revtothelimit - motorbike forum

Horse wrote: Sun Jan 31, 2021 10:31 pm

The Spin Doctor wrote: Sun Jan 31, 2021 9:58 pm

Trinity765 wrote: Sat Jan 30, 2021 11:02 am Something I heard ... it's stuck with me is that the front wheel will find its line on its own and there's nothing you can do to help it.

Errr... well, if it did, there's not much point having handlebars.

I read Trinity's comment as "the front wheel will self-centre to keep the bike travelling in a straight line on its own and there's nothing you can do to help it", not to do with steering.

Well, I'd certainly agree that you rarely 'straighten the bike up' and it does the job itself once you stop inputting a steering force on the bars.

Bugger it... just spent 15 mins composing a response, saving it as a draft and coming back to it to discover the draft didn't have anything I'd edited...

Trinity765 wrote: Mon Feb 01, 2021 5:34 am The same article said that the only reason the handlebars are there is for somewhere to hang the controls. I wish I could remember where I read/watched it but seeing as I can't even remember if I read it or watched it, there's little hope of that. However, I believe it to be true and it has helped.

All I can say to that is that I would love to see the author trying to negotiate twisty road on a bike with no handlebars. We make our steering inputs via the bars - push right to go right, push left to go left whilst the harder we push the quicker the bike rolls off the vertical and the longer we push the greater the lean angle we achieve... and mid-corner corrections are made using subtle variations of pressure on the bars.

Most of the problems riders have on bikes with flat or low bars are posture - the rider leans on the bars and prevents them turning. I had a guy out on a course 7-8 years ago. Brand new Fireblade, and he'd thrown another 4-5k's worth of mods at it "because it didn't steer". Aftermarket springs and cartridges in the forks, WSB standard Ohlins steering damper and rear shock, full professional suspension set-up, replacement tyres, lightweight mudguard. He was just about to order the WSB spec carbon fibre wheels when he thought maybe he'd get his riding checked out first. I spotted the problem before he'd even got out the car park - stiff elbows. We went directly to a car park and spent 30 mins working on his posture, specifically him being able to FEEL what he was doing/

Try monitoring what you're doing next time you're out on the bike. But using the steering EFFECTIVELY is just as important as being able to use the brakes.

While out with an advanced instructor he noticed that when going into a bend with a very uneven surface I tensed up on the bars and he picked me up on it. The next day I read an article about forming new habits. The first step is to recognise when the new habit needs to kick in - so for me, as soon as I notice the road surface is uneven. Breaking the problem down into one very brief moment - the second I notice a bump and then thinking RELAX has worked. By repetition, it's now a habit.

Some years ago I was out with a bunch of people on a group trip to the Alsace. Amazingly, I hadn't ridden in the rain for four or five months despite all the training courses - it had just been a remarkably dry year in SE England. And of course, first day out, it rained, and almost first corner I had a slide going left / right over a narrow bridge crossing a stream. For the rest of the morning I rode really badly. So badly, one of my buddies commented on it. I took myself off to a quiet corner, talked myself through the same kind of diagnosis and advice I'd give a trainee about keeping knees locked and elbows loose, then when we went back out, I rode at my own pace and self-talked my way through that advice in exactly the same way I'd give tips over the radio. Within 30 mins I was relaxing, within an hour I was back up to speed and on the ride back everything was fine. The same guy came over and asked "what happened"?

So yes, anyone can get tense - the important thing is to recognise it, then have a strategy to deal with it.

I went into a fast corner for the first time with someone who rode like this and I nearly fell off myself in surprise As I didn't know him well I wasn't going to ask him about it but as luck would have it, someone else did over dinner. His reply was "I don't know why I do it, but it works". No it doesn't - you just get thinner chicken strips...
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For a left turn, lower the bike to the left but keeping the body upright? That's fine for slow corners or slaloming around drain covers but not for fast corners as the idea is to keep the bike as upright as possible. In lowering the bike down you're using more of the tyre than you need too and therefore you're going to get to the edge of it sooner, no?

Sorry to disagree but I keep having to repeat this point. It DOES work.

Firstly - and as I previously explained - you're moving your own body mass less distance, which means you need less force on the bars to get the bike to turn. It's particularly useful on a flip-flop kind of bend.

