Let's cut to the chase: The 2020 Mercedes GLB can hold an astonishing amount of stuff for a vehicle its size. The specs say there is 24.0 cubic feet of space behind the back seat, which would actually be quite good for this smallest segment of luxury SUVs (Audi Q3, BMW X1, Volvo XC40, etc.), but the space is so configurable that you end up with way more than that. I managed to fit inside roughly the same amount I put into the Subaru Outback, which is a far larger vehicle on paper (32.4 cubic feet) and in person. Wow. We already discovered when we tested the GLC that Mercedes seems to undersell its cargo capacity numbers, and this only reconfirms it.
First, let's take a look at all the tricks the GLB has up its sleeve.
There are two floor heights, and there's quite the difference between the two. This amount of space is needed to squeeze in the available third-row seat. Mercedes didn't have a seven-passenger GLB on hand during the first drive event, which isn't surprising as I can't imagine it being comfortable for anyone. Possibly dogs, but only small ones.
Let's put some luggage inside. This test car didn't include the available roller-style cargo cover, so I'll obviously start without it. As always, I use two midsize roller suitcases that would need to be checked in at the airport (26 inches long, 16 wide, 11 deep), two roll-aboard suitcases that just barely fit in the overhead (24L x 15W x 10D), and one smaller roll-aboard that fits easily (23L x 15W x 10D). I also include my wife's fancy overnight bag just to spruce things up a bit (21L x 12W x 12D).
This is with the floor in its highest position. All of the bags fit and there's room to spare. Already we're doing far better than everything else in this segment and even those above it. Check out all that space between the bags and liftgate edge. It's at least the equal to the GLC, but then that has only one floor height.
Here are two bag configurations with the floor lowered. At the right, you can also see the advantage of the GLB's boxy shape. It allows you to easily stack bags all the way to the liftgate, which is rare with increasingly raked SUV rooflines.
The above photos plainly show how much space is left, but we're not done yet. The GLB also has a sliding and reclining back seat. Thus far, it has been slid all the way back and reclined to what I consider a standard angle.
Above left shows the extremes of its sliding and reclining travel. Above right shows the range of recline using the 40/20/40-split, which is yet another great cargo feature.
Because the seat can slide, you could easily slide it forward, fully recline the seat AND still achieve all the space shown above.
Now, I could slide the seats fully forward and render them mostly useless while stuffing in an absurd amount of junk, but what's the point of that? Instead, I simply slid the 40/20 portions forward by a small amount shown below. The /40 portion stayed where it had been.
And just by doing that, I was able to fit in all of this stuff.
Again, this is what I could manage in the Subaru Outback, and it looks awfully similar to the Honda CR-V and Toyota RAV4 (possibly even a bit better). Now, all of those still have more back seat space, but to underline this point: The GLB's seats are still not fully forward and upright. There is in theory even more space! Yes, that calls for an exclamation mark.
Below is the rear view when fully loaded. You can still see, and nothing will fly forward.
Two final points. Above left is a side view of cargo area fully loaded, demonstrating again the advantages of the boxy shape. Above right is the handy strap and hook that let you prop up the floor while accessing under-floor items. Thoughtful.
Quite frankly, I'm blown away by the little GLB. It is far more functional than the bigger GLC (which is admittedly more luxurious and better to drive) and other compact SUVs, luxury brand or otherwise. Kudos to the engineers and designers.