mixing chain rings
 

I want to put a 39t round inner ring on my oval biopace crank set.The bcd is identical.Is that acceptable?Can I expect any problems?The original ring is 42t and I could use the help on the hills.

In the days when oval/biopace rings were common it wasn't unusual to find them that way from the factory. I still have a Sun Tour labled crank that ismoval, oval, round on the big ring and have put together sets will mixed rings without problems. Roger

Not unless you are in love with the Bio-pace rings.

Ive never had a problem when replacing biopace with a normal chainring.

40T 130BCD Biopace rings are rare, but sometimes come up for sale. A cassette swap could help, too.