# Car tire advice - flat on a AWD car, need answer kinda fast **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 25, 2014, 1:32pm UTC](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606 "2014-06-25T13:32:51Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [June 26, 2014, 6:00pm UTC](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606/21 "2014-06-26T18:00:28Z")
> [@sparky\_1](#): > > If I’m not mistaken, you are supposed to disable AWD by pulling a fuse when using the spare, as well as being below a certain speed. > > But really, for the amount of limited miles and limited speed, the donut shouldn’t cause harm. That is correct, but I was less than 2 miles from home when I flatted, and the tire place is less than 1/4 mile from my house so I didn’t bother. The instructions also say that the spare should only go on the rear of the car, and if you flat a front tire to move one of the rear tires up front and put the donut on the back. ---
**Author:** ![leftfield6](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leftfield6/32/18780_2.png) [@leftfield6](https://boards.straightdope.com/u/leftfield6)\ **Post date:** [June 26, 2014, 6:26pm UTC](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606/22 "2014-06-26T18:26:21Z")
The mystical ways of how AWD systems work, and the myriad of different methodologies amongst manufacturers and even amongst different years means that different cars are going to have different tolerances for tire size variances. I had a Jeep Grand Cherokee that was infamously persnickety about the tire circumferences being exact. I had to rotate tires with a religious zeal on that thing. My 2006 Subaru Outback is apparently not as demanding as newer model Subarus, but it also does not have as effective of a system. That said, I would have done exactly as you did. 4 tires. Now rotate them, and take care of them and you should be good. As for how you can get away with using a doughnut temporary spare, it’s because even though it is skinnier than the normal tire, it actually has the same circumference as the standard tire. ---
**Author:** ![sparky\_1](https://avatars.discourse-cdn.com/v4/letter/s/77aa72/32.png) [@sparky\_1](https://boards.straightdope.com/u/sparky_1)\ **Post date:** [June 26, 2014, 6:57pm UTC](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606/23 "2014-06-26T18:57:36Z")
> [@Telemark](#): > > That is correct, but I was less than 2 miles from home when I flatted, and the tire place is less than 1/4 mile from my house so I didn’t bother. The instructions also say that the spare should only go on the rear of the car, and if you flat a front tire to move one of the rear tires up front and put the donut on the back. Which is a whole lot of fun on a cold/rainy night with no gloves or umbrella! ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [June 26, 2014, 7:46pm UTC](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606/24 "2014-06-26T19:46:39Z")
> [@Gary\_T](#): > > I checked with a Subaru dealer and was told that it’s important that all four tire diameters be within 2/32" of each other. Otherwise differential binding and possible damage may occur. > > Another option is to buy one tire and have it shaved to match the others. Not only are they picky about size but I found out years ago tire sizes are a lot like shoe sizes. Two “identically” sized tires of two different brands might have a different rolling diameter OR have a different diameter at 70mph. ( tires “grow” in diameter as they are spun. Some AWD systems are very picky, others less so and a few pretty much don’t care. [Previous page](https://boards.straightdope.com/t/car-tire-advice-flat-on-a-awd-car-need-answer-kinda-fast/691606.md?page=1)