Ran over a rock on vacation and was forced to resort to two new tires on my rear axle. How bad is it for the AWD system to have different tires/tread patterns between the front and rear axle? Should I replace it ASAP or is it okay? tread depth is the same for all tires

 

How much different in mileage are the old tires, compared to the new ones? Ideally you’d want the same tire height on all 4 corners, and tread pattern so no pulling or odd behavior.

 

For AWD, you definitely need to keep the tires the same. If the tires are fairly new, you can get away with only one, otherwise it would be a set of 2, and they have to be the same tires that are already on the car. If your not happy with them then take this chance to change all 4 to the ones you want. I had to make that choice earlier this year when one of my tires got a gnarly puncture from road debris. It looks like Acura may have built a little more tolerance into their system than Subaru which would require all 4 be changed if a new tire would be out of tolerance from the remaining 3.

 

I will just point out that tires from different manufacturers, or just different models from the same manufacturer, can have slightly different diameters even for the same nominal sizes. You can look up the tires on Tirerack.com, and see the specifications for overall diameter, and for revolutions per mile.

 

The owner's manual for my 2 previous and 2 current sh-awd vehicles is to change all 4 at the same time with the same size, load range, speed rating, and max cold temp rating. Another approved method is to replace the front or rear tires in pairs with the same rating similar to the existing older tires AND keep that pair together on the same front or rear axle together until you replace all four. No cross rotation if the newer tires have more tread or a different type (front to back only).

I had a pinch flat on my RLX Sport Hybrid at 7200 miles and I was able to replace that tire with one OEM tire because the tread depth was very similar to the other 3 existing OEM tires (now have +31,000 miles with zero issues). I had to non-repairable flat on one tire on my 08 RDX after running over road debris. I had to purchase two tires because the other 3 existing tires tread depth was between 6/32nd - 7/32nd compared to 10/32nd new. I kept the newer pair together and moved them to the front and kept them on the front axle 2X longer (front tires get more wear/tear compared to the rears). That way I would be ready for 4 new tires when due. I kept the extra 7/32nd tire and placed it on a rim to be used as a full size spare because it took about 7 days to ship and set an appointment for the replacement tires (Conti DWS 06 tires in late fall).

 

Nothing bad will happen to SH-AWD system if you mix different tires on front and rear axel, for as long as tires are the same on the same axel. The stuff they put into owner manual is for liability reasons as it will impact handling.

This happened to me few times on first gen rdx, nothing bad happed to sh-awd. The most annoying part is that its difficult to go back to 4 tires of same wear and you can not do cross rotations