Secondly - if you lean OUT of a corner, the movement of your own body mass makes the bike lean in further, and then the greater angle of attack of the tyres makes the bike turn on a tighter radius at the same speed.

The physics works at any speed - it may be taught for slow tight turns like the U-turn but it can be useful on faster corners too, particularly if you need to tighten the line suddenly. Pushing the bike DOWN and sitting upright at the same time as you add some counter-steering input will get the bike changing direction very fast indeed.

Why do you think you need "to keep the bike upright as possible"?

The usual explanation is that "it keeps the bike on the fat part of the tyre and gives more grip".

This is another cornering myth. There's no 'fat part of the tyre', front tyres are either rounded (sport touring) or triangular (sports) which should give you a clue. And in fact modern tyres are designed to deform under cornering load to INCREASE the contact patch when leaned over - my Contis are designed exactly that way and they're not even cutting edge tyres - they have been around for quite a while. So if you force the bike upright by leaning in, you're actually reducing the contact patch on these tyres! You may also have dual compound tyres - if you try to keep the bike upright when cornering, you're keeping the bike at least partly on the less grippy harder compound!

Frankly, if you're riding off the edge of the tyre on the road - counterweighting or no - you're leaving yourself with no margin for tightening the line if you need to. And only cruisers and heavily laden tourers are likely to run into ground clearance problems. The days when I used to slide the rear wheel sideways on right-handers on my 400-4 because I'd got the centre stand AND the exhaust collector down are dim, distant memories!

I ride according to the the belief that the further round the tyre the contact patch is the less friction I have so the less braking or acceleration (control) I have. If I'm wrong I'm very interested in exploring that but it's going to get technical, isn't it... because direction of force is also part of the equation

I use all of the techniques mentioned where appropriate.

If I may use Horse's symbols,

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Lean with - This is how I've described police riders and most advanced types that I've ridden with. This, and Lean Out is where I spend most of my time. It requires more positive steering than Lean In to initiate a turn because I'm not using much body weight.

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Lean in - I'd spend most of my time here if I were on a national speed limit, open twisty road with good views. Should I need to brake, the bike is already more upright than it would be in Lean Out and with more friction, I'd have better/safer/more acceleration out of the bend. Approaching a bend I would lower my body weight, forward and to the side. In the extreme and in the bend I may move my body away from the bike to increase the effect of my weight. I'd use counter steering to make adjustments to my line and to go from one bend into another.

!
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Lean out / counterweighting - I do this at relatively slow speeds, to move around objects in the road and to take slow, tight turns. I use this particularly when in a blind left turn on a single track as the overall width of me and the bike it less - I'm taking up the least amount of room to allow for a bigger vehicle coming in the opposite direction.

Trinity765 wrote: Tue Feb 02, 2021 5:42 am I ride according to the the belief that the further round the tyre the contact patch is the less friction I have so the less braking or acceleration (control) I have. If I'm wrong I'm very interested in exploring that but it's going to get technical, isn't it... because direction of force is also part of the equation

It's (nearly) wrong but it's a common misconception.

Essentially, cornering requires the force of momentum - which I'm sure you know wants to go in a straight line - to be constrained so that a curved path is followed.

Stick to a circular path as it's the simplest case but assume that at a fixed speed there's also a fixed lean angle that matches the speed.

The important point is that the 'lean angle' is not the lean angle of the BIKE but it's the lean angle of BIKE PLUS RIDER COMBINED. That's because the momentum is operating through the combined Centre of Mass. The friction of your tyres are constraining the cCoM and keeping the bike and rider turning.

Now, as the rider you can move your own body mass on top of the bike. You can move it forward (as you would to prevent a wheelie) or back (if you're fighting a stoppie). Or - and this is the important bike - you can move it into the corner (by hanging off) or you can move it outwards (by sitting bolt upright and counterweighting).

As your mass moves, so the mass of the bike must move too to balance things - if you lean in, the bike sits up, if you lean out, the bike leans in.

But... and this is the key bit of understanding... the cCoM stays in ROUGHLY THE SAME PLACE (it moves down a little if you lean in, and up a little if you lean out, and this is the source of the belief that by leaning the body into a turn you get more grip, but the effect is so tiny as only to be of interest to racers operating on the edge of adhesion).

Because the cCoM is (almost) in the same place so the forces the tyres are balancing remain (almost) the same. So as I said in the earlier post, you're just riding on a different bit of the contact patch! Sitting up to the bike leans in does not 'reduce friction' and and pushing the bike upright does NOT materially add to tyre trip.

