Joined: Mar 2015
Posts: 1,106
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From: New Zealand
Bikes: Gunnar, Concorde, Peugeot 753, Marin, Pete Tansley, Rocky Mtn, Worldrider, Francis Quinlan, Bob Jackson, Winora, Avanti, Klein, Quintana Roo, Shogun, Carlton, Emmelle, Specialized
700c bikes should ideally be 52cm + IMO .
I ride 56s and i'm 6'2. Long stems and posts are fine for the most part, but there are a few issues sizing down on bikes.
Cranks might be shorter.
Cranks might not be shorter, and toe strike might be an issue (I don't care about this one)
You might need a longer post
The saddle- bar drop will be more extreme, so you probably run a raised stem. This stem is also coming closer to you as it rises. The bar position is what matters for steering, but to get it right, you'll end up with the top of your stem much closer to your legs than on a larger bike.
I had a nasty injury the other day because of this. I dropped the chain downshifting, while standing/ sprinting, and my crank instantly fell sending my knee into the top of my stem. This struck my kneecap and put me off the bike for a week.
A raised stem, especially a quill, will flex a bit too, if you throw around the front end.