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Wheel / Tire FAQ

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#1 · (Edited)
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 wheels 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 wheels 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 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 205/50/17

The 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 225/45/17

The 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 235/45/17

The 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 235/45/17

The 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 225/45/17

The 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 225/45/17

The 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.

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 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.

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 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.

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). 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 wheel
45 sidewall: 2.5-30% wider tire than wheel
35 or 40 sidewall: 0-20% wider tire than wheel
30 sidewall 5-20% wider tire than wheel

For 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:

Tire size 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)

Q: How wide a rim can I use?

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, 165/45-215/45
That means a 7.0" (178mm) wheel can handle 195/50-255/50, 185/45-225/45, 185/40-215/40
That means a 7.5" (191mm) wheel can handle 205/50-285/50, 195/45-245/45, 195/40-225/40
That means a 8" (203mm) wheel can handle 215/50 on up, 205/45-255/45, 205/40-245/40
That means a 8.5" (216mm) wheel can handle 235/50 on up, 225/45-275/45, 225/40-255/40
That means a 9.0" (229mm) wheel can handle 245/50 on up, 235/45-295/45, 235/40-275/40
35 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.

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 wheels 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 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.

Q: I want really wide tires. What does that entail?
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.

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 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.

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 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!

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. Not allowed to link you but go to tirerack dot com and select their tire surveys.

Anyway, here are some tires to consider:

All Season
Cheap: General G-MAX AS-03
Nice: Continental ExtremeContact DWS 06

Winter
Cheap: Dunlop SP Winter Sport 4D
Nice: Pirelli Winter Sottozero 3

Summer (what most people here are looking for)
Cheap: BFGoodrich g-Force Sport COMP-2
Medium: Bridgestone Potenza S-04 Pole Position
Nice: Michelin Pilot Super Sport

Max Performance
Cheap: Dunlop Direzza ZII star spec
Nice: Yokohama Advan Neova AD08

I'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.
 
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#55 ·
My situation? I am sticking with the stock 18x8.5" +55 wheels (cause they're free and nobody would give me decent money for em thanks to their mediocre stock tires) and I bought a set of 07 STi wheels (17x8" +53 clear brembos 5x114) to use in the winter with 245/45R17 Pirelli Winter Sottozero 3. That's not exactly the question you're asking though.

What would I buy for the track? The 08-14 STi could handle 265 width at near stock offset without fender rolling or hitting the strut. You can't find that width for a 17" wheel so if I was going to get new tires/wheels I'd be looking at an 18x9" or 18x9.5" wheel that cleared brembos and had basically as much offset as I could get. If you could find say 18x9" +48, I think you could run 265/35R18 and clear the fenders. The 2015 is new but the fender clearance appears to be somewhat similar. I think on the 2015 you could do the same.

The negative there is the tire height. The stock height is 25.7" and the STi's gearing is overly tight. 265/35R18 is just 25.3". I'm actually considering 255/40R18 on the stock wheels though strut clearance at that height (26.0") at +55 offset worries me. I'd actually prefer 255/45R17 if I could find and afford 17x8.5" +48 5x114 wheels and they made a decent tire in that size (which they don't so it's moot). 275/35R18 seems to fix everything but it's awful wide and requires an awfully wide wheel which I can't imagine having an offset that wouldn't make me puke. Also not sure how the fenders would handle it. 18x9.5" decent offset wheels and 275/35R18 tires is not a cheap option either. Or a nimble one for agility on public roads dodging potholes.

So all that said 245/40R18 on 18x8.5" +55 isn't all bad even if stock doesn't sound very ideal to most people.

The WRX, in all it's years, is a different balance of tire width, wheel offset, fender clearance, gearing, and brake clearance so keep that in mind if your car isn't exactly mine. For example, the 02-05 WRX came with 16x6.5" +53 wheels and 205/55R16 all season 25" tall tires on overly tall gearing. The difference going to a performance summer tire that was 235 wide and shorter (235/45R17) was biblical. The fenders were the same as the JDM STi to boot, which was 235 wide stock. 17x8" +48 to +55 offset 5x100 wheels are cheap and easy to find as well so there was no reason NOT to do it. As I said, my 2015 STi isn't going to easily slap on 30mm more width from a far superior tire for little money and no clearance issues like an 02-05 WRX could. It's pushed already.
 
