Most riders are familiar with the concept that larger diameter rotors help improve braking performance, especially during hard, sustained braking. That's why we're starting to see more and more 220mm rotors on downhill and enduro bikes, and on eMTBs. Those larger rotors offer more surface area, which improves heat dissipation, and require less force at the lever to slow things down.
There's another way to improve heat dissipation – increase the rotor's thickness, and that's exactly what SRAM has done with the new HS2 rotors. The rotors are 2.0mm thick, compared to the 1.85mm thickness of the previous Centerline rotors. That may not seem like much, but that difference, along with a new brake track pattern, is claimed to deliver a 7% increase in power.
HS2 Rotor Details
• Thickness: 2.0mm
• Material: steel
• Sizes: 160, 180, 200, 220mm
• 6-bolt or Centerlock
• Weight: 204 grams (200mm, 6-bolt)
• MSRP: $50 - $65 USD
The new brake pattern also has less material removed and a different orientation of the cutouts, which provides more surface for the brake pad to grab onto. Towards the center of the rotor are spokes that have been painted with a thermal dissipating paint, another step that was taken to keep things as cool as possible.
There are 160, 180, 200, and 220mm versions of the new rotors, with 6-bolt and Centerlock options available. On my scale, a 200mm HS2 rotor weighed in at 204 grams, 14 grams more than a 200mm Centerline rotor. Prices range from $50 to $65 depending on the size and mounting style.
This graph from SRAM illustrates the temperature difference between a Centerline rotor and the new HS2 rotor.
I've been trying out the new rotors over the last month on several different bikes, all equipped with SRAM's Code brakes: a 160mm enduro bike, a 120mm trail bike, and a full-power eMTB. In all instances, the rotors are noticeably better than the Centerline rotors they replaced. By 'better', I mean that they give the brakes an overall firmer bite, and maintain that solid feel even on long, steeps sections of trail.
It's on the heavy e-bike that the improvement was especially apparent. On that bike I'd previously had several moments where I found myself wishing for more braking power. Hot, dry conditions, a 50-pound bike, and an extra-steep track meant that I had to pull extra hard on the levers to control my speed, even with a 220mm rotor on the front. With the HS2 rotors there was less fade, and it took less effort to manage my pace.
In wet conditions the rotors still make some noise initially, but they seem to clear water and quiet down more quickly than the Centerline rotors did. They'll also howl a bit on very steep, very sustained trails, the type where hard braking for minutes at a time is required. I still think there's room in SRAM's lineup for brakes that are even more powerful than the Codes, but that's a different topic. I've managed to avoid falling off any skinnies lately, so I can't comment on how well the rotors resist bending; if anything the extra thickness should make them less likely to fold over from an impact.
Now, the thicker rotors do mean that there could potentially be less pad clearance, although I haven't run into any unwanted rubbing. I've successfully run thicker rotors from other companies with SRAM's calipers before, and as long as you take the time to clean and reset the pistons the extra .15 millimeters shouldn't cause any issues.
New rotors may not be as exciting as a wireless drivetrain, or a fancy shock that has adjustable everything, but the HS2 rotors offer a clear performance benefit with only a minuscule weight penalty - that's a win in my book.