Body steering does not work!

[gigksrc]

Hmmm .... I think I need to practice some more. It all sounds reasonable but I think I'll have to practice some more on my trusty 250.

I like reading these kinds of posts but buggered if I can get it right.
Anyway thanks for the tips. I'll keep trying.

[RG]

I can't go around corners without shifting my weight.
I will fall off if I try to keep upright, especially when the ZZR250 is small n light. But for the same reason, I can't go too low too! Something must be wrong with me...

[aardvark]

Shifting your body weight will do diddly squat. One of the US rider training schools (I think it was the Cali Super Bike School) made a bike with a fixed handle bars. The forks etc would still turn, but the handle bars wouldn't.

They'd put students on it and get them to try steering the bike using body weight alone. Want to know how well it worked? It didn't...

If you want to get a good idea of how this stuff works, try riding in a straight line at a decent speed. Let go of the bars. Then, using your right hand, push fowards on the right bar (Not down, forwards....). Technically you are turning the bars to the left, but what direction does the bike now go?

[Jonno]

Here is that video on the fixed bar bike...

Thanks to Dave#3 early on in this thread for the video clip link.

I for one is convinced.

[Yankee]

another question for you gurus (James!!)

I was talkin' with the local racer guy at the shop (my LBS: local bike shop!), and he reckons they have his back tyre mis-aligned!!
on purpose.... for certain tracks so that he can get better turning in.... NOW THEN....
following the logic of the inner circumference (your cup rolling on a table example James!! ) being smaller.... would this be beneficial?

just wanted to really talk about this subject if we're going to discuss it at all!!! i think it is GREAT!!! very good ideas/logic being spoken about all ready too!! good stuff guys/gals!!

[JamesLaugesen]

Haha, yes that's right, they miss-align the rear wheel so it turns in the direction you'd imagine, no trickies here.
And causes the rear to drift out, just like a fork-lift or rear-wheel steering car like the prelude.
The big difference is that the 'scuffing-free' zone is actually somewhere in a lean, so you've got more grip leaning to that side, but less on the other side.
And remember while scuffing the tyre wants to pull towards the 'scuff-free' zone, so with the tyre miss-aligned it's scuffing in a straight line, and not scuffing leaned over... so the bike is always ready and willing to smack right over into a lean.

The counter-steering becomes extreme too; draw yourself a diagram and you'll see in the split-second of counter-steering, both front and rear wheel are facing in the opposite direction you want the bike to turn. So the wheel (ie, bottom of the bike) are pulled out that way very quickly, top of the bike leans, and away you go.

With a straight rear wheel it's only your front wheel that counters.

Usually when you see a racer sitting slightly off-centre on the bike down straights, that's because the rear is miss-aligned and they've estbalished the 'groove' the can sit in to keep good posture and control in straight line.

[gizmo]

when you see riders hanging off the side of a bike in a corner it basically allows the bike to be more upright as they come out of the corner so you can get more power on more quickly.

The Yamaha Tribe guys(Dan Stauffer/Shannon Johnson/Brendan Clarke)said that @ QR, as soon as you finished turning stand the thing up, get onto the fat part of the tyre & you can get on the gas harder & earlier!

[JamesLaugesen]

See some of the earlier posts gizmo, and the great page Steve linked too, better prepared than the random posts here, haha.
Most race bike's tyres don't have a 'fat part'. It looks obvious when parked in the garage with gravity flattening the tyre out, but when it's leaned there's the same forces squishing the tyre and you get roughly the same contact patch, dependant on tyre design, wear, etc.
Sure straightening up and getting a bigger contact patch might be part of a racer's setup, it's not actually a technical "commonality" amung bikes, it's just a setup.
The biggest factor is that when you're leaned over, you're effectively skidding (scuffing), more lean = more scuff.
So when you straighten up you have less scuffing and more grip to crack the throttle open, that's where most the comfort comes from... and for us roadies the flattened out commuter tyre probably helps a bit too .

Racers are usually so so damn fast it's incredible, but it doesn't always mean they know what's happening. Same as someone who usually knows what's happening, isn't always fast

All we really need to remember is that you have less grip while leaned over, haha.

[Glen]

James

I've been reading your explanations here with absolute awe. You are indeed the physics guru.

Question for you. I get the scuffing concept, with the tyre shaped like the rolling cup and all. When I'd previously tried to explain to students that you've got less tyre for braking when you're leaned over, I'd assumed that it essentially had to do with the bike turning in an arc and therefore the bike and tyres etc were trying to not only progress around the corner but also there were forces trying to throw the whole thing towards the outside of the arc ie a centrifugal effect. Is this correct?

Glen

[Barrabob]

Gizmo we got told that at a top rider course to to stand the bike up at the exit of the corner before getting on the power, possibly more important on a liter bike though.

The reason was it is much easier to spin up a rear with the bike at full tilt than when its stood back up a bit and new players that just screw on the throttle at the exit of corners or in the middle of them have problems with highsides.

