Back in the shop and working on an unusual project. I built John a lightweight kickbike a few years ago. He came back to see if I could do a similar version that would fold to be more compact. It is coming together – I set up an improvised jig on the alignment table, and just about have it all tacked together to test out the folding before final brazing.

Photos as ever by Tina Buescher.

Then having used twin toptubes on the cruiser I built a few years ago, I decided to do something similar on this build. The tubes curve in both planes, with the extra width providing good lateral stiffness to the front triangle, and the twin tubes providing clean routing for the derailleur cable and rear brake hose. I happened to have a piece of headtube sized carbon fibre left, so that went into the front.

With a single ring that isn’t XX1, some sort of chain management is needed, so I added a boss on the seattube and machined a delrin chainkeeper (14g).  For the front end, there is a custom steel fork, with a one-piece stem/steerer, which keeps everything nice and clean (no stem bolts to hit the knees on!), and allows the front hose to run internally from stem to caliper.

The parts kick off with mango R45 disc hubs and headset from Chris King, matching custom decals on the Enve rims, and great color matching for the paint by Eric at Colorworks. An FSA titanium BB, Middleburn Uno cranks, SRAM X.0 9spd derailleur and gripshift and Avid XX brakes complete the build.

This bike was shown at NAHBS 2013 in Denver, and the photos here are by Tina Buescher.

To keep the bike compact, for ease of storage and maneuverability, the seattube has a curve to allow the chainstays to be shorter. With the belt drive, there of course needs to be a way to tension the belt, and also to install the belt into the rear triangle. Neither an eccentric BB or sliding dropouts were a good match for the lightweight goal, so I needed to come up with something else. Having over 20,000 miles on my personal belt drive bike, I have learnt that once the belt tension is correctly set, it does not require further tensioning (and indeed, the Gates CenterTrack belt doesn’t need to be run very tight at all). So the solution I went with on this bike is mainly about allowing entry for the belt, with the chainstay length built correctly for the belt length being used. The end of the chainstay acts as a socket, sliding over a matching stub on the dropout. A 6mm bolt then holds it all together. Should a chainstay length adjustment be required, then it is simple to just add shims inside the socket as needed.

With the design for the belt taken care of, the shape of the frame was then chosen by customer preference, with the dropped seatstays coming in at the top of the curved seattube. The rear brake is under the chainstays, with the cables running internally. A Niner RDO seatpost is set at maximum extension for comfort on city streets.

Carbon tubulars might not be everyone’s first choice for city wheels, but shod with 25C Continental tires, the Enve SES 3.4 rims are a durable, lightweight choice. An Alchemy ELF front hub gives a nice match to the Alfine rear.

The remaining build has Versa dropbar shifters, THM cranks, ee-cycleworks brakes, Enve bar and stem and KCNC titanium pedals.

And then onto the paint! This was an iterative process to go from the customer’s concept to the finished bike, but Eric at Colorworks did a fantastic job of making it all come together. And of course, thanks to Tina Buescher for the photos!

Trying to integrate everything as cleanly as possible took a lot of long rides to think through and try and figure out, and even then there was some trial and error in the workshop too! I really wanted to eliminate any external fasteners to keep it all very clean. My position is not much changed from the previous bike, I just moved the aero extensions a little closer together. I also lowered the BB and decided to go with a single chainring, since I generally only race flat, straight time trials.

Shifters - Having had the opportunity to play with Shimano’s Di2 group on customer builds, I had learnt enough to hack the original 7970 group. With just a single chainring and only the rear derailleur to control, I rewired the harness and machined custom bar-end plugs to hold simple push button switches – up on one extension and down on the other. The control box fits into the stem and is covered by a cap. The wire then runs down the front of the fork/bar assembly, into the headtube and to the battery which is in the base of the seattube, inserted through a hole in the BB shell. Charging is via a micro-usb port located on the seatmast under the saddle. The wire to the derailleur then runs inside the seatstay. The wiring was somewhat tricky to install…. especially at 2am right before shipping the bike to NAHBS…

Headset – Or perhaps just ‘steering bearings’ since there is no conventional steerer tube or headset. This was the biggest headache – how to attach two angular contact bearings and still allow for the brake and Di2 cables to pass directly through the headtube, with no external fasteners. The upper bearing is pressed into the ‘stem’, and secured with a small bolt. Before it was installed, an aluminium receiver was inserted into the inner race. This is slightly longer than the bearing so that it pulls down and locks into the headtube when it is bolted into place. It is also shaped on the top to act as an internal steering lock – this prevents the front of the fork/bar assembly from running into the headtube when the bars are turned. The lower bearing is pressed into the underside of the crown. For assembly, the bolt for the upper bearing is inserted through the lower bearing, passed up through most of the headtube and then locks the upper bearing and receiver in place. The lower bearing then has it’s own, larger bolt that threads directly into the inside of the headtube. This leaves the space between the two bolts open, so that the brake and Di2 cables can pass through. There is a machined slot in both the back of the fork/bar assembly and the front of the headtube to allow for these cable runs.

