Advertise on Bikeforums.net



User Tag List

Results 1 to 9 of 9
  1. #1
    Senior Member
    Join Date
    Oct 2001
    Location
    Arusha, Tanzania
    Posts
    124
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    4 arm vs 5 arm cranks?

    I noticed fubar5 's crank is 4 arm and I have been wondering about mine. My mtn bike has 4 arm and after 18 months the middle chain ring has bent 3 times. At first I thought I had somehow banged it on a rock or log. Last week it got slightly bent and I am pretty sure I didn't bang it. I am pretty good about not cross chaining. It is STX shimano and the chainrings are aluminum.

    Are chainrings on four arm cranks prone to bending?

    Can I bend them just by hammering?

    Can i bend them by changing gear underload ( well maybe it has happened once or twice) ?

    Fatigue on the chainring?

    Slightly bent,
    Mzungu
    Last edited by Mzungu; 03-10-02 at 11:59 PM.

  2. #2
    0^0 fubar5's Avatar
    Join Date
    Feb 2001
    Location
    Rolla, MO
    My Bikes
    Redline Monocog,Surly Crosscheck, Lemond Reno
    Posts
    4,056
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I was just looking at the all the cranks at Pricepoint, and the only cranks that have 5 arms are Race Face, not even the Shimano XTR had 5.


    Just a little info bomb.
    Booyah!!

  3. #3
    feros ferio John E's Avatar
    Join Date
    Jul 2000
    Location
    www.ci.encinitas.ca.us
    My Bikes
    1959 Capo; 1980 Peugeot PKN-10; 1981 Bianchi; 1988 Schwinn KOM-10;
    Posts
    14,819
    Mentioned
    6 Post(s)
    Tagged
    0 Thread(s)
    Because the chainrings on a 4-arm spider have longer unsupported arcs than those on a 5-arm of the same BCD, they may well be slightly more susceptible to warping. After one of my admittedly somewhat heavy friends bent a TA Professional (3-bolt) chainring, he replaced the crankset with a 5-bolt Stronglight, and I put the TA set on my wife's bike, a much less demanding application.

    The new 4-arm designs are yet another stupid fad foisted on the bike-buying public by the manufacturers, to render their 5-arm chainrings and spiders obsolete, and perhaps to save 20 percent on the cost of bolts. Simple physics tells us that, for a given total weight, a wheel with more spokes is stronger than one with fewer. On my mountain bike and road touring bike, I plan to stay with a 5-bolt 110/74mm system as long as I can.

    The wonderful thing about standards, such as BCDs and bolt counts, is that there are so many from which to choose!
    "Early to bed, early to rise. Work like hell, and advertise." -- George Stahlman
    Capo [dschaw'-poe]: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger, S/N 42624
    Peugeot: 1970 UO-8, S/N 0010468
    Bianchi: 1981 Campione d'Italia, S/N 1.M9914
    Schwinn: 1988 Project KOM-10, S/N F804069

  4. #4
    Senior Member
    Join Date
    Oct 2001
    Location
    Arusha, Tanzania
    Posts
    124
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Originally posted by fubar5
    I was just looking at the all the cranks at Pricepoint, and the only cranks that have 5 arms are Race Face, not even the Shimano XTR had 5.
    Hmmmm. I thought this bike was just trying to save money on the cranks. All the "old" bikes in my stable are 5 arm.

    New question. Does this mean i am stuck forever and ever with 4 arm cranks?

    four armed,

    Mzungu

  5. #5
    New to bikeforýms.net
    Join Date
    Jan 2001
    Posts
    2,202
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I just thought about something........once I was camping and I had my P.3 with me, and I went to ride it and the front rings were loose.......so I went down and grabbed them and found out that all the bolts were loose! dont know how that happend because I had been riding it the day before......maybe the underwear gnomes loosend the bolts while I wasnt with my bike!

    Originally posted by fubar5
    I was just looking at the all the cranks at Pricepoint, and the only cranks that have 5 arms are Race Face, not even the Shimano XTR had 5.

    I bet that helps him alot! haha
    Last edited by KleinMp99; 03-13-02 at 04:28 PM.

  6. #6
    0^0 fubar5's Avatar
    Join Date
    Feb 2001
    Location
    Rolla, MO
    My Bikes
    Redline Monocog,Surly Crosscheck, Lemond Reno
    Posts
    4,056
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Have you tried steel chainrings? I think Nashbar has some.
    Booyah!!

  7. #7
    Senior Member
    Join Date
    Oct 2001
    Location
    Arusha, Tanzania
    Posts
    124
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I guess I will try to find steel rings. Nashbar didn't have steel for 4 post rings just for five. It would be nice to know if others experience this or maybe i have another problem.

    Erik

  8. #8
    Senior Member bikerider's Avatar
    Join Date
    Sep 2001
    Location
    Toronto, Canada
    Posts
    376
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Originally posted by Mzungu
    I noticed fubar5 's crank is 4 arm and I have been wondering about mine. My mtn bike has 4 arm and after 18 months the middle chain ring has bent 3 times. At first I thought I had somehow banged it on a rock or log. Last week it got slightly bent and I am pretty sure I didn't bang it. I am pretty good about not cross chaining. It is STX shimano and the chainrings are aluminum.
    The ring will be weaker every time you bend it and bend it back. It does sound a little strange since you wouldn't keep striking the middle ring on something and not the big ring. How gradual or sharp is the bend and how did you come to notice it? Are you sure it's not a bent crank spider (of course this should affect the large ring also)?

    Are chainrings on four arm cranks prone to bending?
    Obviously they have longer unsupported spans but most impacts sufficient to bend chainrings in most cases would bend 5-bolt as well as 4. IOW, I don't think this is the root of the problem.

    Can I bend them just by hammering?
    I assume you mean pedalling hard (as opposed to the hammering you would do to get the ring back into the original shape ;-) )? I doubt it was what bent it originally, but who knows?

    Can i bend them by changing gear underload ( well maybe it has happened once or twice) ?
    Again, I doubt it was the initial cause but who knows?

    Fatigue on the chainring?
    The problem is that you have permanantly deformed the metal repeatedly and subsequently have weakened it - maybe enough for minor things to bend it again. Definitely get a new ring after you rule out a bent crank spider. Don't worry about getting steel, just get something! I just hope your chain doesn't 'skip' on the new ring!


    Slightly bent,
    Mzungu
    Sounds painful!
    Last edited by bikerider; 03-17-02 at 12:45 AM.

  9. #9
    Senior Member bikerider's Avatar
    Join Date
    Sep 2001
    Location
    Toronto, Canada
    Posts
    376
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Originally posted by John E
    The new 4-arm designs are yet another stupid fad foisted on the bike-buying public by the manufacturers, to render their 5-arm chainrings and spiders obsolete, and perhaps to save 20 percent on the cost of bolts. Simple physics tells us that, for a given total weight, a wheel with more spokes is stronger than one with fewer. On my mountain bike and road touring bike, I plan to stay with a 5-bolt 110/74mm system as long as I can.

    The wonderful thing about standards, such as BCDs and bolt counts, is that there are so many from which to choose!
    I couldn't agree more. I still use 'standard' (how's that for ironic) spacing for my beater bike and my 'on-road' MTB. I also have picked up a few old forged 110/74 crank arms as spares for the future. I just hope I can get rings in 10 years.
    Last edited by bikerider; 03-17-02 at 03:32 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •