wallymann

whats the secret?

seems theres not enough swing in the pivots to take up the chain slack running a 53/39 ring combo.

ive optimized chain length, b-screw position, everything i know to do on the rear mech.

if adjusted to work with the 53 there ends up being slack on the 39. if adjusted to work with the 39 there ends up being insufficient chain length for the 53.

ive resorted to running 42 small rings, but since 39s exist....i have to think it can be made to work!

repechage

Works for me with a 39. What is the freewheel range you are using? Including # of cogs. Small chance the lower spring is toast and or you can reposition the jockey cage to the next spring anchor hole.

wallymann

14-25 custom 8sp cogset. 53/39 rings. total of 25 teetth coverin that range.

whats the max range a c-rec rear mech supports?

Bianchigirll 

I think you're asking the RD to wrap too much chain. there is no spring ( or did the later ones have one?) in the attachment point so all you have is the body / cage pivot.

back in those days guys running 39s front usually had 21 or 23 for the 'easy' gear in the back

anyone know max tooth and wrap for a late gen C-Rec?

according to VeloBase the max cog for a 2gen is 28t and max wrap is 27t. I think you either need a smaller cog in the back or live with the chain being a tad slack

https://velobase.com/ViewComponent.as...d5ad1&Enum=108

wallymann

hmm...i'm only needing 25 teeth of wrap and VB says that it handles up to 27 teeth. and these are both the 2nd-gen c-rec rear mechs, neither of which have springs in the upper pivot.

actually, i think it's a combination of my larger sized rear cogs *and* the goofy tear-drop shape of the upper jockey cage. in order for the tail end of that tear-drop to clear the cluster, i need to thread in the b-screw ALOT. threading in that b-screw so much limits the forward swing range of the upper pivot, eliminating alot of the slack takeup range of the rear mech.

i recall seeing pics back in the day of some pros with "trimmed" c-record mechs. i always figured it was to reduce weight, but now i'm certain it was to accommodate larger rear clusters.

repechage

Part of the problem is the 8 cogs, the geometry of the mechanism as it swings inboard rises, that is why you have the interference. The "mod" of yesteryear was probably indeed to help address this problem. The initial C Record was not designed for 8, but 6 and tolerated 7.

wallymann

yep. my super-record rear mechs have the same geometry, but they're still able to work fine with the same 8spd cogset since the mech doesnt have the teardrop upper cage to foul on the cluster.

no worries, my c-record bikes are generally used for relatively less demanding sorts of riding so i'm OK running the 42 small ring to make it work with this cogset. if it gets hilly enough to where i'll need a 39x25 you can be sure i'll be riding one of my modern bike, and probably with a compact chainset!