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Premium Member
2007 Forester XT 4EAT-VTD
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Discussion Starter · #1 ·
I know what you are thinking - that I have either totally lost my mind or am going senile; why would I want to go back to OE sized tires - in my case, P215/55-17?

Before you draw any such conclusions, hear me out...

Back in 2009 I purchased a new set of Rota Tarmac ll wheels, which are 17 X 7.5 with a 48mm offset (stock alloys are 17 X 7 with a 48 offset, 24.5 pounds). Knowing that there isn't a lot of space in the rear for fatter tires - but wanting something larger than the OE size - I settled on a set of Yokohama Advan S4 UHP A/S tires in 235/50-17 to mount on the new wheels. But here is a crucial piece of information - I chose these tires for their narrow cross-section width of only 9.5 inches. All other tires in 235/50-17 range from 9.7 to 10 inches.

The combination of wheel width/offset and tire cross section worked, but with no room to spare - the Yokos cleared my rear strut with a hair-to-spare. I suspect a tire with a 9.7 inch cross section will not clear the struts on my current wheels (which I have no plans on replacing)!

Another factor - the Yoko Advan S4s in that size weigh 28 pounds! Most tires in this size weigh in the 25 to 28 pound range, with a few slightly lighter/heavier exceptions.

The Yokos are toast and I am now doing my research for what tires I will replace them with. The Advan S4 is still available, but I want something lighter. Also, tire technology has improved and there are now better tires available, even in the OE size of 215/55-17. Additionally, the tires in this size I am looking at weigh between 22 and 24 pounds, which will keep my combined Tarmac ll/tire weight around 40 pounds or under (versus 45 with the Yokos, 52 for my stock alloys/winter tires).

Though the 215s are specified at 8.9" in cross section width (7" wheel, 9.1" on a 7.5" wheel), tread width averages only a half inch narrower vs. the typical 235. And of course, tire height between the 215/55-17 and 235/50-17 is identical at 26.3 inches (same wall height). Mounting the 215s on a 7.5" wide wheel should enhance turn-in as well.

Lighter weight for improved acceleration/braking performance, better fuel economy, no issues with clearance, all with only (possibly) a minor trade off in lateral traction/handling performance - chances are you will see my FXT riding some UHP A/S tires in OE size this spring.
 

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07 Forester XT
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6,759 Posts
I say you're nuts :) I do understand what you're talking about, this year I bought new winters and went 225, up from 215 and the tires just barely rub in the rear. I put on a set of 3mm spacers and problem solved, plenty of turns to tighten the bolts sufficiently. I'm not a fan of spacers but painted myself into a corner which necessitated the use. Talked to several local guys who run spacers reguarly for track events (and daily driving) and nobody has had issues with 3mm on stock studs with years of experience runningn such a setup. So right there, a set of spacers may do the trick. Also I borrowed a set of non-hubcentric spacers ($10-20 at any tuner shop) and have 0 issues with balance/vibration at any speed.

I'm somewhat surprised with your findings, not that I doubt you. My daily setup for years were 245/45/17 on 17x8 ET48 wheels and never had a rubbing issue in the rear, even when I swapped back to full OEM suspension for winter time (would swap early while it was warm then run the summer tires till later Oct). Even runnign my FSTI wheels which are ET53 on 235/40/18 tires there's no rubbing in the rear.

Do your current Yok's have "rim protector" sections built in ? These are made to help not curb your wheels by adding a buldge in the sidewall of the tire. This is what is rubbing on my Conti winter tires, the sidewall itself is not. That is what caught me off guard. I had a set of 235/40/17's on the same wheels this past summer and no fitment issues. Most HP tires have nice straight sidewalls , it almost drops 90 degrees from the edge of the tread down the sidewall so like in my case the wider tires actually fits better than the narrower tire.

I highly doubt you'll notice any significant improvement in fuel economy, I've run a million setups from 205-215-225-235-245 with wheel weights from 12lbs to 24lbs and my DD fuel mileage has always remained rather constant. If you were saving $10 @ week then maybe but I am willing to bet we're talking at most $1 @ week. I watch my mileage religiously so I'd know if there were savings to be had. And I can say from experience that dropping to a 215 will greatly reduce your performance spectrum. Sure they'll weigh less but you'll have much less traction so any weigh gains will be more than offset by drop in grip. As an example I started doing track days on the OEM WRX size 205/55/16. I would melt the rubber off those tires like a candle. As soon as I switched to 225's this went away. Same tires/same track, and I was a better/faster driver afterwards. IMO a 215 tire is much too small for the power/weight of an XT. That's more a Miata/Civic appropriate tire. That's the main reason I went with a 225 winter tire. I found even in the dry I was breaking all 4 wheels loose on brisk accel. On top of that, a 215 on a 55 profile is going to feel all wishy-washy, there's nothing high performance about that setup. Its going to feel sloppy. You may very well hate it till the day you wear those suckers out.



Do what you think is right, my 2 cents would say either go:

a) 3mm spacer in the rear

b) 225/55/17 tire to keep same/simular diameter while retaining a reasonable contact patch.
 

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Premium Member
2007 Forester XT 4EAT-VTD
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2,138 Posts
Discussion Starter · #3 ·
Legacy, thanks for your input! I have a few months before I have to make a decision, so I'll be using that time to think this through.

A few of my own observations;

1. I run 225/55-17 Nokian Hakka Rs on my OEM wheels during the winter. They are awesome on ice and in snow, but between the 52 pounds of combined wheel/tire weight and the larger diameter, my car feels sluggish. There seems to be plenty of evidence that more rotational mass = slower acceleration, longer braking distances and reduced MPG. Google "heavy wheel performance" which brings up some good articles on the subject, which seem to mirror my own experience.

