Many AWD cars require replacing tires in sets in the manual
As for the long term ramifications, you’ll definitely see increased wear/camber on the opposing tire(a) and I’ve read it could theoretically cause issues with the diff, but I find that extremely hard to believe at least for the cats I’ve driven, because the front:back power ratio is dynamically recalculated and changed continuously depending on driving conditions. If it were 4WD rather than AWD, that might be the case though.
The AWD would rather stay engaged which puts strain on the transmission to shift harder. Over time this showed up as increased transmission temperatures. My transmission is sensitive to heat but has a poor design which makes any heat a very big deal. At about the same time I was researching new wheels and determined I could fit 9” wide tires in the rear vs 8.5” in the front. A staggered wheel set would give me more rear wheel power bias, but the closest I could get in tire size was still almost .5% larger in diameter.
In all my research it turns out you need tires of the same size within 3/16 wear of each other to avoid non-full time AWD transmissions from doing dumb things like my car does. You see, the AWD clutch simply engages a power transfer unit and then depends on ABS to control power sent by the differential to individual wheels. That system needs to recalibrate itself regularly and it does this when the clutch disengages. When it doesn’t, all sorts of warnings are tripped (in my car I went down 6 floors of a spiraling parking garage exit at 15-20mph and at the 2nd floor a “service stabili-trak” icon appeared on my dashboard)
In cars with a well designed AWD system this will not happen.. but most cars are not designed to engage in AWD for prolonged periods of time and are really there as a beefed up version of traction control. For instance my Torsen Quattro AWD Audi had full time AWD and never had this problem nor would a Nissan GT-R. But for that fancy Lexus or Hyundai AWD, you may want to make sure you stick to the recommended tire rotation schedule
To end my story, I was at the service center and they mentioned I should get my transmission checked out by the bigger repair bay because of the clunking. I suggested it may be the wear of the tires and they agreed to see if that solved the problem. New set of tires and the clunking, extra AWD engagement, and transmission temps went away.
I actually don’t consider a car that doesn’t have full-time AWD to be AWD at all, isn’t that considered 4WD?
4WD (4x4) is full time (typically selectable but cannot be changed while in motion). 4WD has a greater gear ratio to really put power to the wheels that have grip, so while all 4WD cars can be considered AWD, AWD cannot be considered 4WD. I’m sure some jeep owner can give a better rundown on why 4WD is named the way it is..
Not true for a long time now. Manually locking hubs required egress while stopped but at some point 4wd tech progressed.
TBH the line has blurred considerably in recent years and what once would have been 4x4 (manually engaged fixed-ratio four wheel mode) is being marketed as AWD. I’m sitting in a rental GMC Terrain (very crappy car, with or without AWD) and it must be manually switched from 2WD to 4WD mode but it’s an electronic button (rather than gear selection lever) that can be changed at speed, and can also be used in 4WD mode at highway speeds without redlining. This is considerably different from body-on-frame SUVs/pickups with “true” 4x4 mode that have regular 2WD but can be changed into 4L or 4H to get different gearing ratios inside the transfer case for four wheel drive.
And AWD is any system that drives all 4 wheels permanently. In fancy systems, the ratio sent to front vs rear might vary from 50/50 to 0/100, but it's always engaged to some extent. These systems are safe for regular on-road use.
Pick-up trucks and truck-based SUVs usually have 4x4 systems (with a few exceptions like the Land Cruiser and Lexus GX which are both AWD).
Cute utes and cross-overs, plus the odd-ball sedans and wagons (Subaru, VW 4Motion, Audi) are usually AWD.
Edit - as noted in a sibling comment, the line has definitely blurred with fancy electronically controlled and viscous couplings, but generally "truck" = 4x4 and cross-over/wagon = AWD.
9/32 + 3/16 = 15/32 so I guess not
It’s one of the main reasons why that car is notorious in terms of maintenance.
Too bad, I love that car though.
I have a guy at work who has been without a car for 4 months due to Tesla fuckups, and he basically defends Elon’s honor on the internet as a hobby.
Personally I find discussing Toyota on the internet to be far less productive than Tesla.