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08-10-2019, 01:26 PM | #23 | |
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Still, even with the same bushings, the M3 arm #17 still looks way cooler and is a little lighter. |
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08-10-2019, 05:23 PM | #24 |
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Check out the OE vs M3 control arms thread. There's a new product in the works for toe arms that would allow you to go full spherical (in that part) with no deflection or Group N bushings for minimal deflection plus some spring rate contribution....
OE vs M3 Rear Suspension Arms https://www.1addicts.com/forums/show....php?t=1079383 Stay tuned! |
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08-10-2019, 07:16 PM | #25 | |
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??? The factory 135i rear suspension parts are cheap stamped steel with a steel insert that sits inside a soft rubber bushing. The M3/1M bits are light alloy arms with a hard bearing pressed into the arm. The black rubber is quite hard compared to the 135i bits. The differences are night and day. Some pics for reference, from the interwebs.... non M and ///M rear suspension... ///M rear suspension... stock 135i suspension...
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08-10-2019, 08:42 PM | #26 | |
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You can even see in your pic above that the OEM wishbone arms have a bearing on one side and bushing in the other. https://www.1addicts.com/forums/show....php?t=1079383 Last edited by duder13; 08-10-2019 at 08:49 PM.. |
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05-24-2020, 11:03 PM | #27 |
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Those roll centre change and camber gain/loss graphs are fantastic, particularly on the front end. The interplay between a linear loss in camber and an accelerating roll center drop (and its affect on weight transfer front to rear) would be good to understand in depth - or just take home that controlling roll is important for predictable high speed cornering behaviour.
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06-18-2020, 04:20 PM | #28 | |
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Not meaning to look a gift horse in the mouth, I think I've found an error somewhere in your front suspension measurements: Firstly, entering the coordinates for the front upright/strut into cad, I find that the angle between the strut and the hub flange is actually 8.38deg. I've gone through the coordinates multiple times, but can't find my error. Inserting this component into an assembly with the front arms and chassis pickup points, along with the -3deg of camber, I find that the top strut point is some 21.25mm shy of the chassis coordinate in that location. The strut top point is nearly vertically below the chassis point; I aligned the plane of the front axle/strut with the chassis point, so that the strut/hub was constrained from rotating. I get 6.95deg caster. These measurements assume 0deg toe, though that can't account for all the discrepancy. I'm sure the issue is just a typo somewhere, otherwise the diagrams you've posted would look significantly different, but I thought I should share at least this part of my findings in case it helps you or anyone else fix an error. EDIT: I think the error is in the strut top coordinate, in the hub/strut model; I think this should be 0.0, 222.1, 442.5 instead of 0.0, 222.1, 422.5. Last edited by Tambohamilton; 06-19-2020 at 12:02 PM.. |
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06-19-2020, 12:44 PM | #29 | |
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I really appreciate your double checking my work though. |
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06-20-2020, 07:51 AM | #30 |
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Good good! I'm sure you would also have found it, if you'd used the wrong numbers yourself...
Next question; that coordinate for the top of the strut - where is that in relation to the top flange of the strut mount/camber plate, where it bolts up to the chassis, please? I assume the coordinates refer to the centre point of the rubber bushing where the strut attaches to the mount, but in order to get useful geometry for my purposes I need to know where that is relative to the chassis attachment. I've got a functional model in CAD now, but I just need to know that one bit of information in order to transpose it for the e90/1. (And I'm just going to change the rear ride height by the same amount as the front, and pretend that's accurate). Thanks! |
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06-20-2020, 11:30 AM | #31 | |
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06-20-2020, 04:39 PM | #32 |
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Thanks a lot! That's super helpful.
