Needed to get my On-One Fatty with 4" tyres on my Thule proride 591 roof bike rack.
The existing plastic wheel braces are too narrow for the fat tyres, so I looked at using the method from this excellent mtbr post, but unfortunately could not get any suitable ratchet-type straps, so thought of trying to re-use the existing Thule straps. I also priced the drainage couplers here in expensive New Zealand as ~NZ$23 / ~US$ 20 compared to ~US$5 in the States - insane!
This is my take on a solution using mostly pieces I had lying around the garage.
The main idea was to use the t-tracks at the bottom of the rack such that I could slide the bracket in and out as needed as well as for positioning. Bonus was not needing to drill into the Thule aluminium rack.
Another aim was getting a sturdy brace to minimise sideways sway of the tyre, and typical plastic solutions seemed too under-gunned.
(all units Metric)
1) 800mm of some aluminium u-shaped extrusions (the main thing here is that the existing Thule ratchet bracket fits nicely over the bottom of the 'u'). Square tubing of the right size would also work.
2) 4x 200mm stainless steel building strip fasteners (dunno the technical term but check photos). You can go to 300mm length for wider tyres - the main point is that these are not too long to make the bracket sit against the rim, but against the rubber of the tyre.
3) 16x 3.2mm aluminium rivets
4) 8x m6 25mm stainless bolts
5) 16x m6 washers (total diameter ~ 15mm)
6) 8x nyloc m6 stainless nuts
7) zip ties of smallish size
I had to be a bit creative as I could not source t-bolts of the right size for the t-tracks. This is what parts (4) and half of (5) is for. Substitute those if you can get t-bolts of correct size.
Cut the 800mm u-shaped aluminium extrusion into 4x 200mm sections. Each new bracket will use 2 of the cut extrusions.
File and sand the edges to make them smooth and round the corners. This step is important as these strips will sit against your tyre and any sharp burr / point will cut into the tyre.
The strip fasteners already contains some holes, so using those, mark out where to drill into the bottom part of the u-shaped extrusion. Make sure to get these as square as possible. Also position the fasteners a bit in from the edge of the extrusion as the fasteners have quite sharp corners.
Drill the first set of holes using the fastener holes. Rivet them. Then mark out where you would like to put the other and drill through the strip fastener and the alu extrusion at the same time.
Rivet the last remaining holes such that each end has 2 rivets.
Note that in my photo the strips are bend into a half circle - that was to size up the circumference around the tyre. It is best keeping it flat to ease the measuring and drilling. They bend easy, so can bend back and forth during the fabrication.
The Thule ratchet bracket has a small hole in the metal part. We will use this to help secure it to the alu extrusion.
For each 100mm extrusion, measure the mid-point (100mm) to drill a 3.2mm hole to secure the Thule rachet to the alu extrusion.
I wanted to use some sort of bolt and nut to secure the ratchet, but found the space under the ratchet latch too tight and used 5 zip ties in the end. One of the zip ties goes through the drilled hole in the alu extrusion and the ratchet. I think this will be secure and strong enough.
Note: make sure you position the ratchets the correct way on both sides - they should be mirrored to make the Thule plastic strap work correctly in the ratchets.
Next we need to make the t-track sliding bolts.
Measure the mid-point (100mm) on the stainless strip fastener and t-track offset from this mid-point. The t-track seems to be 35mm width. Mark where the m6 holes will be drilled, there will be 2 holes per strip fastener.
Use the m6 bolts and 2 washers per bolt to create a t-bolt for the track. There will be a washer on each side of the t-track slot. I had to file off the washer that goes inside the t-track on opposite ends as it did not fit properly.
Put the bolts through the strip fasteners and tighten the nyloc nuts until they are tight but not too tight as too leave space such that the bolts can still slide in the t-tracks.
Remove the end-caps from the Thule rack and slide in the bolts keeping the washers on both sides of the t-slot.
Replace the end-caps.
Bend the fasteners such that the bracket forms a half circle - just enough to form a cradle for the fat tyres.
Mount the rack to the car and strap on your bike!
In the photo I used a different bracket for the rear as I did not have enough alu extrusion to make another one like the front bracket. The parts list above is for 2 full brackets.
Oh, don't forget to have a beer and share your success.
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