I’ve build about 3 frames now, and all of these were made with tubes I figured would just about work fine.
Right now I’m making a hardtail mountainbike and a racey gravel bike, both are for customers/friends but I’m trying to treat it as professionally as possible. Choosing the tubes is one of the things I struggle with most. I have read about desired stiffness and undesired stiffness, not wanting to use OS tubes with thick walls but also not wanting to use “regular” tubes with very thin walls making the frame noodly. I guess I want to ask if there is a safe way of choosing the “right” tubes? Or is the only answer either a lot of experience or a lot of modelling?
Maybe if you show us the drawings of the two bikes, describe the riders who will be using them (weight, riding style), we can provide some advice.
This is a rough mock up of the gravel bike. Rider is around 70kg and 1,75cm tall. Size would be around 54 seattube and slightly longer top tube. 46 mm headtube and t47 bb. I was planning on using a 31.8 downtube and 28.6 top tube. 35mm downtube with 7/5/7 would also be possible i think.
I would feel comfortable using a 31.8 8/5/8 down tube and 28.6 8/5/8 top tube for that bike. Since you’re new to building it’s probably better not to use thinner walled tubes until your welding/brazing skills are good.
What size tubes you should use is definitely subjective. I’ve found that when I talk to tall or heavy riders who build frames, they usually spec really oversized tubes for everything because they’ve experienced bikes that are too flexible. Whereas medium and small sized folks are willing to use smaller diameter stuff because they haven’t ridden noodles before. The only thing I can recommend is to build yourself frames with different tube profiles and test them. The best thing a builder can do is ride lots of different bikes.
Here’s a good article that discusses frame stiffness, ride feel, and the forces that bike frames go through. He talks about traditional road bikes, but the info can be applied to gravel and MTB frames too.
Thanks so much! I think ill try and make something really noodley for myself to see how that rides. As you said, just ride a lot of different bikes.