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  1. #1
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    Let's talk about braking...

    We often hear that 90% of the braking is on the front wheel of the bicycle, sometimes with the added comment that we therefore do not even need the rear wheel. Let’s look at that idea.

    First maximum braking comes when both wheels are braking at 100%. 100% braking happens when the wheel is being braked as hard as it can be without losing traction. Now let’s break that 90% down into a more understandable statement. Braking force is conventionally stated in negative G. G equals approximately 32 feet per second squared. For simplicities sake lets say a given bicycle with an expert rider can brake at 1G. Now if the front wheel is doing 90% of that, I think that an expert can get 15:85 or even 20:80, but for the sake of this we will use that commonly stated 10:90 braking ratio (You did know that is what is what is meant by that 90% figure, right?).

    OK, now we can look at the silly idea that you do not need the rear brake. Braking with just the front brake reduces your maximum braking power from 1.0G to 0.9G (an 11.1% loss) right up front. Now if I am correct about an expert being able to get a 20:80 braking ratio you do even worse you have reduced your total braking ability by 25% (Insidious things those percentages, aren’t they?).

    An aside: I think that 10:90 figure is about right for a dropped bar rider who does nothing but squeeze the brake levers. My 15:85 would be about right for an upright rider with a setback seat. And the 20:80 would be about what an expert who slides as far back as he can to transfer as much weight as possible to the rear wheel.

    So how do you get maximum braking in a pinch? First you side your body to the rear of the bicycle and transfer as much weight to the rear wheel as possible; next you brake both wheels as hard as you can without skidding. Those who say you should just lift your rear wheel do not understand simple physics for we have shown above that doing so loses 10-25% of your braking power and if the front loses traction you have lost 90% of the remaining braking power (it is generally thought that a skidding tire only has 10% of the traction a rolling one does). In reality you would be trying for about 95% braking on each wheel so you have a bit of a reserve if you hit a rough spot or something. With that technique you should have about 120% of the braking ability you would have with only the front wheel in the same conditions.

    You will also notice that the higher a percentage of the braking you can move to the rear wheel the more total braking power you will have because you are not reducing the front braking power by doing so, only increasing the rear braking power by raising the rear wheel skid point.

    Some other things to consider about braking: If you skid the rear wheel things may get a bit squirrelly, but if you skid the front you lose control of the bicycle and are likely to go down. I have never seen a bicycle take a header at speed from simply braking too hard, what usually happens is that the front wheel skids the rider loses control. The result looks like a header because it happens so fast, but it is not caused by rolling over the wheel as it would be if something got caught in the spokes as you would have to be going quite slow and have your weight well forward to have enough traction to do that instead of skidding the front wheel.

    I have simplified things in this post. One could of course find the actual coefficients of friction for the tires involved and plug in real numbers to calculate things pretty accurately, but that would only prove accurate for that particular bike and rider, so the generalities I used above are of more interest to most of us.

    If nothing else, I hope the above dispels the silly myth that maximum braking comes when the rear wheel lifts. Because at that point you are riding a unicycle with a loose seat and reduced braking power, not the safest thing to be doing in an emergency stop.
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  2. #2
    Spelling Snob Hobartlemagne's Avatar
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    Quote Originally Posted by graywolf View Post
    we therefore do not even need the rear wheel.
    I prefer riding with a rear wheel.

    I do believe too many people underuse their front brake out of the irrational fear of going otb.

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  3. #3
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    I like having that rear wheel as well. Most of my braking is done with the front brake. Going down hills I most certainly employ the rear brake as well. I've never had an endo due to my braking habits.

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    So the moral of all that is: Don't remove your rear brake.

    On the header-from-braking idea, there are actually several You-tube videos that demonstrate exactly that. They're mostly with mountain bikes at slow speeds, not road bikes at high speed, but certainly demonstrate that you can in fact do a header based on braking alone.
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  5. #5
    52-week commuter DCCommuter's Avatar
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    Applying either brake causes weight to shift onto the front wheel. The rearward force of the ground on the tire creates a rotational moment. For a given amount of braking, the amount of rotation is the same regardless of which brake is being used.

