Trail braking, or braking in corners.

[mangocrazy]

On correctly designed and set up front suspension trail braking is used to complement the rebound damping and allow the front suspension to unload gradually and not spring back too sharply, causing loss of front tyre grip. It's one of the main considerations when deciding how much rebound damping to dial in.

Dial in too much and the front fork will 'pack down' over a series of bumps, dial in too little and the fork will rebound too quickly with various negative consequences.

[Le_Fromage_Grande]

To be fair to me, last night I'd been in the garage with my Kawasaki running, so God knows how much warm unburn't petrol I'd breathed in, I woke up with a stonking headache this morning

[Mr. Dazzle]

You're in the right sort of ballpark though Cheesy, it's just a massively complicated set of interactions! This is why you have high and low speed damping, semi-active suspension, magnetorheo..can't spell it!...clever variable rate dampers. etc. etc.

[mangocrazy]

To be fair to me, last night I'd been in the garage with my Kawasaki running, so God knows how much warm unburn't petrol I'd breathed in, I woke up with a stonking headache this morning

Not to mention the carbon monoxide you'd imbibed. Glad to hear you got away with just a bad headache.

[mangocrazy]

I wouldn't be at all surprised if it emerged that Ohlins MotoGP forks had some kind of variable rebound damping based on where they were in the stroke. At almost maximum depth of stroke you'd have increased damping, tapering off as the fork returned to full extension.

Perhaps. Maybe. It's the kind of stuff they'd be evaluating, I'm sure.

[Mr. Dazzle]

I was nearly killed by a CO leaking boiler a few years back...it's fucking sketchy, the very first symptoms are loss of judgement and mild euphoria, so you don't even realise you're getting deaded.

Needless to say, I have CO monitors now!

[Wossname]

Far as I can see, trail braking is the same as the usual kind - on smoothly, off smoothly - it’s just that you’re doing it later than usual, i.e. when in the turn and leaning, as opposed to doing it all in a straight line before the bend.

[Horse]

Now here's a good YouTube training video

[Screwdriver]

Far as I can see, trail braking is the same as the usual kind - on smoothly, off smoothly - it’s just that you’re doing it later than usual, i.e. when in the turn and leaning, as opposed to doing it all in a straight line before the bend.

Hmm, "brakes on smoothly"? Well I guess I'd have to think about that. Depends how you define smooth I suppose. You definitely don't snatch at the brake lever but it's a question of milliseconds of caution rather than the full second or so smoothly coming off the brake.

As an interesting aside, physics has come a long way in the past few decades with the event of supercomputers etc. but so far as I am aware, the actual dynamics of a bicycle/motorcycle are not fully understood. Perhaps I am not phrasing that quite correctly but I remember reading somewhere (probably while researching counter steering and slip angles etc.) that there is no equation or set of equations that describe how a motorcycle/bicycle actually steers!

I appreciate there are many ferociously complex equations which can calculate any number of variables but there are so many interdependent parameters with positive or negative feedback I don't think the process is completely solved. I imagine you could have the worlds most powerful computers along with AI design the "perfect" machine and it would end up steering like a bag of concrete in a wheelbarrow.

[Horse]

Yorick is correct regarding the effect on the steering geometry and it's not a subtle effect either, the steeper rake angle as the forks compress, really quickens up the steering.

And a steeper fork angle also shortens the bike's wheelbase, further quickening the steering.

[Horse]

10 points for the first person to say "traction circle".

@Mr. Dazzle Ooh, sorry, missed this.

1. Is it a circle, quadrant, or oval?
2. Is it a rare occasion where '1' can be worth more than '1'?

[The Spin Doctor]

OK, but why would i need to?

I was taught old-school police-style, 40+ years ago. Back then *any* braking in bends was frowned upon

You'll rarely, if ever need to trail brake on road. However, see my earlier post, does that answer your questions?

Ignore the YouTube hype about "you must".

Did you not have a story about the copper on the training course picking himself and his BMW out of a hedge on a bend and saying proudly to the instructor "I didn't brake in the corner though"?

[The Spin Doctor]

Yorick is correct regarding the effect on the steering geometry and it's not a subtle effect either, the steeper rake angle as the forks compress, really quickens up the steering.

And a steeper fork angle also shortens the bike's wheelbase, further quickening the steering.

But the loading on the front tyre compresses the contact patch making the bike want to sit up and go straight ahead. That's rather significant on squidgy, more rounded road tyres, less so on stiffer competition tyres. Try braking hard MID CORNER to see it in action. Just make sure you pick a bend with plenty of run-off. Braking hard on the way into the bend has the same effect, you just don't notice because it's easier to compensate by adding more steering torque.

On the road, ,ost of the 'quicker steering' effect people talk about is actually the result of the bike losing speed and turning on a progressively tighter radius as it slows down.

[The Spin Doctor]

OK, but why would i need to?

I still don’t get it: apart from braking later, are there any benefits (and why would braking later be a benefit).

Thank you in advance.

1) We don't get every bend right... it's easy to enter too quickly and then being able to brake into the bend is very useful

2) We may misjudge the radius of the corner or it may tighten up part-way round - being able to brake MID-corner is an equally useful skill

3) The road may turn out to be blocked just out of sight - stopping might be essential

The important thing to remember is that if you brake INTO a bend you start hard on the brakes then ease off as you add lean. And if you brake MID-bend then you start light on the brakes, then progressively hard if you can ease your lean angle.

