do i have to replace all four tires? had a flat...

[circmand]

On second thought maybe this is a more appropriate picture:

Now you are just trying to hard.

And the post was unnecesarily wrong and proved my point. These 3 little words "or within 4/32-inch" that is a good amount of wear difference and documents that when mentioning tire size the manufacturer is really concerned about different sized tires not same sized tires with a little but different wear. I pulled a random tire off tirerack
http://www.tirerack.com/tires/TireSe...45&diameter=17

Its specs state that tread septh new is 10/32, its tread warranty is 50,000. If you divide the tread warranty 50,000 by usable tread depth 8/32 (assuming tire wear out is 2/32) you get wear ratio of 6,250 miles per 1/32 of wear. Multiply that by 4 (the allowable difference as stated in audi manual in quoted post) and you have an allowable mileage difference of 25,000 miles.

Therefore I submit for your approval that while NOT AS GOOD AS $ NEW buying 2 replacement tires is acceptable by manufacturer standards as long as the existing tires have less than 25,000 miles on them.

[etlsport]

Now you are just trying to hard.

And the post was unnecesarily wrong and proved my point. These 3 little words "or within 4/32-inch" that is a good amount of wear difference and documents that when mentioning tire size the manufacturer is really concerned about different sized tires not same sized tires with a little but different wear. I pulled a random tire off tirerack
http://www.tirerack.com/tires/TireSe...45&diameter=17

Its specs state that tread septh new is 10/32, its tread warranty is 50,000. If you divide the tread warranty 50,000 by usable tread depth 8/32 (assuming tire wear out is 2/32) you get wear ratio of 6,250 miles per 1/32 of wear. Multiply that by 4 (the allowable difference as stated in audi manual in quoted post) and you have an allowable mileage difference of 25,000 miles.

Therefore I submit for your approval that while NOT AS GOOD AS $ NEW buying 2 replacement tires is acceptable by manufacturer standards as long as the existing tires have less than 25,000 miles on them.

while the numbers presented dont mean anything because tires do not wear at a constant rate, i will absolutely agree with your logic

if the op had said that their remaining tires had 75% tread remaining there would have been no reason to replace all 4 provided an acceptable size/load/tread replacement tire was found. the question asked was at 40% should all 4 be replaced and i maintain an unwavering yes

if you read what i have been saying, my point is not that you ALWAYS have to replace 4 tires. it is that on a vehicle equipped with AWD/ 4wd, it is essential that the tires be close in tread depth. every point i have argued has been with the assumption that the tires not being replaced are below 6/32nds of tread remaining

that being said..
I have seen many vehicles in my shop with differential or transfer case damaged caused my mismatched tires. strictly my personal preference, my VX will never have more than 2/32nds tread difference