I have "MavicD521 SUP" rims on my GT XCR-4000 mtb. My question is: what does the "D" represent and what is "SUP"? The rims have this dark gray coating on them (possible anodizing) and the braking surface is super slick and shiny (not bare aluminum).

https://www.mavic.com/servlet/srt/mav...nosid=18&lg=uk

https://www.mavic.com/servlet/srt/mav...extnum=1&lg=uk

Those should help, as for the D, it's part of the name.

The D is just part of the model #, the SUP is Mavic's welding and milling process that makes the welded part of the rim almost as strong as the rest of it. You have a grey anodized rim. It is also available in silver, and if I remember correctly, a bronze color as well. If it had a CD after the name, you would have a ceramic coating that makes your brakes work better, no matter what the conditions, and decreases rim wear as well.

DEMON

OK, thanks for all of the info. Still got this brake squeal problem and I thought, maybe, the "D" meant that the rims were for disk brakes only. I'm totally out of options for fixing the squeal problem....believe me, I've tried everything, even KoolStop pads. My last try will be to use brake pads for ceramic rims which I understand are a harder rubber material. Maybe this harder material will allow less grab and more slip to stop the squeal.

I thought d meant for DISC. 321d is the 321 model in disc only. Thats my take and what was explained to me.

I hope it doesn't mean "for disk brakes ONLY". The rim has this hard anodized coating and is so super slick on the braking surface that the pads seem to vibrate and cause squeal. So far I tried all different setting and get the best results with the Shimano XTR Extreme Condition pads set flat to the rims (no toe). Still squeals but not as much, only when the pads are cool do they squeal a lot. Will try the ceramic-specific pads when they arrive.

Just took a look at the pic and while you can use v's it won't work well. You dont have much sidewall and the design is similar to my 321d's. Like I said I am pretty sure they are supposed to be disc only.

Yeah, the brake surface is kind of narrow. My pads have about 1mm of clearance from the top and bottom of the braking surface. Funny, though, my rear brakes are totally silent. I took apart the front caliper (XT parallel push) greased the pivots and oiled everything else, put on a Salsa booster but no luck. If the ceramic pads don't work maybe I'll think about converting to disk on the front.

The D521 is not listed as a disc only wheel. I think the "D" is the code letter for the Extreme series of mavic rims.
That squealing is probably those dang xt brakes, they are nototrious for it.

Pretty strange that only the front squeal and not the rear.

Jim, your rim is not a disc specific rim. As far as i can tell the "D" is a designation for Mavics extreme/downhill most durable rims.

D= extreme rims
sup= welded seams
ub= milled brake surfaces
cd= hard anodized
ceramic= ceramic ocating on brake surfaces
disc= disc specific

For instance, a disc specific rim may be sup (welded) but theres no need for UB or ceramic.

Now, on to the squelling problem. Thouroughly clean you brake pads being carefull to remove all imbedded particles form the pads. If needed lightly sand them just enough to remove any shiny-ness. CLean your rims with some rubbing alcohol and one of those green scrubby pads. Any of the orange citrus degreassers will work in lieu of alcohol. Adjust the pads so the leading edge hits first (toe). Adust them verticaly so the top and bottom edges hit at the same time.

Thanks for all of the information. Here's what I've done so far: cleaned rims with alcohol, acetone, laquer thinner, scotchbrite pad, sandpaper. De-glazed pads; beveled leading edge of pads; put automotive anti-chatter compound between the pads and holders; tried toe-in, toe-out; tilting pads up and down; increase caliper spring tension; greased/oiled everything; whatever is causing it to squeal it sure beats the hell out of me! It's probably something simple (it usually turns out to be).

Okay... so you've: "cleaned rims with alcohol, acetone, laquer thinner, scotchbrite pad, sandpaper. De-glazed pads; beveled leading edge of pads; put automotive anti-chatter compound between the pads and holders; tried toe-in, toe-out; tilting pads up and down; increase caliper spring tension; greased/oiled everything".

Alcohol, lacquer thinner, and acetone don't need to be used. As far as I know, they're just cleaners. The pads aren't squealing because they're dirty. If you've toed them, then it's not the toe. Beveling the edges probably won't do it. The sqeal is coming from the contact between the rubber and the metal (unless you have ceramic rims. make sure you have pads that correspond to your rim material). The squeal doesn't come from the brake assembly, so don't worry about oiling or anti-chatter compound. Tilting up and down doesn't affect squealing either. Only sandpaper and toe affect it, but it appears toeing hasn't helped in your case. This happens.

If your brakes work on your rear wheel just fine, then these rims are obviously made v-brake compatible. 1 mm of clearance above and below the pads is alright. It's not much, but it's good, and if you have an xtr assembly, it should be perfect.

Try taking some gritty sandpaper and scraping the hell out of your rims. Don't gouge them excessively, but definately mark the hell out of them. Then get some fine sandpaper and lightly go over the rim again, then scrape about 1mm off your brake pad.

Toe them flat against the rim (small toeing might decrease squeal, but it makes your levers feel mushy. dial them in by not toeing the pads).

If they still squeal, see if they need to be broken in (aka ride on the things squealing and see if it decreases at all?)

I have "ceramic" pads on order and will try them first before I think about sanding the rims. What's weird is that a while back I got some small pieces of #400 sandpaper and stuck them between the pads and rim and rode around my driveway with the brake applied for a while to "rough up" the rims. I didn't sand it enough to remove the anodized finish (or whatever that coating is) but just enough to de-glaze it but the squeal returned after a couple miles of riding. If the ceramic pads don't help then I might just convert the front brake to disk as I really, really hate to remove the beautiful finish on these rims.

Okay, I just received my ceramic pads from PerformanceBike today and installed them into the brake pad holders. Without doing anything else I took a quick spin around my neighborhood and I couldn't believe it.......NO SQUEAL!!!!!! I tried different braking pressures from light application to mashing it and still no squeal. The ceramic pads are of a harder rubber compound so I lost some of the "grabby" feeling that my old pads had so I just boosted up the brake lever leverage and it stops almost like before. So now I will run the ceramic pads in the front and regular pads on the rear. Will check the rim perioducally for any signs of abnormal wear but that coating is so tough I doubt that it'll wear any differently. I can't believe it's finally over!!!