Culprit’s DIY Custom Full-Forearm-Support Armrest Kit

May 3, 2022

Joshua Colp is a man after my own heart. He’s the Slowtwitch resident tinker/manufacturer and he seeks to solve the hard-charging athlete’s problems with his brand's products. My old job.

The latest problem Josh wants to solve? Full-forearm extensions. Whether Culprit's armrests solves the problem I don’t know. What I can do is describe the features for you. This product is available for preorder now, and at $700 is on the light side, pricewise, for the product class. It is not a fully-adjustable, fully-custom, full-length armrest. It is a kit allowing you to fully-customize, fully-adjust your own full-length armrest set.

Let’s discuss the positives, and then the negatives. The positives are that there is no position or posture you want to achieve with this armrest set up that is not possible. The width of the armrest cups; distance of the cups from each other; inward/outward angle of the cups; height of the armrests; fore/aft of the armrests; up/down tilt; length of the extension of the forearm rest; length of the uptilted hand-hold; angle of that final hand-hold tilt; are all adjustable. This is, truly, a full-custom kit.

Another positive: It is one of the only full-length forearm armrest systems allowing you to fully rest your forearm. It has been my griping admonition for about a decade here that companies turn their extensions into forearm rests, not for aero but for ergonomic reasons. Nevertheless, it was for the aero benefit that these armrest types began to take hold. I have no data and not even a guess as to whether the armrests are, by themselves, aero, or whether they succeed in fairing what’s behind them (your forearms, and/or the rest of your body). But they are comfortable, and that's in large part because you can actually displace your weight on these armrests from the elbow to the wrist. (Not all full-forearm systems actually support the full forearm.)

There are two pursuit bar mounting hardware styles. What I have in the images here are typical round pursuit bar mounts. But there’s a hardware bracket for direct-mount pursuit bars, like the PRO Missile. What I find is that the undermount bolt pattern for direct-mount pursuit bars, like the Profile Design Aeria Ultimate, is pretty standard, and Culprit’s hardware lines up with the bolt pattern on this pursuit bar. But, the top side of that pursuit bar must be – or shims or pedestals must offer – a flat surface on which that bracket can mount. Some of these pursuit bars offer this flat mounting surface and some do not.

All bar-end shifting options are accommodated. Obviously in the images you see here I’ve got SRAM Wireless Blips, but the system has built-in tunnels for electric shift wires and I don’t see why shift cables can’t use those same tunnels. There’s an included bracket that allows for a front water bottle cage but in the case of the Quintana Roo PR6 here there’s a Profile Design Aeria Hydration on the bike, which means I don’t need that bracket.

Now for the negatives.

There are a lot of parts. You kind of need all these parts if you want this system to be as adjustable as it is. But look, you’re going to use a lot of blue threadlocker because there are so many threaded elements to this system.

This increases the weight of the system. Every time there’s an adjustable element that is fixed by steel screws or bolts, the weight goes up. I haven’t weighed the entire system, so, my claim here is a guess, but my best sense is that all the joints add up to extra weight versus a system that might not be nearly as adjustable, but lacks the joints, parts, sub-assemblies.

This is a little technical, bear with me, there are 8 bolts that share 4 holes. This is not unique to this aerobar system. You’re familiar with the standard aerobar mounting scheme, where there’s an upward-looking “faceplate” that grips the underside of a 31.8mm pursuit bar, adjacent to the stem. The 2 bolts that affix this piece go into threaded holes, and in the case of this bar 2 bolts come down from the top and affix the system into these same 2 holes. At some point those bolts will meet if the top-down bolt is even 5mm too long, and in this case would keep the system from tightening down. I would like to have a few more threads engage on those top-down bolts but, alas, I am precluded from doing so. But not a deal breaker.

This isn’t an aerobar. It’s an aerobar kit. There is an extension on each side that you must cut to length. You’ll use a miter block for aero seat post cutting. You have one, right? You also need to cut that upturned extension at the terminus of the bar, which is easier. That tool’s either a miter block and Sawzall or it’s an aluminum tubing cutter. Either will work. The included armrest pads are die cut to allow for customizing, which you will have to do, because they must be cut to match your armrest cup width; and the forearm length you choose. It’s fine, but it will leave you with a seam in the armrest pad where two sides meet. Not cosmetically ideal for the persnickety types.

Also, cosmetically, I don’t know quite how best to wrap the ends of these bars. I fear that what I ended up with was not my best effort. I tend to go for function when I wrap bars and extensions, and appearance is often the casualty.

Josh from Culprit has a thread on our Reader Forum on these aerobars, with a lot of imaging I’ve omitted placing here because Josh placed them there, and you’ll get a better sense for how the armrests adjust for width, and just all the parts to this system. Here is the page on Culprit’s site where pre-orders take place.