2. When I first installed the Tarmac ll wheels and the Advan S4 tires in 235/50-17, it was my observation that the inside of the tires just cleared the struts. At that time, I did get a very slight rub of the right-rear tire on the fender lip (plastic trim) with passengers in the back seat when hitting a dip in the road at speed, but it was so rare as to be a non-issue. See my entry here in the wheel thread;

http://www.subaruforester.org/vbull...tc-log-will-fit-11836/index22.html#post695015

Over the last few years, my Swift springs appear to have settled a little bit - compare the ride height of my car in the link above to the more recent photos on the first page of my journal (link in sig section). Not much, but enough to result in a little more negative camber. Interestingly, the right-rear tire no longer touches the fender lip, but occasionally (and very slightly) rubs the strut.

Based on this experience - and reading through the wheel thread I linked to above, it's obvious that this combination of 17 X 7.5 et48 wheels and 235/50-17 tire size is a bit iffy, based on tire cross section width, alignment, etc. Of course, I could add 3mm spacers and roll the fenders, which would solve the issue. Or I could just use a tire size that will fit with a little more room to spare.

Which then brings us to the tires. As we know, they're not all created equal. The Yoko Advan S4 tire still rates pretty well for an UHP A/S tire, but has certainly been eclipsed performance-wise by newer tires;

http://www.tirerack.com/tires/surveyresults/surveydisplay.jsp?type=UHPAS

FWIW, since I do not track my car or do auto-x, the Advan S4 continues to fit my performance needs very well. To push them beyond their capability on the road requires moments of weakness on my part (I still get those), driving in a way that is not wholly responsible. So in terms of grip/cornering performance, they are really all I need.

The biggest issue IMO with going with the 215/55-17 is finding a tire that fits my needs - handling performance equal to the Advan S4 in 235/50-17 (at 28 lbs. each) without sacrificing ride quality (including tread noise) or the lighter weight I am looking for. There are very few choices in this size, but there are a few - including this one which as of now remains at the top of my list;

Nokian zLine

This tire is available in 215/55-17 and 225/50-17. This is a performance summer tire (not an A/S) and based on all of the reviews/tests/surveys I can find online, appears to be highly rated. Based on what I could find, these tires appear to run wide in tread width for their section size. Here is a photo I found of the 225/50-17s;




Since a 235/50 and 215/55 have the exact same wall height (overall diameter), I am speculating that the Nokian Z-Line would outperform the Advan S4, even in the 215 size - not to mention they would be 4 pounds lighter each. I am also considering going with the 225/50-17, which based on the feedback from others on this board, does not appear to have any clearance issues on a 17 X 7.5 et48 wheel - but I'm not sure I want to go from the OE 26.3" tire height to 25.9". But then again, now that my springs have settled a little and the 225/50 version of the Z-Line weighs the same as the 215/55 at 23.5 lbs., I need to sleep on that for a while.

In conclusion, it appears that with the right choice of tire I can attain my goal of equal (or perhaps improved) handling performance while benefiting from reduced rotational mass and 100% eliminating any clearance issues. Our cars aren't getting any newer, but tire technology is certainly something we can leverage to our advantage.

Thanks again for your thoughts on this!
 

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SG9 Forester XT Stick Shift
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I am running 235/50R17 Kumho 4X on 17X8 ET47 wheels with somewhat similar suspension setup like yours. Section width are about 9.8 on 8" wheel. I do not have any rub anywhere but I am running camber bolt in the rear. I am only running -1 deg of camber and have plenty of clearance.

If you do not think you would exceed the performance limit of the narrower tire then by all means go for it. The 235 does gives better grip for the same tire but if it also comes with more tramlining especially with a lot of negative camber and stiff front bar. My 235/50R17 tramline a lot more than my winter 215/65R16 with the same suspension setup. Basically the stiffer the sidewal the more prone the tire to tramlining when combined with more negative camber and stiff suspension.

Continental DW, DWS or General Gmax seems to have pretty low weight in 235/50R17 size. They have soft sidewalls which should give you very comfortable ride too.
 

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2007 Forester XT 4EAT-VTD
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Discussion Starter · #6 · (Edited)
With this miserable winter finally giving up, I put my Tarmac lls back on with a new set of Goodyear Eagle Sport tires in P215/55-17. I made good on my threat!

Initial impressions are favorable - they have nice turn-in and track straight as an arrow with strong on-center feel. What surprised me the most is the ride quality - they are even better than the Nokians winter tires in 225/55-17 yet feel very responsive. As expected, losing the weight of plus-sized tires can be felt in acceleration as well.

The tires look great too - will post more pics ASAP.

 

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2007 forester xt auto
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I am running 235/50R17 Kumho 4X on 17X8 ET47 wheels with somewhat similar suspension setup like yours. Section width are about 9.8 on 8" wheel. I do not have any rub anywhere but I am running camber bolt in the rear. I am only running -1 deg of camber and have plenty of clearance.

If you do not think you would exceed the performance limit of the narrower tire then by all means go for it. The 235 does gives better grip for the same tire but if it also comes with more tramlining especially with a lot of negative camber and stiff front bar. My 235/50R17 tramline a lot more than my winter 215/65R16 with the same suspension setup. Basically the stiffer the sidewal the more prone the tire to tramlining when combined with more negative camber and stiff suspension.

Continental DW, DWS or General Gmax seems to have pretty low weight in 235/50R17 size. They have soft sidewalls which should give you very comfortable ride too.
My Miata runs 9.8 pound Enkei RPF1's and 205 Star specs. There is no substitute for less unsprung weight when it comes to handling IMHO.
Researching some new summer rubber for the XT I will be picking up next week and saw your post
 
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