04-06-2015, 09:27 AM | #1 |
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There's been many questions on should you run squared of staggered on the track? I've been interviewing experienced BMW racers and well as reading endless articles to help everyone out, including myself. Below of pros and cons and suggested fitment.
Squared setup benefits: Reduce understeer and being able to rotate wheels/tires. The F8x doesn't have problem with understeer, so the benefit gained would make a set of tires last longer. Bad thing is 275 really isn't enough grip for the rear, especially if you added more power. Warning: The F8x rear tires diameter are 2.5-2.7% larger than the front. Running the same diameter all around will increase MDM/DSC intervention (as it thinks the rear slips). To get the most out of your track experience, just turn off MDM/DSC. Euro MDM coding can reduce computer intervention, as US MDM is more strict (BMW assumes Europeans are better drivers, and... they're probably right). Staggered setup benefits: Being able to fit wider tires in the rear as our front can only support 275 (285 would push it). The F8x has traction issues in the rear, running wider setup in the rear will reduce oversteer and better acceleration grip. Bad thing is you cannot rotate these front to back. Squared wheel/tire size suggestion: 18x10 ET33 with 5-10mm spacers in front or 18x10 ET25 all around with no spacers or 18x10 ET43 with 15-17mm spacers in front and 5mm spacers rear. Tires: 275/35/18 or 275/40/18 or 285/35/18 (if you have K&W CS, you might want to test fit 285 before proceeding) Staggered wheel/tire size suggestion: 18x10 ET22-25 front and 18x11 ET35-44 rear (brands like Apex EC-7 sizing is x.0" wide) 18x9.5 ET20-25 front and 18x10.5 ET32-37 rear (brands like Volk sizing is x.5" wide) 18x10 ET23-26 front and 18x11 ET42-44 rear CCB need to go with 19", not all brands 19" will clear CCB so ask before you buy. Front tires 265/35 or or 275/35 Rear tires 295/35 or 305/35 or 315/30 (325/30 will fit, but take your own risk as not all tire brand sizing are the same) For 18s, matching diameter front and rear: 255/40 front and 295/35 rear or 265/40 and 305/35 rear Ideal 19s for Euro MDM (or track use with US MDM off): 255/35 front and 295/30 rear or 265/35 front and 305/30 rear (matching diameter front/rear) Ideal 19s for U.S MDM: 275/30 front and 295/30 or 305/30 rear (closer to stock size proportion) Also, the minimum suspension work needed would be camber plates in the front. Unless you want to burn through a set of front tires twice as fast or seeing chunks of tires coming off, get cambers in front (set 2-3 degrees negative - use a temp gauge after a hot lap to see if you dialed it in correctly). TC Kline sells just the camber if you budget doesn't allow the full coilover or you prefer to keep the EDC. Don't test my recommendations above if you're running full coilovers like K&W CS. Clearance is very narrow in front as the coilovers are wider than stock setup. Of course, if you have CCBs then you'll need 19" +. Offset doesn't change from 18 to 19, just tire side walls would be slimmer. There's only a few brands that will clear the CCBs with 19" wheels so check with your CCBs peers before proceeding with a purchase. Volk is working on a custom set for our F8x, which will have custom barrel to clear CCBs. Most high end wheels will clear it, but always confirm with them in writing before you purchase. You'll need an email record for any exchange/refund. Tire pressure: If it's your first time tracking, a newbie mistake is not checking the tire pressure cold and document it. Start with 30psi, it will heat up to 35-36 after 10min. At 38-40 hot, your rear end will break loose. Wheel stud conversion: If you have spacers or plan to track you vehicles, just convert to studs. (a) It will keep the spacers in place. (b) You don't have to worry about using the right length bolt for different spacers (c) Easier to find locking wheel nut vs extended locking wheel bolt. (d) You will change you wheels a lot, it's better to ruin the stud's thread (easy to replace) than the thread of the hub (very expensive mistake). Don't forget to always bring a torque wrench to the track. Our cars are meant to live on the track, so go out there an enjoy it. I hope you'll appreciate this thread. Feel free to comment and make any suggestions. I will make any changes as long as you have facts to back it up. Wheel/Tire Size Calculator: http://www.rimsntires.com/specspro.jsp
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04-06-2015, 09:41 AM | #2 |
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Thanks for the comments and summary.
It is a tough thing to navigate and there is no "right" answer. The more info people have to draw from the better. Also, just to clarify... appropriate starting and hot tire pressures will be somewhat based on the tire. That is, a PSS and a AD-08R may each work better at different hot pressures. You can only really tell at the track based on feel and how much contact patch you are using (you can also get into measuring temp across the tread, etc but that's a bit hardcore for most). It is almost as much art as science
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04-06-2015, 09:46 AM | #3 | |
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Once they graduate to slicks, it's a good idea to invest in a high end laser temp gauge (per FTS, needle thermometer would be more accurate). They would measure 3 spots of the tire flat surface after a hot lap. Inner / Center / Outer. If the center is hot and inner/outer are cold, then there's too much pressure. If the inner/outer are hot and the center is cold, then there's not enough pressure. If inner is hot only, then there's too much negative camber (opposite for outer).
