Threadjacking

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BTW, I did get that video of a UFO that my brother took, but it's very disappointing - isn't it always the way, 🙁 ?!! - the transfer didn't go well, and the contrast apparently has to be just right to see anything - I couldn't, and I knew what it looked like, on his phone! The disappointment has stopped me trying to enhance it, or anything like that - but I will give it a go, at some stage ...
 
Suspension absorbs energy, and makes the bike slower. Street bikes are optimized for speed. Trail/mountain bikes apparently have suspension because, from what I vaguely recall hearing, riders have a hard time tolerating long off-road rides without suspension.

I've ridden street and trail bikes, but both without suspension. I never did much trail riding, so I'm not familiar with the lack of suspension being a problem.
 
Having full suspension can be quite nice for the downhill bits. The back wheel has much more grip, following the ground instead of skipping around as on a hardtail (no back suspension). Rear suspension forgives all sorts of sins when out riding - if you pick the wrong line, it might get a bit hairy, but you'll be able to power through much more easily than with a hardtail.

I'd say a full-suspension bike is faster down a hill than a bike with no suspension. The suspension absorbs the bumps, dissipating the energy internally rather than the whole bike losing kinetic energy.

Chris