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Discussion Starter · #1 ·
after plugging in numbers to 3 or 4 wheel/tire size calculators i dont get what is so bad about running a 215/35-18x7.5 with a +48 offset. The backspacing is the same, the whole thing has a overall smaller diameter. i know you dont want to little offset due to wheel bearing issues.

Help me out guys what am i not seeing/getting. :wtf:


thanks Nic
 

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1999 RBP 2.5RS
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210 Posts
First thing I'm thinking of is that the sidewalls on the tires would be too stiff with that profile.
 

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95/99 Brighton STi
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2,945 Posts
it's not necessarily the rim that's "bad", it's the tire you have to use to make it fit in the wheel well. because the rim is bigger, you have to put a small sidewall tire on which IMO is why 18's are "bad".

if the roads in your area are perfect and smooth, then by all means, do it up but most people will tell you that the ride is gonna be really rough and that you'll ding up your rims.

for a show car that doesn't get driven like a daily driver, hell, i'd put 19's on if I could but it really comes down to ride comfort. smaller sidewall = rougher ride, increased chance of dinged rims, and hella bitch to change which also increases the chance of chewin up the lip

17's FTW
 

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2.0L Turboner
94 RWD WRX & 82 EJ Brat
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8,673 Posts
there is no reason to go with 18's unless you are making 400hp or more and can easily get away with it.
There is really no reason to run anything bigger than a 17"...ever.
Yeah, because there is a direct correlation between horsepower and wheel size :rolleyes:

One of the big reason us GC owners stray away from 18s is because we have crappy fender clearance to begin with, so why try and cram more rim in there when you don't need it?

There are only two reasons for increasing the diameter of your wheels...
1. Fit larger brakes
2. Aesthetics
 

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2005 Baja Turbo
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1,448 Posts
18" wheels would be fine for track wheels, though. Running on the street though, you hit a pothole and you need a new rim. So, there are 3 reasons to run low profile tires on a large wheel: 3) No sidewall flex when racing.
 

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Premium Member
98 RS turbo
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232 Posts
Ive had that exact wheel and tire size for 7 years now, and I've never bent a wheel. trust me, the roads around where I live suck. my wheels don't rub or anything. yes the ride is a little rough, but if you have a decent suspension then it won't be so bad. and if I could figure out how to post a pic of my car I would.
 

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'97 white Impreza Coupe
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458 Posts
Yeah, because there is a direct correlation between horsepower and wheel size :rolleyes:

One of the big reason us GC owners stray away from 18s is because we have crappy fender clearance to begin with, so why try and cram more rim in there when you don't need it?

There are only two reasons for increasing the diameter of your wheels...
1. Fit larger brakes
2. Aesthetics
Apparently you've never heard of "rotational mass". I thought most subaru owners were smart?
 

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Mobile Diagnosis Guy
97 Impreza L
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5,492 Posts
18s just look stupid on GC's.

Bigger wheels = more rotational leverage.

A ten pound ball swinging on a 1 foot pole is hard to stop at pole the opposite end on the ball. That same ball on a 18 foot pole is going to be 18 times harder to stop. Bigger wheels should always = bigger brakes.
 

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ok terrific.
'95 STi RA rep, rhd yo!
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5,223 Posts
Insult a moderator. Way to go. You can purchase a set of 18" wheels and tires that weight the same as a set of 15" with tires, wheel size has absolutely nothing to do with power output.

18" wheels on a classic Impreza just looks silly. The only time I've seen a vehicle pull it off was the Gobstopper, and it has brakes bigger than my wheels.
 

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01 Silverthorn 2.5rs
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493 Posts
18" wheels would be fine for track wheels, though. Running on the street though, you hit a pothole and you need a new rim. So, there are 3 reasons to run low profile tires on a large wheel: 3) No sidewall flex when racing.
18s weigh in the high 20s of pounds.... 18s as track wheels are a joke....if you have R comps, your side walls are stiff as it is.

Our 16s weigh like.. what? 17 pounds?

The goal is to keep rotational mass to a minimum.
 

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1997 Impreza Wagon 2.5T
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45 Posts
Yeah, because there is a direct correlation between horsepower and wheel size :rolleyes:
wheel size has absolutely nothing to do with power output.
I believe the point FuriousGeorge was trying to make was that, if you really insist on running heavy 18" wheels, you better have plenty of power to waste.

Furious, am I right? Seemed fairly clear to me....

_Jeff
 

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2.0L Turboner
94 RWD WRX & 82 EJ Brat
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8,673 Posts
Apparently you've never heard of "rotational mass". I thought most subaru owners were smart?
I have heard of rotational mass smart guy, and the idea (with a performance oriented mindset) is to reduce weight, not increase it. This isn't a tough concept, larger wheels weigh more than their smaller counterparts, not to mention they cost more.

