SundayDriver
New member
It took me countless hours over the course of two weeks to find, buy, and install a GM roofrack on my Sonic hatchback and get my 13.5' kayak safely mounted on it. Why so long? Because: (1) The Sonic doors are funky and there is no Thule or Yakima clamp-on rack that fits them. (2) The GM rack has a funky Euro shape that may or may not fit your Thule or Yakima saddles and other accessories. (3) Anchor points for bow and stern lines are a head scratcher. (4) The instructions that come with the GM rack are terrible---just cryptic illustrations with no text.
I'm posting this for people who aren't mechanics to save you some time. So here's how to install the GM roofrack, kayak saddles, and bow and stern lines and load a kayak from the rear, with a bonus tip for a bike rack.
STEP 1: Know what you're buying. You're buying a roofrack that can only be mounted in a specific limited place with about 28" between the bars. You can't slide them forward or backward or apart; they only fit in one EXACT place (down to the millimeter). 28" between the bars means that there's a high chance that your straps will pass over the coaming rather than in front of and behind the coaming. My coaming is 36" long. That's about the maximum length to be able to place the straps in front of and behind the coaming. The racks are mounted fairly far forward on the car. If you load from the rear you will need to clear about two feet of spoiler and roof before your kayak touches the rack. I was able to overcome these problems. It's not ideal but it's workable.
STEP 2: INSTALL THE ROOFRACK.
1. Install the rubber strip in the channel on the bars. Much easier to do this now than when the rack is on the vehicle. Separate the strip into two pieces lengthwise. Push it into the channel with the round side down.
2. Remove the covers on the feet. There are two small plastic "keys" about an inch long. Insert the key at the top of the foot and turn to release the cover. (These are NOT real keys! They will not prevent rack theft. This is not a lockable rack.)
3. Install the pads on the feet. Each one is marked left or right and front or rear, as are the crossbars. To install the pads, insert the rubber nipples through the holes in the foot. Pull the nipples through the other side with pliers (gently, of course) until they pop all the way through.
4. Clean the door frame where the feet will be installed. Notice the indentation where the clamps will go. This is the only place where the clamps can go.
5. Use the included torque tool to loosen the screws on the feet as far as they will go. Don't worry, the screws won't fall out; there's a stop on the end of the screw to prevent that.
5. Place the crossbars on the roof and place the feet in approximately the right place, with the clamps fitting over the edge of the roof.
6. Get a tape measure with millimeters (or make the conversions to inches online, but mm are more accurate).
7. IMPORTANT: Measure from the center of the foot to the edge of the other door frame (e.g., center of front foot to edge of rear door). The measurements are 365mm front and 340mm rear. That's about 14 3/8" front and 13 3/8" rear. Measure very carefully or the feet won't line up right.
8. Tighten the foot screw with the torque tool. How you do this is important. Start by tightening the screws a bit on one side of the car and then on the other side. Check your measurements again on both sides of the car and move the foot as necessary. Tighten the screws about halfway, meaning you know it's not tight enough to be secure.
9. Now comes the hairy part. You've read in this forum about people denting their roof with the torque tool so you're going to be cautious. Tighten the screws to 4 Nm (Newton meters). Oddly, the instructions assume you know what that means and how to do it. When you get to 4 Nm the torque tool will click and you'll know that’s enough. A poster reported denting his roof at 2.5 Nm, so take it easy.
10. As you're tightening the screws keep a close eye on the underside of the roof edge to make sure it's not denting and check the angle between the edge of the roof and the clamp. They should be parallel, with no large space at the top between the clamp and the edge of the roof. This is one reason why you tighten the screws gradually and move back and forth from the right side to the left side of the car, instead of tightening one side all at once.
11. Everything look good? Grab the cross bar and make sure it’s sturdy.
12. Final step: Replace the foot covers. Put the keys in a safe place, probably the glove compartment.
STEP 3: INSTRUCTIONS FOR INSTALLING THULE 878XT SADDLES
These saddles will fit the GM crossbars with a couple of modifications.
