chojn1

It has been raining here everyday for the last week.
Looks like the forecast is for even more rain for all of the next week.
Being cooped up inside, I am thinking about starting another DIY project.
In keeping with the season, I am toying with the idea of a rear fender to keep my wife's back clean when we do eventually venture out.

Any ideas/suggestions on a good tandem fender?
Wood or carbon fiber?
How much clearance for the tires?
How much wrap around do I need?

How would you design a fender if you have no restrictions of limitations?

Thanks,
CJ

delilo

Coroplast works well, unless you are too concerned about the look...

Fend For Yourself
best part is the price

Alcanbrad

The wheel will throw water tangentially from the tire surface. If your fender ends anywhere above the height of the axle in the back, the potential exists for water to reach the stokers back. For the rear, I would want a fender that started at the bottom bracket and went all the past the height of the rear axle in the back. Similarly for the front, you want the fender to extend low to keep water off of your feet and the drive train. On an older commuter single of mine, I hung a large triangle piece of plastic cut from a laundry detergent bottle from the back end of the front fender. It offered much better protection to the drive train and my feet.

chojn1

delilo,
I am thinking of a fender which I can easily attach and detach from the bike as I only want it on when needed. I do like to keep the bike attachments as minimal as possible. The design should be light and portable, but, I am looking for something more durable and finished. I think either carbon fiber or laminated wood would work better.

Alcanbrad,
To keep things simple, I will only work on the rear fender as I don't have the need for a front one yet. Usually after a ride in the rain and mud, I will rinse off the bike before taking it in anyway. So dirt on the bike is not a big issue. Dirt on my wife is the problem here. Sounds like I will need a 180 degree arc. What about the curvature around the width of the tires? How wide should the fender be? And what is the gap between the tire and the fender should I aim for?

Anyone seen a cool design I should emulate?
Thanks,
CJ

DubT

Check out the DeFender RC11, simple, light and goes on and off very easily.

Bad1

Typically I do not enjoy riding in the rain one bit, but the RC11 rear fender works great with the ability to set two angles one off the seat post, the other angle adjusts to how close to the tire you'd like. Wife approved!

WillFam-Reno

TandemGeek did an extensive review of the SKS quick release mud guards in his blog:
https://tandemgeek.wordpress.com/page/11/
Look for the entries starting on June 7, 2014.
Ideas may come to mind as you follow some of his experience.

Chris_W

Regarding the rear extension of the rear fender: I run full fenders on virtually all of my bikes, and have recently been trimming the back ends. I've found that making the rear fender finish at a point horizontally level with where the rear tire crosses the seatstays gives all the coverage that is needed for anyone on the bike. The rest of the fender only helps those behind you. Since I mostly ride alone, and when I do ride with others, they don't have fenders, then why do I need to carry around something extra just to possibly make them more comfortable?

Looking at the tangential trajectory of the tire spray, cutting the fender this short could just about mean that the rider could get some spray, but in practice the air resistance is enough to cause the spray not to go in a straight line; instead it arcs backwards and doesn't really touch the rider.

I've also got rid of the fender stays on all of my bikes with rear racks and attached the fenders to the racks instead. It's a bit more fiddly to get the fender positioned right, but once it's done, the rack supports are far more rigid than fender stays, so the fender stays in place far better.

chojn1

DubT, Bad1,
Thanks for the recommendation. That Topeak does look really cool. I think that being further from the tires might makes it a little less effective though. I do like the design and will incorporate part of it into my final drawing.

Willfam,
Tandemgeek as always is a great source for all things tandem. Thanks for the link. Judging from his experience, I think designing only the rear is the right way to go. Also, sounds like I must pay special attention to clearance and rigidity.

Chris,
Thanks for sharing your experience. Exactly what I needed. I do love minimalist designs and will follow your guide on the rear length. A few more questions for you: How much of the segment anterior/forward of the seatstay is really needed? The RC11 completely ignore that segment. And, what is the ideal clearance between the tire and the fender?

As always, thanks for the help.
CJ

DubT

The RC11 can be adjusted so that it fits very close to the tire.

Chris_W

I run the front of my rear fender all the way down to the bottom bracket. If not, the back of the rider's legs get a lot of spray, and lots of crap gets dumped on the chain where the tire passes the front derailleur, so without the fender the chain needs more maintenance and has to be re-oiled more often.

