Wheel / Tire FAQ
This 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 FAQ
Q: What is the information on the stock wheels and tires?
The 02-05 WRX use 16x6.5 rims weighing 16.5 lbs with a 5x100 bolt pattern and +53 offset. The tires are Bridgestone RE92 All Season Tires 205/55/16
The 06-07 WRX use 17x7 rims weighing 23.5 lbs with a 5x100 bolt pattern and +55 offset. The tires are Bridgestone RE92 All Season Tires 215/45/17
The 08 WRX use 17x7 rims weighing 23.5 lbs with a 5x100 bolt pattern and +55 offset. The tires are Bridgestone RE92 All Season Tires 205/50/17
The 04 STi use 17x7.5 rims weighing 16 lbs with a 5x100 bolt pattern and a +53 offset. The tires are Bridgestone RE070 Summer Tires 225/45/17
The 05-07 STi use 17x8 rims weighing 19.2 lbs with a 5x114.3 bolt pattern and a +53 offset. The tires are Bridgestone RE070 Summer Tires 225/45/17
The 08 STi use 18x8.5 rims 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. Note they use 26" tires rather than all other WRX/STi models. When reading this FAQ, you will need to account for this (basically any place it says 25", use 26")
*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.
Q: What do all those numbers mean?
This example we'll use a 02 WRX
16x6.5: This refers to the height and width of the rim. The stock rim is 16 inches tall and 6.5 inches wide.
16.5 lbs: this refers to the weight of the stock rim (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 rim. The hub is mounted 53 mm further out than center (positive offset means the hub is mounted closer to the outside than center)
205/55/16: 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. The final number, 16, refers to the intended height of the rim for this tire in inches.
Here are some diagrams from americanracing.com to help:
Q: How big a rim can I use? What difference does it make?
Theoretically, you could pick a lot of things but 15-19" would be most practical. Whatever rim 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 if you picked a 19" rim, you'd have a very small sidewall.
Note though, that having a larger or smaller rim height doesn't tell you anything about fitment issues (like rubbing). You can, and should, pick your tire according to the size rim you choose and the stock tire diameter. If you pick a 19" rim, you'll have a 3" sidewall (top and bottom) to keep the 25" stock height. If you pick a 15" rim, you'll have a 5" sidewall. Either way, the rim + 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 rims and smaller sidewall tires will be expensive. Pick a rim height based on your budget and how many bumps you'll be driving over.
Q: How wide a rim can I use?
The main limiting factor to the width of the rim you can pick is the fender well. The WRX is not designed for particularly large rims/tires so you don't have much room to work with.
You can however fit a larger width rim by decreasing the offset but this will make your tire stick out more and if increased too much, can decrease handling by moving the center of the rim from where the suspension expects it to be. Read more on other offset question for more details on how much you can change offset.
The WRX uses a fairly high offset meaning the wheels mount fairly deep and the center of the rim is expected to be about 2 inches inside the hub mounting point. This is done for suspension reasons but makes larger width rims difficult. Assuming you maintain at least a 48mm offset, the maximum width rim you should select is about 8".
Q: How do I pick a tire size?
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). Generally, the tire should be 10-25% wider than the rim. Here's a table I pulled out of my ass:
6.5" width rim: 185 to 215 tire width
7.0" width rim: 195 to 225 tire width
7.5" width rim: 205 to 235 tire width
8.0" width rim: 225 to 255 tire width
8.5" width rim: 235 to 265 tire width
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. Also, I'm sure somebody will argue you can go wider than 25% wider tire than rim but this can be dangerous mattering on how the specific tire deals with the sidewall not being straight and other concerns.
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:
Tire size calculator
Q: The rim I want has a different bolt pattern than my car. How do I make it work?
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 rims that actually have the correct bolt pattern.
Q: The rim I want has a different offset than stock. How far from stock can I be? Why does it matter?
The stock offset is 53 mm. 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 rims 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 rims to lots of different cars but few have the high offset of a WRX. Since lower offset rims 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.
Q: What size is my spare tire? How long can I drive on 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.
Q: They tell me I can't replace just one tire? What's the deal?
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 3/32 of an inch of treadware AND they must be identical. If you intend to replace a tire with a new one, the other tires should all be within 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 3/32, 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.
Q: Can I run two different tires on my car?
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 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!
Q: What kind of tire do I want?
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 Snow
Winter 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 you
Q: Can you recommend some tires?
Well 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. Here's a link:
Customer Tire Survey
Anyway, here are some tires to consider:
All Season
Cheap: Continental ContiExtremeContact
Nice: Bridgestone Potenza RE960AS Pole Position
Winter
Cheap: Dunlop Winter Sport 3D
Nice: Nokian WR
Summer
Cheap: General Exclaim UHP
Medium: BF Goodrich g-Force T/A KDW 2
Nice: Goodyear Eagle F1 GS-D3
Max Performance
Cheap: Dunlop Direzza Sport Z1 Star Spec
Nice: Yokohama Advan Neova AD07
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