Center the mattress in the middle and put the rope over the length of the mattress.
How to tie a mattress to roof racks.
Then place the rope across the mattress length wise then secure both ends starting with the front then the back to the front and back bumpers respectively.
With the third option crossbars with side rails you can secure an item to the side rails and run tie downs from front to back securing them to the crossbars.
Ratcheting straps are much less likely to fail when moving a bulky item like a mattress.
Put a piece of rope on the roof of the car that goes from back bumper to front bumper.
Use a tie down that wraps around the item and the rails.
Once tightly packed in the mattress bag haul the mattress onto your roof and center it in the middle.
The mattress had lifted up in the front and ripped the roof racks right off.
I came across a guy on the highway that only had a strap going across.
Use strong rope or straps and make sure the mattress is tied down lengthwise and widthwise keeping the fastenings well centered.
If you do secure your mattress to a roof rack or safely in the bed of a truck strap it down with ratcheting straps.
Drive on surface streets if possible to avoid heavy air pushing up on the mattress at the front of the car.
Tie one end of the rope on a handle on the rear inside roof of the car.
On each side of the roof you ll see a rack that runs the length of the roof of the vehicle.
This will stress any knot no matter how securely tied.
If you do put it on the roof of your vehicle have a strap run from front to back as well as from side to side.
Roll down all windows.
First wrap the mattress in a bag new mattresses generally come in one or you can buy one at a hardware store and use packing tape to close the bag and secure any loose plastic.
After the mattress is secure in the plastic place the mattress on the roof.
Tie the rope that you placed the mattress on in place.
Mattresses are large bulky and can pick up resistance from the wind.
Put the mattress on top of the car and rope so that it goes length wise with the length of the car see pics above.
Secure the front end of the mattress and then the other end of the mattress.