David Wilson, Bicycling Science , around page 230 (I don't have my copy with me right now).

The numbers I was citing comes from Bicycling Science (referenced elsewhere) and apply to road conditions. Mountain bike conditions were used as an example of the most extreme braking situation I can think of. A sliding front wheel is just as disastrous on- or off-road. It is a situation that few, even with superior bike handling skills, can recover from.

Your comment (emphasized above) could be used for dry pavement as well. That is the absolute best braking situation you can find yourself in. Both wheels are at the maximum of adhesion and your brakes are operating at their maximum efficiency. Remove one from the equation...by not applying it...and you reduce the overall braking capacity of the system. Why would you do that?


First, I'm not saying that you should use your brakes in a 90/10 or any other kind of ratio. The maximum deceleration a bike can achieve without going over the front wheel, according to Bicycling Science, is around 0.5g to 0.56g with a seated rider. 90% of that deceleration comes from the front wheel. But 10% comes from the back wheel. Remove the rear wheel from the equation and the overall maximum deceleration has to decrease.

The maximum deceleration point of the system isn't when the rear wheel lifts off the ground and the rear wheel starts to skid. The maximum is reached when both wheels are contributing the most to the overall deceleration. That's when both wheels are in contact with the ground. That holds if the pavement is dry, wet, icy, or nonexistent - i.e. dirt;)

That's why mountain bikers release pressure on the front brake. Pitch over is the point where the front wheel is about to stop, i.e. skid. Releasing pressure on the front brake transfers weight back to the rear wheel, puts it back in contact with the ground and increases the overall deceleration. In other words, you stop faster.

Weight shifts also effect this weight transfer...and is, again, something that mountain bikers learn early on. A tandem, for example, has a maximum deceleration around 0.8g. All of the extra deceleration ability comes from the extra weight over the rear wheel. Moving your center of gravity back and down while braking, can increase the rear wheel's ability to stay in contact with the ground and provide more braking power. It works very well in high angle descents on a mountain bike and it's much more effective on level pavement.

Think of it this way: Two riders using identical force in identical situations braking under maximum deceleration. Neither rider is allowed to skid the rear wheel and, for safety sake:rolleyes:, both wheels remain on the ground. Rider 1 uses only the front brake. His deceleration is around 0.5g. Rider 2 uses both brakes. His deceleration is going to be 0.5g on the front wheel and 10% of the deceleration of the front wheel on the back wheel or, overall, 0.55g. Not a huge amount of deceleration but Rider 2 will stop a little sooner than Rider 1.

Now let's let the rear wheel come off the ground. Rider 1's deceleration is the same, 0.5g. Rider 2's deceleration goes from 0.55g to 0.5g (neglecting the slight amount of friction from the sliding tire;)). Their deceleration is now the same and the stopping distance will be the same. If both riders, with the brakes applied, shift their weight rearward, the tires will come back in contact with the ground and Rider 2's deceleration will increase. Rider 1's will remain the same.

Now try releasing pressure on the front brake. Rider 1's bike will come back in contact with the ground but his overall deceleration will remain close to the same, minus what amount he had to give up to keep from doing a pitchover. Rider 2's bike will come back in contact with the ground minus the deceleration needed to prevent a pitchover but his rear wheel is providing deceleration again and his deceleration is higher than Rider 1's. He'll stop sooner.

I can't think of a situation where losing the rear brake's contribution, albeit minimal;), to the overall deceleration of the bike is a detriment. As long as the wheel is rolling, the braking power it adds is significant enough that I'll use both brakes in all situations. I do adjust for extremely slick conditions with more bias towards the back, however:thumb:

The emergency stop, quick stop, or panic stop, depending on what you want to call it, is one of the avoidance drills taught in the LAB traffic skills courses. It's a skill you need to learn and practice, because as you've apparently found out, when you need it, you need it badly ;-)

For all bikes, the braking power of a wheel is directly proportional to the amount of weight that the wheel is bearing. When you're just riding along, your weight is fairly evenly distributed between the front and rear, with maybe a little more to the rear wheel.

When you and your bike are traveling forward, due to your momentum you will slow down only if something pushes back at you from the front. The brakes cause the road surface to push back on the tires, and that push slows the bike down. Because you are up higher on your bike, and the push is down at the road surface level, while the push slows the bike, the rider’s momentum tends to keep him or her moving forward, shifting weight forward to the front wheel.

The stronger the braking force, the more weight is shifted forward. If too much braking force is applied, the weight on the rear wheel is lessened to the point that the wheel loses traction, and tries to come up instead of pushing down on the road, and since there is nothing to hold the rear wheel down, the back end of the bike comes up and the rider is launched over the handlebars.

What you want to do is to use both front and rear brakes, and keep the rear brake from losing grip and tossing you over the bars.