Even gentle braking in a bend will get the bike slowing much quicker than engine braking along on many bikes.

And finally, if you haven't already crashed mid-corner, you have tyre grip to brake... gently.

[The Spin Doctor]

As an interesting aside, physics has come a long way in the past few decades with the event of supercomputers etc. but so far as I am aware, the actual dynamics of a bicycle/motorcycle are not fully understood. Perhaps I am not phrasing that quite correctly but I remember reading somewhere (probably while researching counter steering and slip angles etc.) that there is no equation or set of equations that describe how a motorcycle/bicycle actually steers!

This should offer you some decent info...

https://www.amazon.co.uk/Motorcycle-Dyn ... b_title_bk

[Horse]

OK, but why would i need to?

I was taught old-school police-style, 40+ years ago. Back then *any* braking in bends was frowned upon

You'll rarely, if ever need to trail brake on road.

Did you not have a story about the copper on the training course picking himself and his BMW out of a hedge on a bend and saying proudly to the instructor "I didn't brake in the corner though"?

Braking then wouldn't have been trail braking

There was a suggestion that test candidates would sometimes disconnect a brake light switch. As if the examiner wouldn't notice that he was suddenly closing on the bike ahead ..

[Screwdriver]

But the loading on the front tyre compresses the contact patch making the bike want to sit up and go straight ahead. That's rather significant on squidgy, more rounded road tyres, less so on stiffer competition tyres. Try braking hard MID CORNER to see it in action. Just make sure you pick a bend with plenty of run-off. Braking hard on the way into the bend has the same effect, you just don't notice because it's easier to compensate by adding more steering torque.

On the road, ,ost of the 'quicker steering' effect people talk about is actually the result of the bike losing speed and turning on a progressively tighter radius as it slows down.

No, I think you misunderstand the effect of "quicker" steering, it means you can adjust your line mid bend with less steering input which places less additional load on the front tyre than a bike with less castor.

The effect you refer to when a bike wants to sit up mid bend is because loading the tyre causes the front wheel to countersteer. It is because the contact patch is offset from the centre line of the bike, on the inside of the turn. The wheel therefore steers into the bend and like kicking the bottom of a balanced pole, the top falls the other way.

If I recall correctly, I drew you a diagram explaining the effect of an offset tyre contact patch when discussing hanging off mid bend.

I'll take your word for it if you insist there some squishiness going on but the primary effect is due to the offset contact patch which will be more pronounced on wider tyres.

[The Spin Doctor]

No, I think you misunderstand the effect of "quicker" steering, it means you can adjust your line mid bend with less steering input which places less additional load on the front tyre than a bike with less castor.

Well, it depends on your perspective. I'd say that most people would understand 'QUICKER' steering to be a faster change of direction by speeding up the rate of roll for a given input.

In any case, two sides of the same coin, both of which you can achieve by changing the STATIC steering geometry of the machine.

The effect you refer to when a bike wants to sit up mid bend is because loading the tyre causes the front wheel to countersteer. It is because the contact patch is offset from the centre line of the bike, on the inside of the turn. The wheel therefore steers into the bend and like kicking the bottom of a balanced pole, the top falls the other way.
If I recall correctly, I drew you a diagram explaining the effect of an offset tyre contact patch when discussing hanging off mid bend.

Agreed 100% and I've been explaining how this DYNAMIC change to steering geometry works for at least two decades! I don't think it was me you had to explain it to since I was talking about this sit-up tendency on the brakes way back on my old website, long before the earliest days on VD.

I'll take your word for it if you insist there some squishiness going on but the primary effect is due to the offset contact patch which will be more pronounced on wider tyres.

I don't 'insist' but as far as I know - and my source was the head Avon tyre technician at a rider skills day at Castle Combe - race tyres have a different carcass construction which is much stiffer to give more precise control under hard straight line braking and at extreme lean angles, whereas road tyres have to be a compromise because of the need to be compliant in order to deal with the bumps found on a typical road.

And since the tyres compress more under braking, that broadens the contact patch, and should you be leaning over when you brake, the offset will inevitably be greater on a road tyre - and that will increase the self-centering tendency of the bike and make it want to sit up.

[Screwdriver]

Sorry but if the tyre squidges or is rounder, there will be less offset and less tendency for counter steering which is (I suggest) the principle action here.

Similarly a stiffer carcass will resist movement and maintain the maximum offset (if carcass deflection was a contributor to the effect).

"Explain" is perhaps too suggestive, you wanted my graphic for a book or something... It was showing why a wide tyre has a greater offset meaning the centripetal force from the cog through the tyre (lit. v.v.) could be displaced towards the contact patch, ideally right through it, if you "hang off" the bike.

Again, I would expect a softer tyre construction would actually "smear" out the effect whereas a stiffer construction would maintain a much more tightly focussed action. Like the difference between trying to balance on a bean bag or a basketball. That would tie in with your Avon chaps description because a stiff carcass on a bumpy road would throw you all over the place since the effect is not dampened or smeared out due to contact patch compression.

[MrLongbeard]

Wait, use the rear brake you say