I also think there is a bit to do with how much tourqe your sticking through the back wheel at the time.

[JamesLaugesen]

James

I've been reading your explanations here with absolute awe. You are indeed the physics guru.

Question for you. I get the scuffing concept, with the tyre shaped like the rolling cup and all. When I'd previously tried to explain to students that you've got less tyre for braking when you're leaned over, I'd assumed that it essentially had to do with the bike turning in an arc and therefore the bike and tyres etc were trying to not only progress around the corner but also there were forces trying to throw the whole thing towards the outside of the arc ie a centrifugal effect. Is this correct?

Glen

Haha thanks Glen, I'm a bit of a nerd sometimes.

With the bike upright you've got 1g holding the down.
With it leaned over you've still got 1g holding the tyres down, but something needs to stop the bike from falling inwards, so there's a horizontal force from the centre of the arc (centrifugal) balancing the weight of the bike offset from centre vs the gravity trying to push that weight down.
You need something to pivot on, the tyre, so some grip is used up.

Pretty easy trig.math to figure it out, or you could just lean a bike over and hold it up with your hands; that's how much sideways (latitude I think? haha fancy words) force is on the tyres while leaned over that much.
Buuut, not exactly, coz the front tyre is turned in a tiny little bit, so it's a bit uneven, but no way I'm gunna think about that on a thursday arvo.

There's also the vertical twisting of the rear tyre on the road, and probably craploads of other little stuff eating away at our leaned-over-traction, oh well.

Bikes are tricky tricky things So we love 'em.

Kinda on topic, a personal project of mine is to have a 3-axis accelerometer in my bike streaming data to a tiny PC, for all sorts of fun nerdy analasys.
If it ever gets working I'll definitely be flooding the forum with random g-force graphs from various bikes.
New topic: "Samhasa636 clocks 2.5g horizontal on turn 12 at Oran Park!!!".
I think the most interesting would be a graph of taking a sharp corner and lifting the front wheel under power on the way out... would be near impossible to figure out what's going on from the graphs, woo.

[the kid]

James , Now I am not taking the piss at all , but after reading all the above and your mind boggling understanding of physics (my mind anyway) but what do you do ? Job ? Study ?

[Gosling1]

I think the most interesting would be a graph of taking a sharp corner and lifting the front wheel under power on the way out... would be near impossible to figure out what's going on from the graphs, woo.

Mate, that would fully fry your computer technically, there are no equations that would mathematically explain the ability of a two-wheeled object, on a 45-50deg lean angle, with known parameters of friction, mass, directional vectors and momentum, to maintain a forward velocity with only one wheel on the deck ( I am not taking the piss either mate, I majored in Physics at Uni )

There are so many variables in your above example, with the greatest unknown being the mass of the riders bollocks - this also determines most issues with cornering at speed, wheelies out of corners etc etc. ( This sounds like taking the piss, but I am fair dinkum. Big Balls = Fast Times)

The argument of " to move or not to move' your bodyweight when cornering is one of the greatest biker discussions known, because of the huge *GRIN* factor when you get a set of twisty's " just perfect'

If you feel faster when hanging off, do it. If you feel faster by keeping your knees off the deck, then do that. The stopwatch doesn't lie. Next ride day, you should do laps using both styles, and see what the difference is . For most *average* punters, you will actually be slower by 'hanging' off the bike. Its the top 5% of riders ( ie not most of us ) who can take the most advantage of knee sliders.

Cheerio
KneeTremblerDave

[gizmo]

What about the tyre being smaller in diameter on the edge?

[JamesLaugesen]

I'm a software engineer, not much physics in my job, go figure.
I studied computer engineering, software engineering and some random things like socialogy, neurology and most other crap I could get.

Yeah Gosling it's a nightmare to try to model 2 wheels, even 4 is pretty insane to do propperly... most things on Earth are for that matter
I just want to graph g forces on 3 axis, I don't think I could make a gimble cheap & small enough for the bike, so the 3 axis will be relative to the bike, which is why I ment the graphs would be crazy.
Like, under acceleration the vertical axis would actually be maybe 80 degrees, so some of gravity's 9.1ms/s would register on the vertical axis and the rest would register along the longitude, along with the force of accelerating, which would register on the vertical axis too...

It's possible to calculate the 3 axis on flat ground but with sloaps involved you're screwed with only 3 accelerometers, haha.

BUT, it can be done with 3-axis accelerometers on the "outsides" of the bike, and one in the middle. Since you know the movement of the front and rear of the bike, the angle of the ground, blah blah.
Screw that though, I've light-bulbs to replace and a ZXR to fix

It's a nice dream though... imagine it... 1 acceleromter on the swingarm, and 1 on the subframe, the difference in movement/acceleration = suspension performance

Oops; smaller diameter on the outside of the tyre, refer to the paper cup rolling thing.
But if you mean slowing the bike down; yep, when you're leaned over if you keep the same throttle, the bike slows down since it's a smaller diameter, and loses some stability. One of the reasons you 'power through' corners.