    The limiting point of braking comes at one of two points: either when the tire or brakes reaches the limit of traction, or when 100% of the weight has been transferred to the front wheel and the bike becomes unstable. Typically, the rear brake is limited at the first point, and the front brake is limited at the second point. If the front brake is capable of lifting the rear wheel -- achieving 100% weight transfer -- then that is maximum braking for that bike. If the rear wheel is off the ground, it is not contributing to the braking.
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    Senior Member SweetLou's Avatar
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    Quote Originally Posted by DCCommuter View Post
    If the front brake is capable of lifting the rear wheel -- achieving 100% weight transfer -- then that is maximum braking for that bike. If the rear wheel is off the ground, it is not contributing to the braking.
    That is correct.

    If you can lift your rear tire with the front brake, and you don't lift the wheel, then you are not using all of the front brake's capabilities.

    Now, if you can't lift the rear wheel, then the back brake will help you stop faster. For example, tandems, I hear, can't lift the wheel rear so the back brake will be a factor in maximum braking. Inclement weather when you lose some front braking power will also be an example of rear braking contributing to maximum braking.

    Otherwise, maximum braking will be with the front brake with the rear wheel lifted and right before you lose traction on the front tire.

    Your idea of moving back to keep more weight back will help keep the rear wheel down. If this is enough to keep the rear wheel from lifting while using 100% of the front brake, then yes, it will help you stop faster.

    Now, I don't know about anyone else, but I am a bit uncomfortable about lifting the rear wheel and using 100% of the front brake. I usually don't need to do this. Typically, just using the front brake is enough. Sometimes I need to use the rear also, rarely do I lift the rear wheel. Usually only when my dog has seen a rabbit.

  7. #7
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    Quote Originally Posted by graywolf View Post
    .....Those who say you should just lift your rear wheel do not understand simple physics for we have shown above that doing so loses 10-25% of your braking power...

    ..
    You will also notice that the higher a percentage of the braking you can move to the rear wheel the more total braking power you will have because you are not reducing the front braking power by doing so, only increasing the rear braking power by raising the rear wheel skid point..
    This is not the case. If 100% of the rider's weight is shifted to the front wheel during deceleration, then 100% of the braking force is also shifted to the front and 0% is on the rear. The greater the deceleration, the more weight is shifted to the front wheel. When the rear wheel weight goes negative, the bike flips. To avoid this, a good rider can shift his weight back, allowing harder braking before the rear wheel weight goes negative. Maximum deceleration is achieved when the rider's weight is shifted as far back as possible and the brakes are applied hard enough for the rear wheel weight to reach (but not go below) zero.

  8. #8
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    Quote Originally Posted by graywolf View Post
    We often hear that 90% of the braking is on the front wheel of the bicycle, sometimes with the added comment that we therefore do not even need the rear wheel. Let’s look at that idea.

    First maximum braking comes when both wheels are braking at 100%. 100% braking happens when the wheel is being braked as hard as it can be without losing traction. Now let’s break that 90% down into a more understandable statement. Braking force is conventionally stated in negative G. G equals approximately 32 feet per second squared. For simplicities sake lets say a given bicycle with an expert rider can brake at 1G. Now if the front wheel is doing 90% of that, I think that an expert can get 15:85 or even 20:80, but for the sake of this we will use that commonly stated 10:90 braking ratio (You did know that is what is what is meant by that 90% figure, right?).

    OK, now we can look at the silly idea that you do not need the rear brake. Braking with just the front brake reduces your maximum braking power from 1.0G to 0.9G (an 11.1% loss) right up front. Now if I am correct about an expert being able to get a 20:80 braking ratio you do even worse you have reduced your total braking ability by 25% (Insidious things those percentages, aren’t they?).

    An aside: I think that 10:90 figure is about right for a dropped bar rider who does nothing but squeeze the brake levers. My 15:85 would be about right for an upright rider with a setback seat. And the 20:80 would be about what an expert who slides as far back as he can to transfer as much weight as possible to the rear wheel.

    So how do you get maximum braking in a pinch? First you side your body to the rear of the bicycle and transfer as much weight to the rear wheel as possible; next you brake both wheels as hard as you can without skidding. Those who say you should just lift your rear wheel do not understand simple physics for we have shown above that doing so loses 10-25% of your braking power and if the front loses traction you have lost 90% of the remaining braking power (it is generally thought that a skidding tire only has 10% of the traction a rolling one does). In reality you would be trying for about 95% braking on each wheel so you have a bit of a reserve if you hit a rough spot or something. With that technique you should have about 120% of the braking ability you would have with only the front wheel in the same conditions.

