike for the TT section of the Cotton Patch Stage Race held in Greenville, TX. There was only a week’s time to get the project designed and built.

It may sound odd to replace a carbon fork with a steel one on a carbon time trial frame, but Russ wanted to put a 24-inch kevlar disc wheel in the front, and aero-race forks are not readily available for 24-inch wheels.

Russ "Big Daddy" Walker

The fork was going to be used for strictly for time trialing, so aerodynamics were the most important design consideration.  This immediately ruled out the use of regular bike tubing, and with that any bike fittings like the fork crown and drop outs.

The aerodynamics would also benefit from keeping the clearances between the frame, fork, and wheel to a minimal. Due to the small wheel, and its affect on the geometry a lot of computer modeling was necessary before any building began. I worked back and forth between BikeCAD and regular CAD, and at one point even had 3 computers set up side by side in the Gallus HQ.

I would  rather not focus on the design aspects of the project, because it might put most of you to sleep. I would prefer to show y’all what it involves to build a fork from scratch, when the only part pre-designated as “bike tubing” is the steer tube.

Fork Materials

As mentioned above, the use of the aero blades, which are aircraft grade streamline tubing, required me to make the fork crown and dropouts from scratch. There are probably several different ways to go about a project like this. The eventual process, choice of materials, fabrication  and final product was my resolution to the design constraints.

Cutting drop outs out of plate

After knocking out the design I started off by cutting out the drop outs from a length of steel plate. To get the right thickness, I doubled the plate and brazed them together.

Brazing Drop outs together

I did get some help on this project to  get all the various pieces made in time.  Below is a picture of my friend Lauren grinding out some plugs that fit into the top of the fork blades. You will see exactly what the plugs are for a little further down.

L.T. grind'n

After the drop outs and the crown plugs were cut, the twin plate crown was started. First step was to bore the hole  in each plate for the steer tube to pass through.

I rarely employ the use of any machines to craft my frames. It’s typically just as efficient, and accurate, for small scale production to do things by hand. That, and I don’t have machines of my own. However, in the case of boring the holes for the steer tube to pass through crown plates the best method was using a mill. For the mill work I went to the workshop of Chris Watson, co-owner of locally based cycling accessory house Arundel. Chris is a very talented individual with a deep knowledge of bicycle construction, the “industry”, as well as being very mechanically inclined. His last project was rebuilding a Mini Cooper engine,  then the whole car, and not an old retro one but a new Mini. Honestly, who does things like that anymore? I thought everything these days were disposable.

Chris also helped out with tacking the crown plugs to the crown with his TIG set up. The sides of the lower crown were filed by hand to meet the edge of the fork blades.

Tacking the crown plugs

After the plugs were tacked on, it was time to braze the two fork plates to the steer tube.

Getting Fork Crown Ready for Brazing

BRAZE IT UP!

Once the steer tube and crown assembly was complete I started getting the blades together. First I brazed in the drop outs, carved out the final shape of the drop outs, and cut down the blades to the correct length.

Proprietary drop outs

Unfortunately I stopped taking pictures at this point. I was probably in some kind of frame builders  zen-like trance. Just to give y’all a little indication of the final assembly process, I first fit little rings of silver brazing rod into the fork blades. I then slipped the blades over the crown plugs, and then snug against the top crown plate. I then placed everything in my trusty Anvil fork fixture.

Once everything was nice and lined up I tacked the lower crown plate to hold everything in place. I then “sweated” the blades to the top crown plate, which is done by heating the metal until the silver rings which I had placed inside the blades melt and appear along the edge of the crown and blades.

I then went back and brazed the upper crown from the outside, and laid a fillet along the lower crown. And after all that, this is what the fork turned out like:

Once again, my lack of photographic skills does not do the fork, nor all the hard work it took to make it, any justice. The fork came out great, and with all of the one-off pieces it is about as custom as it gets.

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One thought on “Aero Time Trial Fork

  1. Hey, great looking fork. I met you at the Texas Handmade Show in October. I just had someone ask me about a steel TT fork and while trying to decide what to do for blades I stumbled onto your blog. You did a killer job. Was the fork pretty fork or does it compare to
    a normal steel fork? Anyway, enjoyed reading your post and i hope everything is going smooth. I enjoyed talking to you at the show.

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