banjo_mole 

I've seen many bikes with tubing decals such as "Reynolds 531 (main triangle!)"

Lesser quality tubing was used on the stays and fork of such bikes, AFAIK.

Would it have made more sense to do it the other way, and use the better tubing on the stays, where power transfer is important?

Or am I talking out of my bum with no idea of real world physics?

Let me know.

-Nick

mkeller234

I am guessing it is more of a weight thing. The main tubes are the biggest so they used the lighter, thinner walled tubes there.

roccobike

Interesting question. I've wondered about that. Consider that on the early aluminum bikes like the Univega Neuvo Sport 450, the main tubes were aluminum but the stays and fork were steel for flex and comfort. On new bikes the forks are almost all carbon, and quite a few nicer bikes have carbon inserts in the stays. So the stays and fork provide the flex in the ride.
So how come I find chromoly frames with hi-ten stays and fork more comfortable than straight hi-ten frames?
I just confused myself!

abarth

Actually, thick wall hi-ten steel stays will flex less than the thin wall 531 stays. It is more of a weight thing.

soonerbills

So would you say a bike with cromo forks rides stiffer than plain steel version?

old's'cool

No reason it should, given that the two bikes are designed for the same purpose (i.e. road, touring...). In fact, it should be the other way around. The whole point of Cro-Mo (and other high alloy steels) is that it has higher yield strength, so a thinner tube can withstand the same load without yielding. A side effect of this is that it flexes (elastically) more, which is generally seen as a benefit in ride comfort, and sometimes in energy transfer to the drivetrain (via short-term energy storage in the springiness of the frame).

abarth

If the chromoly steel and the plain steel has the same thickness and same diameter and the fork geometry is the same, then they should ride the same. In reality, chromoly steel has higher yield strength, so they are make thinner and ride less stiff than plain steel.

Kommisar89

I always find it interesting how modernistas who favor compact frames like to point out how the sloping top tube makes the frame so much stiffer (even apart from large diameter aluminum or carbon fiber tubing). Apparently nobody cared about frame stiffness back in the day or they would have been building compact frames back then. Instead tubing kept getting thinner and frames kept getting flexier through the early 90's and the advent of large diameter steel and aluminum tubing. Anyway, as to the OP's question, if what I've heard is correct, a typical complete CroMo steel frame weighs about 2.5 lbs. less than a similar hi-tensile steel frame. If I had to guess I'd say a CroMo main triabgle would probably account for close to 2 of those 2 1/2 lbs. and that's the big difference. A hi-tensile steel frame will typically have a slightly harsher ride due to the thicker tubing but will flex more in the area of the seat tube where the front derailleur attaches due to a thicker, stiffer bottom bracket (or so says Jan Heine in Bicycle Quarterly). This agrees with my seat of the pants experience with CroMo and hi-tensile steel frames.

unworthy1

just an historical note: there are multi-thousands of individual frames, from hundreds of builders, that used high quality DB tubing for the 3 main, and lesser grade stuff for the stays and forks. In early days it was Columbus with Falck stays and blades, later we got all those "Tre-Tubi" framesets.
Word is that a LOT of very costly high-end frames that had the "All-Columbus" sticker actually used Falck and the like for the stays and blades cause nobody would know and the big-name builders saved a few Lire in materials cost. Technically they didn't lie since the decals didn't specify how much of any frame was Columbus, it was just implied that the entire thing was.
People who owned and rode them never knew either, and loved their ride quality just the same. If they bothered to weigh the bare frame, they might have had suspicions, but Falck wasn't as heavy as some of the cheap Hi-Ten or common steel.
Early Reynolds 531 decals were more content-specific and maybe the builders who used 531 were more inclined to honestly divulge the exact content, but maybe not.

cudak888 

Keeping the BB shell planted in one place relative to the front of the bike seemed to be more important back in the day. Peugeot's PY-10 team frames had standard 531SL DB downtubes for this purpose (while the rest was the typical metric tubing).

-Kurt

randyjawa 

There was a time when I bought into the best tubing hype. Though there are engineering issues attached to tube types, my guess is that the average guy, and I am one of those, would not be able to tell the difference, in ride quality, between two identical bikes - one with high tensile tubes and the other chrome moly. All other tings - geometry, size, and components fitted - being equal.

Is there a cost savings to NOT use chrome moly butted tubes? Probably! And that might be another reason for not using chrome moly in stays and forks.

But there is something I have personally noticed about using chrome moly for forks and stays. Actually, this applies mostly to stays.

Chrome Moly stays are have thinner walls, than do their less sophisticated counter parts. And those thinner walls crush easily, when compared to the thicker walled high tensile steel models. And lots of people, in days gone by, liked to install those horrible clamp on side or center stands. And the thin wall chrome moly stays DO NOT LIKE TO HAVE STUFF CLAMPED TO THEM! I have seen several crushed and crushed quite badly, cr-mo stays. I have seen clamp damaged high tensile stays also, but not nearly as badly damaged. And this pushes my though to the next level...

Since the stays, particularly the chain stays, are close to the ground, they are more likely to experience impact (flying debris, sticks and you name it). Would the stays be more or less prone to being dented? I am not even sure that this is as even reasonable concern but I have thought about it.

Finally, the overall diameter of both forks and stays is considerably less than main tubes. The smaller size of the tubes might make any weight saving insignificant for anything but the all out racing bicycle.

Well, that's about it. I have shared my thoughts on a topic that I know very little about. However, I would like to leave you all with another thought, to be presented in another thread, perhaps.

Just exactly what are we talking about when we discuss ride comfort? Remember - do not answer that question here, but at least think about it when considering the comments on this thread.

Mornings are fun!

bbattle

The better steels have the same stiffness as the thicker tubes, they were just lighter. Making the tubes oversized made them even stiffer. Smaller frames(ie. with sloping top tube) are stiffer because the main triangle is smaller. Stronger seatposts allow this design to work.

Frame builders would use the cheaper tubing for the stays because the weight penalty was minimal and it kept the cost of the frame down.