Just to repeat, it's not the lean angle of the tyre that's the issue once speed / radius are fixed, it's the speed the bike and radius of the turn itself. Take a corner faster and you'll need more lean to get round the turn - and THAT needs more grip. But remember - it's the cCoM that's leaning more! You won't increase tyre grip by leaning in, you'll simply be using a different bit of the tread to keep the bike turning.

I use all of the techniques mentioned where appropriate.

Me too. And it's important to be more than a sack of spuds on the seat of the bike. It's probably one of the biggest issues that intermediate riders have to overcome - a feeling that moving around on the bike isn't a bad thing.

The Spin Doctor wrote: Thu Feb 04, 2021 2:50 pmIt's probably one of the biggest issues that intermediate riders have to overcome - a feeling that moving around on the bike isn't a bad thing.

One of the biggest issues for many (most?) riders - me included - is not liking, and so reacting badly to, the feeling that the bike is sliding

Horse wrote: Thu Feb 04, 2021 3:05 pm

The Spin Doctor wrote: Thu Feb 04, 2021 2:50 pmIt's probably one of the biggest issues that intermediate riders have to overcome - a feeling that moving around on the bike isn't a bad thing.

One of the biggest issues for many (most?) riders - me included - is not liking, and so reacting badly to, the feeling that the bike is sliding

There's a difference between "moving around on the bike" and the bike "moving around underneath you".

But getting loose and feeling comfortable moving around helps you stay loose when it's the bike doing the moving. Riders who are stiff are in a really bad place when the bike does twitch.

I wasn't wrong when I said that it was going to get technical and I'm sorry for dragging this thread from steering to grip in corners. I just need about four hours of headspace to really understand it - which I've put in the calendar for next week

Trinity765 wrote: Fri Feb 05, 2021 10:55 am I wasn't wrong when I said that it was going to get technical and I'm sorry for dragging this thread from steering to grip in corners. I just need about four hours of headspace to really understand it - which I've put in the calendar for next week

They're all related

Try this. Stand up with your feet touching and arms by your side.

Lean to the right from the waist. Don't twist, just lean.

Which way do your hips move?

They move LEFT to maintain balance. That's because your centre of mass is somewhere around just under the belly button. As you move mass ABOVE the CoM one way, mass BELOW the CoM has to move the other way to maintain balance. If your hips didn't move, you'd fall over.

The same balancing trick has to happen with the bike. If you sit on it at a standstill and lean off to one side, the bike MUST lean the other way ... or fall over.

The Spin Doctor wrote: Fri Feb 05, 2021 12:11 pm

Trinity765 wrote: Fri Feb 05, 2021 10:55 am I wasn't wrong when I said that it was going to get technical and I'm sorry for dragging this thread from steering to grip in corners. I just need about four hours of headspace to really understand it - which I've put in the calendar for next week

They're all related

Try this. Stand up with your feet touching and arms by your side.

Lean to the right from the waist. Don't twist, just lean.

Which way do your hips move?

They move LEFT to maintain balance. That's because your centre of mass is somewhere around just under the belly button. As you move mass ABOVE the CoM one way, mass BELOW the CoM has to move the other way to maintain balance. If your hips didn't move, you'd fall over.

The same balancing trick has to happen with the bike. If you sit on it at a standstill and lean off to one side, the bike MUST lean the other way ... or fall over.

I get that and I've counted it towards my daily exercise routine. What I don't get is that you have as much traction in a corner as you do in a straight line or that it doesn't matter how far round the tyre the contact patch is.

Try this. Hold a pen vertically on your desk with one finger pushing down. It's quite stable and you can push quite hard. Now move your finger to the side maintaining the same pressure and it slips. The harder you push down the faster it slips. The answer may be above, I've not worked it out.

Trinity765 wrote: Fri Feb 05, 2021 12:21 pm
I get that and I've counted it towards my daily exercise routine.

What I don't get is that you have as much traction in a corner as you do in a straight line

What I said was that when turning on a FIXED RADIUS you have as much grip if the bike is UPRIGHT or LEANING IN... nothing about riding in a straight line.

Remember - you can steer a bike that's upright. You probably do it most days when you get off the bike and move it to where you're parking it.

or that it doesn't matter how far round the tyre the contact patch is.

