Alpinestars Fluid Pro Knee Braces

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Tested: Alpinestars Fluid Pro Knee Brace
With comfort, protection, and durability, these motocross knee braces might be better for you than the uber-expensive options on the market.
Vital Review
The Good
Simple and durable hinges, all-day comfort, not much heavier than Fluid Tech Carbon version.
The Bad
Not as stiff as carbon braces, bike/brace interface takes some getting used to.

Along with boots and helmets, the modern motocross knee brace has become a big-ticket item that we, as riders, expect a lot of performance out of. And with good reason, since knee injuries are some of the most common, devastating, and prevalent in our sport. No piece of protection can ever prevent all types of injury but knee braces certainly offer more overall protection than knee guards. There are some people out there that claim knee braces cause leg fractures that wouldn’t happen otherwise, and while I’m not writing those people off, I would liken that argument to not wearing a helmet because the extra weight might cause neck injuries.

The Fluid Pros are sold as a pair.

Personally, I wear both knee braces and knee guards, depending on the ride (mostly either track or off-road/dual-sport) but also depending on the brace itself. If a knee brace doesn’t fit right, causes mobility issues, or is too uncomfortable, I’m not going to wear it just because it is a brace. Not to hop on a soap box, but when riders wear gear because it is “the best” or because the pro they like wears it, but it is actually not working for their body or riding style, it doesn’t make them safer. OK, hoping off now.

Alpinestars Fluid Pro Knee Brace Features:

  • Constructed from an evolved and advanced fiberglass compound for light, strong frame that retains strength and performance even in extreme temperatures.
  • Incorporating DEFT - Dynamic ErgoFit Tech - an innovative, reduced material design construction for improved weight-saving and excellent ergonomic performance.
  • Innovative knee pivot system incorporates tool-free poly-centric hinge system for fast, easily exchangeable extension stops (0, 5, 10, 15 and 20 degrees) to prevent hyperextension injuries.
  • Ergonomically sculptured and ventilated knee cup system constructed from semi-rigid TPU for durability, backed by shock-absorbing PU memory foam for comfort.
  • Highly ventilated, channeled padding and mesh zones for superb airflow cooling.

First Impressions

Alpinestars offers two versions of their knee braces. The only difference between the Fluid Pro (tested here) and the Fluid Tech Carbon is the chassis material. The Pro is a fiberglass compound while the Tech Carbon is a carbon polymer compound. This is more about stiffness than weight. In our office we weighed both the Pro and Tech Carbon and there is only a 46 gram (0.1 pound) difference between the 700 gram (1.5 pound) Pro and 654 gram (1.4 pound) Tech Carbon. But when manipulating them with your hands, the Tech Carbon is noticeably stiffer. I’ve ridden with both, not back to back, and on the bike I can’t tell any difference.

As with most knee braces, the Fluid braces take a little time to set up for your particular leg/knee situation. I’m lucky enough to not have any knee issues or weirdness, but there are extra spacers that customize the fit of the brace for different shaped and sized knees. I wear the XL/XXL version because I’m 5’8” and 210 and do a lot of cycling, therefore my thighs and calves are pretty big and my knee isn’t. This is where the spacers come in handy. The different thicknesses can suck up any space in the knee area and I use the thickest spacers so that my knees are nice and snug in the brace. You can also adjust how far the brace will extend straight before it locks out. Again, I don’t really have issues so I have the 0 degree extension stops that let the brace be straight up and down, but you can go as far as 20 degrees.

While the focus for braces is mainly on keeping your leg from bending how it shouldn’t, they also have to protect from blunt impact as well. The patella cup is TPU backed with foam, and features a floating attachment to the brace. Both on top and bottom of the cup has elastic straps to hold it centered as you bend your leg, and there are other fixed pieces of protection that continue to cover your leg at any bend angle.

On The Track

Fit is part of function, and the Fluid braces fit my legs fantastically. After the first couple rides, I had the strap up routine down pat, which is pretty similar to any other brace I’ve tried. I put the brace on my leg, bend my knee a few times to make sure it is centered, then strap the third from the top strap (upper calf) which has a buckle so you don’t have to measure every time, then the second from the top strap (lower thigh) which also has a buckle, then upper thigh and lower calf which don’t have buckles, just velcro.

