We get asked this question pretty often and it’s not as simple as it would seem, Subaru’s don’t have very large wheel openings and even so the size of the wheel opening often isn’t even the limiting factor.
Modern Subaru’s all have Mcpherson strut front suspension and the older ones have both Mcpherson strut front and rear suspension. There’s nothing wrong with a Mcpherson strut suspension it’s a good system, modern World Rally Championship cars still use it, the drawback is that the strut and spring are both close to the tire. The inside sidewall of the tire is very close (1/2-3/4″) to the strut body, preventing you from running a much wider tire, however this can be worked around by adding wheel spacers or using lower offset wheels. The top of the tire is also close to to the bottom of the spring perch, usually there’s a maximum of 1″ to spare so you only have room for a tire that’s less than 2″ greater in diameter than your current tire (these measurements are estimated, you will need to measure for yourself). Here are some examples of what I’m talking about measuring:
The cars with multilink rear suspension don’t have the spring perch looming above the tire but the spring and shock are still close to the sidewall but you should measure back there as well just to be safe. These aren’t the only places where you’ll run into clearance issues, all of the modern Subaru’s have trailing arms in back and when you lift them it always pulls the tire forward in the wheel well, Rear Trailing arm spacers for the Mcpherson cars will help with moving it back and on the newest generation of the multilink we have a whole Rear Subframe Spacer kit (included in most lift kits) but the middle generation (2000-2009 Legacy/Outback) we don’t have a solution available yet. It’s also a good idea to do your lift before you order tires, this gives you a much better chance at getting the right size first try.
Now that you know how much more room you have for tires you can begin to shop, this handy calculator will help you compare different sizes and show you how they’re different. This is a link to a tire size calculator:
Shopping for tires with good OFF-Road performance that fit your Subaru can be difficult and keep in mind that the actual size of the tire will vary slightly from what you calculate luckily most manufacturers list a height and width measurement as well as a wheel width range that they’ll fit on. Often the desired model of tire doesn’t come in the size you want especially if you have 17″ wheels, if you run into this try shopping for 16″ tires, most Subaru’s brakes are small enough to fit under 16″, STi’s and 05+ Legacy GT’s will need to have the brakes downsized. Here’s another calculator that will help you see how the various available wheels will fit and to decide if you need wheel spacers (click on link, use BACK to return to this article):
We’ve had good luck with the: BFGoodrich All-Terrain, General Grabber AT-2, Cooper WeatherMaster ST-2 (mud/snow) and the Yokohama Geolander AT-S. Measure carefully, consider what the suspension will do under full bump and turning and full droop, and don’t get too greedy and try a tire too tall or too wide…