Once you get the point about it being the combined Centre of Mass that matters, then you'll see why.

Try this. Hold a pen vertically on your desk with one finger pushing down. It's quite stable and you can push quite hard. Now move your finger to the side maintaining the same pressure and it slips. The harder you push down the faster it slips. The answer may be above, I've not worked it out.

I've seen that demo too - I was taught to use it twenty five years ago on basic training - but honestly, it's just confusing the issue. By leaning the pen over, you're lowering the point of action of the force - what I'm trying to get over is that leaning your BODY on the BIKE hardly affects the height of the cCoM which is the point of action for the cornering force.

The Spin Doctor wrote: Thu Feb 04, 2021 2:50 pm
The important point is that the 'lean angle' is not the lean angle of the BIKE but it's the lean angle of BIKE PLUS RIDER COMBINED. That's because the momentum is operating through the combined Centre of Mass. The friction of your tyres are constraining the cCoM and keeping the bike and rider turning.


But... and this is the key bit of understanding... the cCoM stays in ROUGHLY THE SAME PLACE (it moves down a little if you lean in, and up a little if you lean out, and this is the source of the belief that by leaning the body into a turn you get more grip, but the effect is so tiny as only to be of interest to racers operating on the edge of adhesion).

Because the cCoM is (almost) in the same place so the forces the tyres are balancing remain (almost) the same. So as I said in the earlier post, you're just riding on a different bit of the contact patch! Sitting up to the bike leans in does not 'reduce friction' and and pushing the bike upright does NOT materially add to tyre trip.

Just posted this in the 'cool race pics' thread.

Here seemed appropriate too

Good mash up

I remember pointing out years ago that Doohan had a weird asymmetric riding style, different on left and right handers, Still worked, though.

The Spin Doctor wrote: Thu Feb 04, 2021 2:50 pm
But... and this is the key bit of understanding... the cCoM stays in ROUGHLY THE SAME PLACE (it moves down a little if you lean in, and up a little if you lean out, and this is the source of the belief that by leaning the body into a turn you get more grip, but the effect is so tiny as only to be of interest to racers operating on the edge of adhesion).

Would it be true to say that the amount the cCoM moves is a function of rider weight, for a given weight of bike? And that - maybe counterintuitively - it moves more for a lighter rider, because the lighter rider's weight counteracts the bike's angle less? Or has my brain gone doolally during this lockdown thing?

Scootabout wrote: Sun Feb 07, 2021 11:21 pm
Would it be true to say that the amount the cCoM moves is a function of rider weight, for a given weight of bike? And that - maybe counterintuitively - it moves more for a lighter rider, because the lighter rider's weight counteracts the bike's angle less? Or has my brain gone doolally during this lockdown thing?

If you're a heavier rider, the cCoM will be higher up simply because the bike's mass stays the same.

If I remember right, the higher the cCoM, the more the bike has to lean to get round a particular radius of corner at the same speed.

When you corner (in a car, bike, shopping trolley, whatever) the centrifugal force* 'throws' your CoG outwards radially - so if you're turning left your CoG is being 'thrown' right. Since your CoG is almost always above the point where the tyres touch the ground that centrifugal force generates a rolling moment that makes you roll 'outwards' in the corner. There's nothing you can do with suspension, body position, peg weighting etc. to stop it, it's just Newton's third law.

If you're turning left the rolling moment will be making you roll over to the right. If you don't react that moment somehow you'll do exactly that - roll over to the right!

In a car the reaction moment comes from the uneven loading of the inside and outside wheels. The outer set of wheels have more 'weight' on them than the inside and generate a counteracting moment that is equal and opposite to the rolling moment. Ergo the car doesn't roll over. Note that the car doesn't actually have to move on it's suspension to do this, even a perfectly rigidly mounted car would still generate higher forces on the outside wheels.

A bike obviously doesn't have inside and outside wheels. Instead, you generate a counteracting moment by leaning. Turn left, generate a rolling moment to the right, lean to the left to counteract it. Strike a happy balance and you don't fall over to the left or the right.

The height of the CoG is important 'cause it directly effects the size of the rolling moment. If it's twice as far off the ground you generate twice the rolling moment for the same cornering speed. That's part of the reason race cars are low to the ground. The same is true of bikes, if your CoG is higher you generate a larger rolling moment for the same speed, so you need to lean further to counteract it.

