Reynolds 531 Magic Tubing

[Jamesbike]

Wow this is turning in a very sharp discussion!

So in light of all this, it doesn't seem so impossible to replicate the Eden Rock frame "behavior". By this I mainly mean, vertical compliance, energy transfer and bottom bracket movement. The geometry of a new frame could be slightly adapted from the Eden's for 27,5" disc wheels, the main thing would be finding an equivalent material to replicate the frame mechanical properties.

What is available today to match the 531 Magnum tubes characteristics? Or can those tubes still be found "NOS"-like?

You would need to find a steel mtb bike builder??

There must be a few about.

I agree 531 is a very sweet frame material.

As said previously 725 would be the equivalent tbh. 525 equivalent to 501 I guess...

 

[danson67]

OK, here's the tube spec for your old 531 Magnum.



So:
Down tube 35mm 1.0/0.7/0.9mm butting
Top Tube 31.8mm 0.9/0.6/0.9mm butting
Seat tube 31.8mm 1.0/0.7mm single butt
Chainstays 30/17 oval 1.2mm wall
Seat stays 19/14mm double taper 0.9mm wall

If you wanted another steel frame with the same characteristics, the actual steel alloy used is irrelevant, as all steels have the same unit stiffness...the same stiffness for any given volume of material.
What dictates the feel (aside from the geometry) is the stiffness (or not) produced by varying the tube diameters, tube shapes, wall thicknesses, and the lengths of the butting.

With higher strength steel alloys, stiffness is gained by further increasing the tube diameter, but reducing the wall thickness to keep the frame weight low. With a higher yield strength, the stronger materials can flex/strain more without bucking.
Generally, named butted steel tube sets for custom builders are pretty high end and high strength these days.
Most named bike tube manufacturers do not have much tubing with wall thichnesses like old 531 Magnum these days, since their steel alloys are so much stronger.

So, looking at the three main tube manufacturers:
-Columbus Cromor is a decent Cr-Mo tubeset 0.9/0.6/0.9 for DT and TT, there are no 31.8mm seat tubes with such thick walls. The heaviest is Zona at 0.8/0.6mm wall.
-Dedacciai have nothing as heavy as your frame.
-Reynolds 631 has tubes which are similar.
If you were paying for a custom builder to make you a new frame, I would suggest going for one of the higher grade tubesets. The ride will be better, the builder will be used to working with it, and the price will be only a small amount more, as long as you don't choose anything stainless (Reynolds 953, 921, Columbus XCR).

All the best,

 

[hamster]

Tony Oliver (a very engineering-led framebuilder, he was also a materials lecturer at Bangor Unversity) maintained that 531 Magnum was over-heavy and driven by fashion rather than need. He advised against it, backing up danson's point.

 

[faber26]

Ok thanks for those insights!

Please note I'm not trying to prove that 531 is the best steel out there, or the lightest, etc. but precisely, however heavier it could be compared to bikes made from modern material, this old Peugeot really feels light

It is difficult to explain or to describe, but to give a comparison, I believe that the closest bike I have had in terms of riding sensations was the titanium Dean Colonel X Lite.

After all, replicating the Eden Rock is probably a pointless quest ... maybe I just ought to love it as it is and keep riding it as long as I can. And wait for the next divine surprise

 

[grantoury]

maybe I just ought to love it as it is and keep riding it as long as I can

Absolutely, a bicycle frame is just a couple of tubes fused together until someone starts enjoying it. I have a very humble road touring bike that is a perfect fit, and the Columbus Cyclex tubing is great; stiff and still comfortable. I have thought about having built something fancier, with lugs and nicer steel, but it wouldn't be the same.

 

[danson67]

Tony Oliver (a very engineering-led framebuilder, he was also a materials lecturer at Bangor Unversity) maintained that 531 Magnum was over-heavy and driven by fashion rather than need. He advised against it, backing up danson's point.

Yes, to emphasise the point, Tony Oliver did his loaded touring on a silver brazed 753 frame with standard diameter tubing.
In his own words: "You do not need thick, heavy oversize tank tubes for an off-road bike...The ATB market is demanding heavier and larger tubes...there is a 'megasize' tube set called Magnum 531...I marvel at the extremes to which fashion has driven this market. "



I think it's important to note that the Magnum range (including 531, 501 and 500) were all very overbuilt, presumably as a response to the lack of knowledge at the time on just how much load a mountain bike frame could be expected to receive.
531 was a very good and long established steel alloy, up with any of the 4130 Cr-Mo materials that are still available.
More experience of mountain bikes builds combined with later higher strength alloys, steel mountain bike tubing has changed a lot.

If you look at the rest of the Reynolds chart at the time, you will see that most of the 531 variants have the same wall thickness as Magnum but are smaller diameter...
Stiffness increases proportionally with wall thickness, but increases as a cube of the diameter, so adding 1/8" to the diameter of a 1" top tube, while keeping the wall thickness the same, adds 12.5% to the weight, but 42% to the stiffness. Sometimes that much stiffness is not a good idea.




All the best,

 

[Prodigal Son]

I've just measured the diameters of the diagonal tube (35mm) and the seat and horizontal tubes (32mm), indeed quite unusually big.

BUild a bike w/ those diameters and you will have the ride you like.

 

[Imlach]

Tubesets don't matter.

(Please don't hurt me)

 

[Jamesbike]

Yes, to emphasise the point, Tony Oliver did his loaded touring on a silver brazed 753 frame with standard diameter tubing.
In his own words: "You do not need thick, heavy oversize tank tubes for an off-road bike...The ATB market is demanding heavier and larger tubes...there is a 'megasize' tube set called Magnum 531...I marvel at the extremes to which fashion has driven this market. "

View attachment 650255

I think it's important to note that the Magnum range (including 531, 501 and 500) were all very overbuilt, presumably as a response to the lack of knowledge at the time on just how much load a mountain bike frame could be expected to receive.
531 was a very good and long established steel alloy, up with any of the 4130 Cr-Mo materials that are still available.
More experience of mountain bikes builds combined with later higher strength alloys, steel mountain bike tubing has changed a lot.

If you look at the rest of the Reynolds chart at the time, you will see that most of the 531 variants have the same wall thickness as Magnum but are smaller diameter...
Stiffness increases proportionally with wall thickness, but increases as a cube of the diameter, so adding 1/8" to the diameter of a 1" top tube, while keeping the wall thickness the same, adds 12.5% to the weight, but 42% to the stiffness. Sometimes that much stiffness is not a good idea.

View attachment 650254


All the best,

Unless you need a 25" frame in which case it might help.

Ditto a 19" frame with standard butted tubes might be rather stiff.

 

[Guinessisgoodforyou]

I think whatever your frame is made of, if you like ride it. If you don't sell it. Technical specs and opinions mean nothing to any of us in the real world, if we enjoy what we ride. I think sometimes we are all guilty of overthinking. Ride and be damned