Does chain length need to be increased for new crank?

Discussion in 'Cycling Equipment' started by jojoma, Aug 22, 2014.

  1. jojoma

    jojoma New Member

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    I want to go from a 50/34 to a 53/39 chainring setup. Will the current length of chain accommodate the larger rings?
     
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  2. dabac

    dabac Well-Known Member

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    Depends on what the current chain length is. If it was sized tight before it'll be too short now. If it as sized generously before it might still be OK. But why change? The current crank ought to let you put the power down well past 30 MPH already. Any faster than that, I'm well content to coast, unless I'm on the brakes already.
     
  3. mpre53

    mpre53 Well-Known Member

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    There is no real correlation between crank size and how fast you can go, unless you have the power to turn the 53 on an 11t rear cog at 110-120 bpm cadence. If you're running a compact with a cassette that has an 11 as the smallest cog, and you're spinning out at that cadence, then you need to change to a standard crank. Or explore the cheaper option of replacing the 50/34 rings on your compact with a 52/36 set. Both sets of rings should fit on a compact crank.

    If you think that a 53/39 gives you more "pro" cred than a compact, you're spending money for the wrong reason. On the other hand, if you rarely use your 34 and think that a 39 will be more useful on the flats and rollers, it's an option worth considering. But you can still explore the cheaper option of replacing the 34 with a 36, and run 50/36 on your existing crank, before you spend the money to make the change.

    Running 50/34 or 50/36 will also allow the average rider to run a tighter cassette with fewer gaps in the mid-range, which, lets face it, is where most of us are for the bulk of our rides. An 11-23 with a 50/34 gives me everything I need for where I ride.
     
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  4. jojoma

    jojoma New Member

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    Thanks. The 50/34 (with 11-28) was on an entry-level TT bike I bought last year. I find that I spin out the 50/11 on the pedaling-downhill portions of a TT. Not sure why they put a compact on a TT frame. Not too many steep hills in a normal ITT. Unless it's a pure hill climb TT of course.
     
  5. swampy1970

    swampy1970 Well-Known Member

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    When you're on the tri-bars, you pedal whatever you can pedal and after that you have to come out of the aero tuck.

    Pro-cred? Huh? What kind of statement is that? If you can't stay comfortable on 50x11 then it's an easy decision to move to a 53 or larger chainring if the course depends on it.

    I used to run an odd combo of 56/52 upfront and 11-19 8speed rear back in 96. The 52x19 would, with a few watts, allow you to get up most grades on a semi hilly time trial course and the 56x11 would allow you to stay in the aero bars much longer than others could on the way down the hills. When you have the monster chainring up front, the gaps between useable gears are smaller. Tell me how it feels when you're chugging along on the flat at 29mph and you go from the 12 to 11 sprocket - then realize that going from 56x13 to 12 doesn't feel so leg snappingly bad. I can't recall a worse feeling in a TT that when you're f**ked out of your brains towards the end and you couldn't turn the 13 fast, the 12 felt wrong and you jammed in the 11 and the entire world just locked up. Going through those gears at the end off a TT was like "I'm in too small a gear" to "it's hard but the road is a bit downhill so I need something bigger" to "Jesus H effing Christ, did my axle just snap? If so, why am I not slowing down - oh, I just changed into the 11 sprocket". Avoid that 11 to 12 jump if at all possible as it's a leg snapping, hope draining monster of a jump. If it's a TT specific bike, do a 53 or 54x12 rather than 50x11

    The 11 should be called the Einstein Gear - because relative to everything else, it feels like you're going the speed of light yet pedaling so slow that things don't seem right.

    Did I need 56x11 for the flat? Was I a TT monster? Nope? I was a 140 something pound road guy that could TT s bit when his head was in the right place. On those lumpy TT's I'd often remain even with guys on the flat that I'd take chunk of time back on the slight downhills because they'd have to come out of the aero TT bar tuck in 53x12 (because that's the gear that "people" said you needed as a top gear) when I had that monster top gear. Of course I didn't want to tell them that I'd done some very simple math to calculate the expected top speed at about 110rpm. I was never a very fluid pedaller so that was my limit in the position shown below.

