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On my mountain bike that uses V-Brakes I've always aligned them by actuating the brake lever and letting the brake pads align themselves to the rim. I've never had any squealing or lack of power issues. Why do the instructions recommend toeing in a new brake pad on road calipers? Is there a mechanical reason for this?
 

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I would venture to guess that it's for easier brake modulation. For a complete noob cyclist who knows little about correct brake use the reduced contact area will produce less friction with the rim and stop less abruptly. This could mean the diference between a hard stop and an endo. It's been my experience that the OEM spec requires a rather aggressive brake lever pull to use that last cm of pad, this effectively cuts the friction force by 15-25% (in theory), in the dry that last bit of stopping power is essentially useless, so it's not really a problem.

Also, in the wet, the front edge (before the first groove on the pad) acts as a squegee while the rest of the pad acts to stop the rim. In practice it's not that clear-cut, but it does make sense.

Please note that these are just theories put forth from my crazy engineering mind, they may or may not have any basis in fact.
 

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By design, road bikes see a lot of high speed, as compared to mountain bikes. Toeing in of brake pads on road bikes reduce the tendency of the pads to vibrate and squeal during braking. It also increases brake modulation and therefore decreasing the sometimes shuddering, choppy feel that will eventually effect the braking surface of your rims.
 

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Toeing, squeeling, and pads

jabpn said:
On my mountain bike that uses V-Brakes I've always aligned them by actuating the brake lever and letting the brake pads align themselves to the rim. I've never had any squealing or lack of power issues. Why do the instructions recommend toeing in a new brake pad on road calipers? Is there a mechanical reason for this?
Toe-in prevents chattering of the brake pads. When the brakes are applied, the friction between the pad and the moving rim tends to want to push the pads forward - the top of the wheel is moving forward afterall, and the brakes are attempting to retard this motion. As the pads are pushed forward, it tends to cause the arms of the brake to twist forward, causing the leading edge of the pad to "dig into" the rim a bit more (and for the trailing edge to squeeze the rim a bit less). At some point during the twist, the "spring force" of the brake arms will exceed the friction force of the reduced contact area of the leading edge, and the arms/pads will "pop back". As this action continuously repeats, the pads will "chatter" on the rim, creating noise and reducing overall braking force.

To reduce the tendency to chatter, the brakes can be "toed in". This involves angling the pads so that the trailing edge contacts the rim first, so that there is more pressure on the trailing edge and less pressure on the leading edge. As the brake arms flex/twist, the pressure on the toed in pads tends to even out (rather than be concentrated on the leading edge), reducing the tendency to chatter.

MTB brakes tend to use longer brake pads and holders, with a longer section on the leading edge. This longer leading section tends to help maintain a more uniform pressure on the leading edge as the brake arms flex, so they are less prone to the "dig in"/release cycle. These pads often do not need to be toed-in to prevent chatter.

In any case, brake pads are inherently self-toeing, so toeing of the pads is really just causes a temporary effect after initial installation. If the pads are not initially toed in, the extra pressure on the leading edge of the pads causing the leading edge to wear faster. This increased wear on the leading edge causes the surface of the pads to wear unevenly at first, until the surface of the pad becomes at an angle to the rim, with the trailing edge closer to the rim than the leading edge. After wearing in to this naturally toed in shape, the rate of pad wear on the leading and trailing ends will even out and maintain this angle during the rest of the pad life.

Personally, unless a particular brake is prone to excessive chatter, I don't bother toeing my brake pads anymore. After a few rides and some hard braking, the pads become naturally toed in.
 

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Discussion Starter · #5 ·
ah good to know. Thankyou for the replies.
 

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Mark McM said:
Toe-in prevents chattering of the brake pads. When the brakes are applied, the friction between the pad and the moving rim tends to want to push the pads forward - the top of the wheel is moving forward afterall, and the brakes are attempting to retard this motion. As the pads are pushed forward, it tends to cause the arms of the brake to twist forward, causing the leading edge of the pad to "dig into" the rim a bit more (and for the trailing edge to squeeze the rim a bit less). At some point during the twist, the "spring force" of the brake arms will exceed the friction force of the reduced contact area of the leading edge, and the arms/pads will "pop back". As this action continuously repeats, the pads will "chatter" on the rim, creating noise and reducing overall braking force.

To reduce the tendency to chatter, the brakes can be "toed in". This involves angling the pads so that the trailing edge contacts the rim first, so that there is more pressure on the trailing edge and less pressure on the leading edge. As the brake arms flex/twist, the pressure on the toed in pads tends to even out (rather than be concentrated on the leading edge), reducing the tendency to chatter.

MTB brakes tend to use longer brake pads and holders, with a longer section on the leading edge. This longer leading section tends to help maintain a more uniform pressure on the leading edge as the brake arms flex, so they are less prone to the "dig in"/release cycle. These pads often do not need to be toed-in to prevent chatter.

In any case, brake pads are inherently self-toeing, so toeing of the pads is really just causes a temporary effect after initial installation. If the pads are not initially toed in, the extra pressure on the leading edge of the pads causing the leading edge to wear faster. This increased wear on the leading edge causes the surface of the pads to wear unevenly at first, until the surface of the pad becomes at an angle to the rim, with the trailing edge closer to the rim than the leading edge. After wearing in to this naturally toed in shape, the rate of pad wear on the leading and trailing ends will even out and maintain this angle during the rest of the pad life.

Personally, unless a particular brake is prone to excessive chatter, I don't bother toeing my brake pads anymore. After a few rides and some hard braking, the pads become naturally toed in.
That's funny! I agree with the philosophy but, back when I did toe in brake pads, I toed them the opposite way for the same reason.
 

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Semantics?

Spoke Wrench said:
That's funny! I agree with the philosophy but, back when I did toe in brake pads, I toed them the opposite way for the same reason.
Maybe we are defining leading and trailing edges differently? I'm using leading edge to indicate the end of the pad where the rim first sweeps into the brake, and the trailing edge where the rim leaves the brake. Since the brake is usually on the top of the wheel, and the top of the wheel is moving forwared with respect to the rest of the bike, the leading edge of the pad is actually toward the rear of the bike (i.e. a point on the rim actually travels back to front through the pads, so since the rim first contacts the back of the pad, this is actually the leading edge of the pad with respect to the movement of the rim).
 
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