I recently inquired about a rather nice Coppi made from Thron, the guy replied back and said the frame weighed 6lb: 4lb for the frame and 2lb for the fork. Something tells me this is innaccurate.... a quality 531c frame is around 4lb. I'm sure it's more like 4.5lb frame; 1.5lb fork.
Thron is double-butted cold-drawn cromo - did it replace the 1980's sturdy Columbus Cromor? What year did Columbus bring out Thron? Anybody own/or used to own a bike made from this and how does it compare to say Todays Columbus Brain and Reynolds 525?
The tubeset seems to be most common on bikes circa 1990's. From what's written about it on the web, it would suggest this tubeset is better than Aelle and Gara but below old SL on the quality scale. If SL weighed about 1900g (a little bit more than 531) for a 56cm sized frame, I assume this weighs about 2150g, that is, if Gara weighs 2300g with Aelle(plain cauge) the lowest marque, weighing in at about 2375g?
Here's my take on these tubings from what I've read/heard.
A Brain tubeset consists of double butted Cyclex tubing with seat stays made of standard Chromoly.(Columbus SL/SP was full Cyclex).
Thron is full double butted standard Chromoly (probably just renamed Cromor).
531 is a manganese-molybdenum medium carbon steel.
525 is butted Chromoly (replaced 531).
Thron is better than Aelle and Gara because those tube sets were constant thickness. I don't know exactly when these came out but I would guess sometime in the early to mid 1990's.
Regarding 531 - The Reynolds 531 tubes have been around since the 1950's and have gone through many transformations and were available in many different versions (constant thickness, butted, superlight). In fact some bikes came with 531 stickers that had main tubes made out of 531 with other tubes and/or fork blades made out of another type of steel.
So unless you know exactly which 531 tubeset was used on a particular frame it's hard to compare the weight to another frame. Two identically sized frames made with two different versions of 531 would have different weights.
I believe that 525 came out around the same time as TIG welding became popular. It was a tubeset created to appeal to TIG welders.