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#1. Re: Rear wheel lifting during autox - from fesler@nsc.com
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Date: Thu, 25 Apr 2002 11:04:31 -0700 From: fesler@nsc.com Subject: Re: Rear wheel lifting during autox On 25 Apr 2002, at 9:42, Dorffer, Rich wrote: > Eric says > > > Front roll stiffness really helps reduce oversteer on > > our cars due to the difference in the front and rear camber curves. > > So try stiffening the front sway bar and see if that helps. I was full > > stiff rear soft front and not happy with the understeer. 2 notches > > stiffer in the front dramatically helped reduce the understeer. > > Isn't it contradictory to say "Front roll stiffness really helps reduce oversteer" and "2 notches stiffer in the front dramatically helped reduce the understeer". One of these statements appears incorrect and I am not sure whether I truly agree or disagree with you. Yes, these two statements are contradictory. I meant to say that front roll stiffness reduces UNDERSTEER. A few notches stiffer up front and the car rotates much better. This has been discussed on the group before but it is still worth mentioning as it is counterintuitive. On the chance that this was what you were going to disagree with I will explain further. The strut front suspension looses negative camber as it compresses more rapidly than the rear does. Accordingly if you have reasonable amounts of camber up front, more roll stiffness equates to more camber up front as compared to the rear after the cars weight has shifted and less understeer. Rgds, Eric > Regards, > > Rich > >
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#2. E-Mail Account Closed - from Steve Sun
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Date: Thu, 25 Apr 2002 13:09:44 -0500 (CDT) From: Steve Sun <stevesun@midway.uchicago.edu> Subject: E-Mail Account Closed Your e-mail regarding "Re: [E36M3] Who Cares about spring rate linearity in rebound" could not be delivered because this user no longer has an active e-mail account on our system. *** THIS IS AN AUTOMATED REPLY ***
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#3. Re: Eibach M3 Springs - from fesler@nsc.com
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Date: Thu, 25 Apr 2002 11:19:14 -0700 From: fesler@nsc.com Subject: Re: Eibach M3 Springs > #5. Re: [E36M3] Re: Eibach M3 Springs - from Chester Wong > Top > Date: Wed, 24 Apr 2002 09:20:47 -0700 (PDT) > From: Chester Wong <chester_p_wong@yahoo.com> > Subject: Re: [E36M3] Re: Eibach M3 Springs Well, there are a few > things working here. First of all, a stiffer rear would give more > oversteer...so it would make the car more neutral. Next, you have to > think about how the springs are installed on the car. The front > springs act along a path that leads to where the wheel is mounted. > The rear spring is not...it's mounted more inboard. So...if say you > had ride height adjusters, if you lower the front spring 1", you'll > drop the front about 1". If you lower the rear spring 1/2", you'll > drop the car about 1". See how that works? So...the rear wheels > actually have more leverage on the spring. So an increase from > 300#/inch to 440#/inch would be more like a delta of 70#/inch in the > front. Since the front goes from ~95#/inch to 136#/inch, the Eibach > kit is dialing in just a bit more neutralness. At least that's the way > I sees it :) Chester Or one could say that the rears are 47% stiffer and the fronts are 43% stiffer. This may have been as close as they could get to the same increase in stiffness using stock spring rates or perhaps installed with precompression they are even closer. I belive that this IS the way you should look at it. (% stiffness change) as however far the front and rear rolled they are now (to a first aproximation) rolling 70%F and 68%R as far. I think. Cheers, Eric
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#4. Re: [E36M3] Re: Rear wheel lifting during autox - from Chester Wong
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Date: Thu, 25 Apr 2002 11:32:17 -0700 (PDT) From: Chester Wong <chester_p_wong@yahoo.com> Subject: Re: [E36M3] Re: Rear wheel lifting during autox > Yes, these two statements are contradictory. I meant to say that > front roll stiffness reduces UNDERSTEER. A few notches stiffer up > front and the car rotates much better. This has been discussed on > the group before but it is still worth mentioning as it is > counterintuitive. On the chance that this was what you were going > to disagree with I will explain further. > > The strut front suspension looses negative camber as it > compresses more rapidly than the rear does. Accordingly if you > have reasonable amounts of camber up front, more roll stiffness > equates to more camber up front as compared to the rear after the > cars weight has shifted and less understeer. Huh? More stiffness up front induces understeer. 'Tis why a car set up with sways stiff/soft (f/r) is less likely to oversteer than a car set up with soft/stiff (f/r). I know that at least this has been discussed before on the list. As the front suspension compresses, you actually gain negative camber. You also gain toe-out which I believe is called bump-steer. Chester ===== __________________________________________________ Do You Yahoo!? Yahoo! Tax Center - online filing with TurboTax http://taxes.yahoo.com/
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#5. re: Tire size advise? - from andy radin
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Date: Thu, 25 Apr 2002 11:44:31 -0700 From: "andy radin" <fourfa@mindspring.com> Subject: re: Tire size advise? "Question, is it normal the outer part of the tire to be more worn than the rest of the tire? I assumed yes because of negative camber?" negative camber will tend to wear the inside. Wear on the outside is probably from too much toe-in, or possibly not enough negative camber for lots of hard driving. andy r.
