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PostPosted: Sat Nov 17, 2012 8:43 pm 
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When climbing does a 28T feel noticeably different from a 25T?

I've always used a 25T but fancy trying a bigger cadence on steep hill climbs. Will a 28T make much of a difference?


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PostPosted: Sat Nov 17, 2012 8:51 pm 
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Location: Russia, Moscow
It will make a difference of 12%. Pretty big in my book.


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Posted: Sat Nov 17, 2012 8:51 pm 


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PostPosted: Sun Nov 18, 2012 12:31 am 
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Check out Sheldon Brown's or anyone's cadence calculator and you will see there's a significant difference.

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PostPosted: Sun Nov 18, 2012 4:28 pm 
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Joined: Thu Mar 29, 2012 3:38 pm
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Location: Albuquerque, NM, USA
I have a SRAM 11-28 on my bike, and I've found it really helps on extended 6%+ climbs. I'm strong enough now to make most climbs using the 25, but I still use it during periods when I'm a little more tired. Incidentally, I've preferred the 19-22-25-28 bottom four on the SRAM over the 19-21-24-28 of Shimano. The 24 to 28 jump was a little big for me.

This calculator can help you do some fun comparing: http://www.gear-calculator.com/#

You might want to plug an 11-26 into the calculator also. A little more bottom end ... without the huge steps in size.

Scott


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PostPosted: Sun Nov 18, 2012 5:52 pm 
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The jump from 21 to 24 is the same as the jump from 24 to 28, in terms of absolute speed (because 1/21-1/24=1/24-1/28).

To me, having 21-24-28 instead of 21-23-25 is pretty much a no brainer. I'll only use the two biggest sprockets in the small chainring anyway, so it only makes a difference at low speeds (serious climbing). With the 28 I get a bail out gear and to me the 24 suffice any time I would have been using the 23 or the 25.

I don't like the 19-22-25-28 because of the 19-22 jump (which I occasionally would hit in the big ring). And the 19-22 jump is bigger than the 24-28 in terms of speed.

You could also argue that a 28 will only make you slower compared to the 25.


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PostPosted: Sun Nov 18, 2012 6:34 pm 
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Location: Russia, Moscow
MagnusH wrote:
The jump from 21 to 24 is the same as the jump from 24 to 28, in terms of absolute speed (because 1/21-1/24=1/24-1/28).
...
And the 19-22 jump is bigger than the 24-28 in terms of speed.

This is not true: 28/24 > 22/19 > 24/21.
But I agree with you in that I much prefer Shimano cog sizing to SRAM.


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PostPosted: Sun Nov 18, 2012 6:39 pm 
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If you're looking at speed comparing ratios of sprocket numbers is completely irrelevant. Your speed is proportional to the reciprocal of the sprocket number:
Speed=cadence*wheel circumference* chain ring size/sprocket size

So if you're comparing speed difference between two different sprockets it will be proportional to (1/sprocket(1) - 1/sprocket(2)).


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PostPosted: Sun Nov 18, 2012 6:47 pm 
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Location: Canada
It all depends on your terrain and your power production. On certain climbs, I simply cannot ride a 25 and need the 28 or 29. If I am at 440 watts in the 29, I will completely blow with a 25.


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PostPosted: Sun Nov 18, 2012 8:24 pm 
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Location: Russia, Moscow
MagnusH, Ok, I see what you mean. Rather strange approach in my opinion, but if you like it better...


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PostPosted: Mon Nov 19, 2012 4:47 am 
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I set up my uncle's bike with 28T last weekend and it was quite a difference when I took it for a spin.

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PostPosted: Mon Nov 19, 2012 9:09 am 
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Thanks for the replies.

Does anyone know if there is a weight difference between the 25T and 28T? It doesn't tell you on the Shimano website.


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PostPosted: Mon Nov 19, 2012 3:35 pm 
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Location: Greater Pittsburgh
Also, keep in mind that a wider spaced cassette will have bigger steps between the gears so you may not be able to find the right cadence after all... one gear might be slightly too big and then next will be slightly too small.

11-25: 11-12-13-14-15-17-19-21-23-25
11-28: 11-12-13-14-15-17-19-21-24-28

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PostPosted: Mon Nov 19, 2012 9:38 pm 
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1. Helps you ride steep stuff without going into the red
2. Helps you deal with temporary increases with grade without shifting out of the big ring.
3. For long climbs at a near-constant grade, you might find the 21-24 jump slightly big. It's not a huge deal, though.

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PostPosted: Tue Nov 20, 2012 12:44 am 
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This is pretty simple. When you're climbing, do you max out on your gears and max out your heat rate? If the answer is yes, then you should get easier gears. The question then becomes is 12% enough or should you look at compacts.
Tl;dr, yes 25 to 28 is noticeable, but if you suck at climbing it might not be enough.


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PostPosted: Tue Nov 20, 2012 12:46 am 
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Joined: Tue Oct 23, 2012 5:02 pm
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kulivontot wrote:
but if you suck at climbing it might not be enough.

True:
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Posted: Tue Nov 20, 2012 12:46 am 


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