#57 ·
I advise against XXR's because they're a junky cast (they break/leak/crack) and that's not enough offset for a subaru. 2011 WRX can handle 18x8.5 +48 very well. I'd use a 255/35R18 tire on it. I'm assuming you have the pulled fenders the USDM got in 09+ WRX models as opposed to the original 08 WRX fenders.
 
#60 · (Edited)
you could take a picture of your car, that always works
Fyi.. That dents been fixed.. Lol

And just curious.. What modifications would need to be made to accommodate lower offsets so that handling is maintained? As well as a closer to accurate speedo/odo reading?
 

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#61 ·
looks like a 2011 USDM WRX fender to me. Those are 235 width tires in that picture correct? 255 at +48 should fit.

Ideal offset is really a very low level parameter of your chassis. It's defined by the suspension geometry. The strut's angle to the hub, the distance from the center of mass, the positions of full compression and decompression of the shock, the lateral connections across the axle, it's a lot. You can't really change that stuff. On top of that the car's body work is cut around these and an assumed tire. Although body work can be done it's not a lot of fun to look at compared to the clean lines of a stock car.

Why do you want to lower the offset? Most people do this because they see track cars with wheels sticking out and they want theirs to do that too. Truth is a pure race car is not going to look much like a retail product once you take off the skin. Even a car that started it's life as a retail product and has been transformed into a race only vehicle is quite different. Sticking with anything like a stock chassis you're still going to maintain that stock "ideal offset" type parameter keep in mind. Race cars will often demand extreme tire widths and are willing to sacrifice some offset to get it but even this is a balance. The GD platform I have the most experience with even with fenders removed performs better with a high offset wheel. Clearing the factory strut while fitting huge tires means cutting this and there's a balance point. More tire becomes not worth the reduction in offset pretty quick. A lot of drivers figured out the hard way that this was somewhere around 285mm of width, give or take a size, and still maintaining offset within 20mm of stock. And that's an EXTREMELY not stock suspension setup with fender clearance being irrelevant and budgets well into the 5 figures for suspension alone. Those big tires will stick out quite a bit but what you may not notice at first is they're just as close if not closer to the factory strut as the stock ones were. More offset would help but then the super nice sticky wide tires wouldn't fit! You get the idea. On a basically stock car, offset loss for visual reasons is a straight determent to the car, no if's and's or but's.

Spedo's read based on assuming a diameter of your tire. They read accurately as long as you maintain a near-stock tire diameter. Remember tires wear over time so an exact diameter even on the exact stock size is not a given. Most cars assume a significant error on the order of 2% giving you quite a range of tire diameters to choose from. Increasing the width of the tire or the width of the wheel does not necessarily mean increasing the tire's diameter. You can lower the sidewall ratio (the middle number) accordingly and generally maintain a reasonably stock tire diameter. On your car, for example, 235/45R17 stock size refers to a 17" wheel surrounded by a tire that's 45% of it's width tall on the top and bottom. Total diameter, from top to bottom is (235mm*45%) + 17" + (235mm*45%) = 25.3". The size I recommended is similar (255*35%)+18"+(255*35%) = 25.0". The WRX has pretty tall gearing so better to be on the shorter side with a tire (particularly a summer/AS tire) than taller. Also, 25.0" diameter is pretty close to the stock diameter 25.3". Note that "35" sidewall is a smaller ratio than "45" sidewall that was stock because we've just gone up a wheel size and up some tire width.

I'd also note that 18" wheels on a Subaru are not necessary. STi brakes fit under 17" wheels just fine. If I could I'd get rid of my 18"s. I got 17"s for the winter already but I'm at least going to wear out some stock tires before changing out the stock wheels. 18" just cuts your tire's sidewall for no reason. It will make the ride worse and won't help your performance any. It also leaves a nasty visual gap between the brake and the wheel. Larger wheel diameters are for larger brakes IMHO and even if you upgrade your WRX brakes, you still won't need 18" wheels.
 
