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Cost of tracking
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| 03-03-2015, 03:18 PM | #45 | |
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For additional perspective, I have M3 bushings and wish I went solid delrin... |
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| 03-03-2015, 03:41 PM | #46 | |
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I am stuck trying to find a balance between decent track car and decent daily driver. I don't want to make it too harsh or end up with squeaks and rattles. Cheers, Burn |
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| 03-03-2015, 03:47 PM | #47 |
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Yes NVH on a street car is something to think about when modding. Subframe bushings won't add too much NVH but diff bushings can. Stiffer (read: not liquid filled) suspension arm bushings will also add some stiffness penalty but not too much noise. Most noise will come from pillowball bushings which are too extreme for this application, or race camber plates up front, mounted on coilovers. If you avoid those things, you shouldn't introduce offensive levels of NVH.
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| 03-03-2015, 04:09 PM | #50 | |
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 An especially in relations to the Xi, the problem with understeer on the Xi isn't related to the chassis, but to the fact that you're now asking the front tires to share BOTH the driving and steering. In a FWD/AWD chassis it's very difficult to fully set up a neutral to rotation happy car simply because you're always asking for a percentage of the traction up front to use for acceleration. The proper way to fix "understeer" in an AWD chassis is all software, not hardware.
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| 03-03-2015, 04:28 PM | #51 | |
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| 03-03-2015, 05:10 PM | #52 |
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You gotta understeer problem? Brake harder (but still trail brake). Wait for it... Now roll on power till WOT. Problem solved. (You should be WOT or thinking about getting to WOT at apex if not before. Don't add ~full~ power until you can "make it": you should be looking at corner exit - or even beyond that!- before you're even at apex, you'll know when you can "make it". Um, don't forget to unwind. Steering wheel "winding" is inversely proportional to gas pedal "steppage". Again, you should be "unwinding" at the latest at the apex, if not before. Disclosure: do this sh!t at your own risk.)
Shameless plug: I have a set of ~brand new and never-used-still-in-the-box~ Pagid Yellows, front and rear for stock 335 brakes. Make offer. Also, get tires. Geesh. 
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Last edited by IN54NITY; 03-13-2015 at 07:21 PM.. Reason: added "~full~", "thinking" |
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| 03-03-2015, 08:44 PM | #53 | |
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From your comments above it sounds like trying to solve understeer on AWD is similar to solving on a FWD system. Would you agree with that? I've got a fuck ton of reading to do on this shit now because I see the rear sway bar advice all over the awd forums. I'm not saying you're wrong I just don't like to take the words of a few and ignore the many without a better understanding. Have you built a x for the track or know someone who has? Thanks, Burn |
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| 03-04-2015, 09:50 AM | #54 | |
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General rules of thumb is to treat your x drive 3er as a red chassis. Get square 255 tires for all four corners and go from there |
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| 03-04-2015, 10:48 AM | #55 | |
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 Thanks guys for the great info you saved me 300 bucks and a buncha bullshit. Cheers, Burn |
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| 03-04-2015, 10:53 AM | #56 |
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I want to talk more about cornering so I'll start a new thread. I have some ideas I want to run by the more experienced guys.