(1) The bolts are too short because the GM bars are thicker than Thule square bars. If you don't mind paying $15 for 4 bolts, you can get longer ones from Thule. Part name: Adapter Kit Xadapt3 #13810. There's no actual "kit." It's just 8 bolts, 80mm long. If you don't want to pay $15, note that the threads on these bolts are "fine" rather than standard and you won't find them at Home Depot or Lowes. The thread has to match the thread in the knobs. Alternative if you can't wait for Thule to ship the bolts: Buy carriage bolts 1/4" x 2.5"; locking washers, and wingnuts. The wingnuts will be harder to tighten than the original knobs; you'll need to use gloves to get them tight.
(2) The plates on the saddles don't fit the shape of the large aero bar all that well. You can overcome that by cutting rubber pads about 1/4" thick to go over the top and bottom of the bar. Cut them to the shape of the saddle feet and the plate.
(3) Tighten both sides of the saddle feet together so they end up evenly spaced on the bar. Otherwise they will tend to lean and slip off the bar.
Tip to prevent your kayak from falling off the side of the car while loading: I use four L-shaped saddles instead of L’s in the front and flat saddles in the rear. The flat saddles don’t hold the kayak very well. The L saddles need to be covered with something slippery so the kayak will slide over them. Easy solution: socks!
STEP 4: BOW LINE
There are a number of holes on the frame under the hood that could be used to secure a bow line, but they're very small so you won't be able to pass a strap through them. I screwed a small steel plate about 3/4" x 4" into one of the holes. The plate just happened to have a slot in one end that would accept a strap. When I closed the hood the plate made a tiny dent in the underside of the hood. An alternative is hood tie-down loops like these: https://www.amazon.com/Shoreline-Marine-Propel-Trunk-tie-Down/dp/B07NVWL3RP/
STEP 5: STERN LINE.
This is harder. I only found one suitable hole under the rear of the car that could take something like a hook for a stern line. It's attached to the spare tire well on the passenger side, about 14" (?) from the center. There is no place for a stern line in the center. There are four holes in the frame members going the length of the car on each side, but the first hole is quite far in. So I chose the hole next to the spare tire well. This is problematical because of its location so far from the center. Fortunately I carry my kayak on the passenger side, not in the center. If you carry your kayak in the center, you could run a line from each side using the holes in the lengthwise structural members. Another alternative: same tie-down loop as above, inside the hatch. Normally a good solution is an anchor point installed under the car, but there isn't enough space for this between the hole next to the spare tire well and the back of the bumper.
STEP 6 MAKE A REAR KAYAK LOADER SO YOU DON’T BREAK YOUR SPOILER
Luckily, the spoiler isn’t terribly delicate. Here is the simplest way to load a kayak from the rear without spending hundreds of dollars on a Thule or Yakima loader:
(1) Get a block of high-density foam about 4” x 4” x 14”. The foam kayak blocks made by Riverside work very well.
(2) The kayak needs to slide on the block, so cover it with something slippery. I simply duct taped a towel around it.
(3) Get a piece of ¼” high density foam, about 14” x 14”. Place it on the spoiler for protection.
(4) Thread a Thule or other cam strap through the space between the open hatch and the roof of the car so that the buckle end of the strap ends up at the top of the window on the outside and the other end of the strap wraps around the back of the hatch.
(5) Place the foam block on the foam pad, under the strap. The block should be pushed back behind the spoiler so minimal weight ends up on the spoiler.
(6) Cinch the strap quite firmly so the foam block doesn’t move while you’re loading the kayak. But not firmly enough to break the spoiler.
(7) Place a 6’ runner rug about 5’ behind the car to protect the keel of your kayak.
(8) Place the bow on the edge of the spoiler and lift it onto the foam block. It should just barely clear the edge of the spoiler.
BONUS FOR CYCLISTS: The foam block strapped behind the spoiler can be used in exactly the same way for a trunk-mounted bike rack! Allensports 102DN is just $50. The foam block will keep the rack straps just above the spoiler. There will be little to no weight on the spoiler.