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#6. progressive? - from Kit Wetzler
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Date: Thu, 25 Apr 2002 11:54:09 -0700 From: Kit Wetzler <kitwetzler@mindspring.com> Subject: progressive? > Isn't it true that the design of Bilstein's (monotube) valving is such > that it's velocity-sensitive? All shocks are velocity sensitive. Good shocks are digressive, which means that for high piston speeds, the shock damps compression and jounce less than for low shock speeds. Low shock speed events are stuff like body roll, etc. High speed events are damped less, so the car absorbs bumps... The problem is that the higher the speed of shock movement, the less damping you get... this is obviously a problem if you use stiffer springs. The shock velocity will increase, in jounce! I've found that progressive springs ride ok for a very limited set of bumps. These are very small bumps on virtually perfect roads. The problem arises when the bumps get larger than that... typically aftermarket lowering springs are too short to keep the car from slamming into the bumpstops. All of the aftermarket M3 springs I've used with the exception of the H&R OE sports and H&R race springs do this to some extent. Why is this? Slamming into the bumpstops is relatively safe behavior in corners. You simply end up with terminal understeer, which, to the general populace, is safer than going off the other way. Almost all of Eibach's springs have about a 20% wheel rate increase. Unfortunately, this is not nearly enough to keep the car off the stops after you take out over half of the travel! Remember, hitting the bumpstops a little bit is fine, but pulverizing them is bad. -kit
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#7. Re: [E36M3] Who Cares about spring rate linearity in rebound - from andy radin
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Date: Thu, 25 Apr 2002 12:01:00 -0700 From: "andy radin" <fourfa@mindspring.com> Subject: Re: [E36M3] Who Cares about spring rate linearity in rebound "Isn't it true that the design of Bilstein's (monotube) valving is such that it's velocity-sensitive?" think back to freshman physics... a classical damper has a force proportional to velocity, by definition. (the spring force goes by displacement and the inertia force by acceleration, it's the classic differential equation whose solution gives you a decaying sine wave. anyway...) Look at any shock dyno - for almost any shock, damping force increases with piston velocity. This is definitely true for Koni and Bilstein, although I'm not positive about the POS Gabriels on my van! The manufacturer does have the choice of rates, but changing or adjusting the valves, and they're free to have different rates in different directions. "If you had a fixed size oil passage in the working piston that allows a fixed maximum flow rate of oil, slow or small piston excursions that push oil at or below this fixed oil flow rate would be hardly damped, and any piston excursion that pushed the oil at a rate above this maximum flow rate would be damped at a fixed amount." no. a simple fixed orifice will yield higher forces at higher speeds, simply due to the viscosity of the oil. That's why the simple classic case is linear velocity-sensitive damping force. "Koni, on the other hand, allows you to manually adjust the rate of oil flow through the working piston, but it's still a static setting once it's adjusted." it's a static RATE, not a static FORCE. Still velocity sensitive. When Bilstein describes this property as a feature, it's like the TV antenna ad I saw that claimed to "pull the TV signal RIGHT OUT OF THE AIR!" Where this all deviates from classical theory is that there are progressive and digressive shocks. In practice these have a knee in the velocity/force curve, above which force will increase above linear (progressive) or below linear (digressive). This turns out to be useful, as you can classify a lot of suspension deflection into high speed and low speed events. Cornering, braking, and accelerating loads are relatively low-speed. Bumps, surface roughness, potholes etc are high-speed events. A progressive shock will be either unbearable on rough roads or underdamped in cornering - there were a few aftermarket shocks like this before they figured it out. A digressive shock, on the other hand, will soak up road noise but clamp down hard on cornering. Digressive shocks and progressive springs (set to increase rate at hard cornering loads) are how Mercedes gets their combination of smooth ride and good handling (at least that's what the engineering press says). The H&R coilovers also have digressive shock valving. andy r.
