Kommisar89

I've thought about this for a while and never really come to a satisfactory answer. All of the bikes in this series (AO8, AE8, UO8, UO18, UE8, UE18, etc.) come with 27-inch wheels. The corresponding French models have different model numbers but seem to vary from 700C to 650B depending on the model. Because of the different model numbers and the fact that I don't have an actual French market bike available to compare, I can't really tell. But if you look the picture below of my UO8 setup with 27-inch wheels and 27x1 3/8 tires. Look at where the wide point of the tire is relative to the indentations in the chain stays fr tire clearance. They don't line up at all. Even a 700C is only 4mm smaller in radius so I don't think that would line up either. But a 650B just might. I'm going to take some measurements and see how it works out. What do you guys think?

Jon T

The UO8 was designed for 27x1 1/4 tires, not 27x1 3/8. You need the proper tires.
Jon

jj1091

I have 2 French-market lower-end Pugs, PX-8 which came with 700c wheels, and a PX-50 which came with 650b wheels. The chain-stay spacing on the PX-8 is about the same as on the UO-8, but is wider on the PX-50 for the 650b clearance. Those 650b-equipped models you're looking at were PX-50's, PE-41's, etc, not the AE/AO/UO-8 series bikes.

John E

I did put a set of 27 x 1-3/8" knobbies on one of my bikes for awhile. I thought it was the UO-8, but chainstay clearance is already a bit close with 27 x 1-1/4". I think I could barely clear a 27 x 1-3/8" tire with the rear axle pulled back in the dropout.

You are correct that US export A/U-08s came with 27x1-1/4" tires, usually Michelin or Hutchinson.

Kommisar89

I'm not buying that explanation. First, unless these frames were specifically made for the US/Common Wealth market, the French would never design a frame around a 27" wheel. Second, the rim itself is already more than halfway into the indentation in the chainstays so putting a 27x1 1/4 inch tire is still not going to make it line up. Now the 4mm shorter 700C would help in that regard. I'll try a 700C rim later when I have a chance.

Kommisar89

It probably was the PX-50 that I saw in the catalog with 650Bs but I couldn't tell if the frame was different. So if they aren't designed for 650B, how do we explain the chainstay indentations not lining up? How do they line up with you PX-8 with 700C?

Kommisar89

Production variances maybe? The 27x1 3/8" knobbies fit pretty good in this frame. The picture makes the clearances look tighter than they are. I've ridden this bike all over with those tires even on single track and it was fine.

Kommisar89

I'm going to try an experiment this weekend, time permitting. I have 27" and 700C wheels that will fit this frame and 27x1 1/4" and 27x1 3/8" tires and 28mm and 38mm tires (and maybe some 32mm if they arrive in time). I'll mount them up and take pictures to see how they align with the chainstay indentations and what the clearances look like.

Hoopdriver

My 72 UO8 came with 27x1 1/4 tires. Seems like a reasonable assumption that the frame was designed for these. On the other hand, it's also reasonable that the US market was supplied different sized wheels. Still, I would expect that the French would have used 700c instead of 650b.

Keep in mind too that the stay crimps may have been done the same distance from the end of the tube so that when the BB end of the tube was trimmed, the resulting position would vary. Also, the crimps could have been done by hand so more variability.

Kommisar89

All possibilities. Let's see what my experiments show this weekend. It may be that the 700C wheels & tires line up perfectly. There is definitely enough brake reach for it.

Kommisar89

That gives me an idea on a completely different topic. I wonder if a frame builder could add crimps like that to an existing bike for more tire clearance. My Panasonic PT-3500 comfortably fits 700x38C tires but it does not have any sort of crimp or indentation in the chainstays. If they could be added it could probably go 42mm.

63rickert

OP has a good question. I've wondered myself.

Peugeots were not designed for 27x1-1/4. They were fitted with that size for the American market. America is not the center of the universe. Paris is. Or you should assume it is if you want to know anything about French bikes. St. Etienne and Valentigney are satellites of Paris. America is somewhere in the outer darkness. Too many qualifiers on my part here, for any Frenchman it is unequivocal that Paris is the center of the universe.

Bikes used to need far more wheel clearance than they do now. 'Need' is the correct word. Ordinary bikes never had wheels that were particularly true. Spokes broke, regularly and predictably. Frames needed enough clearance to get home when the spoke broke. Low strength flat rims in wheels that have erratic spoke tension go way out of whack when a spoke breaks. In France there may have always been some sort of bike shop nearby, cell phones did not exist. Uber did not exist. The 27x1-3/8 tire shown above may rotate without scraping paint off the chainstays. It does not have nearly enough clearance for anyone who ever would have designed a vintage Peugeot.

Did Peugeot build frames that could be painted and stickered and built up as either 700 or 650? I don't know. But it is a fair question. Remember that 650x32 was a common size.

Road Fan

Kommisar89

True, I'll take a look when I get home but I generally pull the wheel back as far into the dropout as it will go. Forged dropouts typically have adjustment screws to set the wheel position but these low end bikes don't. I've also see some of the low end bikes with a derailleur adapter in the dropout slot that would prevent the wheel from going all the way back but I don't recall what my Peugeot has. I'll take a look tonight.

