puchfinnland

I got a 42-52 and I swear I saw a 39 somewhere,

Is this correct?
Trying to do something to get me arse up the hill after photogravity.

(Now how long will it take to see that funny picture with the mounting points outside the cogs?!)

Ex Pres 

41t is smallest possible, but 42t is the most common you'll see

repechage

And don't try to use a 41 with an older Regina or Reynold chain, the side plates are too big, they will hit the spider arm tab between the rings.

Homebrew01

Put on a compact and off you go. Sell the 52/42 on Ebay

rhm

The 39T you saw was probably a Shimano 130 bcd 39-52 crank, like an Ultegra or something.

I have seen photos of some interesting workarounds where people have drilled new holes in a smaller ring, getting alarmingly close to the teeth. It looks like a lot of work for very little benefit. Making your freewheel bigger by one or two teeth makes a bigger difference in your gearing than reducing your chain wheel by the same amount.

Italuminium

Campy 135 BCD is min. 39., so that could be campy as well. Shimano can go down to 38, with 130 bcd.

Anyway, Sheldon got us all covered.

https://sheldonbrown.com/cribsheet-bcd.html

ThermionicScott 

I imagine the worst part was getting beat up the hill by a guy with an IGH.

smontanaro 

I thought someone on CR manufactured a 40T ring for 144BCD. Wasn't a lot of spare meat as I recall. Ah yes, here it is:

https://groups.google.com/d/topic/cl...6Wo/discussion

I suspect you will have to subscribe to view it. I've attached the one image that Google Groups will show at the moment.

photogravity

That is EXACTLY why puchfinnland is asking about the smallest cog.

As smontanaro mentioned, you can go to 40, but it is not recommended. 41 is pretty much the limit on a 144BCD.

Pars 

I thought there was someone that would drill and tap a NR crank for an inner 74BCD or something like that ring?

photogravity

I have heard of that being done also. I know some of the folks on the CR list have a tool to do that.

cudak888 

The fact that current chains work with 41t rings mounted on such cranksets is a fluke. A 144bcd crankset designed for 41t rings will have a step on the spider arm to clear the chain. Crankarms without this feature were originally intended to use nothing smaller than a 42t - though they can have said step machined or filed into the spider arm to accept 41t rings properly.

-Kurt

repechage

For a triple. Campagnolo made some specifically this way and others just machined the spider arms. One can tell a "factory" part from an aftermarket modification by the milled flutes in each arm, on the Campagnolo issued part the flutes stop short of the fastening hole, on the aftermarket efforts the threaded hole stops in the flutes. Campagnolo, Galli and probably a few others made the extension bolts to mount the inner ring. I forgot what was the smallest Campagnolo offered, 36 comes to mind. Aftermarket work could be different of course. Bob Freeman of Elliot Bay Cycles in Seattle was known to have done or sourced a number of modifications.

Pars 

^ Looks like he still does?

https://www.flickr.com/photos/8379107...7622574585267/

jeirvine 

Maybe not - the pics are from 2007. I emailed him about the bolts and never heard back.

Pars 

Hence the ? Was kinda expensive then also ($160?). Including chainring (TA).