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12-30-2012, 11:10 PM | #1 |
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Ideal Rake?
I just finished installing my new TCK setup today and will be taking it to the shop in a few days for alignment and corner balancing.
I've searched a fair bit on the topic, but I can't seem to find a solid answer. It would make sense that our cars would benefit from having front rake (to reduce understeer), but how much is ideal? If it makes any difference, I'd like to lower the car about 1-1.25" from stock.
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12-31-2012, 12:08 AM | #2 |
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I don't know of any race car that runs rake (usually squat) and the only reason I can think why the z4 car could benefit from rake is to counter the stock staggered set-up.
Did TC run rake on his cars? Last edited by seank; 12-31-2012 at 12:14 AM.. |
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12-31-2012, 12:14 AM | #3 |
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Rake is for the poseurs in the "stance" crowd. Worry about cross weight and roll center. Don't worry about "rake."
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12-31-2012, 09:21 AM | #4 | ||
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Then again, it all depends upon what you're using your car for. If it's relatively slow speed stuff, aerodynamics are less important. But for flying around the Nurburgring, I want all the aerodynamic advantage I can get. Last edited by exdos; 12-31-2012 at 09:36 AM.. |
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12-31-2012, 09:55 AM | #6 |
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12-31-2012, 09:58 AM | #7 |
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By rake or squat of a certain vehicle I understand the inclination when looking from a side.
If the front of the vehicle is lower than the rear of the vehicle, then it sits a little bit inclined to the front. This inclination is called "rake". If the inclination is the other way around (= the vehicle is higher in the front than in the rear), that is called "squat". Please correct me if I'm wrong. |
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12-31-2012, 10:01 AM | #8 |
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12-31-2012, 10:02 AM | #9 | |
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(caster is the angle of the suspension strut compared to the normal measured in the driving direction) caster: (picture from book 'the automotive chassis') Last edited by GuidoK; 12-31-2012 at 10:10 AM.. |
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12-31-2012, 10:27 AM | #10 | |
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Rake is irrelevant. It is FAR more important that the cross weight is as close to neutral as possible and the car is as low as the roll-center allows while still maintaining a reasonable front/rear weight balance. IF lift or aerodynamic grip is your concern, find ways to add or subtract downforce while minimizing the impact on drag, rather than fix the "rake." If your chassis is set-up right, "rake" will fix itself. Rake is for "stance" crowd poseurs. You might as well lower the car PAST its roll center with massive negative camber in order to tuck your 10.5" F, 12" rear wheels shod with 205f/225r tires into your fenders.
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12-31-2012, 11:39 AM | #11 | |
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I've recently written in another thread on the forum: "The Z4MC's suspension is too soft at the front which allows pitching on braking and lifting on acceleration, which makes the steering floaty and imprecise, and at the rear it's too stiff, which makes the ride very uncomfortable. The 3 centre coils of the rear springs are 19mm thick whereas the front springs are just 11mm thick: obviously there's a huge mismatch between front and rear spring rates, yet BMW cars supposedly have a weigh balance F:R of 50:50. I've fitted AC Schnitzer Racing suspension (basically Bilstein PSS9 made to ACS's specification), which has rear springs of 16mm and front springs of 14mm, which redresses the mismatch of F:R spring rates. Instantly, this helps to overcome the inherent ride and handling problems of the Z4MC with OEM suspension." With my ACS Racing suspension the car is considerably more balanced with considerably reduced tendency to pitching and lifting, which, of course, will simultaneously reduce the dynamic rake change that previously occurred. You ask: "How often do you drive an entire course while doing exactly 200km/h?" As you know, aerodynamic effects are working at ALL speeds and not just 125mph (200km/hr), and have greater effect at higher speeds. At The Nurburgring I will be doing a lap time averaging in the order of 90mph and reach speeds above 125mph several times and touch above 140mph. As the figures for lift of the Z4 3.0CSi show, the lift is unequal F:R so again any corner weighting done at 0mph goes completely out of the window in the dynamic situation, especially at higher speeds. As always, it's "horses for courses"; maybe for your purposes you can ignore rake, but for my purpose I consider that it is an important consideration, which I have adressed. I couldn't give a toss about "stance", and I'm not interested in lowering for the sake of it, it's only the performance and handling that concerns me. This is a photo of me in my M Coupe (S54) at the Nurburgring. It looks to me like my car is very well balanced with minimal lateral bodyroll and a preserved rake angle due to the lack of pitching/squatting. I have also heavily modified that car and it's handling is now superb. Last edited by exdos; 12-31-2012 at 11:50 AM.. |
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12-31-2012, 02:33 PM | #12 |
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ideal rake:
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12-31-2012, 02:43 PM | #13 | |
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01-01-2013, 07:46 PM | #14 | |
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01-02-2013, 01:39 AM | #16 | |
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Check how a Z4 is setup by BMW and listen to what Hack has to say. I'd say corner balance that sweet ride and forget about its stance. If you really want to impress someone, go do the following: 1- Euro headers 2- Decat Spipe leaving the chamber to pseudo- resonate. 3- Buy a straight-through muffler like RE diablo or RPI or SS or eisenmann. 4- Get evolve NA software 5- Shift @ redline Pure DTM aural sex. I can post a video if you're interested. |
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01-02-2013, 02:15 AM | #17 |
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Tika ,exdos, is soooooo far from a stance idiot, he other end of the scale he's a proper engineer. He added rake angle to his car for nothing other than performance I can assure you :-)
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01-02-2013, 04:01 AM | #18 | |
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less caster means stronger steering effect when turning into a corner and more caster means more steering effect when leaving the corner (and increases straight line stability) |
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01-02-2013, 05:12 AM | #19 | |
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You're talking drivel! This is a photo of how I've set up my Z4MC on ACS Racing suspension (adjustable), with H&R E46 M3 ARBs F&R and with 10mm spacers F&R and RTAB limiters. I have also reconfigured the geometry. It has been set up by the way it feels and performs to my handling taste and requirements. The appearance of the final result has been of no interest to me, all the mods and set up have been refined by performance, only. Go on, tell me I'm a poseur who's just gone for stance. |
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01-02-2013, 05:19 AM | #20 | |
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By increasing the caster and running less static negative camber, you'll get less tyre wear, have better self-centring and great turn in, due to the increase in dynamic negative camber. |
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01-02-2013, 06:07 AM | #22 |
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