    You will also notice that the higher a percentage of the braking you can move to the rear wheel the more total braking power you will have because you are not reducing the front braking power by doing so, only increasing the rear braking power by raising the rear wheel skid point.

    Some other things to consider about braking: If you skid the rear wheel things may get a bit squirrelly, but if you skid the front you lose control of the bicycle and are likely to go down. I have never seen a bicycle take a header at speed from simply braking too hard, what usually happens is that the front wheel skids the rider loses control. The result looks like a header because it happens so fast, but it is not caused by rolling over the wheel as it would be if something got caught in the spokes as you would have to be going quite slow and have your weight well forward to have enough traction to do that instead of skidding the front wheel.

    I have simplified things in this post. One could of course find the actual coefficients of friction for the tires involved and plug in real numbers to calculate things pretty accurately, but that would only prove accurate for that particular bike and rider, so the generalities I used above are of more interest to most of us.

    If nothing else, I hope the above dispels the silly myth that maximum braking comes when the rear wheel lifts. Because at that point you are riding a unicycle with a loose seat and reduced braking power, not the safest thing to be doing in an emergency stop.
    So in a nutshell. Maximal braking occurs just when the rear tire is about to lift off. Then you flip over and faceplant.

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    I've been over the bars a few times when I've hit a rut or rock on steep mountain bike descents, but I'm not sure you can do it under normal circumstances on a road bike, at least if you're not a complete novice. That whole long description of braking technique is accurate, but don't most people do it instinctively anyway? Could be just because I've been riding for 35 years, but for me, hunkering down a little and shifting my weight back is as much a part of braking as squeezing the levers.
    And do people REALLY ride without using the rear brake? They don't look at the handlebars and say, "Oh, look, there's one of those handle thingies for the BACK brake, too! Maybe I'll try that"?

  10. #10
    Senoir Membre Rosso Corsa's Avatar
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    This is an exercise in skepticism. Although one may bring numbers, science, and physics into their supporting points, and make it sound possible, it is not always the case, and one shouldn't assume they are right.
    I did disagree with this post, and the way he tried to belittle those subscribing to the front-brake practice, but didn't know how to say it exactly. Those in this thread, as well as Sheldon Brown, have said it so eloquently. Thanks!
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  11. #11
    Senior Member wahoonc's Avatar
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    Well the bike I am currently using only has a working front brake...mainly due to the fact the rear rim is toast and the brake is spaced so widely to be useless...been that way for a bit, but I am a relatively conservative rider. Besides I rode coaster braked bikes for years with only the the "weak" rear brake...'course wore a few tires in the process.

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    Quote Originally Posted by graywolf View Post
    We often hear that 90% of the braking is on the front wheel of the bicycle, sometimes with the added comment that we therefore do not even need the rear wheel. Letís look at that idea....
    DId you mean all bikes, or just the kind of bike that you ride?

    Many recumbent bikes don't have these problems (skidding/lifting the rear tire under hard braking).

    .....

    If a recumbent can stop in a shorter distance than an upright bike is an interesting question, but not one that I have the technical equipment to accurately answer.
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  13. #13
    BEEP BEEP IMMA JEEP darksmaster923's Avatar
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    never like my back wheel so i took it off. its easier biking nao
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    Senior Member coldfeet's Avatar
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    1. For a conventional bike ( not longtail, recumbent or tandem ) The greater the braking force, the more weight transfer to the front. ( It can be true for these as well. )
    2. As deceleration increases, there is less grip available at the rear wheel.
    3. Therefore, in maximal braking situations, there is little or no braking force available at the rear wheel.

    Limitations:
    1. Total grip available at the front tire. If the front tire cannot generate enough grip, it generates less deceleration, and therefore less weight transfer, and therefore, there is more opportunity to provide deceleration at the rear wheel.
    2. Skill: If you cannot accurately regulate the front brake and deal with the instability caused by maximal front braking, don't do it.

