Hot_Air wrote: ↑Thu Nov 19, 2020 10:26 am
The Spin Doctor wrote: ↑Wed Nov 18, 2020 9:23 pmthe idea that weight transfer gives the front tyre more grip isn't one that Code agrees with, which is why he talks about getting on the power through the corner to get the front steering.
If so, then Keith Code is mistaken. Weight transfer onto the tyre increases the downward force on it, which increases traction.
In a straight line, yes. But think about what's happening in a corner. If you're slowing, you're also increasing the vector force that makes the tyre want to slide out. I'm not good enough to do the maths - I think it's in Vitori Cossalter's book - but it should be pretty obvious that if you're leaned over whilst braking THEN hit a zero grip surface, all the downward force in the world won't create any traction since the surface isn't giving its part of the deal. You'll crash. If you're 'only' steering, then you'll still lose grip but it won't be as dramatic.
The Spin Doctor wrote: ↑Wed Nov 18, 2020 9:23 pm
If you slow by rolling off whilst leaned over you compress the forks [...] In my experience in the wet on a road bike on road tyres, rolling off mid-corner - let alone braking - the bike feels 'edgy'. I assume that is down to 'slip angles'.
I don't believe it's down to slip angles. As the brakes are applied, and the weight shifts forward, the forks compress. This compression changes the steering geometry – decreasing stability, which is why the bike can feel 'edgy'. But it also means the bike changes direction more readily, doesn't it?
I'm pretty sure that I covered this with you in the theory session before one of your courses. I've also covered it fairly extensively on my FB page, and on TRC.
This 'bikes steer faster on the brakes' stuff is another myth showing that the people who write this stuff for magazines don't understand what's going on. The bike changing direction 'more readily' is simply the result of the machine turning on a progressively tighter radius as the bike slows, and nothing to do with the geometry.
In fact, it works the other way, thanks to the fact that your front tyre is flexible and compressible. As you brake and load up the front, the very effect that's giving you more grip - the wider contact patch, is also making the bike more reluctant to steer.
Think about where the contact patch contacts the ground. Upright, it's directly in line with the steering axis.
But as you lean, the contact patch moves sideways out of line with the steering axix.
This creates a torque that tries to turn the front wheel INTO the corner - it's this torque that creates the self-centring steering. If you take your hands off the bars when the bike is leaned over, this torque steers the bike upright again. It's also why you need to maintain a reduced counter-steering pressure on the inside bar to MAINTAIN lean through a corner - that offset contact patch is creating a torque trying to steer the bike upright again.
Now try this - brake hard in a straight line and try to steer - you'll find it much more difficult to get the bike to move off line because you've flattened the tyre - the result is that the moment there's any lean in the wheel, the contact patch moves much further to one side or the other and in turn creates a greater self-centring torque.
Now try this - brake hard whilst leaned over and feel what happens - the weight transfer flattens the tyre, and moves the contact patch further out of line with the steering axis, which generates a greater self-centring torque which steers the bike upright... which is why so many riders who panic mid-corner run wide.
Lastly try this - get all your braking done upright, get back on the throttle UPRIGHT, and THEN steer. Now, there's no extra loading on the front tyre, the contact patch gets skinny and when you lean, the offset is closer to the steering axis, which minimises the self-centring torque trying to steer the bike upright... which means you only need finger-tip pressure to steer the bike.
The Spin Doctor wrote: ↑Wed Nov 18, 2020 9:23 pm Code … talks about getting on the power through the corner to get the front steering.
Are you sure it's Code's reasoning?* Acceleration-while-turning increases the bike's cornering radius!
Interesting that you should be pointing that out whilst not spotting that deceleration DECREASES cornering radius!
a) perhaps I should have said "you apply some throttle". Due to vector effects if you run into a corner at constant speed (and assume zero friction and no power input) the bike would decelerate. So it's necessary to apply some throttle to maintain speed.
b) Code is talking about the track but his point is that you pick a point to roll on the throttle, then you continue to roll on progressively as the lean angle reduces - you don't chop and change throttle settings once leaned over because the fore-aft loading in the suspension which happens AT THE SAME TIME as the suspension is absorbing cornering forces will destabilise the bike. That makes good theoretical and practical sense to me [and incidentally this is why the advice in Roadcraft about opening and closing the throttle mid-corner as the limit point moves around is - IMO - completely wrong. The way to adjust to moderate changes in radius is to enter the corner with plenty of stopping distance in hand and then match LEAN ANGLE to the radius whilst maintaining speed, rather than try to maintain lean angle by changing SPEED. It obeys the basic stability rule of separating anything that makes the bike do a rocking horse impersonation from angle of dangle.]
