DIY: Mod Rear Rack & Fender for Full-Suspension

[Kingfish]

Overview:
Beginning last winter I had pondered many hours on creating a custom rear rack for my full-suspension ebike (P1). With the 2011 New Year I finally cut the Gordian knot and migrated over to the new frame: All the parts were there right in front of me just waiting to tinker and play, and that's how the solution came about. It’s possible this may work well for other folks with similar frames.

My story begins with a newly minted ebike with full-suspension and specialized fenders to go with.

Unfortunately these fenders are shite! :x The rear fender wanders around the seat post; it cannot be fastened down tight enough – period. In addition the front and rear fenders are far too high and removed from the tires to be effective for anything other than a Photo-Op when first mounted. My don’t they look pretty.

Another troublesome issue is that there is not a reasonable place to mount fenders, let alone a rear rack. They say that necessity is the mother of invention. Thinking outside the box I first evaluated how the original bike (P0) employed these devices:

The Rear Rack & Fender were previously attached at a hard-point already provisioned on the rear framework. The front fender was a kludged assembly with soft attachments on the forks and off the front brake fixture. I’ll begin with the front mod.

Phase 1: Front Fender Mod
After I put my new bike together – including the studded tires, the first ride had me headlong into the muck and crud of winter, and those studded tires threw crap all over the place. The image below well displays the results. Notice how far away the fender is from the tire (slightly protruding from beneath the front faring).

It dawned on me that I could re-use the fender from the old bike; mounting it on the new wouldn’t be too terribly difficult as the soft-points would essentially be the same. The small challenge was how to tie it off where the brake support would have been. The newer fork lowers are nicely supported by an arc of reinforced material and this made for a good spot; not perfect, but workable. Apologies for the dirty bike photos.

No guidance here; I would just conjure up any way of affixing so long as the mounting is static relative to the lower part of the fork and not rubbing against the tire. The soft-points actually fit better on the newer model forks because they are wider in diameter. So that’s it; a 3-point attachment and the fender is secured.

But, we are not done. The old fender on the new fork with the studded tires was still allowing a voluminous amount of crud to fling past. I resolved this by taking the now-removed front fender and cutting off the rear section to make a wider front extension. Reference image below:

The section scavenged is directly behind the front fork, and nipped-off about where the battery bag touches. Before mating the extension I swabbed down the contacting surfaces with Isopropanol, let dry, then slathered on Urethane, mushed the parts together – being careful with alignment, and allowed to dry overnight. The extension provides excellent forward coverage by about 6 inches, and nearly eliminates all overspray in the worst of conditions.

More in a moment…
~KF

 

[Kingfish]

Phase 2: Rear Fender & Rack Mod
The next trick was to figure out how to mount the rear fender. At first I just moved the item over, affixing the front to the frame with zippy tie-wraps exactly how I did it before, with the middle tied-off at the upper hinge. The rear points however did not have a home on the frame to mount to. Eventually I zipped-tied them to the frame near the axle for a week, although that later proved to be a mistake because the metal wire of the rear support moved around and scraped up the nice pretty new frame. In theory though, the concept was working out relatively well: The rear fender essentially travelled with the rear suspension and assuaged a massive amount of rear tire spray.

About this same time I pondered each night with the former bike rack literally in hand, and the thought occurred to me: “What if I just re-used this rack instead of building a new one?” With a bit of trickery I balanced the rack on the frame without any modifications and just imagined how it could be mounted. (With good strong coffee, anything is possible!)

Just looking at it, the pivot points seemed like the obvious choice for attachment. I took them apart, measured, determined the size, where to source them, and then spent a day finding the parts. It was snowing and very cold, but I travelled about 40 miles looking for the exact bolts as they are not common, and I modified them further when home. The front pivot bolt would be replaced by an M6 x 110mm bolt with a long unthreaded shank, and I fastened it with nylon nuts. Likewise the rear pivot bolt with an M5 x 40mm bolt, and I re-used the custom nut. Note: It is important to have enough thread so as to cut down to the proper size.

The bike rack required slight bending to accommodate the wider full-suspension frame. This was accomplished using a pair of 2x4 lumber in the vise. First, I widened the distance between the attachment points by about 2 inches, and then followed with the lumber and vise to bend the rack framework so that the mountings pointed straight down, sort of like the legs of a bow-legged man.

Next, the support bars from the pivots near the seat post were fabricated from ¾ inch wide x 1/8 inch thick x 3 feet in length tin-plated CRS bar. I divided this in half to craft two supports which were fairly easy to bend into the desired shape. Note: Twisting the bar adds rigidity. Mounting holes were located and drilled out. Edges were filed down, then the objects were wiped down with Isopropanol and painted with high-temp black paint (it’s what I had handy). I knew the paint wouldn’t cure in the cold weather, so after an hour of degassing outside I placed them in the oven at 150°F for an hour which after cooling allowed handling without ripping the paint off. Note: Use an old cookie sheet; something sacrificial to place the parts on when in the oven.

Now all the pieces of the puzzle were together: fasteners, brackets, fender, rack, & bike. Being lazy I didn’t remove the rear tire, but did flip it upside-down. Beginning with the rear pivots, I popped them out and slipped the new fasteners in with the rack next to the frame followed by the fender supports, then bolt. Rinse & repeat on the other side. Bolts were left slightly loose, and then I flipped the bike over. The front pivot fasteners had a custom washer which neatly covers the bearings; I was able to press that off the bolt and nut and re-use them in the next assembly: Custom washer, bracket, plain washer, M6 bolt – passed through the bike frame, then custom washer, bracket, plain washer, and nylon nut, synched down but not tight. Affixed the other ends to the bike rack with M5 x 10mm hex bolts and nylon nuts. Adjust position of the rack as required and synch it all down tight. Bike rack is now mounted.

Rear fastening: Hex bolt passing through the pivot and secured with a frame-specific custom nut.

Forward Pivot and bracket mounted with a hex bolt.

Fenders still needed a little bit of TLC. Once they are fixed at two end points the fender will flex up/down in the middle as the rear suspension moves, so the best that can be done is to reduce side-to-side wobble, and I did that at two points imaged below.

And that is it: Essentially a simple mod, though just a bit tedious in execution. It may work for you.

Completed rear assembly of fender and rack. Note: The bike will sag about one inch with rider on board and this will bring the rack into level. It is very much secured into place – exceedingly more than was on the previous bike frame. :wink:

Enjoy, KF

 

[etard]

Nice mod KF, I have been thinking about adding a rear rack to a FS bike and from your report I gather it is laterally strong enough to do, so I might copy a few points from yours if i ever attempts this, thanks for the write up.