Disc brake compatibilty question

[aflook]

Hello everyone.
I would be grateful for yuour collective wisdom. I am having a bike built by Stanforth and Simon has emailed me "We've been having problems with the GRX and Hope calipers - when I say we it's my hydraulic brake expert who does all my hydraulic brakes - he's spent yesterday afternoon and all day so far today trying to set them up with a few issues. He thought he was finally there until the GRX seal popped...

What we know will work are Shimano XT hydraulic calipers so I recommend we use those. I'll also order a new GRX lever...".

I wanted Hope calipers for their reputaion for reliability and I'm not sure what went wrong. Could it be related to the GRX cross-top lvers? I would go with Simon's recommendation but Shimano brakes have had a poor reputation. Is this now old news? Would XTR be more reliable? I think the calipers he mentions are two piston, is this going to powerful enough for a steep descent with 20kg of camping gear on the back? (I weigh 74kg). I have come across offerings from Magura and Formula, are these worth pursuing?

Thanks in advance for your thoughts
Adrian

[PH]

I'm a little surprised that they were trying to match Hope and Shimano, I thought one used exclusively DOT brake fluid and the other mineral, though it may have changed since I was last looking for brakes.
I didn't know Shimano brakes had a reputation for unreliability, I thought it was just the opposite, mine have been great. Any Shimano caliper will be more than capable of your requirements, but I think the current XT are four pot. That wouldn't be my choice, extra pistons is extra maintenance regardless of make. If you're using GRX levers isn't the obvious choice GRX calipers? However if they know what works, trust that.

[rareposter]

I'm a little surprised that they were trying to match Hope and Shimano, I thought one used exclusively DOT brake fluid and the other mineral, though it may have changed since I was last looking for brakes.

Hope make calipers compatible with both DOT and mineral oil. Their systems use DOT but they know that people, especially for gravel, will mix and match all sorts of stuff.

I assume the builders were using the correct caliper...?

Honestly though, the simple option if you're using GRX levers is to fit GRX calipers. I've never heard of any unreliability issues - mine are faultless, as are the Shimano disc brakes on my road and mountain bikes.

[aflook]

Thank you both for those thoughts. The Hope are available as either mineral or DOT, btw. Yes, my thought was GRX but they’re exclusively flat mount. Cura seem to be recommended. But I’m happy to be corrected about Shimano reliability.
Cheers
Adrian

[Stevek76]

Think there's been some issues with pistons shattering. However there's possibly been the common issue that if eg both Shimano and hope have 0.01% failure rates then we're going to see far more Shimano problems reported.

As far as the calipers go, two and four piston options exist for all 4 tiers from deore up to xtr. I have the 4 piston slx on my mtb and they're very strong. Sufficiently so that I tend to glaze the brake pads over time on my local trails from not braking aggressively enough...

[aflook]

Think there's been some issues with pistons shattering. However there's possibly been the common issue that if eg both Shimano and hope have 0.01% failure rates then we're going to see far more Shimano problems reported.

Good point about relative numbers. What I’ve read about is Shimano showing inconsistencies in the bite point. As I have no experience to date of hydraulics I don’t know how significant this is.
Good to know about the 4 piston options.

[rareposter]

Yes, my thought was GRX but they’re exclusively flat mount.

Check to see if you can get some adaptors. I fitted flat mount calipers to my post mount frame when I swapped to GRX.

It's the kind of thing you'll probably have to ask for rather than searching through online retailers because there are countless options out there for all manner of frame mounts converting to all manner of caliper mounts!

[Stevek76]

Interesting, that's not something I've noticed on mine in normal operation.

They are a bit tricky to get a perfect bleed on and if you don't have that then inverting the bike eg to get the wheels off for transport, can get air in the lines which can result in spongy brake feel until the air is back up in the reservoir.

I was aware that at least for the mtb setups Shimano brakes were thought to have sharper bite points than eg SRAM's. There's an element of personal preference here and also just what people are used to.

Which is one thing to note if this is your first bike with hydraulics. The brakes are likely to feel very light and sharp regardless of brand compared to cables so possibly be careful until you get used to that, if you grab a fist full of brakes cable style strength you're probably taking a trip over the bars

[TheBomber]

Yes, my thought was GRX but they’re exclusively flat mount.

From this I’m guessing your frame is post mount - in which case post to flat adapters are now available that should work for many setups:

https://www.sjscycles.co.uk/brakes/cinq ... m-caliper/

[slowster]

Post mounts and IS mounts on the chainstay often necessitate a curve at the base of the seatstay to provide sufficient space for the caliper. One of the reasons for the flat mount standard is that it allows conventional straight seatstays.

A consequence of this is that clearance may be very tight/insufficient when a post mount caliper is fitted to a flat mount frame. This can be seen in the photograph below: if the seat tube of that frame were much smaller, resulting in a smaller angle between seatstay and chainstay, the post mount caliper would foul the seatstay. That particular frame is a pre-production medium Singular Peregrine, which has a horizontal top tube. Obviously an equivalent sized frame with a sloping top tube will have a correspondingly smaller seat stay to chain stay angle.

[aflook]

Thank you Rareposter and TheBomber but I think I would rather avoid adapters unless there’s a very good reason to go for grx over xt or xtr. It makes sense that the bleeding is at fault for the inconsistencies. I’ll just have to learn proper maintenance before I go any distance. And I will take special care with the increased power having recently come off over the bars when I hit a huge hole.

[aflook]

Post mounts and IS mounts on the chainstay often necessitate a curve at the base of the seatstay to provide sufficient space for the caliper. One of the reasons for the flat mount standard is that it allows conventional straight seatstays.

A consequence of this is that clearance may be very tight/insufficient when a post mount caliper is fitted to a flat mount frame. This can be seen in the photograph below: if the seat tube of that frame were much smaller, resulting in a smaller angle between seatstay and chainstay, the post mount caliper would foul the seatstay. That particular frame is a pre-production medium Singular Peregrine, which has a horizontal top tube. Obviously an equivalent sized frame with a sloping top tube will have a correspondingly smaller seat stay to chain stay angle.

Thanks Slowster it’s a post-mount frame.

[rareposter]

Thank you Rareposter and TheBomber but I think I would rather avoid adapters unless there’s a very good reason to go for grx over xt or xtr.

To all intents and purposes, the calipers are exactly the same.

Shimano are trying to move to a marginally more integrated and compatible set-up where (for example) the same set of calipers is used across 2 or 3 different "levels" of groupset.

[aflook]

Thanks again to everyone for your help and advice. Just to close the thread, I have asked Stanforth to go ahead with the XT calipers, preferably 4 piston.

Now I can't wait to get to the Alps next year!

Cheers
Adrian