Unfortunately I'm getting lost now. I've measured my struts, top mount flange (@ chassis) to the top datum of the knuckle; 466 at full droop; 367.6 at ride height. Using a measurement from your Ohlins install thread (372 top mount flange to knuckle datum @ 326mm ride height; 2mm lower than these geometry measurements), the top mount flange to knuckle datum for this setup should be 373.92. Now, my car has stock non-sport springs, koni special active struts, and Xd top mounts...I seriously doubt it's lower (367.6 vs 373.9) than your track setup! I thought I could just plug in your coordinates, adjust based on strut length @ ride height, and arrive at my geometry...but it's not worked out. I don't really think that the wheel arch/fender reference will be the same on both chassis, but at this stage I think I might have to use it. Ride height on mine is 354; 26mm higher than yours to the arch...that sounds like the right ballpark. And I doubt that the fenders are as much as 30mm-ish higher relative to the suspension points on the e90/1. Come to think of it, how sure am I that all the suspension points transfer 100% between the two cars? Time for me to take stock, and figure out a better way to get my model set up All this just for some spreadsheet fun in the evenings, while I contemplate shoehorning M3 springs into the front of my car Last edited by Tambohamilton; 06-20-2020 at 04:45 PM.. |
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06-26-2020, 12:44 PM | #33 |
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Eventually figured I could just measure the Z height of a reference point front in each of the front and rear (wishbone inner end at the front, and camber arm inner end at the rear). I measured from a string line under the tyres, with the wheels up on a couple of 1" boards just to make sure the string line was off the ground.
At some point I'll need to go back through the whole model and check it all, but for now I'm content that it's giving me reasonable figures. Magic number spreadsheet is coming together now...just a few bumps to iron out. Thanks again, fe1rx for the data! |
06-26-2020, 01:46 PM | #34 | |
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Good to see that you are cross checking your assumptions against real world measurements. This is definitely essential! |
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08-24-2020, 03:55 PM | #35 |
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fe1rx Amazing thread and I am slowly trying to wrap my head around it piece by piece. I did have a question about the ride height. It looks like you used 328mm for the front and rear. Based on this is it fair to assume the wheel arches to hub center are the same front to rear when at 0 rake?
I am trying to dial in my ride heights and i wanted to start a 0 rake for the track and go from there. Would all i need to do is make sure my hub center to wheel arch is the same front to rear? |
08-24-2020, 05:29 PM | #36 | |
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To answer your question, we need a clear idea understanding of what datum feature rake is measured from. The simplest approach is simply to define zero rake as equal wheel-arch ride height front and back, which makes the answer to your question "yes" by definition. The way I actually look at it is to treat the 4 jack pad attachment points as points on the rake reference plane. My aero underbody does use the jack pad attachment points as attachment features and my underbody centre section is parallel to that plane, so that definition seems logical for aerodynamic purposes. Using this reference plane, when the wheel arch ride heights are the same front and back, the jack pad reference plane is positively raked by 0.6° or 27 mm when measured between axles. You would have to lower the rear by 27 mm to achieve zero rake using the jack pads to define the datum plane. At the moment I am running 0.4° rake relative to the wheel arches, which is 1° relative to the jack pad (aero) datum. This is probably way too much information ... The most useful rake definition is probably the one that is most easily measurable. I suggest that you stick with the wheel arch datums, but realize that that does give your underbody a bit of rake. Also, lowering your rear to get zero aero rake would put you hard on your rear bump stops. |
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08-24-2020, 05:35 PM | #37 | ||
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01-29-2023, 11:46 AM | #38 |
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Hi, that is a great project and I can still learn a lot from it in 2023!
I want to do the same thing on an M4 F82. When I read your description, I don't understand why the laser plumb bob is necessary. As a traditional plumb bob can also put the projection on the ground and mark on the tape. If you can kindly reply, i will really appreciate it. |
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05-16-2023, 10:23 AM | #39 |
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Fe1rx, did you publish the strut top coords at any point?
I saw the photo of you running a plumb line down so assume you took at least the x/y coord? I’m running an E81 130i and trying to determine the base configuration. From what I can see I can derive everything else from what you’ve very kindly shared, but without the strut top constraint (yours is set at -3deg camber and 7.3deg caster), it’s hard to create a model of the standard setup. I could of course use the 130i alignment data to feed in camber and caster to derive the top mount xy position, but it’d be good to know the inherent camber/caster with the real measured constraint you have. Thanks for any help Dave |
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05-17-2023, 10:59 AM | #40 | |
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Of course my datum point is not a point you are readily going to be able to locate on your own vehicle, so all this needs to be verified by you in some manner. |
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05-17-2023, 11:07 AM | #41 |
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That’s very helpful indeed, many thanks for taking the time!
I’ll draw things up wrt 130i and do some confirming measurements and add them back here for reference, once I get around to it all. |
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