Hope’s road-gravel brake calipers are a good example of a component that looks small on paper but changes how a bike feels every time the road turns rough or the descent gets long. In this article I’m breaking down what the current RX4 family actually is, how it fits different lever and frame standards, what you can realistically expect on the trail or road, and when it makes sense to spend the money on a premium brake upgrade.
What Hope’s current road-gravel calipers are best at
- The original RX4 has been superseded, so the current conversation is really about the RX4+ and RX4+SL versions.
- Compatibility depends on both the lever family and the fluid type: Shimano and Campagnolo use mineral oil, SRAM uses DOT.
- The upgrade is mostly about better modulation, stiffer feel, and cleaner fitment, not a miracle jump in outright stopping power.
- Hope currently lists the RX4+SL PM at £115 ex tax, which puts it in premium territory.
- For UK riders dealing with wet roads, grit, and winter muck, the serviceable design is part of the appeal.
Why Hope revised the RX4 family
The original Hope RX4 made sense in a very specific moment: road and gravel bikes were moving to hydraulic discs, but the available calipers often felt like a compromise. Hope’s answer was a compact four-piston road caliper with the brand’s usual emphasis on machining quality, rebuildability, and feel. The problem is that bike standards did not stand still, and Hope’s own documentation makes it clear that newer mount patterns and frame clearances pushed the design beyond what the first version could do comfortably.
That is why the current story is no longer just about the old caliper. Hope says the RX4+ superseded the RX4, and the newer RX4+SL adds a slimmer body, updated bleed hardware, and broader fitment. In plain English, the family has moved from “good caliper” to “good caliper that is easier to live with on modern frames.” That shift matters because on a road or gravel bike the brake is only as good as its match to the lever, rotor, and frame it sits on.
| Version | What it means | Why it matters |
|---|---|---|
| Original RX4 | Older four-piston road/gravel caliper with narrower fitment assumptions | Still relevant on existing bikes, but less flexible on newer frames and mounts |
| RX4+ | Redesigned replacement with a monobloc CNC body | Stiffer feel, better modulation, and broader compatibility planning |
| RX4+SL | Slimline current version with updated bleed and bore-cap design | Better frame clearance and the cleanest fit for new builds |
That is the big picture. Once you understand the naming, the next question is the one that actually decides the purchase: will it fit your bike without becoming a headache?
Compatibility is where most people get it wrong
The caliper family is designed around drop-bar hydraulic systems, but the fluid and lever matching is not interchangeable. Hope’s current pages split the product into Shimano-compatible mineral-oil versions, Campagnolo-compatible mineral-oil versions, and SRAM-compatible DOT versions. I would treat that as a hard rule, not a suggestion. If the fluid type does not match the lever system, the brake is the wrong choice.
| Setup | Fluid type | What I would check before ordering |
|---|---|---|
| Shimano GRX, Dura-Ace, Ultegra, 105 Di2 | Mineral oil | Match the RX4+ mineral version and confirm rotor size |
| Campagnolo Ekar, H11, Record, Super Record | Mineral oil | Use the Campagnolo-friendly version and verify mount style |
| SRAM Red, Force, Rival, Apex, S900 | DOT fluid | Order the DOT version only, and keep the rest of the system DOT |
| Frame or fork mount standard | Depends on the brake version | Check flat mount, post mount, or the +20 direct-fit option |
The mount standard matters just as much as the lever brand. Hope’s current RX4+SL documentation covers flat mount, post mount, and flat-mount +20 variants, which is exactly the sort of detail that saves you from buying an expensive part that needs adapters or does not clear the frame. The current slimline version is also designed for 140, 160, and 180 mm rotors, but the exact choice still depends on your frame, fork, and whether you are fitting front or rear. In other words, the caliper is not the whole answer; it is the last piece of a fitment puzzle.
That leads straight into the practical question riders usually care about next: once the system is matched properly, how does it actually feel on the bike?
What it feels like on the road and on rougher ground
What I like about this kind of brake is that it usually reveals itself in control before it reveals itself in raw power. The best tests I have seen and the experiences I trust most point in the same direction: the RX4 family is about a more confidence-inspiring lever, cleaner modulation, and a calmer feel under load. BikeRadar’s test of the RX4+ found strong fine control and stable performance in wet gravel conditions, while a long-term Singletrack review of the older RX4 suggested the gains were real but subtle, with the bigger difference coming from feel, quietness, and serviceability rather than a dramatic jump in stopping distance.
