Correct and a quick sanity check shows this to be true. Let’s look at two tubes of the same length and a standard 28.6mm outer diameter. If you look at a Tange #5, plain gauge, CrMo seat tube which has a wall thickness of 0.9mm you get a cross sectional area of 78.3 square millimeters. Now, if we take a high tensile tube which has an inner diameter of 25.4mm (which is fairy typical), we come up with a cross sectional area of 135.6 square millimeters. Since all steels vary very little in density, the relative cross sectional areas can be equated to relative weight and the CrMo tube is 57.8% the weight of the hi-tensile tube. That’s pretty close to the 60%.

Yes, the difference will typically be less. Even if the manufacturer used a full Tange #5 tubeset, they would probably use lugs and shells that weighed the same or very similar. This will cut down on the weight advantage of the CrMo frame.

The better material frame will probably also have more fittings. The rear dropout will likely have a hanger that adds weight while the hi-tensile frame likely has a hangerless, stamped dropout. The better frame probably has shifter bosses, which weigh less than the cable stops for the stem shifters on the hi-tensile frame. The CrMo frame probably has an extra water bottle boss. Basically, the better frame likely has more convenience fittings which add weight and further compromise it’s weight advantage over the hi-tensile frame.

However, the biggest compromise are the stays and forks. In these applications CrMo’s potential weight savings cannot be fully realized because the forks and rear triangle would be too whippy. Stiffness in a round tube is a function of the material’s modulus of elasticity, its outer diameter and its thickness. In the case of CrMo and 1020 hi-tensile, the modulus of elastic are similar and the stiffness primarily becomes a function of diameter and thickness.

A main triangle can maintain good stiffness, primarily due to the larger diameter tubes. But shrink the diameter, as in the stays and fork blades and things start to get whippy. In order to maintain the necessary rigidity, Tange used CrMo stays that are about 80% the thickness of their hi-tensile stays. So, in these regions you lose about ½ the potential weight savings of CrMo. This is why designers often substitute lesser grade material in the stays and forks. It saves money without affecting the weight as much.

Then there is the whole question of how much the designer wants to push envelope in either direction. Does he want to go heavier than the norm, knowing it is more likely to be abused and used in all sorts of applications? Or can he make it lighter, knowing that it will be used only in certain applications and that the extra cost will result in better care? A designer of an X-mart bicycle is going to build in a heavier safety factor than a standard hi-tensile frame, while a designer of a time trial frame will build in a lot less than your typical CrMo frame.

Back in 1983, Bicycling did a comparison of entry level bicycles. A Pansonic Sport with a full 1020, 21"frame weighed 6 lbs 9oz. An identically sized KHS Citation (notice how I found a KHS for you) with a Tange #5 main triangle, weighed 5 lbs 9 oz. Obviously there will be some differences in weight savings due to actual tubing gauges, geometry, choice of lugs, fittings, etc., but it looks like a roughly 1 lb weight savings by going to plain gauge, CrMo, main tubes over hi-tensile.

Now, here’s the bonus. I found a road on a 1985 KHS Fiero with a Tange 900, seamed, double butted, main triangle. Frame weight was 5 lbs 2.5 oz and it’s a 2" larger frame. So you’d get about an additional ½ lb saving by going butted CrMo in the main triangle.

You’ve missed one very important point of my previous posts. I was referring to the cost saving of seamed butted CrMo tubesets. Butting is the most expensive operation of tube making. While there are savings in going from seamless to seamed in a plain gauge CrMo tube, they’re relatively small compared to going from seamless to seamed in a butted, CrMo tube.

Let’s take a look at the two previously mentioned KHS bicycles. In 1983 a KHS Citation with a seamless, plain gauge CrMo main triangle cost $219. Two years later the KHS Fiero costs only $20 more, yet it’s got a ½ lb lighter frame, thanks to going seamed, butted CrMo. To top it off, the rate of inflation over those two years was about 7.5%, so the adjusted price increase was only about $5. The components were comparable and, if anything, arguably better on the Fiero. They were certainly lighter based on overall weights.

Seamless, butted, CrMo tubes were pretty much restricted to mid-range and higher models. The best you got for an entry level price up to the very early 1980s was a plain gauge, CrMo main triangle. The mid-1980s seamed tubesets brought butted CrMo butted into the entry level. You got the weight savings of butted tubes but perhaps more importantly you also got their more resilient ride quality. A couple of years earlier you would have had to pay a lot more to get the weight savings and resiliency.