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04-22-2014, 12:47 PM | #45 | |
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Typically, these cars come from the factory "fairly" balanced, however they do not account for variances in driver's weight or other modifications. The end result, say, your left front+right rear is about 50 lbs heavier than the right front+left rear, then one of the adjustment collars will be moved slightly to tilt the car one way or another. Keep in mind, the OP's car came with 450/550lbs springs. That means to alter the ride height of one corner by no more than 1/10" to achieve the desired effect. One. Tenth. Of an inch. If that 1/10th of an inch alters the dynamic height enough to reduce the front aerodynamic force enough to be a concern upon acceleration squat, I've got another calculation for ya. Our car makes 265ft-lbs of torque at the crank. Let's call it 240 at the wheels to be generous. Given that aerodynamic forces aren't significant on this chassis under 80MPH, we'll call it middle of 3rd gear. 3rd gear multiplication is 1.66 * 3.65 = 1,454.16 ft-lbs of potential twisting force being applied at the rear wheels, since the overall radius of the wheel/tires is pretty darn close to 1'. The MZ4 has a wheelbase of 96" (8.06'), so that means the leverage that 1,454.16 ft-lbs of torque being applied at the rear wheel translates to a whopping 180.27 lbs at the front axle. So at full throttle, on OP's car, with front springs at approximately 450lbs/in, the car will lift or squat...Wait for it... 4/10th of an inch. At full throttle. In 3rd gear. That number decreases at even higher speeds, in higher gears, where aerodynamic forces are more important. The next thing I want y'all to do, is go out and measure the height of the chassis right in front of the rear wheel, and right behind the front wheel. Tell me what the difference is there. Then I want you to measure the clearance between the mid point of the front bumper to the ground, then measure the midpoint of the REAR valance to the ground. And tell me the difference there. I'm willing to bet even on OP's car, the rear valance clearance is inches higher than the front. And then go ahead and tell me that it's going to make a difference AERODYNAMICALLY if you move one of the front or rear collar 1/10th of an inch. I'm going to let you all in on another secret. I'm not proud of it, but I will share it to make a point. Right after I got my MZ4 Coupe corner balanced, I didn't like the "stance" of the car. Plus on straight roads it pulls to the right, or I have to crank the wheel to the left. So I figure I can probably HACK this by adjusting the easiest parameter I can mess with, by turning the right front adjustment collar to raise that corner just a bit. I turn the collar 3 turns, which in turn, move the right front up by about 1/8". Didn't do sh*t for the issue with the car pulling to the left (I'll explain this later). I took the car back to the place that CB'ed the car. Kept my mouth shut, and the owner of the shop came back and said "I don't know why but your setting was all f*cked up, especially the front right corner. We had to go through the whole process again." He was going to suggest I check the rest of my suspension to find out why, especially the front right setting, was way off from where they set it a few weeks ago. 1/8th of an inch. Turns out the car was simply following the crown of the road, but since the front end was toe-ed out slightly it dramatically enhanced this effect. I drove the car on a road that crowned to the left (the sewer drains were in the middle of the road) and sure enough, it pulled to the left and I had to crank the wheel to the right. This is why I insist that corner balancing has zero effect on rake, and rake is irrelevant. It's far more important you set the cross weight correctly. Rake is important only to those who are far more obsessed with stance than functionality, I've never in my life seen any club racer worry about the car's rake. Because, even if you set the rear axel height of the car lower, the front facia is still much lower than the rear opening. And it's hard to set the car so far out of wack that the rear of the car is LOWER than the front, since the rear of the car is several inches higher than the front to begin with. Corner balancing does not alter the ride height enough to lower the rear by inches and raise the front by inches. You'll have a bigger negative effect on static rake and dynamic aero lift by going with the WRONG aspect ratio tires than corner balancing, IMO. And I am going to address your last point by pointing out you're looking at a picture taken with what likely is a wider angle lens commonly found on cell phones. At an angle. Which typically exaggerates the dimensions of objects closer to you and diminishes those same dimensions of objects far away from you. If you can accurately say that his car has zero rake from a simple picture taken by a simple camera posted on a simple forum, I applaud you for your super human deduction skills. Because frankly, I can't see it.
