When your truck is full of other stuff it's nice to have secure spot for bikes.
I think Thule makes a truck mounting system but this is definitely way less expensive.
4 U bolts
16 large flat washers
8 large rubber washers
1 foot (or less) of PVC pipe
8 Sealing washers
Bike fork mounts
Bike wheel mounts
A truck with a cap
Saw (hack saw or band saw)
Step 1: Measure
As always this step is important. Measure a bunch of times before you drill your holes.
First, it is important to measure the distance between the fork and the back wheel of your bike. There is some variation in this distance from bike to bike and for the trays I have the amount of adjustment is fairly minimal.
Next measure the top of your truck cap as precisely as possible. This is a potentially difficult step because of the curves on the edges of the cap. I measured to the edges of the side windows with a flexible measuring tape to make sure I had a consistent starting point on both sides.
Remember that you want your U bolts on the outside of the trays and fork mounts so that it is harder for someone else to take parts of your rack or your whole bike.
I put the bolts 8.5 inches from each side and 14.5 inches from the ends but you should do measurements of your own.
Step 2: Drill Baby Drill
Now it is time to make your holes. It is a bit nerve racking (pun intended) to drill holes in your truck but this should end up being a waterproof system so it's not so bad.
Drill your holes with a bit that is exactly the same diameter as your bolt. Any extra space is going to make it less likely that the washer seal the hole up correctly.
Also make sure the holes are exactly the right distance apart to fit the U bolt.
Step 3: Cut the Tube
You will need 8 pieces of PVC pipe exactly the same length. Depending on the size of your U bolts this length will vary. Mine were approximately an inch and a quarter long. These are the spacers between the truck cap and the cross bars of the rack. They need to be long enough to get the fasteners for the rack attachments on but short enough for the bolts to reach through the holes.
I used a band saw but it might actually be easier to cut them with a hack saw. If you are using a band saw be careful. Cutting round things is dangerous.
I ground a notch in the tubes on one end so that if water does get inside there is an easy way for it to get out that is not through the truck. I do not recommend using an angle grinder for this but it was the most convenient tool I had and it worked.
Step 4: Bolt It Together
The U bolts should have come with a cross bar. If they didn't you will need to make one. Tightening the nut from the bottom is the hard part here. It might be helpful to have someone on the outside push down on the bolts.
Thread your parts onto the U bolts in this order:
Cross bar (plate)
The load bars for the rack should go over the U bolt cross bars.
Step 5: For Mount, Trays, and Bike
Now it is time to add your fork mounts and trays and put the bike on. There are a variety of types of rack parts. Mine are used Thule rack parts but other brands might attach differently. I had two bikes up there for a long drive today and it didn't move around at all.
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