Bicycle Mechanics - Lower gears

Hi - I'm planning on doing a fair old tour over Europe on my 60s Mercian King of Mercia. Shamefully, however, I'm not particularly clued up on gears.

The image below is my current double - which is great sans "load", but I'd rather go lower for my trip. Ideally, I'd keep the smaller ring size as my largest, and have a smaller (granny?) ring as my smallest.

I don't exactly know how I'd do this... I assume it's not possible for me to simply add a smaller ring, so would I have to get a full new crank and ring set? If so, could I just pick any up?

Many thanks!

http://img59.imageshack.us/img59/1272/438709080o.jpg

You'd need a crank with a smaller BCD (that one looks like 144mm) to fit smaller rings. If your BB is "english" or "italian" threaded then you can use nearly anything but if it's something else you will need to look for a crank whose BB is available in the correct configuration.

while I like carbon fiber and it's great for cranks I'd get something more retro looking for that bike. T.A makes some appropriate cranks.

I can't tell if the FD mount is braze-on or clamp. If it's braze-on then you will be limited in how small a chainring you can use.

Your chain is wider than the current 10sp standard but you can get chainring spacers to increase the space between rings if you need to do so on a modern crank.

perhaps a TA tripleizer and a longer BB axle ? then the 42 has a second set
of bolt holes
for 74mm BCD. say a 26t.

Or pick up a modern Campag triple chainset, 52,42, 30,
then substitute a 26 for the 30.

cable over the BB route limits too small an outer chainring, as the bottom end
of the FD cage starts plucking the gear cable when you shift

What are you running in the rear? 6 speed?

I would get a tripleizer and new spindle and build it with half step gearing. But that would be period correct and a lot of money (I'm just slowly collecting my parts for that build), especially if you didn't find good deals on the chainrings. You could probably pick up a mountain front crankset (24/34/44) and BB for what a tripleizer would cost if you looked for a good deal.

I am assuming friction shifting so yes, any manufacturer should be fine and any 7/8/9s marketed system should work without any, or many, issues.

If you decide to go with a half step lus granny, I have a very nice SR Apex 48/44/30 that would do the trick. Even have an assortment of english 68mm spindles & will include the one (or two, like 122.5 and 127) you think would fit. PM me if interested.

perhaps a TA tripleizer and a longer BB axle ? then the 42 has a second set
of bolt holes
for 74mm BCD. say a 26t.

I suggest this route; mainly because you get to keep your nice looking vintage crank set. In addition to the TA version, a company called Willow made one as well, they show up on ebay from time to time

Gippiemme made a nice crankset for triples
at the time Campag had a triple,
drilled and threaded the arms for a 36t only. "1048/5"
GPM instead thickened the spider arm,
and blind drilled and bottom tapped the holes .
in I think an 86mm circle ,
allowing the Stronglight 99 pattern 28t ring to be fitted.
I thought is a more elegant solution

I used mine in a wide step double back in the day
52t + 222 polished <C> chainguard, and the GPM triple ring.

now it sleeps in a parts bin..