Sarra, sidewall flex is an issue with tires, not rims. Sidewall size is also called "aspect ratio" or "profile" and it's the second set of numbers in the tire size.
 

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'99 2.5rs
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195 Posts
I believe the point FuriousGeorge was trying to make was that, if you really insist on running heavy 18" wheels, you better have plenty of power to waste.

Furious, am I right? Seemed fairly clear to me....

_Jeff
That's what it sounded like to me.

Also, even if you found 18" and 15" rims that weighed the same, the 15" rim would have a lower moment of inertia due to more of its weight being closer to the rotational axis.
 

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2005 2.5rs Dark Blue
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102 Posts
my 18's weigh way less than my stock 16's... I'd guess 20 lbs lighter each but I haven't weighed them, just picking them up when rotating them. Almost threw my 18's over my head expecting the 16" weight
 

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Premium Member
98 RS turbo
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232 Posts
My 18's weigh 18lbs. each. overall with the tire included , they weigh less than my oem 16s. and if you boys would step up on the power, the "extra" weigh at each corner wouldn't be an issue!
 

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2.0L Turboner
94 RWD WRX & 82 EJ Brat
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my 18's weigh way less than my stock 16's... I'd guess 20 lbs lighter each but I haven't weighed them, just picking them up when rotating them. Almost threw my 18's over my head expecting the 16" weight
My 18's weigh 18lbs. each. overall with the tire included , they weigh less than my oem 16s. and if you boys would step up on the power, the "extra" weigh at each corner wouldn't be an issue!
What kind of wheels and tires do you two have?

I'm not saying "all 18s are heavy and all 15/16/17s are light." Obviously you can buy heavy 16s and light 18s but that's like comparing apples to baby wolverines.
 

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The Silverback Mod
05 Black OBS
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8,896 Posts
Geez, not this topic again...

This is sort of an endless debate that really falls into only ONE category, personal taste.

Rotational mass, unsprung weight and the likes are very real concepts. Now consider we are for the most part talking 'street cars' (some spending time on the auto-x track), these concepts become trade-offs and compromises. No different then setting up a race car ~ you gain in one area with a change, yet loose something in another area with the same change. As in the set up of a race car, there is NO PERFECT set up...

When I went from the OEM 16" to 17", by careful wheel selection and even MORE careful tire selection... I was able to find 17" rims that weighed 7 lbs less then the OEM wheels. Tires I found in 17" that were 4 lbs less then the 16" OEM. That is 11 pounds saved on each corner of 'rotational mass' and 'unsprung weight'.

In racing they use a simple formula to explain just how important loosing this unsprung/rotational mass is. Losing 1 lb. of unsprung weight = 10 lbs of 'chassis weight'. So, by me loosing 44 lbs of unsprung/rotational mass on my little N/A car would be the same as me stripping out 440 lbs!

Did this modification slow my car down? What do you think?

No, it was like someone handed me 20-25 hp for free! Plus the shorter sidewall made my car handle even better and more precisely. Out of all the mods I have done to my car for performance, NONE (including the cams) made the significant performance gains that this simple wheel/tire swap made!

Finally, I run 18's on the street... with the exact tire size the OP mentions. The tires weigh exactly the same as the 17" (45 aspect on the 17" vs. 35 aspect on the 18" ). The rim was one pound heavier. So, going to the shorter 35 aspect tire kick my gearing down just a touch to compensate for the slight gain in unsprung weight and rotational mass. Result? No performance/acceleration loss at all.

I prefer the stiffer shorter sidewall and the trade off in ride was nothing as severe as my experiment with coilovers for the street (that lasted a month).

I have rims that are very affordable, so if I bend a rim it is not the end of the world. The roads in Oregon are NOT smooth and my rims have gone without a bend for over a year.

Finally I prefer the look of the 18's with a stretched tire ~ purely taste, but MY car, MY taste! :sunny:


BTW ~ Why is there this big debate about rim sizes, when everyone on the boards gives 'high fives' to big brake kits? Anyone ever picked up the rotors and calipers of one of those kits in just one hand???

There is NO reason to hang more unsprung weight on an N/A car with a big brake kit! Upgrade your brakes, but don't increase you unsprung weight. I simply kept everything OEM size and went with EBC performance pads, drilled and slotted EBC rotors, SS brake lines, master cylinder brace and ATE Racing fluid. Huge improvement, no weight penalty! Ask anyone who follows me on the twisties ~ I drive my car very, very hard and never have any issue with brake performance or fade with this simple upgrade.
 

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2004 Forester XT
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1,148 Posts
The right wheel and tire combination will set you free. :D

18x8.5 and they feel about the same if not lighter than stock. Less sidewall does suck for daily driving tho. .02
 
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