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12-27 vs 12-29 Cassette

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

12-27 vs 12-29 Cassette

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Old 04-21-13, 10:14 PM
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calgary_jim
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12-27 vs 12-29 Cassette

I recently purchased a 12-27 cassette and am a little nervous about some upcoming hill work. Am I going to see a big advantage jumping to a 12-29 cassette?

I should point out I am running 53/39 on the front and I suck at hills - big time
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Old 04-21-13, 10:21 PM
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switch to a lower chain ring like 32tooth. That will make a difference.
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Old 04-21-13, 10:24 PM
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^^^ You would have to change BOTH chainrings as, IIRC, the max difference supported by Shimano is 14T - so a 32 small ring requires a 46T large chainring.

This may have changed so I would verify the actual allowable difference.

EDIT: I just realized that 53/39 is 130BCD while 32/46 would have to be 110BCD. This means swapping cranksets and perhaps FR der as well.
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Old 04-21-13, 10:25 PM
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Originally Posted by alexaschwanden View Post
switch to a lower chain ring like 32tooth. That will make a difference.

BCD not compatible
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Old 04-21-13, 10:26 PM
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OP, if you suck at hills just work at them until you dont suck. Stress is necessary for your body to adapt.

If you only want to ride if its easy, then get an electric bike and cruise the flats.
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Old 04-21-13, 10:26 PM
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^^^ Sniped!
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Old 04-21-13, 10:33 PM
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I ride a compact (50/34), so a little different, but I went from a 12-30t to a 12-27t and really didn't notice a whole lot except that I got up the hill faster. It really didn't feel that much harder. As others said, just keep working.
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Old 04-21-13, 11:10 PM
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Originally Posted by Bob Dopolina View Post
EDIT: I just realized that 53/39 is 130BCD while 32/46 would have to be 110BCD. This means swapping cranksets and perhaps FR der as well.
Who makes a 32T 110 BCD ring? I wouldn't think the bolt spacing would allow that few teeth.

OP definitely needs a compact which does require new cranks since that will make far more difference than a a couple more teeth on the big cog. FD should be fine if it's just dropped a bit.
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Old 04-21-13, 11:10 PM
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I'm pretty sure that 32 tooth chainrings don't exist in 110BCD form factor either. They would have to be too small (even 34T rings have bolt holes less than 1/4" from the edge of the ring). 33T 110BCD chain rings do exist, but they are extremely rare.

In 130BCD, the lowest you can go is 38T.

Triple cranksets have two sets of bolt holes, usually 110 or 130 outer for the two big rings and a 64 or 74 for the granny.

Shimano definitely supports front difference up to 16T (duh... 50/34?) I'm not sure what would happen if you tried to stretch this by one or two teeth, but I don't see why it would cause any problems.

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Old 04-21-13, 11:15 PM
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I run a 12-29 but only use the 29 in the steepest hills. This weekend I climbed a hill that rises 700+ feet in 9/10ths of a mile. It averaged 14% so yeah the 29 went in to play.

Better have it and not need it.
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Old 04-21-13, 11:17 PM
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Originally Posted by BykOfALesserGod View Post
I run a 12-29 but only use the 29 in the steepest hills. This weekend I climbed a hill that rises 700+ feet in 9/10ths of a mile. It averaged 14% so yeah the 29 went in to play.
That would not be Pine Creek, by any chance?
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Old 04-21-13, 11:29 PM
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Originally Posted by hamster View Post
Shimano definitely supports front difference up to 16T (duh... 50/34?) I'm not sure what would happen if you tried to stretch this by one or two teeth, but I don't see why it would cause any problems.
This is why I no longer trust myself to pull numbers straight out of my head. Too many numbers and too small a brain...I do not, however, have any problem pulling them from an orafice of my fundement.

If more than 16T shifting will suffer and the odds of dropping a chain go up.
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Old 04-21-13, 11:31 PM
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I may be a dumass, but believe the OP will get more benefit toward easier climbing by switching to a compact crank (or semi) than from changing your cassette. Cost be damned....
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Old 04-22-13, 12:23 AM
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Originally Posted by hamster View Post
That would not be Pine Creek, by any chance?
I climbed Los Gatos in the DeLuz/Sandia Creek loop between Temecula and Fallbrook. Great now you have me seeking this "Pine Creek". Can you post a segment link?

Here is Los Gatos.

http://app.strava.com/segments/635336
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Old 04-22-13, 01:04 AM
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Originally Posted by BykOfALesserGod View Post
I climbed Los Gatos in the DeLuz/Sandia Creek loop between Temecula and Fallbrook. Great now you have me seeking this "Pine Creek". Can you post a segment link?

Here is Los Gatos.

http://app.strava.com/segments/635336
Pine Creek http://app.strava.com/segments/609840 The last mile is right around 14% and it's actually worse than that (mile 1.24 to 1.48 is 20%).
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Old 04-22-13, 05:01 AM
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27 to 29 is a 7% difference. Hard for anyone here to know if that's enough for you.
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Old 04-22-13, 06:03 AM
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Of course the best move without buying a new bike or refitting the existing one to Apex or such would be a compact crank AND a 12-29 cassette. That is worth 23% relative in gear ratio. But that is a lot of investment and bother if this is a one time thing. So in order of expense and aggravation we have new cassette, new crank, new both. Your call, OP.
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Old 04-22-13, 07:27 AM
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So much is put into the numbers and ratios, and while these are good guides, I find that not knowing the hard numbers and relying upon the feel is best. One of my bikes is a compact (50/36) with a Tiagra 12-30 in back. That gets me up any hills in this mountainous region. The commuter bike has a standard road trip (52/42/32) and a 12-25. The latter spins a bit more up hills, but have never had to drop to the granny combo. Triples can be your friend if you let them, and longer cage RD with larger, even mountain cassettes can help. there is a weird thread on pages 1 or 2 about a 1x10 with a 54t front, 36t rear.

But the simplest way is to ride hills with your 12-27 until you can do it without worrying.
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Old 04-22-13, 08:38 AM
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Originally Posted by Homebrew01 View Post
27 to 29 is a 7% difference. Hard for anyone here to know if that's enough for you.
This link will help get your head around what that 7% means in terms of rpm, speed, gear inches.

http://www.gear-calculator.com/#

Or just try it out. Find a grade that's as steep as the toughest grade your going to be riding. Ride up it in your low gear, if you can climb it comfortably, with an effort you could sustain on a long climb, you don't need a lower gear. If it's just a notch too hard, the 29 should be enough. If it's really hard to the point you can't sustain it, you likely need to go to an even bigger cassette, a compact, or both.
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Old 04-22-13, 09:30 PM
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Originally Posted by merlinextraligh View Post
This link will help get your head around what that 7% means in terms of rpm, speed, gear inches.

http://www.gear-calculator.com/#

Or just try it out. Find a grade that's as steep as the toughest grade your going to be riding. Ride up it in your low gear, if you can climb it comfortably, with an effort you could sustain on a long climb, you don't need a lower gear. If it's just a notch too hard, the 29 should be enough. If it's really hard to the point you can't sustain it, you likely need to go to an even bigger cassette, a compact, or both.
Yeah, I might spring for the 12-29 but a new crank isn't going to happen. Ill just keep riding hills till I can. Thanks guys.
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