11-28

[elvisparsley]

Hello all
I'm getting a frame replacement as part of the warranty with free rebuilding from the lovely chaps at Edinburgh Cycles so I thought it might be an opportune moment to replace components i.e change the chain and maybe cassette. I have a 50/34 Tiagra compact with 12-27 cassette just now and because I have the Polka Dot Challenge coming up (I need all the help I can get!), maybe I could try an 11-28. Would this be feasible with what I have at the moment? Not sure what size cage the rear mech has though. Small or medium, I'd think
Thanks

 

[kyuss]

I think if it's a short cage mech Shimano recommend a 27 tooth maximum, though I've heard of people getting away with 28's and even 30, especially if using a compact chainset, as it also comes down to tooth capacity (ie difference in teeth between front and rear which determines how much slack in the chain the mech is capable of taking up). I'm sure someone more knowledgable than I will be along shortly to confirm this, but in the meantime I found the quote below handy when building my last bike and choosing components. You can find out the max capacity of your rear mech by downloading the relevant tech doc pdf from the Shimano site here. The capacity will be listed under 'specifications'.

"The total capacity is calculated by subtracting the size of the smallest chainring number from the largest chainring and adding it to the difference between the largest and smallest cog in the rear. For example, if the front chainrings were 24-36-46 and the rear cluster were 13-28t then, the front difference of 22 (46 minus 24 = 22) would be added to the rear difference of 15 (28 minus 13 = 15) to achieve a Total Capacity of 37 teeth. Total Capacity is a rating to express the most extreme comfortable working conditions for a given rear derailleur."

Would you really need a 28 though, especially since you've got a 34 up front front? A 34/27 gives about 33" gear which would get you up most stuff without too much trouble. 34/28 is only about 32, so not a great deal of difference.

If you do go for a 28 I'd imagine a 12-28 would give you a more useable range of gears and is still good for nearly 40mph at 120rpm. That's personal preference though, I prefer the spread of gears to be closer together.

 

[jpembroke]

I run an 11-28 SRAM cassette on my 'cross bike for some races with a 105 short cage mech without any problems whatsoever. 27t is supposed to be the maximum but in practice 28t works just fine.

 

[fossyant]

27 - 28 won't make much difference, and you are also increasing the gap between smaller and larget sprockets, so more gear jumps. 34 - 27 should be fine....

 

[jpembroke]

True. Whilst you could change to an 11-28, I don't really see the point. 12-27 should be ideal.

 

[jimboalee]

If the bike NEEDS a new cassette, go for it.

If it doesn't, no need to spend the cash. 34/27 is lower than my 30/23 but not as low as 30/25 ( which will be my next cassette when the time comes ).

 

[Tim Bennet.]

If you look in the gear tables, the switch from 27 to 28 doesn't do much, but the switch from 12 - 11 is a significant step up giving you one more higher top gear.

But why do you want a higher top gear on a hilly sportive? To get it you will effectively be removing one of your gears from the mid range, where they're useful. Or in other words you are switching from a 9 to an 8 speed set up.

 

[jimboalee]

+1 Tim Bennet.

Not many riders use an 11 sprocket, it's there for show on most bikes.

 

[dellzeqq]

+2. By the time I'm out of revs on a 12 sprocket I'm doing over 40. Time to freewheel.

 

[Dave5N]

34- 28? Be quicker to walk.

 

[elvisparsley]

Thanks gang- I already have a 12-27 but I think I was just trying to wriggle out of the inevitable hard work I'm going to have to do by seeking out and lower lower gears. I'll stick with what I have and try to make sure my body doesn't let me down!

 

[dan_bo]

'ere elvis. Fancy coming along for a bit of prep?

 

[andy_wrx]

You can run it on your bike, there are quite a few manufacturers supplying 'sportive' style bikes with a 50/34 and the SRAM 11-28 cassette, with a short cage rear mech

It might be beyond what Shimano specify, but these are big manufacturers shifting a lot of bikes, so it must work.

But yes, as others say, you'll probably not notice any improvement between 34-27 to 34-28 and you'll highly likely never use 50-11, so all you're doing is losing a gear in the middle and introducing bigger gaps.

Specialized for instance did it with the lower-spec Tarmacs last year, leading some people to say they weren't really race bikes with a 50/34 and 11-28 but were really sportive bikes (as well as the Roubaix !) whereas the higher-spec ones came with conventional 53/39.