I have a 3 bike hitch mount bike carrier that has worked for my family for the last few years. Now that my youngest is getting into the sport, I've run out of room and was in the market for a different solution.
I decided the day before our next trip that I'd better do something about it. It seemed to me that if I could get two bikes up top on the roof, I could have the two kids bikes on the hitch mount and be happy. Since the decent rooftop racks were $150-$200 each up here in Canada, I figured it was time to come up with a home-built solution!
I saw a few examples of others constructing similar racks but none of them met my needs. Here's what I came up with.
Step 1: Go Shopping
I was in our version of REI here in Canada (Mountain Equipment Coop - MEC) and found a fork mount called the swagman claw mount. This is a 9mm QR fork mount for $22 each that would fit the bill. Then I had a quick run over to the homedepot and picked up some 1 1/2" galvanized slotted steel angle. Since the front axle to bottom of the rear tire of my bike measured 38" I need the 4' length rather than the 3'. I also found some u-bolts that were 3" between holes and that fit my oval profiled roof rack bars perfectly.
Swagman Claw fork mount - $22
4' x 1 1/2" slotted steel angle - $11
4 x 3" u-bolts - $4
Old leaky bike tube - $ free as you haven't thrown it out yet
Locknuts/washers - $ free - kicking around your shop
Step 2: Measure and Drill Front Mount
Place the channel on the roof of the vehicle and figure out where your front u-bolt is going to go. Mark the location of the holes you need to drill.
Pick your drill bit. I initially drilled one size up from the diameter needed for the bolt leg. After realizing this was a bit naive, I stepped up a few sizes realizing I'm never that accurate.
I have a drill press in my garage and a nice little vice so I used that. However you drill the angle steel, hold it tight (not your hands) so when the bit catches, you don't tear holes in your hands. It's a little hairy drilling into the inside of a v shape.
I also like to use a metal file to clean-up the drilled holes, so there are no sharp pieces ready to wreck your paint job or slice holes in tires.
Step 3: Measure and Drill the Rear Mount
Use a u-bolt to mount the channel to the front rail. don't worry about tightening it. Measure and mark the location for the holes to mount the channel to the rear rail.
Step 4: Install the Fork Mount
Place the fork mount over the channel to determine where you want to protect your rails.
I used an old punctured bike tube to wrap the rail where the hardware will go. Overlap the tube about half and use some duct tape to keep it in place. If you have black duct tape it will look better than mine. Also, I don't know how well duct tape sticks to rubber, but it sticks really well to itself, so use extra and overlap to ensure a long-term stick.
Don't forget to wrap the back rail as well. I'm a little finicky about this as I know how brutal small vibrations can be over sustained periods of time. I also fit some tubing over the feet of the fork mount before clamping it all down.
Use two more u-bolts over the feet of the fork mount. Make sure you add a lock washer under every single nut so that vibration thing doesn't haunt you. I had piles of split lock washers on hand from another project, but I think nylock locknuts would be the best choice if you have them.
Step 5: Admire Your Handy Work for a Moment
Things are looking pretty good so far. It's good to take a moment to see if everything is adding up.
The only thing I noticed at this point was that I had to spend a minute making sure the u-bolt clamp on the inside of the channel was lined up properly to make the "V" shape stay upright and not lean to one side.
Step 6: Test Fit the Bike
to cut a threaded bolt down, two steps are best.... cut it with a hacksaw and then add back the rounded profile at the cut end. this will de-burr the cut but also slightly knock down the thread so the but is easier to start.<\EDIT>
So basically make sure the fork mount is nice and tight and don't forget to use a strap or bungie cord on the back tire to keep it from bouncing out of the channel.
PROTIP 1: Make sure your pedals can't hit anything up there. If they can, use a bungie cord to make sure they can't spin.
PROTIP 2: Make sure if you have a rear hatch, that the channel and/or back tire don't impact the opening of the door. If it does, try to move the whole works forward or cut the channel down to get it out of the way.
Step 7: Make One More
You can hardly make something this awesome for just yourself right?
In my case, I put another one together for my wonderful wife. This one of course goes together in about a third of the time as the first one because you know what you're doing now.
And so I've made my first highway trip with this rig and neither bike moved an inch. I stopped a couple of times as there's a fair amount of money riding along up there. Nothing moved, everything stayed solid for a few hundred miles.
Oh yeah, $40 is a lot easier to swallow than $200.
Step 8: Paint
Although everything is galvanized, I'm planning to paint the whole works with some zinc paint. It'll turn black and blend in better and have the added benefit of staving off the rust plague that loves steel.
Step 9: Paint
Overall it has turned out just fine and has now survived a few multi hundred mile trips.
So, if you paint, use a regular rust paint as it will definitely have a better finish.
Post a picture if you build something similar!