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I have a road bike with 50/34 compact crankset and 12/27 10sp cassette.

While I don't think I could run a 53/39 one given the hills I happen to climb, but sometimes I get the feeling the right gears are precisely close to the cross chaining limit.

I get the feeling when riding on the 34 that it is always too easy unless I ride on the 12/13/14t cogs, or when on the 50, that it is too hard unless I get on the 21t cog...

I mean, when on the flat, I feel better on the 50 as I could get faster spots when smaller cogs will definitely be better, but when riding at ~25kph, it just feels like I am all the time "in between"...

Any tips?

Also, given that the crankset only has two rings, is the cross-chaining less of an issue than on a triple?

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Its only a big problem if you are all the way over on the otherside so you should avoid 50/27 and 34/12, otherwise you should be fine. It might be preferable on shallow slopes and flats to be on the 34 ring and switching up and down 15/14/13 as the change is small enough that you wont lose too much momentum going in to and easier gear or too much cadence going to a higher gear. –  robthewolf Oct 24 '13 at 16:16
    
I vote for cross-chaining. Its just a bicycle. Do what you want. –  Ritch Melton Oct 25 '13 at 0:42
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5 Answers

Analyzing your figures, assuming your wheel circumference is 2110mm ...
At 25kph, riding the 34X14 gears, your cadence is about 81.
If you switch to the 50X21, your cadence is about 83.

If you then push your cadence up, at a cadence of 100 on the 50X21 you are doing 30 kph. You can then drop to the 50X19 for a cadence of 90.

So this all looks pretty normal.

Since you are not complaining about hills, I say your gears are about right for you. You are complaining of feeling "in between" on the flat, so I have one and a half suggestions:

  • Practice riding with a higher cadence. It always feels weird at first, but you'll get used to it. If you start "bobbing", then concentrate on pedaling smoothly (ankling). Think of riding at a higher cadence like running a car at higher RPM. The higher the RPM the higher the power. And think how many steps per minute you would take if you were running. Not everybody would agree with me, but I say that 90 should be your slowest cadence (when you should change to a lower gear), with 100 as your average. For practice, try this game. Ride with a friend, starting at, say 20 kph on the 34X17 gear. Now in the same gear find out how fast you can go. You will be surprised. Then try the next higher gear, and so on.

  • You could test some 53/39 front rings. But you would lose more at the bottom end than you would gain at the top end: the gearing range is lower, with more overlap. To make it work, you still need to teach your legs to ride at a higher cadence :-)

Does it matter if I got your wheel size wrong? Not much. Does it take long to learn to ride at 90+ all the time? It can take a month or two. You have to train your legs to do it, and part of that is your circulatory system has to change. Both need time. What is the benefit? There are three benefits: you will overcome that "in between" feeling, plus greater efficiency and power. Enjoy!

PS You'll notice I didn't mention cross-chaining. That's because I don't think it's an issue.

PPS After posting, I realized I left out an option: to change the cassette to one with smaller gaps in the cog sizes, something like 12-25 or a custom built job. That won't work for you if you need that 27 cog for the hills.

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It is very interesting! Actually I was riding recently in a group where all were way slower than me so I played a game to stay on the 34 to refrain myself. And ended up realizing I got used to it pretty well and that it is usable when on the 14 cog for example. –  Nic Nov 4 '13 at 10:37
    
Your cassette change suggestion is actually a good idea: it is cheaper than changing crankset, does not require derailleur adjustment nor chain replacement (which might have been the case to handle the 53t ring), I can switch the 12/27 back for climb rides. And the cassette I was considering would be a 11/25. The gaps are smaller which is good but the best about it is the 11 min cog, which means that the smaller usable cog with the 34 ring will be 12 rather than the current 13 which is cool IMHO. And I hope the rear derailleur adjustment to chain-handle the 34/11 set-up will be minimal! –  Nic Nov 4 '13 at 10:41
    
Happy to have helped. In the end you've got to do what's best for you and your objectives. Some people like to push a big gear to build strength, at the risk of damaging knees and back. Others go for cadence and aerobic fitness. If you start building your own clusters you can get whatever result you want. Enjoy –  andy256 Nov 5 '13 at 3:45
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A 53 x 39 won't really make things better for you as you'll be even more cross geared in your 53. That said, riding a 50 x 21 on your 12-27 cassette can't really be considered cross gearing.

