I’ve build around 25 bikes with non-butted CrMo 4130 tubes here in Brazil and I’m about to start making some Columbus Life frames.
Since I’ve got no experience with these amazing tubes my doubt is about wall thicknesses. For the DT I’ve got two options:
OD38 0.65 over 40mm / 0.45 on length / 0.65 over 100mm - full length 670mm
OD38 0.9 over 150mm / 0.6 on length / 0.9 over 180mm - full length 670mm
The cyclist is 1m61, average weight. She wants to use her bicycle for everything: commuting, bike-packing gravel on week-ends. She’s investing in Columbus hoping to get her frame a little lighter.
With no experience I’d just go for the reinforced version, but am I exaggerating? Is the standard version more than enough and I should go fo lighter? I’ve heard Columbus material and heat treatment make them really tough but I’ve got no real idea.
Any tricks and good practice to cut/weld them that I may ignore and should know will be very much appreciated!
the mid section of the thin 6/4/6 tube is very fragile for dents and dings, especially in this use case. I’d be less worried if it was a time trials bike, or a track bike excluively for the velodrome… But a daily?
Not 100% sure but as far as I remember, those tubes are meant to be used with lugs and silver brazing exclusively. Apart from that, welding 0.65mm is hard. Very hard!
Yes the thin one is too thin to be robust in a daily-rider that will get dented. But both of those are too large in diameter IMHO. I haven’t done the math to see if the stiffness is “off the chart” but I think it is. I’m one of those who believe it is possible to be too stiff, that a little “give” in the frame makes you actually faster. Not to mention that a smaller tube can be lighter as well.
For such a small rider I would use 1-1/8” (28.6 mm) DT and 1” (25.4 mm) TT, as thinwall as you trust your joining skills to make, without burn-though or kinking. Unless she’s a sprinter.
I have made track sprint frames for top riders (4x US champion, 2x Olympic team rider for one example, another got silver at Worlds) and for those, the stiffer the better. But unless you are a steroid-drenched freak of nature you don’t benefit from it.
I hear some people like it though, so this is just one man’s opinion.
0.9/0.6/0.9 is very normal wall thicknesses and what is probably being used on most of the bicycles you see on here except for the incredibly lightweight or incredibly burly builds. And as @Luniz82 said there is a world of difference between welding .9 and .6 mm thick tubes. You can even feel the difference between .9 and .8mm, it’s really remarkable how different the two behave. If you do end up welding .6 mm material for whatever reason you’ll want to go down to a 1mm tungsten electrode and get some .035 (inch, sorry lol) filler metal.
I dont think there is a Life Downtube with the 38mm .9/.6/.9 Dimensions (at least not in the current catalogue). Probably Rather Cromor or stuff - usually you can see it on the surface finish on the tube.
If light then of course the thin wall tube. 38mm with 0.9Wall is quite a banger and too much for most applications - I would only use that for a heavy duty travelbike or similar….
A 38mm DT for a slightly shorter ride on a do everything bike is way overkill. Even 35 is getting fairly stiff for that size frame. Persoanlly I’d be going the 31.8 x 8/5/8 only for teh load carrying resistance.