I am currently running a 53/39 front with a 12/27 rear. I am wondering if I replace my short reach rear derailleur with a long reach (triple dura-ace) rear derailleur, can I then run a 12/29 or 12/30,31,32??? While still using my 53/39 Dura Ace crank.
I just changed my DA 39/53 to a compact 34/50. I can say it give you alot on the lower end, but...... It certainly changed my pace as well. I used to push bigger gears because I had to, now that I don't I find myself going to smaller gears and spinning up hills which is just as hard in a different way.
I think it will take a little getting used to. I can say that I made it through my first hilly century yesterday and could not have done it without the compact.
A Shimano road triple derailleur should work on up to a 32 tooth cog.
IRD makes 10 sp clusters in MTB-like gearing. You'll need a longer chain too.
Using a cluster with big cogs is a good way to get appropriate gearing for very steep/long rides/races if you only need that a few times a year. You'll have some large gaps between the usual flat road cogs, so it's not the best overall solution for permamant use.
No one currently makes Shimano 10sp clusters with 29 or 31 t cogs. Miche has a 30t but they are hard to find and I have heard that they are not the best shifting. IRD has clusters with 28 and 32t large cogs.
A Shimano long cage road derailleur has the same max cog size as a short cage road derailleur. Shimano states that max is 27; others say 28. I've heard people say 30, but never 32. (I believe Sheldon Brown has written on this subject.) If you run 9 sp, you can mount a mountain bike derailleur with capacity for a 34 tooth cog. That was the good thing about Shimano 9 speed, full compatibility and interoperability between mountain and road groups. Not so with 10 speed road. If you need lower gears and have 10 sp, your choices are to either get a compact crank (less expensive; crank only, everything else works) or convert to a triple (more expensive; needs new shifter lever and rear der.)
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