Beside the decals, is there any way to tell the stays and fork were make from 531 tubing? Special marking, unique measurement, etc....? Thanks

Seat tube diameter is generally larger on bikes with good tubing, due to the tube wall being thinner. I believe 27.2mm is diameter that fits 531...if it's smaller, the tubing is most likely not as good.

Except for metric 531 which usually has around a 26.4 seat tube.

You'd need a way to measure the tube wall thickness. Many bikes used lesser tubing on the stays and forks especially. If you know the bike model, you can do research to find if it was a full 531 or just the three main tubes.

I think the larger sized bikes tended to use a beefier tubing on the stays and forks; at least for some builders.

Columbus had a "tre tubi" sticker to denote the three main tubes being SL or whatever.

The short answer is, no. Unless you can ID a specific model through frame features or components there's no way to tell.

And while Reynolds and Columbus tended to supply seat tubes butted only at the lower end (BB), the Japanese manufacturers of (equivalent) quality DB tubing butted the top end, I think -- so their seat tube diameters are smaller at the post opening. Miyata is mainly 26.8 mm, Tange often 26.6 I think, for DB sets. Vitus (French) could be different too.

Trek made a lot of models with frame tubes Reynolds 531, and all the fork and stay tubing Ishiwata. While that may have added a few ounces, these are bikes with a ride that people really like. And they're no slouches in the weight department, either. So if you eliminate frames with straight-gauge forks/stays, or mixed tubing sets, you're excluding a lot of nice bikes (more for me!) from your C&V universe.

The basic criterion for judging a frame with unknown tubing is weight. Stripped of everything except the pressed-on fork races in the head tube, a quality steel bike frame should weigh in the 2.0 - 2.2 kg range -- I think that you will find very few that weigh less than that (let the brag-fest begin). Of course, smaller frames will shade on the lower end, and larger a bit more, but the differences are smaller than you'd think. My experience is that forks vary twice as much, percentage-wise: stripped of everything except the lower headset race, forks that I have in the 57 - 63 cm frame size, and that I know to have butted blades, range from 698 g to 832 g -- that's a 20% difference, and the high one is actually on the small side of the frame size, so it has a shorter steerer tube. Of course, the frame it goes with is, strangely, the lightest one I've owned, and I have to say that I once missed a turn on that bike, hitting a low concrete wall head on (at fairly low speed), stopping the front wheel dead and sending me and the bike right over the bars onto the (fortunately) grass/earth on the other side, and the bike suffered no damage at all!

It is the frame of my early 70s Moto Grand Record. It has no Reynolds decals on the Frame. I have a faint mark on the seat tube where the decal used to go and nothing on the fork. Based on my research the early (pre-73) GR are 3 tubes only, but I have no solid evident. Anyone has a Moto catalog older than 1973 that want to look it up for me?

As I recall, the early Grand Records were fully butted Reynolds. Might be catalog info somewhere on the web...

The tops of the fork blades and bottom of the steer tubes were stamped "REYNOLDS 531 BUTTED" but these marks were often lost when the tubes were trimmed and brazed.

The Ishiwata 022 stays and fork blades used on many Trek "531 main tubes" models were identical in composition and physical dimensions to Columbus SL stays and blades so it is unlikely that any weight was added in using these parts. They were used because they cost less than Reynolds 531 and provided a salient distinction between models.

John, just out of curiosity, would you know if Tange ever did such stampings on main triangle tubing (like Columbus, and as opposed to the steer tube), and if so, where one would expect to find it?

-Kurt

I don't recall any, and I just check a couple sets of Tange tubing I have here and found no markings. Tange steer tubes are rifled like Columbus, but have 6 ridges vs 5 with Columbus. But even this isn't definitive because Vitus also used 6 helical ridges in their steer tubes.

Just went through steer tube like an archaeologist and didn't find any markings on the tube. It does have campy dropouts. Anyone has pre-73 Moto catalog?

I assume the OP is refering to his circa 1973 Motobecane Grand Record, in which case it is Reynolds 531 (butted) for only the main tubes.