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  1. #1
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    Stupid Question on Replacement Chainrings (shimano)

    I decided to stick with the stock ultegra 9sp crankset (~2003) and replace the worn 52T and 42T but there are lots of chainrings to choose from. Original chainrings say "shimano SG A-52" and "A-42". Am I looking for shimano 6500 or 6600, specific part numbers?

    Could I go to 53t (or 54T) and 39T? Would I want to? I already went from 30T to 28T, and that was good.

    We're running 11/23 (sometimes 11/26) cassettes and spin out with the 52/11 descending long medium grade passes.

    I know this is out there but a quick search didn't help, individual cases and all.

  2. #2
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    I switched from 54 to 53 a while back and miss the extra size on those tandem screamer descents. If/when worn, I'll try to find a 54 to replace it. I run 11-28 or 11-32, depending on terrain and mood.

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    Shimano does optimize its chainrings' ramps and pins in sets. Your A-42/A-52 set is designed to work in a triple set-up. If your go to a 39/53or54 set-up, be careful to locate a 39 made for middle duty, and with a matching 53/54. The nominal Shimano 39/53 ("B") setup for doubles will fit, but small-to-middle shifting will be degraded as the 39 doesn't have ramps/pins.

    Does sort of depend on how finnicky you are about shift performance - after all, triples have been around since before ramps/pins - but indexing and expectations have evolved.

    Tom

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    Thanks for bringing up those considerations. I'm thinking a 39 for triple, if it's too low it's easy to change to a 42. And at least a 53 big ring.

  5. #5
    Nigel nfmisso's Avatar
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    Here are some options for you:

    http://sheldonbrown.com/harris/chainrings/130.html

    Your LBS should be able to get the same.
    Nigel
    Mechanical Design Engineer

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    As usual something that sounds as simple as changing ring size can be complicated. Besides the minor shimano issue or non-issue of A-set versus B-set, it turns out that shimano only made a 42T middle chain ring for 9-speed.

    It's possible that an early ultegra 10-speed (6603) middle 39T ring might bolt up and have workable spacing, would also require a matching front der.

    There's also a current cheap shimano 9-speed (2200, below sora) 39T that I couldn't bring myself to buy.

  7. #7
    Clipless in Coeur d'Alene twocicle's Avatar
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    Quote Originally Posted by 2frmMI View Post
    I switched from 54 to 53 a while back and miss the extra size on those tandem screamer descents. If/when worn, I'll try to find a 54 to replace it. I run 11-28 or 11-32, depending on terrain and mood.
    A true "screamer decent" does not require any pedalling. If you need to pedal, it isn't a screamer.

    Most of the current tandem cranksets come with a max 52 chainring which is still plenty when paired with a 11 on the back. We never needed anything larger than a 53x12 and I guarantee that cornering skill is a lot more important to going fast than pedaling @ +35mph.

    I've got the new Ultegra tandem MegaExo cranks (6301/6303) coming - they are 52/39/30. After a late discount I managed to price them at $790 (w/2-BB6700 included) including shipping.

    According to the specs posted on the bikeforums elsewhere, I believe the new Ultegra crankset weight is just a tad less than what the FSA SL-K MegaExo were (being discontinued), and the Ultegra are one of the stiffest crank arms available vs. all FSA which are near the flexiest.

    ie, though they rated the double cranks, these ratings still apply for the tandem sets...

    http://weightweenies.starbike.com/fo...hp?f=3&t=65958

    For flex with 40kg:

    1 ) Shimano Ultegra 2.08mm
    2 ) Time ASX Titan Carbon 2.12mm
    3 ) Shimano Dura Ace 2.20mm
    4 ) Campy Chorus Carbon CT 2.48mm
    5 ) Campy Record Carbon 2.59mm
    6 ) Campy Chorus Aluminium 2.62mm
    7 ) Campy Centaur Carbon CT 2.76mm
    8 ) Campy Record Aluminium 2.78mm
    9 ) Campy Centaur Aluminium 2.99mm
    10 ) FSA Gossamer Megaexo 3.05mm
    11 ) Zipp 300 3.40mm
    12 ) FSA SLK Megaexo 3.41mm
    13 ) FSA K-Force 3.76mm
    Last edited by twocicle; 03-29-12 at 04:44 PM.

  8. #8
    Senior Member diabloridr's Avatar
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    Quote Originally Posted by twocicle View Post
    Most of the current tandem cranksets come with a max 52 chainring which is still plenty when paired with a 11 on the back. We never needed anything larger than a 53x12 and I guarantee that cornering skill is a lot more important to going fast than pedaling @ +35mph.
    Obviously written by someone who's never tried to hold a wheel at 40 MPH.

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    Quote Originally Posted by twocicle View Post
    A true "screamer decent" does not require any pedalling. If you need to pedal, it isn't a screamer.
    I should have checked on the rules with you before posting...
    We love 53 x 11 even on more gentle grades if we get in a little urge to drop the singles. We'll jump and spin way up, often with a bit of screaming. If the singles don't catch us at the jump, they normally can't bridge. If they do manage to hang on, they always love the vortex.

  10. #10
    Clipless in Coeur d'Alene twocicle's Avatar
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    Both responses do not apply to the true definition of a "screamer decent" and I'll take bets you will brake more than pedal on those.

    Sure if you are jamming 40mph on a lesser grade that is another story, but irrelevant to suggest as a general recommendation that everyone should be compelled to follow that example.
    Last edited by twocicle; 03-29-12 at 10:21 AM.

  11. #11
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    I always thought a screamer decent was the point at which the stoker loudly voices her displeasure at the downhill speed.

  12. #12
    Clipless in Coeur d'Alene twocicle's Avatar
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    Quote Originally Posted by Sprout97 View Post
    I always thought a screamer decent was the point at which the stoker loudly voices her displeasure at the downhill speed.
    Now you're getting the gist of it.

    Screamer descent definitions also include:
    - my eyes were bleeding
    - my cheeks (face) started flapping (not to be confused with puckering on the other side)
    - our tires were scrubbing around the corners
    - we passed a Ferrari 308 (yours truely)

    diabloridr, correct, couldn't care less about "needing" to flail at the pedals in order to suck wheels @ 40mph on a tandem, but another topic as it has zero to do with screamer descents.

  13. #13
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    Quote Originally Posted by diabloridr View Post
    obviously written by someone who's never tried to hold a wheel at 40 mph. :d



    We had to pedal to stay in touch with a faster (heavier ) team at 50mph, sure glad we had a 54t to close the gap!
    Last edited by teamdonterri; 04-07-12 at 08:13 PM.

  14. #14
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    Well, OK, one last effort to talk to twocicle. Why is your definition of anything THE definition. Why are you not "getting the gist of it". Any old high speed descent fits most of your points,single or tandem. What sets the "tandem screamer" apart is something unique to tandem, and I'll maintain that a moderate descent with the tandem spinning out in 53/54 - 11 is the true screamer. Ask you single bike friends what makes a tandem scream. My best buds have learned to watch for the jump, 'cause they know it is a very narrow window or they're off. Yahooooo!

  15. #15
    Clipless in Coeur d'Alene twocicle's Avatar
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    Quote Originally Posted by 2frmMI View Post
    I'll maintain that a moderate descent with the tandem spinning out in 53/54 - 11 is the true screamer.
    Yeah, wahoo.
    Last edited by twocicle; 04-08-12 at 01:14 PM.

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