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.
Thanks, I appreciate very much your detailed insight. Until now I’ve learn by my self welding bikes using oversized tubes and non-butted .9 tubes with thick welds because although I’ve a mechanical engineering background I worked only in the energy sector before I decide to change my career and build bikes. So I’ve never done any frame math but just over dimensioned from what I saw and just welded to get the skills because here in Rio de Janeiro I’d never find anyone close who could help, I’m a lone framebuilder in the entire RJ state we’re not even 10 in the whole country. Now I get some skill welding I’d like to try lighter frames. So if you have any documents I could investigate to learn the math on that subject I should be able to do it. Actually pretty excited to learn!
From the comments I read since from Ceeway (UK) there’s no 25.4 Life tube, I’ll go for a combo 28,6 TT / 31,75 or 35 DT.
Guys, thanks again a lot for your insights, in Latin America we are so few and far from one another that we have to learn by ourselves and make our own tools. So really it’s very much appreciated you guys taking time to answer!
It is! I’m having always more clients from there. Here in Rio cars still kill too much (actually cars are the second biggest cause of external death in Brazil, just after guns), most of my friends would like to buy me a bike but there’s no infrastructure so they could start and gain confidence riding. Every day cars drivers honk at me and yell that I’m note supposed to be on their way while it’s written in the code I’m not supposed to be on the sidewalk but on the street. The craziest is although I came here from Paris, I got use to it.
At least bikes are gaining space I always say we’ll remember when a ton of steel could drive at 60km/h in small urban streets (probability of a pedestrian survive to this is 3%) like we remember when we could smoke in restaurants haha!
haha!