Compatible tire sizes
 

I'm trying to find the right winter tire (lookin at some Blizzaks) and when I select my FRS as my vehicle, it keeps coming back with "tire not compatible with this vehicle."

Would P215/45R18 work? I understand 17 is stock. What are all the advised sizes?

Stock is 215/45/R17. For 18's it would be 215/40/R18 and Tire Rack close to stock fitment for anything.

If you're shopping snow tires, I highly recommend going with 205/55-16s on either cheap alloys or preferably, cheap steelies. Narrower cross section and taller sidewall typically makes snows work better. Not to mention, cheaper... And unless you've got a BBK, there's no reason NOT to use 16s..

+1 for snow/ice tire being narrower better.

16" would be good for comfort and maybe also tires would be cheaper, but as my own mindset is set on getting one set of good wheels and using it everywhere, i see nothing wrong on using my aftermarket 17" in winter too. Just as car is meant to be driven, so are wheels. Not too keen on getting too careful and going for heavy steelies just because of winter.

As for tire search using selection of car model using some automated scripted selector, yes, most probably error of using R18 instead of R17, that is stock.

My own choice would be stock 215/45/R17 (just of gripier rubber compound) for summer daily driving, and 205/50/R17 or 195/55/R17 for winter (if on stock, 7" wide wheels. on 7.5-8 wheel width i'd drop 195 tires, and on 8"+ wide wheels would use stock size, to not overstretch tires). As side gain, 205/50/R17 would also net you +5.7mm and 195/55/R17 - extra +10.5mm ride height, also handy to get over unplown snow, even if it slightly reduces acceleration.

Lol
Yeah tire noob. Your trying to buy a tire that is bigger than your wheel size.

Ok here's a quick crash course on tire sizes.

The first letter is not important. It's usually "p" for passenger tire's.
The first number is the width of the tire in milimeters
The second number is profile or side wall size. The bigger the number the taller the side wall and vise versa.
The last number usually after the "R" is wheel or rim size.

You can play around with the frist two numbers but the last one you can't.

Ok thanks. And for snow is there a recommended size? The roads are usually paved quite well here anyway.

17" wheels go with 17" tires :)

I would like to be educated on the subject. I have my own ideas, but half of the time my ideas are just plain wrong, so why exactly are snow tires better when skinny? (I mean, I know they are, there is a reason all rally cars go super skinny on snow stages, they cant be all wrong).

The wheel breaks through the frost and grips on the surface beneath.

If you're on tire rack, pick a tire in the stock size, then look at other sizes. You'll see an asterisk beside other sizes that are close to the same diameter. You do also realize you can start with the car first, then find winter tires for it and see what's available instead of picking a tire then looking to see if it's available in a size to fit the car...

I'm running 205/50/17's for snows on the stock wheels, but if I was buying new wheels for snows I would get 16's.

Icecreamtruk: same car weight (little of it, as ours are relatively light cars) but narrower tires = more pressure per tire contact patch. Easier to push through snow slush / mud / water to grippier surface, if tires are studded, easier to press those studs in ice, easier to stick those mini rubber thread edges to road/ice/snow. Mud/water bits works also for summer tires, as the narrower tire is, it's less suspect to aquaplane (when in wet, tire has to get some volume of water through it's threads, and how many litres of water that amounts to depends from 1) vehicle speed, 2) tire width.)
If you take a look at rally cars at snow/ice stages, take notice how skinny tires on them are. Even high powered turbo WRC ones, they sometimes look as if on studded spacesaver donut tires :).
In winter you don't need much extra grip in better road situations, as there you can simply be easier on accel/brakes/maneuvering. But you need in winter all extra grip you can get for worst cases, when there is little of grip, even if in most cases road/grip situation is better, so that you don't get stranded in snow storm, don't have to wait for tow truck, don't roll back when going on icy uphill, so that you don't have to shovel too long to get on road out of snow, so that you have that all extra grip you can get in emergency braking when someone looses control in front of you or looses grip when braking in crossing from side of you not stopping in time, or when you emergency steer around some obstacle on road.
http://cdn.epicski.com/a/a9/a9b58845...ubbiesnow.jpeg
That was all about tire width for winter tires.
But i also mentioned, that it's worth to have slightly taller tire sidewall profile. Yes, acceleration will be a bit less, due bigger tire diameter (=different overall gearing ratio). But extra sidewall will give more comfort on bad roads (often more common in winter), and extra hight can be difference if our low cars even as stock will dig in with their bulldozer shaped front bumper and you'll stop after few metres and bring out shovel again, or you'll go above deep snow and will hear less often ice scraping underside of bumper/car :)

Generally skinnier tires will give you less resistance in cutting through snow. Think of it like using knives to cut; you don't use a wide knife to cut something, and if you do, it is more difficult. A skinnier tire will also mean there is a small contact patch on the ground, therefore providing more weight spread across the smaller contact patch. This in theory should give you slightly better traction potential, and is similar in theory to putting something heavy in your trunk (for RWD cars) to put more weight on the drive wheels.

As for recommended winter tire sizes, my research is pointing to going with either -1 sizing (i.e. 205/55R16, 195/60R16), or with a narrower tire but higher sidewall 17 such as 205/50R17. These are really close to the stock size tires/wheels. Note that deviating too far from the stock tire dimensions will cause your speedometer to be slightly inaccurate, and some slight changes in fuel economy. It's generally minimal if you are staying close to size (as I have in the sizes I gave above), so not a huge concern.

I agree on the 16 incher and skinner and taller is better, unless you have a BBK.
Look on craigslists for subaru wheels and winter tires and there are great deals. Even if you get a 17 setup for cheap, it will make a big difference if you need to use it year round.

Also check out, [ame="https://www.youtube.com/watch?v=OlrNtSPAk_I"]WR TV Project BRZ Winter POV Update - YouTube[/ame] he is running 195/60/16 Blizzak WS-80 Winter Tires on 16x5.5 Compomotive TH2 Wheel

That's the next size I'm trying after my 205/55-16s wear out...205 is too big for a winter tire for a car this size, IMO..