The upper and lower straps are connected making them less likely to migrate and more comfy on the back of your leg.

The fastening system of a brace can easily be a deal breaker because the need to be both secure but offer movement and not bind. The both the top two and lower two straps form an “X” of material, one behind the calf and one behind the thigh. I think this is a smart move for a couple reasons. First, unlike four independent straps, they are less likely to move around since they are connected. Second, having the straps connected offers a larger contact patch on your leg and doesn’t “dig in” like single straps can. Also, the strap material is surprisingly thin which helps them not snag on riding pants or bind up, for the most part. Lastly, with any brace it is important to get the top buckle of your boot as tight as possible to help keep the brace in place.

The hinges are small, and have different extension stops. But if they were larger or a little farther forward they would offer a better grip on the bike.

On the bike, the braces work perfectly. Meaning, I didn’t really notice they were there. Bending or straightening my legs, they didn’t limit mobility or change the way my leg bent. I like that they go up pretty far on the thigh which offers both extra protection and extra security.

The bike/knee interface is just OK. When squeezing the bike with my knees, I could feel where the hinge was and it wasn’t uncomfortable to my knee in the brace, it was just sort of awkward how the brace meets the bike. Basically, the way I wanted to squeeze the bike was putting the brace’s hinge not flat against the bike but slightly angled inward making my contact point more the front edge of the hinge, not the flat side. I did get used to it but it isn’t the most solid feeling contact with the bike. This could just be the way I ride or the way the brace works with my legs but if the hinge was either bigger or farther forward, it might offer a better bike contact patch.

The only other issues I had with the brace was some migration and some bunching with a particular pant. First, all knee braces slide down on me no matter how tight I cinch them, and there is a point of over tightening when they become painful and cramp-inducing. That being said, the Fluid Pro braces only slid down a tiny bit and I would just give them a little tug before hopping back on the track before a moto and I was good to go. No, I haven’t tried the Leatt knee brace tights that wrap around your braces making it pretty much impossible to slide down, but I plan too in the future.

The inside of the patella cup.

The last issue was with some bunching while wearing just one pant, the Fox Legion Off-Road pant. I’ve worn these braces with a ton of different pants from pretty much all the main gear brands with no issues or bunching. But for some reason on the Legion pant there is a seam in the inner leg leather patch that is just in the right spot to get pinched by the brace and grab some skin with it sometimes. It wasn’t unbearable, but it wasn’t great either. But, I might call it the pant’s, rather than the brace’s, fault.


I’ve worn the Fluid Pros for over a year and the only durability issue has been one of the screws holding on one of the inner knee pads backed out. I checked all the others and they were tight, so I just screwed it back together and haven’t had an issue since. I haven’t had any twisting or wrenching crashes (thankfully) to test the braces main job, but I have taken a few nasty spills on some rocky off-road rides and the patella cup took some serious impacts. In fact I didn’t even realize that my leg took a hit until after the ride where I saw my pants ripped up and marks on the knee cup.

Crash damage from landing in some rocks trial riding. Pants were ripped but leg was fine.

The hinges have stayed tight and and the inner padding is still soft and holding up. No rips, popped seams, or even sweaty smell. The velcro is still closing and the buckles snap tight without problems. I do notice the white sections are a little off-white and some of the red from the logo is spreading but nothing to be concerned about. I’ve never washed them once.

The Last Word

Knee braces are expensive. We get that for a lot of riders, on top of expensive helmets and boots, and bikes for that matter, another $500 bucks is a hard pill to swallow. But the Fluid Pro Braces have held up their end of the bargain by being a comfortable and solid choice for knee protection for more than a year of riding. The Tech Carbon are tiny bit lighter and moderately stiffer, but for all day riding, I think the Fluid Pro’s fiberglass material might contributed to their comfort and fit. For the rider who has decided that knee braces should be in their gear bag, these braces would be a solid choice for years to come. If you want ultimate stiffness and lightness, there are other, much more expensive, options out there.


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Alpinestars Fluid Pro Knee Braces
Knee Braces
Constructed from fiberglass compound. Utilizes dual strap system.
Available in sizes S-XXL.
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Where To Buy
Free 3-day express shipping on orders over $79.
Free 3-day express shipping on orders over $79.
Free shipping on orders over $85.
Free shipping on orders over $100.
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