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When I apply both brakes going at moderate speed, it takes a few feet before the bike stops and I can hear the rear tire skidding.

The brake pad seems to be working fine since the wheels themselves quickly stop rotating, it's just that the bike continues to skid even when the tires are locked in place.

Is this normal behavior, and what can I do to improve the power/responsiveness of my brakes? Might it be a tire rubber issue?

  • How old is your bike? What kind of brakes to they have, rim or disk? If rim, how old are the brake pads? I suspect your brake pads are old and oxidised, therefore are hard, and are either OFF or ON. Newer brake pads are softer and have more modulation... "OFF, a little on, medium on, ON, Panic-ON." The tyres skid on the ground cos the brake pads should be sliding and they're not. – Criggie Apr 13 '17 at 1:21
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    If the wheels lock immediately that says that the traction between tires and roadway is the issue. Nothing you can do about it, really, if the tires have reasonable tread on them. In rare cases the tires might be old and too hard, or you could have an oddball tire brand with extra hard rubber, but this is unlikely. – Daniel R Hicks Apr 13 '17 at 2:11
  • If your complaint is that the tires lock TOO easily, that's generally a problem with the brake pads. You can exchange them for a set that is less "grabby" -- a good bike shop can help you here. – Daniel R Hicks Apr 13 '17 at 2:12
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    What surface are you riding on? Roads? Dirt tracks? Some of the bike lanes round here collect gravel etc. and the grip is greatly reduced. It's quite easy to skid a back wheel especially if you don't weigh very much - much harder to skid the front but much more of a problem if you do. Perhaps you need to use the front a little more. – Chris H Apr 13 '17 at 6:37
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    That's the point where you have to diminish the pull on the levers i.e. modulate the braking power, the way the ABS system in your car does. A skidding wheel has less braking power than a turning wheel. – Carel Apr 13 '17 at 8:10
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To answer the question shortly: yes, it is normal.

When braking, the inertia of the rider (and the bike) causes the load on the rear tire to decrease. It leads to lower friction against the surface, and possibly skidding. In extreme cases, when braking with the front brake, the rear tire is lifed off the ground completely.

Especially in fast mountain biking, the rider must lean back or "hang" as far back as feasible when braking, to maintain better traction and prevent possible falling over the handlebar.

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    Both your and "Suspended Users"'s answers were extremely helpful. It was hard to choose between them. In the end, I chose this answer because it brought up a viewpoint I didn't think about before (namely, that lower weight on the rear wheel causes lower friction which contributes to skidding. I did notice my rear wheel seemed to skid much more than the front.) – Asker Apr 14 '17 at 7:15
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Yes, as completely normal as it is for a car. Many people think that brakes "are for stopping". In reality they are for reducing speed.

Objects have two coefficients of friction, static and kinetic. Generally, static is higher and once you break it, you move into the kinetic phase which is generally lower. When your tire is rolling you are actually using the static coefficent (the higher). The rolling surface of your wheel is in "static" contact with the ground as you are moving. Any decent brake should be capable of "locking up" your wheel. However, doing so will move you into the kinetic phase of friction as your tire actually slides along the ground. Since the coefficient of kinetic friction is generally lower, this is actually a less efficient manner of braking (under normal conditions, against regular surfaces).

Good brakes also have modulation. That is, they allow you to control the action of braking so that you can maintain the maximum braking force before you lock the tire and move into less efficient state. So, if your brakes are already capable of locking your wheel, your braking power has already surpassed what is useful. You need to learn to either better modulate your brakes, or find a set with better modulation.

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    This was a very helpful and thorough answer. Thank you! – Asker Apr 14 '17 at 7:16

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