Thanks again, Burn |
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| 03-04-2015, 12:12 PM | #57 | ||
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Of all the BMW chassis I've driven extensively on track, the E92 I owned will remain the ONLY BMW chassis I've never taken to churn a hot lap. Well, the E92 and the E60, but that's another story. I've driven my E30, E46, Z4 3.0i, MZ4 Coupe on about a dozen tracks around California for the last 15 years...Sprinkled in between a few other brand's chassis (350Z, Subaru WRX, and my current DD, a Hyundai Veloster). I've driven FWD, AWD, and RWD chassis on track and driven them ANGRY, so I can probably share with you how each different layout behaves, and how to adjust the car's operating system to get the most out of each layout's short-comings (they ALL have their short comings). But if you require "set-up" expertise on the E9X Xi chassis, I'm afraid I have absolutely zero knowledge to offer up there. Quote:
I recall, LONG time ago, when I was but a wee little noob starting my HPDE career, I once told the chief instructor of our chapter that he can solve all his understeering problems with a new set of swaybars for his stock M3. He gave me a little knowing smile and said "oh really? I'll have to keep that in mind." Little did I know he has been club racing for years and have been finishing first in his class consistently, and had forgotten more about setting up chassis than I will likely learn in my lifetime...He TAUGHT the instructor that taught me about some basics of chassis set-up that I've been spewing on various forums as fact. In reality, he spared me the embarrassment of trying to learn all that black magic that is chassis dynamics knowing that I didn't know enough at the time to comprehend 1/2 of what he'll be able to impart. It wasn't until much later, when I advanced to advanced level in the program did I start to pick up on some of the subtleties that changing chassis settings would do to effect handling. And in all honesty, up till that point, ANY change I would and could make to the car, I could really only take advantage of a small fraction of its capabilities, and in fact, due to the car's operating system still in 0.X release, the behavior of the chassis was far too erratic to extract any meaningful feedback from it. (and if you still don't get the reference, the car's operating system is the driver. You can't solve ANY chassis dynamic issues without fixing that first.)
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| 03-04-2015, 02:01 PM | #58 | |
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I don't think I'm the best driver or even close. I do realize seat time is the key and I continue to gain experience. I just want to make sure I understand why a car is behaving a certain way and what I, as the driver, can do to take advantage of or mitigate behaviors. I really appreciate the help and I'm not trying to get into a pissing match or argue. I took what you said and researched, as best I could, to find evidence to support your claim, not mine. I simply want to learn from those who have done it and are competent, not the 1 million people out there spewing useless shit. Sometimes, it's hard to determine who is who quickly enough to not offend the real deal by being skeptical of their claims. I don't want to be spoon fed and I'm willing to do the work myself. I think your insightful comments have saved me from heading down the wrong path. A perfect example of why shutting your mouth and listening is something I firmly believe in. Thanks again, Burn |
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| 03-04-2015, 02:18 PM | #59 |
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Got this one? http://www.amazon.com/Tune-Win-scien.../dp/0879380713
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| 03-04-2015, 02:24 PM | #60 | |
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| 03-04-2015, 03:14 PM | #61 | |
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A car's chassis dynamics is a complex system. Maybe not as complex as weather, but it as a system is highly dependent on a number of variables and factors that all affect each other. While distilling it and isolating each factor may result in a desired result for one instance, it may not produce the same exact result consistently across different platforms and, most importantly, DIFFERENT DRIVERS. Let's take one single subsystem for instance. I'll be honest. I spend an inordinate amount of time on a wide range of forums, because I'm a glutton for punishment, and also I have problem concentrating on the same project for prolonged periods of time at work. On a very mature chassis like the E36 M3, there seems to be absolutely zero consensus as to what to do with a simple component like swaybars. Some driver on the motorsports forum on a popular E36 M3 site seem to suggest that running without a rear bar is the best and only way to go, while others contend that they've tried this method and they would lose 1/2 a second on the same AX course. Then the no-rear sway crowd would cite their own results and results of various national champions that "champion" the no-rear bar method, until, of course, said national champ was dethroned by another that runs a chassis that has rear bars. So what is it exactly that I'm trying to say here? Actually, I don't have a point to make. Except there seems to be zero consensus. That seems to be the universal truth. So that leads me to form one conclusion. The ONE single variable that YOU as a driver can control, is the operating system behind the wheel. The cure for any and all handling ills needs to start with the DRIVER, not