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.
Wow. Great work! Why V-brakes up front? Are you using different levers to accommodate for different cable travel, or do the levers have adjustable travel? Perhaps there is a travel agent somewhere that I”m missing, though seems like one would generally prefer to use the same type of brakes front and rear for this kind of bike.
Thanks for the great post.
The brake levers are designed for V-brakes or canti/caliper brakes. They have an option to select between them.
I may put V-brakes on the rear too, but it isn”t too high of a priority. I don”t really like the long reach caliper brakes and canti brakes aren”t a good option on a mixte (heel clearance).
I”m not a stickler for having the same types of brakes front and rear.
Oh, and I had to switch to V-brakes on the front because the crown to rim distance is a bit longer on the new fork. That was necessary to keep the original geometry (my plan before deciding to move the head tube too). A higher offset fork increases the tire to crown distance if you keep the same axle to crown distance.
You could always try mounting a roller brake too — the rear ones aren”t too bad (the front ones have a really low limiter).
Don”t move that chainstay bridge! I had tried to convince you before to modify the dropout to make it easier to get the wheel out without deflating the tire, but the answer was right there — replace the bigger spacer with a spring! I”d been planning on doing the same on my Kogswell, maybe we can do it at the same time.
The noodle on the front brake looks pretty close to the rack stay — would a Cane Creek Direct Curve fit? That would have the cable housing come nearly right down the middle.
Great idea, Alex!
Now I”m also tempted to take my wife’’s step-thru to the table. The older Trek 420L’’s have similar issues to the Soma: steep seat angle, long reach, too low bb with 584mm wheels, etc… this is a brilliant solution!
Is the chainglider noisy at all? Seems like it would be…
Cheers,
John
Fred — A roller brake isn”t a bad idea. The bike already is getting pretty porky, but it would solve some other issues. I”ve done the spring loaded fender mount before, but it works best with a through drilled bridge and this one has a threaded hole. If I moved the bridge it wouldn”t be so far as to cause wheel removal issues, I”d just like to get the spacers down to 5mm instead of 18mm.
John — The chainglider makes sort of a light wooshing sound. It isn”t silent, it isn”t loud. It is quieter with a heavy lube, and I”ll be applying one once the final buildup of the bike occurs.
Oh, and if you do this John I”ll say that mitering the mixte stays is the hardest part. I was shooting for a bit longer top tube length, but nibbling away to get all of the miters right caused me to eat up 1cm. If I were doing this again I”d shoot for removing less top tube than you plan on.
Are you using a rapid fire shifter or the twist for the NExus? I noticed the un-housed cable along the downtube, has the shifting performed the same as completely housed?
I”m thinking about removing some of the housingwith my alfine/triger shifter on a Kogswell P/R
Thanks for that tip, Alex. Fortunately, the Trek is a step-thru, not a mixte. Here’’s a pic before the Nexus 8, dynamo front, lights, and huge Wald basket:
http://www.flickr.com/photos/thingsofdotnature/2436887028/
That ought to make the mitering a tad easier!
Seems like the chainglider is a good compromise. I”ll buy one for her to try out.
Ben — Trigger shifter. The Alfine trigger shifter is really nice. I didn”t notice any issues with shifting once moving it to exposed cable. The chainstay cable housing stop is in the wrong place on 99% of bikes for having exposed cable though.
John — If you modify your frame I”d be interested in seeing the final results. The Trek is closer to good already, it seems like just making a slightly taller fork would do the job.
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