How Did This 600-Horsepower EV Sports Car End Up With Smaller Brakes Than a Honda CR-V?

You know how your phone sometimes freezes when you really need it to work? Well, imagine that, but with your car’s brakes. That’s apparently what some owners of Xiaomi’s shiny new SU7 electric sedan are experiencing, and folks, it’s not great.

For those who haven’t been following the “tech companies building cars” trend, smartphone manufacturer Xiaomi jumped into the EV game with their first car earlier this year, the SU7. It launched with some genuinely impressive specs for the top trim model, the SU7 Max. It boasts up to 673 horsepower, and can sprint to 60 mph in under 3 seconds. Xiaomi made a big fuss about its performance credentials, boasting it could outperform the Porsche Taycan Turbo in many respects.

Here’s the thing about performance cars—people expect them to perform. The problem with the Xiaomi SU7 is that, when it comes to track use, it might not have the stopping power to match its hefty amount of go.

Hold Up

Since the SU7 launched earlier this year, a number of owners and enthusiasts have been putting the vehicle through its paces. While it’s the debut vehicle for Xiaomi, the SU7 is built under contract by BAIC, a Chinese manufacturer with many decades of experience. Thus, you would expect a certain basic level of quality—that the vehicle would go and stop as commanded. Indeed, the vehicle has won many fans, including Ford CEO Jim Farley himself.

[Ed Note: Per our Chinese car-market expert, Tycho, BAIC wasn’t actually involved in the development. From Tycho:

Xiaomi: BAIC is not the manufacturer. It is complicated. Initially, Xiaomi didn’t have a car-producing license, so they piggybacked on BAIC’s license. This is allowed in China for start-up automakers. That usually means that the start-up pays a fee per car produced to the established automaker. BAIC has not actually been involved in making the SU7. The factory is, and has always been, fully owned and operated by Xiaomi. Earlier this year, Xiaomi got its own car-production license so it doesn’t have any ties with BAIC anymore.

Interesting stuff! -DT]

Few doubt the SU7’s ability to fling itself down the road at great velocity. It’s plenty capable of fast launches, a party trick shared with many other luxury performance EVs. However, the problems appear to crop up when the SU7 is tested more broadly as a sports car during actual track use.

Videos of an on-track crash first surfaced in April. A Xiaomi SU7 Max was driven at the Shanghai Tianma circuit, with influencer Tang Zhu Liao Che (堂主撩車) at the wheel. In a video of the incident, we see that as a tight left approaches, the car goes straight on instead of turning, barely losing speed as it plows into the barriers. The crash had occurred after several hot laps of the circuit.

The crash in question. You can watch the full original Chinese video—which racked up over 13 million views—here. Embedded player removed due to autoplay.

The car was significantly damaged in the crash, with both front airbags deployed. Thankfully, no serious injuries were suffered, thanks in part to the tire wall at the circuit. The vehicle was recovered by crane. As reported by Sina.cn, in a video after the event, Tang Zhu explained that he’d had little warning something was wrong. He’d heard a loud grinding noise in the previous braking zone, indicative of severely worn pads. He had—perhaps naively—hoped he could still complete his current lap, only to find in the next braking zone that he could not stop the car.

Video shared by Tang Zhu from after the crash shows the SU7’s Brembo brakes in a severely degraded state. The pads can be seen worn down almost to the backing plates. The vehicle had done five laps prior to the incident. We don’t know how many miles the vehicle had done before this. Regardless, given this happened in April, the vehicle was only a month or so old at most.

The crash caused quite a stir in the Chinese EV world. The video quickly racked up millions of views on Chinese website Bilibili, pushing Xiaomi to release a statement on the matter. The company basically came out and stated that the vehicle was not built for track use.  Translated, it reads as below:

We strongly remind you that Xiaomi SU7 Max is a high-performance luxury car for road use. Please do not try extreme driving such as on professional racing circuits.

The braking system of Xiaomi SU7 Max uses NAO friction pads, which are suitable for daily driving. They are mainstream products that balance braking noise and braking performance and meet the needs of public road driving.

In addition to meeting national standards, NAO friction pads also meet special performance standards and performance verification for braking performance:

• AMS performance: after 10 consecutive 100km/h-0 full-force braking events under full load conditions, the braking distance decay is less than 2m;

•100km/h-0 braking distance is 33.3m, which is at the leading level in the industry;

Under the simulated conditions of ordinary driving, the wear of the brake pads remains at an acceptable level.

Due to the high speed, large kinetic energy accumulation, sharp braking, and rapid wear of components under continuous high load and high temperature under track conditions, all core components of the vehicle are required to meet requirements far beyond those of daily conditions. Professional drivers need to perform system-level professional maintenance on their vehicles before driving on track.

Track driving is the most extreme and demanding test for both drivers and vehicles, and requires a deep accumulation of vehicle expertise and professional driving. We once again call on people not to take the challenge of driving the Xiaomi SU7 on track lightly. Thank you for your understanding and support.

The statement specifically calls out the NAO (non-asbestos organic) compound brake pads for being optimized for reduced noise as opposed to performance. As covered by PowerStop.com, these pads are known as being particularly soft compared to other compounds. Indeed, brake manufacturer Bendix notes that NAO pads aren’t ideal for performance vehicles driven hard.

