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#1. Re: [E36M3] Re: AA Turbos - Was 99t - from Matt Henson
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Date: Fri, 12 Jan 2001 17:49:08 -0800 (PST) From: Matt Henson <hensonator@yahoo.com> Subject: Re: [E36M3] Re: AA Turbos - Was 99t Right.. I apologized to Neil in private but I'd like to extend that to everyone. It is bad form to include excessive quotes in an e-mail and I broke that rule. I've been using the internet/USENET for nearly 10 years so I won't use inexperience as an excuse. Sorry to those of you with slower connections. -Matt > > Nick, > > Maybe you should see somebody about that memory > problem <g> > > Everything Matt quoted in his most recent post - all > 213 rewrapped lines - > is is stuff we've seen from those two just in the > last couple of days. > > It wasn't all useless the first time around, but > after that... > > Neil > 96 M3 __________________________________________________ Do You Yahoo!? Yahoo! Photos - Share your holiday photos online! http://photos.yahoo.com/
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#2. Re: [E36M3] Unsprung Weight - from Matt Henson
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Date: Fri, 12 Jan 2001 18:15:29 -0800 (PST) From: Matt Henson <hensonator@yahoo.com> Subject: Re: [E36M3] Unsprung Weight Okay buddy you got it.. From Hugh D. Young's "University Physics" 8th edition.. I'm going to make some assumptions. First I'll assume that all of the mass is on the outside of the tire. This will give a maximum amount for the ratio between wheel/tire and sprung weight. Second I'll assume that the tire is not sliding. The kenetic energy of our wheel is going to be equal to the energy due to translation + the energy doe to rotation. K=1/2Mv^2 + 1/2(MR^2)(v/R)^2 Where K=kenetic Energy M=Mass of tire/wheel v=linear velocity R=radius of the wheel/tire We can reduce the rotational energy(second half) of the equation to 1/2Mv^2 since the R's cancel out. This gives the total kinetic energy as K=1/2Mv^2 which is twice the energy due to translation. Every sprung part of the car has a kinetic energy of 1/2Mv^2 so my assumed wheel/tire requires twice the energy for a given mass or, conversly, the mass of the wheel reqires a maximum of 2 x the energy as the sprung weight. Now what about our assumptions? First, if the weight is not on the outside then the energy doe to rotation decreases. If we take that to the limit with a R=0 then there is 0 energy required to rotate it. Secondly, if the tire is slipping then your car isn't accelerating as fast as it should so who cares. If your tire was on the verge of breaking loose and you get a lighter wheel then you might be able to break loose, causing the sensation of accelerating faster. Same goes for having a lighter wallet from the light wheels. Now... aside from linear acceleration there may be a bigger benefit from the light wheels. According to Fred Puhn's "How to Make Your Car Handle," it is desirable to have a sprung to unspruing weight ratio of 5:1 or better for best suspension control and handling. Maybe this is what Tire Rack et Al. had in mind when they claim 10:1. Okay for the flywheel. In lower gears there is a fairly significant percentage of the engine's torque used up to overcome the inertia of that 20lb slug. It has a smaller diameter than the wheel and it's weight is more concentrated to the center but it spins faster - by a multiple of the rear end ratio and the tranny ratio. So if your 1st gear is 4:1 and the rear is 3.5:1 then there is a 14:1 difference in rotational speed. Even if the flywheel is 1/2 the diameter of the wheel and it's weight is 3/4 as much as a cylinder then it has a rotational inertial ratio of ..5*.75*14=5.25:1 compared to each wheel. Divide by 4 cuz' there are 4 wheels and the ratio is 1.3. So reducing your flywheel weight by 1/2 is the same as reducing the wheel weights to about .38. That's like replacing all 4 of your 22lb stockers with 8lb unobtanium disks. That's for 1st gear only. It doesn't help as much in the higher gears. I think my math and reasoning are okay but if anyone has anything to add/debate, please chime in. I'm always happy to learn, especially when I'm wrong. -Matt --- Sean Hester <seanh_race@hotmail.com> wrote: > Date: Fri, 12 Jan 2001 09:10:29 -0800 > From: "Sean Hester" <seanh_race@hotmail.com> > Subject: Re: [E36M3] Unsprung Weight > i haven't done the math myself (becuase, like i > said, i'm lazy) but i've > seen the 10 to 1 number quotes alot. tire rack's > web site quotes it, in > among other places, an article about why not to put > huge tires on your > underpowered SUV. almost everyone i race cars with > also quotes the 10/1 > figure. i just took their word for it. > > the one time i heard people who WERE trying to do > math, (i don't remember if > it was this forum) and getting different results, > argueing among themselves > it came down to weight distribution. the easy way > to do the equations > assumes the weight is distributed evenly around the > disk to be accelerated. > while in reality 80% or more of the weight in our > case is at, or near, the > outside rim. this makes a HUGE difference in the > equations. (and also > quadruples their size if i remember) > > if you did the math, i'd love to see it. while i'm > too lazy to rip out my > calculus book(s), i'm not too lazy to look at > someone else's answers. ;-P > > >Now the flywheel makes a much bigger difference. > > how come? i would have figured a flywheel to be a > pretty even weight > distribution, that it made LESS difference, not > more. i guess maybe it's > been too long since i did the math. ;-P > __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/