When you're just rolling along and need to do a panic stop, here's what you do:

Squeeze both the front and rear brake levers -- the front brake about two to three times harder than the rear. As the bike slows and your weight shifts forward, most of your braking power is going to be in that front wheel. At some point, you'll feel the back wheel start to skid, or even start to come up off the road, because it's no longer bearing much weight, and has lost traction. That's a signal to let up a little on the front brake until the back wheel no longer skids.

To help the matter. level your pedals. stand up, and thrust your butt back off the saddle and over the rear wheel to shift your weight back. This is where some experience mountain biking really helps, if for no other reason than mountain bikers find themselves needing this little trick more often than road riders. A good rider can put his belly button or his chest over the saddle and really shift that weight to the rear.

As soon as you slow down enough, unclip one foot and put it down when you stop. Depending on the situation, you might need to come to a full stop, or you may find it safer to use the panic stop to slow down significantly, and then do a quick turn to avoid whatever it was that caused you to brake in the first place.

It's a good skill to practice... get out in a vacant parking lot somewhere and practice coming to a stop as quickly (and safely) as you can from your usual cruising speed...

Tom

I have an odd but effective stopping-on-a-dime routine. I don't know exactly what I do mechanically, but I think I can explain what happens.

Basically, I nail both brakes and unclip from the pedals all at the same time. I then somehow plant both feet firmly on mother earth while locking front wheel, so nothing moves. The sass end of the bike lifts up behind me and comes to a stop when it hits me in the back.

Like I said, I have no idea how I do this; it's all automatic. It works like a champ, but I am a little concerned that I might do damage to my back or knees with this technique.

That's almost a controlled bail-out rather than a panic stop. You're just hucking the bike behind you rather than trying to leg-over. (If I'm picturing it correctly...you wind up standing on both feet, mostly off the saddle with the handlebars around your thighs/knees somewhere?)

Pretty much what everyone else said... I don't let my wheels get locked up, and I use both brakes in balance to get maximum stopping power.

A biggie that some faster riders around here don't realize tho... you need to look ahead just as far on a bike as you would in a car, or even further. You can't avoid all emergency stops that way, but it does help. Coasting a bit or using a lower cruising speed can eliminate a lot of emergencies too. Around here, some of the major arteries have light timings where the main road has long enough lights that a 15mph rider won't have to stop, and pushing to 20mph can mean a lot of sudden stops. (there are roads that are just the opposite too of course)

Yep, completely off the saddle, bars at...call it, mid-thigh.

As you can imagine, I feel a lot of impact force through my legs and thighs when I do this. I am currently working on another method which keeps my butt int the saddle, but the other day, when I E-stopped, I noticed that I went right back to my Semi-Bailout technique.

Yes, I used to do that a lot as a kid. I don't do it so much anymore as most of my current bikes have very little standover clearance. So I get hit a little lower. Ahem.

I know what you mean about the force you absorb in the legs/knees and back too. It's probably not the best technique. If ski injury rates are any indication, it's probably worse for you as you get older.

The joys of hydralic discs.

Btw, as the hydralic discs may suggest, I am a mountain biker, and was on a mountain bike, and as such can get my weight so far back I can get virtually sit behind the rear wheel. May have something to do with my my front wheel skidded, althought I don't recall going THAT far back.

Also, curiosity again, why is locking the front wheel so much worse than the back? I can understand if it gets airbourne and comes slamming back down when locked up hard, but why is skidding it so bad?

All this stuff people are saying though, I was kinda after actual stories, I'm wondering if you actually end up doing a perfect textbook stop when your about to go headlong into a stream of traffic or if something else takes over, and what generally ends up happeneing.

disaster averted by controlled skid into an embarrassing, graceless sideflop, followed by incoherent fist-shaking and then nervous frame inspection.

Locking the wheels is always a bad idea. You just switched from static friction to sliding friction, so you're getting a LOT less braking power, plus you just lost control. You're putting your feet down instinctually because you just gave up all other control of the bike. If you'd keep from locking the wheel in the first place you probably wouldn't have to put your feet down, and you'd stop faster too.

I didn't have to put my feet down. I know that a locked wheel slows you down less, but why is the front worse than the rear?

Typically I pull hard on both brakes. My rear wheel may or may not start skidding. I approach the cause of the stoppage at an angle so that if I must I can go around.

I haven't read every single word posted here,but just wanted to make sure the point was made to brake as hard as possible as early as possible. Don't wait until you realise you're not going to stop in time before you apply maximum braking. Several articles from the motorcycle world discuss this and explain that the earlier you start to brake,the lower your speed,and the more time/distance you have to maneuver.

That's probably the most useful thing I've gotten out of this thread.

Also, there's no way the OP or anybody else locked up a front wheel on dry pavement short of sticking a pump in the spokes. Might seem like that when you're skidding out of control, but it doesn't happen.