Unfortunately, not everyone heeded Xiaomi’s call. Further influencers took the SU7 to the track, with predictable results. One driver shared a video in June this year, with the crash itself later reposted in October by YouTube channel HandsOnTheWheel.

In much the same way, the driver found they had no brakes at the end of a straight. This time, however, the driver lost control and spun out as they attempted to slow the car, with the rear of the car hitting the wall instead. The driver can be seen being flung around the cabin during the impact. Amazingly, despite the apparent severity of the crash, the vehicle was able to limp away from the incident with plenty of damage to the rear end.

In the wake of these crashes, photos of the Xiaomi SU7’s brakes were shared far and wide across Chinese social media channels. They’re quite surprising if you’re familiar with performance brakes. While the calipers themselves look big on the outside, they are only four-piston units, and are fitted with relatively small brake pads.

When it comes to brakes, size matters. On performance vehicles, brake pads, rotors, and calipers are typically quite large. This isn’t because bigger brakes can slow a car down faster. In fact, braking performance is limited by tire grip in most cases, and even moderately-sized brakes can lock up a wheel beyond the tire grip limit.

Instead, performance brakes are large because of heat. Larger rotors, pads, and calipers have greater thermal mass, so they take longer to heat up. They’re also typically better at shedding heat to keep the brakes in a safe operating range. That’s important on track. Bigger brakes let you turn hot laps for longer before they get critically hot and lose braking capability.

In this regard, it’s worth comparing the SU7 Max to a similar vehicle—like the Porsche Taycan Turbo. It weighs 5,119 pounds and has 616 hp. Those are very similar figures to the SU7 Max which weighs 4861 pounds and has 673 hp. However, they have very different brake setups. Xiaomi doesn’t include the size of the SU7’s brakes on its official spec sheets, but more on that later. What we do know is that it’s rocking four-piston brakes up front with those rather small pads and cast iron ventilated rotors.

In contrast, the Taycan Turbo has larger six-piston calipers up front, and four-piston calipers at the rear, with 410 mm (16.14 inch) front rotors, as a guide. The Taycan Turbo S doesn’t add any more power, but it steps up to 10-piston calipers up front and larger 420 mm (16.5-inch) ceramic rotors for even better performance. At the bottom end of the range, even the 321-horsepower base Taycan has bigger brakes than the SU7 Max.

A Taycan Turbo S has similar weight and power to a Xiaomi SU7. It’s also got a much beefier set of brakes.

Indeed, Xiaomi has recognized this limitation. While the SU7 Max is a fast road-going vehicle, it’s simply not cut out for track use. Thus, enter the SU7 Ultra. This model is yet to be released, but a prototype version smashed the Nurburging lap record last month. Xiaomi has equipped the race-tuned vehicle with massive 430 mm (16.9 inch) carbon ceramic brake discs up front, and 410 mm discs at the rear. These brakes can handle temperatures up to 2372 F, according to Xiaomi, and are far less subject to brake fade during track driving.

As shared by Fast Technology, there’s a shot comparing the SU7 Ultra’s brakes with what appear to be those of the lower-end model. Taking a rough measurement from the image, I think I’ve got a rough idea of the regular SU7’s brake size. Take it with a grain of salt, but they look to be 74% the size of the larger ceramic discs. If the SU7 Ultra brake is 430 mm in diameter, the lower SU7 models are using discs just 318 mm (12.5 inches) in diameter. That’s pretty titchy (small) for a car weighing almost 5,000 pounds with over 600 horsepower.

To give you an idea, you’d find brakes of similar size on something like a Honda CR-V. That’s a regular road-going SUV, which weighs under 4,000 pounds with maybe one-third the power of the Xiaomi SU7 Max. In contrast, something like a Tesla Model Y Performance with 530 hp has much beefier 385mm (15.16-inch) rotors—note how that’s much closer in size to the Porsche Taycan than the Xiaomi SU7 Max.

Basically, it comes down to this: The SU7 Max is a heavy electric car. It’s really heavy. And it’s got lots of power, and really small brakes. It’s also got soft brake pads that are built explicitly for road use. Fling that electric heifer down the track, and you’ll enjoy its great acceleration—but you’ll also be chewing through your brake pads in no time quick. They’ll be turning to dust every time you try to haul it up for a corner. When they run out, when you hear that first little grind? You’re flirting with disaster. Pull it to a halt, don’t try to run hot into the next hairpin. You’ll regret it.

If you absolutely have to take one out on track, you’ll want to consider some serious brake upgrades. That is, of course, if you’re intending to keep it out of the wall.

Xiaomi likely hasn’t said anything we can find that indicates it believes it’s done anything wrong. Some enthusiasts may disagree. Personally, I’d say if you go out boasting how your 600-horsepower car is better than a Porsche… you should probably expect that somebody’s going to test that on a track at some point. For their own safety, and to avoid your own embarrassment, you should equip it with suitable brakes to handle that circumstance. Just saying.

Image credits: Xiaomi, various via YouTube screenshot