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I need to replace a front brake for a city/folding bicycle. but I am not used to these "brake bridge" system; I am more into the MTB scene.

for some reason the calyper in the picture destroys the left brake pad but keep right pad intact. why?

As requirement, the height and width has to support the installed mudguard as you can see in the picture.

In fact I 've seen that some good brakes for road cycles are not designed to have a mudguard, so they are not in the shopping list :)

The questions are:

  • How many types of standardized brake bridges are?
  • Differences about effectiveness?

Experiences about brake calypers for legacy bicycles? An exactly to reach around 7cmm height, 7cm height

front brake systems width height

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Your photo shows a single pivot caliper brake. The main measurement is how much "reach" it has from the single mounting bolt down to the brake pads and represents a range.

Any replacement caliper needs the same reach to get pads to the rim track.

The other variable is the bolt - older bikes use a threaded post which has a clearly visible hex nut on the rear side.

More modern brakes tend to have a recessed threaded "nut" with a hex socket. These might be described as "half of a Chicago nut/bolt set"

As for your options, the single best fix for any brake is to replace the pads with something more modern. The rubber compounds harden and oxidise with age and UV, and performance drops. Koolstop have excellent options - your bike might take road cartridge shoes with replaceable brake pads.

Second is to replace the brake cables, both inner and outers. They degrade over time and add friction. Check first that you can get an inner cable that matches your existing brake levers. There are multiple common standards as well as other rare ones.

Third is strip, clean, lube, and reassemble the brake. It should have buttery-smoothness when you press the two pad-arms together by hand. Do take photos as you disassemble, and use a lubricant like white lithium grease.

Finally - if you can find a dual-pivot brake caliper with the right reach and same mounting bolt, then it could be a useful upgrade on the front of your bike. The brake at the back doesn't contribute very much to braking effort, so there's less gain by uprating it.

enter image description here
Here's a longer-reach dual pivot brake, but the bolt at the back probably doesn't match your mounting.

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  • I added the measures and distances to reach the rim, 7cm from top bolt, 7cmm among pad fixation points
    – Daniel Perez
    Commented Sep 17, 2022 at 12:29
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    @DanielPerez This is heading toward Off Topic because specific product recs are off topic, as mentioned in the tour. Google-searching for "long reach caliper brake" returns several options like the Tektro R559 claiming "Extra long reach caliper 55mm to 73mm" and the shimano BR-R650 and the VeloOrange Grand Cru. Good luck!
    – Criggie ♦
    Commented Sep 17, 2022 at 21:52
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There are two common types of brake bridges for caliper brakes: The one with recessed nut where the bolt from the brake doesn't reach through the bridge or fork crown, but the nut is a long tube that is inserted from the other side. There nuts are made in different sizes to make the same brake fit larger fork crowns. The other type with non-recessed nut has the bolt simply reach through the bridge. This is probably what the bike in picture has.

The other parameter is reach. Racing oriented or inspired bikes typically have short reach brakes that fit only a narrow tire and no fender. There are long reach brakes that allow a wider tire or a narrow fender and some extra long reach ones that could possibly fit the bike in the picture. These names are not standardized, and the only way to be sure is to measure the distance from the brake mounting bolt to the rim and check that it is within the brake manufacturer's specification.

In my experience the style of single pivot brake shown in the picture is not very good. The short reach brakes will always have best performance of rim brakes because they have the least amount of flex, but even no-brand extra long reach dual pivot brakes are improvement over these. Brake pads also make a huge difference. I have had good experience with Kool Stop Salmon.

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    Do you think that the "single pivot brake" system is the reason to destroy left pad and keep intact right pad? or is it a bad setting
    – Daniel Perez
    Commented Sep 17, 2022 at 12:27
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    @DanielPerez Did you actually destroy a brake pad with dual pivot brakes or have you been reading certain posters' opinions? Anyway, that's worth a new question.
    – ojs
    Commented Sep 17, 2022 at 12:55
  • unfortunately the destroyed pad is based in facts, as this pad was closer to the rim I assume that the pressure over the rim was much higher than in the other side
    – Daniel Perez
    Commented Sep 18, 2022 at 13:32
  • @DanielPerez usually it's double pivot that is blamed for asymmetric brake pad wear and single pivot is believed to be self centering. If the pad "self destructs" instead of slowly wearing down, it probably wasn't a good one and you should buy one of the known good brands next time.
    – ojs
    Commented Sep 18, 2022 at 19:10

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