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07 FSXT
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Discussion Starter #1
What would 18's do to my forester on stock springs? Would I loose any of the wheel gap, gain any handling? Would my speedometer be off and what would happen to gas mileage? Anything else that I may missed let me know good or bad. Thanks.
 

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2008 FSXT M/T
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4,167 Posts
it all depends on the tire size you put on them... 245/40/18s will keep the speedo correct but will not fill up the gap. 225/45/18 would be ok and 225/50 would prolly be the best option your speedo would read ~3mph lower though.
 

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07 FSXT
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211 Posts
Discussion Starter #3
Thanks Fourortwowheels. How would the ride it self differ? Im interested in seeing what this would look like, anybody have pics of this? Thanks again.
 

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2009 Forester X 5MT
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4,320 Posts
When you go with a bigger rim, generally, the sidewall of the tire gets shorter. While the overall diameter remains the same, visually, it'll look like a bigger gap. It'll look weird. Look at those SUVs with 20" wheels. The tires look like rubberbands and the gap looks huge. I wouldn't upgrade unless you plan to increase the diameter of your wheel/tire setup, but then your speedo will be off.
 

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2017 VW Golf SportWagen 5MT
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Unless you spend a good chunk of change, your 18" tire/wheel combo will be a good bit heavier. This, along with lower-profile tires, will make the ride rougher and your acceleration will suffer.

As far as loosing gap or gaining handling -- I wouldn't look at wheel size to do either, it won't, really. You can fit wide tires on 17s if you wanted to, and you are keeping the wheel/tire package around the same size as stock anyway, so gap will be the same.

18s can look pretty good on our cars, but there are tradeoffs.

Stan
 

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07 Forester XT
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6,759 Posts
What would 18's do to my forester on stock springs? Would I loose any of the wheel gap, gain any handling? Would my speedometer be off and what would happen to gas mileage? Anything else that I may missed let me know good or bad. Thanks.
Wheel gap will depend on the size of the sidewall. You could run a truck tire like a 255/70/18 and have no gap left (will handle like a truck too)

Handling will depend again on which tire size/aspect ratio you choose. Depends on what you're coming from, as improvements are relative to your starting point.

Speedometer will depend on the diameter of the tire you choose. There are calulators all over the web that will do this math for you.

Gas mileage depends on a number of factors: Weight of wheel/tire, width of tire, design of tread, diameter of tire (smaller diameter will spin more , cause motor to spin at higher RPM which may consume more fuel....)

Hope that helps and here's some pics of my XT on SSR GT2 18's. They're lighter than most 17's and some 16's. Winter picture is on OEM suspension, summer is on coilovers.



 

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'09 STI
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4,129 Posts
It's not ideal. As mentioned unless you go with light wheels the added rotational weight will increase significantly and the stock suspension wont be able to keep up. Not mentioned is the fact that the stock suspension is too soft to maintain the camber so you'll be rolling over onto the sidewalls. 17" is a better compromise on stock suspension.

Ultimate grip will increase because the 18" tires are usually softer. If you do it the right way wheel gap is determined by your ride height.
 

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07 FSXT
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211 Posts
Discussion Starter #8
Thanks a lot guys. So from all your comments I take it that springs are still my best option. Oh and thanks for the pics Legacy, that was a great comparison just what I was looking for.
 

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02 Foz 4eat
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5,536 Posts
I guess add my 2 cents of contradiction.

There are lots of "low" priced "light" weight 18" wheels out there. Many are right around 18-22lbs, which isn't that much more than stock weight.

A nice 245/45/18 tire will fill the gap, a little.

Again, it's all in the wheel/tire you choose. You'll obviously get better asthetics (and handling) combining the new shoes with new springs too.

As for 18" tires not performing as well as 17" tires, I call BS. If anything, a generalization could be made that an 18" tire will usually have a shorter sidewall thus resulting in less flex/roll. I've had several sets of 18" tires that handle and outhandle 17" tires that I've had. Again, all tires have different designs and resulting different performance.
 
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