    It is possible with motorcycles and bicycles to make a stop of such force, that you come to a halt with rear wheel 2-3 feet off the ground. I have done this several times with a motorcycle, sometimes intentionally, once in an incident which saved my life. I have done it once or twice with a bicycle, intentionally. I usually try to provide a more even braking for preference, but I am always aware that the greater part of my braking is available at the front wheel, in good grip situations

  15. #15
    i got nothing. Crash716's Avatar
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    Quote Originally Posted by coldfeet View Post
    1. For a conventional bike ( not longtail, recumbent or tandem ) The greater the braking force, the more weight transfer to the front. ( It can be true for these as well. )
    2. As deceleration increases, there is less grip available at the rear wheel.
    3. Therefore, in maximal braking situations, there is little or no braking force available at the rear wheel.

    Limitations:
    1. Total grip available at the front tire. If the front tire cannot generate enough grip, it generates less deceleration, and therefore less weight transfer, and therefore, there is more opportunity to provide deceleration at the rear wheel.
    2. Skill: If you cannot accurately regulate the front brake and deal with the instability caused by maximal front braking, don't do it.

    It is possible with motorcycles and bicycles to make a stop of such force, that you come to a halt with rear wheel 2-3 feet off the ground. I have done this several times with a motorcycle, sometimes intentionally, once in an incident which saved my life. I have done it once or twice with a bicycle, intentionally. I usually try to provide a more even braking for preference, but I am always aware that the greater part of my braking is available at the front wheel, in good grip situations
    That's called showing off.....as someone who has spent a considerable amount of time on sportbikes you WILL stop faster with both wheels on the ground, not with the rear 2-3' off the ground...watch professionals race....rear wheels remain on the ground...and they stop a hell of allot more effectively than guys trying to endo to show off.

    The same goes for a bicycle....use your front brakes AND keep your rear wheel on the ground slightly dragging...ie modulate the rear brake to the point of adhesion and you will stop faster than just using the front.
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    I taught motorcycle safety classes (and rode sportbikes) for about a decade.

    The maximum amount of total braking power that you have is determined by the total weight that is on the wheels and the coefficient of friction between the tire and ground. If you have weight transferred to the front, you have more traction and can brake harder on the front, and will need to brake lighter on the rear.

    Both motorcycles and bicycles have sufficient braking power to cause the front wheel to skid in most situations, and the vast majority of braking-related accidents are caused by applying the front brakes too fast. A fast application can not only exceed the available traction at the start, it also causes a rapid weight transfer that can have the same effect.

    The best technique is to squeeze the front brake lever progressively, and to reduce the amount of rear braking as the weight transfers. In the real world, you only have so much attention, and it's more important to spend the time on the front brake than the rear one, so rear brake application is often at a steady low amount.

    As for lifting the rear wheel, it's not an indication of the best possible stop, but it *is* true that the harder the stop (ie the faster the decelleration), the more weight transfer and the more likely the rear is to get light.
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  17. #17
    CRIKEY!!!!!!! Cyclaholic's Avatar
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    brakes are overrated... they only slow you down.

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    Senior Member coldfeet's Avatar
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    ericgu and Crash716, I agree with both of you,
    "I usually try to provide a more even braking for preference"
    And I rarely use maximum braking anyway, enough that I am in practice for when it is needed. Endos are indeed mostly about showing off, it did once however, save may life. ( I am convinced anyway. ) Moving away from a green light, movement in the corner of my eye prompted a vicious application of brake, both as it happens, the slow speed and abrupt weight transfer resulted in ( I am told ) about a 45% nose down tail up angle, at which point the dink jumping the red light smashed my front wheel from under me. I did a quick 360 roll and landed on the road, with hardly a bruise to show for it. ( Bike needed some work though ) EDIT: it's about 50/50 that I would have maintained control had he not hit me, I didn't slide the front tire, but I may not have kept the bike upright when the rear end returned to terra firma. My subconscious decided, quite rightly in my opinion, that this was not a moment for half measures.

    "Both motorcycles and bicycles have sufficient braking power to cause the front wheel to skid in most situations, and the vast majority of braking-related accidents are caused by applying the front brakes too fast. A fast application can not only exceed the available traction at the start, it also causes a rapid weight transfer that can have the same effect."


    This, to my mind, is more of an indictment of the lack of skill too many riders show.
    Last edited by coldfeet; 01-28-08 at 11:13 PM.

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    Quote Originally Posted by ericgu View Post
    I taught motorcycle safety classes (and rode sportbikes) for about a decade. ...
    If you want to see a "stoppie", just find a 18-yr old kid on a sportbike with leaking fork seals, and ask him to show you how it's done.

