Diy rear fender seatpost mount for a fat bike


Well-Known Member
Feb 5, 2010
We purchased a family gift of a 3D printer for Christmas. Up to now I have just printed trinkets, Kinect Scans of my Children, toys and keychains. Today, I decided to put the printer to better use.

Is is high time to put a rear fender on my ride. The bike and I got muddy enough to require a trip to the carwash a few rides ago. There are few good options for fenders on a fatty; the "Mud Shovel" looks like a good option - but I chose the DIY route.

I whipped up a model for a mount in OpenSCAD ( and cut a piece of corrugated plastic for the actual fender. Seven hours and 80 grams of PLA later. I screwed the fender to the mount and attached it to my seatpost. It looks good for a first attempt I think.

It could use a bit more curvature and other tweaks, but I will ride it as is and see how it works. I have attached the files if anyone wants to have a go with it. It is configured to a 27.2mm seatpost, but can easily be changed to other diameters.


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If it doesn't work as a fender, It may be a good fan blade.
OK...folks...this is what happens to people in the Northern tier States in the dead of Winter.

We call this, "Cabin Fever". Happens about this time every year.

Only when it happens to cyclists with too many frozen brain cells, a 3D printer and snow piled 4' deep outside the door...this is the result: political yard signs recycled in fat bike fenders with a $300 mounting bracket!

Dang, Maydog! Between that floppy fender on my Cat. 2 bud's new Pivot gravel racer and your yellow splash guard, I'm looking at the newest generations of bicycles in a whole new light! Nice job on the bracket design and build.
Cabin fever is for those who choose to stay indoors.

I also made a front fender. I cut a 6" wide section of corrugated plastic with a notch for the head tube and fixed it to my downtube with 3 heavy duty zip ties - it sounds flimsy, but it is actually solid and stays in place. The yellow plastic just happens to match the color of my rim strip nicely.

I gave the new fenders a thorough test on Sunday. The temps were in the 40's Saturday and Sunday which made the snow very wet. The ride consisted of a lot of slipping, sliding and one fall. I ended up taking some muddy snowmobile trails to get more traction. The fender worked for the most part, but I still got a muddy bottom. The rear fender could be longer, or I need to slide it up the post. Its also possible that on the bumps it serves as a scraper for the rear wheel. The front was golden.

I found that In need to tie down the fender during transport - or it will eventually flap away. Version 2 of my mount will include a easy removal mechanism for transport.
Some of the commercial fenders I've seen mount with zip ties. Between zip ties and duck tape there is nothing a man can't make!

A trip to Menard's for one of those 400-zip tie assortments, a sheet of thin plastic and you're in!

We've just been through a nice warm spell and mostly dry roads. Yesterday we got about 1/2 of snow and maybe another 1/2" to an inch is supposed to fall today. Temperatures are going to drop this week into the low teens. I think I'll take a little time off the trainer and start walking the woods.

BTW, one of the local ski resorts-slash-golf courses had a fat tire event scheduled with a bunch of dealers on hand for demo rides, a course laid out for riding and some of the industry reps invited to come in and give seminars and talks on FT riding. It had to be cancelled due to warm temperatures and the ground not being frozen. The fairways and greens would have been torn up with all the bike traffic so it died.