CliffordK

I've found that simply having a rear rack with a solid central strip helps a lot. Not perfect, but it does help.

vrooom3440

I have bought these more than once and run a set front and rear when needed:

Planet Bike Full Hybrid Fenders - Modern Bike

Note that Planet Bike makes two different fender types: one with stainless fender stays and one with black painted stays. I actually MUCH prefer the black painted. The stainless are much more commonly carried but have lots of adjustment "stuff" out on the fender. Can you say UGLY? Well the painted stay version just uses a simple U bend of the stay wire around the fender. There is some adjustment at the drop out mounting end of the stay wires but mostly you trim them to length.

These fenders are actually a very good fit for 28mm roadie tires, on the larger 32-35mm they claim they get so close as to be a clearance challenge and have to be just right.

I modify them a bit, part of the installation game for me. I move the mount tab on the front to rotate more fender towards the back and get the end closer to the ground. I also remove the mounting clip on the crank end of the rear fender and just bolt it to the stay. The clip never worked for me. They are floppy enough that you will need the stays for mounting. I also mount to the brake bridge in the rear and shorten the stay rods until I get a nice even gap all around.

You say you are going to forget about the front? How much have you ridden in the rain? That front tire throws up just as much stuff as the rear tire, they are the same size after all running through the same stuff Plus the grit tossed up makes great abrasive for your chain and sprockets as you ride and work it in. Honestly the front is so much easier to mount/unmount I would do it first.

With your skills you could use some of these as starting points and customize and fabricate from there. Replacing the stays with carbon would be pretty easy for example.

If you are just building... you need to go across the full width of the tire more so than wrap around. And you need to run far enough around the back to keep spray from vectoring up from tire to rider: if you can draw a line from tire to rider without hitting fender the fender is too short. It really does not take much separation between tire and fender depending on how closely you follow the tire and how rigid the mounting/fender are.

zonatandem

If you have a rear rack, put a wide venetian blind slat on top of it.

chojn1

After the storm and flooding around here in Texas last night, I thought we were not going to be able to ride. But it was clear enough this morning for our usual Tuesday coffee run. The streets were generally dry but there were occasional water puddles and mud patches. After the ride, my wife took a look at her back and inquired when I will be finish with the fender.

We do try to avoid riding in the rain. But days like today calls for some type of stoker's back protection. Mud on the bike is no big deal and is easily taken care off with a rinse and a lube.

I am currently running 38mm 650B, so the generic one size fit all fenders are not ideal. Thus the impetus to build my own. Perhaps when we finally find time for some serious touring, I will build a more complete set of fenders. But for now I just need a "fair weather" version that is long enough to protect the stoker's back.

My design goal is for some thing light, rigid, easily detachable, and looks good. We don't ride with a rear rack, so the blinds option will not work. I do like the Planet Bike classic wrap around fender design and the U bend fender stay. Will definitely add that to my drawings. Ideally the bottom surface should be completely smooth with no attachments as to not impede the flow of water and mud. I am still not sure the appropriate clearance between the tire and the fender. Also, what do you think about incorporating LEDs into the fender?

Thanks for all the advise,
CJ

Bimmer74

I have ghetto fenders like this, made out of landscaping edging... 6" wide black plastic. It was free to me after tearing up some flower beds around my house. It's pliable and durable and easy to cut to shape. I think it looks better (definitely more conservative) than the multi-color campaign signs.


My ghetto fenders attach with zip-ties (I drilled holes in the plastic). It would be a 5-second job to zip-tie them in place, or to cut them off.

Like somebody else said, avoid fender stays... Mine just attach to the frame and the rack.

chojn1

Here is my DIY fair-weather custom carbon fiber fender finished:



It's made of four layer of carbon fiber around a foam core. The fender mounting bolts were embedded into the foam leaving the underside completely smooth.
Here it is on the bike:


I thought it turned out rather nice. But, my wife took one look at it and proclaimed that "there's too much black." I tried to remind her that my second choice of frame was a nude Calfee, but she wouldn't budge. So before I do something silly like painting the thing, I need your opinion. Too much black or just right?

CJ

vrooom3440

Looks great to me.