Hayes Dominion A4 Brakes Mix High Power With Broad Modulation [Review]

Having squeezed Hayes motorcycle brakes on at least one occasion, and used their cable-actuated calipers on a cyclocross bike or two, I finally had the chance to check out their fully revamped mountain bike offering. The shortest conclusion: the Dominion A4 brakes are some of the most well made on the market, appropriately earning a place alongside top gravity stoppers.

Do you prefer the safe feel of lever modulation or a more precise on/off sensation in your mountain bike brakes? Having tested a load of bikes over the past couple of years, I have come to appreciate the benefits of both speed scrubbing methods. With one or two exceptions, most mountain bike braking systems fall close to one of these poles, and a lot of riders have an acquired preference.

The Dominion A4 brakes from Hayes are a 4-piston system that leans hard toward the modulation side of the game, though the power ramps up far more than some of the hyper-modulating competition. The levers offer a great deal of power between the point of initial pad contact and a fully locked rotor. If asked to compare them to another popular model, I would say that the SRAM Code RSC is the most similar feeling brake that I have tested. Both systems have an intentionally wide range of modulation, backed up by the appropriate caliper clamping power that gravity enthusiasts need to ride fast with confidence. The main difference is that I never once managed to pull the Dominion A4 levers to the handlebar on longer descents, which regularly happens with Guide brakes unless they are brand new.

Setup

Hayes Dominion A4 brakes
Dual bleed ports are located on the rear end of the caliper body.

Installing the Dominion A4 brakes is as quick and easy as any other, aided by the fact that I tested them on a bike with external brake routing. I had them bled and ready to burnish (bed-in) after about fifteen minutes of work. The brand’s clear installation video took all of the guesswork out of the process.

The calipers use a dual-port bleed system to more accurately clear the last bubbles of air lurking inside. This added a minute or so to the bleed process, and made for a crisp and solid feeling brake following the bleed. After a few months of use the brakes feel as good as the day I bled them. It will be a while before I need to bust out the DOT 5.1 fluid again.

Lever, caliper, and rotor specifications

Hayes Dominion A4 brakes
The shifter sits too close to the brake lever.

To start off where our hand does, the Dominion lever is exactly the same on either side, making the levers reversible when you loan your bike to someone who rides with their levers on opposite sides. This symmetrical lever design also allows riders to try riding with their front and rear levers on opposite sides before committing to a full hose swap and bleed. Identical lever bodies mean that you only need to purchase and pack one backup brake lever on race day; though it would take a spectacular collision to break these robust brakes. For riders with smaller hands, the levers are also available in a “Small Finger Lever” size.

The lever blade reach on the Dominions is adjustable with a gloved hand, via the round dial at the base of the lever. Pad contact adjustments can be made by turning the hex head that sits between the blade and the master cylinder body. Unlike some brakes from other brands, the pad contact adjustment on this model actually does something. I like my levers adjusted close to the bar, with the pads adjusted to contact as quickly as possible. I’m able to achieve this with the Dominion lever, and the brakes maintain their broad range of modulation following the pad contact.

Hayes Dominion A4 brakes
Reach adjustments are made with the black cylinder in the lever blade, while pad adjustments happen behind the lever.

The brake’s cozy ergonomic lever glides on ball bearings, and requires unnoticeable effort to pull with a single finder. The aluminum piston in the master cylinder is said to “operate smoothly across operating temperatures, and I can confirm, that’s not mere marketing copy. These are one of a small group of brakes I would recommend to folks who enjoy fast 20-30 minute descents. I have yet to experience arm pump or undue hand fatigue with this stopping setup, and the bite point is always in the same place when it’s time for a quick nose press.

My one criticism of the levers is that the PeaceMaker integrated shift mount for a Shimano shifter does not allow the shifter body to rotate far enough away from the lever. If you mount the brake levers relatively parallel with the ground for an optimal wrist angle while descending, the shift lever will remain tucked far under the handlebar at its most rearward adjustment. This is easily remedied by using a 22mm bar-clamp style shift lever that you can place anywhere, but it would be nice to see more gravity brake manufacturers consider this ergonomic element with their shift lever adapters.

Between the lever and caliper, a tough Kevlar-lined hose keeps the front and rear brakes performing with similar power. Down near the hub, a husky two-piece caliper houses four 17mm pistons in a burly bronze-colored carcass. If you plan to keep these brakes around for the long run, Hayes has created a helpful video to aid the eventual full caliper rebuild process. No matter how great a brake is, the pistons will eventually need to be cleaned and the seals replaced. With their lifetime leak-free warranty, owners will likely be stoked on this set of brakes through more than one bike build.

