Hope RX4 - Noisy

This won't help but

I have a set ( rx4+ if it makes any odds) on my cutthroat with hope floating rotors with the stock gravel pads - is that the reds ?

They are silent even in the wet.

I do have ultegras with ice techs on my propel. Unless it's been dry for about 3 weeks. They are noisy buggers.

I am running RX4s with shimano centre lock rotors and don't have a noise issue.

I’ve both RX4 and RX4+ both running on either XTR Ice Tech or Hope Floating - they’re silent in the dry, but after say 10mins in rain or very wet roads, the first application of the brakes will have them howling until cleared. I had Shimano XTR and R9170 callipers before this and they were exactly the same.

My RX4s used to be completely silent and now squeal badly in the wet. It's very odd.

My RX4s used to be completely silent and now squeal badly in the wet. It’s very odd.

My theory is road grime,oils and salts.

My cutthroat hasn't been exposed to that. My propel has exclusively and never sees mud to remove the contaminants

Agree with the above, but also check which Shimano rotor you have. Some of them are resin pad only and wear worryingly fast with stock Hope pads. I can’t remember about IceTech

IceTech are fine with sintered pads, it’s only the entry level rotors that are resin only.

My theory is road grime,oils and salts.

This - along with cold polishing of the pads from never getting hot enough

As we’re on an RX4 thread- anyone had to deal with one overactive piston?

I can’t for the life of me get my RX4 pistons balanced and it’s currently beating Juicy 3s as my ‘most pain in the neck brake ever’.

As far as I can tell:
-It’s bled. Or at least, it feels ‘tight’ when braking.
-The caliper is centred on the rotor.
-Three of the pistons behave as I would expect.
-The fourth advances very fast, making balancing the pistons tricky. Even if I get it balanced and running free in the stand, after a few miles and a bit of braking it over-advances leaving the pad canted in and dragging on the rotor- badly enough that lifting the bike and spinning the wheel rarely gets more than a rotation or more.

I’ve been round the setup loop several times and been out for a few hour-or-so rides to see if it’ll bed it in, but it doesn’t seem to take. Any suggestions?

This – along with cold polishing of the pads from never getting hot enough

And I don't think road discs ever get PROPERLY bedded in, not in the same way that a long off-road descent hard on the brakes can bed a rotor in. Someone did a good write up somewhere, the '20 hard stops' process just mates the pads to the rotor, you then need a much more prolonged period of braking to deposit the later of pad material ('burnishing' the rotor).

That being said I swapped my MTB rotors onto my gravel bike have properly cooked them in the Cairngorms and they squealed just as badly despite using same brand/compound pad, so that theory might be bunk.

Yep mine really squeal when either not warmed up or wet. Decided it means I’m unlikely to run over a granny/dog/small child. Thing is I really like the braking power so prepared to live with it.

swanny853
Full Member
As we’re on an RX4 thread- anyone had to deal with one overactive piston?

I can’t for the life of me get my RX4 pistons balanced and it’s currently beating Juicy 3s as my ‘most pain in the neck brake ever’.

As far as I can tell:
-It’s bled. Or at least, it feels ‘tight’ when braking.
-The caliper is centred on the rotor.
-Three of the pistons behave as I would expect.
-The fourth advances very fast, making balancing the pistons tricky. Even if I get it balanced and running free in the stand, after a few miles and a bit of braking it over-advances leaving the pad canted in and dragging on the rotor- badly enough that lifting the bike and spinning the wheel rarely gets more than a rotation or more.

I’ve been round the setup loop several times and been out for a few hour-or-so rides to see if it’ll bed it in, but it doesn’t seem to take. Any suggestions?

You could try lubing the pistons to help free them up. Hope recommend Hunter Silicone Lube.

Pump each piston out in tern, lube it, push it back in and repeat.

That being said I swapped my MTB rotors onto my gravel bike have properly cooked them in the Cairngorms and they squealed just as badly despite using same brand/compound pad, so that theory might be bunk

Did you clean em first ?

Find a hill and brake down it, drag the brakes until they they go silent, it's also good to give them a few harder pulls. Douse the rotor and pads in cold water. Repeat the whole process a few times until the brakes are biting with ease. That should help. But this will need to be done fairly regularly if you live in a flatish area as the brakes won't have chance to clear the dirt and grime from the road etc.

Another thing I've noticed is that my front brake (RX4 caliper) doesn't have the initial bite and is noisier than the rear brake (Shimano GRX caliper).
But this is probably because the RX4 is four pot and the GRX is 2 pot.

I was out on my cross bike yesterday in wet snow and needed to slightly drag my brakes on descents just to clear the water and to keep some heat in the pads and rotors.
Cold and wet are the worst type of scenario for disc brakes IME.

For the amount of threads we have on noisy brakes, maybe there needs to be a super abrasive type of brake pad (or maybe a dual compound?) for the folk that don't ride alpine descents in the summer.

Did you clean em first

Probably, I'm usually pretty methodical in my endless quest for quiet brakes! 😂

I was optimistic as had been out on MTB last winter in slushy snow melt conditions and brakes were silent for the whole ride. Swapped rotors over to gravel bike and they were loud again.

Used same Swissstop yellow pads on each bike, Deore hydraulic on MTB, TRP Spyre on gravel bike. Wondered if pad shape might have had something to do with it.

maybe there needs to be a super abrasive type of brake pad

If the squeal comes from a stick-slipping pad vibrating against a wet rotor, then I think you would either need to secure the pad to the piston somehow to stop it vibrating, or maybe a longer pad (4 pot callipers?) that vibrated less easily? That's what drew me to an RX4 thread as I wondered if the design might make them less noisy ☹️

Most quiet brakes I have are cheap Magura with Decathlon pads on unbranded rotors. 🤷‍♂️

You could try lubing the pistons to help free them up.

That’s a possible next on the list but given I can push the pistons back with my fingers it didn’t seem like a high priority to be honest.

Douse the rotor and pads in cold water.

This is not a great idea - thermal shock.  Its not needed as a part of bedding in.  Bedding in is 3 things.  conforming the pad to the disc, curing the pad via heat and pressure and depositing a microscopic layer of pad material on the disc

maybe there needs to be a super abrasive type of brakepad

Disc brakes work mainly on adherent friction not abrasive friction although all are a mix of both but its in abrasive friction that you get the rapid wear and adherent friction that you get the smooth sustained braking

Squeal is a result of the pad gripping and slipping in a very rapid cycle.  Contamination is the usual culprit.  Some frames and forks amplify it

And I don’t think road discs ever get PROPERLY bedded in, not in the same way that a long off-road descent hard on the brakes can bed a rotor in.

In theory you should be able to get them hotter in normal riding.
Higher speeds, more traction and essentially the same system weight.

I know i've got to the point i can smell burning "stuff" from my road discs several times. That's just riding round the lanes near me.

Worth checking there's no fluid leaking out from the pistons - recently encountered two brand new RX4+ callipers with leaky pistons!