Measuring approximately eleven inches from top-to-bottom (size M/L tested), slipping the Speed Knee Sleeves on is as easy as you would imagine. Size wise, they felt pretty good from the outset and retained their fit and feel despite the mileage, both from the bike and the washing machine. Lacking any form of adjustment, the elasticated sleeve takes care of size variables while the large silicon gripper strip, which runs around the circumference of the top opening and does a superb job of keeping them in place. The 4mm thick, or should I say thin, D3O pad, covers your kneecap and ends just past the top of your shin. The coverage on offer is intended to take the edge off slow-speed falls and crashes which it does rather well, especially considering how little of it there is.
The addition of D3O is, of course, the defining element that will get people's attention, especially on an attractive knee pad that retails [at this price]. Providing more bang for your buck that also translates into more protection from bangs to your knees is not to be sniffed at, although 4mm of padding will only do so much. After having a big crash days before writing this, I can solemnly say that while the level of protection on offer from a 4mm thick D3O pad is eye-opening, it is by no means enough for the kinds of high-speed impacts associated with gravity riding. That said, had I not been wearing any protection on my knees, the outcome of that crash could have been far worse.
Coming from a background in downhill and as someone who almost always wears knees pads, I didn't get any noticeable signs of discomfort on rides of around 2-3 hours and I'd go as far as to say they're some of the comfiest I've tried. This is down to a number of factors. For starters, the elasticated material used for the sleeve itself is incredibly soft, but it also hugs the leg perfectly without bunching, which was an initial concern. During long days in the saddle, especially during the summer months where a ride would go up to and over four hours, heat build up did become noticeable. The heat didnt get to the point of distraction and my knees never looked like they'd been dragged through a carpet factory, but I would pull them down during pit stops to let me knees breath. While the attributes of their construction offer superb short-term comfort and increased long-term durability, especially over a mesh-based alternative which can all too easily get snagged and torn on pedal pins and vegetation, they do also translate to heat build up which could be an issue for some, especially those of you in warm climates. It's something to bear in mind.