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touringza
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Have seen a set of mtb rims designed for rim brake use and the braking surface is ridged. About 20 or so concentric ridges. Why? Surely this effectively reduces the pad / rim contact area and reduces braking efficiency.

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Those ridges are the remnants of lathe work done on the rim after it was welded, to make it nice and smooth.

 

They actually increase the surface area, not reduce it.

 

They are standard on all rims nowadays and there is nothing wrong with it.

Edited by Johan Bornman
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Don't the ridges act as 'knife' edges cutting into brake pads? Does this apply to welded rims only or also to the pinned variety?

Edited by touringza
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Don't the ridges act as 'knife' edges cutting into brake pads? Does this apply to welded rims only or also to pinned rims?

No, the pads come to no harm and you can't see the difference between a pad that worked on a smooth or ridged rim.

 

AFIK there are no non-welded rims on the market anymore.

 

Even welded rims are pinned. Inside the weld you'll find either two steel pins or a big fat aluminium lug.

 

Welding and machining of rims is another one of those practices that didn't do anything for us other than raise the cost of rims. Pinned rims were fine and for years we rode with them until Mavic (I think it's them) invented "Sup" (froggie for Weld) rims. The weld leaves a big notch and thus has to be machined.

 

Mavic's last non-welded, non-sup rim was, I think, the MA 40 circa 1995 or so. But there are some Mavic buffs here, they can correct me.

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