I Need Help With Tire Sizes (2012 WRX / OEM 8" Wide Wheels) - Subaru WRX Forum
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post #1 of 27 Old 05-20-2013, 02:15 PM Thread Starter
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Exclamation I Need Help With Tire Sizes (2012 WRX / OEM 8" Wide Wheels)

Hi all,

It's my first post, but I've been browsing this forum (and many others) for years. I have some questions regarding tires now that I share the enjoyment of having a turbo Subaru (2.5i was my first Subaru).

I have searched around quite extensively, but I have ended up with more questions than answers. Also, most of the threads that I have visited touch on the topic but then quickly stray into aftermarket wheel fitment and tire choices.

I have the stock 8" wide wheels on a 2012 WRX sedan. For reference, the stock tire size is 235/45R17. I'm leaning towards the Michelin Pilot Super Sport tires and the only disadvantage I have found is people saying the sidewalls are a bit more compliant than the OEM Dunlop's.

So here we go:

Should I stick with the OEM tire size or are there enough benefits to going with a wider and/or shorter tire as in a 245/45R17 or 245/40R17 to warrant the change?

Obviously, I understand that a wider tire "should" provide a better contact patch and therefore "better" grip.

From what I've read a shorter tire than OEM (i.e. XXX/40R17) is better for the WRX gearing, but I don't know if this applies to the 08+ models are just the older models. I also admit that I don't understand what "better for gearing" actually means. Also, going from a XXX/45R17 to a XXX/40R17 is a minimal change in height, but I really really want to avoid the "big wheel / small skinny tire" look. I'm not a rapper or a pimp. The ride height is also still stock, so I don't want the wheel and tire to look too small for the wheel well either.

I think the car handles great now for how I drive, it's a daily driver in the Northeast, and I do drive on some pretty bumpy / crappy roads. My main goal was to go a bit wider, but after searching I have so many more questions and concerns that I may just go with the OEM size and be done with it and potentially miss out on some performance advantages.

Would you guys mind sharing your thoughts on this? 235/45R17 (OEM), 245/45R17, or 245/40R17?
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post #2 of 27 Old 05-20-2013, 03:37 PM
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The 45 in the tire size is an aspect ratio which represents 45% of the section width. So when you go wider to a 245 you need to drop the sidewall down to a 40 series to maintain the OE overall diameter. So basically, as you go wider each size you need to go "shorter" in sidewall height. If you go with a 245/45R17 you'll be over the OE overall diameter and that's a def no no.

IMO I'd say run a 245/40R17 as that will be the closest to OE diameter without going over. Its better to be 2" under OE than 1" over. The OE 235 also looks slightly narrow on the 8" wheel IMO and a 245 will solve that problem as well.

235/45R17 = 79.5
245/40R17 = 77.6
245/45R17 = 80.6


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post #3 of 27 Old 05-20-2013, 04:07 PM Thread Starter
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The 45 in the tire size is an aspect ratio, so when you go wider to a 245 you need to drop the sidewall down to a 40 series to maintain the OE overall diameter. So basically, as you go wider each size you need to go "shorter" in sidewall height. If you go with a 245/45R17 you'll be over the OE overall diameter and that's a def no no.

IMO I'd say run a 245/40R17 as that will be the closest to OE diameter without going over. Its better to be 2" under OE than 1" over. The OE 235 also looks slightly narrow on the 8" wheel IMO and a 245 will solve that problem as well.

235/45R17 = 79.5
245/40R17 = 77.6
245/45R17 = 80.6


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Awesome, thanks so much for the reply. I've been reading around and see you replying and giving input on all kinds of stuff, so again... thanks for taking the time!

245/40R17 is what I was leaning towards too after looking at the calculators and taking into account what I've been reading. My initial want was to just get wider 245's to fix the narrow look that you mentioned, but my lack of knowledge coupled with extreme anal retentiveness has led me on a week long search to try and understand the in's and out's of tire size choices.

I think going from 235/45R17 to 245/40R17 would make for a tire that is 0.7" shorter in sidewall height than OEM, which is where my concern about much of a "low profile" look I will have compared to how the OEM's look on the wheel and also within the wheel well. My worn out OEM Dunlop's are probably pretty close to what I would see on new 245/40R17's if I was to somehow measure how much tread has worn off since they were brand new.