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#8. Re: [E36M3] Re: Rear wheel lifting during autox - from fesler@nsc.com
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Date: Thu, 25 Apr 2002 11:59:49 -0700 From: fesler@nsc.com Subject: Re: [E36M3] Re: Rear wheel lifting during autox On 25 Apr 2002, at 11:32, Chester Wong wrote: > > Yes, these two statements are contradictory. I meant to say that > > front roll stiffness reduces UNDERSTEER. A few notches stiffer up > > front and the car rotates much better. This has been discussed on > > the group before but it is still worth mentioning as it is > > counterintuitive. On the chance that this was what you were going > > to disagree with I will explain further. > > > > The strut front suspension looses negative camber as it > > compresses more rapidly than the rear does. Accordingly if you > > have reasonable amounts of camber up front, more roll stiffness > > equates to more camber up front as compared to the rear after the > > cars weight has shifted and less understeer. > > Huh? More stiffness up front induces understeer. 'Tis why a car set up with > sways stiff/soft (f/r) is less likely to oversteer than a car set up with > soft/stiff (f/r). I know that at least this has been discussed before on the > list. > > As the front suspension compresses, you actually gain negative camber. You > also gain toe-out which I believe is called bump-steer. > > Chester On our cars (well on the 96+ I don't know about the 95) The rate at which camber changes on the front and rear are different enough that a stiffer front can substantially reduce understeer. I was advised to try this either on the list or by somone at an autocross. I did as I had run out of room to stiffen the rear sway bar and was still pushing badly at autoX. The effect was obvious. There was substantially less understeer. I have seen a few peole mention this since then on the list. It usually goes without much comment. It may be that if you have more than a certain amount of camber (or less) then the understeer/oversteer balance is more affected by the change in compliance front/rear than by the camber. For my car and for several others front sway bar stiffness reduces understeer. It is likely that if the front is already stiff enough to control the camber (aftermarket springs) then further stiffening would yield the traditional result of more understeer. Regarding front negative camber increasing in compression: This may be the case but if the rear is adding negative camber faster then the front and the amount of -camber available is substantially less than optimal for racing..... Maybe we can get one of the tuners to chime in here although it may not be something they see as they run so much more camber already. Rgds, Eric (crashbolts+stock=~ -2.1degrees) > > > ===== > > > __________________________________________________ > Do You Yahoo!? > Yahoo! Tax Center - online filing with TurboTax > http://taxes.yahoo.com/ > >
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#9. RE: [E36M3] Who Cares about spring rate linearity in rebound - from Juan Rico
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Date: Thu, 25 Apr 2002 12:06:26 -0700 From: Juan Rico <juan_rico@captionsinc.com> Subject: RE: [E36M3] Who Cares about spring rate linearity in rebound Ron wrote: "So, for small amounts of suspension travel, the spring will travel a longer distance, and smooth out the ride. For larger travel distances (acceleration, braking, hard cornering), the springs will stiffen up as they compress, firming up as needed to limit the travel distance." After 3 weeks with the Eibach/Bilstein setup, this has been exactly my experience. The car has an amazing amount of body roll comparatively speaking at low speeds, but the more you push it, the flatter it corners. It's somewhat disconcerting at the beginning because, in a way, it's totally counterintuitive... It does the opposite of a stock setup. This is purely my subjective interpretation of what I feel driving this setup, and although I don't track my car, I drive my car 35K miles a year... -----Original Message----- From: Ron Buchalski [mailto:rbuchals@hotmail.com] Sent: Thursday, April 25, 2002 11:05 AM To: E36M3 Subject: Re: [E36M3] Who Cares about spring rate linearity in rebound
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#10. Re: [E36M3] Re: Rear wheel lifting during autox - from Chester Wong
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Date: Thu, 25 Apr 2002 12:27:11 -0700 (PDT) From: Chester Wong <chester_p_wong@yahoo.com> Subject: Re: [E36M3] Re: Rear wheel lifting during autox I didn't realize you were talking about the front w.r.t. the rear. I thought you were just talking about just the front. =) Chester --- fesler@nsc.com wrote: > On our cars (well on the 96+ I don't know about the 95) The rate at > which camber changes on the front and rear are different enough > that a stiffer front can substantially reduce understeer. ===== __________________________________________________ Do You Yahoo!? Yahoo! Games - play chess, backgammon, pool and more http://games.yahoo.com/
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#11. Re: [E36M3] Re: Rear wheel lifting during autox - from nabli@earthlink.net
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Date: Thu, 25 Apr 2002 15:31:19 -0400 From: <nabli@earthlink.net> Subject: Re: [E36M3] Re: Rear wheel lifting during autox Not sure what we're saying here but ... ----- Original Message ----- To: "E36M3" <e36m3@bmw-m.net> Sent: Thursday, April 25, 2002 9:15 AM Subject: [E36M3] Re: Rear wheel lifting during autox > > On 25 Apr 2002, at 9:42, Dorffer, Rich wrote: > > > Eric says > > > > Front roll stiffness really helps reduce oversteer on > > > our cars due to the difference in the front and rear camber curves. > > > So try stiffening the front sway bar and see if that helps. I was full > > > stiff rear soft front and not happy with the understeer. 2 notches > > > stiffer in the front dramatically helped reduce the understeer. > > > > Isn't it contradictory to say "Front roll stiffness really helps reduce oversteer" and "2 notches stiffer in the front dramatically helped reduce the understeer". One of these statements appears incorrect and I am not sure whether I truly agree or disagree with you. > > Yes, these two statements are contradictory. I meant to say that > front roll stiffness reduces UNDERSTEER. A few notches stiffer up > front and the car rotates much better. This has been discussed on > the group before but it is still worth mentioning as it is > counterintuitive. On the chance that this was what you were going > to disagree with I will explain further. > If you increase the stiffness in the front of the car it increases understeer. See: http://www.kormanfastbmw.com/thandling.htm for a basic analysis. > The strut front suspension looses negative camber as it > compresses more rapidly than the rear does. Accordingly if you > have reasonable amounts of camber up front, more roll stiffness > equates to more camber up front as compared to the rear after the > cars weight has shifted and less understeer. Not sure wht this means. CHeers, Jim E.