Wheel / Tire FAQThis FAQ will be mostly my findings and ways of looking at things. I don't guarantee anything here is 100% accurate and if anything you read here causes you do damage your car, that's your own fault. Anyway, on with the FAQThe 02-05 WRX use 16x6.5 wheels weighing 16.5 lbs with a 5x100 bolt pattern and +53 offset. The tires are Bridgestone RE92 All Season Tires 205/55/16The 06-07 WRX use 17x7 wheels weighing 23.5 lbs with a 5x100 bolt pattern and +55 offset. The tires are Bridgestone RE92 All Season Tires 215/45/17The 08 WRX and 09 GT use 17x7 wheels weighing 23.5 lbs with a 5x100 bolt pattern and +55 offset. The tires are Bridgestone RE92 All Season Tires 205/50/17The 09-10 WRX use 17x7 wheels weighing 23.5 lbs with a 5x100 bolt pattern and +55 offset. The tires are Dunlop SP Sport 01 Summer Tires 225/45/17The 11-14 WRX use 17x8 wheels weighing 22 lbs with a 5x100 bolt pattern and +53 offset. The tires are Dunlop SP Sport 01 Summer Tires 235/45/17The 15-16 WRX use 17x8 wheels weighing 24 lbs with a 5x114.3 bolt pattern and +55 offset. The tires are Dunlop Sport Maxx RT Summer Tires 235/45/17The 04 STi use 17x7.5 wheels weighing 16 lbs with a 5x100 bolt pattern and a +53 offset. The tires are Bridgestone RE070 Summer Tires 225/45/17The 05-07 STi use 17x8 wheels weighing 19.2 lbs with a 5x114.3 bolt pattern and a +53 offset. The tires are Bridgestone RE070 Summer Tires 225/45/17The 08-14 STi use 18x8.5 wheels weighing 28 lbs with a 5x114.3 bolt pattern and a +55 offset. The tires are Dunlop SP Sport 600 Summer Tires 245/40/18.The 15-16 STi use 18x8.5 wheels weighing 24 lbs with a 5x114.3 bolt pattern and a +55 offset. The tires are Dunlop Sport Maxx RT Summer Tires 245/40/18.*NOTE* If anybody wants to submit other car's info here I'll add it. If any of this info is incorrect, please let me know.This example we'll use a 02 WRX16x6.5: This refers to the height and width of the wheel. The stock wheel is 16 inches tall and 6.5 inches wide.16.5 lbs: this refers to the weight of the stock wheel (not including tire).5x100: This is the bolt pattern of the wheel. The hub it attaches to uses 5 bolts in a 100 mm diameter circle.+53: This is the offset of the wheel. The hub is mounted 53 mm further out than center (positive offset means the hub is mounted closer to the outside than center)205/55R16: These are the dimensions of the tire. 205 is a measure of width from sidewall to sidewall. 205 mm converts to about 8 inches. The second number is used to describe the height of the tire (the size of the sidewall). It's expressed as a ratio between the height of the sidewall and the width of the tire so every '55' tire does not have the same sidewall unless they're the same width. The smaller this number though, the smaller the sidewall. 205/55 means the sidewall is 55% of 205 wide, or 113mm (a little under 4.5 inches) top and bottom. The final number, 16, refers to the intended height of the wheel for this tire in inches. Together we can calculate the total tire height by adding a sidewall height on the bottom + the wheel diameter + another sidewall height on top. This tire is 24.9" in diameter.Here are some diagrams from 1010tires.com to help:NOTE: the picture above shows a wheel with a substantial POSITIVE offset. The center of the wheel does not line up with where it gets bolted up. Most of the wheel sits further in towards the car. Most modern cars use positive offset. Less offset for a constant wheel width means the wheel pokes further from the car with the wheel bolting up closer to the wheel's middle. Higher offset means the wheel sets in the car more and bolts up closer to the wheel's outer edge.Theoretically, you could pick a lot of things but 15-19" would be most practical. Whatever wheel size you pick, you need to find a tire for it that will keep as close to stock height as possible. The Stock Height for all WRX tires is 25" so (slightly taller after 2011) if you picked a 19" wheel, you'd have a very small sidewall.Note though, that having a larger or smaller wheel height doesn't tell you anything about fitment issues (like rubbing). You can, and should, pick your tire according to the size wheel you choose and the stock tire diameter. If you pick a 19" wheel, you'll have a 3" sidewall (top and bottom) to keep the 25" stock height. If you pick a 15" wheel, you'll have a 5" sidewall. Either way, the wheel + tire still stands 25". You just have to get the right tire sidewall size accordingly.The smaller the sidewall, the stiffer it will be. Stiff sidewalls can improve handling by reducing tire flex. They however also give a stiffer ride and are more sensitive to rim damage from bumps and pot holes. Also, bigger wheels and smaller sidewall tires will be expensive. Pick a wheel height based on your budget and how many bumps you'll be driving over.The tire width should be selected to match the wheel width and the tire sidewall can than be selected to match the stock wheel diameter (25" in a WRX). Also, the size difference between the tire width and the rim width is very important. The lower the sidewall, the closer they need to be. Generally, the tire will be wider than the rim. However, if you get extremely low profile tires (25 or 30 sidewall), there can be very specific rim widths required.