If you'd like less of a jump in ratios when shifting the front chain ring, might I suggest a cyclocross crankset? Shimano's cx50 and cx70 offer a 46x36 up front. They'll let you ride more in the middle of your cassette on the 46 and still give you a decent low ratio. You do lose a little top end but few people are exceeding 50kph for any length of time.

I have a cyclocross bike with a 46x36 and a 12x27 and find it fully useable for the speeds I pedal at and shifting the front doesn't result in 3 gear changes in the rear.

Here's a link to the Shimano cross cranksets: http://www.shimano.com/publish/content/global_cycle/en/us/index/products/cyclocross/cx70.html

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Cross-chaining on a double-ring crankset is really only an issue on the two most extreme combinations (50/27 and 34/12); so avoid those for high-power or prolonged use and you're fine on the cross-chaining issue. With the one big caveat to always trust your ears over guys on the internet - i.e. if it sounds wrong (like its rubbing much more than other gear combos), it probably is wrong.

As for the "how to use" question, once you get fairly strong, you'd pretty much always be on the big ring in front except when you're doing extended climbs, which I'd define as anything long enough that you can't just stand up the whole way.

Until then, I wouldn't worry too much that the only cogs (in back) that feel comfortable w/ the big ring (in front) are your 21 and 24 (assuming you avoid the 27 due to cross-chaining) - if you're mostly riding on flat ground all the time, there's no need or expectation that you'd be constantly shifting between cogs. When you encounter a climb, you just shift from the 50 to the 34 in front, when you get to the top/flat, you shift back from 34 to 50. All while remaining on the 21 or 24 in back. If that's too easy for a little climb, you'd shift up the 21 in back one or two cogs - or just stand up if it's short (e.g. bridge overpass), as standing up generally makes it feel like you just downshifted (i.e. easier) by 2 or 3 cogs.

Feel free to ping me if you have any follow-up questions.

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First: Don't worry about cross chaining, with modern chains and gears it just doesn't cause any problems or is any less efficient. Ride the gears that work for you.

Second: You've discovered the limits of Compact Cranksets. They just don't work very well unless you can do almost all your riding except for climbing on the big ring. If you do a lot of riding in the 25 kph range, the standard setup just doesn't work very well.

You need to either make the big ring smaller, or get a cluster in the back that has more gears in the range you want rather than the kinda of useless 12,13,14.

IMHO, 48/30 or even 46/30 would be a whole lot more useful for average folks if you're going to have 12-27 in the back. But almost nobody makes a road crank that would have those gears.

Another approach would be to look into Junior racing cassettes. You can get a cassettes with a 14 or 16t top cog that provide more choices around the speeds you actually ride.

http://www.wiggle.com/shimano-ultegra-6600-10-speed-cassette/

Lastly, you can just bite the bullet and get a triple.

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I SO know what you mean. Whenever I ride my winter bike, that has 50/34, I'm forever swapping cogs and rings. My tips? Try a triple. My personal views on a triple can be read elsewhere

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This is at least the third time I have seen you promote your site here. Please do not use this site for self-promotion. Also, Stack Exchange sites frown on URL shorteners, which I am reasonably sure that you've also been previously advised of. bicycles.stackexchange.com/help meta.stackoverflow.com/questions/99136/… –  jimirings Oct 24 '13 at 19:31
    
does not answer the question. Possibly if it was expanded it might. –  Mσᶎ Oct 24 '13 at 22:40
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