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03-19-2012, 09:42 AM | #1 |
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Questions on the Right Square Setup (Apex Arc-8's)
Ok, so I'm considering picking up a set of Apex Arc-8's for the upcoming track season but I'm having a hard time deciding the best package. The weight differences are negligible in the 1-2# I save from going to 18->17 since I pick up the same difference by going to a higher profile tire. So I think the decision comes down to running a 40 profile vs 35 and having to run a spacer vs not....
I know a higher profile can adversely affect turn-in, and spacers in general are not something I'm crazy about but I know plenty of people run them without issue. Maybe I'm wrong but I view the non-M Z4's comparable to the e36's and I think 17's are pretty common for them so I'm thinking it should not be a issue but again, I might be wrong on that one. Can anyone provide input? 17x9, et 30 - no spacers, 255/40 square vs 18x8.5, et 40 - 5mm spacer on front, 255/35 square vs 18x9, et 42 - 12mm spacer on front, 255/35 square Also on a similar note, when looking at the benefits of running a square setup, aside from same width wheels & tires, does it also assume/require the same offsets? For example, if I ran a 18x8.5 square setup, but the fronts were say 40 offset and the rears were 35, would the wider track in the rear make a difference? Last edited by 3002 tii; 03-19-2012 at 10:57 AM.. |
03-19-2012, 10:14 AM | #2 |
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are you panning on coilovers/springs?
if not, the 9.0" et30 is not going to work at all in front, and the rear will be past flush ~ 0.5". 8.5" et40 in rear is perfect. up front, if you install a 5mm spacer it will rub on the liner, and without the spacer it may rub on the strut housing. i'd try it without the spacer first. while track front vs. rear does change balance a bit, i think the bigger issue is the difference in contact patch in a staggered setup. i believe the understeer is due to two things: too little grip in front relative to the rear, and not enough front neg camber. going to a square setup will certainly relieve one of the issues. also, if you're lowering the car, remember your brake bias will move rearward. |
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03-19-2012, 10:19 AM | #3 |
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Get same tires and wheels and just run a small spacer in the rears this way you can swap and rotate tires to minimize tire wear at the track. If you get different offset wheels you may not be able to rotate on all corners.
Other thing to consider is buying a tire that is OT directional this way it doesn't matter what side of car you put the tire on. In the dry it really doesn't matter but in damp of wet conditions it will. I had to swap my front direzza's this weekend because I was chewing up outside on FL wheel and inside of FR wheel even though they are a directional wheel. I would go with the 17's simply based on cost...ESP if the series tire you need is readily available by multiple manufactures. If not I would go with what ever wheel will offer you the most tire options possible for the track. Don't get too caught up on spacers... At NJMP I had 10mm spacers on the rear and 5mm in the front just because I didn't feel like removing them from the car when I mounted them. |
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03-19-2012, 10:59 AM | #4 | ||
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Nick - you're running 5's and 10s on a square setup? If so, are you doing it just to keep it flush on both front and rear? Last edited by 3002 tii; 03-19-2012 at 12:21 PM.. |
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03-19-2012, 11:31 AM | #5 | |
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remember that your 8.0" et34 197's with 235 tread rubbed. granted they were a bit taller, but where you're decreasing in height by 4.5mm, you're adding 10.5mm to the width. |
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03-19-2012, 12:48 PM | #6 |
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my math was off by 0.5mm...
the decrease in height should have been 4mm, not 4.5mm. increasing width should be 11mm, not 10.5mm. the error was due to me using the incorrect aspect ratio in the initial calculations. sorry. |
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03-19-2012, 12:50 PM | #7 | |
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So on 9" width et 30 with 255, I have about 1.2mm clearance strutside, and -6mm on fender side. That's only fifth of an inch... throw in some camber and I would think it fits? |
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03-19-2012, 01:05 PM | #8 |
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it could be a difference in shoulder profile on the tires, but with the 235/40 BS Potenza RE760's i was running, there was only 2-3mm clearance at lock. that was with max oe camber on eibach pros.
one of the reasons why i moved the DIY brake ducting down and in towards the center of the car was so that the mounting bolt in the liner wouldn't contact the tire. a 245/35 might have had more clearance, but not by much. |
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03-19-2012, 01:11 PM | #9 | |
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Garage List F15 X5 xDrive35i [8.75]
E86 Z4 M [10.00] F10 550i (Retired) [9.17] F25 X3 xDrive35i (R ... [9.43] E82 135is (Retired) [9.50] E85 Z4 M (Retired) [9.41] E90 328i xDrive (Re ... [9.25] E86 Z4 3.0si (Retired) [9.24] |
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max 17" w/o spacer 17x8.5 et40 245/40-17 max 18" w/o spacer 18x8.5 et40 235/40-18 (a 245/35-18 would be better but not typically offered) max 18" with 5mm spacer & camber 18x8.5 et40 255/35-18 Last edited by 3002 tii; 03-19-2012 at 01:41 PM.. |
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