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I have a Cannondale Synapse with Compact Cranks - with a 34/50 set of chainrings and an 11-21 cog on the rear wheel. All components are dura-ace. I live in Florida and only ride on the flattest of roads. Since I have owned the bike, I have never used the smaller chainring because it is simply too easy to spin. My bike shop told me it would cost about $100 to replace my current 34/50 chainrings with bigger39/54 chainrings - this was based on my inquiry, not their recommendation.

I generally have a cadance of between 85 and 105 and only go into the 11 or 12 cog on sprints and then for very short differences. I am certainly NOT overspinning my 11 or 12 cog. My typical speed for group rides is between 20 and 25 mph. Will replacing my 34/50 chanrings with the 39/54 chainrings offer any imporovement in speed or any other benefit? Any advice is very much appreciated and I'd probably spend the $$ if it even offered a slight speed improvement. Thanks!
 

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thoughts..

A compact crank in your area wasn't a wise purchase to start with. I've never seen compact rings in a 54/39 and they might be too flexy with the small 110mm bolt circle. I'd think it would be better to swap to a standard crank.

As for the "improvment" , a 54/12 is the same a 50/11, so you would gain one more top gear with the 54/11.

You might even look into a 54/42 crank with a 130mm bolt circle (standard hole pattern).
 

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Compact chainrings are for climbing and the only climbing you'll do in FL is up parking garage ramps and highway overpasses.

That said, I race a compact crank with a 52 x 42 combo. No flex at all. So the least expensive way forward would be to just buy 110 bcd chainrings in the combination you need (e.g. 53x39, but in FL, you might go with 52-53x42 which is better suited for your terrain). Specialites TA and Stronglight both make the chainrings you need and can be bought via mail order (e.g. http://www.xxcycle.com/chainrings-and-kit,en.php)

Cheers
 

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davidgator said:
I have a Cannondale Synapse with Compact Cranks - with a 34/50 set of chainrings and an 11-21 cog on the rear wheel. All components are dura-ace. I live in Florida and only ride on the flattest of roads. Since I have owned the bike, I have never used the smaller chainring because it is simply too easy to spin. My bike shop told me it would cost about $100 to replace my current 34/50 chainrings with bigger39/54 chainrings - this was based on my inquiry, not their recommendation.

I generally have a cadance of between 85 and 105 and only go into the 11 or 12 cog on sprints and then for very short differences. I am certainly NOT overspinning my 11 or 12 cog. My typical speed for group rides is between 20 and 25 mph. Will replacing my 34/50 chanrings with the 39/54 chainrings offer any imporovement in speed or any other benefit? Any advice is very much appreciated and I'd probably spend the $$ if it even offered a slight speed improvement. Thanks!
I could be wrong, but did you mean 39/53?

I'd be inclined to go with "standard" 42/53; sounds like you're strong enough, and Florida's definitely flat enough, for it.

Your gearing will have its "range" shifted to higher gears in general, with a little narrowing, so that the jumps between gears will be lower. You can go to any one of a number of websites (Sheldon Brown's is good) to find out exactly how much.
 

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Agree with the 53/42 recommendation. I ride with a 52/42 and really like that moderate increase in cadence when shifting into the 42. I also like the overlapping gear ratios, they're good to have on the flat. Not sure if they still do and if it matters to you in the slightest, but the pros used to put on something like a 52/50 for flat Paris-Roubaix.
 

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If you are not spinning out your current gearing, going to larger chainrings won't make you any faster.

It would give you more gearing choices in the range that you use. That would let you select the perfect gear at all times, which might mean a delay in the onset of fatigue on longer rides (vs having to use a slightly too high gear).

If it was me I'd get 52/42 chainrings for the crank you have.
 

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I'd go with a 42 smaller ring and at least a 52. Phillppec said a 52/42 is available for a compact. That's the cheapest way to go because then you don't need to replace your crank or bottom bracket.

Most triples are a 42 and I go up most of the hills in my small mountain range here in the 42 but at a push. You don't have these hills so a 42 would be a much better choice than a 39. You'll find a 1/2 gear difference (with 1 cog change) with a 42 from the larger chainring.
 

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I must be crazy, since I switched out my chainrings from 50/34 to 52/38 and I barely could tell the difference before and after. Both with my 12/27 cassette.

I didn't switch for gearing though, I had cheapo chainrings to begin with... so I figured I might as well go higher.
 
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