Yes, Code's progressive acceleration pushes the bike onto a wider line but that allows you to exploit the width of a circuit. The problem on the road is a narrow lane a fraction of the width of a circuit which is why I talk about applying a bit of positive throttle right through the corner to maintain or very slightly increase speed, but delaying harder acceleration until the bike is upright and pointed where you want to go next.
When banked over, forces from the front brake and the deceleration causes the bike to lean.
As explained, quite the opposite.
In contrast, the back brake generates a torque that tends to straighten and stabilise the motorcycle.
I don't see how it 'straightens' the bike. There are gyroscopic effects since the wheel's fixed in the swing arm, and the swing arm only moves vertically with respect to the chassis, but decelerating would reduce them. I'm guessing that applying the rear brake causes the bike to 'squat' at the rear which means less forward weight transfer which means less loading on the tyre resulting in less deformation of the contact patch and less of the self-centring torque effect I've just described. So the bike doesn't try to sit up so much when decelerating.
So I think RiDE is giving bad advice about apply the rear brake mid-corner (but I'm happy to be corrected).
I haven't read the article (a scan would be good as I'm not dashing to a shop to buy it right now - I'd rather get a copy of the Beano with the pull-out 'Beano for grown-ups' special section actually
) ) but any brakes applied mid-corner destabilise the bike.
And on a wet road especially, you're adding crash-risk because the tyre's grip is split between braking and cornering forces.
ANY cornering is a split between forces. We just dial in the ratio. At a constant lean, we've balanced straight line momentum which wants to throw the bike OUT of the turn with gravity that wants to pull it DOWN, but we have to use the tyres' grip (at both ends) to keep the bike on that smooth curve where the 'out' and the 'down' forces are perfectly balanced. The trouble is that the SURFACE can upset this, because we rely on the coefficient of friction between the two to generate the force that keeps the bike steering - what's why we have to reduce lean angles on a wet surface.
Your advice is much better than RiDE's, and in line with what I learnt from Code's superbike school:
The Spin Doctor wrote: ↑Wed Nov 18, 2020 9:23 pmgo in slower, and when you see where you want to go next, turn the bike tighter deeper in the turn and get it upright and on the throttle again.
* It's not what I remember from doing Code's superbike school, but I may have forgotten because it was some years ago. Is this reasoning in one of his books?
Nope. It's my own Point and Squirt, which you covered on my course.
It is partially based on Code, though, since I use a modified version of his 'two-step' reference point system adapted to the road (with narrow lanes, remember) where the point in the bend where you gain sight of the EXIT (where you can - as Code puts it - "pull a wheelie because the bike is upright pointed where you want to go next) is the point where you TURN-IN to the corner, cutting across from the wide 'vision line' onto a straighter line that takes you out of the corner (if other issues allow). The other point, you should remember, is the ENTRY where the bend forces you to steer or run off the road. So essentially, you do in slower and square-off the corner late on, then get on the gas early and out of the bend faster - you point it THEN you squirt it.
It's the opposite of the 'racing line. It's sometimes called the 'late apex' line, because you don't cut across the turn for a mid-corner apex as you would on a corner between two straights on the track. Interestingly, I have a video from about 2005 from West Midlands BikeSafe where the commentary talks about 'widening the line' through bends to 'reduce the load on the tyres', then shows the same rider doing a perfect deep in / late turn 'Point and Squirt'.
This late apex P&S line was covered in Bike some years ago by one of the Rapid trainers but it's what I've been talking about online since 1994 on Compuserve and my webpages, and it's what I've been teaching on my courses since I set up Survival Skills in 1997.
?
and that's what thought. I'm baffled why RiDE recommends braking mid-corner, not on corner entry. And I agree about it making crashing more likely - the only time I flipped a car on track was when I was learning how to trail brake.
