stykthyn

Ive been scouring the site and I can't find a definitive answer. I have a Peugeot with a nervar crank. Uses the same damn 122bcd as stronglite. No aftermarket rings in this size. Has anyone on a vintage French crankset successfully run a 10 speed chain?
I have DA index 10spd downtube shifters and matching rear mech. Drop outs have been cold set and new wheels fitted. Only piece to the puzzle is the crank. Not opposed to getting a different crank, but would like to keep this one if I can.

Revracer

I run a 10sp chain on a Shimano 600 crank and just compared chainring thickness to my Nervar rings. They are the same. I cannot speak to tooth profile. On my 10speed setup, it will occasionally drop a chain but I think that is more the front derailleur not being happy with the range as it too is vintage (Shimano Golden Arrow).

I have often been tempted by Red Clover Components to get more range out of 122bcd, but have not taken the plunge. Perhaps not helpful here as it sounds you real hope is to leverage the 10speed setup you already have.
122 BCD Conventional Chainring, 37 Teeth

stykthyn

if a ring swap is out there im game. This project started with spare parts in my workshop and has completely escalated. What I really want is to keep the vintage vibe and still run a modern compact drive.

Revracer

I feel like I have been pursuing that for some time and tried the 10speed route to find that I had built a heavy bike (using freewheel). Ultimately I started looking for the 50.4bcd cranks that take the TA Cyclotouriste chainrings. While I am currently setup with a 52-30 chainring on my Nervar crank and a 13-28 freewheel, I think dropping the 52 to a 48 like many of the VO / Herse cranksets will make for more comfortable shifts down. Oddly shifting up is super smooth with a Simplex SLJ front derailleur.

stykthyn

I'll be keeping the slj up front. It seems to have plenty of range. This bike is a tank. It's a pleasure to ride for about 45 minutes. Im completely spoiled with the modern amenities we take for granted on even low end road bikes now. If nothing else a little more money might get this bike there. I love the look of it. Just need it to perform a little closer to its contemporaries. I dont want to ruin any of the stock parts. I do have a spare Stronglite crank with a stripped pedal thread I can experiment with. I may see if it's feasible to flip the inner ring to reduce the distance and possibly file every 3rd tooth inward to help the chain make the transition..

old's'cool

XXcycle used to have quite a range of 122mm BCD chainrings. Now it seems they're down to 2 (44 & 51T).

elcraft

I thought that Nervar used 128 mm BCD chain rings! I recall reading some where that someone successfully altered the bolt opening with a rat tail/ round file to alter the more commonly found 130 mm BCD chain rings. If your Nervar are actually 122 mm rings, then XXCycle is the only purveyor that stocks 122 mm rings.

JohnDThompson 

Most Nervar rings used 128mm BCD, but some used Stronglight's 122mm BCD:

gesta

I’ve currently ridden ~5k hassle free kms using stronglight 105 crankset with modified large chainring paired to srampagnolo 10spd specific derailleurs.

Chainrings are 48-40 and originally there were massive problems with 10spd chain getting stuck between chainrings when shifting chainrings under any amount of power. I modified the large chainring by adding extra layer of material (chemical metal/epoxy filler) to chainring’s inner surface and then sanded/chamfered it to resemble modern 10spd chainring profile.

This way, I did not need to modify the crankarm. Chainring teeth are technically still too wide apart for 10spd chain (8spd ok), but large chainring has a nice inner slope for chain to find it’s place when shifting. Some epoxy did chip off during first few hundred kms (probably due chainrings flexing), but apparently there doesn’t need to be as much added material as I initially thought.

gesta

Long story short - chainring teeth thickness should be about the same from 5spd to 12spd, as chain inner width is not changed*.

Modern chainrings on the other hand, need to be closer to each other to accommodate narrower chain outer width required by narrower rear sprocket spacing.

* 5-8spd chains have 2.38mm inner width while 9-12spd have 2.18mm inner width, which is close enough to work on any number of multi-speed sprockets. Outer width determines chain in-/compatibility with cassettes with different number if sprockets.

more info: Bike gremlin

non-fixie 

I have 122bcd cranks on several bikes. 50/40, 50/37, 52/37. Combined with a 14-28 FW, and a short cage RD, they work well for me.

stykthyn

I'm a hugely visual person. Can you give me a picture?

gesta

Sure.


Epoxy applied

Some filing to do

stykthyn

That's shockingly simple. Thanks!

HTupolev

Good to hear that this sort of thing is viable. I'm putting together a bicycle right now where I intend to use a definitely-not-11-speed triple with an 11-speed chain, and I've been contemplating my "what happens if the chain is able to fall between the rings" options. It doesn't seem to happen when I fiddle with things in the stand, but real usage can be unpredictable.

stykthyn

I am staring at a modern 2015 crank and my spare stronglite. Side by side. Consensus is the 6spd rings are too widely spaced to accommodate a 9/10/11 speed chain. Aside from tooth count which has minimal effect in throw of the chain from big to little the most glaring factor is the size of the spacers for the chainring bolts. Will modern chainring bolts fit?