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Making this car handle
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12-07-2008, 08:57 PM | #45 | |
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12-07-2008, 09:35 PM | #46 | |||
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The after market kits have been design for peg leg differential approach for suspension tuning. The progressive springs are not what you want on track car ever. The only way around is to put on a big friggen tire up front. This is just a Band-Aid and only delays the onset of under steer. Quote:
The quick solution is: 230 lb/in front spring on with an 800 lb/in rear spring. Put a UUC front sway bar on and buy H&R bushing to get rid of the crap ones that come with the bar. Buy a H&R rear bar which does fit the xi. The rear sub frame bushing will not work well with the incresed stiffness so you need to upgrade them M bushing. The bushings are cheap and the install is low for cost when doing a rear bar. You been warned if don’t replace the bushing the car will bounce around a lot and yu will not get good rear grip. There is two link in the rear you can also change to M link if you wish and they do matter a lot FWIW. This setup will get you back to BMW OEM pitch which is a frequency of 12% higher at the rear than the front. The spring I selected is within the working v3 range. The wheel spring rates are: Front 215 lb/in (KW stock is 258 lb/in) Rear 285 lb/in (KW stock is 205 lb/in) In the mean time increase front rebound as much as you can...it is the only thing you can do. How I got the info is much longer story…… Quote:
Orb Last edited by Orb; 12-07-2008 at 10:02 PM.. |
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12-07-2008, 10:08 PM | #47 |
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JRZ makes some nice product and they also make some of the OEM products for Dinan. Too bad we can't copy your JRZ setup since our mounting positions are different...... I would love to have a squeak free, no coil binding, and appropriately tuned suspension setup.......
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12-07-2008, 10:54 PM | #48 | |
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12-08-2008, 09:07 PM | #49 | |
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Cheers.
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12-08-2008, 09:22 PM | #50 | |
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EDIT: Thanks for all the input, I'm sure you have spent countless hours figuring this out.
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12-09-2008, 10:10 PM | #51 | |
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The rear motion ratio for this car is about 0.32 after being squared (it truly sucks). The problem with this is that when you have such a high motion ratio it is difficult to get a stiffer rear spring and damper to work and this is mostly due parasitic losses in the system so you have inconsistency in suspension action and this is a really a big deal!! I know the rear spring rate stated with the M bushing will be okay and maybe a bit more but the damper craps out around 900 lb/in the rear for adjustment as the adjustments go very non linear near the end. You can go higher with rear spring rates but you need some M link and a variation of my custom links as well. All the soft bushing and links must go. If anyone thinks the spring are to stiff then you will realize they are not so do the math below and the wheel rate is what you feel and is the only thing that is important to you. The rear spring rate on the KW is 570 lb/in. Coil spring rate x 0.32 = wheel spring rate 800 lb/in x 0.32 = 256 lb/in Sorry about the error in my numbers in the previous post. Orb |
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12-10-2008, 01:04 PM | #52 |
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Are you kidding??? How does that make any sense?? Why would BMW design a AWD system that disengages at a set speed?
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12-10-2008, 04:09 PM | #53 | |
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To reduce drivetrain losses. Supposedly the AWD system also reverts to "RWD mode" at very low speeds to assist in parking lot maneuvers and so forth. Back to the major topic - I would be curious to know if Orb has an xdrive or a RWD 335 (I suspect the latter). He clearly knows a great deal about the suspension setup, and has put a lot of time into making improvements. I am just curious whether his comments specifically relate to the xi suspension problems or pertain to the 3 series in general. |
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12-10-2008, 11:49 PM | #54 | |
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The rear suspension are the same and the front is similar as well expect more mass and there slightly higher front frequency. The thing I am looking at is total load transfer for your car so the details on 2wd vs 4wd is not a significant issue but a consideratio. The purpose of this is to see the load distribution on each tire in a steady state roll which dictates car balance. The statement applies for 3 series in general including the M3. Orb Last edited by Orb; 12-11-2008 at 02:53 AM.. |
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12-10-2008, 11:59 PM | #55 |
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+1 I've never heard of it either. I always thought the XI was slower up top because of the driveline loss. If it disengaged at 75mph then it would be just as fast as the RWD 335.
