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I have a 2013 Scott CX Team Cyclocross which has an FC-CX50 Crankset. Unfortunately, I cannot afford a road/triathlon bike right now and I have been using this for triathlons. I now have road tires on it which has helped a lot but am tired of being passed spinning away maxed out. I am looking for the cheapest option for an upgrade and I thought that I could look at switching the Crankset's Chainring to a 50 from a 46. That should give me a little more speed. I am pretty new to bike mechanics and I did not want to order a chainring till I was sure it would work. Would someone be able to point me to a Shimano unit that will work or is this even possible? If so, can I assume that I will probably need a new chain as well? Thanks in advance.

  • Have you thought of changing your rear cassette so that it has a smaller smallest cog? That'd give you a faster top speed and is likely more compatible and less hassle than changing your front chainring. – RoboKaren Apr 5 '17 at 19:16
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A CX-50 is usually fitted with 46-36 and is 10 speed. Occasionally I replace the 36 with a 34 on mine. Any flat 110mm BCD ring of 50/52 will fit instead of the 46 ring and the 36 is the usual combination with a 52.

The chain will have to be 2-3 links longer and the FD must move up by one or two mm to clear the big ring.

(Note: You may even change the rings without having to remove the crank from the bottom bracket, as they can easily be manoeuvred around the arms and the pedal.)

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http://bike.shimano.com/content/sac-bike/en/home/mtb1/drivetrain/crankset/fc-cx50.html

That crank uses 5-hole chainrings with a 110 mm bolt circle diameter. Make sure it's narrow enough for 10-speed chains. That's a very common combination, you shouldn't have trouble finding one.

Yes, you'll definitely need a new chain.

The bad news: you might need to also replace one or both derailleurs. A front derailleur has a limit on the range it can handle (the difference between the largest and smallest chainring). You need to look up the specs on your derailleur model. And no matter what, you'll probably have to move the front derailleur higher.

A rear derailleur has two numbers: the maximum sprocket size (irrelevant here, since you're not changing the sprockets), and the "chain wrap". There's an article here which explains the concept; it's about Campagnolo parts, but you'll get the idea. If you widen the gear range too much, you'll wind up with slack in your chain when you're on the small ring in the front and in the back. Can you live with that? If so, then disregard this paragraph. Otherwise, look up your derailleur specs and see if the new range will work.

Another way to get around the derailleur problems: get a larger small ring as well, so the range stays the same.

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