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#3. Re: : [E36M3] Stero Specialist Needed.... - from Matt Henson
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Date: Fri, 12 Jan 2001 19:01:09 -0800 (PST) From: Matt Henson <hensonator@yahoo.com> Subject: Re: : [E36M3] Stero Specialist Needed.... Paul, Hey a question about stuff I do at work every day! The 4V output isn't about distortion or clipping, it's about noise floor. A wire in a car environment will pick up all kinds of electrical interference. Raise the signal level and the ratio of the signal to noise gets better. You shouldn't be running any part of your car system at any appreciable distortion. The best strategy is to: 1) Burn or buy CD with some 0dB test tones. 100, 1k, 10k. 0dB here means all the way up, not down. Play in deck. 2) Turn the amp gain way down and adjust the Head unit volume until it's outputs are the maximum value where you don't exceed it's outputs (4v) or the AMP's input stage. Use your ears or a scope on the output of the amp to see when it gets distorted. Hopefully it won't get distorted when the head unit it turned all the way to it's 0DB (or max) output level. 3) Turn up the AMP gain until you reach either its distortion level or the physical limits of the speakers. This will get loud. The other alternative is to just turn it up until it's loud enough for you (but not clipping) and save your hearing. Good Luck! -Matt Now your system will be --- Paul Elliott <pelliott@rcn.com> wrote: > Date: Fri, 12 Jan 2001 20:23:40 -0500 > From: "Paul Elliott" <pelliott@rcn.com> > Subject: : [E36M3] Stero Specialist Needed.... > > Sean, > > >>meaning you're gonna have to turn up the volume > alot (which is bad > too) you'll get more noise, and you'll be runinng > everything hotter.<< > > I've got a gain setting question for you....I have a > Kenwood Excelon head > unit driving my Excelon amp via 4 volt pre-outs. > I've always read that to > set the levels to best keep distortion at bay, you > should turn your amp > gains all the way down, and turn your head unit > volume up....Then, when your > get a comfortable listening volume, youre supposed > to slowly raise your amp > gains to provide you with the loudest listening > level you might ever use, > without distortion.. > > Now, here's my question. Are you more apt to > receive a clipped signal by > turning the Head Unit volume up high using 4 volt > preouts, or by turning the > amp's gains up high, producing the same ultimate > listening volume. ie, > there's 2 ways to get to the same loud volume: with > a relative higher HU > volume setting with a lower amp gain setting, or > vice versa. Assuming a > given high listening volume, is it best reached with > more HU volume and less > amp gain, more Amp gain and less HU volume, or a > mixture of both somewhere > in the upper middle? Thanks. > > _____________________________ > Paul Elliott > '99 Alpine White M3 <25000 mi Forged M dbl-spokes; > Rotex pads; Dinan Stage > II Supercharger; Stygar Short Shift kit and Clutch > Stop; Skaggs Pedals; > X-brace; Sound by Kenwood Excelon, Polk, JL Audio > > > > ************************************************************* > List Commands > UNSUBSCRIBE - (in subject line) unsubscribes you > from the mailing list. > DIR - sends a listing of files available in the > list's GET directory. > GET filename1.ext,filename2.ext - sends the > requested file(s). > > To issue a command/request to the server: > Send a message with the command you wish executed as > the > subject of the message. > ************************************************************* > > __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/
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#4. Re: [E36M3] Stero Specialist Needed.... - from Thomas E. Tice
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Date: Fri, 12 Jan 2001 22:42:33 -0500 From: "Thomas E. Tice" <tetice@worldnet.att.net> Subject: Re: [E36M3] Stero Specialist Needed.... Ben, Historically, BMW has used a somewhat modular head unit/amplifier stereo system. What I mean here is that they designed a system that can mix and match, add and delete components. On low end models the head unit would drive the speakers directly (with low power output - approx. 3 watts per channel). The next step up would be to use the same low end head unit and insert an external amplifier into the path to increase the power. Most 80s model US BMWs with the premium sound had this configuration (perhaps with a slightly better head unit). To simplify things they simply used the high level (more accurately termed speaker level) outputs from the head unit. BMW head units of that era had no Preamp level outputs at all. The next upgrade would simply add a head unit with more features and/or external amplifiers with more power. In Europe you may have been able to select the head unit with the features you desired independant of the size of the external power amp or even choose not to have an external amp (if you were happy with 3 watts). So while I haven't dug into my M3 audio system, I believe the E36 cars use the same system so the most compatible signal from an