Hope RX4 road disc caliper review

Hope's aftermarket disc calipers promise to increase braking performance beyond comparison

Hope RX4 road caliper
Cycling Weekly Verdict

It's not often you can purchase an upgrade that makes a genuinely massive difference to the performance of your bike. But with Hope's RX4 disc calipers I can honestly say that you will wonder why you ever put up with sub par braking performance. There really is nothing to fault with the RX4 - it will fit almost every disc brake frame and fork, is more powerful and offers better modulation than any other brake and is almost jewel like in its build quality and looks.

Reasons to buy
  • +

    Phenomenal power

  • +

    Superb lever feel

  • +

    Build quality

  • +


Reasons to avoid
  • -

    Needs to be fitted by a competent and experienced home mechanic or bike shop

You can trust Cycling Weekly. Our team of experts put in hard miles testing cycling tech and will always share honest, unbiased advice to help you choose. Find out more about how we test.

The Hope RX4 disc brake calipers were selected for an Editor's Choice award in 2020. This year's list contains 78 items which scored a 9 or 10/10 with our tech team - this gear is the best of the best, and has received the Cycling Weekly stamp of approval. 

Hope RX4 disc brake calipers are intended as an aftermarket upgrade to improve braking performance on all all road and gravel bikes that currently use hydraulic disc brakes manufactured by Shimano, SRAM and Campagnolo.

The upsurge in disc brake use amongst road and gravel bikes has opened the eyes of a whole generation of riders into the advantages of this style of braking. More powerful all-weather and therefore safer braking is now available across the board, to the extent that there really is no reason not to go for disc brakes.

However one thing I have noticed over testing countless disc brake equipped bikes is that performance can in reality be wildly inconsistent, even with identical set ups. There are plenty of reasons why this might be the case; hose routing, air in the system, pad compound or even brake set up can all have an impact. In all honesty I've probably had just a handful that I've been really happy with in terms of performance. So what do you do if you want the best performing disc brakes? Well, it seems you could just fit the Hope RX4.

Hope RX4 road disc caliper

The Hope RX4 road disc caliper was selected for an Editor's Choice award in 2020. This year's list contains 77 items which scored a 9 or 10/10 with our tech team - this gear is the best of the best, and has received the Cycling Weekly stamp of approval. 

Hope knows a thing or two about disc brakes. It has been making them in its Barnoldswick facility for over twenty five years and has built up a phenomenal reputation within the mountain bike world.

The RX4 is its first road and gravel specific disc caliper and Hope has managed to inject all of its expertise into these little lumps of machined aluminium.

The first thing you will notice is Hope has opted for a four piston design for the caliper rather than the usual two pistons that most stock road brake calipers use. Utilising four pistons provides far better brake performance for a couple of reasons. Firstly having two pistons on each side of the caliper increases the contact area with the pad, providing more powerful braking for the same amount of lever throw/hydraulic pressure. Secondly four pistons increase the area over which the hydraulic fluid is dispersed which in turn increases brake modulation (the ability to accurately control the force of the brake applied to the rotor).

The best disc brake wheels for road bike 2020

The second important design feature that sets the RX4 apart is its monobloc construction. Most stock calipers are made from two separate halves that are then bolted or bonded together to create a single unit whereas Hope machine the entire caliper out of a single billet of aluminium, creating a much stiffer and lighter unit. This also improves performance as the stiffer construction resists any flex, expansion or twisting that can cause brake pad rub or a vague lever feel.

The RX4 is designed to work with your existing shifters (as long as you already have hydraulic brakes) and comes in either Shimano/Campagnolo or SRAM compatible configuration owing to the differing hydraulic fluids each use.

I opted to use the Shimano compatible RX4 in conjuction with a set of Shimano GRX RX810 levers to fit to my Kinesis Tripster ATR.V3 gravel bike. The RX4 is also available in both post mount and the most recent flat mount standard to fit the majority of disc brake compatible frame and forks past and present. The flat mount RX4s have different shaping for front or rear use whilst the post mount version is universal. Like all of Hope's components the RX4 is available in a multitude of anodised colours, I opted for purple because well, purple is the ultimate 90's cycling colour and my favourite.

Since the RX4 only comes as a caliper you will need to set up the brake yourself, or get it fitted by your local bike shop. Hope supply comprehensive instructions that are really easy to follow and each brake comes with all the olives and other fittings necessary to attach it to the brake hose as well as both organic and sintered pads. You will also need the correct bleed kit for your chosen lever system and a bottle of associated hydraulic oil; mineral oil for Shimano, DOT oil for SRAM.

The fitting process is relatively time consuming to do it properly as you will need to repeatedly bleed the system to ensure no air is trapped behind any of the pistons. If you can, complete the setup whilst the brake is off the bike as it will make it easier to work on, however with internal routing being favoured on many frames you might not get the choice.

The one piece of advice I would give anyone is to not try and take a shortcut, follow all the steps and repeat as necessary. This way the brake will perform optimally. One additional trick I employed was to pull the levers and zip tie them overnight with the calipers off the frame. This ensured any residual air bubbles were easy to get rid of as they end up rising to the lever. I finished off with a repeat bleed and each has been completely reliable since.

Why do disc brakes squeal?

The final part of the set up is ensuring the caliper is aligned with the disc rotor and doesn't rub. This can often be a incredibly tricky task in order to eliminate any pad rub but the RX4's four piston design enables the pads to sit a little further away enabling a rub free setup to be achieved pretty simply. The RX4 comes without rotors so you will have to factor in this as an additional cost (although you can use your existing rotors). Hope recommend the use of its own rotors and I have been using its Road 6 bolt rotors (£50 each)to great effect, although I have also experienced very little down turn in performance whilst using both Shimano and Tektro rotors.

Which brings us on to the performance.

The first thing I noticed was just how good the modularion is. You can lightly tickle the brakes to make minor adjustments to your speed but as soon as you pull the lever further there is a really progressive ramp up in both braking power and lever feel. It doesn't feel wooden or dead and lacks the 'on-or-off' feel of some set ups yet also doesn't feel too spongy - it's just right.

(Image credit: Daniel Gould)

The ultimate braking force also comes into play before the lever gets too close to the bar and because of the power and the way the brake actuates full power can be achieved with a single finger, even on the hoods. It also achieves this performance with the minimum of fuss and so far has been completely silent with none of the dreaded squealing that can plague other brakes.

Thank you for reading 20 articles this month* Join now for unlimited access

Enjoy your first month for just £1 / $1 / €1

*Read 5 free articles per month without a subscription

Join now for unlimited access

Try first month for just £1 / $1 / €1