Guerciotti geometry... :O
12-03-18, 10:57 AM
#1
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Guerciotti geometry... :O
The basic details of this latest addition to the attic are on this thread right here. I've just taken it out for the first time with nothing changed but the saddle, and noticed something odd when we stopped for coffee.
The photo is deceptive in that it's a smooth curve on the TT ot a sudden one, but all the other tubes are straight. No visible cracks, stress or anything else just a bit odd, like André the Giant rested his butt there while on a break from riding.
*
The photo is deceptive in that it's a smooth curve on the TT ot a sudden one, but all the other tubes are straight. No visible cracks, stress or anything else just a bit odd, like André the Giant rested his butt there while on a break from riding.
*
12-03-18, 11:04 AM
#2
Banned
might he A, heat distortion, B alignment adjustment..
bike boom meant 'get then shipped out fast..
bike boom meant 'get then shipped out fast..
12-03-18, 11:52 AM
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I remember this one. It's definitely post boom era, by about a decade. The bicycle boom was 1971-1974, inclusive.
12-03-18, 12:05 PM
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Are you sure the level isn't bent? Sometimes they get dropped and kicked.
12-03-18, 12:15 PM
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I'm not particularly heavy, so I'm not worried about bending my top tube - and I'll routinely sit on my top tube at stop lights etc. Maybe somebody in the past did this on this bike? Or maybe a previous owner stacked something heavy on the top tube?
01-27-19, 06:18 AM
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They say that whatever sport you do, the best bits of kit are the ones that you don't notice. Just done my first proper ride on this wee beastie, and it did everything asked of it, no fuss, no bother. If I had a bag of oats to hand, I'd hang it on the handlebars and let it gorge itself. 
01-27-19, 09:38 AM
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One of the frame building books I've read suggested rolling the top tube to see if it was arched, and marking the high side if it was, so that you could miter so the arch would be up.
(Maybe Paterek, but not certain) So, arched tubes may be more common than we think.
First generation Cannondales were famous for it.
(Maybe Paterek, but not certain) So, arched tubes may be more common than we think.
First generation Cannondales were famous for it.
custom by crash. ( check the “as built” geometry ) here I would look for a very slightly steeper Seat tube and slightly shallower headtube.
think roof rack mounted bike meets garage header.
as built condition, at least the bow in not lateral.
Steel is quite tolerable of... enduring stress and still working.
01-27-19, 10:37 AM
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It comes from the old practice of leaning your bum on the bike while hanging out pre or post ride.
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01-27-19, 06:30 PM
#13
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A mistake non-framebuilders make is assuming bicycle tubes are straight. They seldom are straight. In my frame building classes I have my students roll the tubes on the alignment table to find and mark where the bend in the tubes are so the miters will place the curve in the plane of the frame. It is common for them to be as much as 1/8" out. The reason they are not more accurate is because they would cost a lot more to make.
While we are marking curves we also mark where the butt transitions are located. These can be pretty far out of spec too. Both of these references let us know where to best place the miters. These are examples of how a well made custom frame can be made in a superior way to production frames where the factory workers aren't looking for individual variations.
While we are marking curves we also mark where the butt transitions are located. These can be pretty far out of spec too. Both of these references let us know where to best place the miters. These are examples of how a well made custom frame can be made in a superior way to production frames where the factory workers aren't looking for individual variations.
01-29-19, 02:38 AM
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A mistake non-framebuilders make is assuming bicycle tubes are straight. They seldom are straight. In my frame building classes I have my students roll the tubes on the alignment table to find and mark where the bend in the tubes are so the miters will place the curve in the plane of the frame. It is common for them to be as much as 1/8" out. The reason they are not more accurate is because they would cost a lot more to make.
02-01-19, 02:25 PM
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Sorry! If there is any viewable sales literature see if you can align your bike with them. Someone might be able to help you narrow down the year if you can measure the geometry carefully.
02-01-19, 03:48 PM
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02-01-19, 11:12 PM
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Happens on even top of the line limited production frames. I have a frame that the DT and ST are similarly curved. I was quite upset about it at the time. It takes a straight edge to notice and I don't recall why I even determined the frame had the "problem". The frame rides just fine and I had not thought again about the curve until I read this.
02-02-19, 12:24 AM
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On my Steyr, both seatstays are mildly arc'd, one curves forward and the other hangs back, which makes it doubly noticeable.
I imagine the upper ends were scalloped in an extremely fast process where no care was taken to create proper left and right stays that would be parallel in appearance.
It's something that would only be noticed by the owner.
I imagine the upper ends were scalloped in an extremely fast process where no care was taken to create proper left and right stays that would be parallel in appearance.
It's something that would only be noticed by the owner.
02-02-19, 09:55 AM
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Happens on even top of the line limited production frames. I have a frame that the DT and ST are similarly curved. I was quite upset about it at the time. It takes a straight edge to notice and I don't recall why I even determined the frame had the "problem". The frame rides just fine and I had not thought again about the curve until I read this.
02-07-19, 11:50 AM
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I have now measured the angle with a very simple mobile phone-based inclinometer. 74 degree head angle 70 degrees seat tube. Aesthetically one of the things I really like about this frame is how delicately the tops of the seat stays are attached to the cluster. Is that any kind of clue to model?
02-07-19, 12:56 PM
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Is it me or is the toptube ovalized going into the lug?
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02-07-19, 01:10 PM
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No it's a trick of the light. Or bad photography...
02-10-19, 12:41 AM
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After much searching on Google and looking at as many detailed pics as I can find it looks like this is a Super record. I found some of the catalogue head angles and seat tube angles and it's close enough to be fairly sure. the only difference and it could just be the age of the frame is that a lot of the photos of the cable guide for rear mech as a braze on above the bottom bracket. Either way I am enjoying it more and more every ride, it's fabulous!
02-10-19, 01:27 AM
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I had a 1986 Cannondale SR400 that had its seat stays arc after (presumably) heat treating. Looked fine from the side, "down the line" sighting revealed the curve. Rode fine of course. I now have a 1991 SR800 and the down tube is banana'd when you sight down from the head tube to the BB. Lol. Unnoticeable from a side view, and of course as the paint is nearly flawless and there are pretty parts on it, I couldn't care any less! I still want to test ride it though, but we've had some wacky weather lately and now there's a bunch of snow on the ground and it doesn't look like it will abate for at least a week. Temps out of the 20's would be nice, too.
