Steel Wall Thickness and Rider Weight

[559Rando]

Hi guys, I've been googling a little and coming up dry. Do any of you have tips, rules of thumbs or tubing manufacturer's tables that relate wall thickness and outer diameter to rider's weights?
Thanks!

[fogrider]

I'm not a frame builder, and I think a frame builder is better suited to answer this. but my two cents...853 and OX tubing is different from older tubing in that its air harden and gets stronger after welding...so what do you care about wall thickness?

[559Rando]

so what do you care about wall thickness?

I guess I wonder how far can you chase "planing" before it's just sloppy?

[keevon]

I'm not a frame builder, and I think a frame builder is better suited to answer this. but my two cents...853 and OX tubing is different from older tubing in that its air harden and gets stronger after welding...so what do you care about wall thickness?
Strength is not the same as stiffness. Tube diameter and wall thickness determine stiffness.

http://www.vendettacycles.com/vendettacycles/stiffness.htm

The overall stiffness of the frame determines its ride characteristics.

[keevon]

I guess I wonder how far can you chase "planing" before it's just sloppy?
Probably best to talk to someone like Mike Kone at Boulder Bicycle. I think the biggest concern is shimmy: too light of a tubeset for a bigger or heavier rider will be more likely to cause shimmy.

[InspectorGadget]

I called Waterford this morning about an ebay listing and was told the weight limit for the bike pictured below (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=161093970107&ssPageName=ADME:X:RTQ:US:1123) is 220 pounds.

http://i.ebayimg.com/t/Waterford-R33-S3-Superlight-Steel-953-Stainless-Steel-54cm-Work-of-Art-/00/s/OTI3WDE2MDA=/z/fe8AAMXQb2JSGmic/$(KGrHqFHJE!FIBZTB-edBSGmibPF,!~~60_57.JPG

Not much help, but that's all I have to contribute.

[soulspinner]

That Waterford is steaming.........

[InspectorGadget]

That Waterford is steaming.........Yes it is.

[oliver1850]

Just an anecdote, but in the days of Columbus SL and SLX wall thickness was increased with frame size. The assumption may have been that bigger frames were going to have heavier riders, but that's clearly not always true. On the Nova, Serotta put an SP downtube (.1 mm thicker than SL) on frames 58 cm and up. I think 60 and above had an all SP main triangle.

[ultraman6970]

IMO the reason for increasing the thickness of the tubing was not rider weight but to keep the integrity of the frame, stiffness wise.

The larger the frame the flexy it gets if you put the wrong tubes in them, not the same a 50 frame than a 64 frame if the same tubing is used, the triangle in the larger one will flex a lot under load even if the rider is not that heavy.

[bikingshearer]

About the only general rule of thumb I can think is that, in general, for a given application, the bigger you are, the thicker the tubing probably ought to be. Nto so much for strenth, but for ride characteristics.

Beyomd that, my guess (and it is exactly that) is that, if you ask 10 different top-rank frame builders about tubing choices for a given weight rider, you will get approximately 10 different answers, but first you will get more questions. For certain there will be questions concerning what kind of riding the frame is intended for, whether the rider prefers a stiff or less stiff feel, the height of the rider and the length of certain key parts of the rider's body. Some have a more lengthy list than others.

The reading I have done over the years (not even remotely exhaustive) suggests that each builder develops their own beliefs and key measurements that tells them what they need to know. The resulting frames aren't likely to be way off from each other, but there will be subtle (and sometimes a bit less than subtle) differences.

Some builders like to mix and match tubing. For example, both my Ron Cooper and my Eisentraut (neither built for me) are a mix of tubesets. I do not know what they used and, except for curiosity's sake, I don't really care - they know how to do this stuff than I ever will, and if the tubing was good enouogh for them, it's plenty good enough for me.

[Mark McM]

Just an anecdote, but in the days of Columbus SL and SLX wall thickness was increased with frame size. The assumption may have been that bigger frames were going to have heavier riders, but that's clearly not always true. On the Nova, Serotta put an SP downtube (.1 mm thicker than SL) on frames 58 cm and up. I think 60 and above had an all SP main triangle.

These tube sets were designed in standard diameters for lugged construction with standard lug sets. Increasing the diameter was not a practical option, so greater strength/stiffness was achieved by increasing the wall thickness.

The stiffness of a tube in bending is inversely proportional the cube of its length, and its stiffness in torsion is inversely proportional to its length; even to maintain the same stiffness, the longer tubes in the larger frames needed to have thicker walls.