(these are approximate and estimated from recommended tire sizes of modern STIFF sidewall tires)50+ sidewall: 5-50% wider tire than wheel45 sidewall: 2.5-30% wider tire than wheel35 or 40 sidewall: 0-20% wider tire than wheel30 sidewall 5-20% wider tire than wheelFor example, 02-05 WRX wheels are 16x6.5" can handle 225/50/16 tires easily. 06+ WRX 17x7.0" wheels shouldn't be pushed past 225/45/17. Similarly, aftermarket 17" wheels should be at least 7.0" wide to fit 225 tire width. For 18" wheels, you want at least 7.5" of rim width to fit 225/40/18. Note how as the sidewall shrinks, you need a rim width closer to the tire size.Note though, that going wider than 225 on a WRX with a 48mm (the min you should use) or higher offset wheel is probably too wide. Use larger tire widths sparingly. WRX's that fit wider tires often sacrifice offset, roll the fenders, adjust the struts, widen the body, etc. These modifications are possible but may lead to reduce handling despite a larger contact patch. It is often not worth sacrificing offset to increase tire width.Tire sidewall ratio is then selected according to the width of the tire (above) and the diameter of the rim. To find this out, the easiest way is to use a tire calculator. Remember you want to stay fairly close to the 25" stock diameter (26" for 08 STi). Generally, within 1% but within 2% would not be horrible. More than that starts to mess with things because it will change your final drive ratio as well as make your speedometer inaccurate. Here's a link to a tire calculator:For the example of a 225 wide tire for 02-10 WRX:15" wheel should be 225/55/15 (24.7" tall)16" wheel should be 225/50/16 (24.9" tall)17" wheel should be 225/45/17 (25.0" tall)18" wheel should be 225/40/18 (25.1" tall)19" wheel should be 225/35/19 (25.2" tall)2011+ WRX sizes using 235 wide tires:17" wheel should be 235/45/17 (25.3" tall)18" wheel should be 235/40/18 (25.4" tall)19" wheel should be 235/35/19 (25.5" tall)08+ STi using a 245 wide tire:17" wheel should be 245/45/17 (25.7" tall)18" wheel should be 245/40/18 (25.7" tall)19" wheel should be 245/35/19 (25.8" tall)This is determined by the tire you want to run. The sidewall rating of a tire roughly equates to the wheel range by the mentioned chart above.That means a 6.5" (165mm) wheel can handle 185/50-245/50, 165/45-215/45That means a 7.0" (178mm) wheel can handle 195/50-255/50, 185/45-225/45, 185/40-215/40That means a 7.5" (191mm) wheel can handle 205/50-285/50, 195/45-245/45, 195/40-225/40That means a 8" (203mm) wheel can handle 215/50 on up, 205/45-255/45, 205/40-245/40That means a 8.5" (216mm) wheel can handle 235/50 on up, 225/45-275/45, 225/40-255/40That means a 9.0" (229mm) wheel can handle 245/50 on up, 235/45-295/45, 235/40-275/4035 and 30 sidewall tires you can pretty much use the listed 40 values but make sure to check if you're near the extreme. Not that you will find tires in these sizes for every wheel diameter.Short answer, you don't. The hub expects an exact bolt pattern and changing it is not easy. Replacing the whole hub is possible (although expensive) but it's not exactly a common custom part. Also, this could require changing the entire suspension of the car (ridiculously costly). There are some spacers out there that can change bolt patterns but these are extremely dangerous. The cheapest and best performing option for you is to get some wheels that actually have the correct bolt pattern.The stock offset is 53mm or 55mm mattering on year. This means your rim is mounted to the hub about two inches further out than center. The suspension expects the center of the rim to be there accordingly. Changing the offset more than a few mm is unwise. You can seriously hinder the stock suspension's capabilities. Try to stay within 5 mm of stock so, basically, no less than 48 mm. Is 47 so bad? No, but <40 sure is. It's a gradual thing. 