vysis

I don't understand. I recently learned that when cycling, a cyclist should use the front brake most of the time and use the back brake only for supplementary power. Also a cyclist should never use both breaks at once...

I'm curious, why? I sort of understand why front brakes should be favoured instead of rear brakes... but why is it bad to use both at once?

sprintr

Wisdom...

mrvrsick

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Start discussion:

I fell pretty bad when I has in third grade, scared me for a good while.

sprintr

Most of my bike handling comes from my motorcycle training. The idea that 65-70% of the braking power is in the front wheel (on a motorcycle) really drove it home for me then... especially when considering momentum: as you stop, your weight shifts forward, which puts more force on the front wheel thereby increasing traction. Traction is very important when trying to stop.

gbg

With all the S*** (sand) on the road after the winter I almost exclusively use the back brake.
Once the streets are cleaner I try to start to use the front but sometimes I go to the back out of force of habit. It is funny because on my sport bike (motorcycle) I might as well not have a back brake.

daxr

You wouldn't have to look hard to find the opposite: always use both brakes when you're stopping. Just to scrub off a little speed, the front is fine and (it seems to me) gives you a better feel or modulation because you can feel the weight transfer, but for actually stopping or any hard braking its best to use both.

You get the most stopping power out of the front, but you stop most effectively when using both. Getting into the habit of using both and getting a feel for the limits makes you a better bike handler.

tntyz

Try stopping hard while using both brakes. Most of the time the back tire will lock up because there is so little traction as the weight shifts forward. It is obviously supplying some drag (else there wouldn't be that cool-looking black streak on the road), but not much.

I don't think this means that using both brakes is "bad", but locking up a tire is seldom a good idea.

I tend to use the back brake for feathering or loosing a little speed or sometimes right at the end of stopping. Front brake for most of the heavy-duty stuff.

DannoXYZ 

Back brakes are good for trail-braking and getting a quick turn-in at the start of the corner.

cyccommute 

You are locking the rear wheel under hard braking because you don't shift your weight back as you brake harder. The rear brake doesn't provide the stopping power of the front brake but it offers 10 to 20% of the overall braking power of the whole system. Failing to use that 10 to 20% effectively means that you aren't getting the most out of your brakes.

What Sheldon Brown...and others...fail to take into account is that once the rear wheel starts to skid, you've gone past the point of maximum deceleration for the bike. Maximum deceleration is not the point where the rear wheel skids, i.e. lifts off the ground, but maximum deceleration occurs just before the rear wheel lifts off. Once you've transfered the stopping power of the rear wheel completely to the front wheel, you can't get that 10 to 20% of braking power back...except by releasing pressure on the front brake. This puts the rear wheel back in contact with the ground and recovers the rear brake's contribution to the deceleration.

Releasing pressure on the front brake is standard mountain bike practice. Braking there is far less efficient than road bike braking because of the the surfaces mountain bikes ride...and stop...on

Cdy291

When you use only your front to stop you don't want to lean forward like a dumb ass, because you will then flip like a dumb ass. You should be pushing your weight in the opposite direction, toward the rear of the bike.

daxr

...braking on an MTB is a whole different problem. You have a higher center of gravity to begin with - the BB is higher and the riding position is usually more upright. Then you have a front suspension fork that loads up, dropping the front end and beginning the "pitching you over the bars" motion. I commute on an MTB and shifting back in the seat to "panic stop" position is a regular habit braking.

brians647

I see your point, and question Sheldon's take too, but this portion is not completely correct.

Maximum deceleration is that point (and as your weight transfers, that point changes) right before you lock up the brakes. Comparing suspended bikes to non-suspended bikes is misleading at best. The loading/unloading the suspension is an art all it's own (yes, i know you load/unload tires, but the movement of center of gravity is vastly less) Likewise, your coefficients of friction and adhesion on the road vs. dirt are vastly different.

Just my 2 cents..

Phantoj

In an ideal sense, truly "maximum" braking would occur with the rear tire right at the point of liftoff - with a downforce of zero pounds. Ideally, the rear brake would contribute 0% of the force under maximum braking.

So under that idealized situation, you wouldn't need to apply the rear brake because it would just lock up anyway. On the other hand, it wouldn't matter if you did, because zero lbs of downforce isn't adding any lateral stability either.

Someone "crunched the numbers" once and found that a "single" road bike on flat ground can decelerate at a maximum of about 0.6g before the rear tire will lift. It is important to note that most cars can do better than that... and that you'll probably be less than 0.6g if you're going downhill, which is probably why you're braking in the first place.

