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  1. #1
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    Compact with SRAM Force - How big cassette?

    Want to buy a new cassette for my training wheels so I don't need to switch over. Current setup is (stock) SRAM compact front (50/34) with a Force rear derailleur on a 12-25.

    I was thinking it might be nice for the spare cassette to be useful for bigger climbs, say 27 or 28 rear. The Shimano Tiagra 10-speed cassette is way cheaper than anything else and barely heavier than my SRAM. Available ratios are 11-25, 12-28, and 12-30. The 28 is 11% bigger and the 30 is 20% than my current setup.

    1) Will either the 12-28 or 12-30 work with the current derailleur (Force only comes with short cage)?

    2) Is there any reason why the bargain Tiagra 10-speed cassette is a particularly poor choice?

    Many thanks.

  2. #2
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    if it were me, I'd go for the 12-28 if I expect to climb anything longer than 2 miles at 7%+.

    and 12-30 if expecting 7%-10%+ for anything longer than 5 miles.

    Makes very little sense to use a compact with a 12-25 cassette unless all you do is 2%-3% rollers all day long and nothing else.

  3. #3
    So. Calif.
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    You need to lookup your rear derailleur's "chain wrap" spec at SRAM website.

    Chain wrap = (difference in # chainring teeth) + (max difference in # cog teeth).

    Eg, for the 12-30 cassette, the total "wrap" required would be
    = (50-34) + (30-12)
    = 34

    A 12-30 is going to have some huge gaps in gearing, probably fine for touring and rec riding, but would be very annoying for me.

    I'd probably install a new longer chain if you went to a 30t cassette.

    Unable to answer your Tiagra question.

  4. #4
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    Thanks, guys. I was definitely thinking of the 12-28, not the 30. The 11-25 hasn't been a problem for most of my riding, although my fat @ss would have appreciated a little help on a few local hills.

    And thanks for making me look this up myself. I found this 2010 guide
    http://cdn.sram.com/cdn/farfuture/SB...nual-rev-a.pdf
    If I'm reading page 6 correctly, the max rear sprocket is a 28T and the max chain wrap is 33T, so the chain wrap (50-34) + (28-12) = 32T which is less than the 33T spec'd. Or I could even go 11-28 (SRAM has that combo).

    So 28 it is. Now I gotta decide if I want to spring the extra bucks for a SRAM or Shimano 105 or Ultegra for at least twice the cost of the cheapest Tiagra price ($35). Opinions welcome

  5. #5
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    For future reference, here's drive train compatibility chart from SRAM
    http://cdn.sram.com/cdn/farfuture/tG...components.pdf

  6. #6
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    You might be able to get that Force RD to work right with a 30t rear cog.

    They do make the Force RD in a midcage now which gets you up to 32 in back. Since it's your training rig, an Apex or Rival midcage works. They are $60-90 iirc. You are then free to choose whatever cassette you want to run that day.

    I run an 11-32 on the back with an X.9 10 spd RD. There are a lot of long climbs around here. For flatter ride in the valley, I do put the 11-27 on. I don't do that too often because I like my DH..
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

  7. #7
    'brifter' is a lame word.
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    Quote Originally Posted by tom_h View Post
    You need to lookup your rear derailleur's "chain wrap" spec at SRAM website.

    Chain wrap = (difference in # chainring teeth) + (max difference in # cog teeth).

    Eg, for the 12-30 cassette, the total "wrap" required would be
    = (50-34) + (30-12)
    = 34

    A 12-30 is going to have some huge gaps in gearing, probably fine for touring and rec riding, but would be very annoying for me.

    I'd probably install a new longer chain if you went to a 30t cassette.

    Unable to answer your Tiagra question.
    chain wrap capacity is one half of what he needs to know. the other half is 'max cog size'. don't forget that...on a short cage derailleur the 30 might work. SRAM specs the derailleur for 28t max, which means a xx-30 cassette might (as in a big maybe) work but you'd have to try it on your bike to see. it all depends on the length of the derailleur hanger.
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  8. #8
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    12-30 works with short cage SRAM, as long as you don't go big-big.

  9. #9
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    Personally, I don't really like either the 12-28 or the 12-30 Tiagra cassettes. With them you lose the 16t cog, which some ppl find to be pretty useful.

    A 12-28 SRAM cassette wouldn't any better, 'cuz you keep the 16t but then have that lame jump from 19t to 22t. Derp.

    If it was me, I'd move up to a 105 cassette (price difference is like 25-30 bucks over Tiagra) and go with a 12-27, if possible. It's the same jumps as your current 12-25 'sette throughout most of the range, just a slightly wider spread on the last couple of climbing gears.

