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Why 17" vs. 18" wheels?


ZinFreak

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Posted

OK, I'm sure this will probably start a debate, but here goes.

 

The taxman was good to me this year. I was expecting to pay up, but in fact according to my CPA it looks like I may get to keep $1800 that I planned for paying taxes.

 

So, looks like new wheels and rubber for me!

 

That got me to thinking about wheel size.

 

Legacy GT arrives with 17" x 7" wheels (and 215/45/17 tires).

 

Legacy Spec.B arrives with 18" x 7" wheels (and 215/45/18 tires).

 

Why the difference? Clearly Subaru had something in mind with the different wheels and I'm sure it isn't looks.

 

First the differences between the cars

 

1) The Spec.B has a 6-speed tranny, the LGT (MT) has a 5 speed tranny

2) The Spec.B has a different suspension with the Bilstein sport-tuned shocks.

 

So the big question is -- Does the Spec.B have bigger wheels because that is the optimized wheel size for the suspension and the transmission?

 

OK, so if I put 18" vs. 17" wheels on my stock LGT what does that do for me positive and negative?

 

Larger wheels - Changes the mass hanging from the mass-dampers (struts) which will change dynamics of bump suck... Larger wheel and tire gains has more K.E. that imparts on the suspension. Would it be a negative on a stock LGT? Does it really matter?

 

Larger wheels - Increases the proportional rotational inertia, thereby impacting (decreasing) my acceleration? The drive train has to work harder to get the wheels rotating.

 

Larger wheels and rubber - More $$$

 

Do I gain anything by going to 18" ?

 

My needs -- This is pretty much my daily driver, I don't do track driving, but would like to. I spend much of driving time going out the California coast which has roads that are about 98% twists, turns, and hairpins. My driving style is somewhat spirited. Let's just say I bought a turbo charged car because I like to go fast (similar to the reason I like to fly airplanes)

 

My goal -- Purchase a second set of wheels with maximum performance tires for the summer (not M+S). Seriously considering the Eagle F1 GS-D3 or the Potenza RE050A.

 

Stick with 17" on the stock LGT or go to 18" ?

 

Comments?

-Zin

06 LGT LTD GRP 5MT

07 FXT LTD OBP 4EAT

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Posted
subaru put 18s on the spec b for marketing, not for performance reasons. the STi comes with 17s for a reason. 17s are cheaper for you, and you'll likely save some weight. the only gain with 18s is bling. some argue steering response is better with 18s. that's sort of true but you can get plenty of steering response from a 17, like the RE070s for example.
Posted
Indeed, wider not bigger. 18s for bling. Somebody correct me if I'm wrong but you just want the widest tire/wheel you can find. Besides, better to stay with 17s so your speedo won't be as off :).
Posted

Scott, I'm having the same thoughts regarding wheel choices. Go with 17x8 and you will have improved contact patch (the whole point of upgrading) while maintaining comfort, rim and tire protection, and the cheaper prices of 17" wheels and tires.

 

I'm trying to work out the logistics of my wheels/tires. I don't know how guys like Xenonk and Wukin or anybody with multiple sets keep track of everything. Here is what I have:

 

4 stock wheels on the car with the M3's

1 stocker with an re92

3 unmounted re92's

and I'm planning on getting some summer/3 season rubber and some new wheels soon.

Posted
You can get an "upsized" wheel and still have your speedo be correct if you get the right tire. You just need to get one with the same overall diameter as stock.

:icon_twis Slide It Sideways :icon_twis

Posted

^^^^^

 

Indeed, wider not bigger. 18s for bling. Somebody correct me if I'm wrong but you just want the widest tire/wheel you can find. Besides, better to stay with 17s so your speedo won't be as off :).

:icon_twis Slide It Sideways :icon_twis

Posted
You can get an "upsized" wheel and still have your speedo be correct if you get the right tire. You just need to get one with the same overall diameter as stock.

 

Then you'll end up with a thin strip of rubber for a tire that blows when you look at it the wrong way. :lol:

Posted
Then you'll end up with a thin strip of rubber for a tire that blows when you look at it the wrong way. :lol:

 

nah its not that bad...I believe my overall diameter of my tires is marginally larger than stock, and there is still plenty of rubber with the 18s. Actually fills the wheel well much better.

