Stainless Superlight

Well this one has been a long time in the making! Back in 2014 I had been studying the various stainless steel alloy tubesets from Reynolds, Columbus and KVA. And also investigating the best rod and flux to use to join them. Stainless, although with similar properties in terms of strength and stiffness to cromoly, cannot be joined with brass fillets. It is best brazed with a silver based alloy – this is a low temperature process and generally silver is much more fluid than brass, which makes it harder to build a fillet at the joint. I was keen to build a prototype frame to test the tubing and process, and was planning to do so that summer for English frame number 100. I duly ordered some Reynolds 953 tubing, and some Fillet Pro rod and flux. But then I had my little run in with a tree and was on the couch for three months. Once I got back in the shop my priority was getting caught up with customer builds, so the stainless tubes got put on the shelf and sat there for over a year.

By the fall of 2015 I was close to being caught up, and also figuring out bikes to show at NAHBS – so it was time to resume the stainless project. The latest stainless alloys have some pretty impressive numbers for strength – which means some very thin (0.3mm) wall thicknesses, which potentially makes for a very light frame. But with that strength comes hardness, so working with the material is very hard on cutting tools. I think if I do much more work with this tubing I will need to figure out an abrasive mitring setup. For this first frame I just started with a fresh set of cutters – if I was careful I could get two cuts from each before they were done! Once all the tubes were mitred and prepped, I polished them, and then sent the downtube and headtube to have my logos laser engraved.

The brazing went well, small fillets to keep the weight down. There aren’t quite as many small parts made in stainless, so I had to machine my own seat binder, direct mount brake bosses and cable stops. The frame will have wireless eTap shifting eventually – for the show I put regular SRAM Red parts on there, so made a removable headtube sleeve to provide temporary cable stops.

When looking at the tubing specs, I figured I should be able to shoot for a frame weight right around 1kg. To check progress towards this goal, I actually weighed each tube before the final assembly. It was a little disappointing to discover that I would have hit that goal if it wasn’t for the chainstays! A set of S3 chainstays are almost 100g lighter. I spoke to Reynolds about this – they are aware of it, and working to improve their process. Knowing how hard the material is I can appreciate the difficulty of ovalising and tapering a tube whilst trying to control the wall thickness down to 0.5mm. Hopefully the weight gets lower in the future. In the meantime, having a few extra grams in the chainstays isn’t a bad place to have it.

With the frame done, it was time to look at the components for the complete bike. At NAHBS in 2012 I showed a 10.8lb bike. So I thought it would be cool for the show this year if I could figure out a way to get this one under 10lbs – with pedals, ready to ride. It is a lot of work to chase every gram, but a pretty fun project. I was very happy to do the final assembly and see 9.94lbs on the scale!

I haven’t had a chance to ride it yet – I’m waiting for the eTap parts to arrive, then I will put some regular wheels on and start clocking up some miles. Based on the material properties and the tubing sizes I used, it should ride very similarly to my other bikes, but I’ll report back on that in due course.

Full specs and weights listed below – scroll down for the gallery; thanks to Tina Buescher for the photos!

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