Bicycle Mechanics - oval chainring help required
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09-25-06, 03:56 AM
Whilst dumpster diving I came across a biked covered with spilt paint, no wheels but all the remaining running gear. aside from the paint spillage it was in exceptional condition.
Whilst dismantling the chain ring to clean off the paint I realised the cogs were oval.
Silly me, I didnt notice beforehand so now I have no idea where the long axis of the oval should be in relation to the cranks.
Usually there is a stamped mark, chain peg or 'lump' on the chainring that lines up with the crank. What make of cranks and chainrings have you got (we can't see them)?
09-25-06, 07:30 AM
Its Shimano, the ring has Shimano Biopace on it and the crank has Mountain LX.
The large ring has a peg, each other ring has a tab, if the tabs and the peg are aligned all 3 rings aligned equally.
There is no mark on the crank that I can intuitively say should be aligned with the peg on the large ring.
OK problem solved.
Found it here http://en.wikipedia.org/wiki/Biopace
All other references pointed to Sheldo browns site but I cannot seem to get access at the moment.
09-25-06, 07:48 AM
The marker on the Biopace chainring aligns with the crankarm, but people have often rotated them to get a different action. Bobby Julich's celebrated O.Symmetric chainrings, for example, are elliptical in the opposite way from Biopace. It all depends on your personal pedalstroke and what you're hoping to achieve with them.
BioPace cranks are highly prized by loaded touring bikers and look for them on E-bay. They command very high prices! 48/38/28 is most wanted and include the BB with the auction so they know what size to replace it with if it's bad. You can buy a new crank set for what these people will pay for a good used BioPace crank. They have been out of production for years and all the old stock is long gone.
09-25-06, 08:54 AM
Sheldon Brown thinks highly of the biopace chainring design for lots of cycling applications. His site is down right now, but there's a good article on biopace chainrings linked at
I think the link is
09-25-06, 08:59 AM
The "peg" is there to keep the chain from wedging between the crank's spider and the crankarm if the chain spills to the outside from a bad shift or poor derailleur adjustment. Therefore, the big ring is always installed with the peg to the outside and aligned with the crank arm.
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