Body steering does not work!

[Gosling1]

James you have a better handle on this than most punters what you are looking for is out there, but you need to be on a MotoGP team to get any of their software etc. so you can measure suspension movement, accelaration/deaccelaration etc. I don't think they use gimbles on the GP teams (but you never know what the tyre companies do with their testing, so ????).

Here is a thought for the no-bodyweight-difference punters : When you lean over, while riding through a corner, where is your bodyweight relative to the COG ? (NOT the centre of mass - that is different....)

*Eagerly awaiting a response*

cheers
WhyIsItSoDave

[ttc]

geeks geeks geeks geeks

[JamesLaugesen]

When you lean over, while riding through a corner, where is your bodyweight relative to the COG ?

Well considering I haven't ever fallen over turning into a corner, one might say it's right on the COG :O Hahahaha.
That's a nice way to make people think about it.

Do they even use accelerometers or any kind of linear movement sensors in motogp? I not up-to-speed with their tech, but those sensors stuck all over the bikes are damn tiny, so little magnet setups or slicon accelerometers?
It would be so hard to get good data about something like swingarm movement from any kind of motion sensor though, since it goes in an arc, and might be difficult to get enough accurancy to calculate distance traveled, blah blah?

Some kind of transmitter/receiver sensor setup would work better I think?

Man what a topic

[Gosling1]

Well considering I haven't ever fallen over turning into a corner, one might say it's right on the COG :O Hahahaha.
That's a nice way to make people think about it.

If you did not have any forward momentum, you would most certainly fall over..... there's a clue

Do they even use accelerometers or any kind of linear movement sensors in motogp? I not up-to-speed with their tech, but those sensors stuck all over the bikes are damn tiny, so little magnet setups or slicon accelerometers?
It would be so hard to get good data about something like swingarm movement from any kind of motion sensor though, since it goes in an arc, and might be difficult to get enough accurancy to calculate distance traveled, blah blah?

Some kind of transmitter/receiver sensor setup would work better I think?

Man what a topic

From my limited understanding of GP-technology, they have sensors that measure everything from suspension travel/speed front and rear, brake pressure/time, basically if it can be measured and improved to give you an edge, it is on the bike somewhere.

See how many others have a nudge at the COG / COM thing..........its pretty logical when you think about it.....

cheers

[Jonno]

KISS

Keep It Simple Stupid

[Gosling1]

OK it is simple - your COG when sitting upright, is directly over the centreline of the bike. All things being equal, you will be in a state of balance when moving ahead in a straight line.

As soon as your body weight moves off the centreline, as it does when you ride through a corner, the COG will vary - if I could draw a picture it would be heaps easier anyway, depending upon the lean angle, your COG will be anywhere between 0mm up to approx. 450 mm from the centreline of the bike. This is because gravity only works in a direct vertical plane.

The COM also varies, but not anywhere near as much as the COG, because most of the mass of the moving object ( you and the bike) is concentrated much closer to the centreline of the bike, and therefore does not move anywhere near as much as the COG.

There is a very easy test to demonstrate the need to move your bodyweight ( which is done subconciously for 99% of the time):

Try riding through a lefthander , and lean to the right ...... see what happens its ugly. ( Having said that, this method can actually be used in a *some* circumstances - see below)

Jase - the reason that the Calif 'fixed bar' experiment works the way it does is also simple - if you just lean the upper half of your body one way or the other, the overall effect is that small, it makes no difference to the direction of the bike.

If however, you were to stand on the LH peg, and place as much weight as possible on the LH side of the centreline of the bike, you would see an immediate result, and probably a prang as enough weight would now be moved away from the COM to have an effect.

*Some* circumstances - If you have run wide through a RH quick corner, and still need to get on the gas to catch up , then it is possible to stand up on the LH side, putting full weight on the LH peg, while leaned over to the right, and give it the berries. You *should* not highside, the bike will want to try and stand up with the weight on the LH side, however you are forcing it down to the RH side - Result ? you run wide but are still able to keep up good speed and catch your mate at the next corner.

If you don't use this method, you will simply run wide, wash off heaps of corner speed, and he's gone.

sorry for the long-winded post

cheers
Dave

[JamesLaugesen]

Sorry Gosling I'm pretty confused now, haha.

COG is a bit of a tricky term to use here since forces other than gravity are determining the balance point; balance point is the import part.
Centre of mass is slightly important, in that most mass should be as close to the centre of most gyroscopic forces to allow the bike to "roll" around this point easiest, which is usually about smack-bang where the wheel hubs are.

