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  1. #1
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    Using Rim Brakes on Disc Rims

    Due to a parts availiblity issue and a builder mixup I Got a set of wheels with a Mavic A317 DISC rims instead of a Mavic A319 rims. How safe is it to use rim brakes on this wheel? The extrusion looks like it has a flat for rim brakes but the rim just hasn't been machined.

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    not the same product as A319 rims.
    A319 is 595g
    A317 is 540g

    take a guess as to where the weight savings come from.

    http://www.mavic.com/en/product/rims...lon/rims/A-319
    http://www.mavic.com/en/product/rims...ims/A-317-Disc
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    IMO, not ideal, but not immediately critical either. It's not silly light, so I'd expect it to hold up to rim braking not much worse than any other rim of comparable weight. Modulation might be off until you've worn it down to bare metal.

    Are you sure that the sidewalls are wide enough to comfortably receive the brake pads?

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    The A317 DISC is narrower than the A319 so the weight savings is not nessasarily from the braking surface. The "braking surface" is wide enough for rim brakes but I'm not sure how thick it is because I don't have a micrometer (yet). How thick of a braking surface should I be looking for? What type of brake pads should I start with?

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    Quote Originally Posted by Bezalel View Post
    Due to a parts availiblity issue and a builder mixup I Got a set of wheels with a Mavic A317 DISC rims instead of a Mavic A319 rims. How safe is it to use rim brakes on this wheel? The extrusion looks like it has a flat for rim brakes but the rim just hasn't been machined.

    Keep it simple. You say builder mix-up. You paid for A319 wheels, therefore you are due just that. No, don't go using the disc version with rim brakes. I'm sure not one person at Mavic would say it's OK though. Why not ask them? No one here knows anything more about Mavic rims than Mavic.

    If the builder doesn't have the correct parts in stock, either wait or get a refund. It's their F'up, not yours. They should be paying your return shipping also.

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    biked well well biked's Avatar
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    If you do this, the "brake surface" you'll be using will suck as a brake surface, because it's not really a brake surface. I agree with the above advice to get the wheel builder to make it right with the correct rim.
    Last edited by well biked; 09-28-10 at 08:04 AM.

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    One big issue is that most disc rims have a curving and painted rim surface whereas a rim brake surface has the brake track that is perpendicular to the ground. Sure it will stop your wheel if you use a rim brake but it's going to be a lot lower friction and potentially dangerous.

    I wouldn't do it. Whoever made the mistake should suck it up and fix the problem.

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    Quote Originally Posted by Garthr View Post
    Keep it simple. You say builder mix-up. You paid for A319 wheels, therefore you are due just that. No, don't go using the disc version with rim brakes. I'm sure not one person at Mavic would say it's OK though. Why not ask them? No one here knows anything more about Mavic rims than Mavic.

    If the builder doesn't have the correct parts in stock, either wait or get a refund. It's their F'up, not yours. They should be paying your return shipping also.
    Quoted for truth.

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    The reason I'm asking is beacuse the mixup was because I never told the seller that I was using rim brakes. The origional order was for a set of silver wheels that were also disc compatible (the A319 was part of the seller's description not something I specified). Silver was unavailible so the seller asked for permission to subsiitute it with black which I accepted (without ever telling the seller that I needed rim brakes). When the seller built up the wheel he subsituted the rim for one without a braking surface due to the fact that the hub was disc compatible.

  10. #10
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    Machined braking surfaces are a recent innovation; I've used rims far lighter than that (e.g. Super Champion "Medaille d'Or"; 260gm and "Arc en Ciel"; 340gm) and lacking machined sidewalls with rim brakes for decades without problems. The only potential problem I can think of is if the sidewalls are painted or hard-anodized the brake pads may not grip as securely until the surface treatment has worn off the rim.

  11. #11
    coprolite fietsbob's Avatar
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    disc rims need and so have no parallel side faces for the pads to grip,
    If thats what you got,
    send them back..
    triangular cross section is great when there is no rim braking needed.

    If there are parallel faces but the extra step of machining was not done,
    Don't sweat it , get some really abrasive brake shoes
    and you will grind it down yourself.. with each stop.

    I used some on my CD treated rims, the hard anodized layer wore thru
    then I switched to a different pad compound.
    Last edited by fietsbob; 09-28-10 at 10:26 AM.

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    Quote Originally Posted by fietsbob View Post
    , get some really abrasive brake shoes and you will grind it down yourself.. with each stop. I used some on my CD treated rims, the hard anodized layer wore thru then I switched to a different pad compound.
    I had some Mavic Open 4 CD rims (predecessor to the Open Pro) and the hard anodizing wore off of the brake track in almost no time even with standard Shimano brake pads.

    The CD-treatment was a marketing gimmick with no real value and it had the unintended effect of making the rims more crack prone.

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    Fietsbob, in this case that was my immediate thought as well. But when I looked up the two rims at Mavic they are the same shape with flat brake tracks. The only difference being that the disc version has paint, powder or anodizing on the sides where the other is machined. Otherwise it's the same extrusion shape that is suitable for rim braking.
    Model airplanes are cool too!.....

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    coprolite fietsbob's Avatar
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    Since I have Magura Hydrostop brakes I used a set of their Greenfrog compound pads

    these brakes and those pads made a nice smooth resurface thru the CD layer
    on the ex721 rims on my Koga WTR
    then swapped out to the original black ones , will try a set of red pads next,
    they get Koolstop to mold the salmon insert for them .
    so the parts have 18 timezones of travel to Germany and back to the same state.

    Powdercoated you may have to use carborundum grit abrasive 'sandpaper',
    and 'elbow grease' ..

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    The wheels are being returned. I might have kept them but the seller was acting like a real jerk by claiming that they were sold as disc wheels and since they were custom are not retunable. I contacted eBay and now the seller has agreed to allow a return.

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    Quote Originally Posted by Bezalel View Post
    The wheels are being returned. I might have kept them but the seller was acting like a real jerk by claiming that they were sold as disc wheels and since they were custom are not retunable. I contacted eBay and now the seller has agreed to allow a return.
    All for the best then. Always a bit annoying when one has to start off with parts bought new that aren't as expected.

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    Quote Originally Posted by Bezalel View Post
    The wheels are being returned. I might have kept them but the seller was acting like a real jerk by claiming that they were sold as disc wheels and since they were custom are not retunable. I contacted eBay and now the seller has agreed to allow a return.
    Good, I'm glad it will work out. I've always considered e-bay to be a crap-shoot even when you know exactly what you want.

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