The Comp had several versions through the years and was sporadically even out of the catalog. The first generation 1969 was different from all of them. That info you got doesn't apply to this bike, unless you found actual measurements.

You're right of course. Silly me for looking at the '78 catalogue on Sheldon's site...

my method for determining frame geometry when existing information such as from catalogs is not available is to take as perfect of a "profile" shot of the bike as possible, with the bike perfectly level and the camera located midway between the wheels, and from at least 4-5 feet away. then i use architectural drafting software to superimpose lines over the frame tubes. the software calculates the angles of the lines. it's not a perfect method because perceived angles vary with camera angle and distance, but so far my method is consistent +/- ~0.5 degrees with published numbers. of course, drawing lines by hand or cutting paper, and comparing against a protractor works about as well, but takes longer.

here are some angles that i have calculated on a few of my bikes:

1951 raleigh DL1: 66 degree seat tube (talk about *slack*!), 68 degree head tube:


1978 raleigh competition GS: 74 degree seat tube, 74 degree head tube (jibes with published data):


1985 shogun 2000: 72 degree seat tube, 73 degree head tube:

First of all, those Raleighs are top notch. Love them!

It seems as if that would be because that Peugeot has no trail, correct?


Does anyone know some approximate values that one typically finds in a 'twitchy' frame? Ex: head tube angle, seat tube angle, chain stay length, top tube length, wheelbase, etc?

What might someone surmise about a frame like this?

I have a Peug UO-8 from the early '70s, just like yours but with a smaller frame. Mine has a 72 degree seat tube, a 73 degree head tube, and 70 mm of rake, with a BB driop of 7.5 cm. The trail works out to 31 mm with 700x28c tires on it. Combined with the giant 46 cm chainstay length, it handles with the stability of a locomotive, which I think I'll like when I get tired. I can make it turn either riding or no-handing. I haven't tried any descents on it yet - some folks have opined that such stretchy bikes don't maneuver well when descending.

Measure the numbers for your Uni, I'd be glad to speculate based on them.

My UO-8 does fairly well while descending - I've had it to about 35 mph before and it stays just as stable. Again, I'd love to tour on a bike with similar geometry.

rat fink;

Per my understanding modern theory is that large fork rake and minimal trail makes for a twitchier bike rather than more stable. The French used such geometry in a lot of frames due in part to it giving better handling and bike feel with a front load; think Randonneur and Porteur bike geometry.

Frame dimensions and angles seem to be so interrelated though that it is hard to separate them out from one another. Seat tube angle seems to be the angle that would least affect handling normally I suspect.

Going back to what Robbietunes and myself said earlier; that rear tire is nearly touching the FD, and the toes of your feet may make contact with the wheel when turned from side to side (not sure) -- definitely a racing frame.

In looking at C &V frames, also realize that some French built bicycles in particular were built as Randonneur bicycles. They were made for racing long distances unsupported; you wanted a stiff frame for maximum speed, but with enough clearance so that you could install fenders and fat tires. They also had a longer wheelbase, that along with the steering geometry made the bike stable enough to be to be handled by a fatigued rider in the middle of the night without being overly slow. Here is a good example:

https://www.heronbicycles.com/rand.html



The art of bicycle geometry can get pretty complicated.

-James

I think you've got it backwards. If the seat tube is longer than the top tube - racier... if the top tube is longer than the seat tube - more relaxed.

No. if it had no trail it would be super twitchy. It probably has a lot more trail than the other bikes Mickey85 listed if it steers so slow, the picture just doesn't show that.
-Gene-

Nice looking bike. Any more pics?

https://velospace.org/node/26040

-Kurt

Early Diamondback mountain bike. Looks almost as relaxed as some of the Raleighs posted here.,,,,BD



And one of my own creations, back before I stopped playing with the welder so much.. This thing could practically spin on the rear tire, despite the
geometry, hehe.

Okay, yeah I looked at it all wrong. I seem to get it backwards a lot.

Sweet Swingbike!!

also one you'll see all over the place with slack Geometry...the Schwinn Varsity

I'm not sure either of you are wrong. Some think there's high trail, which is fairly stable, and mid-trail, which can be rather twitchy, low trail, and very low trail, which is pretty stable. I don't have a handle on all the physics of this, save to say my UO-8 and those of others I've talked to are not twitchy in the least, even with modern tires on the bike.

Seat Tube: 58cm
Wheelbase: 100cm
Chain Stays: 40cm
Top Tube: 56cm
Fork Length: 370cm
BB Drop: 7cm

What else should I measure?

Bikedued;

Most of the early mountain bikes had very relaxed geometry as they were based on the geometry of the old pre WW2 Schwinn cruiser frames used by the original MTB builders in Marin County.

But not always....

I'm sure Road Fan intends the correct meaning, but I'll get up on my soap box briefly and say that a digital gauge may offer precision (high resolution) without good accuracy. I prefer accuracy over precision but having both together is nice.

Seat tube and head tube angles. Fork rake would be useful, too, but it's not as easy to measure. Did you do seat tube center-center, center to top, or what?

I did the seat tube center of the crank to top of the seat tube. I don't have any way of determining those other angles, unfortunately.

Easiest way to measure fork rake: remove wheel and stem, set fork down straddling one end of a ruler, sight down the steertube at the ruler

My old Japan Built Univega had 73/73 in the angle department. Very nice ride.

Ok, well I'd say the chainstays are rather short, in the racing category. BB drop around 7 cm is kind of high, since touring bikes get as low as 8 cm typically. Richard Sachs, however, likes a low BB as part of his trademark design.

High BB generally is done to improve pedal clearance while pedaling. This combined with teh short seatstays suggests a racing orientation. A 58 cm c-t seat tube is around 56-57 cm c-c, and hence this frame is not far from square.

You can tour on almost anything, but this was not designed to make touring easier, IMHO.