Down-gearing options

[simonn]

come on, I can spin 39/12 at 45+ kph, don't tell me that everyone commute faster than that And the chainline is more straight

How long for? Your cadence would have to be 110rpm or so.

I'd much rather be on 52/13-14 (AT) ~90-100rpm.

Maybe I'm just unfit .

I went through a similar thing, thinking of going compact, a few months ago and I have a triple (52/42/30 & 12-26). I found changing to the 30 annoying in general. No matter how it was tuned (by myself and 'professionally') it was never smooth, but then it is a Truvative Touro with Tiagra FD, so bottom end stuff. So, I tended to stay on the 42 and grind slightly if needed.

So, there are two places in my commute where I can't spin... pfft. Who cares, there used to be five or six, so one day there will be none (when I have HTFUed ) and I'll be faster.

42 is a very convenient utility ring for riding around the city while the 34 is a tad small and 50 is a tad too much for most.

+1-ish (no experience with 34 or 50, but the vibe seems right your honour).

[il padrone]

It involves putting a special cutting tool onto the BB shell or head tube to cut back the paint and metal a small amount so as to ensure the two faces each side are exactly parallel. Hence the bearing will work as smoothly as possible. As sogood implied, this is normally done when a bike is built up and shouldn't need to be repeated unless the frame bearing faces have been knocked around.

[sogood]

I thought similarly. I've changed the BB on my tourer 2 times since I bought it - never refaced the shell. No problems resulted.

Even removed and refitted a few head sets in my time with no refacing of the head tube. I think it's all a bit over rated.

I think it's reasonable to check the facing when servicing the BB but just don't reface it every time. Once the width has been reduced beyond the spec, the frame is junk as it wouldn't be able to properly retain at least some of the crankset/BB setups eg. Campy's UT crankset. Not sure about traditional square taper BBs though.

[RepcoMonaco]

come on, I can spin 39/12 at 45+ kph, don't tell me that everyone commute faster than that And the chainline is more straight

How long for? Your cadence would have to be 110rpm or so.

I'd much rather be on 52/13-14 (AT) ~90-100rpm.

Well... I think on a flat I can sustain 45+ for a few minutes max, regardless of cadence/ring I'm in. I don't think I can sustain _any_ decent cadence in 53/12... I doubt I ever used this combination except when test-riding the bike.

Which worries me - I paid for that ring and it's not being used

[il padrone]

Once the width has been reduced beyond the spec, the frame is junk as it wouldn't be able to properly retain at least some of the crankset/BB setups eg. Campy's UT crankset. Not sure about traditional square taper BBs though.

Square taper BBs are probably more accommodating. You'd just set the cups, tighten the lock ring, and if the LH cup is sitting out 2-3mm more it's no big deal.

These integrated BBs though I'm not so sure how they'd cope.

[RepcoMonaco]

Be aware of that 50/34 gap. ... Based on my past experience, 42 is a very convenient utility ring for riding around the city while the 34 is a tad small and 50 is a tad too much for most.

Hmm... something to think about...

[Nobody]

If you want to go external BB, you need to remove the BB you have, get the BB refaced (for $15) at the bike shop.

Why do you need to reface the BB? BB should have been properly faced in the factory. Shaving more off may move it out of spec for width.

The bearings cups of these systems thread into the bottom bracket, and press against the shell face. The bearings then sit outside of the shell. It is important that the left and right shell surfaces are adequately machined square to the threads and one another. Miss aligned shell faces can cause the bearing cups to twist as the seat into the bike.

http://www.parktool.com/repair/readhowto.asp?id=122

[Nobody]

Be aware of that 50/34 gap. If I started my return to cycling on the CT, I would have either stayed in the 34 or had to jump b/n 50 and 34 a lot. Nowadays, I pretty much just stay in the 50 for all the regular city rides. Based on my past experience, 42 is a very convenient utility ring for riding around the city while the 34 is a tad small and 50 is a tad too much for most.

The only problem I find with the 34/50 (12-25 9 speed) is changing to the 50 at too slow a speed and not wanting to change down any further on the back because of chain line. Other than that I think it is one of the better bicycle developments of recent times.

[ausdb]

Well, changing 12/26 to 12/28 only gives 7.1% difference in the granny gear. Changing 53/39 crankset to 50/34 gives 12.8% in the granny plus lowers the larger ring by 5.6%, which is good because currently I hardly ever use it. I think I'd even be happy with something like 48/30, if such thing exists (does it? will other cyclists point fingers at me? )

Be aware of that 50/34 gap. If I started my return to cycling on the CT, I would have either stayed in the 34 or had to jump b/n 50 and 34 a lot. Nowadays, I pretty much just stay in the 50 for all the regular city rides. Based on my past experience, 42 is a very convenient utility ring for riding around the city while the 34 is a tad small and 50 is a tad too much for most.

I have a set of truvativ compact cranks with 36/50 coupled with a 12-28 sram road cassette. The old bike I was riding had 52/42 at the front and 12-25 on the back. For a lot of the rides around the river in Perth I could happily cruise on the 42 at the front. Now I spend about 50/50 on either chainring and the 36-28 helps getting up mount st in the city!