5mm is just a rule of thumb. Balance the decrease in performance due to offset issues against what you'll be gaining in tire though.The reason for all the offset concern is people wanting wheels that are not designed for a WRX. Other cars out there mount closer to center which means they have smaller offsets. Wheel companies want to sell their wheels to lots of different cars but few have the high offset of a WRX. Since lower offset wheels will indeed fit (they'll just stick out more and move the center line further towards the hub), lots of companies will be more than happy to sell you them despite the reduction in handling.Offset because of this also limits how wide a rim/tire you can use. Even at 48mm offset (already about as far as you should go), putting fatter than about a 225 tire on there can cause rubbing, especially when lowered. This corresponds to about an 8" wide rim.Well, most people should stick to 225 width tires for their subaru (except 08+ STi). However, for those that simply want more width, there are options. You should note that all have sacrifices. Your main problems are: strut clearance, fender clearance, and suspension geometry.Strut Clearance: The main weapon for combating strut clearance is reducing offset. This will shift the rim further out. WRX's run a lot of offset and sacrificing it will hurt your suspension geometry. For every 5mm of offset removed, you should be able to fit a 10mm wider tire. Of course, this pushes all of the added tire width towards the fender which will also make fender clearance harder. Also, a stiffer suspension (springs/struts) will keep the car from falling as far during turning which will help with strut clearance. Note negative camber HURTS strut clearance as well.Fender Clearance: Generally, fenders along with the struts help define your maximum tire width. However, struts can't really be moved. Fenders can. For those that demand more width, fender modification is common. Fenders can be "rolled" which means basically rounding off the fender to permit the tire to have more room. Fenders can be "pulled" as well which means bending the sheet metal outwards to gain some more clearance. It's worth noting that many shops will not do fender rolling. The risk to your paint is extreme. The entire fender may peel or crack requiring expensive touch-up or re-paint. Also, a stiffer suspension (springs/struts) will keep the car from falling as far during turning which will help with fender clearance. Note negative camber helps strut clearance as well.Suspension Geometry: For those who really know what you are doing, there's a lot of suspension modification that can be done to deal with wider tires. The problem is that the center line of the tire starts to move when you sacrifice offset. Also, the natural lever created by the suspension and tire against the road is extended by width independent of offset. Some coil-over setups are specifically designed for wide wheels extending further out.It's important to note that lowering springs often do not have stiffer than stock spring rates and will actually hurt your clearance. A firm suspension will keep the car from shifting around and thus help clearance but note that is countered by drop.How wide can you go? What is needed for X width? This is an in-exact science filled with trial and error, stopping at walmart in the middle of the night for a baseball bat to stop from destroying your tires when you try to load in too much crap, and unless you have a good reason for needing that extra tire width, it's generally not worth it.02+ Subaru Impreza's of all trims do not come with full size spares. Most have 135/70/16 tires although STi's more recently come with 135/70/17s. Subaru says you can drive on your spare for up to 50 miles. Be aware though that particularly the 135/70/16 spares are only 23.4" tall so they're quite a bit lower than stock. They're dangerous to run for long periods of time. If you have another tire/rim laying around (like say your summers or winters) you'd be much better off throwing that on for a few miles. Even the STi spare is .6 inches too short.AWD cars are very very sensitive to differences in tire height. The stock tires are all around 25" but even a small difference can be a major problem for your differential given enough miles. Subaru will refuse to mount a tire on your car that's not within 1/4" circumference AND they must be identical. If you intend to replace a tire with a new one, the other tires should all be within 1.3/32 of an inch of new tread depth.Ok, lets be fair here that many guys want to sell you more than one tire to make more money. However, this is still a valid