Leaning left while turning right is just messing with the balance point but can still be done np, it's not breaking any law of 2 wheels or anything, it just means the bike will be more upright than the design (front fork rake and tyre profile) dictate the bike should be leaning for optimum equalibrium on the tyres (which is why putting different profile tyres than your bike is designed for usually makes it handle like crap and feel unnatural).

If you park a bike on flat ground and stand behind it like a sexually frustrated ducati owner. (Made that bold coz this is probably a good test to demonstrate counter steering and stuff) Lean it over to one side, notice the front wheel turns in a little. This is the "perfect" lean/turn-in combination for that bike at that lean with that turn radius. Chuck sliding, scrubbing and shifting the balance point (by moving off the seat) into the equation and things change, but my point is that there's a position that bike wants to sit, and however you acheive that position (planted on the seat, shifting off the seat, whatever) it will work fine... for that position.
Now if you wanna get real tricky, get friend to play 'sexually frustrated ducati owner' while you roll the bike foward by the bars and turn them sliiightly to the left, BUT, make sure the centre'ish of the bike (say, the engine) remains in the same longitude... don't let it move sideways (which is what gyroscopic force is about, and what your ducati-boy is ment to be stimulating, I mean, simulating.).
Seems impossible, but it's not, the only way the engine can remain in the same longitude is by rotating it -and the whole frame obviously-, so the front wheel can keep going where it wants to go, and the engine doesn't need to move sideways (which gyroscopic force will always resist against, in case you don't beleive me )...
And now, wow, the bike has leaned over to the right.
And if you let go of the bars, the front wheel will fall into the turn, facing to the right.

Hence why we're taught to apply light input to the bars in the opposite direction to start a turn (counter-steering).
The bike leans.
Then we're taught to relax and be very very loose on the bars, and allow them to fall into the corner naturally (steering).
We're also taught to stay relaxed on the bars during the corner, because, when the front wheel goes over a bump, the angle of the tyre relative to the road changes, so the wheel needs to turn in some direction. Resisting the wheel and trying to hold it in the same position is equivalent to counter-steering, or normal steering, either of which is bad since you've already decided where you want to go and have no way to predict where those bumps will send you. So the tyres scuffs, then skips, then hopefuly grips again before you need a lift home and you're lefting thinking "geez, my suspension is crap".
Then coming out of the corner you need to counter-steer again, to pull the bike up straight (try it again in reverse with the ducati-lover, get the bike upright without changing the engine's longitude ). So apply input until it's upright, then relax again.

I've been taught to keep my feet on the outside pegs/pedals on anything with 2 wheels but don't know exactly why. I guess coz it's something I've just always thought "pfft, duh" so I've never thought about why.
Will do some tinkering and see what comes up.
I think definitely it's more anatomically possible and easier on the knees, haha.
Also on the ZXR with standard rearsets I need to lift my inside foot right up so the peg can fold up.
I'm sure the bike feels more stable with more weight on the outside peg, hmm.

[Gosling1]

You are dead right, there are *heaps* of other factors apart from the 2 simple ones I have referred to - COM and COG. One day I will sit down and do a proper full explanation of what I have been taught/read about/listened to over many years. It could fill a book !! ( OR bump up my post count to buggery )

Weighting the outside peg is done as a method to maximise grip from your tyres - when you weight the outside peg, you are effectively transferring your body mass to a point that is (a) low, which assists COG, and (b) enables you to more effectively control the contact patch, which is where all the tricky physical forces are concentrated ( the scrubbing effect etc that you mentioned before being one of them.) Most riders do it subconciously. Of course these methods are really only for *faster* riding, normal riding with weight evenly spread on both pegs is just fine and dandy.

I will kid you not, I have spent hours and hours discussing these issues with mates at rallies, until the Green Steam takes over , at which point the physics just confuses the shit out of everyone its a great topic, once you understand the basics.

cheers
ScrubbedOutDave

[Steve_TLS]

Knock yourselves out (not mine, but I've had them a while).

http://www.wotid.com/tls/files/CofG.xls
http://www.wotid.com/tls/files/bike.xls

[JamesLaugesen]

It doesn't matter where our body-weight is attached to the bike though, the eventual static force in the tyres will be the same (ie, a S shaped hook). The 'active' force (centrifugal) will alter the balance point as lean & speed change but I don't understand how that can change the force in the tyre (asside from changing lean angle) depending on using the inside or outside peg.

I've always figured it's a mechanical thing, so the bike can move around better and let the suspension work. At least on a mountain bike that's why, mostly so your leg doesn't break.