#62 ·
looks like a 2011 USDM WRX fender to me. Those are 235 width tires in that picture correct? 255 at +48 should fit.

Ideal offset is really a very low level parameter of your chassis. It's defined by the suspension geometry. The strut's angle to the hub, the distance from the center of mass, the positions of full compression and decompression of the shock, the lateral connections across the axle, it's a lot. You can't really change that stuff. On top of that the car's body work is cut around these and an assumed tire. Although body work can be done it's not a lot of fun to look at compared to the clean lines of a stock car.

Why do you want to lower the offset? Most people do this because they see track cars with wheels sticking out and they want theirs to do that too. Truth is a pure race car is not going to look much like a retail product once you take off tthe skin. Even a car that started it's life as a retail product and has been transformed into a race only vehicle is quite different. Sticking with anything like a stock chassis you're still going to maintain that stock "ideal offset" type parameter keep in mind. Race cars will often demand extreme tire widths and are willing to sacrifice some offset to get it but even this is a balance. The GD platform I have the most experience with even with fenders removed performs better with a high offset wheel. Clearing the factory strut while fitting huge tires means cutting this and there's a balance point. More tire becomes not worth the reduction in offset pretty quick. A lot of drivers figured out the hard way that this was somewhere around 285mm of width, give or take a size, and still maintaining offset within 20mm of stock. And that's an EXTREMELY not stock suspension setup with fender clearance being irrelevant and budgets well into the 5 figures for suspension alone. Those big tires will stick out quite a bit but what you may not notice at first is they're just as close if not closer to the factory strut as the stock ones were. More offset would help but then the super nice sticky wide tires wouldn't fit! You get the idea. On a basically stock car, offset loss for visual reasons is a straight determent to the car, no if's and's or but's.

Spedo's read based on assuming a diameter of your tire. They read accurately as long as you maintain a near-stock tire diameter. Remember tires wear over time so an exact diameter even on the exact stock size is not a given. Most cars assume a significant error on the order of 2% giving you quite a range of tire diameters to choose from. Increasing the width of the tire or the width of the wheel does not necessarily mean increasing the tire's diameter. You can lower the sidewall ratio (the middle number) accordingly and generally maintain a reasonably stock tire diameter. On your car, for example, 235/45R17 stock size refers to a 17" wheel surrounded by a tire that's 45% of it's width tall on the top and bottom. Total diameter, from top to bottom is (235mm*45%) + 17" + (235mm*45%) = 25.3". The size I recommended is similar (255*35%)+18"+(255*35%) = 25.0". The WRX has pretty tall gearing so better to be on the shorter side with a tire (particularly a summer/AS tire) than taller. Also, 25.0" diameter is pretty close to the stock diameter 25.3". Note that "35" sidewall is a smaller ratio than "45" sidewall that was stock because we've just gone up a wheel size and up some tire width.

I'd also note that 18" wheels on a Subaru are not necessary. STi brakes fit under 17" wheels just fine. If I could I'd get rid of my 18"s. I got 17"s for the winter already but I'm at least going to wear out some stock tires before changing out the stock wheels. 18" just cuts your tire's sidewall for no reason. It will make the ride worse and won't help your performance any. It also leaves a nasty visual gap between the brake and the wheel. Larger wheel diameters are for larger brakes IMHO and even if you upgrade your WRX brakes, you still won't need 18" wheels.
Thank you for the really detailed reply and recommendations..its helped me fill in knowledge deficits on the subject..and i'll keep it in mind..well u seem to be the expert on this..and the things you've mentioned are well worth knowing prior to purchasing!the tire dealer's only concern is to sell the product..even stretch the wheels!never mentioned any of the things and issues you've covered...
its not soo much the low offset im looking for..it's the style that comes with it.. Heck if there were more optimum offsets for the styles i want, would definitely go for em..im not looking to track the car..but i dont wanna lose too much in terms of handling or spend more tryna sort out unwanted issues as a result of a mod..so thank you for that... Ill shop smarter now.. Onee other fitment query..

