bike longevity

[mercalia]

Living in London I see lots of manky old bikes locked up all over the place. many have chains so rusty you wonder how on earth they turn surely must be seized solid? Brookes saddles so old and worn they have a sag that must do some damage to something. brakes not connected any more, the levers dangling loose. mudguards in tatters , carriers missing some of the bolts attaching to the frame. derailleur gears stuck on one ring and sprocket.

[JohnW]

The two bikes that I'm riding at the moment are built onto one 1981 Pennine frame, and one 1993 Pennine frame. There's a mixture of parts - some quite recent (I rebuilt around the 1981 frame 3 years ago, using parts of varying ages - only the wearing parts and the quill and stem were new - bringing bars and stem up to date). My 1979 Pennine frame was destroyed by the driver of a Volvo estate, by running into the back of me; I don't know whether it was me or the bike he'd taken a dislike to, because he also broke my leg.

I'd had the 1979 re-sprayed and brazings updated a couple of years previously, and my 1981 Pennine had the same treatment to fill the gap left by the death of the 1979 frame.

Honestly, if you look after a bike from those days, it will last a lifetime providing you look after it, and replace worn parts with new when they need it. Some of the non-wearing parts may be obsolete now, but certainly better than modern equivalent. Current ready-builts, of various materials and with sophisticated, planned obsolescent parts won't last anything like as long.

My mileage reduces as I age - I'm 74 - and my 1981 bike is down to about 5,000 miles a year, and my 1993 (which I use for shopping and utility rides, and only use for half-decent rides in bad weather, gets about half that, but will the modern offerings still be doing such mileages in 30+ years time? - will we be able to get the parts? - will any parts be compatible with anything?

I think that the frames will probably be another limiting factor.

The OP has asked a good question.

[Gattonero]

I have always been surprised how much upkeep is required for most bicycles. Where I live I see many, many bicycles of every sort used -and neglected- for transport. There are many old-school racing bikes, often equipped with lovely equipment from the 70s and 80s, which clearly never see so much as oil on the chain. Given the knowledge and experience I read about on this rather wonderful forum, it astonishes me that failures of some sort are not a common thing with such bikes, but I don't think I have ever seen such. How come we enthusiasts spend so much time and money looking after our machines when many of a different persuasion just do not? No doubt these bikes run rough and suffer from poor gear changing and so forth, but really, they still go. It strikes me that there is some inconsistency between what people such as yourselves think and what some others -often in the possession of rather nice equipment and who don't know or don't care - think. Or am I wrong?

Most of those old bikes, if they are in a bad state, nobody cares if "the BB creaks" so it becomes a "see no evil, hear no evil" thing
By contrast, on modern bikes several people get rather paranoid and seem to feel play in their headset even if there isn't, so they crank it up until the bearings are destroyed; or they lube the chain until it's spraying oil everywhere and silver rims become black
Or the opposite way, they ride those bikes really hard and never clean them so they end up with bad rust and corrosion... just like a bicycle of the early 80's or 70's.

A bicycle it's a simple or complex object depending how do you see it. For sure, you have to make compromises in its overall weight and it's rolling parts, i.e. you may do a frame that never cracks by using 1/4" thickness in the tubing and wheels with rims weighting 2kg each, but then you will have a very hard time in moving it, which is the main reason for a bicycle to exist.
To replace a chain, or a headset or a bottom bracket it's not the end of the world, nor is to dedicate 15 minutes every weekend to wipe down your bike, the wheels and the chain.
We all have different ways and roads to ride in different weather. I very much doubt that any bike can survive a 5-8000km/year of city commuting without the bare minimum of cleaning and lubrication, let alone having the bike still looking in a reasonable state. Some people doesn't care, but then you see so many people walking around with grubby trainers (let alone trousers bought with holes already on )