If you're riding on some super-sketchy surface, front-brake-only is obviously not the smartest move.

Is a little rear brake here or there going to hurt anything? Probably not. Just remember that your front brake is your primary stopper in most cases and you'll be fine.

daxr

...worth saying that the "point of lift-off" is significantly affected by your position on the bike, and shifting back makes a huge difference. I've seen video of the pros panic-stopping with most of their body shifted behind the saddle, pulling hard on both brake levers.

Phantoj

Even if you don't shift back, you have to brace yourself against the handlebars. If your arms are limp, you'll flip over the handlebars easily... IMO, most of the front brake horror stories are caused by riders failing to brace themselves for the force of braking.

Also, I think it's impossible to really brake effectively if you've only got one hand on the handlebars...

JTGraphics

My primary stopping brake is the front I use the back as an assist. Motorcycle racing and riding habit which also made me switch all my bikes levers to right brake lever being the front, I just couldn’t get us to the front being on the left as bikes come.
For those who don’t like using it that way just do not fill comfortable should just continue with what they like because if you don’t fill comfortable using the front it may be dangerous but if you’re willing to learn how, how much and when you will fill the difference in stopping power.

cyccommute 

Braking on a mountain bike is only slightly different from a road bike. The bottom bracket and the center of gravity are slightly different, however the differences aren't as great as you'd think. As you have pointed out, braking on a mountain bike is less than optimal compared to a road bike. Using the same techniques that you would use on a mountain bike would only increase the braking ability of a road bike.

cyccommute 

In nearly all situations, the mountain bike braking ability is less stable then that of a road bike. Suspension dive transfers more weight towards the front of the bike then a rigid fork will. The geometry also steepens which puts more weight on the front end and makes pitch over even more likely. The surfaces are less likely to have the same friction and adhesion as you have pointed out, with the possible exception of wet pavement.

However, if you take the same techniques that work so well in a less than ideal situation and apply them to a more ideal situation, wouldn't they work just that much better? Whereas a mountain bike is pretty easy to skid the rear wheel because of the lack of friction and adhesion, a road bike should almost never break the rear wheel loose on good pavement...wet pavement not withstanding

And, as an added benefit, if you have some experience with how to brake well in a bad situation...such as a wheel sliding out to the side...you'll have no problems with the mild things that the road can throw at you.

cyccommute 

Bicycling Science by David Wilson. The numbers he gives are a maximum of 0.56g before pitch over on a single bike (tandems can decelerate much more and cannot pitch over). However, I would argue that the maximum deceleration occurs long before you reach the point where downward force is zero. At the point where downward force equals zero on the rear wheel, you gone past the point of maximum deceleration.

Consider: At maximum deceleration, the front wheel is providing 80 to 90% of the deceleration, or roughly 0.45g to 0.5g, and the rear is providing 10 to 20%, or 0.11 to 0.06g. If the downward force on the rear wheel goes to 0, the rear wheel is no longer contributing the 10 to 20% and it's deceleration drops to 0 g. The front wheel is only contributing 0.5g so you've lost deceleration ability. Keeping the rear wheel in contact with the ground, i.e. not skidding, doesn't zero out the rear wheel. You approach an asymptotic limit just before the downward force on the rear wheel reaches zero. Go past that asymptote and you've lost braking power.

It works the same whether or not the bike is a road bike on flat level ground or a mountain bike on a steep pitch.

Please note that I have not said that you shouldn't use your front brake. Nor have I said that your front brake doesn't provide your primary stopping force...on any vehicle. However, relying on only one brake in any situation is not going to provide you with the best deceleration your bike can give you. Relying completely on the rear, as in a coaster brake, give only marginal braking ability. Relying completely on the front just doesn't squeeze out the maximum stopping power of the bike.

yhelothar

I'm not sure why you're holding the front wheel's deceleration constant in your example. The front wheel can't contribute .5g at what you call maximum deceleration and still contribute that same .5g when the rear loses traction. Either the rear wheel has traction when the front is producing .5 or it doesn't. To me, the Sheldon Brown assertion makes sense. So long as the front has traction maximum deceleration is achieved when downward force on the rear wheel is zero.

prathmann

Note that the way he calculates the maximum braking force is by determining how much deceleration can occur before the bike begins its pitchover. I.e. the maximum deceleration is precisely at the moment when the rear wheel just starts to lift from the ground.
You can 'argue' that, but here you are just asserting it to be true without giving any justification. The physics of the situation, as applied by Wilson above, shows that it is not the case. If there is any significant loading left on the rear wheel that is an indication that you still aren't using the front brake to its maximum potential. Applying it more strongly will then add to your stopping power (or deceleration) and reduce the loading on the rear wheel (ideally to zero but in practice it is hard to keep it at exactly zero without having a pitchover event).

