redshift1

I have been looking on and off for a PX10 from the mid-70's ( with decal scheme example as in photo below ) for maybe 10 years and have pretty much given up due to never seeing a frame that is sized suitably for me. I have seen a few dozen bikes or frames advertised on-line in this time.

My size is a 54 cm ( C-C ) seat tube frame but whenever I see any PX10's in this size, I always seem to see an accompanying top tube length of 57 cm, which is just too long for me. Especially when I see the usual 120 mm stem lengths.

That effective top tube length combination ( 57 cm + 12 cm ) is way too long for me.

So I have concluded that the common ( 54 ) frame size combination for this model is 54 S.T. / 57 T.T. ( both C-C ).

Was this "long top tube" sizing a feature of the PX10 ?

I manage very well on a "square frame" i.e. 54/54 ( with a short stem length e.g. 6 cm ), as found on a mid-80's Peug. Aneto.

I could not comfortably ride 54/57, even with the short 6 cm stem.

non-fixie 

It seems that various manufacturers used the same standard TT length for all sizes in those days. Raleigh also comes to mind.

This site may be of interest, if you like geometry data: Geometry Geeks

ehcoplex 

I'd always heard that 60s & 70s Pugs used (more or less) the same length TT for all sizes. I've got two '72 PX-10 frames, a 58cm and a 62cm and just took a quick measurement of the TTs, c-c. Like I said, 'quick', and probably not exact, but it seems like the 58cm frame TT measures 58 and the 62cm measures 59. They're in an awkward place in the 'laboratory', and a bit hard to accurately measure, but I'm concluding that they're actually the same length.

Mr. 66

That setup does not look comfortable. You have the saddle all the was back on the rails, and a very long stem. I would be surprised if that bike came with that stem. For starters, I would move your saddle forward drastically, like a half inch. A stem of about 80mm would be a better positioning. But only do one change at a time.

ehcoplex 

My reading of the original post is that the photo is for a decal-scheme reference, and not the OP’s bike..

redshift1

Correct.

John E

I can confirm that my 21"/53cm C-T UO-8 has a longer top tube than any of my 55cm C-T frames do.

Schreck83 

I have measured two 1972 PX10's and the top tubes were different lengths:
57 cm seat tube - 57 cm top tube
62 cm seat tube - 60 cm top tube
(all center-to-center)

The decal scheme you posted was used in 1977 and 78, which is after the PX-10 frame geometry was changed with steeper seat tube and head tube angles, so the earlier practice re: top tube length may have changed.

dddd

The pictured bike looks like a PX10LE, which I believe went into production alongside a revised PX10E in 1973. Both models had similar geometry.

I have a couple of PX10's from that mid-70's era and the 56cm frame (as I measured the frame size) has a 56cm (Edited, 57cm) top tube.
My 60cm example has a much longer top tube.
I don't know what the 54cm frames had, but I might expect it would at least be somewhat shorter than 56cm (er, 57cm).

These Thevenet-era bikes had radically-steep frame angles, not that such geometry hadn't been tried on French production bikes decades earlier (it had).

With 75+ degree frame angles, these bike's frames are aimed at the needs of professional cyclists, who are very thin, very flexible, and who highly prioritize racing speed over relaxation and comfort.
As such, the rider is positioned rather far forward of the bottom bracket, in a more-aerodynamic position, and where pedaling intensity forces easily mitigate the additional balancing force on the rider's hands caused by the rider's mass positioned ahead of the bottom bracket. The relatively forward saddle position tilts the rider's lower body to a more-forward angle, lessening the bend angle at the waist that would otherwise result from the generous reach (forward and down) to the bars.

For anyone that buys one of these bikes, know that it might only work well for use on shorter, more-intense rides, where sufficient pedaling torque can be maintained and where the added force on the rider's hands might be sustainable for that shorter length of time. And that optimistic scenario asssumes that the rider doesn't have a lot of upper-body weight, and is both flexible and fit.

Using a shorter stem to reduce the reach will upset the intended weight distribution, making the steering uncomfortably light and hyper-responsive.
Using a longer stem makes sense not only because of the weight distribution, but because the racing position tilts the entire body forward, also downward in front, meaning that a shorter/smaller frame can be used without the rider feeling too much drop from the saddle to the bars.

For better and for worse (restating what I've just said), these bikes simply are very much a "go fast or go home" kind of ride!

redshift1

Thanks everyone for your input and for measuring top tube lengths for me.

Great analysis "dddd" !

I guess it's far better to be comfortable on a nice bike than uncomfortable on your grail bike.

ehcoplex 

'72 and earlier PX-10s have more relaxed geometry and not-radically different graphics/look. Good tire clearance at 700c (even better if you go 650b, which they lend themselves nicely to). I love my '72 and feel like I can ride all day on it.

