There are only very, very steep climbs here in the area. Instead of the standard 50/34 I would choose a larger big ring. What I'm worried about is how that would compromise shifting. Would there be any problems? (Yes I know, 55-34 is a huge gap [EDIT: in cadence])

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    I fail to see the connection between steep climbs and a bigger big chainring? Are you referring to going down these steep climbs in a big gear? Normally riders want a smaller small ring on the front (compacts or triples) and a bigger rear cog for climbs. – Criggie Jul 26 '16 at 9:02
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    In terms of FD shifting, a 10% increase in chainring diameter would barely be noticed, so long as the FD has sufficient range (mainly a matter of the size of the rectangle-like thing that moves the chain). The 5 added teeth will require a longer chain, however, and may (as noted below) exceed the link capacity of the RD (which is determined largely by the length of the jockey wheel arm and how far it can swing). – Daniel R Hicks Jul 26 '16 at 12:09
  • I understand that. But I would never choose the big ring in the front to go with 32t or even 28t on the back. So as long as I avoid these gears, shouldn't I be fine? – AzulShiva Jul 26 '16 at 13:37
  • With the FD adjusted to clear the 55 ring it is likely that the chain will rub on the link between the cage sides when shifted to the 34 ring. – Carel Jul 26 '16 at 14:20
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    If you have very steep climbs, you'd want to choose a smaller big ring, not a bigger big ring. If you're maxing a standard road config (say 53 front big ring, or even a compact 50 with a small gear of 11), you're going at around 30 mph @ 80 rpm; I doubt you could do that uphill, and doing more than that downhill (possibly with a higher cadence) would be pretty uncontrollable. – Batman Jul 26 '16 at 15:06

I think you answered your own question. The huge gap will mean you need to use a long chain for the big ring and you may not have enough movement in the rear mech to tighten it if you're in the small ring.

My guess would be you'll suck the chain into the rear wheel in some combination of gears and, at best, snap your hanger, at worse damage your frame.

Why not use a mid-compact (52-36) and a large cassette (11-32)

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  • When I said 55-34 being a huge gap I meant a huge gap in cadence when shifting the front ring. I will get a mountain bike cassette, thank you very much. – AzulShiva Jul 26 '16 at 8:41
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    The big difference may require a rear derailler cage that is medium or long,so it can take up more links. Changing to a mountain cassette may require a rear derailleur that can clear the biggest cog. – Criggie Jul 26 '16 at 9:03
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    Can you explain a) how he'll suck the chain into the rear wheel, b) snap his hanger, c) damage his frame? – andy256 Jul 26 '16 at 10:40
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    I would like to know too, this had me petrified – AzulShiva Jul 26 '16 at 13:35
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    Too long chain can catch in the cassette, the subsequent pull can rip the rear mech off and if the hanger snaps badly then it can do the frame. Happened to me on a dropped chain recently (except it jumped into the rear wheel); frame is finished. – atlaz Jul 27 '16 at 18:11

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