Brakes – I chose the USE Tula brake lever pods for their super aero profile and ease of access to inside the bar. For the rear brake there is a short 90 degree tube brazed inside the fork/bar which then connects to a short piece of ilink cable housing to travel from fork to frame. This two inch section of outer cable is the only piece on the bike. The cable then runs directly to an exit in front of the BB, over a brazed-on guide to the TriRig Omega brake. I really didn’t want to have to make custom brakes for this bike (it was a lot of work on the first machine), but I couldn’t find anything that would fit quite how I wanted it for the front. So I machined a small cantilever brake. The bare cable runs directly from the lever (which I had to modify to increase the cable pull), to a pulley on the left brake arm, then it is clamped on the right. A titanium spoke provides a central spring for both brake arms.

Crankset – Back in 2007 I built a prototype brazed cromoly crank, but hadn’t had time to return to the project until last year. The BB axle was actually the first part of this bike that I built. I have to give credit to John and Miles Kingsbury for the idea of using a tapered cut to align the two halves of the axle. The internal sleeve is a precision fit to keep the axle perfectly straight. There are two bearings on the drive side and one on the non-drive. The axle is 22mm, and the shell is a reduced diameter of 34mm. I considered doing a really super narrow crank, but decided I wanted to be able to run a regular spaced rear wheel, and so the chainring has to be located correctly. The cranks still have a q-factor reduced by about 20mm from normal though. The crankarms are airfoil shaped cromoly tubing, the same as used for the bars. For the chainring, Fibre-Lyte in the UK made me a custom carbon 55T ring, with three bolt spacing to match the cranks.

Frame – My original bike used round tubes that I ovalised. This one uses actual airfoil shaped cromoly. I could only find these in a thicker wall than I would normally use, and so I was reluctant to use tubes that heavy. But upon reflection, I realised that the thicker wall would add stiffness and allow me to use a narrower profile. The downtube is only 14.5mm wide, with an 18mm wide seatmast. Lateral stiffness is maintained by using an ovalised toptube, which being horizontal doesn’t increase the frontal area. My personal bikes generally have a fixed height saddle, and this is the same – I used a Thomson clamp assembly here. The rear dropouts are different – the drive-side uses a Breezer style to allow a clean exit for the Di2 wire, whilst the non-drive has a flat dropout, which is particularly clean when the minimal Tune skewer is used. The dropouts are vertical, which can be a problem with a tight seattube cutout. To allow for easy wheel removal, the dropouts are rotated back ten degrees so that the tire doesn’t jam on the brake during removal.

Components – There is not much else needed after all the custom parts! When I told Colorado-based Dash that I would be showing this bike at NAHBS, they stepped up with their brand new, 700g flat disc wheel, and a TT saddle to match. The front wheel is an Enve SES 8 rim laced to my custom extra narrow aero hub.

Total weight comes in under 17lbs. The paint scheme was designed by Jonathan Hill and executed to perfection by Eric Dungey at Colorworks. Thanks once again to Tina Buescher for the fantastic pictures.

I was honored to be awarded ‘Best in show’ for this build at NAHBS 2013 in Denver. If my legs co-operate, then hopefully it will go fast in races this year too!

I just built the first two wheelsets up with the new hub. It is available in both 10spd and 11spd (meaning that if you are not planning on changing to 11spd, you don’t have to give up rear wheel strength/stiffness by having an unnecessarily long freehub body). Built onto Enve SES 3.4 clincher rims with Sapim cx-ray spokes, the weight comes in at 1392g. Set two uses NoTubes Alpha 340 rims and cx-rays and weighs 1278g.

The Campagnolo version should be available in a few weeks.

In fabrication news, I have a lightweight FRC frame underway, hoping to get that finished and off to paint this week. And in racing news – I have my first race of the season on Saturday, so I’ll get to find out how my winter’s training has gone….

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