How different are the different grades of steel used for bike tubing?
Would Reynolds 725 be noticeably different to 853? Are the numbered Reynolds grades noticeably better than basic cromoly?
Without a clear definition of "better" the answer is no.
Better - something that lives up to the usual descriptios of steel....lively, springy etc. Not lumpen, harsh, heavy and corrodes easily - like hi-tensile....
I think the key thing to remember is that for 2 tubes of equal diameter, wall thickness and butting profile, the 2 tubes will behave exactly the same in terms of stiffness regardless of the steel alloy and will be the same weight.. A theoretical frame constructed from the cheapest, lowest 'quality'* steel will ride exactly the same as a frame constructed from the highest quality available steel if the tube profiles are identical. It wil also weigh the same.
In practice, the higher strength (better quality) steels can be drawn with thinner walls and shorter butting profiles without compromising the strength (among other things) of the frame. This is why higher end tubing produces lighter, stronger (and possibly better riding) bikes.
To answer your question, the higher end Reynolds steel will be better. If you count lighter, stronger and stiffer as attributes of being better. But not (directly) because of the material but because of the tube profile.
Interestingly Genesis steel frames don't all get lighter as they use better steel!
Older steel frames are smaller guage and ride quite differently to modern ones IMO.
Stiffness is related to tube diameter. The stronger tensile strength of higher end steels means the walls can be drawn thinner - so lighter. But they are then made with larger outer diameter to increase rigidity.
A standard Reynolds 520 or 525 frame will ride just like an old 531, geometry being equal. And this is in my opinion THE big deal; road bike geometry has settled on reasonably aggressive 73 degrees parallel frames, this is a little steeper then historic (track bikes excepted). Mountain bikes have become a lot slacker.
An oversize 953 frame will be stiff and light and expensive. There is little difference in performance (weight and stiffness) between 520, 525, 531, 631 and 753. Outer tube diameter will be the big determinant of perceived differences.
Light? Relatively, maybe...
Indeed, but 953 is now giving titanium a serious run for its money. But still a pound heavier than carbon. And I have three steel bikes in three flavours (fixed road, TT and mtb). I do like them, but don't have a really high end steel frame - the TT is Columbus Aero tubing and a work of art , but stiffness would not be an adjective that springs to mind when it is sat in the turbo trainer. A high end Pegoretti or Volare will be much stiffer and a little bit lighter.
A high end Pegoretti or Volare will be much stiffer and a little bit lighter.
That depends. I have a pegoretti and another Italian road bike of similar construction and very similar tube sets (Columbus spirit) same top and down tubes but different stays and one has a tapered head tube. To look at you would expect them to ride quite similarly but they couldn't be more different. Both stiffer than old lugged stovepipe frames but the pegoretti is a magic carpet compared to the Chesini where you get feedback from the tyres as you can feel them compressing, not much difference laterally as neither handle like a wet noodle and both are identical geometry but the pegoretti is a lot more vertically compliant.
I don't think an expensive tube set guarantees good ride quality as a lot of high end frames are the first of their kind from a small frame maker who doesn't have the experience of building many frames or rider feedback to know how that frame will ride as its all guesswork and a fancy paint job.
I'm amazed how thin the better tubesets are, .38 in the middle of the butting and you can see it deform when you squeeze it with your fingers 😯
My pipedream is 631. Feels nice to me. Can say it feels any difference to the 501 bike it replaced.