vintage Chainrings question
 

(long time reader, first time poster)

I bought an old road bike, handbuilt Roberts form around 1975. It's all dura ace and campy nuovo record and very nice.

But it has been geared pretty oddly and is a nightmare on anything not dead flat. it's 13-20 at the back (5 speed) and 55-44 on the front. (170mm cranks and 27-1 1/4 wheels)

at the top end it's fine but at the bottom I'm struggling, especially as it's not keen to go to the lowest gear at the back. So I have a couple of questions ( the chainrings are all DA, with no pegs or teeth to lift the chain):

If I swapped the inner chainring to a 38 or 40 would I be able to shift to the 55 or would the step be too big? and would I need to swap the 55 as well? I'd rather not as it looks pretty cool. I'm guessing the front derailer might not handle that? (it's campag)

If I buy a modern set of chainrings will they fit the 5 speed chain, or how do I know what will fit?

If I buy NOS, where is a good source of chainrings.


Is there a better way to sort this? the rear derailier doesn't look like it would handle a much larger rear sprocket, i'm not sure changing the crank arms would work with the frame size.

Thanks in advance

Well congrats on the find first of all. Sounds like you've found a bike that was set up for crit racing and/or time-trials with those gears. As far as chainrings go, I'm pretty sure that your crankset is going to be 144bcd (you specified what the rings are, but what model crank is it?), so you simply will not be able to find a 38 for the inner chainring. If you are extraordinarily good at tracking down vintage parts, you may be able to find a 40 tooth, but I think these are becoming uber-rare, so most likely a 42. Personally, I would replace the outer chainring with a 52 or a 53. You'll also have to do some looking around for a five speed freewheel but yes, you should be able to run a bigger rear cog, but it sounds like you will need to do some adjustments in regards to shifting. Stuff from '75 is a few years before my entry into bike mechanics, so I may be off slightly, but don't worry....there will be lot's of advise here!

I think they are 130 BCD
 

I think it's actually a 130 BCD, looks to me like this one but without the outer chain guide
http://www.sheldonbrown.com/shimano1973/pages/da6.html

I think this is it
http://www.velo-pages.com/main.php?g...geViewsIndex=1

If the chainrings are DA I assume the crank is too. So, it should have a 130 mm bcd unless Shimano also used the Campy 144 mm bcd back that far.

If it has a 130 mm, you have a lot of choices as it can take down to a 38T chainring and that bcd is very common. If it's really 144 you have little to choose from.

some photos

http://www.flickr.com/photos/mralistair/5564550316/
http://www.flickr.com/photos/mralistair/5564552180/
(a new seat is being considered and I'm looking for a darker grey bar tape)

hillrider:
excellent, so will ANY 130 bcd chainring fit? and work with the chain?

eg this one?
http://cgi.ebay.com/Shimano-Ultegra-...item4cf61bb16b

or
http://cgi.ebay.com/STRONGLIGHT-DURA...item3cb579f792

It looks, according to the Shimano literature provided, that it is indeed compatible with a 39 tooth chainring, good news! The one thing I would say is because you can still get unpinned/unramped chainrings (such as Sugino), I would stick with them...unless anyone can confirm that modern chainrings will work satisfactorily with the older front derailleur. By the way, I haven't seen a BigTrak in a looooooooooooooooooooooooooooooooooooooong time!!!! Nice vid!

That's a nice looking bike, mralistair.

Well biked: it is my pride and (once more ridable) joy, someone has obviously spent a lot on it and looked after it very well... though it could do with a re-spray. The original maker (or his son at least) is still going so i'm going to ask how much they'd charge to respray.

Redtires: Ha, they re-released the big Trak in the uk,
http://www.maplin.co.uk/big-trak-396290
I'll swap it for a chainring!

Back in the day, long before index, shift gates, or ramps and pickup pins on chainrings bikes were commonly set up with 36/50 or 36/52 chainrings. They shifted passably, though not great, but as I said that was with comparatively primitive hardware.

I suspect your limiting factor might be the height of the bolt at the bottom of the FD cage. It's possible that there isn't enough height or depth to handle a 17t drop regardless of shift performance.

Regardless of what you decide on the rings, you can do yourself more good by replacing the freewheel with a wider 5s model. There are a number of choices and going to a 13-23 or 13-26 might give you better gearing with less loss of performance. BTW- you might also consider an ultra-6s (6 speeds in the width of 5) allowing greater range with reasonable steps in between.

a 39 53 set is going to get you back to contemporary combinations,
though a 130 bcd would allow a 38, pair that with a 48,
and that should be more pleasant Sunday rider.
another 5 speed freewheel maybe a 13-26 for the back cluster..
New chain, of course..

Any 130 mm chainring will fit on 130 mm bcd crank arms but the spacing between the rings may be too narrow for the wide 5-speed chain to fit. For example, 9-speed and 10-speed rings are space closer together to keep the narrow chains from dropping between them. If you use older rings, say 8-speed era or before, you should be fine.

BTW, the Ultra-6 freewheel FB recommended was, IIRC, only offered by Sun Tour and required a narrower chain than a 5-speed freewheel. Any 7/8-speed chain will work fine if you can find one of those freewheels.

what are now sold as 3/32" Single speed chainrings would probably be fine

Surly's Stainless steel for the inner , and Salsa 7075 for the outer ,

as above, some shim spacers around the chainring bolts
can spread out the 9-10 speed chainrings

Yup. That's a 130mm BCD crank. Any 130mm BCD ring ought to be fine.

I'm fairly certain there wouldn't be any problem running modern rings, unless the 5spd chain is wide enough to catch the pins on small/small combos... I'd be tempted to throw some narrower chain and a 7spd Hyperglide freewheel on there anyway.