aftermarket head unit would be the speaker level outputs. I have installed several aftermarket head units in E28 and E30 cars using the factory amps (it was cheaper to get a head unit and CD changer than buy a BMW changer) and had no problem with a connection of this type. If you use the preamp outputs of the head unit you likely will not get satisfactory levels from the BMW amp. You would also be less likely to damage the head unit driving from the speaker level outputs as these outputs are designed to drive very low impedances (8 or 4 ohms). Most preamp outputs are designed to drive something in the 10K ohm range. For those electrically challenged, low impedances are much harder to drive (requires more current). Most preamp outputs should be current limited (ie protected) but if not, this is the mode more likely to damage the head unit if the amp is not intended to operate this way. I don't think it will cause damage either way as I believe the BMW amps have high input impedance (relative to a speaker) even though they receive a high voltage signal. Note that an additional complication is that most high power head units have differential speaker outputs. I won't attempt to explain that here but you need to be sure to only use the positive speaker output to connect to the amplifier. The negative speaker output should be left floating. So if anyone still reading this is curious why the aftermarket uses the preamp outputs to drive amplifiers, its to avoid distortion. The power amp stage that is designed to drive the tough load (the speaker) usually is the dominate distortion generator in the signal chain (especially the wimply ones in a head unit). In BMWs system, you are adding the distortion of an unnecessary high power amplifier stage. Sorry for the long winded response to your question. I believe the original installation was correct. Tom Tice '98 M3/4 '99 540/6 with Audio system so integrated into the car electronics I wouldn't dare attempt an upgrade. "Ben C. Tickner" wrote: > Date: Fri, 12 Jan 2001 13:08:49 -0800 > From: "Ben C. Tickner" <ben@infofusion.com> > Subject: Stero Specialist Needed.... > > Hello all, > > My alpine head unit stopped sending a good volume signal to the amplifier. I > placed the stock unit back in for now and everything works ok. The audio > store sent my alpine cd unit back for repairs, stating that the amp (in the > head unit) went bad. > > Here is my problem. The install they did originally had the high outputs > from the radio go straight to the amp. Is this correct. I thought that only > lows (RCA connections) should go to the amp. By the way I am using the > factory amp. I am recieving my alpine head unit back this weekend and I am > debating installing it myself, and correctly. What would be the correct > procedure to install an aftermarket head unit on an otherwise stock 95 M3. > > Thanks in advance... > ben > 95 m3 -Cd player > > ************************************************************* > List Commands > UNSUBSCRIBE - (in subject line) unsubscribes you from the mailing list. > DIR - sends a listing of files available in the list's GET directory. > GET filename1.ext,filename2.ext - sends the requested file(s). > > To issue a command/request to the server: > Send a message with the command you wish executed as the > subject of the message. > *************************************************************
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#5. RE: [E36M3] Smoothing/Polishing inside header surfaces - from Seth Thomas
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Date: Sat, 13 Jan 2001 11:02:23 -0500 From: "Seth Thomas" <porsche993@mindspring.com> Subject: RE: [E36M3] Smoothing/Polishing inside header surfaces I found the place that I mentioned would make crossover pipes for our cars. It is www.burnsstainless.com They don't actually make a pipe designed for M3s. What they will do is make one to the specs that you are looking for. These are very nice pipes. The welds are some of the best I have seen and the internals are very smooth. They quoted one of my friends $275 for a crossover pipe on his E36 center section. Maybe what somebody could do is find the measurements for one of Dr. Gas' pipes and have them made. Seth Thomas www.m3ltw.com www.m3power.com -----Original Message----- From: Chris Gant [mailto:cgant@home.com] Sent: Friday, January 12, 2001 7:23 PM To: E36M3 Subject: RE: [E36M3] Smoothing/Polishing inside header surfaces Date: Fri, 12 Jan 2001 18:19:45 -0600 From: "Chris Gant" <cgant@home.com> Subject: RE: [E36M3] Smoothing/Polishing inside header surfaces I noticed that Turner has a complet racing exhaust on their web site with the crossover designed into it. While I'm not too worried *why* this is a good thing, I would like to know what kind of low-end torque gains could be realized with Turner Exhaust and a Super Sprint Header. Chris 95 M3 ************************************************************* List Commands UNSUBSCRIBE - (in subject line) unsubscribes you from the mailing list. DIR - sends a listing of files available in the list's GET directory. GET filename1.ext,filename2.ext - sends the requested file(s). To issue a command/request to the server: Send a message with the command you wish executed as the subject of the message. *************************************************************
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#6. E30 Alternator Replacement - from Jim Powell
