I was wondering if anyone had input on common diameters for tubing on steel frames. I was thinking of breaking down answers by tube and bike type. The format I had in mind is as follows.
Top Tube Road Bike - Diameter/Thickness Gravel Bike - Diameter/Thickness Mountain Bike - Diameter/Thickness
Down Tube Road Bike - Diameter/Thickness Gravel Bike - Diameter/Thickness Mountain Bike - Diameter/Thickness
Seat Tube Road Bike - Diameter/Thickness Gravel Bike - Diameter/Thickness Mountain Bike - Diameter/Thickness
Chainstays Road Bike - Diameter/Thickness Gravel Bike - Diameter/Thickness Mountain Bike - Diameter/Thickness
Seatstays Road Bike - Diameter/Thickness Gravel Bike - Diameter/Thickness Mountain Bike - Diameter/Thickness
This was the format idea I came up with, feel free to copy and paste or answer the ones you feel pertain to you the most.
If there are a good amount of responses, I can create a PDF/Master Post for people to reference in the future.
I think there’s too many variables you’ve left out for anyone to provide a complete list. For instance, if I were making a road bike for a 5’2" rider weighing 110lbs, I’d use different tubes compared to someone 6’0" and 200lbs.
Still, it’s an interesting topic that doesn’t get talked about much. Maybe if you provide an example rider and draw up a frame in BikeCAD for each bike type, some people will respond.
An early side project of mine has been measuring real-world torsional stiffness of the frames in my shop and correlating that to “ride feel.”
While not the most scientific metric, I think there would be some merit to a relative benchmark test to help inform some tubing profile decisions.
Arbitrary example: for the same load, a frame that deflected 6mm rode smoother than a frame that deflected 4mm. A frame deflected 8mm felt noodle-y, etc
Useful information Daniel. Because you mentioned contemporary steel bikes, how do you see things like stiff wheels and carbon forks influencing tubing selection? Sounds like there’s a concern that they might not play well with flexy frames. The thing that stands out to me is the DT size, which is one size larger than what you’d call “traditional” OS tubing.
It’s true that diameters matter the most, but when I’ve done the beam deflection math it does look like thickness matters. My rule of thumb is that a 7/4/7 tube rides like a 9/6/9 tube one size smaller (so a 7/4/7 28.6mm top tube has similar ride characteristics to a 9/6/9 25.4 (or standard) top tube). The larger diameter but thinner tube is lighter, but more expensive and probably easier to dent.
Personally I like the ride of classic “standard diameter” tube sets for road and gravel bikes and only go up in diameter if I’m also reducing wall thickness.
I can only see using 34.9mm downtubes on bikes with a really long front center (like a progressive MTB). I have a mountain bike made by someone else with a 38mm downtube and like most aspects of the bike but look forward to making its replacement with skinnier tubing.