As neteon said, this is the single most important piece of advice in this thread.

To throw in my two cents, the very fastest way you can possibly stop on an upright bicycle is by sitting the furthest back on your seat and applying the front brake until the rear wheel barely begins to lift. That is putting a huge amount of normal force on the front fire due to the torque from braking, so unless there is lose ground you really aren't going to be losing traction. If you want to use the rear brake you have to let up on the front.

I've only braked like that twice, and honestly it's because I wasn't paying enough attention. The other posters have mentioned that you want to keep the rear wheel on the ground so you can brake with it and I completely agree - not because it helps you stop faster (though the difference in stop distance would be really close) but because you have more control over the bike with both wheels on the ground.

Generally, with two wheels you can either turn hard or brake hard, but not both.

Yep: Brake early and often.

This is the truth of the matter, you just have to get out there and do it. We can tell you how to kick a soccer ball but until you actually do you are still without enlightenment.

Trust me on this, the front wheel was no longer turning. I did have knobblies on though, and maybe my weight was further back than I realised.

When the back wheel locks up, the rear end will swing around the headset pivot. You, the rider, can usually adjust your body weight with hip movements and steering the front wheel to keep the bike upright. If the front wheel is skidding, you can't steer the bike...well you can but it just much harder:rolleyes:...to compensate for the change in balance. Additionally, the momentum and weight transfer on the front wheel is such that when locked, the likelyhood of going over the handlebars is much greater. Most of the time, a front wheel skid will result in you laying on the ground either in pain or in shame;)

I would never go headlong into a stream of traffic because I pay better attention than that:rolleyes: That's the key to stopping anywhere. Since you are ride a mountain bike, I assume that you don't fall of cliffs with regularity. How do you avoid that? By paying attention to the trail and anticipating what is coming up. It works the same way in traffic. If anything, it's easier in traffic because traffic is generally more predictable.

So much focus on the cure. So little on prevention.

Go to A&S for the safety nanny discussion.

By making sure that when I go off a cliff my wheels are facing downwards (I suppose technically it's still falling, I just like to think it's done with a bit more style than the word generally suggests).

I do keep an eye out in traffic, this was only because a jerk sped out infront of me.

I bought mine used from a dealer, and I remember hearing about the braking situation from other riders after joining a club. If the dealer did tell me, I missed it. I had already learned how to brake before I got the goldwing, and the idea bothered me at first. After all, I had spend hours learning how to control the front and rear brakes independently and in the proper amounts, who were they to do such a thing???? But the darn thing is so massive, and I can't think of a single instance where it caused a problem. the net effect is that you can't rear only brake, and maximal front braking requires you use the rear pedal as well.

When the front wheel looses traction, it doesn't take much for it to slide out from under you - that's the real reason I would avoid a front wheel skid. You probably learned how to fish-tail a rear skid just minutes after you learned how to ride, and spent at least some time of your youth seeing who could do it the farthest. Front skids are a lot harder to control, and you can be on your side in a blink. I have locked up the front wheel of a motorcycle a few times, scares the hell out of me. That front wheel starts to go in a different direction the instant it stops rolling, if you don't get it rolling again you are going DOWN! I never locked up the front wheel on a bike other than maybe once when practicing braking.

But what really happens when its time to do or die? You do what you have trained yourself to do. I was riding a motorcycle in unfamiliar mountain territory outside of San Diego once. The cars where bombing around the roads, and I just kinda went along. Big mistake, I found myself in a turn I was going too fast for. My training taught me to suck it up and lean the bike over more. But then the turn became a decreasing radius turn, and the rock wall on the outside stopped and was replaced by a sheer dropoff of hundreds of feet. I did what I had trained myself to do - I decided EARLY that I was in too deep and too hot, I stood the bike up, braked maximally straight up until I was just shy of the shoulder with loose debris on it, then leaned the bike over further than I had ever done before in my life and finished the turn. Afterwards I realized that I had done exactly what I had trained, during the episode I was pretty sure I was going off the cliff to my death. I finished the day riding well below the speed limit. edit: oh yeah, I don't know how close I got to the edge - you never look where you don't want to go! my eyes were glued to the exit of the turn where I wanted to be, for all I know the back of the bike hung over the edge of the cliff.

As for bike training, Twice I have realized I had no way to stop in time but braked maximally anyway (might as well collide going slower, right?), then saw the room to do a hard right and escaped. A few times I have stayed straight up and maximally braked stopping just short of collision, often with the rear wheel popping off the ground when try to put a foot down. I have stopped faster in a panick situation than when I practice panick braking, I think you are willing to keep squeezing when it really counts, but for just practice you might stop at "good enough."

THANKS!

I am off to order a copy. I like reading stuff like that.