the chassis. Now, it may end with some chassis modifications, but the first, and foremost "fix," is you have to figure out how you're operating the car bridges the result that you have now, and the result that you seek. It's all the "zen of driving" if you ask me. Now, I don't know you. I don't know your experience level. But if I were to advise you, I would say, set a baseline first. Assume nothing, go out and drive to your max capability, collect data, and figure out the baseline. If you find yourself suffering from understeer on a lot of corner exit, then, as your baseline, you have established that the chassis understeers on corner exit (which is common amongst AWD and FWD cars based on what I postulated). Then the next step you need to figure out, is can you cure that understeer by altering the way you drive AND pick up time throughout the course. Since we know AWD and FWD has a tendency to understeer on corner exit, due to the fact that traction is shared between lateral and forward forces, you need to figure out a way to shorten the time that the front end spends doing BOTH. But let's take a quick step back. The reason why I gave you a metric ton of example of all the different cars I've driven on track, is because I learned how to drive on track on a RWD car, then, while still driving a RWD platform, I experimented with an AWD car that has very similar characteristics (my '09 WRX Wagon is ~3,200 lbs, high torsional rigidity, with ~300 HP on tap and about as close to 50/50 weight distro as any chassis can get, while splitting power from the turbocharged boxster 4 symmetrically to all 4 wheels at all times). My "baseline" driving style is based on the RWD chassis (at the time, an MZ4 Coupe that I still drive to and from the track today), and I quickly figured out that the WRX doesn't "understeer" like a b*tch, it understeers like a b*tch because I was trying to drive a AWD chassis like a RWD car. The logical way to drive it was to take full advantage of the fact that AWD has forward traction to all 4 wheels and can actually laid down power longer through a curve than RWD can, but in order to do so, the front end needs to be pointed as straight (or relatively straight) for as long as possible through a turn. The way to accomplish this is to trail the brake into a turn longer than I would in a RWD to put more grip up front, use that available grip for the first 1/3rd of the turn-in process mostly for the act of turn-in, turn in MORE and later than I normally would in the RWD, but spend LESS time on the turn-in, getting myself and the approach angle to the exit set for a more deep angle, then straighten out the front wheel much earlier and applying throttle much earlier than I would in a RWD. At the end of the day, I was churning equivalent times in the WRX as I would in the MZ4 Coupe, if the WRX was equipped with better R-comps (Hoosier R6 vs. Nitto NT-01 at the time) on the same course. When I started driving my Veloster Turbo on distant tracks, out of sheer desperation (I wasn't going to sit through 800 miles and 8+ hours of driving to and from the track in the MZ4 Coupe. Plus the missus, that came with me to the event, wouldn't be too happy about riding in it for that long either), I realized that in addition to the propensity to understeer, unlike the AWD on the Subaru where I can continue to apply more throttle and eventually the rear end will come around and point me the right way, the FWD chassis does not rotate under power, and that the more power you give it, the more your drive wheel will continue to spin underneath you and the SLOWER you will go. So the FWD chassis is even more of a "point and shoot" style driving, if you can't get the front end pointed to where you want it to go, you can't get on the throttle (RWD on the other hand, you NEED to roll on the throttle almost immediately after you turn in). So why am I telling you all this? You need to set a baseline. If you start messing around with the suspension now thinking that you're fixing ills that you haven't even experienced, you're wasting your time. Take the Xi to the track, churn some laps, figure out when and where there are troubles with the chassis. Then change one component at a time. Start with tires. Try squared vs. staggered. Check wear patterns. Try different pressure front and rear. Then based on wear patterns, align the suspension so you're using as much tire as evenly as possible across front and rear. Check tire temp after each run. Align until you get even temp across tire surface. Then, if you're getting uneven tire pressure/temp between the front and rear tires, you can increase/decrease spring rate front vs. rear*. Then, if you're not happy with the rate of weight transition in a corner, i.e. it takes too long to take a set, or if the front end sets while the back-end is struggling to catch up (and if you can actually feel that), you can firm up the dampers according to which end is lagging. At that point, if you're still understeering on exit for one or two of the tightest corners, and that's eating into your lap time according to data, then you can stiffen up one bar or loosen up the other based on the data to get you all the way there (and keep in mind you will NEVER have a truly, completely neutral chassis...All chassis will understeer or oversteer depending on input and condition. A truly, completely neutral chassis is something that doesn't have enough HP to overcome the rear tires, but have enough mechanical grip or aerodynamic grip to NEVER overcome the front and rear tires in a corner. A car like that would SUCK to drive). AGAIN...Why am I telling you all this? You need to set a baseline. Otherwise