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04-22-2014, 01:28 PM | #46 | ||||
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If you think that rake angle has no effect on performance try telling that to Adrian Newey, the designer of Red Bull FI cars. |
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04-22-2014, 04:01 PM | #47 | |
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Our street cars have very little in common with F1 cars in terms of aerodynamics. In fact, you can't apply most of the aerodynamics in F1 to our cars simply because one factor: Open wheel. That has far more aerodynamic effect on a chassis than the rake angle EVER WILL. Anytime anyone says "hey F1 cars do this, why aren't we doing it in our street cars" ala aero or brakes or whatever clearly has zero understanding of chassis dynamics. Formula 1 is all the vehicle dynamics pushed to the very limit of laws of physics. Comparing modern passenger cars to Formula 1 car is like comparing gliders to Gulf Stream jetliners. Sure, they both have wings. But they're vastly different in their propulsion method and technologies (okay, bad analogy, because when you distill down to the basics the propulsion method is the same between F1 and passenger cars, but the EXECUTION of the two is drastically different. Drastically). Again. I ask you. Go out and measure the height behind the front wheel, to the height in front of the rear wheels. You'll see the natural "rake" on modern passenger car is far larger than the actual range of height adjustment a typical corner balancing will ever come close to exceeding. And no offense. Seriously, you're arguing that adjusting perches for a few millimeters = 10mm of height difference? Have you actually seen how our front struts are designed? I'll grant you that a few turns of the collar on the rear springs may exceed a few millimeters, but again, go back and re-read what I posted. You're talking about 1/10th of an inch of ride height adjustment to achieve 50 lbs of difference in corner balancing. Honestly, I know you mean well. And what you're trying to say actually MAY apply to Formula or open wheel race cars. But they do not apply to our cars. Not the way you think it does. And I'll bet Adrian Newey will agree with me.
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04-22-2014, 05:00 PM | #48 | |
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When I'm travelling at 150mph down to Schwedenkreuz at The Nürburgring Nordschleife, give me a car with a bit of positive rake, rather than one which has perfect static corner-weighting, everytime. Last edited by exdos; 04-22-2014 at 05:14 PM.. |
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04-22-2014, 05:53 PM | #49 |
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Stupid question here,
When you set 'rake', aren't you effectively changing the roll axis on a car by shifting weight from the rear to the front on positive rake? |
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04-23-2014, 03:36 AM | #50 |
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Yes. Likewise, if the OEM car has a static positive rake angle as does the Z4 and you reduce it, then you will do the reverse, and shift weight to the rear. When you start loading the Z4 with driver, passenger and luggage, all that additional weight will progressively load the rear axle more than the front, which will tend to reduce rake angle. If you were to start with zero rake unloaded, then you will soon be into negative rake. Therefore setting static rake, like the setting of all other geometry, is a compromise in anticipation of what might happen in the dynamic situation.
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06-16-2014, 02:07 AM | #51 | |
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I just installed GC Coilovers and new wheels/tires and I'm getting a little bit of rubbing on full compression. My next step is going to be an alignment, and hopefully add more rear camber to prevent rubbing. If that doesn't work I'm going to need to roll the fenders... Ah, the joys of aftermarket...
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06-16-2014, 07:35 AM | #52 | |
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I found that I was rubbing in the fronts but I think that's a reflection of the rather soft springs I was running relative to the r-comp tires. I just bumped up from 450/550 to 550/650 and added a thicker front sway. I was rubbing in the rears slightly but a quick fender roll addressed that. The rears are really easy. |
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06-16-2014, 01:14 PM | #53 | |
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06-16-2014, 01:24 PM | #54 |
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I didn't have trouble with the rear fenders, true it's thin but use a heat gun and take your time and it should be fine. I was able to roll maybe 90% of the 'arc'. The final 10% where it meets the adjacent panel was the only part I didn't bother since the rub was only primarily above the wheel, not in front or behind.
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06-16-2014, 01:35 PM | #55 |
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Gotcha. So are you running -2.8* and 1/16 toe out in front, -2.6* and 1/8 toe in on rear now? How is your tire life? My Z4M is a weekend driver. I guess you can say I'm trying to dial in as much rear camber as possible without chewing up the tires before 10K miles.