Hayes Dominion A4 brakes
These Crosshair grub screws on either mounting bolt help align the caliper.

In addition to their dual bleed port brilliance, the Dominion A4 calipers have a unique Crosshair alignment setup. The Crosshair system consists of a pair of grub-screws alongside the two main mounting bolts that can be turned in to set and refine caliper positioning. You can turn the grub screws slightly while pressing the caliper inward until the pads are evenly spaced on either side of the rotor. Then, maintaining pressure on the caliper, tighten the mounting screws and go ride.

At the sharp end of the system, Hayes has a 1.95mm thick set of D-Series 180 or 200mm rotors that they claim were designed to cancel out the resonant frequencies (squealing) that result in poor braking performance. I did manage to make the rear rotor squeal on a long descent in Finale Ligure, but a thorough rotor cleaning took care of that in short order. They have otherwise been silent and reliable. For optimal performance, Hayes recommends pairing the Dominion A4 brakes with their Semi Metallic T106 pads or Sintered T100 pads. I stuck with the sintered set throughout most of the test and was happy with their performance and wear characteristics.

Trail time

Hayes Dominion A4 brakes

While there is somewhat of a dichotomy between tack-sharp brakes and high-modulation models, this set could come close to satisfying all users’ slowing preferences. The best part of having all of that “high modulation” is that you can easily apply the desired amount of pressure without accidentally locking up the wheel. The trade-off is that those systems can require more hand strength to use, in some cases also leading riders to drag their brakes in order to stay closer to the power point. The benefit of a more on/off brake feel is that all of the brake’s slowing power is available with very little effort from your finger. Here the rub is that riders can grab too much power too easily, resulting in an unplanned skid or somersault.

The Dominions, alternatively, offer the same wide range modulation of the best high-modulation models on the market, with a precise and certain point of extreme braking power. The brake’s power progressively ramps up through the lever stroke in a predictable and confidence-inspiring manner. To top it off, their most powerful bite point doesn’t fade. This is where the real dichotomy between good and great gravity brakes lies. A well-designed brake shouldn’t fade (lose power) as it heats up on a descent. These 4-pistons provide dependable power every time you pull the lever in a way few other brakes can. There are stronger brakes out there, and there are models with even broader modulation, but I have yet to test a set that finds a useable balance between those characteristics like the Dominion A4 does.

Hayes Dominion A4 brakes

I have been working on braking technique this season, with a focus on braking less, dragging as little as possible, and trying to scrub speed before turns and features rather than in them. This focus is helping me ride faster and, particularly on this all-mountain Norco Torrent hardtail, to corner with additional control. Having dependable brakes is a key piece of that whole equation. These brakes didn’t take any time to grow accustomed to. With the angles and adjustments dialed to my liking, they felt comfortable and forgettable from the jump. Their power output is impressive, though not exaggerated, and my hands feel better for it.

When I first discussed testing the Dominions with the folks at Hayes they asked if I would want a 2-piston Dominion A2 in the rear, “since it’s a hardtail.” Prior to the Coronavirus pandemic, my plan was to race this bike in a few local enduros, so I opted for the full four cans front and rear. In hindsight, the massive power at the fork is likely sufficient. A 2-pot model out back would shave some weight, and these brakes are not the lightest to begin with. The other aspect worth considering is that it’s convenient to only pack a few sets of pads that will fit both the front and rear caliper, so in the end, I’m happy having eight pistons in total.

Hayes Dominion A4 brakes

The sturdy rotors have held up admirably, and both are about as true as they were when I bolted them on. I ran a 180mm out back and a 200mm on the front to make the wheelset compatible with my other bikes, though a pair of 180mm plates would have been sufficient. The braking surface is consistent, and despite contaminating the rear with a solid urban puddle splash they have worked flawlessly.

Conclusion

Gravity riders of all stripes will be stoked to squeeze these brakes. Their consistency is noteworthy, the bleed precision is second to none, and the cost is similar to any other high-end system. They are a little heavier than some, at roughly 310g, but like trustworthy tire casings, that heft is worth it when you don’t have to mess with them. Dominion A4 brakes sell for $229.99 (€235) each, and the D1 rotors retail at $49.99 (€51) at your local Hayes dealer or directly through the company website.

⭐️ Find the Hayes Dominion A4 brakes online at JensonUSA and Amazon.

We would like to thank Hayes for sending the Dominion A4 brakes along for testing and review.

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