Actually, I've never had to file the spider. BTW, there are also 38T 130 rings, although conventional wisdom is 130 only goes down to 39T. I've mounted these 38T rings on original DuraAce arms with no problems.
Fred Rednor <email@example.com> wrote:
> Avocet/Ofmega and TA also made 41T rings for
> the 144mm BCD. The TA rings are still available
> and reasonably priced. Be aware you may have to
> file the spider slightly for the chain to seat
> fully with the 41T ring.
By the way, that effort will bring your low gear all the way down from 40.5 gear inches to 39.5. (Assuming a 28 tooth big sprocket at the rear.) To me, it does not seem to be a worthwhile modification. Fred "opinionated" Rednor Arlington, Virginia (USA)