Sugru, Crud, and Fenders for Mud


I declare February Fender Awareness Month. Riders, please remember to use the right fender for the job. Though there is certainly a place for polished metal fenders…their hammered finish glittering like the facets of gemstones…that place ain’t bouncing on muddy singletrack. You’ll want something light, secure, and able to take a thrashing. Crud Products’ Raceguard clip-on rear mudguard has been my favourite for several years. But while it performs splendidly on mountainbikes, the Raceguard needs a little help on 3T’s “aero gravel bike”.


3T Exploro with Crud Products Raceguard clip-on fender

One colloquialism in place at the bike shop since long ago is the phrase rack & fender rules, which is to mean by any means necessary. Over the years I have drilled, ground, hammered, melted, bandsawed, and as well as performed countless other techniques to wrangle fenders to fit bikes, but this hack is probably the most etsy so far.

The problem is that the Crud Raceguard seatpost bracket is designed to fit a round seatpost, and 3T chose to go with an aero-shaped shaft there. Specifically, the 3T “Charlie Sqaero” seatpost is a truncated airfoil shape sometimes known as a Kamm-tail. Imagine a teardrop shape with a more elliptical leading edge, but the back third of the tail is chopped off.  A round clamp bracket can’t get a good grip, and if the point of the Crud Raceguard is to handle rough roads and singletrack, you want to have it fit securely. And anyways, the Raceguard bracket is designed to fit a 32mm round seatpost (a selection of shims allow for smaller diameter seatposts). The 3T Charlie Sqaero post is 35 x 20mm.

On the surface, this doesn’t really seem like a feasible plan. A more conventional solution would be to purchase a mudguard from another company that used a more pliable rubber or woven strap to affix to the seatpost, but I find that those designs wanting for a firmer grip and often in need of mid-ride adjustment. I really wanted to use the Crud item, and I just happened to possess some information that Crud doesn’t have on their website. Namely, that you can ask Crud for a 35mm bracket clamp. Unlike the injection-moulded stock clamp, they 3D print the 35mm clamps one at a time by request. For a small sum, they will post said clamp from the UK directly to you. The special XL bracket is still round though, but it is big enough to encircle the Charlie Sqaero. Now the situation calls for a little arts & crafts inspiration.

Have you ever heard of Sugru? It’s a mouldable glue/silicone putty that is sold online in small sachets that come in a variety of colours. You form it into a shape, perhaps stuck onto some craft project, and in 24hrs it becomes a firm yet flexible object. Honestly, it’s a little pricey (and a little messier than the website suggests), but I knew it could be used to form a competent gasket to fill the space between the Crud’s round bracket and the Sqaero’s shaft. First I would need a mould for the inner surface of the gasket.

Sure, I could have slapped the Sugru directly onto the seatpost, but while the end result would have been fabulously secure, it would have also been permanent. A good trick would be to wrap the seatpost with plastic food wrap and then razor a break through the Sugru and plastic wrap. Conveniently, I even had a section of seatpost saved from when I shortened it for my saddle height. I ended up using the better part of three sachets of red Sugru.

The Sugru cured. The rest of bracket had been in place to assure the fender would be aligned after hardening.


Maybe I should have chosen white Sugru. Notice that the Crud bracket appears to be stained red? Like many 3D-print products, the oversize bracket has a rough, porous surface compared to the glossy shine of injection-moulded mass production items. It was impossible to avoid getting some of the Sugru on the outside of the bracket. Perhaps I could have sanded it clean and somewhat smoother, but that seemed like a whole lot trouble for no functional benefit. I assembled the entire bracket so that the gasket would harden with the fender properly aligned. I let the Sugru cure overnight, and then cut it free from the seatpost stub. I used a razor to trim the excess Sugru.

All in all, this project was a cracking success. In fact, I’m so happy with the results that I’ve been thinking other practical uses for Sugru on bikes. What I’m not thinking about is my Crud because it just does its job…bombing the trails and stretching my legs over long gravel roads, the Raceguard has been silent, secure, and effective on the back of the 3T bike.


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