[559Rando]

Thanks for chiming in. One thing that I remember reading, too, that also convolutes the issue is the length of the butts.

So you could have two .8/.5/.8 tubes of the same length, but one will be more flexible if the length of the butts differs. And if we said it both were 58cm long, but one was for a 200# rider and one was for a 160# rider, the tube for the heavier guy would likely have longer butts. As an aside, though, I don't think there'd be much weight penalty there. Do the armchair physicists and mechanical engineers agree?

I was hoping that there was an old Reynolds table somewhere that showed a frame built with 531c was appropriate up to x pounds, or maybe there's a more exhaustive matrix out there in the recesses of the framebuilding canon.

[Mark McM]

Thanks for chiming in. One thing that I remember reading, too, that also convolutes the issue is the length of the butts.

So you could have two .8/.5/.8 tubes of the same length, but one will be more flexible if the length of the butts differs. And if we said it both were 58cm long, but one was for a 200# rider and one was for a 160# rider, the tube for the heavier guy would likely have longer butts. As an aside, though, I don't think there'd be much weight penalty there. Do the armchair physicists and mechanical engineers agree?

The butts actually don't have much affect on the stiffness, for two reasons. Firstly, the butts are relatively short compared to the (thinner walled) middle section. Secondly, stiffness of any system is dominated by its most flexible elements (which is the thinner center section of the tube).

Consider two tubes, each 100mm long. One had a constant 0.6mm wall thickness, and the other had 10mm long 1.0mm thick butts and an 80mm long 0.5mm thick center section. Each tube would weigh the same, but which would be stiffer? The constant cross section tube would the stiffer one (close to 20% stiffer in torsion), because it is thicker for a longer length of the tube.

The butt lengths of a tube aren't selected for the weight of the rider, but for the geometry and locations of the joints. Tube manufacturers make tubes with different butt lengths, and then the builder selects the butt length so that after the tube is cut to length, there is a sufficient length of the butt left near the joint.

[oliver1850]

These tube sets were designed in standard diameters for lugged construction with standard lug sets. Increasing the diameter was not a practical option, so greater strength/stiffness was achieved by increasing the wall thickness.

The stiffness of a tube in bending is inversely proportional the cube of its length, and its stiffness in torsion is inversely proportional to its length; even to maintain the same stiffness, the longer tubes in the larger frames needed to have thicker walls.

Right, but my point was that in that era off-the-shelf frames got thicker walls at a size (length) point. I don't know of any that were sold with an SL/SP option in the same size, which would indicate rider weight was the major consideration as opposed to length of the tube. Seems it would have been easy to do from a builder's perspective if it had been deemed desirable.

[merckx]

It is heart-warming to read a fervent discussion regarding the attributes of steel tubing that is of the vintage of SL, SLX, SP, 531 in this day of ubiquitous plastic machines!

[seat_boy]

I had a Rawland Nordavinden, which has standard gauge tubing with a 7/4/7 top tube. Even in an XL frame, I didn't find that too noodly for my 175 pounds.

[Grant McLean]

I don't know of any that were sold with an SL/SP option in the same size, which would indicate rider weight was the major consideration as opposed to length of the tube.

Did rider weight vary as much back then as it does today?

I recall mostly skinny white guys on road racing bikes in the 80s,
now cycling is popular with people of all shapes and sizes.
Maybe back then, they didn't anticipate the market need for
building a model of high end frame specifically for Clydesdale
riders?

-g

[ultraman6970]

The difference with back in the day and now is that back in the day nobody cared about being healthy and the habits of chubbies were different too.

The other factor is that back in the day or you had a 100 bucks POS colegiate bike or you had a custom or italian 2000 bucks high end bike and thats it, so pretty much if you were not into the sport it was rare to see a refrigerator perry riding a high end bike or riding a bike at all, now a days everybody can get a 1500 bucks bike w/o too much of a problem, add that a growth in population and there you have it... a lot of chubbies like me riding everywhere.

Bike manufacturers had to adapt to this issues aswell and started designing stuff for bigger people too, besides the fact that you can sue anybody for the most stupid reason, manufacturers had to engineer the products so could be usefull by anybody too.

Anybody remember when the tubes manufactures introduced butted tubes??

[cachagua]

According to Wikipedia, the Reynolds Tube Company in Birmingham, England, patented a process for making butted tubes in 1897.