Not sure if we’ve done this before…

[video]https://www.youtube.com/watch?v=oZAc5t2lkvo[/video]

good video!

Gyroscopic precession …

‘Ghosties’ : )

Interesting point about the mass being in front of the steering axis. I wonder how this changes as you move to a shorter stem. Presumably it makes the bike less stable.

Cheers for that eltonerio….

Interesting point about the mass being in front of the steering axis. I wonder how this changes as you move to a shorter stem. Presumably it makes the bike less stable.

Spot on. Bikes with shorter stems will have more direct steering, ie twitchier than those with a long stem. Similarly, bikes with a steep head angle are also quicker steering. Combine the two and you have something that will fly around multiple tight corners but will but the fear of god into you on long, fast descents.

The trend to short stems is off the back of the latest “Enduro” bikes with slacker geometry and longer tts. The only way to stop them steering like barges is to put on a very short stem. FWIW I like these bikes, but my old Turner Flux was the fastest bike I’ve ridden on tight, switchbacky singletrack and it got seriously twitchy once you went below a 90mm stem

The video , tho interesting, relates more to a riderless bike. Front-end geometry has an effect on how steering input works, but bikes have been built with gyroscopic forces negated (counter-rotating wheels/mass) and 90 degree head angle /zero trail/rake and they’re all rideable. The geometry of upright bikes is as much to allow the rider to reach bars/not clip wheels. There’s a bit more variation with recumbents because hands/feet are in different locations, tho they often use similar geometry – but some have a v steep head angle with reversed forks.

Mike Burrows Ratracer:
http://www.advancedvelodesign.com/ratracersl/ratracersl-recumbent-bike-index.php

IIRC Tony Foale – centre hub steering blokey -and later Burrows have done a lot of work /experimentation on the subject.

If they had have taught physics like this when I was in school, I might have a) enjoyed it more, and b) actually understood it.

They had this on the news last year……it’s all down to torque apparently