Practicing emergency braking... marks left on pavement?

Placebo effect.

This study appears to contradict your statement:
http://www.promocycle.com/documentations/studies-eng/amorfrein_e.pdf

In fact they suggest completely disengaging the clutch for the entirety of the braking maneuvre.

I mountain bike a lot. Mostly X-country type single track; the most technical I get is rock gardens. My bike also has very good hydraulic discs on it.

If you have good experience with that kind of brake, you are already better at modulating your squeeze and knowing to SQUEEZE and not grab than most people on the street already riding motorcycles.

Very hard braking leaves rubber on the street whether or not you lock the brake. YOu may be very close to locking the brake though, so be cautious. As mentioned, if the brake locks the front wheel, the bars will lose all feeling, and you can recover by releasing the brake enough to get the tire rolling again.

What was not mentioned is that this will happen in about a second or two, and if you don't release the brake well within that time frame, you are going down. Two wheeled vehicles with rake and trail in the fork need the front wheel to be turning and gripping a surface or the bike can't stand up for long!

Keep at it.

Hang on to the bike with our knees and try to keep weight off the bars. Also try the same braking with a passenger if you carry a passenger on occassion.

LuciferMutt finally said it right. When you are effectively braking hard, the front tire contact patch is distorted by the loading as it squashes down and spreads out. All that deflection of the tire contact patch "shears" off rubber under heavy braking. Totally normal.

If this weren't the case how do you explain tire wear? Just the normal everyday action of acceleration and deceleration causes very slight shearing action of the tread at the road contact patch. Under heavy braking the shearing is increased, and if braking is increased until traction is broken, the tire slides/skids. Just up to the point the tire is still rotating, but there is sliding already taking place at the contact patch. This is the basic principle of ABS brakes.

All ABS systems rely on this shearing action. In fact, ABS systems don't even activate until the tire under braking is going 10% to 20% slower than the actual vehicle speed. That speed difference at the tire contact patch is shearing, almost sliding. That's why under ABS braking you'll hear tire squeal and see a tire track on the pavement. Here are some pic of braking practice I did a few years back. Repeated high effort stops from 60mph:


Those are tire marks on the pavement from the front tire. I practiced repeated stops to learn what I could do and to see how hard I could brake before the ABS system took over to avoid loosing traction. The action of heavy braking caused a much wider scuffed area on the tire than would be normal for just riding down the road. That was the result of about 20 stops, all from 60 mph.

No argument. The only issue is that often newbs mistake the rear for the front. A better way to be sure you're getting max braking is to practice and measure speed and distance--then there's no doubt. Imagine if you'd been leaving marks thinking you're at max but it's actually the rear (light and hovering)...in the emergency situation you've trained yourself to underbrake.

It's worth it to bust out a tape measure. Idaho STAR has published this:

"Some minimum standards for stopping performance (these are the standards that beginner level rider training or the DMV state test might use):
• 20mph – 23 feet
• 25mph – 31 feet
• 30mph – 44 feet

Skilled riders should be able to stop their motorcycles in less distance:
• 20mph – 15 feet or less*
• 25mph – 20 feet or less*
• 30mph – 30 feet or less*

*NOTE: these distances require pretty aggressive braking. Be careful, be smooth, and work toward these over time."

http://idahostar.org/_blog/News_Room/post/That%E2%80%99s_the_BRAKES!/

Those distances are equal to what we use for the 20 and 25mph quick stop braking exercise in the MSF BRC. Yes they take some effort and practice to attain but are not out of the realm of any cycle rider.

The pics above were taken on a day I practiced high effort braking from 60 mph. I used 150 feet as my standard for a 60 to zero stop. On a rural road I measured off 150' with a tape measure, marked the start and 150' mark with a paver brick I could easily see. Then I made repeated stops in both directions. When the bike was stopped, I'g get off and measure from the 150' marker to the leading point of the tire vertically to the ground. With practice I was regularly stopping within 135 to 142 feet. I made at least 20 stops, in both directions to compile enough stops to develop my average. Some stops did engage the ABS, most did not.

On a braking distance calculator I found, for 60 mph in 150' it calculates to 0.80G stopping force. So even at 150' from 60 mph, there is room to stop shorter yet assuming good traction and a possible 1-G force. Someone earlier said if you are leaving "blackies" there isn't much left, traction wise. True, as in this case the blackies I left were indicative of sliding action at the front tire beginning during the braking event. Since I was able to achieve shorter than 150' stops from 60 mph, I was doing more than 0.80-G stopping force. But just because you leave some blackies behind does not necessarily mean you are on the edge of traction, but you are getting close. Practice, practice, practice, know what you CAN do before you HAVE to do it. Develop the memory and the muscle action of these techniques to overcome the PANIC reaction common to those who do not practice.

Try it.

Not sure why anyone should believe anything without understanding how or why it works.

A lot of guys here could tell you thousands of things you'd never understand.

Yet another vote for practicing with both brakes. You are building the muscle memory necessary to do the right thing "when it counts" and practicing something else is not going to help you with that.