That is how I would frame it for a UK rider. If your lanes are wet, your winter rides pick up grit, and your descents are long enough to expose any flex or fade, a stiffer monobloc caliper can make the bike feel more settled. The main benefit is not “more brake” in a dramatic sense. It is more predictable brake. That matters because predictability saves energy on technical descents and makes it easier to brake later without second-guessing the lever.
There are limits, though. If your current setup is badly bled, the rotor is undersized, or the pads are cheap and contaminated, a premium caliper will not magically fix the bike. In those cases the upgrade you notice most may come from a better bleed or a larger rotor, not the caliper body itself. That is why setup deserves its own section.
Setup details that matter more than marketing claims
Hope is refreshingly honest about one part of ownership: bleeding is not the lightest-touch job in the world. The current RX4+SL pages point to a new bleed nipple design and provide dedicated instructions, and that is useful because clean bleeding is part of why these brakes feel so good when they are working properly. If I were fitting one for a rider who does not already bleed brakes at home, I would not rush the job. I would either use the right kit carefully or hand it to a good shop.
Bleeding is the part worth respecting
A good bleed is not just about lever feel at the stand. It decides whether the brake stays consistent on a long descent. A rushed bleed can leave you with a spongy lever, inconsistent bite point, or a caliper that feels good for ten minutes and then becomes vague once the pads heat up. Hope includes the relevant instructions and a specific syringe for the system, which tells me the brand expects riders to treat the process properly rather than improvise.
Read Also: Hope E4 Brakes - Optimize Your Trail & All-Mountain Ride
Pad and rotor choice are not afterthoughts
I also pay close attention to pad bedding and rotor condition. A well-fitted caliper with dirty rotors or unbedded pads will still sound rough and feel weaker than it should. On the other hand, the right pad compound and a clean, straight rotor often produce a bigger improvement than people expect. If the bike is a gravel build that sees winter use, I would lean toward a setup that favours consistency and wet-weather bite over chasing the lightest possible part count.
- Confirm the lever family and fluid type before ordering.
- Check whether your frame or fork needs a direct-fit, post-mount, or +20 option.
- Choose rotor size first, then caliper version, not the other way around.
- Bedding the pads in properly is non-negotiable.
- Inspect mount faces and rotor true before blaming the brake for rub.
Once those details are right, the brake starts to show what Hope built it for: a clean lever feel and a controllable, confidence-heavy response instead of a vague hydraulic squeeze. From there, the next decision is whether the cost makes sense compared with other upgrades.
Which version makes sense for your bike in 2026
Hope currently lists the RX4+SL PM at £115 ex tax, so this is not a casual spend. I would not put it in the same category as an ordinary service item, and I would not buy it just because it looks good in the stand. I would buy it if I wanted a premium brake that I could match cleanly to a modern drop-bar build and maintain for years. That is where Hope tends to earn its keep.
| Rider or bike type | Best fit | Why |
|---|---|---|
| New Shimano GRX gravel build | RX4+SL mineral version | Clean match to lever family, good clearance, strong wet-weather feel |
| Campagnolo road or gravel bike | RX4+SL mineral version | Proper lever-fluid pairing and a premium finish |
| SRAM AXS drop-bar bike | RX4+SL DOT version | Keeps the fluid system consistent and avoids compatibility mistakes |
| Existing bike with decent OEM brakes | Maybe not first choice | A better rotor or pad upgrade may deliver more value per pound |
My own rule is simple: if the bike already has a good brake system and the issue is mainly power, I look at rotor size first. If the issue is feel, rub, serviceability, or I want a brake that I can live with through UK winters, the Hope option starts to look much stronger. That balance between cost and ownership is what separates a smart upgrade from an expensive vanity part.
The checks I would make before ordering one in the UK
Before I buy, I always run through five checks. First, I confirm the lever family and fluid type so I do not mix mineral oil and DOT by accident. Second, I check whether the frame or fork wants flat mount, post mount, or a direct +20 arrangement. Third, I decide on rotor size before I touch the caliper order, because a 180 mm rotor can be a more sensible gain than a new body in the wrong size. Fourth, I budget for pads and bleeding tools if I am doing the work at home. Fifth, I make sure I can get spares easily, because a premium brake only stays premium if maintenance is easy.
That is the practical case for Hope’s RX4 family: strong control, broad modern compatibility, and the kind of rebuildable ownership that makes more sense the longer you keep the bike. If I were building a serious gravel bike in the UK, I would put it near the top of the list, but only after checking the mount standard, fluid type, and rotor plan with the same care I would give a drivetrain choice.