concern. Demand they give you the measuring device (or better yet own one yourself, they're cheap) and simply measure the tread depth between the tires on there and the new one. If they're within 1/32, they shouldn't give you any gripe about replacing just that one. If they're not, you should listen to them and buy a new set.Tire rack and some other vendors will shave a new tire down for you (for a price). If your tires are about 4/32" worn, you can pay a few bucks and get a new tire shaved down that far to match. Not always an option if they don't have your tire in stock anymore and may not be cost effective destroying a new tire just to match the old ones.Basically no. For emergencies, it'll work fine (as long as it's ~25"). The spare Subaru gives you is way small so clearly the differential can handle it for a few miles. For longterm use, tires wear differently so it's not a good thing to do. Your car's tires should be within 1.3/32 of an inch of each other! That's not very much and different tires with the same size can be more different that this. One type of tire is always a big deal with cars but with AWD cars, it's a must!There are several basic types of tire. People group them differently but for our purposes, lets settle on the following groups.All Season: Tires intended for Dry, Wet, and Light SnowWinter Tires: Tires intended for winter conditions including heavy snow. Compounds often not good in the heat. Not intended for year round use in climates with varying seasons. There are multiple types of winter tires that specialize in various conditions but most of us will be interested in "performance winter" tires which work well in snow but are not designed exclusively for it.Summer Tires: Tires intended for Dry or Wet conditions but not designed for snow. Not intended for year round use in climates with varying seasons. I include in this category all manner of "performance" tire. Most manufacturers have many different tiers of performance. Tire rack calls this category "Ultra High Performance" and "Max Performance".Max Performance Tires: Although some do have moderate rain capability, these tires are primarily for Dry only conditions. Snow would be very dangerous. Also, the compounds used are not designed for cold weather. Low temperatures can cause poor performance and poor treadlife. Performance in wet conditions and general treadlife can also be poor. The trade-off is of course superb dry grip. These tires are referred to on Tire Rack as "Extreme performance".So, what do you need? It matters on your climate obviously. Also, lots of folks who live in seasonal climates enjoy having two sets, one for winter and one for summer (this is where they get their names). Be aware when selecting a tire of their limitations. Some are dangerous in the snow and some of the most extreme tires are even dangerous in the rain. If you intend to get track tires that's one thing but if it's your daily driver, you should pick tires that will work well in all conditions you'll see. If you get occasional snow but hate the thought of all season tires cramping your performance, consider two sets. Changing tires doesn't take but a few minutes and you'd only have to do it twice a year.The stock WRX tires are All seasons and not particularly high performance oriented so a great deal of gain can be had from switching to a more aggressive tire. Better tires will help you stop faster, turn harder, and give much better steering response. There sometimes are negatives of increased road noise and a little stiffer ride though so keep that in mind. Tires are probably the single best mod to do for your car however, and won't effect your dealer's willingness to fix things for youWell sure. This is my biased opinion but I'll recommend a cheaper tire and a nicer tire in each of the four classes. If you want a more impartial opinion, I suggest visiting Tire Rack's tire survey section. Not allowed to link you but go to tirerack dot com and select their tire surveys.Anyway, here are some tires to consider:All SeasonCheap: General G-MAX AS-03Nice: Continental ExtremeContact DWS 06WinterCheap: Dunlop SP Winter Sport 4DNice: Pirelli Winter Sottozero 3Summer (what most people here are looking for)Cheap: BFGoodrich g-Force Sport COMP-2Medium: Bridgestone Potenza S-04 Pole PositionNice: Michelin Pilot Super SportMax PerformanceCheap: Dunlop Direzza ZII star specNice: Yokohama Advan Neova AD08I'd also like to note that the Dunlop Sport Maxx RT tires found on the latest WRX/STi are arguably the most competitive stock tires the USDM turbo Subarus have seen. They're not terrible.