Changed brake pads last weekend on my Guide RS brakes.

Was previously on kool-stop organic pads which were very good, but following perceived wisdom I thought I should fit SRAM original sintered pads, so did so before rides last weekend. 😒

Even though i followed the same bedding in procedure I have been using for years, these pads just kept getting worse at both ends. Howling at slow speeds, really howling when hot after a big descent, horrific turkey gobble and resulting severe flutter from front forks, and just a general lack of braking power.

Things came to a head yesterday, the fork flutter (that word doesn’t do justice to the severity) was incredibly bad. Also realised during the ride that the forks had also lost air.

A quick bit of googling suggested that it may be air escaping into the lowers, perhaps due to the flutter. Zip tie in the wiper seal followed by hiss confirmed that air was escaping, but I could only suspect the cause.

Rummaged about in the bike cellar bin to find the 4 old pads I had taken out previously. Found 2 that were least worn, quick IPA wipe, then put them in the front (I’ve got more pads on the way, but needed a solution pronto at least for the front). Rode hard and fast today with no problems, good braking power (from the front at least).

Most importantly, no more flutter, and no more loss of air. Whoda thunk? 😆

Some tyre / brake disc / spoke / rim / fork / headset combinations have quite low resonance frequencies.

Normally no problem.

Only problem if you exite these frequencies – then you have the fork flutter as described…

Biggest source of exitation: brake pad / brake disc

If this “combination” falls into the range of above resonance: big problem!

Your sintered pads on your brake disc cause “howling”?

So: the pads alone might be good and won’t cause issues on other bikes.

But for your tyre / brake disc / spoke / rim / fork / headset combination these more expensive brake pads are bad…

Proposal: after such fork flutter events check headset and spokes!

And: you might try other brake discs. If the ones you use right now appear to be “stiff” in pitch direction user softer ones. If the appear to be soft use stiffer ones. With this strategy you are able to tune the resonance frequency a bit.

Also here: the price tag of the disc doesn’t matter. It’s just the stiffness you have to tweak. The cheaper ones might be stiffer?

Good points cheers! Had checked headset, was OK, but will also checked spokes.

I am sure the pads can be good for someone else, it really was a most violent flutter that started like the old avid ‘turkey gobble’. It is remarkable that this was so severe it resulted in the air loss from the air spring.

Good news is that with Kool Stop organics, everything seems fine.

I’ve not really thought about ‘stiff’ Vs ‘soft’ discs, do you mean that there is a varying level of ‘give’ engineered into different types of brake disc? (Like, standard Shimano disc Vs Hope floating rotors?)

I

What IPA are you using on your pads? The Fintry Inn has a wonderful one on tap at the moment that makes me ‘turkey gobble’ on the climb back out of the place.

Hope builds the rotors pretty stiff.

Example of rotational soft rotors: Magura Storm

These two design approaches guide to different resonance frequencies.

But those resonance frequencies depend onto the whole “system” tyre / brake disc / spoke / rim / fork / headset… and maybe even the frame.

In other words: one rotor (or pad type) might be not better than the other. Only in connection with the complete system problems might show up.

If so: you can start “swapping” parts. And in fact – with the pads you did that already.

Low cost part you are able to change / play with / tune the stiffness: the discs / rotors.

Fork flutter: you are right. Severe stuff. You can’t ignore it. Or you endanger the frame and fork and wheels…

Funny so: most bike manufacturers don’t have any money to “test” this. Means: we are the testers…

You seem to know a lot about what brake and fork manufacturers can and can not “test”.

edit – oh, you said bike manufacturers.

so fork flutter causes air to come out of forks….

how ever tracking the ground and impacts as it rides along , heavy landing off jumps , basically any non compressive load doesnt cause this ?

are your fork bushes ok ?

I had the “Flutter Effect” you describe several years ago when using an LX calliper on a (old 32mm version) boxxer, I assumed it was due to the Bushes being on their way out and/or my insistence on having almost no low speed damping, after taking the bike apart I noticed the seals on the disc side seemed to be leaking, and so and the fork has sat unused in the garage ever since (a good couple of years), a resonate frequency interaction between the brake/fork/wheel never occurred to me as a possible root cause…

I do keep thinking that if I just recommission those boxxers with fresh seals and bushes, find a cheap bouncy 26″ frame and a few other parts I could lash together some sort of retro, uplift day hack machine…
This thread has oddly made me think about renewing the idea again, so long as I use different brakes next time…

Hmmmm.

I find a Double IPA hits the spot nicely 🙂

trail_rat – I can only reflect my experiences. Wiper seals and o rings all replaced recently. Flutter really doesn’t cover it, it was really bad with those pads.

So, new pads, horrific flutter, fork loses air into lowers (first time any of these things has ever happened).

Old pads back in, usual smooth strong braking, forks no longer lose air. Both situations with usual riding.

I can feel suspicious cat’s eyes boring into me! 😆

My better half had a Merida with the same problem. The frame, combined with the Recon Fork and Hayes brakes generated horrible ‘flutter’ or vibration. tried a few remedies including facing the mounts etc. But in the end changing out any one of the brake/fork/frame solved it. All the components on different bikes were fine. Impossible to test every frame/fork/brake/rotor combo in the lab.

I had a 180mm rotor on the front, one of the Shimano ones marked ‘organic pads only’ however I was using sintered pads.  It fluttered on hard braking, albeit mildly.  Switched to some 160mm discs suitable for sintered, and it went away.