What make a motorcycle track round a bend?

[Grip Fast]

So, I'm talking about traveling along a road towards, say, a left hand bend. As I get to the bend, I apply a pressure to the left bar to lean the bike over (I believe in countersteering as the only way to consciously or subconsciously get the bike leaning over at speed).

I completely understand how countersteering gets the bike leaned over. It's what I perceive next that puzzles me. I've read descriptions of countersteering which say that, once the bike is leaned over, you then steer into the bend to track round it (i.e. you point the front wheel left).

I'm not entirely convinced. What I feel when I focus on it, is that I apply pressure to the left bar to initiate the lean, but if in the turn I ease off the pressure, the bike will want to sit up. So it feels to me like I need to hold the bike in the turn/leaned over, by maintaining some pressure on the left bar (in a left turn). To come out of the bend onto a straight, I ease off that left bar pressure (maybe a slight right bar pressure). The bike sits up and we are heading straight again.

So while in a left bend, I'm holding it in with left pressure - so the front wheel is in effect pointing ever-so-slightly out of the turn. If you look at the ultra-slomo shots of Rossi et al in a bend, it looks to me as if they still have countersteer on. I always thought it was an optical illusion. But is it?

So my question is... If I am correct in that the front wheel is not pointing into the turn, what makes a leaned-over bike track round the bend? Is it the different tyre profiles front and back? Does the narrower front tyre take a smaller radius route than the fatter rear tyre?

Can you tell it's cold and raining here?

[tanneman]

Yes, yes and yes. You are correct in thinking so.

[SP250]

Few points you raise there.

Top racers are always on opposite lock when going round a corner.
They have to be, as the rear tyre is wider than the front, so the rear of the bike is moved off the bikes' centreline more than the front (narrower tyre) when banked over. This means that the frame centerline is pointing too far to the inside of the corner (oversteer), hence the need to have a slight bit of understeer applied at the steering / forks, so they don't tighten the radius too much and hit the inside kerb. Front takes a larger radius corner than the rear by half the difference in the sections of F & R tyre.
It also eases the transition from slippage in the rear tyre to spinning it up and laying darkies because there is a certain ammount of opposite lock already on. Movement of the package CG (bike and rider) by hanging off, also has a effect relative to the width of the contact patch (weighting the inside or outside footpeg).
Once laid over and in a steady state, constant radius corner, steering towards the inside to tighten the radius tells you if you have any more grip left available at the front. That way you know you can corner faster than you were - if there was any grip left. Or, if no grip left, the front tucks and most of us not called Marquez would be on our ear.
Bear in mind that a race slick has very different sidewall construction to a road tyre, which is much softer and so warms up in cold poor weather conditions to give adequate grip levels. Whereas a race slick has much stiffer sidewalls so as not to flex too easily and put too much heat into the tread and thereby overheating the compuond.
Generally the race bike is set up with much more compliant and controlled suspension spring and damper rates, unlike our road bikes.
If Rossi ate a pie the night before, then the suspension guys would be altering the spring rate in forks and rear shock and then adjusting the four damping rates at each end to suit.

Yes its hissing down here too

[slparry]

Think of cones on their side and it all "clicks" into place

and as John will confirm my previous handling yardstick was related to pies but now I'm on my mega diet I'm having to rethink the plan

[Grip Fast]

Thank you for the answers, especially the very detailed one from SP250, which I'll need to read a few times. I hope my reference to Rossi didn't imply any comparison between my futile wobbling around a track (see below) to the MotoGP guys.

The cones on their side helps the picture, but it makes me think that these custom bikes, with same sized knobbly tyres front and rear, can't handle too well.

image.jpeg (799.1 KiB) Viewed 5555 times

[BigRob]

I can testify to the cornering problem I have a bike with 240 front and rear....it is interesting

[fontana]

it makes me think that these custom bikes, with same sized knobbly tyres front and rear, can't handle too well.

No such problems here

[dark_knight87]

This is very cheesy but it may be of interest:-

https://youtu.be/t0vUr5oUdNM

Regards,
Russ

[fontana]

This chicken strip thing sports bike riders are so obsessed with makse me chuckle.
There used to be a guy in Kent who provided a service for these morons.
For £50 he'd give your tyres the full cooked track day look.

[Grip Fast]

This is very cheesy but it may be of interest:-

https://youtu.be/t0vUr5oUdNM

Regards,
Russ

Thanks for all the responses.

I've just watched that video over the last couple of evenings. Worst acting ever, but some interesting bits. I went to a talk by one of their guys (California Race School). It was a 2-hour talk, so I thought we'd cover a lot of ground and learn all sorts of stuff. He spent the whole 2 hours approaching a bend! I don't think we even got to go round the bend. It was in all sorts of minute detail, from how we see / don't see things, tunnel vision, positioning, gear, throttle, everything - but just involving the approach. To find out how to get round the bend - well come along to one of our courses...

It was fascinating stuff, but left me slightly - I don't know... erm, deflated or something. A bit like a big sneeze that doesn't happen...

[SP250]

I started to watch the video, but got so hacked off by the length and slow pace of describing things (and the cheesyness) that I gave up after 10 minutes.
Went and got the books out of the bookcase where all my car and bike books are kept and put then out ready to read again.
Bought them all when they first came out and I was still racing.
Twist of the Wrist 1 & 2 and also The Soft Science of Road Racing Motorcycles.
All are useful books and easier to delve into, to clarify a question, than sitting through the video half a dozen times.

[boxerscott]

That is an interesting question. I have often pondered that and have not been able to focus on it clearly as my mind wanders. I reckon there are too many factors to mention and one could get quite technical about it. You could simplify it into 3 categories. The set up of the machine, the capabilities of the rider and knowledge of the bend. Do not make it too complicated. Keep it simple. Practise makes perfect. I think a lot of it is intuitive. Reading a book about it would not help me but following somebody who was betterer than me would make my bike track round the bend

[SP250]

This illustrates the opposite lock bit of cornering.

https://www.facebook.com/MotoGP/videos/ ... 0276085769

Sorry I won't be with you all on the Welsh weekend (Welsh GP) when you are all putting it into practice!