Butted Forks and Stays - Is there a real advantage?
 

Been following numerous threads mentioning tubing lately, and had a question: what is the technical advantage of double butted fork and stay tubes? I can clearly see the advantage in the main tubes, especially allowing lighter tubes with sufficient "meat" where the tubes are brazed into the lugs, but given how small diameter the stay tubes are (and they are not always brazed into a lug), and the fact that fork tubes narrow down significantly at the front axle, is there a true advantage to a double butted fork or stay tube?

Mark

It would affect the ride, and somewhat on the lightness. I have noticed butted stay bikes seem to ride just a touch nicer than their straight gauge cousins, more lively and a bit less harsh. Straight gauge or high ten stays, it always seems like the saddle soaks up everything on the road. Maybe I am imagining it?:D,,,,BD

I'm mot aware of any vintage tubesets with butted stays or forks. This is a common misconception due to the Reynolds 531 decals which stated "butted tubes, forks & stays" The "forks and stays" reference was added to indicate that they were made from Reynolds 531, not that they butted. Reportedly, this confusion led Schwinn to prompt Reynolds for decals that clarified matters by stating, "fork blades, stays & butted frame tubes".

Reynolds 531 decals stated "butted frame tubes" are meant to indicate that only the 3 main tubes are guaranteed Reynolds 531. The stay and forks are may be lesser grade and/or from another manufacturer.

Many other manufacturers followed Reynolds nomenclature, so the misconception grew.

Interesting, you learn something new every day. That would confuse anyone. Maybe it was just the quality of the frame in general, that made them ride nicer over the rough stuff:),,,,,BD

I was thinking what T-Mar said, but I wasn't sure enough to post it. Wasn't there a special Schwinn Reynolds sticker that clarified the issue?

I would expect geometry to impact ride quality more than butted tubing for those parts. I had the same question 30 years ago and made the assumption that they were not butted due to their size and the challenge of shaping them. That was during my undergraduate engineering educaion. My cockiness may have worked this time!

I have always assumed that butted tubing gave a more vertically compliant frame, while remaining laterally stiff.

Food for thought!

yes:

http://www.mrmartinweb.com/images/bike/paramount531.jpg

To answer the original question, double butted steel forks are used today in several modern rigid MTB and CX frames. I suspect that the advantage is a stronger fork that deals better with pounding (like landing on it after jumps) I do not see a real benefit for a bike with a front wheel that is intended to stay on the ground at all times during its use. There were a few models that featured butted stays (the Jamis Dakota comes to mind) and I suspect that the practice was for the same reason (landing on the rear wheel) but it was not as wide spread as butted forks.

Thanks all - T-Mar's response clarified a misconception I have carried with me for 30+ years! I had indeed assumed the sticker meant forks and stays were also butted.

Mark

I don't have my Reynolds decal sheet at work, but weren't some of the 531 tube sets supplied with what they called "taper gauge" forks and stays? I always assumed that meant thicker at one end than the other - but instead of a "butt", a more continual thinning.

Exactly what I was coming to the bottom to add. I'm pretty sure I can find a reference for this also.

That would be all of the Reynolds 531 stays and forks

complete Reynolds tube set stickers from the 80s with descriptions:

http://equusbicycle.com/bike/reynold...-transfers.jpg

Also here (http://equusbicycle.com/bike/reynold...-transfers.jpg ) if it is too small to read in the embedded img

edit: the site does not play nice, so here is the URL to copy and paste: equusbicycle.com/bike/reynolds/Reynolds-transfers.jpg

And, for that matter, that decal has also popped up on '70s Raleighs. Likewise, the standard 531 transfer also made its way onto Paramounts - my '72 being one of them.

-Kurt

Correct on the stays TTBOMK but not the forks. As the Reynolds tubing chart shows, Reynolds butted the fork blades on all the high end road tube sets. I imagine Columbus did the same thing but I don't have that information.

Yes. Fork blades start out as plain ol' round tubes that are tapered, ovalized (sometimes), and raked. When you taper a straight-gauge tube, the end that becomes smaller in diameter (the dropout end) becomes thicker as well. Reynolds' "taper gauge" blades start out as a round tube with a gradual decrease in wall thickness from one end to the other. The thin end gets tapered, and the wall thickness increases such that the tapered blade has more or less uniform thickness from the crown end to the dropout end.

This used to be a patented process owned by Reynolds, but it has long since lapsed into the public domain so by the 1980s every reputable steel tubing manufacturer was using taper-gauge blades for their higher end tube sets.

pretty sure tapered seat stays also start out thinner at the ends before they are tapered, or else they would be a lot thicker than they are.

This is directly contradicted by Reynold's own information (as referenced above) which shows that the wall thickness on the high end forks varied from 1.0mm to 0.5mm.

I think that's true. I measured the wall thickness on my old frame built from Reynold's 700* tubing and the seat stays appear to go from 0.6mm at the seat tube to 0.7mm at the drop outs, while the chainstays go from 0.6 to 0.9. The product of diameter x thickness is thus more or less constant for the chainstays but reduces on the seatstays.

*700 was a weird experiment by Reynolds in the 80's apparently similar to 708 but with a different internal shape. I was told that 700 had elliptical internal profile while the 708 was octagonal but that isn't true, I can find no lateral variation in wall thickness in any of the main tubes on the 700 frame.

** wall thicknesses measured with a high precision ultrasonic echo - echo thickness gauge (Nova 800 series). I have confirmed the accuracy of this unit on tubes down to 15mm diameter, not sure how well it performs below that (curvature may become an issue)

Rooting about on the equusbicycle site, the section on Ishiwata tubing also had some interesting information: their 024 set had butted main tubes (double butted top and down, single butted seat) and plain gauge stays and fork blades, the 017 set was db all main tubes, with plain gauge stays and taper gauge fork blades. In all cases the decal says, just like reynolds, "double butted tubes, forks and stays".....looks like "decal marketing" was common in the day!

If you explore further the Ishiwata catalog gives very clear illustrations of how their stays and forks are formed and should be used.

Related question: my 1983 Trek 600 has 531db main tubes, but the catalog only specifies "manganese alloy" for forks and stays....anyone know who made the tubes? 1982, similar model, shows Ishiwata Manganese Alloy for those components. I couldn't find Ishiwata manganese alloy in the Ishiwata catalog on the equus site.....

Thanks, Mark

ps. Should have named this thread "Everything you ever wanted to know about stays and forks but were afraid to ask"!

Whatever you named it, markk900, this is an excellent thread so far!!

Like equusbicycle I have also collected vintage Reynolds info on my site.

Ishiwata's manganese alloy was called Magny. During the period in question, there were two grades, Magny V and a lighter Magny X. Tange also offered manganese alloys under their Mangaloy range. Columbus countered with Aelle.

Often, forks have a stamped impression on the steerer tube to indicate the manufacturer. If you're willing to remove the fork, you may be able to confirm its origin.

On the Columbus website, they have diagrams of their tubes. They have butted chain and seatstay tubes and butted fork tubing as well. Here's a link to their Zona (heat treated steel) tubing:

http://columbustubi.com/grafica/zona_img2.gif

And SL (as they made it in 2009)

http://columbustubi.com/grafica/sl_2009_img1.gif


Off-topic, anyone know a builder using Columbus' XCr tubing?

I suspect this may be referring to the gauge of the untapered tube. I just checked some raw, tapered blades here (531 and 753) and found them to be 1.0mm thick at both the crown and dropout ends.