“You aren’t meant to stand up in it.” Not the phrase you expect to hear the first time you put on new kit. But this wasn’t just any old kit – this was the Pearl Izumi Mach 5 – and it’s not meant for sitting upright. No, this is a kit meant to be in one position, and one position only – aero.

But let’s back up for a second and start with what we are reviewing. The Mach 5 is Pearl Izumi’s fastest of the fast kits. Meant for races where only the time against the clock matters – this is the kit that years previous you would find on the BMC Racing Team when racing time trials in Spain, Italy, and France. Rohan Dennis wore this kit when he set a the Tour de France Individual Time Trial speed record. And Molly Van Houweling wore one when she set the UCI masters hour record.

We tested the long sleeve Mach 5. This one-piece long-sleeve suit is made of Pearl Izumi’s 4-Way stretch P.R.O. Transfer material. The Mach 5 is crafted with minimal seams and contains aero material placed in the patented speed sleeve construction. Pearl Izumi tells us the Mach 5 was constructed to be the fastest speedsuit in the world.

The kit fits tight. Not “I just had thanksgiving dinner and need to unbutton” tight. No, this is “I hope remembered to use the bathroom before I put this on because it’s not coming off again” tight. And don’t even bother trying to stand straight up. You aren’t meant to. It’s specifically designed for you to be hunched over – either in the drops of a road bike or preferably in your aerobars. By the way, we only learned this when we called Pearl asking for a larger size after we tried to stand up the first time we put it on. Lesson learned… don’t stand up.

But all that is OK when you remember the purpose of this kit. Put it on, ride the heck out of your bike, collapse in exhaustion. Speedsuits like the Mach 5 aren’t made to get you to the run faster. They are made for time trials and road races. When the bike is over, so is the race. So to test the Mach 5, we entered the relay portion of Ironman Miami 70.3 – a 56-mile time trial in South Florida in October (where it was still above 85 degrees F). To prep, we trained from August through October regularly in the Mach 5 (in some occasions, with an additional jersey over it as the Mach 5 has no pockets, but flats do happen in training rides, so extra tubes are needed). And in no instance did we ever over heat. And keep in mind that included rides with training temps well into the 90s. Even with full-length sleeves, we never felt the need to strip it off as soon as the ride was over. We were extremely pleased with its ventilation abilities.

Pearl Izumi hasn’t shared in-depth data, but they did share the video below detailing a trip to A2 with a number of their kits, including the Mach 5.

At around 1:26 they share that, when compared to a standard training jersey, they saw benefits of as much as 25.4 watts. Pearl Izumi tells us the weighted average was based on four yaw angles across three speeds, 25, 30, and 35 mph. The watt savings are from an average speed of 29mph.

The suit retails for $499; however, as it is currently only available via their custom shop, prices may vary depending on the quantity of suits ordered. We have been told that it may become available for individual purchase, but to date it hasn’t shown up (we are keeping our fingers crossed).

So yeah, you can’t stand up in the Mach 5. But considering that the only time you would want to is if you are standing at the top of the podium, we will take that as an acceptable compromise.