What are ## thoughts on the rota g forces 18 x 8.5 offset +44 for 2011 wrx?any issues fitting that without rolling fenders?running stock suspension..
 
#64 ·
So finally found a rim to my liking on stock suspension! Being a daily driver.. I guess i dont have that trained sense of detail to feel and handling.. It feels the same to me.. I dont go too hard on tight turns if thats what u referring to difference in handling..i go quite spiritedly only on straights.. =p

So running

18x8.5 offset 45 on hankook 225/40/18

Pretty happy.. ?thanks OP for the advice!
 

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#65 ·
Hi,

That is an awesome write on on wheels/tires. Thanks for that.

I'm hoping you can clarify and maybe give me some advice. I have a 2016 WRX (first WRX), it's the Sport Trim (Canada), so it comes with the oem 17x8 235/45/17 wheels/tires (same as 2015). I know the 2016 WRX Sport Tech or Premium models include the oem 18x8.5 245/40/18 tire/wheels (no performance difference, accept inverted struts). I'm looking to go 18's, so would running that size wheel and tire be an advantage performance wise? I'm looking to get new summer wheels, not wanting anything extreme, hoping to stay within a +45 offset or higher (pref 48 to 55). Just looking for strong and lightweight (thinking maybe Enkei pf01 18x8.5 48 offset, with 245/40/18). The tire calculator seems to recommend sticking with 235 width, however the difference is 1.5% with 245/40/18. Would the change cause any problems with the car speedometer? You say that percentage is "Not Horrible", but is it any good? I figured the extra width will look better (suit the wheel size) and maybe give some extra grip?

I don't plan on adding any power or suspension mods anytime soon, and use my car only for spirited street driving (will likely never use it on a track). I want to get the most out of my car with summer the wheel/tires i choose (handling and acceleration being the most important factor) . What would you recommend? That includes 18's or 17s

Thanks in advance.
 
#66 ·
No problems on the car. Speedo and odometer will be slightly off, but not terribly so. The taller tire will slightly help with your gearing though since it's so short. 17" tires will ride better, tires cost less, and the wheels tend to be lighter but 18" wheel look better and work just fine. It's really personal preference.
 
#67 ·
Oliver Melo, the 2016 WRX's setup is pretty well balanced. 02-10 WRX's came with needlessly narrow tires (and all seasons pre 09) but to upgrade a more modern WRX's tire performance you have to compromise in one way or another. The only real improvement you can make will come from adding tire width without reducing offset. Your stock tires are 235 wide. One simple choice is to oversize the tire and cut some sidewall while you're at it using 245/40R17 tires on your existing wheels. There's not much selection in that size these days so you might also consider 255/35R18. This is a more extreme choice (a lot less sidewall) but it will fit assuming you keep the offset around ~48. 255 wide tires will require at least 8.5" of wheel width. 18" wheels offer no performance advantage but do offer superior tire selection 255 and wider.

The Enkei PF-01's you've mentioned are great wheels. They're very light for their size and have a very respectable offset. You should be able to throw 255/35R18 tires on there and not worry much about fitment. It will be a rougher ride in several ways 1) the overall diameter is reduced 2) the sidewall is less cushy and 3) you'll probably pick a more aggressive performance tire than stock. If you go this route though, you will substantially improve the handing, acceleration, and braking of your WRX. Another wheel choice is the OZ ULTRALEGGERA 18x9 +55. They're slightly heavier but they're 9" wide and have even more offset. With the mentioned OZ's, you may even consider 265/35R18. I am unsure how much strut clearance there is in the front for this setup but rumor is it'll work. You'd be running some of the widest tires on a stock fender'd WRX ever.

As brfatal mentioned, 18" and wider tires like I've mentioned are not really going to help you much on public roads. Your stock wheels can run 235/45R17 which provides a good bit of sidewall and a very respectable width.
 
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