Bicycle Mechanics - Third Chainring on a Campy SR Crankset?

I have a Campy Super Record crankset and BB on my '81 Bruce Gordon light touring bike. I need lower gears than the 42 tooth lowest ring will give me, so am considering ading a third chainring. Can anyone suggest a suitable chainring and/or replacement spindle (or whole bottom bracket assembly) to do this addition? I'd like to keep the equipment in period if possible. Thanks!

I've done this upgrade on a Shimano equip. bike before, I assume that it will be the same for Campy. Not only you will need to replace the BB for a longer one but also, you need to replace the front dérailleur for one design for triple and also the rear dérailleur with one with longer cage. This is an expen$$ive upgrade. Compact crankset could be a cheaper solution, a 50-36 or 50-34,.

If I understand your question, you currently have a double crank, and want to add a 3rd ring to that same crank? If so, it can be done. Its called the "tripilizer" Or you could just get a real triple crank, or as already mentioned, a compact double.

http://www.sheldonbrown.com/chainrings.html#135

If 3 teeth will do it for you Stronglight used to make a 39-tooth ring that fit those cranks.

If 3 teeth will do it for you Stronglight used to make a 39-tooth ring that fit those cranks.

41 tooth is the smallest you can fit on the old 144bcd SR crank. Campy made some of those cranks as triples and I see them on eBay every now and then. Look at the catalogues on this (http://www.campyonly.com/history/catalogs.html)
site to give you the spindle length required

Klein used to drill and tap SR crankarms to fit a third chainring. I don't know of a 144 triple conversion chainring but perhaps they exist.

There is such a thing as a "tripilizer" for the 144 BCD cranks as forensicchemist mentions above, at least there is for Nuovo Record cranks, which are 144 BCD. But the SR derailleurs likely don't have the capacity to handle a triple, so that's another thing to consider.

I should have scrolled up instead of down on that link...

41 tooth is the smallest you can fit on the old 144bcd SR crank. Campy made some of those cranks as triples and I see them on eBay every now and then. Look at the catalogues on this (http://www.campyonly.com/history/catalogs.html)
site to give you the spindle length required

Wrong.

I used to sell the Stronglight 39-T (144 bcd) rings in my shop. They were drilled out and looked cool, but most inportantly they gave you those last 3 teeth and they fit Campy NR & SR perfectly.

A 39 tooth chainring is what I'd prefer to install, and add a couple of larger freewheel sprockets. I guess I'll just keep my eyes open for old Stronglight cranks!

Thanks, everybody!

Are you sure rmfnla?
39t x 25.4/2 = 495.3mm circumference/ PI = 157.7mm diameter

With a 144mm BCD, this gives 13.7mm total difference in diameter between the centre of the chain and the centre of the chainring bolts. Slightly less than 7mm difference in radius, I don't think this can work.

With 135mm BCD, the total difference is 22.7mm, giving just over 11mm radius difference, still quite tight.

Repeating the calcs with 41t and 144mm BCD gives 21.7mm total difference, which almost matches the difference of a 39t 135mm BCD chainring.

A 39 tooth chainring is what I'd prefer to install, and add a couple of larger freewheel sprockets. I guess I'll just keep my eyes open for old Stronglight cranks!

Thanks, everybody!

Watch eBay for a Stronlight 99 triple with drillium chainrings. They're not as finely finished as your SR crankset, but they're beautiful!

I'm thinking about doing the same thing with my PX10. it has a SR crank and NR derailers now. I want to swap the crank for a stronglight 99 triple and get a last generation Rally RD. The last generation Rally is really a long armed Victory and it's a superior derailer. The NR front derailer will work with a triple.

Are you sure rmfnla?
39t x 25.4/2 = 495.3mm circumference/ PI = 157.7mm diameter

With a 144mm BCD, this gives 13.7mm total difference in diameter between the centre of the chain and the centre of the chainring bolts. Slightly less than 7mm difference in radius, I don't think this can work.

With 135mm BCD, the total difference is 22.7mm, giving just over 11mm radius difference, still quite tight.

Repeating the calcs with 41t and 144mm BCD gives 21.7mm total difference, which almost matches the difference of a 39t 135mm BCD chainring.

Pretty sure, but it's been years and as you know (or will find out) the memory will play tricks.