> , but an aluminium frame will inevitably succumb to fatigue cracking around the bottom bracket after a few tens of thousands of miles, no matter how well it's cared for.
That is a urban myth.
I know several bikes with alu forks and bottom brackets who have been in use for more than 30 years and +50000 kms and they are all good. In fact the glue bond between the tubes is what fails and they have been reglued several times.
Stuff don't strip or seize if torqued correctly, the right kind of greases/compound are used and the bike is disassembled/reassembled once a year.
Having said that, I wouldn't expect a courrier to do it himself nor to have an LBS do this for him.
I've seen it first-hand. The old lugged and bonded Trek frames are much more resistant to this than welded frames, because that construction method minimises the stress concentrations that initiate macro cracks. E-bikes are probably more vulnerable, partly because the structure is compromised to allow for battery installation and wiring, but mainly because there's a bunch of extra torque going through the chainstays.
An aluminium frame used in all weathers is vulnerable to galvanic corrosion. Aluminium is less noble than steel, so steel fasteners will rot out aluminium threads. In a perfect world this would be prevented by a suitable assembly grease, but a delivery bike being used through winter in London or New York is about as far from a perfect world as you could imagine. There's salt on the roads, the bike never gets a chance to fully dry out, so any amount of aluminium-to-steel contact is going to lead to very rapid corrosion.
Tubes in the rear triangle are more susceptible to breaking as they twist ever so slightly during use. Steel will gladly take up this sort of springy torsion, aluminium not so much.
Yes the popular vitus and alan aluminium frames of the late 80's to mid 90's had aluminium tubes glued to aluminium lugs. Also many early carbon frames of that era from TVT, Alan, Vitus, Trek, Giant or Specialized) were built the same way with carbon tubes and aluminium lugs. In the early 2000's there were also some frames with an alu front triangle and a carbon rear triangle bonded together. Usually they were mid tier bikes below full carbon ones.
This is still a popular method for frames built with mixed materials.
That is a urban myth.
I know several bikes with alu forks and bottom brackets who have been in use for more than 30 years and +50000 kms and they are all good. In fact the glue bond between the tubes is what fails and they have been reglued several times.
Stuff don't strip or seize if torqued correctly, the right kind of greases/compound are used and the bike is disassembled/reassembled once a year.
Having said that, I wouldn't expect a courrier to do it himself nor to have an LBS do this for him.