So, would this equate to 0.35" less tire sidewall above and below the wheel (I guess "all around" the wheel since it's round)?

Does anyone have any photos for comparison?
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post #4 of 27 Old 05-20-2013, 04:32 PM
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I'd get new wheels if I were you. If you want to keep the wheels I'd use 235/40R17. The 5-speed is tall. Shorter tires would be better. 245/40R17 will work but that's a very wide tire for an 8" wheel. It actually exceeds the 120% rule for 40 sidewall tires by a very small amount. Certainly safe, but I doubt the added width is going to help much against the added flex. Then again, if the 245/40R17 is cheap then go for it. However, I would expect the 245 would cost a good bit more and have a crappy selection and thus really not be worth it.

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Exactly OP. so take that height difference and divide that by x4 and that'll give you what you'll actually "notice" in wheel well gap difference from the top of the tire to the top of the wheel well. You'll BARELY, if at all be able to tell the difference in wheel well gap.

Good tire options IMO woul be the below. Tires are the one thing you never skimp on in any way, but seeing you've already mentioned Michelin you're already on the right track. Good luck OP

Michelin Pilot Sport A/S+
Bridgestone RE970 A/S



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post #6 of 27 Old 05-20-2013, 04:59 PM Thread Starter
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Originally Posted by mosc View Post
I'd get new wheels if I were you. If you want to keep the wheels I'd use 235/40R17. The 5-speed is tall. Shorter tires would be better. 245/40R17 will work but that's a very wide tire for an 8" wheel. It actually exceeds the 120% rule for 40 sidewall tires by a very small amount. Certainly safe, but I doubt the added width is going to help much against the added flex. Then again, if the 245/40R17 is cheap then go for it. However, I would expect the 245 would cost a good bit more and have a crappy selection and thus really not be worth it.
I would definitely buy new wheels if it was in the budget at this time!

I ended up with the Michelin Pilot Supersport's at 245/40R17 @ $203.00 each. The 235/45R17 OEM size was $175.00 each for comparison, so yeah it's a bit of jump in price but not too much to scare me away.

I'm taking a bit of a shot in the dark, but I really don't like the narrow look on my OEM Dunlop 235's. I'm only speaking about how it visually looks, and I know it's not all about looks so I am taking a minor risk. I'm reading that different manufacturers measure out differently so a 235 width might be slightly different across multiple brands. I hoping the 245 Michelin gives me a nice square look without losing and performance.
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post #7 of 27 Old 05-20-2013, 05:23 PM
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Nice choice OP! That's what I plan on going with soon as mine are done. Where'd you buy em at that price? Tire Rack has a promo on Michelin right now and they're $179.50 per after rebate.

And yes all manufacturers specs are slightly different. So no 2 tires will ever be identical. Michelin makes some of the widest specs out there so that 245 is gonna be sitting nice an square 👍


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post #8 of 27 Old 05-20-2013, 06:10 PM Thread Starter
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Yep, I got them from TireRack.com. You're right they do have a rebate too! Sweet!

I'll take some pictures and post them once they are installed so you can see how the 245 Michelin sits on the stock wheel.

Now I need to maybe start thinking about better springs and shocks/struts. I would love coilovers, but I can't skimp on those and also can't drop $3000 or whatever on a proper kit. I already can't push in my desk chair because under my desk is storage for a bunch of suspension/chassis goodies. I really want to lock down the chassis and suspension before I start adding power.
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post #9 of 27 Old 05-20-2013, 06:40 PM
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Suspension was actually a pretty recent convo had on here in another post. Here's the link for some ideas man. You're def going down the right mod path though. Glad to have you be part of the forum.

Reduced Pull at Higher RPM?


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post #10 of 27 Old 05-20-2013, 07:20 PM
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then there are the bfg kdw's and Kumho XS that have some of the stiffest sidewalls available... just an idea. 8" wide = 235/40/17 or 245/40/17

Tire size calculator

But Mosc is right....

Paul
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2007 WRX Sold
2007 STi totaled
2007 Foz XT sold
2007 MS3
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post #11 of 27 Old 05-21-2013, 07:47 AM
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OP I'm replying to your suspension question here rather than in that other thread to help keep forum searches a little more well placed. That thread is a diag thread so others searching would prob be doing so in this section. But....

