Full Stop Full Stop

Full Stop

All Stories
Tuesday, December 22, 2015

Starting in 2016 the UCI has cleared the pro peloton to use disc brakes in competition. To get a better understanding of the benefits of disc brakes to both pro and amateur riders and take a deeper look at some of the design considerations made when engineering hydraulic disc brakes, we talked with SRAM Disc Brake Design Engineer, Mike Weiner. 

Have you done testing that compares the braking performance of hydraulic disc brakes versus mechanical rim brakes? What about in wet conditions? 

In dry conditions most people will immediately notice the lower hand effort required to slow the bike with hydraulic disc brakes. This is due to the increased power of hydraulic brakes versus rim brakes. In other words, for a lower force applied to the brake lever you can achieve the same braking power. Over a long ride this translates into less hand fatigue. But wet conditions are where disc brakes really shine. For those people who have ridden in wet weather with rim brakes they’ve likely noticed a big drop in braking power when the rims get wet. With some carbon rims the loss of braking power in the wet can be downright terrifying. With disc brakes there is little to no loss of power in the wet. It’s important to note that the limit to the stopping distance is the traction that the tire has on the riding surface, and both rim and disc brakes are capable of skidding a tire. But having consistent braking regardless of the conditions is a key advantage to disc brakes. For those people who are not ready to upgrade to disc brakes our Zipp carbon rims with ShowstopperTM braking technology would be a great alternative as they offer top wet braking performance for rim brakes. 

What rotor size does SRAM recommend for road bikes? 

SRAM recommends 160mm rotors for road bikes. 160mm rotors provide a good balance of heat management and power.

Mike Weiner working on the flat mount caliper variant of SRAM's hydraulic disc brakes.

SRAM makes multiple disc brake pad compounds. Can you review what those are and when would you use each type? 

All SRAM road hydraulic brakes are shipped with a specially formulated organic pad compound that we have found gives exceptional braking performance and minimal noise. For cyclocross we also offer a metal sintered brake pad that has increased wear resistance for muddy or sandy conditions where pads can wear much faster. It’s probably a good time to mention that all of our testing is conducted using SRAM branded components so we would encourage our customers to only use SRAM components to maintain their brakes.

SRAM road hydraulic disc brakes have received plenty of praise for their ride feel from editors in the cycling press. Was the feel of the brake system a primary design goal when SRAM set out to engineer their road hydraulic brakes? 

We are very proud of the ride feel of our brakes. We have specifically designed brake systems that make it easy to apply just the right amount of braking power needed for the situation. It doesn’t make sense to have a brake with high power if the power is not controllable. 

For sure the feel of a brake is a big focus of the design process. We verify ride feel in the test lab and through test riding of our products. There are many pieces of the brake system that contribute to ride feel, so it was not a small effort to ensure everything worked together the way we intended. We’re happy to hear that our customers are enjoying the final product. 

You mentioned that you use lab testing and ride testing to verify ride feel. How exactly do you test the feel of a brake? 

In the test lab we can simulate very specific braking conditions. This allows us to verify our mathematical predictions for brake performance. But what the lab testing cannot simulate is how a brake feels to a rider. It doesn’t matter if our calculations tell us a brake should perform well if a rider says it doesn’t feel right.  

How important is brake pad compound to ride feel, or is feel more a function of the brake’s hydraulic architecture, lever geometry, or some other variable?

As you might imagine brake pads have a huge influence on the power of the brake. But what people might not expect is that brake pads can also have a big impact on the feel of the brake. The brake pad works together with our hydraulic system and the other brake system components to create the feel at the lever. But the brake pad can make or break the performance. For example, if a brake pad is very “grabby” then your ability to control the braking power would not be very good. Conversely, if a brake pad has very low friction then you would also not be happy with the performance. The best brakes are the ones you don’t notice because they work just like you expect them to.

You said that SRAM wanted to avoid selecting a “grabby” brake pad. Can you elaborate on why SRAM chose to design its disc brakes to apply braking power smoothly?  

Power needs to be usable. If braking power comes on too quick, or unexpectedly, or digitally (off or on, no in between), then you can actually lose control because you break into a skid before you intended and your wheel washes out and you go down. If you can meter your braking and create just the right amount of braking you need, feather braking to scrub just a little bit of speed, or heavily braking just before a corner, and everything in-between, then you have much better control of your bike as well as your speed.  

When trying out a new bike with grabby brakes sitting on the showroom floor, the brakes might feel great. And when you try out that bike in the parking lot you might love the power. But in a real world situation like a group ride or pushing hard down your favorite descent, you will want the control. All of the parts of our brakes work together to give you that control when you want it, and power when you need it.  

To learn more about SRAM disc brakes, click here.

All Stories