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12-11-2008, 12:20 AM | #56 |
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I seriously doubt this claim too. I've taken the car to the track and seriously pushed the car between 50-120mph with traction control on and boys and girls it is on - there is no mistake. From a safety standpoint you would want to turn it off to eliminate the irrartic behavior at the edge.
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12-11-2008, 12:32 AM | #57 |
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Whether xdrive disengages the front axle at speeds in excess of 100 mph has not been substantiated by any BMW technical document (to my knowledge). However, this idea has been mentioned several times on e90post and it might be best to consider it an urban legend until somebody can provide credible documentation. Nonetheless, if true, the rationale would most likely be to prevent excessive drive train loss.
On the other hand, BMW's website does state that the clutch pack disengages at low speeds to improve maneuvering. "when parking, the system reacts to the need for high manoeuvrability at low speed by opening the clutch completely so the powertrain functions optimally." http://www.bmw.com/com/en/insights/t...icle=mm_xdrive I recall reading somewhere that this occurs at speeds <10mph. Unfortunately I can't remember the source. |
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02-24-2009, 10:53 AM | #58 |
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you know, i have an '06 325xi and i think it handles fairly well. i mean ya, its nothing compared to any of the M classes, but its not as bad as people want to make it sound. it "feels" more floaty and like it can't take the hard turns, but i've done on ramps at 55 in 4th and though it kinda feels like i'm unstable (the body roll) but i know all 4 wheels are on the ground and keeping me in line. the suspension isn't great but its not at as bad as people want to make it seem. also, i've gotten up to 130mph on the highway and again, it feels floaty but perfectly maneuverable. ive had zero problems switching lanes and such at high speeds. (then again i'm used to driving a 4runner that is highly unstable at speeds over 60)... i do agree that it should not feel like its going to explode when i go over a speed bump though :\ .... i've never read about the xdrive disengaging, but i do know that its normally kept at 40-60 split. so most of the power is going to the rear wheels
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Last edited by Xi021; 02-27-2009 at 10:01 AM.. |
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02-27-2009, 10:12 AM | #59 |
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Dinan now makes a full stage 3 suspension for the xdrive cars.
Anyone try these yet? |
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02-27-2009, 11:22 AM | #60 |
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02-27-2009, 12:39 PM | #61 |
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What does the kit consist of ?
EDIT: Nvm, just camber plates.
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02-28-2009, 09:52 AM | #62 |
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02-28-2009, 11:54 PM | #63 |
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Oh Come'on guys, is the handling really that bad?
To O.P have you ever driven a Ford Taurus? Sure the Xi might now have the exact same characteristics of the i, however Lets be realistic here, your still not driving a Taurus, your still not driving a Civic (though Hondas have some decent Handling for FWD). Your driving a BMW, you still have so much more feel then the poor schmuck in the Toyota Corolla running down the road in full out 4x4 Height, with tons of body roll and understeer... Sure the car could be better, but thats what the aftermarkets for... Personally, ill prob just do the sways to stiffen her up a little and get rid of some of the roll... that and runflats shouldn't be a bad combo... theres really no need to stick 1000lbs race springs and slam your DD.. I put a track ready set up in my Old TSX, and that was half the reason I sold it, Sure it was fun for AutoX, but after scraping on a daily basis and knowing what side the quarter was on (heads or Tails) after running over one, im more then happy to have my "Floaty" Xi and enjoy the driving experience. and just remember that when there is a nice steep hill with 3 inches of ice and snow, well make it up, while the "better handling" 330i is still spinning the tires |
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03-01-2009, 07:04 PM | #64 | |
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