JMT114

I use both at the same time most times I stop/slow down. I use the front sparingly or not at all on loose surfaces or when there is sand or gravel on the pavement.

cyccommute 

Why not? At maximum deceleration, the front and rear are contributing as much as they can. Lose the deceleration available from the rear wheel, i.e. skid it, and the front wheel can't pick up the difference. The front wheel...and the bike... are limited in the amount of deceleration that it can provide because the bike wants to pivot around the front axle and allow the load to be transferred in front of the wheel. That's what a pitch over or endo is. A complete transfer of the system weight ahead of the front axle.

Moving weight towards the rear of the bike during braking increases the bikes deceleration by increasing traction to the rear wheel. The rear brake contributes more and the bike decelerates faster. Transfer weight forward and the bike doesn't stop any faster...in fact it decelerates slower. Have you never skidded a bike just for fun? You get the longest skids by moving your body all the way up to the handlebars.

Tandems can experience much higher deceleration for the same reason...more weight over the rear wheel.

Phantoj

Here's a question: have you ever had a reason (on the road) to need 100% maximum braking? Me, never. I have had to grab a good fistful of brake on a few occasions, but 80% of maximum or whatever I was doing was good enough. Paying attention and riding defensively is worth wayyyy more than the difference between 90% braking and 100%.

AEO

use the front brake, but shift all your weight to the back, because you're less likely to fly over the bars.

on tandems you can't use the front brake only because you will fishtail if the rear loses all traction.


if you find yourself in a situation requiring 100% braking, you're likely to hit whatever is in front of you anyways, but at a much slower speed.

ghettocruiser

But at least on my mountain bikes, my default position and longer wheelbase has my weight further back then on my road bike. They are not easier to endo, even with a bit of fork dive. My XC bike probably has the same dry-pavement stopping distance as my road bike.

My freeride bike, due to the way-back centre of gravity from the long wheelbase and long fork rake, has a much shorter stopping distance under all conditions. It's almost impossible to go over the bars on that thing on level ground, even slamming on the front hydraulic... it's more likely to drag both wheels.

merlinextraligh

The weight distribution on a tandem makes it much less likely to lose traction on the rear wheel.

You use more rear brake on a tandem because you have more traction on the rear wheel.

merlinextraligh

1) panic stop, i.e. car pulls dead in front of you, or is about to T-bone you. A one m/s difference in the rate of deceleration could be life or death.

2) racing, for example solo descent at speed into a tight turn. Braking hard and late, will be faster than gradually braking early.

ghettocruiser

Last year, once I realized I wasn't quite going to plow into that truck, I eased up on the brakes... and felt the back tire drop six inches back onto the road. I had no idea it was off the ground until then.

It wasn't really life or death, but I would have looked pretty stupid rear-ending a truck on my road bike.

cyccommute 

Let's go back to the mountain bike model*. Any mountain biker will tell you that a spinning wheel stops the bike faster. In other words, you don't want to skid the rear wheel if you want to stop the bike quicker. That's why you learn, pretty quickly, to release pressure on the front brake if the rear wheel skids. You also learn, again pretty quickly, that if you want to skid the rear wheel (somewhere around 10 years old), you move forward towards the bars and the rear wheel will slide for ages before you stop. You can even do that without a front brake at all. Another lesson you learn, perhaps a little more slowly and hopefully before you break any teeth, that you should shift weight rearward during hard braking to keep the rear wheel on the ground.

All of these 'tricks' are meant to maximize your braking ability in situations where the bike's brakes aren't performing at their absolute best, i.e. high angle braking, loose surfaces, varying surface and traction conditions, etc. Well, except skidding...that's just done to be cool!

If, on the other hand, the assertions that the front brake is the only brake you should use (or at least should need), wouldn't you want to transfer weight to the front wheel as soon as possible during braking to maximize the braking efficiency of the bike? In other words, you'd want to slide towards the handlebars during braking so that the front wheel is carrying the maximum load and has the maximum traction. I dare anyone to try it whether on the road or on dirt. Unless you have some very mad bike skillz, you'll end up on the ground with the bike on top of you. A nose wheelie isn't the best strategy for maximum deceleration.


Most everyone slides rearward as a reflex when braking. Why? To transfer weight towards the rear wheel. This keeps the bike from pitching over by putting weight on the rear wheel and by increasing the traction of the rear wheel and keeping the rear wheel spinning for control. That additional traction also equates to better braking when the rear brake is used.

I don't have my copy in front of me right now but the numbers for the deceleration contribution of the rear wheel come from his book. I'll find a more formal reference tonight.


*I know you guys hate the mountain bike model but road bikes and mountain bikes help develop complimentary skills. A road bike is great for endurance and leg strength. A mountain bike is great for building power and handling skills. If you know how to handle a mountain bike when the wheels...front and rear...are going all of the place because they are bouncing off of stuff, a simple slide on a road bike in a corner, on a slick patch or in a braking situation is a piece of cake to handle.

Phantoj

The problem with the mountain bike model is that traction on pavement doesn't tend to be a limiter, but on dirt, it frequently is.

Sixty Fiver

Yes.

Working downtown as a messenger in tight traffic with crazed pedestrians, cabbies, and homicidal soccer moms warrants some well developed skills, among those is the ability to do a full on panic stop without going otb.

I was out for a pleasure ride on my fixed gear the other day and a fellow stepped out from between some parked cars in the middle of the street... when he saw me he froze and am sure he thought he was going to get run over.

