So I've got the 21" rims on my 2020 GLC63 and as I pull out of my driveway/parking stall backwards or forwards, depending on how far i turn the wheel, as soon as i change direction to leave, i feel a "thud" from the front tires. Is this normal because of the large rims or is something messed up?

Do a search on crabbing defect !

From what I've heard, this happens on the 63 with 21" run flats. Those with the 20" wheels with all season tires don't seem to have the crabbing (thud) that you're experiencing. Not sure if putting all seasons on the 21" wheels will fix it, but I believe it will help.

The car is crabbing. I can report that it does this less with my 21" snow tires on the stock 21" rims, but will still do it very subtly.

Well that’s cool having an $83k car doing that. Anyways, it only does it like once, so I can live with it. It just threw me off guard. Thanks for the diagnosis guys.

It comes down to the contact patch of the tires. Tires with less solid rubber on the ground, either because of a smaller size, or because of a lower tread-to-void ratio (like a winter tire or all season) don't grip as much, so they don't create the same "skipping" effect.

Believe it or not, I have the same issue on a Polaris RZR now that it has an AT tire that has more solid contact patch than the OE.

I had no crabbing ony 2018 glc63 with either oem or aftermarket (even wider) 21s...not sure why but not once even

Yeah, not everyone seems to run into it. From what I've read, it affected the right-hand drive models more than the left-hand drive we have here in the States. But then again, some people like the OP have had it on their LHD cars, so it's anyone's guess I suppose. But it does seem to be relegated to those with 21" run flats the most. Again, near as I can tell in doing my research (I still have my 43 on order and don't plan on cancelling because of this issue).

My first post but long lurker here... wootz

I have a '19 GLC63S with the 21" rims/ Michelin 4S tires and at the start of winter season noticed the "thud' or "crabbing" issue was quite pronounced. Forward or in Reverse with wheels turned in either direction it would skip. Just yesterday I had a hair brained idea to adust the pressure in my tires to 36 Front and 32 Rear, up from 32 Front/28 Rear - and no more skips, crabs, or thuds .. so far. Huge improvement I'd say. My wife would think I was hitting curbs it was so bad before.

Hope this helps.

I have the 21 inch with summer tire Continental on a 43 and even in San Diego when the temp is under 45 (not often) it's crabbing !
Last week before going to ski in Utah ,I got all season tires installed .I went 1 size up front and rear (265-40-21 front and 295-35-21 rear" Pirelli Scorpio all season plus" ) and no more crabbing except when the temp was 16 degrees in Utah .The ride is much smoother too .
I also get the chance to test the car on snow since we got 17 inch one night .No problem to go anywhere on snowy road even with those wide tires .