Posted

1) The Spec.B has a 6-speed tranny, the LGT (MT) has a 5 speed tranny

 

2006 Spec B was a 5MT.

 

Since you are changing anyway, go 18".

Posted
2006 Spec B was a 5MT.

 

Since you are changing anyway, go 18".

 

But why 18"? I've seen a couple of reasons for moving to 17x8.0 (edited)

 

I'm not going for bling here. If I change to 18", I want to rationalize my money outlay based on technical reasons not looks. I'm willing to pay for performance, I get queasy laying out $500 (extra) for filling up a wheel well, especially if it has a negative impact on acceleration, ride quality, or handling.

-Zin

06 LGT LTD GRP 5MT

07 FXT LTD OBP 4EAT

Posted

Scott,

 

It's all a matter of tradeoff. You WILL get better steering response from 18's if all other factors are equal (wheel width, tire width, tire diameter *note - sidewall is narrower*, etc).

 

If you choose carefully, you *can* get a set of 18" wheels that are comparable in weight to 17" wheels. For all intents and purposes though, a good 17" wheel and tire will probably afford you the best of both worlds with a little more ride comfort than an 18" wheel and better grip and handling than what you already have in the stock wheel and tire size.

 

The last consideration is that by going with 18" wheels, you at least have the option of going with bigger brakes if you were so inclined. Of course, not the best plan if you still plan on using those stocker wheels for winter duty.

 

And yes, as others have said ... the Spec.B comes with 18's for looks only.

Posted

Go with wider tires unless you plan only use the wheels as all season and live in a snowy area...even then I'd still go wider.

 

As to the diameter I believe if you increase the diameter of the tire and wheel, you can have the dealer adjust the speedo so that it reads the speed correctly correctly.

 

The only real performance reason I could see you wanting to upsize the tire is to decrease your 0-60 times as you don't have to shift in to an extra gear I believe.

 

Maybe you increase the handling as well because there is less sidewall, but you've increased the weight as well. Going with a 17 w/ a smaller sidewall sounds like you could also technically increase the handling as well plus you get less weight.

 

That said economical shouldn't play too much into this as you bought a legacy not a hyundia.

Performance shouldn't play as all the factor as you bought a legacy not an sti.

Class shouldn't play as all the factor too as you bought a legacy not a mercedes.

 

I'd go w/ 18*8 unless you have a lot of potholes in your area.

Posted

 

I'd go w/ 18*8 unless you have a lot of potholes in your area.

 

:lol: Well it is California, we don't repair our roads. The city just south of me is referred to as Pothole-uma (Petaluma).

 

Now that is a good reason not to go with 18"'s then.

-Zin

06 LGT LTD GRP 5MT

07 FXT LTD OBP 4EAT

Posted
But why 18"? I've seen a couple of reasons for moving to 17x8.0 (edited)

 

I'm not going for bling here. If I change to 18", I want to rationalize my money outlay based on technical reasons not looks. I'm willing to pay for performance, I get queasy laying out $500 (extra) for filling up a wheel well, especially if it has a negative impact on acceleration, ride quality, or handling.

 

I think 18 boils down to aesthetics. The LGT is a bigger car so an inch up fits well. It think the 18 on the Spec B and even the JDM Tuned by STi version looks hotter just because of bigger wheels.

Posted
I'm a fan of 18's because they look nicer in terms of filling the fender gap better than 17's. I have a set of Axis Seven Mods that I really like a lot. If I had put 17's on my car it would of looked funny, even with it lowered because the wheel well is huge. I think 17's or 18's on the LGTs both look good though.
Posted
nah its not that bad...I believe my overall diameter of my tires is marginally larger than stock, and there is still plenty of rubber with the 18s. Actually fills the wheel well much better.

 

 

got a pic of that you can share?

258k miles - Stock engine/minor suspension upgrades/original shocks/rear struts replaced at 222k/4 passenger side wheel bearings/3 clutches/1 radiator/3 turbos

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