    Quote Originally Posted by ericgu View Post
    ...The best technique is to squeeze the front brake lever progressively, and to reduce the amount of rear braking as the weight transfers. In the real world, you only have so much attention, and it's more important to spend the time on the front brake than the rear one, so rear brake application is often at a steady low amount. ...
    As true as this is, somehow I doubt this is how it works.
    I'd be willing to bet that in panic situations, many people just grab both brakes as hard as they can.

    -------

    I would question the assertion that it's possible to lock the front wheel of a bicycle up on clean pavement. The MTB's I had in years past couldn't even come close to it with V-brakes, and neither will the recumbent and semi-recumbent I have now (both with disk brakes). Both these bikes have a lightly-loaded front wheel (carries only about one-third the weight) which should be easier to lock up than a wheel normally carrying ~50% of the weight, and they still won't do it.

    I've not rode anything with hydraulic brakes, which might make some difference in braking power.
    ~

  20. #20
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    I do mini stoppies for fun when I come to a stop. I guess it's my "I wish I had the nerve to ride motorcycles" coming out. For the record I was petrified at 35 mph on a motorcycle - pedaling makes me feel more secure for some reason.

    Anyway, I unclip one foot, stick it out like I'm about to do a motocross hairpin turn, and I can lift the rear wheel using the front brake. Usually I'm sitting on the top tube. Sometimes I do it while still clipped in.

    Regardless, the point is that it'd be very easy to squeeze the front brake just a bit more and flip myself over the bars.

    I tell people to hit both brakes somewhat evenly. When the rear wheel starts to slip around a bit you're just over your safe max braking since it's possible they simply dump the bike if they lose control. The rear slides around because it has very little traction. It's helpful because it acts sort of like an indicator of your weight transfer. It only takes a second or so to stop so keep the pressure on till you do so.

    cdr

  21. #21
    52-week commuter DCCommuter's Avatar
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    Quote Originally Posted by ericgu View Post
    Both motorcycles and bicycles have sufficient braking power to cause the front wheel to skid in most situations,
    I don't believe that is true. I've never ridden a motorcycle, but on a normal-wheelbase bicycle you can't skid the front wheel, you go over the bars first.

    Quote Originally Posted by ericgu View Post
    ...and the vast majority of braking-related accidents are caused by applying the front brakes too fast. A fast application can not only exceed the available traction at the start, it also causes a rapid weight transfer that can have the same effect.
    This isn't quite true either. The same amount of braking from either front or rear wheel with cause the same amount of weight shift. What is true is that on a two-wheel vehicle, when you reach the limits of your brakes you run the risk of unstability. With the front brake, this limit is sudden and catastrophic -- you go over the bars. With the rear brake, the limit is gentler, because as the rear brake applies more force, more weight is transferred to the front and the rear becomes less effective. However, when the rear is unloaded it tends to skid, which will destabilize you if not corrected.

    Quote Originally Posted by crash716
    watch professionals race....rear wheels remain on the ground...and they stop a hell of allot more effectively than guys trying to endo to show off.
    The problem with braking at maximum, with the rear wheel off the ground, is stability. When the rear is lifted bikes have a nasty habit of pivoting around the steering tube and falling over. If you brake just a little bit less than maximum and keep the rear wheel on the ground, you are much more stable than at maximum, with almost as good decceleration. When the rear wheel is lightly loaded it will skid at the slightest braking force, and a skidding wheel provides much less directional stability than a rolling one, so it is best not to use the rear brake at all in this situation. So maximum control is given by front brake at 99% of maximum, rear brake off.

    Quote Originally Posted by Doug5150
    If a recumbent can stop in a shorter distance than an upright bike is an interesting question, but not one that I have the technical equipment to accurately answer.
    All things being equal, a bike that has a long enough wheelbase that you can skid the front tire rather than going over the bars will stop faster than a shorter one. In that case, the rear brake is helpful, and maximum braking occurs when both wheels are just before the point of skidding. Braking is more complicated because you actually have to coordinate both brakes.

    A typical diamond frame bike will put you over the bars at about 0.65g of braking. I would imagine a bicycle tire skids at about 1g.

