Emergency stop - rear wheel lock?

[yorkie_chris]

Who says you shouldn't change down while emergency stopping?
Edit: except the DSA and since when do they know sh*t all about riding bikes.

If you're stationary in 6th gear how are you going to get around the obstacle, or possibly avoid that truck behind you that was late braking and is about to squish you?

[Viney]

Originally Posted by yorkie_chris

Who says you shouldn't change down while emergency stopping?

If you're stationary in 6th gear how are you going to get around the obstacle, or possibly avoid that truck behind you that was late braking and is about to squish you?

Exactly, as long as you know the consequences of your actions when you do these things, the thing is to stop/avoid the obstacle.

I'm almost 100% certain that during my emergency stops on my MOD 1 I changed from second to first every time when practising and then even on my test?!

Originally Posted by yorkie_chris

I've got to. How the devil did you ride an SV underwater?

Rear wheel locked up and put me in the sea... Or river, wherever turbot's live.

Stupid iPhone auto correct!!

[Paul the 6th]

Originally Posted by Daveog

I shall be practicing heavy braking and avoid changing down - somehow I've rode for three years and never heard that you shouldn't change down while emergency stopping. Additionally, I'll attempt a little blip of the throttle on the down change in practice.

tbh in the past when something has changed in front of me and caused me to shed a lot of speed I'll happily get hard on the brakes and drop down the gears - but always brakes before gears or you might end up in a situation like you've just found yourself today...

Then the times where it's a code brown emergency stop and there's nothing to think of other than "F**KING STOP YOU BASTA*D!!!!" bring in the front brake and increase pressure *quickly but smoothly* (no yanking, save that for self love time) and introduce the back brake a half second after you're on the fronts..

[Paul the 6th]

Originally Posted by yorkie_chris

Who says you shouldn't change down while emergency stopping?
Edit: except the DSA and since when do they know sh*t all about riding bikes.

If you're stationary in 6th gear how are you going to get around the obstacle, or possibly avoid that truck behind you that was late braking and is about to squish you?

Because obviously when you've done your emergency stop you do the two lifesavers (one over each shoulder) see the truck coming, get off calmly (left foot down, right foot over the bike and down on the tarmac all the while holding the front brake to maintain control of the machine) and push it to the side of the road, while still making observations all around you.

Pretty certain that's the DSA method of "How to avoid being squashed by HGV and/or other large goods vehicles after performing an emergency stop in higher gears, 2007 edition"

[yorkie_chris]

There are 3 things at play to make the wheel slide or become skittish excluding the brakes.

Engine braking
Inertia of the engine
Inertia of the drivetrain

Engine braking is fairly straightforward, there isn't as much as you'd think.

Inertia of the engine is where you fail to match road speed to engine speed with your blip, as you ping the clutch out the engine must immediately speed up from near tickover to some higher rpm which it cannot do immediately, the difference means the rear breaks traction a bit and slides for a while until the engine matches the road speed.

Drivetrain inertia is where you're braking realllly hard, and the drivetrain can't actually slow down fast enough to keep up with the slowing of the wheels and you get the waggly floaty feeling at the back due to the rear wheel still driven forward by this inertia. A bit of a tap of the back brake will knock this on the head.


All of these are made worse by any front braking, which by it's nature unloads the rear, thus reducing traction. Of course if you're REALLY braking with the front then the rear has ZERO traction 'cos you're at the limiting case, the hardest you can possibly brake, about to do a stoppie. You can't slow down ANY HARDER than that. (turn your pockets inside out as air brakes maybe?)
At that limiting case there is nothing to do with the rear except to downshift steadily to keep it somewhere near road speed.


Way I'd interpret the physics of it:
You're better off learning good, smooth downshifting way in advance as part of normal riding. It pays off massively.
When in an emergency apply 100% of concentration to using the front brakes as hard as possible without lock or stoppie. Ignore what the rear is doing. Chances are downshifts will happen automatically, if not no worries, you can't spare any concentration to thinking about them.

Originally Posted by Viney

Exactly, as long as you know the consequences of your actions when you do these things, the thing is to stop/avoid the obstacle.

and one day we will learn that its better to do it with the bike still under you, not nessesarlily going over the top of the obstacle alone

Personally I don't touch the rear brake on emergency stops because I like to stop under control. The engine braking is enough at the rear. YMMV

I was taught to leave the gears alone cos while practising I was changing down while doing e stops.

When I did my trackday on my sprint, couple of times early on, I was braking into a corner off the long straight and had the rear end squirm and slide a bit cos I was changing down without a big enough blip.

It's much harder to get right on my sprint, it was easy after a while on the sv.

I had my sprints rear end at 45degrees when I locked it up on a greasy road back in October.
Thought the rear was gonna come right round, but let go of the rear brake and re applied then it slid out the other way, in the end I just coasted past the thing I was braking for, it was safer.