    Of course, if you don't think 34/27 is low enough as a bottom gear, then it's a no-go. But I think you'd be hard-pressed to tell the difference between 34/27 and 34/28, if you think the latter is low enough.

    SRAM also makes a 12-27, but I forget if they make a cheap one.
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  10. #10
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    I'm running an 11-28 10 speed cassette on my bike with the compact cranks. Not had any problems with it....

  11. #11
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    Quote Originally Posted by SystemShock View Post
    Personally, I don't really like either the 12-28 or the 12-30 Tiagra cassettes. With them you lose the 16t cog, which some ppl find to be pretty useful.

    A 12-28 SRAM cassette wouldn't any better, 'cuz you keep the 16t but then have that lame jump from 19t to 22t. Derp.

    If it was me, I'd move up to a 105 cassette (price difference is like 25-30 bucks over Tiagra) and go with a 12-27, if possible. It's the same jumps as your current 12-25 'sette throughout most of the range, just a slightly wider spread on the last couple of climbing gears.

    Of course, if you don't think 34/27 is low enough as a bottom gear, then it's a no-go. But I think you'd be hard-pressed to tell the difference between 34/27 and 34/28, if you think the latter is low enough.

    SRAM also makes a 12-27, but I forget if they make a cheap one.
    This is very helpful. I hadn't really considered the ratio steps all the way through the range. Should make a little spreadsheet and post the ratios.

    Also agree about 27 vs. 28 max. Truth is, I almost never even use my smaller chainring. My only real reason for trying something else is that I don't want to switch cassettes to switch wheels, and if a cassette must be bought, then it might be nice to add a little capability. Thx.

  12. #12
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    Quote Originally Posted by AJ88V View Post
    For future reference, here's drive train compatibility chart from SRAM
    http://cdn.sram.com/cdn/farfuture/tG...components.pdf
    Whoa. Figuring out that chart is a challenge, especially the shifter/derailleur compatibility. Only by already knowing/understanding what's compatible was I able to figure out how the chart works...
    ... 'cuz that's how I roll.

  13. #13
    'brifter' is a lame word.
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    Quote Originally Posted by skinewmexico View Post
    12-30 works with short cage SRAM, as long as you don't go big-big.
    ^ another example of crap advice ^
    there is NO way you can be sure this will work on every bike, AND not being able to go big/big means it doesn't work. sorry, but you're doing it wrong.
    guess i'm back to my old self...
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  14. #14
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    Quote Originally Posted by aclinjury View Post
    Makes very little sense to use a compact with a 12-25 cassette unless all you do is 2%-3% rollers all day long and nothing else.
    I use an 11-23 for the +/-6% stuff. 50x12 is too short...
    They do anything just to win a salami in ridiculous races. I take my gear out of the car and put my bike together. Tourists and locals are watching from sidewalk cafes. Non-racers. The emptiness of those lives shocks me. It was the illest of times, it was the dopest of times. And we looked damn good. Actually the autobus broke down somewhere on the Mortirolo.

  15. #15
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    Quote Originally Posted by cxwrench View Post
    ^ another example of crap advice ^
    there is NO way you can be sure this will work on every bike, AND not being able to go big/big means it doesn't work. sorry, but you're doing it wrong.
    guess i'm back to my old self...
    How about this, your Highness? 12-30 works on a Cervelo RS with a short cage SRAM. With a longer chain, it might make less noise in the big-big. I found it to be an acceptable weekend alternative when I had a ride with some big hills. Better? I don't want to be the person who makes you screw up your new found reputation as a nice guy.
    Tis the season for all of us not hard enough to play to belittle those not hard enough to win. We are a funny lot. - dave @ November Bicycles

  16. #16
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    Quote Originally Posted by cxwrench View Post
    ^ another example of crap advice ^
    there is NO way you can be sure this will work on every bike, AND not being able to go big/big means it doesn't work. sorry, but you're doing it wrong.
    guess i'm back to my old self...
    We're glad your are back.

    I almost never go big/big because I hate the chain noise. It' odd as I like things as quiet as possible on my road bike. However, on my mtb, I like the loud "angry bee" buzz of my Chris King hub. I like the loud grip shift click too.

    I do agree with you that it should be able to shift big/big without rippping the RD hanger off. Sure, one may be like me and rarely use it. If you can shift into it, it should be there.
    It's a fire road.............
    I'm on a road bike..........

    They have enough in common to blast down it.

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