whatever tinkering you do is a waste of time (at least, a waste of time in the grand scheme of things. If you just want to tinker just to tinker...nothing I say here will stop you**). Once you have a baseline set, alter each component starting with the one that will give you the biggest effect to the one that will have the least change in system behavior. * Springs, are a little hard to justify changing all the time because they're so much harder to set right. This is where setting it to a recommended rate based on expert and manufacturer feedback will pretty much be the only way to do it. Most of us, at least most that I know, for HPDE purposes, set their springs once and almost never change it. Racing is another story all together. ** To be completely honest, most of what you read on the intarweb will have been based on some sort of truth. Will stiffer rear swaybars take away some understeer? Technically? Yes. And in some, if not most instances, it probably will. But it decreases understeer by promoting oversteer and take away rear grip at the limit. BUT what it also does is actually promote grip at lower end of the grip limit, thus creating the illusion that the car handles better, despite the fact that your overall grip level in the rear has been decreased. I put this footnote here, mainly because I don't think people shouldn't tinker with their car unless they're going to the track and know what they're doing. In fact, I encourage tinkering because, that's how *I* got started. My first track car had springs, swaybars, dampers, shifters, tune, intake, big brakes...you name it, it had it, before I turn a single lap on track. So I'd be a total hypocrite if I keep spewing the "baseline" crap. But now? Knowing what I know? I know I wasted a lot of time and money on setting up a car that probably would have handled just as well prior to me dumping what would have easily been over $10,000 on it, had I spend that money on upgrading the "operating system." Okay I'm done with my annual brain dump on E90Post.
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| 03-04-2015, 03:53 PM | #62 | |
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All joking aside. I've got my lap times from last year for a baseline. Things I know: I need to deal with cooling. FMIC and upgraded radiator. That may not be all I need to do but it's a start. The rear end feeling unsettled was mostly due to rear subframe bushings. The runflats have to go. I am going to take a chance and shoot for a square setup. Currently, the car has 8.5's in the rear and 8's in the front. I think it's a safe assumption that 8.5's and sticky rubber all around would be a solid move. Must have pads and proper fluids to hopefully avoid my braking issues from last year. Now what I didn't mention was the extreme body roll the car has when transitioning in a few of the corners or on the sweepers. One of the instructors that was following me even commented on it. He complimented me on driving the shit out of the car but said I should really look into reducing the roll. I figured the kw v1's would help with that but perhaps I should hold off. What worries me is how much roll I had on shitty runflats. With some proper rubber on I can see that becoming even worse. kw's will lower the car slightly and stiffen things up a bit. That should reduce roll, right? Of the things listed above it doesn't seem there is much a driver could do to make them behave any differently, except of course drive slower. But these are all stock handling characteristics of the car that I'd like to improve upon. So if I take the "pick the low hanging fruit first approach", I should try to improve the deficiencies that are not related to my input. Does that seem like a solid plan to you? Thanks again, Burn |
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| 03-04-2015, 06:21 PM | #63 |
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That was a good read.
To offer a different perspective, it doesn't hurt to stiffen up this particular chassis by switching to stiffer rear subframe bushings and control arms bushings like the M3. The stock non-M is very soft and imprecise in its stock form. That and a slightly more aggressive alignment (more negative camber front, and less toe in or even a bit of toe out as well) should provided all the things you need to start things out. The next step you should really focus on is actually getting to know the car. Unless you are absolutely sure that you have max the potential current setup, I would refrain myself from pouring too much money and effort on modding the suspension. |
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| 03-04-2015, 06:28 PM | #64 |
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9" in wheels would fit for both e90 and e92 (if you are tracking a 4000lbs e93, you are doing it wrong lol) if you get et30. I know apex sells those and they have group buys pretty often. A good tire for our car would be ha look r-s3 or something that can handle heat just as well, since our cars are heavy.
You might want to look into brass brake guide bushing as well. I had tapered pad wear issue last year even with PFC01 pads due to the flexing of rubber stock bushings under heavy braking, which leads to a annoyingly soft pedal. At $40-50 per axles, they are cheap insurance for a firm predictable pedal. |
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| 03-04-2015, 11:06 PM | #65 | |
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That would be ideal. So 18x9 et30 all around? |
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| 03-05-2015, 12:51 AM | #66 | |
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