Tubing diameters as measured. I note that Sutherland's 4th dates to '85.
Calipers are zeroed w/ masking tape across the flats, measurements are ~averaged across a few locations on each tube, so I'll call these measurements 'pretty close'. Paint is fairly thick. My numbers are in brackets, Sutherland's to the left.

Top Tube 34.9mm [38.5 mm / ~1.5 in]
Downtube 44.4mm ('84 ST 38.1mm) [38.55 mm / ~1.5 in]
Seat Tube 31.7mm [31.88 mm]
Head Tube 34.9mm [36.2 mm]
Steering "column" 25.4mm [Yet to pull fork, interested to see if any markings exist. 1" threaded fork]
Chain Stay 25.4mm [22.0 mm - circular cross-section]
Seat Stay 19x25.4 [19.4 mm - circular cross-section]

Crude measurements of chainstay length and wheelbase roughly match those given in the '84 catalog for the largest published size in the SR series (SR appears first in '84): 40 cm, 100.3 cm, respectively. The largest size listed in the '84 catalog is 63 cm and does not match this bike no matter how you measure (CTT = 65 cm, CTC = 59 cm, CTC+1 cm = 60 cm), not sure what to make of that. Top tube measures 57.5 cm CTC.
http://vintagecannondale.com/year/1984/1984.pdf

The ’84 catalog does show a single eyelet on rear dropouts (absent here). Starting in the ’85 catalog, chainstays are dimpled, the stays on this bike are not.

Vintage Cannondale - Cannondale Catalogs

Most catalog photos show DT shift lever bosses, which are absent on this bike, though there is a single circular boss on top of the DT at what would be the shift lever location. This circular boss measures 6.2 mm dia x 2.4 mm height. I assume it is intended to anchor a band clamp for shift levers…



The bike has cable guides/stops at the DT/HT junction to accept bar end shift lever cables. This does not match any catalog pics I’ve come across yet.



The TT cable guides also differ from those in the early C’dale catalogs.


Looks like someone may have tried to address the TT cable guides in the past. I have an idea or two about how to re-repair, but it involves epoxy and is permanent, which would be nice to avoid (likely a challenge for a feasible solution) - any recommendations here?

The fork crown does not match that given in the earliest catalogs (which shows a window a la Cinelli OR crown), but does appear to match the fork crown of the Tange fork first appearing in the ’86 catalog (for all SR models but the SR1000, which still has the window in ’86).

More questions than answers. My gut still says some sort of Cannondale, prototype or some other one-off, but I haven't closed out other options yet. So far I'm focusing on the racing/SR models as this bike seems to have racing/crit geometry. Angles appear close to my '83 Colnago to my eye, though that's tough to calibrate... I have toe overlap with med toe clips on this C'dale, this does not happen on the Colnago (or others). Short wheelbase.

I wasn't expecting a match to any one model/year, and that's what I got. I'll add here as I make progress. Any suggestions are of course more than welcome.

SWAGs at this time are either: prototype, or built after-hours by a worker for their stash, or built for the team, or not a Cannondale at all, or.......?

A few quick photos:

DO/stay treatment. This also appears to differ from the catalogs.


BB cable guides.


BB cable guides and chainstay bridge.


27.4 seatpost



I've yet to take a close look at components - rear der. dates to '75 and crankarms to '80. I'll add other dates as I start to clean the components. The build doesn't match any catalog (not that the frameset does either), and given the range of parts and dates it appears that someone built this up with either parts on hand or with their dream build at the time.

I'll add more detail as I go, but here are some highlights:

3ttt record AR stem w/ black bolts/nut
3ttt Superleggero bars
Suntour 3090 shift levers (sans 'plastic grip')
SR headset
SR seatpost
SL pedals
Record crankarms w/ Sugino super mighty rings (maybe replacement) and black chainring bolts, plus gold anodized Al/alloy crankarm bolts (I think, yet to pull them)
Press fit BB (yet to inspect closely)
1st gen. Suntour cyclone FD
Early SR RD
Record hubs (high flange rear, low flange front, 28 hole f/r)
Unknown gold anodized tubular rims w/ eyelets (Fiamme Gi 8??)
Maillard 6sp freewheel (replacement? - would expect a tighter range for racing, though this is suited to CT's terrain)
Record calipers
SR brake levers w/ Modolo hoods (replacement?)
Dia Compe brake blocks (replacements?)
Unicanitor saddle (my addition, had gel saddle at time of purchase)
Silca pump
Cobra bottle cage (one set of bosses on DT)

I hope to start the disassembling, cleaning, reassembling process this weekend as time permits, though I haven't been riding much and that urge may win out.