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  1. #1
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    How do i measure the "reach" for brake calipers when converting from 27 to 700c?

    On the schwinn I'm fixing up, I am rather pondering possibly converting to 700c. At first i wasn't going to but now I'm thinking again I might want to.

    The thing that is confusing is how do i measure the caliper reach so I can get the proper replacement calipers in there?

    Currently the bike has a set of sidepull single pivot sidepulls and the front one is rather bent up. Even if I do not convert to 700c, I still would like to convert to double pivot caliper brakes but I'm not sure how to measure the calipers to get the right size, standard or long reach.

  2. #2
    coprolite fietsbob's Avatar
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    reach is the distance between The place where the brake is mounted
    a horizontal line
    to the top and bottom of the mounting slot for the brake-shoes.
    a vertical perpendicular, 90 degrees, off the horizon line.

    centers of bolts,holes, is the place dimensions are taken as standard practice.


    4th post has a Picture , saying same thing..
    Last edited by fietsbob; 03-04-15 at 03:06 PM.

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    + 5 mm? Check out tektro, they might have what you need.

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    Okay, so i should mount the 700c or 27 inch wheel and measure like the following picture:
    Attached Images Attached Images

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    And in reference to the above picture, I have not cold set my frame to allow for the 130 spacing of a more modern road hub but I can safely assume that if I measure with my existing 27 inch wheel in place, I could add 4mm and be within a safe range for the caliper for a 700c wheel?

    in other words, I want to measure the distance like the above picture and look for a caliper that has my measurement within the specs of the caliper. So if I measure 38mm, I want to look for a brake that might have a reach of 35 to 40 mm or whatever spec is available. And if I am thinking of converting to 700c, add 4mm to the overall measured reach so it would then be 42mm as an example if I do decide to convert to 700c.

  6. #6
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    Quote Originally Posted by bobotech View Post
    And in reference to the above picture, I have not cold set my frame to allow for the 130 spacing of a more modern road hub but I can safely assume that if I measure with my existing 27 inch wheel in place, I could add 4mm and be within a safe range for the caliper for a 700c wheel?

    in other words, I want to measure the distance like the above picture and look for a caliper that has my measurement within the specs of the caliper. So if I measure 38mm, I want to look for a brake that might have a reach of 35 to 40 mm or whatever spec is available. And if I am thinking of converting to 700c, add 4mm to the overall measured reach so it would then be 42mm as an example if I do decide to convert to 700c.
    Correct and correct.

  7. #7
    Senior Member Bill Kapaun's Avatar
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    Theoretically, it's 4MM.
    It might vary a little bit depending on the "angle" of the rim braking surface and/or width of the rim.

    I swapped on a 700C wheel to an old 10 speed last summer and only had to move the pads about 2MM in the slot.
    I have to admit that I didn't check pad alignment to the old wheel first, so maybe they were already a bit too far toward the spokes???

  8. #8
    Member eddiexchoi's Avatar
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    interesting... I ma having a same issue with an older frame and newer wheelset. newer groupset came with the calipers that did not fit... even if I lowered the pads... Now I am in need of a new calipers with longer reach...

  9. #9
    Nigel nfmisso's Avatar
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    Quote Originally Posted by eddiexchoi View Post
    ... Now I am in need of a new calipers with longer reach...
    Tektro is your friend.
    Nigel
    Mechanical Design Engineer

  10. #10
    Andrew R Stewart Andrew R Stewart's Avatar
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    I'll add that the geometry of forks and rear frames usually place the wheel a bit ahead (forks) or behind (rear stays) the face of the frame's brake hole. So that with a fork there's often about 2mm of less actual pad positioning within the arm slots then a measurement might suggest. And about 1mm more for the rear.

    Usually this isn't a big deal if the arm reach is that the pads will sit toward the center of the slots. But when pushing for the last few mms this offset/difference can be just enough to be a problem.

    I deal with this with frame building and trying to get both brakes to have similar pad placement (and not be 3-4mms different between ft and rr). Andy.

  11. #11
    Member eddiexchoi's Avatar
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    Quote Originally Posted by Andrew R Stewart View Post
    I'll add that the geometry of forks and rear frames usually place the wheel a bit ahead (forks) or behind (rear stays) the face of the frame's brake hole. So that with a fork there's often about 2mm of less actual pad positioning within the arm slots then a measurement might suggest. And about 1mm more for the rear.

    Usually this isn't a big deal if the arm reach is that the pads will sit toward the center of the slots. But when pushing for the last few mms this offset/difference can be just enough to be a problem.

    I deal with this with frame building and trying to get both brakes to have similar pad placement (and not be 3-4mms different between ft and rr). Andy.
    Thank you for this information... now it kinda throws me off... I see Tektro 559 vs 539 and I am thinking 559 since I measured it around 2.45(62.23mm) in the front and 2.25(57.15mm) in the back but I guess it all depends on "HOW' you measure it... I measure the opposite ends from the brake calipers where (stupid) so it should be off... thank you again. I almost ordered the wrong ones

  12. #12
    Andrew R Stewart Andrew R Stewart's Avatar
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    My way of measuring is from the brake mounting hole (facing front for the ft brake and facing rear for the rr brake) to the center of the rim. This usually is easiest if the old brakes are removed from the frame. Using this measuring method my prior comments about "correction" factors apply.

    Like with spoke calculating, standardizing one's methods of measuring helps to keep things consistent and allow one to make better judgments. Andy.

  13. #13
    Senior Member Velocivixen's Avatar
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    Every frame is different, but I just did this 2 days ago on my '85 Nishiki Riviers Mixte. Removed really pristine 27" wheels and installed 700c wheels. I could have continued to use the Dia Compe N500 calipers, but in general I don't like them. So I started with the Tektro R559 and they were HUGE and way too long. I could have used them, positioning the pads at the very top of the slot, but it looked ridiculous. So I took them back and bought the Tektro R737 and they are perfect.

    NOTE: The difference between the Tektro R539 & R737 (on Tektro website their specs are identical) is that if you look at the rear arm of the brake on the R539 the metal is cut out into a triangular "window" & you can see the top of the spring in back (if you're in front of the bike looking at it). The R737 is solid in that space and, aesthetically, looks more like the R559. The R559 has a niftier looking barrel adjuster though.

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