Hayes’ Dominion A4 takes everything we liked about the two-piston A2 brake and distils it into a gravity-riding package. With that in mind, it gets all of the neat bleeding features but significantly ups the power, making it a dark horse contender in the best mountain bike brake category. Although, its dead stroke isn’t as short as promised and its bite point adjuster is redundant.
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Hayes Dominon A4 - Technical details
Back in September last year we tested the two-piston Dominion A2 and praised it for its easy bleeding, and alignment as well as its decent overall power. The A4 version not only doubles the number of pistons and uses larger pads to boost power, but also gets fatter levers to make the brakes more comfortable to use during extended descents.
It gets the two-stroke dual-port bleed system that allows the brake’s lever and cold-forged caliper to be bled independently. There’s also the brand’s Kingpin pad retention bolt that’s said to add strength to the caliper - it uses Hayes’ very cool but very simple Crosshair caliper alignment screws.
The lever is built with what’s dubbed as LOFI which is said to be a low-effort system but with a predictable and progressive ramp-up along with a crisp bite point. The lever benefits from a cartridge bearing and a glide ring on the piston in a bid to achieve a super smooth lever pull. The brake is factory-set to have the lowest dead stroke possible.
Wrapping up the brake is that the pistons are made from metal for durability and greater heat dissipation and the lever’s reach is adjustable via a dial built into the lever.
Running on DOT 5.1 fluid, strengthy Kevlar hoses connect the lever and caliper.
Hayes Dominion A4 - Installation and bleeding
Thanks to both the Crosshair adjustment system and Two-Stroke Dual-Port bleed system, the Dominion A4 is probably the easiest brake to install and adjust towards a problem-free setup. There are more steps in the process, but they’re well worth doing to achieve an incredibly thorough bleed, but also to align the caliper as accurately as possible.
First off, the Two-Stroke bleeding uses a two-step process. You’ll bleed your brake exactly the same as how you would a SRAM and Magura brakes but once that’s done, you open up the second port on the caliper to bleed that part of the brake completely separately to the lever.
This is something that no other brake on the market does, and this results in a thorough bleed that’s very easy to achieve, without much extra effort at all.
There’s that Crosshair adjustment which is a bit of a marvel. It allows for fine adjustments of the caliper without having to loosen and tighten bolts to ensure no rubbing against the rotor.
Crosshair does this by employing a pair of grub screws that slowly push the caliper against its bolts, which are only just tight enough to keep the caliper from freely wiggling about. Again, this is yet another step towards installation but it makes it incredibly easy to set the Dominion A4 up perfectly.
Hayes Dominion A4 - Performance
As with the Dominion A2, I really gelled with the A4’s lever feel but, because it’s fatter, it’s a lot more comfortable as pressure is spread more evenly onto the finger and much less fatiguing during hard braking.
The curvature of the lever blade is equally as great, too. It’s of a similar shape to Shimano’s and TRP’s levers but it’s not quite as aggressively angled. The indent dots provide a great level of grip, too.
It’s not just about the shape of the lever that results in the Dominion A4’s stellar lever feel though as Hayes’ efforts to add a cartridge bearing and the LOFI system make the lever’s pull incredibly smooth. The smoothness aids modulation past the pad bite point, making small adjustments in braking power easy to pull off.
Though with the bite point adjustment screwed all the way in, I found that there’s a lot of free play before the pads make contact. But I quickly learned to work around this and became quite fond of way it operates.
On the subject of brake lever adjustments, the Dominion A4 makes tweaking the reach as easy as it gets. There’s a tactile dial on the lever which you can spin to find the perfect spot. It’s quick, simple and requires no tools. The bite point adjustment is the very opposite, which is a shame. It requires a small 2.5mm Allen key and it’s not in the most easy-to-reach place in the world. But this adjustment doesn’t do an awful lot and, with the lever having so much free stroke, this doesn’t need to be touched.
The lever’s feel in action is similar to Shimano but power doesn’t set in quite as instantaneously. There’s a decent range of modulation with plenty of power and the pads are pretty large compared to other four-piston offerings. All of that power is easy to modulate, too, which helps massively in retaining grip when pushing down steeper, more brake-intensive sections.
However, the Dominion A4 brakes get very hot and noticeably more so than competing units. On my favourite UK trails, I didn’t notice much of a negative effect but if your descents get particularly lengthy you might experience some fade.
Hayes Dominion A4 - Verdict
The Hayes Dominion A4’s £200 price tag places it in line with Hope’s Tech 4 E4, Shimano’s XT four-pot and the SRAM Code RS brakes. Out of all of those, I think that the Dominion has impressed the most thanks to its excellent power and modulation, as well as its ease of setup. That’s without touching on its mega-comfy lever.
The Shimano XT four-pot comes in at £200 and performance is similar, but the Dominion offers more modulation, which many will appreciate.
It doesn’t quite match the build quality of the Hope Tech 4 E4 but the Dominion is much less finicky to install. It gets the same adjustments, too, though the bite point doesn’t work as effectively. The Hope brakes will set you back £225.
SRAM’s Code RS comes in cheaper at £170 but doesn’t get any form of bite point adjustment. Its brake feel isn’t quite solid either but that’s a personal preference.
The Hayes Dominion A4 brings an awful lot of features such as the Twin Port bleeding and Crosshair alignment. It’s plenty powerful enough for all riding scenarios but offers enough modulation to keep all of that power well under control. It’s super easy to set up and maintain, too. All of that comes at a price that’s seriously competitive. The bite point adjustment could be improved though.