Anyone know if the Mark V and the Mark V Pro use the same or diffierent tube sets? I seems odd that people would pay 50 dollars more for the Mark V Pro only to have a frame that is not drilled for a rear brake and is devoid of braze-on's. Is it just more for less?

The Mark V Pro uses heat treated tubes.

And I suspect that the tubes are 8/5/8 rather than 9/6/9.

-thanks for the info...btw, what is 8/5/8 and 9/6/9? do you know who makes the tubeset? -reynolds, columbus, TT -etc?

First off, my answers are educated guesses. I'm not sure about the exact nature of Tony's frames, but I have a pretty good idea. Tony would be the authority, of course.

9/6/9 and 8/5/8 refers to the wall thickness of double butted tube in the main triangle: the top tube (T/T), down tube (D/T), and seat tube (S/T).

A double butted tube has five sections from end to end:

butted - tapered - thin - tapered - butted

On a 9/6/9 tube, the butted ends are 9/10s of a mm thick and the thin center section is 6/10s of a mm thick. And the tapered sections go from 9 to 6, or vice versa.

8/5/8 tubes are 1mm thinner in the butted and thin sections.

The IRO web site states that the Mark V Pro uses heat treated tubes. I suspect that Tony spec'd the heat treated main tubes as 8/5/8. Heat treating raises the strength of a tube. So thinner walls can be used. This results in a lighter frame.

I could go on and talk in more detail about the tubing, but I'd like to get Tony's nod before doing so.

Let me just say that the Mark V Pro is a VERY nice frame, as are all IRO products.

This drawing:

click here

shows a typical Kogswell frame and the tube dimensions that are used.

I'd be glad to talk about those tubes too.

An interesting one is the D/T. We call a 'bulge butted' D/T. The diameter and wall thickness get larger at the top. This allows for the use of a standard 27.2mm seat post while maintaining enough material (1.2mm) to support the use of a seat clamp.