I think I've covered everything. This whole process was aggravating and time consuming. The Sonic isn't well designed for cyclists and paddlers---the very people who favor hatchbacks---but if you like the car you can probably make it work for you with some creative thinking.
I'm posting this for people who aren't mechanics to save you some time. So here's how to install the GM roofrack, kayak saddles, and bow and stern lines and load a kayak from the rear, with a bonus tip for a bike rack.
STEP 1: Know what you're buying. You're buying a roofrack that can only be mounted in a specific limited place with about 28" between the bars. You can't slide them forward or backward or apart; they only fit in one EXACT place (down to the millimeter). 28" between the bars means that there's a high chance that your straps will pass over the coaming rather than in front of and behind the coaming. My coaming is 36" long. That's about the maximum length to be able to place the straps in front of and behind the coaming. The racks are mounted fairly far forward on the car. If you load from the rear you will need to clear about two feet of spoiler and roof before your kayak touches the rack. I was able to overcome these problems. It's not ideal but it's workable.
STEP 2: INSTALL THE ROOFRACK.
1. Install the rubber strip in the channel on the bars. Much easier to do this now than when the rack is on the vehicle. Separate the strip into two pieces lengthwise. Push it into the channel with the round side down.
2. Remove the covers on the feet. There are two small plastic "keys" about an inch long. Insert the key at the top of the foot and turn to release the cover. (These are NOT real keys! They will not prevent rack theft. This is not a lockable rack.)
3. Install the pads on the feet. Each one is marked left or right and front or rear, as are the crossbars. To install the pads, insert the rubber nipples through the holes in the foot. Pull the nipples through the other side with pliers (gently, of course) until they pop all the way through.
4. Clean the door frame where the feet will be installed. Notice the indentation where the clamps will go. This is the only place where the clamps can go.
5. Use the included torque tool to loosen the screws on the feet as far as they will go. Don't worry, the screws won't fall out; there's a stop on the end of the screw to prevent that.
5. Place the crossbars on the roof and place the feet in approximately the right place, with the clamps fitting over the edge of the roof.
6. Get a tape measure with millimeters (or make the conversions to inches online, but mm are more accurate).
7. IMPORTANT: Measure from the center of the foot to the edge of the other door frame (e.g., center of front foot to edge of rear door). The measurements are 365mm front and 340mm rear. That's about 14 3/8" front and 13 3/8" rear. Measure very carefully or the feet won't line up right.
8. Tighten the foot screw with the torque tool. How you do this is important. Start by tightening the screws a bit on one side of the car and then on the other side. Check your measurements again on both sides of the car and move the foot as necessary. Tighten the screws about halfway, meaning you know it's not tight enough to be secure.
9. Now comes the hairy part. You've read in this forum about people denting their roof with the torque tool so you're going to be cautious. Tighten the screws to 4 Nm (Newton meters). Oddly, the instructions assume you know what that means and how to do it. When you get to 4 Nm the torque tool will click and you'll know that’s enough. A poster reported denting his roof at 2.5 Nm, so take it easy.
10. As you're tightening the screws keep a close eye on the underside of the roof edge to make sure it's not denting and check the angle between the edge of the roof and the clamp. They should be parallel, with no large space at the top between the clamp and the edge of the roof. This is one reason why you tighten the screws gradually and move back and forth from the right side to the left side of the car, instead of tightening one side all at once.
11. Everything look good? Grab the cross bar and make sure it’s sturdy.
12. Final step: Replace the foot covers. Put the keys in a safe place, probably the glove compartment.
STEP 3: INSTRUCTIONS FOR INSTALLING THULE 878XT SADDLES
These saddles will fit the GM crossbars with a couple of modifications.