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Last edited by JNoSol; 04-06-2015 at 11:28 AM.. |
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04-06-2015, 11:15 AM | #4 |
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Thank you for the summary, we should keep inputting more data going forward.
Couple of notes:
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04-06-2015, 11:27 AM | #5 | |
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You can reach out to TC Kline. He tracked his M4 often enough to dial in the camber/toe/shocks setting. I spoke with him the other day, I can tell he's very passionate about racing and his product. He's a wealth of knowledge.
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04-06-2015, 04:34 PM | #6 | |
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EDIT: thanks everyone for the tips on the tire pressure. I used the 30psi cold / 33-35 psi hot for the stock PSS and it was a good recommendation |
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04-06-2015, 04:50 PM | #7 | |
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04-06-2015, 04:56 PM | #8 | |
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More info: http://www.fluke.com/fluke/uses/comu...eTrackTemp.htm
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04-06-2015, 06:14 PM | #9 |
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I think you are being overly optimistic with those rear offsets. I currently run RS40s with 18x10+25 frount 18x11+35 rear with 275/35/18 front and 305/35/18 rears. I have about 2mm to spare from rubbing the fender on the back. To fit anything over a 305, I believe you need +40 in the back on an 11. This setup works though. No rub, no scrubbing, and finally the car feels balanced. Hell, even the steering feels decent now. It only understeers if you drive like a grandma.
Also, why invest in a setup that needs spacers? That just seems like extra unsprung weight, and potential for problems. If you are going to get a track setup, get one that works without them. Last edited by slavearm; 04-06-2015 at 06:22 PM.. |
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04-06-2015, 07:28 PM | #10 | |
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On spacers, there are 2 reasons: (1) not everyone has the budget for custom forged wheels with exact offset for racing. Apex for example are very good wheels for the money, but their offset aren't perfect. (2) if you run square setup (all 4 wheels have the same size and offset), you'll need spacers in front as ET33 or ET43 18x10 will hit the suspension.
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04-06-2015, 09:59 PM | #11 | |
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04-06-2015, 10:25 PM | #12 | |
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See photo below. Formula uses more high tech gadget than a probe to measure their tire surface temp. They use a very sensitive infrared camera to monitor the tires around a new track or setup. Notice the left tires are heating evenly (which is good), while the right tire is only hot on the inner. This will tell the engineers to reduce negative camber on the right front corner so more tire will make contact with the track. When your tire pressure and camber are ideal, the temp across your tire surface would be very close to being the same = good contact = less tire wear. The second photo illustrates why it is important to prob 3 points of the tire surface to see if you have your tire pressure correct.
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04-06-2015, 11:06 PM | #13 | |
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However, if you are trying to narrow down your alignment for a given track, a needle-type pyrometer is necessary. I never use it for my purposes, approximations are good enough for me |
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04-07-2015, 12:45 AM | #14 |
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04-07-2015, 10:12 AM | #15 | |
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To start, set your camber at negative 2 degrees in front. Set tires to 30psi cold. You can make adjustments from there after the first few track sessions. (including your suspension rebound and compression rate)
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04-07-2015, 11:43 PM | #16 |
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great thread!
I'm still pretty green but thought I'd throw out a cheap/perhaps effective method for determining ideal tire pressures. I've seen (the experienced instructor type) guys use a grease pencil to make markings on the outside of the tires (on/near the small triangles on the shoulder area) to see if you're rolling over... if u wear the markings off, add air. if you aren't getting to the markings, let some air out. this may not be as effective for some setups but maybe someone can expound on this? also the 18x10 et33 square setup sounds like a possible option and doesn't require spacers iirc. going square for me came down to rotation possibilities... some tracks absolutely abuse a certain corner and it's nice to spread out the love. also with grippier tires and some throttle control I'm hoping 275 will be okay for a while. I can always add a couple wider wheels later if i wanna I wanna go staggered. 2cents worth.
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04-08-2015, 07:48 AM | #17 | |
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Most of us will likely graduate to a staggered setup as we get more comfortable on the track and reached the 275 rear limitation. The 911 guys have no choice but to go staggered. We may have to join the boat.
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04-08-2015, 09:51 AM | #18 | |
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04-08-2015, 11:59 AM | #19 | ||
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I do have 10mm spacers on order. can't wait to try it out! if it's really wet I may stay on my MPSS though
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04-08-2015, 12:20 PM | #20 | ||
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http://www.racerpartswholesale.com/p...455/Pyrometers
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04-08-2015, 06:57 PM | #21 |
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I agree with going square - I have that on my E46 and I love being able to pick and choose which tire I want where, depending on the track and existing wear.
I am also concerned with using spacers at the track. Doesn't that put a LOT more pressure on the hub, accelerating wear and potentially setting up for deformation? Can someone confirm? An ET33 offset for an 18x10 wheel will work well for front and rear, with 275-width R888, using stock suspension (no camber plates... yet) and no spacers?
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04-08-2015, 07:51 PM | #22 | |
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