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02-17-2014, 04:46 PM | #24 |
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02-17-2014, 07:25 PM | #25 |
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You are allowed +/-0.25" offset difference in stock classes. 0.25" = 6.3mm. Stock front wheels are +48, and the E46 wheels are +41. I don't think anyone would really hassle you for the extra 0.7 of a mm.
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02-18-2014, 11:22 AM | #26 |
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I ordered a set of 17x7.5 42mm wheels.
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01-21-2016, 03:12 AM | #27 |
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looking into this same question and took some measurements and fitment today.
This is for F-Street autocross, so I'm looking to fit as much rubber under the front as I can rules allow 7.5x 17",18",19" ET56-42 on the front. front strut mount pins are removed and -0.6 camber. -- Cannot use camber plates. The car and my driving style consumes front tires much quicker than rears. I'm hoping to use the same size tire and front and rear. this would allow buying a new pair for the front, where grip is needed, and moving the older ones to the rear. I was considering 17" wheels: 17" competitive autocross tires are $100-$140 less per pair than the same width tire in 18". 17" wheels are typically lighter and cost less than 18" a wide (245/255) 25" diameter tire squeezes onto a 17x7.5 more easily than on a 18x7.5, as the 17 has more sidewall so.. the 17" seems like a no brainer at first. most important thing i noted today is that the strut angles away from the hub plane. at a 2:5 ratio*. this means an 18" wheel can use a wider tire than a 17", as a 17" wheel/tire is about 5 mm closer to the strut than an 18"wheel tire. I think I'll reserve 17" wheels for the rain tire F-Street setup. the style 168 look like a good choice for that. (17" wheel has 13mm less radius than an 18"; assuming the wheel bulg / curb guard is the same distance from the wheel lip on both wheel tire sets then the 17" set's bulg is 13mm higher (5:2) => 5mm closer). I'm hoping to fit a 255 up front. last season I ran ZII 235 in front and 255 in rear both on the oem 18's with no spacers.. the 235 had 9mm clearance from the tire curb guard to the strut. Today, I found a little bit of rub on the fender, from when the wheel is turned and loaded. not sure if this was from this year though. in 2014 I ran some 245 Kumho V710's at an event, as well as some ET 32 wheels, so I'm thinking the rub was from one of those and not the 235s. for the next practice session I will be testing 255/35/18 ZII's on the 7.5" with a 5mm space for ET44. A national champ used 275 hoosiers on 18x7.5 ET45 in the front in 2008. I did a front fitment today with the ZII 255's as they were on the 8.5 ET52 wheel and used a 10mm spacer => ET42, the curb guard on the tire was rubbing the strut. the sidewall had 1mm clearance. I'll get the tires remounted on the 7.5 ET49 wheels and try a 5mm spacer. since the 7.5 will pull the curb guard in 13mm it won't be a problem at ET44. Hopefully the sidewall gets pulled in enough too. I have the BMWPS (26.5 kinked) sway bar; If there is rub, I'm thinking a much stiffer FSB and slower dampers would help prevent rub. The marks that were on the fender lip look like very transient, as it didn't even pull the plastidip off the inner fender lip, but just left some rubber-haze. *I measured this on the 135is BMW brembo brakes. -- don't know if the smaller brakes have the same hub plane. that would change the clearances to the strut, but the 5:2 angle is in the knuckle regardless of brakes. can anyone confirm that the hub plane is the same on all 3 (non M) e82 oem brakes 135i, 128i and BMW performance. if not what the offset differences are. Some Questions I still have about wheels: 1. what is the tolerance for wheel width. It's measured inside between the lips, so the wheel must be unmounted to get a true measurement. if an aftermarket wheel is actually only 7 3/8 wide or 7/14 that would change the mounted section width profile of the tire. 2. How much does the top side of the wheel/tire deflect under load or bump conditions. |
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03-15-2016, 12:50 AM | #28 | |
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Today I mounted 255/35/18 RE-71A's on the front 18x7.5ET49 313 wheels.
They clear the struts by 3-4mm without spacers. I have the strut pins pulled and about -0.6 degrees camber. I'll check for fender rub at this weekends event. If there is no rub then I may try the 17/255. the tire is 3 pounds lighter, wheel about 5 pounds. Quote:
F-Street spacer allowance allows to 42ET so I can get the tire off the hub. |
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03-21-2016, 03:48 PM | #29 |
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concerning the front and fitment of a 255/40 17 RE-71A on the front.
ran an autocross with the 255/35/18 on the oem 18x7.5 ET49 on the front yesterday - no fender rub. I'll run with a 5mm spacer ET44 next event and if that doesn't rub I'll try the 255/40/17 on ET 42. |
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