(1) The bolts are too short because the GM bars are thicker than Thule square bars. If you don't mind paying $15 for 4 bolts, you can get longer ones from Thule. Part name: Adapter Kit Xadapt3 #13810. There's no actual "kit." It's just 8 bolts, 80mm long. If you don't want to pay $15, note that the threads on these bolts are "fine" rather than standard and you won't find them at Home Depot or Lowes. The thread has to match the thread in the knobs. Alternative if you can't wait for Thule to ship the bolts: Buy carriage bolts 1/4" x 2.5"; locking washers, and wingnuts. The wingnuts will be harder to tighten than the original knobs; you'll need to use gloves to get them tight.
(2) The plates on the saddles don't fit the shape of the large aero bar all that well. You can overcome that by cutting rubber pads about 1/4" thick to go over the top and bottom of the bar. Cut them to the shape of the saddle feet and the plate.
(3) Tighten both sides of the saddle feet together so they end up evenly spaced on the bar. Otherwise they will tend to lean and slip off the bar.
Tip to prevent your kayak from falling off the side of the car while loading: I use four L-shaped saddles instead of L’s in the front and flat saddles in the rear. The flat saddles don’t hold the kayak very well. The L saddles need to be covered with something slippery so the kayak will slide over them. Easy solution: socks!
STEP 4: BOW LINE
There are a number of holes on the frame under the hood that could be used to secure a bow line, but they're very small so you won't be able to pass a strap through them. I screwed a small steel plate about 3/4" x 4" into one of the holes. The plate just happened to have a slot in one end that would accept a strap. When I closed the hood the plate made a tiny dent in the underside of the hood. An alternative is hood tie-down loops like these: https://www.amazon.com/Shoreline-Marine-Propel-Trunk-tie-Down/dp/B07NVWL3RP/
STEP 5: STERN LINE.
This is harder. I only found one suitable hole under the rear of the car that could take something like a hook for a stern line. It's attached to the spare tire well on the passenger side, about 14" (?) from the center. There is no place for a stern line in the center. There are four holes in the frame members going the length of the car on each side, but the first hole is quite far in. So I chose the hole next to the spare tire well. This is problematical because of its location so far from the center. Fortunately I carry my kayak on the passenger side, not in the center. If you carry your kayak in the center, you could run a line from each side using the holes in the lengthwise structural members. Another alternative: same tie-down loop as above, inside the hatch. Normally a good solution is an anchor point installed under the car, but there isn't enough space for this between the hole next to the spare tire well and the back of the bumper.
STEP 6 MAKE A REAR KAYAK LOADER SO YOU DON’T BREAK YOUR SPOILER
Luckily, the spoiler isn’t terribly delicate. Here is the simplest way to load a kayak from the rear without spending hundreds of dollars on a Thule or Yakima loader:
(1) Get a block of high-density foam about 4” x 4” x 14”. The foam kayak blocks made by Riverside work very well.
(2) The kayak needs to slide on the block, so cover it with something slippery. I simply duct taped a towel around it.
(3) Get a piece of ¼” high density foam, about 14” x 14”. Place it on the spoiler for protection.
(4) Thread a Thule or other cam strap through the space between the open hatch and the roof of the car so that the buckle end of the strap ends up at the top of the window on the outside and the other end of the strap wraps around the back of the hatch.
(5) Place the foam block on the foam pad, under the strap. The block should be pushed back behind the spoiler so minimal weight ends up on the spoiler.
(6) Cinch the strap quite firmly so the foam block doesn’t move while you’re loading the kayak. But not firmly enough to break the spoiler.
(7) Place a 6’ runner rug about 5’ behind the car to protect the keel of your kayak.
(8) Place the bow on the edge of the spoiler and lift it onto the foam block. It should just barely clear the edge of the spoiler.
BONUS FOR CYCLISTS: The foam block strapped behind the spoiler can be used in exactly the same way for a trunk-mounted bike rack! Allensports 102DN is just $50. The foam block will keep the rack straps just above the spoiler. There will be little to no weight on the spoiler.
I think I've covered everything. This whole process was aggravating and time consuming. The Sonic isn't well designed for cyclists and paddlers---the very people who favor hatchbacks---but if you like the car you can probably make it work for you with some creative thinking.
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