I used a camber gauge last night and I'm probably running 2.0-2.2* in the rear already. I'm not sure what 0.5* is going to give me ... actually I do. S = r*theta where r ~= 18.0 (rim dia.) + 2.0 (tire sidewall) and theta = 0.5*(pi/180) = 20*8.726E-3 = 0.175 inch ... 4.45 mm hrm... 4.45 mm is a lot! A good rule of thumb, then, is that 1.0* of rear camber can yield approx 9mm of top-of-tire clearance. Sorry, I just nerded out.
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06-16-2014, 02:28 PM | #56 | |
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From a personal experience standpoint I used to run 3.0* to 3.2* of camber on my rear wheels and they ended up lasting around 11-14k miles as a daily driver. I believe I got a little more out of contis over some of the nittos and yokes that I frequented, but keep in mind I was also running a little over a full degree of toe as well. (My rear was a black hole of issues on my Z3). Additionally this was on smaller tires for some time (245s) and at the end I wound up pushing around 16k miles out of a set of 275s. Not sure if there was any real correlation between tire size, but rim size definitely played a factor there. Anyways thought I would share, enjoy the low life. |
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06-16-2014, 02:36 PM | #57 |
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Damn it, I made a mistake.
S = r*theta where r ~= 9.0 (rim RADIUS.) + 2.0 (tire sidewall) and theta = 0.5*(pi/180) = 20*8.726E-3 = 0.096 inch ... 2.43 mm. Rule of thumb is 1.0* rear camber gives approx 5mm of top clearance. Skiddish, Surprised to hear that you could run that much 3.0-3.2* rear camber and get pretty good tire life. For reference, I'm using summer tires (Bridgestone S04). Can you please tell me your full alignment spec? I think I'll drop off my car to Dinan tomorrow.
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06-16-2014, 02:45 PM | #58 |
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I read on another forum that Shipkiller "Rear camber, maxed out stock arms: -2.0" (link). He's driving a Z4MC I believe. It's an old thread, though.
What is the max camber out back for an ///M?
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06-16-2014, 03:30 PM | #59 |
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Keep in mind that this was a Z3 and not a Z4, also it was a 2.5 and not an M.
My rear suspension was blown out at the end of five years and I decided to replace it with KWs. When I did so I was already running the max camber in the rear with the OEM set up due to wear and just general sag. I lowered the car maybe 3 to 3 and a half inches in the rear providing it with around 3.1-3.2 degrees of camber. It did have a bad toe in problem on the rear right which I also corrected, I ended up running about .25 toe on the left rear and about .4 on the right rear. This was done with RCABs (knowing it wouldn't last forever). Regardless even at stock camber of right around two degrees and a full degree of toe I was still able to run about 10-12k miles on my tires. I do not have an answer to what you're looking for as far as maxing out the rear camber, but I feel like I've since seen threads and builds that incorporate much more than -2* of camber. I would look at Rated M, he's generally a wealth of modded information. Sorry for jacking, but I figure this will make things more clear. Also on softer tires I didn't notice that big a difference in tire life. At least in "general quality sport tires" not slicks or anything crazy. The wear maybe progressed a little faster, but that may have been due to driving as well. Expect maybe 2-4 thousand less out of "performance tires" Last edited by Arsonism; 06-16-2014 at 03:43 PM.. |
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06-22-2014, 10:31 PM | #60 |
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Just came back from Watkins Glen, first time up there but car handled great. I was pretty much trailbraking every turn and using throttle oversteer to rotate the rear. New (stiffer) springs & sway made a big difference. Fastest lap was 2:20:28
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06-18-2015, 07:49 AM | #61 |
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Well doesnt it matter what you do with it. If you like to do autocross aka turning circles on a empty parking lot then you might want less camber and maximizing the contact patch for low speed. If you drive a track like the Nordschleife with high speed corners, elevation and camber changes then you need more camber. I'm at 1º,1' front and 2º,25' rear. I went up on rear camber from 1,55º and the new setup feels better to me. Toe is set at near 0 front and rear. If anything I would probably try a stiffer front antirollbar now to kill some roll in the car.
It still does this, so I certainly not too much rear camber I think: Last edited by glnk; 06-18-2015 at 07:55 AM.. |
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