The best option was to stop and not try to swing around him as he may have decided to dart across the street.

yhelothar

You said it yourself. Pitch over is the limiting factor when braking. At your "maximum deceleration" both wheels are NOT contributing as much as they can for the simple fact that in order to lift the rear wheel the front has to contribute more stopping power. You're acting as if the front wheel has some maximum that you can reach and treating that as the limiting factor. The problem with this is that you can't reach the front wheel's full braking potential due to pitch over. Max braking occurs when you use as much of the front brake as you can while you remain upright.

cyccommute 

Like I've said...over and over...if the technique works in bad conditions, think of how much better it works in good conditions. Mountain biking is the worst case scenario.

cyccommute 

Pitch over is the limit, however, you approach that limit asymptotically and the only way to do that is to approach the limit using the maximum braking contributions from both wheels. That's the reason you can't reach the front wheel's full braking potential...it's a limit. You can't get there from here. Once you've pitched over, you've gone past that limit and the rear wheel's braking contributions are zero.

Phantoj

A technique that is ideal for "bad conditions" - conditions where traction is poor - may not be ideal for contitions where traction is good.



(Myself, I always use both brakes, I just never squeeze the rear brake very hard.)

Phantoj

What do you mean when you say that you approach that limit asymptotically?

cyccommute 

Like all mathematical limits, you approach the limit, maximum braking in this case, to some arbitrary difference between the real value and a theoretical value but you can't quite reach it. For the braking of a bicycle, the limit is some infinitesimal faction of time before the rear wheel's downward force goes to zero and is removed from the deceleration equation. If you zero out the contribution from the rear wheel, the total deceleration available to the bike is less than just before you zero it out. As long as approach that limit and don't go beyond it, the bike will experience it's maximum deceleration since the rear wheel is contributing something no matter how small. You've hit the top of the hill, so to speak.

Remove the contribution from the rear wheel and you'll never achieve the full deceleration potential of the bike. If you could, then nose wheelies or rear wheel skids would be the best way to stop in any situation since the deceleration contribution from the rear wheel would always be zero.

If you think about the way you brake a bike you already do this naturally. Most people push back on the bike during hard braking. Someone else here said that you should brace for braking. But what you are really doing is loading the rear wheel so that you don't lift it off the ground. Even without [breaking] it [loose], the rear wheel will contribute to the deceleration of the bike by keeping both wheels in contact with the ground. If you use the rear brake, that just adds to the deceleration that you have available since you can't reach the limit of the maximum deceleration.

cyccommute 

Name some. Personally, I can't see any. I can see some techniques that are ideal for good conditions that won't work in bad conditions but I can't envision anything the other way around.

Phantoj

So where's the asymptote? What's the function?

Phantoj

When traction is poor, flipping the bike is no longer an issue, so the ideal braking technique is to have both wheels just at the point of locking up. If you use the same technique (braking up to the point just before the wheels lock up) on a normal road bike, you'll flip it.

[Actually, locking and skidding the wheels brakes faster (with less control) on some surfaces like snow and gravel (for cars -- I wouldn't want to try skidding the front wheel on a bike).]

Phantoj

Can you elaborate on this statement? I'm confused...

cyccommute 

Sorry that should have read 'breaking it loose'. I corrected it in the original post.

cyccommute 

You can flip a bike during braking independent of the quality of the traction. You are probably more likely to flip a bike under poor traction conditions because those conditions tend to be variable. You may have good traction one second and bad the next. The wheel can dig into sand, increase traction, change the center of gravity and you'll find yourself on the ground. Happens all the time to mountain bikers. If anything mountain bike riders stay away from having their wheels near lock up...depending on the conditions...to keep the front wheel from stopping abruptly.

I don't know where you live but I've got decades of snow and gravel driving. Locked brakes on either surface will not result in shorter stopping distances. That's why they invented antilock brakes. Those of us who learned how to drive on snow without them generally hate them because we have to learn how to brake all over again. I have noticed that some of the antilock systems work only on the rear wheels. On ice the front wheels lock up and just slide forever. I could do much better if I could pump the damned things

cyccommute 

Look at the analysis on pages 241-245 of Bicycle Science, 3rd edition.

Wilson does say that the maximum possible deceleration (on level ground with a crouched rider) by taking the moments of force around the front wheel level with the center of gravity when the force on the rear wheel is set to zero. That's where the 0.56g figure comes from.

However, further on (p. 245) he states that the limit of deceleration in a car, tandem or recumbent is the limit of the tire-to-road coefficient of friction. The only reason that these vehicles have much higher deceleration rates is because the vehicle is biased more biased towards the rear wheels. They can flip over the front wheels so the rear wheel provide more stopping power to the system.

At no point in his discussions does he say that only the front brake should be used. He goes to great lengths to say that rear wheel braking only is completely inadequate for stopping a bike in an emergency situation, to which I fully agree. He does not, however say that only the front brake should be used.

p. 245. "Thus, the rear wheel is in only light contact with the ground. Only a slight pressure on the rear brake will cause the rear wheel to lock... The front brake therefore has to provide over 90 percent of the total ******ing force at a deceleration of 0.5g..."

bac

It's really all about the conditions.

If the road is clean and I'm stopping in a straight line, I'll use a lot of front brake along with the rear. However, in low traction situation or if I have to brake while turning, I'll use the back brake more.

... Brad