    Quote Originally Posted by velo dog
    And do people REALLY ride without using the rear brake?
    I never use the rear brake unless the front brake fails.
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    Cycle Dallas MMACH 5's Avatar
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    In normal riding/stopping situations, I almost exclusively use my front brake to stop.
    Once stopped if I'm on a hill and have to fiddle around with something or get a drink, I'll use the rear lever as a "parking brake."

    In emergency situations, I grab both brake levers (or whichever I can get to first and then grab the other lever also).
    That's gonna leave a mark.

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    Well, some understand and others do not. My point is that with proper technique you get 10-25 more braking power by keeping the rear wheel on the ground and using both brakes.

    Yes at low speeds (2-3mph) it is very easy to lift the rear wheel. That is one of the reasons that bikes for small kids are not fitted with a front brake. With body english you can do it at higher speeds. Maximum braking comes just before the tires start to skid. If the front is at that point and you are not using the rear brake, either through choice or poor technique, you have do not have as much slowing as you would if both wheels were at that point. If you lift the rear wheel you also do not have maximum braking at the front for that matter, because it is not near the skidding point.

    The rear brake adds 10-25% to your slowing when used with your front brake. It also gives better control of the bicycle in low traction situations when used gently by itself.

    Yes when the front wheel is the only one braking you that is 100% of your braking power, but it is only 75-90% of your total available braking power. That is the point folks miss by using undefined percentages.

    I am not in anyway telling folks what they should do. I am merely trying to increase understanding of the dynamics of braking.

    Note to the recumbent guy: yes I was talking about conventional bicycles.
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    Hooligan Abneycat's Avatar
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    On longtails, the design makes it *very* hard to go "over the front", since your rear wheel has that much farther to swing and the weighting of anything on the rear wheel is more pronounced. Loaded with even a moderately small amount of weight in tow, its nearly *impossible* to lift the rear at all, and both brakes work much better than front alone. Unloaded, while you are unlikely to lift the rear wheel it just doesn't have enough weight on it and will simply lock and slide quite easily.

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    Senior Member coldfeet's Avatar
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    Quote Originally Posted by graywolf View Post
    Well, some understand and others do not. My point is that with proper technique you get 10-25 more braking power by keeping the rear wheel on the ground and using both brakes.

    Yes at low speeds (2-3mph) it is very easy to lift the rear wheel. That is one of the reasons that bikes for small kids are not fitted with a front brake. With body english you can do it at higher speeds. Maximum braking comes just before the tires start to skid. If the front is at that point and you are not using the rear brake, either through choice or poor technique, you have do not have as much slowing as you would if both wheels were at that point. If you lift the rear wheel you also do not have maximum braking at the front for that matter, because it is not near the skidding point.

    The rear brake adds 10-25% to your slowing when used with your front brake. It also gives better control of the bicycle in low traction situations when used gently by itself.

    Yes when the front wheel is the only one braking you that is 100% of your braking power, but it is only 75-90% of your total available braking power. That is the point folks miss by using undefined percentages.

    I am not in anyway telling folks what they should do. I am merely trying to increase understanding of the dynamics of braking.

    Note to the recumbent guy: yes I was talking about conventional bicycles.
    The maximum amount of braking is dependent on many factors, the force level when the tire skids is a function of weight, and the nature of the tire compound and road surface.

    The problem here is you are talking about one specific situation. If the surface, tires, and skill level are good enough, and you are talking about coming to a halt. i.e. not simply slowing down for a corner, lifting the rear wheel as you stop, means you are stopping shorter. If you want to do better than that, then you can get off the saddle behind, that is, your arms are stretched out and your pelvis is actually behind the saddle. Doing that and lifting the rear wheel is darn near impossible, because it's harder to do and reduces weight transfer anyway. This is a technique taught by some safety course for shortest stopping distances. It's difficult because it requires you to plan your stop, in a sudden situation it's hard to remember.

    I will also say, as some others have, that skidding a bicycle tire on good tarmac is darn difficult, in most situations the grip is too high, a front flip is much more likely. (Road tires that is, I have less experience with knobbies, don't know if it's the same.)

    Having said all that, using both brakes is recommended for most riders because they aren't going to put in the effort to practice with the brakes, and even when they have, most people aren't paying 100% attention anyway, which you need to if you are going to be trying to get 100% out of your stopping.

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