Kommisar89

I do tend to push the limits on tire size and gearing. The 27x1 3/8 knobbies on that one gave it some additional utility that it would not have had with 27x 1 1/4 road tires. The factories are very conservative. The worst that happens if my bike breaks down is I call my wife to pick me up.

79pmooney

I had a '67 UO-8. Never paid any attention to the chainstay indentation. US market 27 X 1 1/4. 1973 I went to 700c sewups, adjusted the brake blocks down and never looked back. Bike rode so well as a small tired 700c that I never felt it was designed or built for 27" despite that being how it came new.

One drawback to riding Peugeots with skinny 700c's, the low BB gets even lower. I call the conversions "slinkies". Ride them with sturdy pedals or expect to coast with the pedals at 3 and 6 o'clock for speed bumps. Riding fixed with leotard platforms, I spun off the left dustcap regularly. Pedal strike was a regular event.

Ben

jj1091

On the PX-8, I have 25c width tires, currently using 27-inch rims, and they line up similarly to your example with the 1-3/8 knobbies. The rim braking surface falls at/near the center of the chainstay dimple, with the tire being close to the end of the dimple towards the bridge. On my 650b bike, the rim falls towards the beginning of the dimple towards the axle, and the tire falls at the center of the chainstay dimple. I measured the location of the center of the dimple to the rear axle center on both bikes, and both are dead-on 12-1/2 inches, and both have the same width of chainstay bridge. In other words, the 650b equipped bike can handle the extra width, because the tire falls near the center of the dimple, where there's more clearance. I'd say that if you change out the rims on your UO-8 to 650b's, you'll gain extra clearance for the 1-3/8's. tires.

ryansu

Since the French sent Millions of UO-8s to North America and then built a plant in Canada to make millions more I think its safe to say they did in fact design the UO-8 around 27" wheels. Check out bike boom Peugeot and look at the American flyers

Kommisar89

So if I'm reading that correctly, the PX-8 and the PX-50 actually have the same bridge, chainstays, crimping, and spacing. Is that correct? And it also sounds like the 27" wheel/tire combo fits the PX-8 frame about the same as my UO-8. If that is true then it would appear that they all use essentially the same frame design. It could be that the frame was designed to fit both wide 650Bs and narrow 700Cs or that it was originally designed for wide 650Bs and the 700Cs were added later and there was no need to modify the frame. And then the 27" was added for the US & Common Wealth markets.

I will take careful measurements when I get home but I strongly suspect that I can run it with 650x38b and possibly even 650x42b although I'd have to carefully check the clearances on that.

Kommisar89

I have to admit that it would certainly have been economically feasible to do that given the volume of the bikes sent over during the boom. Whether they actually did or not is another question. But based on the measurements that jj1091 has taken on his French market PX-8 and PX-50, it sounds like they are all the same. I'll take careful measurements this weekend and see what it looks like.

Hoopdriver

Absolutely! I crimped the chainstays on a 90's vintage Bianchi frame so that I could fit 650b wheels with fatter tires. I carved a male pattern out of dogwood (very hard) in the shape of the crimp + a concave piece for the outside of the stay, and then used them with a C-clamp to do the deed. I did practice on one of my wife's metal broom handle first. She wasn't too happy.

Kommisar89

Well, I was going to seek out the services of a local frame builder and let my wife keep her broom.

63rickert

So I did check out Bike Boom Peugeots. The big year was 1973 when they sold 168,909 bikes in America. That ain't millions. And they thought you were completely out of your mind wanting that obscure tire size. Even putting the different size tire on the bike was a huge accommodation. It was a French bike. It was not an American bike. It was not about you. It was not about Americans in 1973.

Kommissar --- It was not about factory being conservative. It was about a bike made for a different time. It was not possible for a Frenchman to call his wife. No cell phone, remember? Did wife have a car? Did wife know how to drive? Was there even a phone in the house? I remember many houses in Chicago that did not have phones then, not even in the 80s. Peugeot wanted a reliable bike you could sell in France.

cudak888 

I've seen the same thing done by framebuilders, just with a steel equivalent of the same tool described...

-Kurt

jj1091

You're correct, that the stays are the same. I measured everything on the 2 rear triangles (both bikes are 56cm/56cm frames), and everything is the same within a 1/16th of an inch. The only difference is in the forks. On the PX-50 with 650b wheels it's 15-1/8" axle to top of crown, and the PX-8 with 700c wheels is 15-3/8". Also, the fork widths are different, with the PX-8 having a 3-1/8" wide crown, and the PX-50 having a 3-5/8' wide crown. They just provided a 1/4" shorter, and 1/2" wider fork on the PX-50 to accommodate the 650b tires.

But, placing my 650b wheel into the PX-8, with a 584x40 Kenda 650b tire, there's about 5-1/2cm spacing each side of the tire. So, you could easily fit 42mm tires into the stock UO-8 fork, however the Mafac Racer calipers won't reach if you do it with 650b wheels, since there's fully a 1-1/4" gap under the fork crown.