If you're up for the added costs up front of struts along with springs then complimenting either Eibach or H&R springs with a strut from Koni or GTWorx would be the way to go IMO. Obv lowering the car is going to decrease the life of the struts and paying x2 for the install of struts down the road is kind of silly when thinking of it unless you have your own shop and you're not going to be paying x2 know what I mean. But doing it all at once isn't in the cards for some so riding out the OE struts might be the way to go too. The OE struts could last 5k...or could last 50k you never know really.

For some, running a spring like an RCE Black would be another good option for springs as there's a very slight drop difference and that would "potentially" allow for longer strut life. But again, there's no way to know how long the OE struts will hold up to the lowered springs.

I've personally not done mine yet so hopefully some more forum members will chime back in with their opinion. Reach out to someone like 'brfatal' too if he doesn't notice this thread and give his 2c as he's quite knowledgable on suspension work with Subaru specific vehicles. My opinions on suspension mods/brands comes from conversations with other trusted forum members and conversations with TiC about my own plans and ideas for suspension work. Tires/Wheels is a little more my specialty. But I hope the above helps and just know you're on the only forum worth being a part of. The guys here are top notch! The other guys posting/mentioned in this thread are just a few to speak of when it comes to trusted names.


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post #12 of 27 Old 05-21-2013, 09:46 AM
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Most of the suspension options on the market are designed to achieve an astetic drop and function safely with the stock suspension. Handling improvement is not a concern whatsoever. If you want that type of thing, lowering springs and stock struts are perfectly safe. They will degrade your handling slightly, your ride quality will be completely destroyed, and your struts will not function correctly. Again, safe but astetic only is an understatement.

Correct suspension design is to raise the spring rate in proportion with a corresponding drop as well as a stiffer strut that can handle the new spring rate. Your stock setup is balanced with these three factors: springrate, ride height, damping. To actually improve things, you must change all three and you must also keep all three in balance. In other words, you need higher spring rate springs with only a reasonable drop and much better struts.

Or, you know, just slap on some lowering springs and do some burnouts in the pep boys parking lot. Your call.

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post #13 of 27 Old 05-21-2013, 10:13 AM
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Specific brand recommendations for achieving all 3 of these things Mosc?


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post #14 of 27 Old 05-21-2013, 11:18 AM
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WRX struts are pretty junky. For many years, they were the same as the Impreza struts. All impreza's also use a tall strut design in the front which allows for more throw (important in off-road rally). These factors mean your stock strut is just not going to cut it, especially up front, if you plan on either a drop or increasing spring rate or both. The STi struts are considerably better but many years have compatibility issues between the WRX and STi (04 STi is compatible with 02-07 WRX only. 05-07 STi is not compatible with any WRX, for example) and they're also not that cheap. I'd recommend D-spec struts to all who want to improve performance on a street car. They can handle a ton of spring rate and still function.

Assuming a strut like D-specs, you have several spring options. A classic lowering spring would be silly as their spring rate increases over stock are fairly mild (since they are designed for stock struts). A correct spring rate for that much drop would be quite stiff, but with the D-specs would be functional and a great performer on level surfaces. Swift is one company that makes both lowering springs and performance springs. Their performance springs are called R-spec I believe, and are well in excess of the stock STi springrates and have a similar drop to most WRX lowering springs. The ride quality of having a functional strut with that much spring rate will still be better than an overwhelmed WRX strut dealing with the drop of a "lowering spring".

RCE makes two very nice spring choices as well, their "yellow" and "black". They say both can be used with stock STi struts but they're a little much. D-specs or similar struts would be better. The Yellows are like the Swift R springs, designed around a very high spring rate and the corresponding drop. The Blacks are a hybrid spring, more graduated than the stock design. The springrate is fairly high but the drop is only moderate. This delivers a lot more ride quality than the all out racing springs while only sacrificing a fraction of the handling. It does, however, keep more "wheel gap" in the front if that's a concern.

The Impreza's frame and suspension geometry is purposely designed for rally. That means 15" wheels with 25" tires and lots of room for throw. That way you can keep both wheels down on uneven terrain and deliver power to the front wheels around a turn. Driving around with your wheel at the fender level looks cool on a flat asphalt road but would be a severe hindrance on a bumpy dirt road.

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post #15 of 27 Old 05-21-2013, 12:25 PM
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Thank you very much for detailed info 👍


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