[JamesLaugesen]

Knock yourselves out (not mine, but I've had them a while).

http://www.wotid.com/tls/files/CofG.xls
http://www.wotid.com/tls/files/bike.xls

Hahaha, nice stuff! I based a robot around the same maths used in the 2nd one, pretty accurate but still not enough to keep the poor bugga upright. Need to consider so much more that it's just not worth it. Best bet is to measure real-world input and do some real-world action to correct it... bike falls to the right, turn front wheel to the right.

Google for RoboBike, or RobotCycle, or whatever it's called. That beast is chugging along pretty good nowdays

[Gosling1]

Where your body-weight is on the bike makes a huge difference. If it didn't matter, then you could weight up the inside peg. If you do this, the weight ( or more corectly, the COM) is on the inside of the centreline, and will 'push' the tyre beyond its friction limit ( the scuff 'maximum' i s'pose you could call it), and then your tyre slides, and you fall off This is no good.

I guess if you looked at it from a stationary point of view, it is easier to lean a stationary bike over to the left, then push it from the left with your weight bearing down on the LH peg, and what happens ? The tyre will slide. If you put all your weight on the RH peg, and push from the left, it will need a larger push from the left in order to make it slide. This principle still applies when the bike is moving. Its a friction-v-COM equation.

happy trails ( trail ?? did someone say trail ???? now there is a good thread )
SlideRuleDave

ps thanks Steve, those charts are great !!

[Glen]

Professor James and Professor Gos

You're about to make my head explode I think.

Weighting of the outside peg I can attest to in a practical sense from dirt bikes. Dirt bike gurus will tell you in a flat corner to keep your body upright, with your arse crack on the top edge of the seat, your leg pointing to the front axle and apply weight to the outside peg as you go through the turn. Because you can try this on a dirt bike without killing yourself we did and the results are quite impressive when you vary the weighting. You can get through a corner carrying much more speed when you weight the outside peg.

I never really knew why but now I do.

Thank you

[JamesLaugesen]

Haha ok, done some tinkering with numbers and I dissagree sorry Gos.
A stationary bike with a static weight on either peg won't change how hard it is to slide sideways, there's still going to be the same amount of force (from gravity) holding the tyre down so same friction.

I think it's more important acting on the horizontal plane, any vertical force is static (weight... gravity...) so will only determine the initial balance point (lean angle) of the bike, and the grip gains/losses that come with the leaning.

But, there's centrifugal force acting horizontally @ whatever angle the bike's leaned over - So there's our input force
The front wheel is always slightly closer to the inside of the corner than the rear wheel - The pivot
The inside peg is lower, so closer to the pivot on the horizontal plane.
The outside peg is higher, so further away from the pivot (horizontally).
So you effectively have a lever, where the outside peg has a larger moment, thus more torque & more vertical force on the rear tyre.
This might be diagram-worthy, but I'm too lazy so I'll make a little ANSI diagram EDIT: note, pretend the little dots aren't there... the forum removes multiple spaces.

Imagine viewing a bike from directly behind along it's path around a sharp corner... it looks something like this:
. . .\ \___\ \
. . . \ \. . . \ \
Hahaha, it does though Front wheel on the left and rear wheel on the right, on a left hand corner, get it?
Now with stupidly huge pegs in there:
. . .\ \__|_\ \
. . . .\ \. `. .\ \
Ok, even more stupid, but see the right/outside peg is up higher, coz the bike's leaner over... hahaha. Now a diagram of the two possible levers there; (o is the pivot, > is the input force, \/ is the result force)
Outside peg:
. . . . >
. . .__|__ . . .or. . >
. . |. . . . |. . . . . . |
. . o. . . .\/. . . . . .o-----\/
Inside peg:
. . ______
. .|. . >`. |. . .or. .>
. .o. . . . .\/. . . . . o-----\/

Picture the horizontal force in the inside peg, and now add a bumpy/uneven road... it seems possible (if the front wheel is higher than the inside peg, probably need a lot of lean or a BIG bump) to go past nuetral and actually end up pushing the rear wheel off the ground, haha.

I'm pretty conviced that's where the 'feel' comes from anyhoo, makes perfect sense when thinking about the mountain bike, which would be more exagerated coz of sharper turns and less weight (static force).

EDIT: Fark!! My diagrams didn't work, damn spaces. I'll add dots...

[Gosling1]

Professor James and Professor Gos

You're about to make my head explode I think. Thank you

Can't have that mate ( remember Scanners !!! what a great movie...)

Jimmy - that is a very detailed explanation, but my slide-rule started to smoke badly at the sight of your diagrams .

One day we can sit down and go over the finer details, I am sure we have thrashed it enough for now ( but it is a great topic, when you start to factor in the lesser grip of Shinko's v the superb grip of *just about any other tyre*, well, blah blah blah yadda yadda yadda )

cheers
LifeBeginsAt45DegDave