How high is too high?

I bet you could make a good way to prevent the wood from falling with a feedlot panel. back to your height quest 4ft without barrier / 6ft with basic barrier / any height with strong barrier.

You might want to protect the sheetrock wall.
I would suggest cheap luan or plywood.
Been there done that.

screw the vertical wood into a stud in the wall.
might help to slowly stagger the wood as it gets higher; like a retaining wall. just a hairs width per row up.

4 feet should be just fine. I usually stack 6-7 feet high without end bracing, but I crib the ends at least 4 feet high. 20” wood will be more stable than 16 or 18. If you are worried about the car, you can use small angle brackets and screw them to 20” pieces of 2x2 and then screw the brackets to the wall studs to make them stick out. Put the “pegs” every few feet and about 3 feet off the ground(if you are stacking to 4’ or a bit higher. Then stack your wood around the pegs. The pegs should become part of the stack, and the friction will keep the pile from tipping over. You can use as many or as few pegs as you want. Another thing that can give more grip is chopping grooves into the pegs with a hatchet before mounting them to the wall.

If this is beside the car, just lean the stack towards the wall purposefully.
If this is at the front end of the car, where the stack could get hit by the car, you'll probably find holes in the sheet rock made by splits getting pushed thru any time the car bumps the pile pulling in. To help with that you can suspend a tennis ball from a string so it touches the windshield to mark where "in" is so you don't have to pull in any further.

The slats on those pallets(?) look a little flimsy and might want to sag under the weight of your firewood, causing the stack to become unstable. You could easily cut some scrap 2x4's to make extra stringers, and insert one into the middle of each section to increase strength and stability.

Stacking your wood on the concrete is fine and will be more stable.

Dmitry said:

View attachment 233607 View attachment 233608 View attachment 233609 View attachment 233610 View attachment 233611 View attachment 233612 Here is final product . I’ve attached 2by4 to studs and use metal braces to secure pallet to wall. The wood is fairly stable , stacked about 6 feet high and being 20”. Wife went bananas about taking garage space . But became happy when I came with extra storage space by placing runs on a top of build rack. Here is pictures.

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Looks good, I have a 6 x 6 x 8 rack on casters so I can move it around, if I had the wall space I'd do something similar to what you did.

nice, only thing i might do different is put a sheet of 1/4" lauan or other cheep plywood behind the racks if you're worried about marring up the walls, if you're not then you're good to go.

ingenious design, looking good

Dmitry said:

View attachment 233607 View attachment 233608 View attachment 233609 View attachment 233610 View attachment 233611 View attachment 233612 Here is final product . I’ve attached 2by4 to studs and use metal braces to secure pallet to wall. The wood is fairly stable , stacked about 6 feet high and being 20”. Wife went bananas about taking garage space . But became happy when I came with extra storage space by placing runs on a top of build rack. Here is pictures.

Click to expand...

What are you doing with all that Portland cement? Looks like your cooking up some project.

Dmitry said:

Ha, its actually leftover from summer patio project. Need to find a use for it.

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I have two bags of s type mortar sitting in my barn like that. Don't even remember why I bought them.

Your garage is very clean compared to mine, I need a barn/shop.