I've got a PX-10 in an incomplete state (missing rear wheel, crappy aftermarket stem, chipped paint, etc.). It's a beautiful bike, and I want to turn it into my new commuter. My plan is since it's already incomplete and missing original components, to upgrade the drive-train to 7 speed shimano. I'd like to set it up with the RSX gruppo, which has STI shifters. I've got several questions about the feasibility of this, however.

-The current dropout spacing is 120mm. Will I need to cold-set the frame, or can I get away with just spreading the dropouts when inserting the 126mm 7 speed hub?

- Will I be able to keep the original stronglight 93 crankset and use it with a 7 speed chain?

- If not, will I be able to attach a modern shimano square taper crankset to the spindle of the original bottom bracket?

- Is this a bad idea, should I just keep it at a ultra 6 speed with friction shifting, or (god forbid) a 5 speed? Not that 5 speed isn't cool, but for a commuter bike I want lower gears and easier shifting.

- How good are the RSX brifters?

I haven't built this exact setup but I'd be surprised if it all doesn't just plug and play. The RSX brifters have a good reputation and are somewhat easier to overhaul if needed than the later models. The 93 crankset if a wonderful piece and should work fine with a 7 speed chain. You can squeeze a 126mm hub into a 120mm frame but if you have the tools, I'd cold-set the rear so you can re-align the dropouts to the new spacing. Non-parallel dropouts are a recipe for broken axles IMHO. If you want to replace the RD be aware the dropout is different than the modern standard. There are lots of threads here about how to handle that.

Sounds like it will be a fun commuter. Good luck and post some pics when you get going on it.

If you want lower gearing, you could always keep the 6 speed freewheel, but user smaller rings on the model 93.

The 93 crankset might play nice with an HG70 chain (it's borderline, but usually ok), but many 7-speed chains are narrower at only 7.1mm width. With the stock 52X45t chainrings the Shimano HG chain is usually ok.

Find a 7-speed Shimano cassette road wheel and remove a 1mm washer from both of the axle's spacing stack to maintain wheel dish.
Measure the inside dimension at the dropouts, it's usually 121mm at least. The narrowed (124mm) axle will slide in easily w/o undue stresses.

You may need to trim away at the driveside dropout adjusterwith a file or Dremel to clear the chain and lockring. No biggie there.

You will need to add a notch under the derailer hanger tab for the B-tension screw to puch against, and tap threads into the hanger's mounting hole.

You can use a 13-34t cassete with a mtb derailer for wider-range gearing.

RSX shifters are somewhat precious on the market, expect to pay $100 plus for a pair of 7-sp STI shifters. You would need a downtube cable stop to go with those.

What the other guys said, mostly. The crank thing, I'm not sure about.

But if your chosen crankset bottoms out on the Stronglight spindle that
came with these originally, you can get a sealed unit BB square taper
that will work that has French thread cups from Velo Orange for about
40 bucks. If you're a big spender, Phil Wood has an infinite array.

Look at Sheldon Brown for both French tubing dimensions (some differences
even in the 531 frames ) and also read what he has to say about swapping
out square taper cranks and spindles between JIS and ISO.

https://sheldonbrown.com/bbtaper.html

There's a strong possibility that your chosen Shimano crank will be JIS and
won't work on a Stronglight spindle, but the Stronglight crank should work
fine with your other stuff if it's not worn out.

The rear derailleur hangar might be a simplex style which won't work with anything but a simplex derailleur. It's considered gauche by some to modify the frame. I wouldn't do it to a px-10 myself, but would try and use a claw-type adapter on top of the simplex one... but I've never wanted to switch my simplex RD out on my px-10 so I can't really vouch for the claw idea yet.

IRD makes great new freewheels so you can avoid cold-setting the frame if you haven't done it before.

Stronglight rings have a 122mm bolt-circle-diameter too, so if you aren't satisfied with the ring size you have right now you might want to change the cranks and I would recommend just using a VO sealed unit or if price is a concern, I think that Harris still sells a 20$ old-school french-threaded bottom bracket and then you could use any crank you wanted to.

I have a PX-10 that I kept in "as-found" condition and I'm quite happy with it. I have thought about seeking out some campy bar-end shifters but I doubt I'll go that route... I will eventually get an IRD freewheel so I can have a wider range of gears for my big self to get up hills. I'm also keeping an occasional eye out for smaller rings for the stronglight crank but am not holding my breath.

They are lovely bicycles and I think putting brifters and shimano on the frame might be more trouble than its worth, mind you my cleanup on this bike was a lot of effort too.

I ran a seven speed corn cob on my '72 PX10 for a while just for grins. The Stronglight chainring handled it just fine... don't recall what chain I was running at the time, though.

I'm not usually one to suggest modifying a vintage frame, but the older Simplex hangers were a 9mm unthreaded hole, easily tapped to M10 for a standard threaded mounting bolt. This modification does not remove any functionality from the frame, as a Simplex derailleur with an unthreaded mount will work perfectly well in the threaded hole.

I'm not sure a claw over the Simplex hanger would work well, and it would be butt-ugly besides..

Or, you don't need to modify the hanger at all if you use one of these,

What is it?

Without any difficulty, I hung a SunTour Cyclone on my 1980 PKN-10 and later converted back to the original Simplex when I gave the bike to my son.

I should have mentioned that my rear dropout has already been tapped to fit a Japanese standard RD by the previous owner. It came with a Suntour Vgt luxe, which is a very nice derailleur in it's own right. I'll need to check the hangar for the b-lmit notch, I think it's there. I'm starting to second guess the build, though. The cost of the brifters, and bending the frame are discouraging. I would hate to mess up the frame. Something that occurred to me though, is to run a ultra 6 rear freewheel, and get the RSX brifters. They should work as, according to Sheldon Brown, the cog spacing is the same. In any event, I've decided that I don't want to bend the frame.

Fixed it (the bike design) for you.

That wouldn've been my preference from the start, though. Good luck!

Good decision.......easily done when it goes well. You will kick yourself if
one of the bridges separates or it otherwise does not go well.

I ride several of these, stock, all the time (well, one at a time),
and they do fine around here, even in some moderate hills.

You should be able to get the overall range you need with
2 in the front and siz in the back.

A Campagnolo Rally or Shimano Crane will fit a threaded Simplex dropout without further modification to the hanger.

+10
These bikes are good climbers to begin with, so a mishap bending a frame would be unnecessary as well as tragic.