Slowride79

I have a px10 of this exact color way and decal set , I think perhaps 1976. Seat tube is ctt 21” (53.34) and top tube is 22” ctc (55.88). I think with a very short stem (45mm) this could work for you not withstanding what dddd said about ideal weight distribution for this frame geometry.

dddd

I believe that the suitability of the frame geometry will depend on yet more variables, such as a longer torso/arms proportion perhaps(?).

That is the opposite of my own proportions, yet I have done quite a few rides on a larger-framed one with a modest 10cm stem and ~forward saddle somewhat moderating the reach.

I remind myself though only to use this bike for rides where I might want to be taxing my output limits for a limited amount of time, such as when a fast tandem might be attending one of our 25-mile club rides, when one has to literally ride at their limits to hold that tandem's wheel, on the verge of cramping just waiting for the next recovery stop.

I briefly joined and jousted with a passing fast racer's training paceline on my ride to one such club ride, and one of the riders in this younger group commented that it was "great' or "refreshing" to see one of these vintage racing bikes being ridden the way it was meant to be ridden, man he had no idea (I was fully at my limit for that short period of minutes including one or two decently-long pulls)!



Photos showing the 1973 PX10E having the new geometry, but having returned with the former Nervex Pro lugset.
The Holdsworth "reference frame" has 73x73 frame angles, and you can easily see (helped by the camera's parallax angle) the difference in how the post-1972 Peugeot geometry moves the saddle forward and extends the forward reach (the Holdsworth actually has the same 57cm long top tube as this 56cm 1973/74 PX10E).

3alarmer 

.
...I guess it depends on whether you are stuck on that graphics package, but I have had a number of these PX-10's here over the years, and they do vary quite a bit on geometry. This one is pretty comfortable for me, but as you can see it's a larger bike. Maybe a 59cm ?



Based on personal experience with them, they got a lot tighter and might fit your preferences better in the late 70's and early 80's.
Those are much 'quicker" bikes, in terms of handling. With the possible exception of the really steep Nervex lugged frames you see sometimes like this one.


(No, it's not bent. But it does have 27" wheels and a steep head tube.)


But compare those to some of the more colorful, later PX10 LE (and other various alphabetical variations over the ensuing years.) Shorter, tighter, squarer, and more nimble...but somewhat less steady on something like the Paris-Roubaix course roads.









I haven't measured any of these. They are all about 58 or 59cm frames, so it wouldn't help answer your question. But in terms of how they ride and handle, I think maybe what wouild make you happier is something from later in the history of production, like early 80's. But the paint and graphics changed a lot by then.

dddd

By 1979, the PX10 Super Competition model as well as the lower-tier PH501 and so on had been given a contemporary geometry around 74x73.5 degrees in the 57cm size, roughly in between the pre-'73 and post-'72 models. These bikes are lively, but don't so much call attention to their geometry numbers.

sbarner 

Here's my '74 PX10E. I think the geometry was the same as the LE, but I don't see that I recorded the measurements. '74 might have been the first year they brought a size below 21" into the US. This one is a 20" (51 cm) and has a 55 cm top tube as I recall. With the stock stem and long-reach handlebars, I'm pretty stretched out on it. I don't how Peugeot measured their frames and mine is a bit hard to get to right now, so I'm going from memory. I have not found it to be an uncomfortable ride at all. It has pretty long stays and, with the longish top tube, it ends up with a generous wheelbase in spite of the steeper angles.

Long top tubes seemed to be a thing before the mid-1970s, especially in smaller frames, until people started paying more attention to fit. It's hard to imagine the thinking (or lack thereof) that went into top frames with a 54 cm seat tube and a 57 cm top tube, but I've seen exactly that. In some cases it appears the designers were seeking to insure toe clip clearance, but there are more effective ways of doing that, if one really deems it necessary, than making it impossible to get a good rider fit.

mikestr

I can confirm that I have recently acquired a 1974 PX10L (same as LE in US) that measures 54x57 c-c. It seems to me unlikely that Peugeot used a constant-length top tube for frames of different heights, as some have suggested; much more likely that they simply made proportionately longer frames for a period of time, which coincides with the appearance of the unusually steep head angles and shallower fork rake. Peugeot stated at the time the this bike (at least the L/LE version) was identical to the team bikes, and It is not hard to see that a reach suitable for a pro rider might seem too long for a recreational rider. It does not seem probable that a company like Peugeot, the largest maker of racing bikes and sponsor of history's most successful pro teams (even now) would be as indifferent to frame design as some above suggest.

BTW, can anyone here confirm that they have a 54 (c-c) PX10 from this same period that has a more normal-length top tube (around 55 cm)?

dddd

The issue with longer-than-normal (for production frames) top tubes can be because of the need for toe clearance, but only on smaller frame sizes.

Since a 75+ degree head tube angle combined with an appropriately less-raked fork can steal a couple of cm from the frame's "front-center" dimension, even frames also having a fairly steep seat tube angle may need a minimum of perhaps 57cm of top tube length to prevent dangerously-short front center length if the head tube angle is very steep.

