When every bike looks like a project…
Having the ability to modifybicycle frames means that I always modify bicycle frames.
I rebuilt the front of Christine’s bike, turning it from this:
into this:
It started with a pretty simple plan of building a low trail fork and a front rack. When I had the bike apart I measured it and discovered that the seat tube angle was 75 degrees (very steep!). Christine has complained a little ofwrist pain, and this might be the culprit. I couldn’t slacken it without making the head tube angle very slack and screwing up the handling. I debated selling the frame and building a new one from scratch, but ultimately decided just to modify it.
I gave it some thought and decided to move the head tube back and make the head tube angle steeper. This would allow me to raise the front end, and slacken the seat tube angle. I went from a seat tube angle of 75 degrees to 72 degrees (this made the saddle sit 3cm farther back from the cranks), and also have a head tube angle of 72 degrees. Rotating the bike back around the rear wheel raised the very low (for 650B) bottom bracket by 20mm. Raising it 10-15mm would have been ideal, but this is still within acceptable parameters. The top tube is now 50cm instead of 53cm, which gives us more options for adjusting reach. The drawing above shows the old (grey) and new (red) geometry.
While I had the bike “under the knife” I also made some other modifications.
I made this “sunburst” styled rack. It was influenced by the Ahearne rack that was on his 2007 NAHBS mixte.
The fork is new. It has much nicer blades and 23mm additional rake. The additional rake will help with the handling when there is a front load and kept the front center (distance from the bottom bracket to the front hub) from getting too short. A too short front center results in bad toe clip overlap.
There is a new chaincase and I moved the chainstay cable housing stop forward to be compatible with the Nexus hub. The chaincase is a Hebie Chainglider. It works surprisingly well for not mounting to the frame, it just floats on the chain. It isn’t too much work to get on and off.
I removed the right downtube shifter boss and added a hole for routing the taillight cable through the downtube. I like to reinforce such holes with a water bottle boss.
There are still a few things to do before getting the frame powder coated (which might not happen until fall, because Christine uses this bike regularily for commuting to work):
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Cable routing for the headlight and taillight wires on the fork.
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Remove the rearward chainstay cable stop.
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Maybe remove the left shift boss and put on a split shift cable boss.
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Maybe move thechainstay bridge 2cm closer to the dropouts. It is crazy far right now.
If I worked at Soma I’d argue for some revisions to the basic frame. The 50cm mixte should probably be built with 26″ wheels (not 700C) in mind. This would allow the top tube to be shorter, so the seat tube angle could be 72 degrees from the factory. A 75 degree seat tube angle is way too steep for a bicycle with an upright seating position. Finally if the chainstay cable housing stop were about 2″ forward of the stock location it would work well with Nexus and SRAM internal hub gears or a rear derailleur. The current location only works with a rear derailleur.
