[Closed] when fitting disk brake calipers should pads brake the 'spokes' of the rotor?

What size rotor?

What size adaptor?

Is it in the front or rear?

What design is the disk?

I only use round discs now. I stopped using the wavey ones. I found they juddered on the front under braking.

What size rotor? --180mm

What size adaptor? --Dunno

Is it in the front or rear? --Rear

What design is the disk? --Plain round

I might add I fitted some washers to see whether it improved things...as yet untested

Cheers

The easy way to tell if the disc has too small or large a braking surface is to place a pad directly against it in the position it would be in the caliper. If the pad surface is the same or smaller than the braking surface then it's just a case of alignment, if the pad surface is larger that's bad. If the pad rubs the spokes by a large amount then it'll wear that part thinner faster so it'll break there eventually. Hard to explain in text but easy with the parts in front of you.

The judder can be caused by the design of the rotor some are worse that others. Can also be play in the headset or fork bushes etc.

I always have the pads sitting mid rotor braking surface. Sometimes this requires a washer or 2 to achieve. I bought some Hope ones ages back and use those.

SRAM centerline rotors by any chance?

Just basic Avid or something rotors...using ancient Hayes Mech calipers (simple but effective!)

I always assumed the pads are generally bigger than the rotor braking surface in most designs..perhaps mistakenly.

I love manualling (badly) and I feel the rear brake judder is hampering my brake feathering.

Thanks all for replies.

Had a similar "fluttering" sensation from the front brake years ago, most noticable on tarmac, never really caused a problem, and never really tried to cure it specifically, but over a long period of time, I changed everything that could have caused it other than the disc (which, incidentally, was specced by the manufacturer for that brake), which, like yours, braked a little on the spokes. A change of disc to a deeper, full round braking surface type, when the old one had worn out, saw the flutter vanish instantly. Been running that style ever since, with no problems.

Is it a hardtail or full suss?

If it's on the back and a full suss is it the suspension? Have you checked for movement in the bearings?

It's a hardtail Damascus but thanks yes that might have been a culprit.

Thanks for your experience Coatesy.

Cheers all.

Well designed brakes should have a constant surface area. If you look at drilled and grooved car disks you notice the pattern of the holes means they pass under the pad at a constant rate and the holes are actually drilled in a pattern thats slightly non-cocentric with the hub so that each part of the pad gets equally exposed to them.

Wavy disks shouldn't oscillate but badly designed ones do.

After a few rubbish combinations I just stick with the original disks the brakes came with now, or at least stick with the shimano/magura/sram/hope disks rather than aftermarket ones.

While you’re playing about with alignment etc make sure you don’t space the caliper too far the other way so that the pads overhang the top of the rotor.

If you do and wear the pads far enough you can have the top of the pads touch each other before they squeeze the disc.

Not sure if I explained very well so I found a pic

Yeah, that's a whole world of wrong there.lol

Yup. Do you have any spacing washers between the caliper and the frame posts?

The SRAM/Avid Centreline rotors on my cargo bike donut really badly with my Magura brakes. Really need to swap to different rotors.

I forgot to say, if you do maybe remove some so the caliper is closer to the axle

Just take a file to the bits that overlap so they're and add a chamfer towards the backing plate so that the pad doesn't touch the edges/spokes. That should sort it.

Wavy discs are a bit frustrating in that the theory of wiping the surface clean probably has some merit but the bits that are constantly in touch with the disc surface wear more than those that aren't which causes the fluttering. I just file off the high spots and chamfer down as above whenever I feel it happening

Had exactly this recently. Could feel the rotor "spokes" shredding away at pads. Used a couple of washers to move whole brake out a couple of mm so that the overhang is on the smooth radius outside. But now get loads of squeal and drag.

@samunkim see my picture above as to why that’s a bad idea.

Is it not obvious to you chaps why the pad surface is curved. Like to the same degree as the section of rotor it's in (or supposed to be in) contact with..? 😀

Thanks all for your collective thoughts and experiences.

Singletrack forum is a great resource 🙂

Cheers + ride safe

My 2003 xtr rotors have thinned significantly at the spider arms, much more than the braking surface. If I CBA I'll upload a pic.

This is due to using any old calipers and pads with them.