Moving around on the bike doesn't change the cornering forces, which are just a function of your mass and how fast you're cornering. What it does change is the height of the CoG - and hence how much rolling moment you generate - and the relative locations of the CoG, ground and tyre contact patches. If you hang off and 'down' you can lower your CoG and reduce the amount you lean and you can generate a large counteracting moment. As Spin says, moving around doesn't actually change how much grip you need to go around a corner, all it can really change is the amount you need to lean for a given speed and hence get you onto a more advantageous bit of the tyre.



*That's right, centrifugal force. It really does exist, it's just a question of what you choose as your reference system

Mr. Dazzle wrote: Mon Feb 08, 2021 4:35 pm There's nothing you can do with suspension, body position, peg weighting etc. to stop it, it's just Newton's third law.

Not quite true... it depends on the relative magnitude of the forces.

...if your CoG is higher you generate a larger rolling moment for the same speed, so you need to lean further to counteract it.

Moving around on the bike doesn't change the cornering forces, which are just a function of your mass and how fast you're cornering. What it does change is the height of the CoG - and hence how much rolling moment you generate - and the relative locations of the CoG, ground and tyre contact patches. If you hang off and 'down' you can lower your CoG and reduce the amount you lean and you can generate a large counteracting moment. As Spin says, moving around doesn't actually change how much grip you need to go around a corner, all it can really change is the amount you need to lean for a given speed

Hanging off DOES lover the cCoM but it's not by much - as I said it might be of interest on the track but for a road rider...

and hence get you onto a more advantageous bit of the tyre.

This is the bit I don't get. Road tyres are pretty rounded in profile, dual compounds give you the softer compound on the shoulders, and modern tyres actually are designed to deform and grow the contact patch under cornering load.

Trying to sit the bike upright mid-corner doesn't seem to have any positives.

*That's right, centrifugal force. It really does exist, it's just a question of what you choose as your reference system

Someone pointed out years ago that as a practical scientist he used a centrifuge on a daily basis.

There's nothing you can do in the sense that turning left generates a reaction force* to the right. That's just plain old physics. If you're 250kg then you'll always generate the same forces if you're cornering at the same speed. That's a fundamental fixed point if you will.

Anything to do with hanging off, tyre shapes etc. is kinda next level down effect. You can't make it so you need any less force to get around the corner any more than you can pick yourself up by your own shirt collar!

I don't know enough about the relative differences between race and road tyres to know the tradeoffs of lean vs grip TBH and I can well believe that a road tyre might actually be sticker on the edges. Thats before you even throw in such complexities as suspension geometry/kinematics being different when you're leant over or springs and dampers being different etc.

*just to keep the pedants happy, turning left doesn't actually generate a reaction force to the right on you. You feel a force pushing left on you, the road feels a reaction force to the right on it. However from your POV there's a 'fictitious force' throwing you off to the right due to your own inertia. If that is confusing don't worry, these inertial forces are what first got Einstein thinking about relativity

Racers do it best. Rolling on power as the bike sits up. Less chance of wheel sliding out. I don't know but would imagine, not many riders slip off when bike is balanced in the apex. No brake, no power.

Mr. Dazzle wrote: Wed Feb 10, 2021 10:54 pm There's nothing you can do in the sense that turning left generates a reaction force* to the right. That's just plain old physics. If you're 250kg then you'll always generate the same forces if you're cornering at the same speed. That's a fundamental fixed point if you will.

If your speed is very low then the force which tries to make the bike roll outwards is very small - and you can counter it by shifting body mass the other way. It's really only of academic interest but it does mean that direct steering works at slow walking pace.

Anything to do with hanging off, tyre shapes etc. is kinda next level down effect. You can't make it so you need any less force to get around the corner any more than you can pick yourself up by your own shirt collar!

I don't know enough about the relative differences between race and road tyres to know the tradeoffs of lean vs grip TBH and I can well believe that a road tyre might actually be sticker on the edges. Thats before you even throw in such complexities as suspension geometry/kinematics being different when you're leant over or springs and dampers being different etc.

Dual compound road tyres are DEFINITELY grippier on the shoulder - that's why they are dual compound!

Racers use multi compound tyres too though and have for a long time, yet they still go to great lengths to make the bike stand up again....