Let me preface this by saying that there is certainly a place for disc brakes on electric scooters. Just like cars, bicycles, and almost everything in the world, one specific type or style isn't right for everyone. If you are talking about high powered/high speed scooters most of this doesn't apply, but for most of the scooter comparable to our Wire Ohm electric scooter, the following will stand true.
Lets start with a little background. The type of disc brake used on electric scooter [as well as many other parts on electric scooters] come from the performance mountain bike industry. I'll get to why this is important in a bit.
How disc brakes work
Disc brakes can be actuated with cables or hydraulics. For most electric scooters, they are cable actuated, but we are starting to see hydraulic brakes on very expensive high-end electric scooters.
There are two primary components--the rotor, which is mounted coaxial to the wheels axle and the caliper, which is rigid mounted to the frame that holds the axle.
When the rider actuates the brake by pulling the handlebar mounted brake lever, the cable is pulled [or hydraulic fluid is pushed] and the caliper clamps two opposing brake pads around the rotor. This in turn slows the wheel down.
So why are they good for bicycles but not scooters?
The biggest reason is that when these types of disc brakes [whether cable actuated or hydraulic] are mounted on a bicycle, they sit over a foot off the ground. This allows natural protection from damage because they are far out of the way of being kicked or bumped.
This matters because disc brakes run with relatively tight tolerances. This means that when a rotor is laterally out of true [when the rotor appears to wobble when the wheel spins] the rotor will rub on the pads when the wheel spins. It makes annoying "wish-wish-wish" noises and creates unwanted friction when the brakes are actuated.
The other thing to consider is inertia [a property of matter... the generation who grew up watching Billy Nye will get that ;) ]. Most bicycles use 700c/28"/29" wheels [these are actually all the same size]. These wheels are much larger than scooter wheels, which means they need much more force to clamp the wheel to overcover the forces in motion.
What results in many cases is that scooters with disc brakes make it very easy to lock up the wheels. Though there is nothing inherently wrong with this, in many cases with inexperienced users, this can make thing more dangerous because a locked wheel can't cant directions and can cause a rider to lose control in a panic situation. This is the same reason why ABS is mandatory in cars.
Are disc brakes better?
Yes and no. Do they provide more stopping power? In general yes, but this can vary a lot based on pad material [just like cars there are many different friction materials that can be used] and moreover they need to be adjusted within proper spec. This can be difficult to maintain with the cable calipers used on electric scooters. There are cable actuated calipers that are quite good at mitigating problem caused by out-of-spec adjustments, but they are expensive relative to the price of electric scooters.
This brings us to the bigger issue we discovered through experience.
After a year of running the USA's first nation-wide electric scooter subscription program, we found that disc brakes are not only a pain for people to maintain and adjust but they also can create a bad situation for inexperienced riders. Many people are attracted to electric scooters because they are easy to ride and less intimidating to bicycles. We found many of our customers had little experience with electric scooters and would often grab the brake too hard and lock up the rear wheel. In most case, this doesn't cause too much of a problem, but in panic situation this could cause a crash.
Why we ditched disc brakes for the Wire Ohm Electric Scooter
After learning from all of our customers, countless hours of rider observation, and lots of testing, we found that to build the best all-around scooter for everyday use we needed a better solution. This is why we moved to an electric brake for the primary brake. The Wire Ohm electric scooter used an ABS [anti-lock brake system] electronic regenerative brake.
This not only prevent riders from locking up the brake, but also make the brake easier to modulate. Since it matched the thumb throttle, the thumb brake lever allows inexperienced riders to apply as much or as little braking force as needed.
THIS IS NOT A BRAKE
Another thing we learned from our first few hundred subscribers was there is a natural inclination to rest your back foot on the rear fender. On our first scooter, the rear wheel had a disc brake and a simple plastic fender to protect you pant leg from getting sucked into the wheel and help keep road grime from being spit up onto you from the spinning wheel.
We thought this was smart. Many competing scooter brands still use this design, so they must think so too. However with our first hand experience we found that it resulted in dozens of people breaking off fenders. At first our solution was to put warning stickers on them telling people not to step on the fender, but it did not help--they still were broken off quite often.
One of my design professors in university once told me, "if you need a sign, its because of bad design". What she was saying is, that design should accommodate for real use. In this case it meant, instead of trying to change behavior, we should change the product. This is why we designed the rear foot actuated brake for the rear wheel to compliment the front electronic brake--if people are going to try to use the rear fender as a brake, it would be smart to just make it a brake.
Why do you need to know all of this? You don't. This whole series of posts is trying to explain in detail why we think the Wire Ohm is one of the best electric scooters out there. It's for the nerds and the people who need to know everything--the people who message us at all hours delving into hour long conversations about scooters. However, if you aren't one of them, I hope I still helped you understand why the Wire Ohm electric scooter might be the right one for you.