Larger frames can use more of a range of top tube length (typically increasing proportionally with frame size), so the top tube length tends to be more normal even if a steep HT angle is used.

The steep head tube angle keeps the front-center from being too large (for best drafting effect without touching tires), but is usually not so much part of the design of smaller frames since it forces use of a longer top tube and/or steeper seat tube angle, and thus shorter stem, to fit the rider (a combination that may make for twitchy steering response).

I can confirm that the PX10LE's top tube length is much longer in the larger frame sizes, my 60cm example having a 58.5cm top tube.

mikestr

This makes a kind of sense to me. It assumes a conscious decision to make steeper head angles, which in turn forced the need for longer top tubes in smaller (shorter ST) frames to prevent toe clip overlap. Of course the converse could be true: A decision to make longer top tubes driving the need for steep head angles to preserve frame front length (BB to front axle). If the former is true, would one not expect that the bikes were typically supplied with shorter stems to keep the reach reasonable for the typical rider of smaller frames? According to OP redshift1, the "usual" stem is 120mm, quite long. My bike is equipped with a 105mm stem, which still makes for quite a stretch on a frame sold to smaller riders.

As for your 60 cm LE frame, is a 58.5 cm "much longer" than the 57 cm TT of a 54 cm frame? Did you mean to write the opposite?

dddd

I considered the 58.5cm to be much longer than the 56 (oops, it's actually 57cm) of my own 56cm PX10 from this era.

I'm thinking that these "team replica" kinds of geometry was provided with the expectation of the rider running the saddle somewhat forward, which by itself reduces the reach to the bars, so that the longer stem lengths got spec'd.
And as well, that racers tend to use a bit shorter frame sizes, with the bars set relatively low compared to the saddle.

I'm still waiting for a very small PX10LE frame to come along, to see if it has the same steep angles (HT and ST), and if the same 57cm "minimum" top tube was used(?).

**Back from my basement, tape measure in hand...
Ok, seems that I earlier mis-stated the toptube length of my 56cm 1974 PX10E (one of the ones with the steep geometry). It's actually 57cm, and which means that the OP's 54cm bike's top tube length is no anomaly, since it seems that 57cm is simply the shortest top tube that Peugeot felt was safe to use with the steep angles and minimal fork rake.

This suggests that their priority was on using the 75+ head tube angle, and that the top tube lengths followed, using their "minimum safe" 57cm dimension for frames shorter than 58cm or so.
I think that slamming the saddle rails forward in the Simplex setback seatpost would be expected for most rider's bodies that found themselves riding the 54cm frame.
I encourage riders not to fear a forward saddle, especially as it allows retaining a decently-long stem for best handling. It may not be the best for all kinds of riding or for longer rides, but perhaps best suits the kind of riding these bikes were designed for.

mikestr

It's a reasonable hypothesis; one could add the growing interest in criterium racing at the time, for which steeper front ends were considered advantageous. But can we be certain that all PX10s during this period had this geometry? The question here is about the smaller frames having such long TTs; do we see this equally for the E and LE versions, for example? During this period the LE (or L in Europe) was stated to be the "team replica" model; was this only a question of componentry or was the frame geometry different?

I'm not sure it's relevant at this point, but I'm still confused by your statements concerning your bike or bikes. You mentioned a 60cm frame with a 58.5 cm TT; now it's a 56cm with a 57cm TT. Are there two bikes, both PX10E?

dddd

Yes, I have two of the PX10's from the 1973-1975 era, a 56cm and a 60cm. Both have similar measured angles, but different lug styles. The 56cm is a PX10E and the 60cm is a PX10LE.
Both are pictured about 8 or nine posts up from here (not the post showing my later white 1979 PX10 and red 1985 PH501).

It would be mildly interesting as to what top tube length that 58cm or smaller than 54cm versions of these bikes had, I just don't have the data points.

mikestr

I'm not sure I've seen one of these in a 50 or 52 cm, but it's hard to imagine a 57 cm TT on such a small frame.

I will post pictures of my 54 (c-c) '74 PX10L when I have time; I just finished reassembling it.

mikestr

Isn't it most likely that the TT was lengthened in an attempt to offset the instability of a steep head angle and shallow fork rake combined with a short TT? That problem should be immediately apparent to the rider/customer and could even be dangerous. Did any manufacturer make a road bike with such a head angle (on my bike 76+ degrees) and fork on a small/short frame? Does such a bike exist? From what I've seen the smaller/shorter frames had more modest head angles than this.

repechage

Peugeot really jumbled the frame designs in the 1970’s.
no telling.

Bicycle Trail Calculator | yojimg.net

if one can measure accurately will provide some numbers of trail.
a steep head angle and less fork rake can be counterintuitive to what one expects.