one-eyed_jim
Old School Grand Master
His name was David Jones.GeoffApps":26v3ugfp said:
Here we go again
- Thread starter Dr S
- Start date
Oooooh! I was a fan of the gyroscope theory until you said that, Jim.one-eyed_jim":151u1kpd said:
I think you may have designed the experiment that ends the debate: if a rider finds it just as difficult to stay upright on ice at high speed as he/she does at low speed, then the higher angular velocity of the wheels on the speeding bike isn't giving much of a "gyroscopic effect". (Perhaps gluing some lead weights to the rims would help!
)
one-eyed_jim
Old School Grand Master
The important point isn't the front axle, but the contact patch of the front tyre. That's already behind the steering axis (because of the slope of the head tube) but reversing the fork increases the distance between the contact patch and the steering axis.JohnH":1oeohcul said:
That has two effects. When the bike is upright there's a speed-dependent force that tends to centre the steering, like the wheels on a supermarket trolley. When the bike is tilted, the reaction force at the contact patch steers the front wheel in the direction of the lean.
How so?one-eyed_jim":3gq85ihh said:
Surely it's a valid point - when learning to ride a bike, it is something to exploit, because the more difficult corrective slower speed skill comes with practice, learning and conditioning.
I'll repeat, a bike - or for that matter, motorcycle - travelling with sufficient speed, wants to (notwithstanding I'm not really anthropomorphising a motorcycle or bike...) stay largely upright (assuming it's already upright and not at some odd angle or lean). Now true enough, the mass of the rider has a bearing - it just makes that speed a bit higher than an unmanned cycle / motorcycle.
Consider a racing motorcycle cornering. Leaning is used to counter the natural forces at play, and assist with and significantly reduce any steering input required. And even with such considerable angles of lean, they're not usually in any danger of falling.one-eyed_jim":3gq85ihh said:
Now true enough, I'm not suggesting that this is purely because of gyroscopic effect - it isn't - inertia becomes a significant factor, but all the same, the faster the speed, the more influence of the gyroscopic effect, and the more relevance of inertia, and very much reduces the need for corrective input for balance.
Point being, though, that with cycles and motorcycles, with a certain speed comes gyroscopic effect, inertia, and a natural tendency to stay upright. That isn't just because of effects of leaning being minimised - that's all chicken / egg - there will be less need to lean, or for that matter, less chance of leaning - it's just as likely there will be minimal lean, because of lack of requirement to do any corrective movements to keep it in balance. The reality is, as the speed increases, gyroscopic effect increases, the effects of inertia increase, much less corrective action is required, or desired, because if it was done, it would probably largely become unstable.
Now the ice thing has some bearing - but when I was talking about friction, I wasn't just thinking of friction between tyre and surface... What I would say, though, is that for a bike, or motorcyle, that suddenly hits a brief patch of ice, but travelling at fairly normal speeds, it doesn't necessarily mean that all balance goes out of the window and a crash ensues. If the bike / motorcycle is travelling straight and true, and the surface suddenly loses a lot of friction, briefly, the bike / motorcycle may well stay upright - it just depends on whether much in the way of corrective action was required (or happened out of panic) whilst on the very slippery surface.
Clearly were the bike / motorcycle cornering, or truly having to correct much lean - then true enough, a crash almost a certainty - but running straight and true, at a normal speed, and suddenly loses grip briefly? Not necessarily catastrophic.
one-eyed_jim
Old School Grand Master
Because the example you give assumes what you're trying to prove.Neil":xs4gt0sj said:
There's a clear relationship between speed and the angular momentum of the wheel. There's a clear relationship between speed and ease of balancing. That doesn't demonstrate a causal relationship between the angular momentum of the wheel and ease of balancing.
But leaning and turning are inseparable. If you turn without leaning, you fall. If you lean without turning, you fall. All that's important is that the reaction force at the ground passes through the centre of mass of the rider. There's no gyroscopic element involved.
Think of a skater in a tight turn: the same principle applies. The higher the speed, the tighter the turn, the greater the lean required to counteract the centrifugal force (mv²/r).
http://www.youtube.com/watch?v=NDhw5TMn9jA
Yes... and?one-eyed_jim":vnimhalv said:
That doesn't make it a circular argument. I'm not suggesting that ease of balance, inherently, necessarily equates to, or produces increased speed.
Which is?one-eyed_jim":vnimhalv said:
My agreement that the gyroscopic effect makes it easy for kids to learn to cycle, if they increase speed, is based on:-one-eyed_jim":vnimhalv said:
1) The gyroscopic effect increases with speed
2) The gyroscopic effect helps to balance a bike
Both are true.
Some quibble about the significance or impact of 2. Which is fine, but it most certainly exists, and there's defintely an effect that with speed comes ease of balance on a bike. Feel free to speculate or hypothesise on that if you don't believe the gyroscopic effect is having any bearing.
When I was a kid, I had a gyroscope and a little pointy stand, and discovered, then, that when spinning the gyroscope fast, it balanced on it's pointy stand and resisted falling or being deflected, until it's speed of rotation decreased. So when I was slightly older, and told the same gyroscopic effect has a bearing when on a bike with two big wheels spinning fast, I can accept the logic and rationale.
edit: also worth consideration to what I've been saying.
If you're cycling slowly, it's perfectly feasible to turn without leaning - same with skating. It's only when a degree of speed is added that you need to deal with cornering forces.one-eyed_jim":vnimhalv said:
With two large-ish wheels are spinning fast, there's always going to be some gyroscopic effect. I'll buy, though, that it's not the most significant effect to deal with when cornering fast, though.one-eyed_jim":vnimhalv said:
one-eyed_jim
Old School Grand Master
I'll quote this passage from Witt and Wilson's "Bicycle Science" which corresponds quite well to my understanding of the different factors involved in steering and balancing:
http://tinyurl.com/6hynkef
http://tinyurl.com/6hynkef
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