Looks like you're just pulling numbers out of the air. Where does this idea of only 80 - 90% from the front brake come from? Wilson makes it clear from the force analysis in the book that his maximum of .56 g for the specified geometry is coming entirely from the front brake - i.e. 100%, not 80% - 90%.

Sixty Fiver

I still believe that maximum stopping power can be generated solely by using the front brake but this requires expert level technique and skills that need to be practised over and over until that braking action becomes reflex.

When that rear wheel begins to lift you have reached your maximum braking point and this can be done very easily with a single front brake of good quality that is properly set up... being able to modulate the braking force is of utmost importance.

I ride a number of fixed gear bicycles that are equipped with single front brakes and can scrub off speed by resisting the pedals and can skid the rear wheel but the real stopping power comes from the front brakes.

My dual brake equipped bikes cannot stop any faster.

I cannot stop my fixed gears any faster when I resist the pedals as upon hard application of the front brake I experience nearly immediate unweighting of the rear wheel despite my rearward positioning... being a lighter rider I need to have some mad skills as it is pretty easy to get my 150 pounds headed up and over.

This also allows me the ability to do a skip stop as once the rear wheel lifts it can be stopped dead and backing off the front brake will bring it back down at which point it will skid... by then my speed will have been reduced considerably.

I have seen tests that suggest an expert level rider can generate as much as .7 g's in a panic stop and all of this braking force can be generated by the front brake alone... a rear brake can only supply a small percentage of the force one can get from their front brake.

In doing some personal tests I have found that the difference between a rear skid and using the front brake alone (from the same speed) increases the stopping distance by more than 200% and would consider myself an expert class rider.

I practice braking all the time and even when it is not needed work on full on panic stops... I find that as soon as I brake I automatically shift my weight back even if it is a low speed stop without maximum braking.

The dynamics change between different bicycles and this is how well one can re- distribute their weight but in any case one has to shift their weight as far back as possible while applying maximum braking force and modulate that braking to prevent an otb experience.

My folder has me set well back of the centre point of the bike and much of my weight is over the back wheel...the design is such that it is very difficult to endo the bike...even under the hardest braking.

My mtb uses a disc front and with the suspension the front end dive has to be considered, even if that is a minimal amount as it changes the geometry of the bike as it brakes. A mis-applied brake and wrong positioning would send one over the bars in an instant.

Technique is all important and even the best riders can go otb... it is very a fine line between generating that high stopping force and exceeding it.

In teaching new riders I encourage them to test the limits of their front brake at lower speeds and then gradually build up their speed to learn how their bike responds under hard braking... there are too many people who are afraid of their front brake and don't use it and this puts them at higher risk.

My 9 year old daughter can ride at nearly 30 kmh and will do hard full on stops with only the front brake as this is how she was taught and she practises this all the time... she has never gone over the bars on her mtb as her position is already lower than her bars and well set back. I had to upgrade her stock brakes to Avid V's with Kool Stop pads since she does ride so fast and she needed greater stopping power.

Her rear brakes get little use unless we are on the trail and that is another skill set one has to learn

BobLoblaw

At least no one on this thread has suggested the rear brake alone is better. When I was teaching motorcycle safety, I had a few students who actually believed that.

If I was an android capable of sensing the moment where the rear wheel was at the point of almost losing contact with the pavement, I'd only use the front brake. As I am merely a human being, I use both brakes for stopping, and from time to time I practice.

BL

merlinextraligh

Do these guys running all these numbers about when the rear wheel lifts, and that being the limiter understand that you're supposed to hang your butt off the seat over the rear wheel, chest on the seat?

I guarantee you I can put my weight far enough back that the limiter in the amount of front brake I can use is not lifting the rear wheel, but skidding the front wheel. Thus you can have the front brake on to its limit and still be getting braking force from the back wheel.

Key is to learn to modulate both brakes independently.



Thus the fastest stop is going to be front brake to the threshold of locking, weight cantilevered as far as possible to the back, and rear brake modulated just short of skidding.

JTGraphics

Here is what they can get G-Force meter, manual, AAA batteries mount it on the handle bars and you're good to go. Joke Ok please not setup for braking