    To the guy that started this topic - gear for the downhills that you regularly encounter on your TT's at a pedaling rpm that'll allow you to stay in the aero bars. If you have to come out of the aero tuck mid TT because of the gearing, add a few more mph and gear for that. TA make some very nice chainrings. Make the bottom gear suitable for not having to mash a gear out of the saddle. The gears in between will sort themselves out. Tony Martin used a 58 ring with an 11-32 cassette in the final TT of the 2014 Tour so he could stay in the big ring longer on the hills. That gearing suited him. Chose a gearing that suits you.

    The gearing I picked worked on the old round tube frame with the cranks that had the square taper bottom brackets where you could custom chose bottom bracket length. Your ability to chose the inner ring of your choice may be compromised by whatever you can fit on your frame.

    Back when I was a lad and sheep were scared...
    [​IMG]

    A nice selection of chainrings that may help...

    http://www.peterwhitecycles.com/chainrings.asp
     
  6. mpre53

    mpre53 Well-Known Member

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    Quote:
    Originally Posted by jojoma .
    Thanks. The 50/34 (with 11-28) was on an entry-level TT bike I bought last year. I find that I spin out the 50/11 on the pedaling-downhill portions of a TT. Not sure why they put a compact on a TT frame. Not too many steep hills in a normal ITT. Unless it's a pure hill climb TT of course.


    Ah, a TT bike. You didn't mention that the first time.[​IMG]

    50/34 and 11-28 does seem a bit odd. Downright weird, in fact.
     
  7. Felt_Rider

    Felt_Rider Active Member

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    An easy solution if money is a constraint and if the OP's crankset will allow is just get 52/36 chain rings.

    I have a Quarq/SRAM 110 BCD crank with 52/36 rings and on flat course do quite well. Actually I like it pretty good because on one of my course there is a section about 4 miles long with some sharp steep rollers. I use a 11-28 cassette and with the 36 / 28 ratio I can manage to get over those without getting too bogged down. I am a notorious big gear mashers as well with a much slower cadence than most and have yet to spin out with the 52 / 11 ratio. If anything I just need to teach my legs to spin faster.
     
  8. swampy1970

    swampy1970 Well-Known Member

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    Not as odd as 58/42 with an 11-32 cassette and long arm rear mech for a fairly flat TT...

    [​IMG]

    But when you're probably the fastest TT rider in the world, you can run whatever gearing you like and still smash everyone.

    [​IMG]
     
  9. dabac

    dabac Well-Known Member

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    So basically a version of half-step gearing?
    The tooth counts look weird but the ratios makes sense.
     
  10. swampy1970

    swampy1970 Well-Known Member

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    It wasn't meant to be 'half step' if you mean changing between the chainrings to get a smaller difference in gear rather than making a change on the cassette. This was back in the days before chainrings where pinned and ramped. The front shifts were quick but I'd only make the shift up front if really needed.

    I used that gearing because there were times I needed that top gear and times when the bottom gear was just small enough. The difference between the 56 and 52 aint really all that big but the chainline in 56x19 was crap and the Campag sprockets made odd noises that didn't feel me with confidence when out of the saddle on the flex-a-noodle bike, so an inner ring was added.
     
  11. cyclintom

    cyclintom Well-Known Member

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    Most people cannot turn a 50-11 up on flat ground. That the OP wants to increase his gearing because he can spin out on downhill sections isn't saying a great deal. If you have a downhill section you have to ride up it in the first place and a 34 11-speed 28-11 is about all anyone can handle unless they're 21 and growing into pro-performance. On those sorts of courses you win on the uphill portion and not the downhill.
     
  12. Jesica Miller

    Jesica Miller New Member

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    so much new information.
     
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