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Date: Fri, 12 Jan 2001 22:46:16 -0800 From: Jim Powell <jsp98m3@apexcone.com> Subject: E30 Alternator Replacement Gotta replace the alternator on the '90 E30 325i. Headlights and interior lights flicker. Brush assembly on this one isn't replaceable. Anyone care for a writeup? It's easy to do but if it's helpful..... Jim
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#7. Re: : [E36M3] Stero Specialist Needed.... - from Sean Hester
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Date: Sat, 13 Jan 2001 00:27:13 -0800 From: "Sean Hester" <seanh_race@hotmail.com> Subject: Re: : [E36M3] Stero Specialist Needed.... >Now, here's my question. Are you more apt to receive a clipped signal by >turning the Head Unit volume up high using 4 volt preouts, or by turning >the >amp's gains up high, producing the same ultimate listening volume. ie, >there's 2 ways to get to the same loud volume: with a relative higher HU >volume setting with a lower amp gain setting, or vice versa. Assuming a >given high listening volume, is it best reached with more HU volume and >less >amp gain, more Amp gain and less HU volume, or a mixture of both somewhere >in the upper middle? Thanks. wow. god only knows. (de-je vu intentional) short answer: both in the middle to upper middle range. long answer: see... car audio stuff is so non-standard that you can't answer that. with pro audio stuff (studios, and PAs) it's completly backwards then what you wrote. since the "gains" on PA amps are unity gain (meaning they only "cut" they don't "amplify") you set the gains on the amps all the way up, unless there's a really good reason not to (trying to balance two amps for instance). and "all the way down" for a PA amp is "off" so you can't very well start from there. ;-P ah... but i degress... sorry about mentioning how good it could be, let's talk about how bad car stuff is in comparison. every single one is different. for instance, the alpine amps i had in my M3 were also "no signal" at "all the way down". so i couldn't use your method. but... i know most amps are "low" all the way down. which is an ok place to start. EXCEPT... the alpine head unit i had, had a "bug" where the output stage of the head distorted if you dialed the volume over 28 (out of 35), so again... problems with your method. there is a "right" setting for the gains on an amp. it's the one where the gain knob does nothing. no cutting of signal, no boosting of it. it's usually marked as "normal" on the dial. for alpine it's the middle. for some amps it's the high end, for some it's the low end. for some you have to guess. i try to start everything there. but even that is not 100% for car amps. some amps have no headroom. meaning they distort if you go over 4v, even a little bit. if you have a head unit with a strong output signal (even though they all say 4V, i've seen it rance from 2.5 to 5.5) you're gonna get distortion unless you cut the signal by turning the amp gains down. it's all so headache inducing. sorry for babbling... here's my patented "method"... i set the amp to where i think no gain is. (somewhere in the middle usually) i set the head unit to the middle of it's range. then i play some tunes. i turn the head unit up until i get distortion. if it's speaker distortion you're fine. if it's "amp running out of balls" distortion you're also fine. if it's "preamp stage" distortion you have some work to do. (hopefully you can tell which distortion is which from hearing it. here's some clues if you can't. speaker distortion sounds like the thing is gonna rip apart (which it would if you kept going). with "running out of balls distortion" the music sounds fine until a big bass note kicks in, then it sounds dumb. you can keep turning it up, and it gets louder, but sounds worse and worse as you get louder. pre amp distorion is usually "buzzy" all over, and won't let the sound get very loud at all, if you try to turn it up, it DOESN'T get louder, it just gets buzzyer) if you have preamp distortion, it might be the input stage of the amp doing it, or it might be the head unit doing it. you gotta experiment to figure out which it is, and adjust the gains based on that. (turn the amp gains down. if it gets better it was the amp. or vice versa) once you're done you have two more tests. hopefully you pass these, if you don't you're kinda out of luck. the tests are: 1. play something really soft (between songs, the handy "zero bit" track on a test cd, etc...) but turn the head volume up alot. hopefully you don't have much "hiss". if you do, you can turn the amp gains down some to get rid of the hiss, but you'll be cutting your max volume when you do that. compromise however suits you. 2. turn the head unit all the way up. hopefully you're at max volume now. if not, you can turn the amp gains up to make it louder. but you're gonna increase the hiss (from step 1) and also increase the distortion. again... compromise however suits you. ------------ i hope all that was more help then confusion. ;-) _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com
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#8. Re: Turbos - from Chris Casey
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Date: Sat, 13 Jan 2001 09:49:37 -0800 (PST) From: Chris Casey <ccasey1@yahoo.com> Subject: Re: Turbos Dinan is not CA legal - it's marked (on the web site): "This product is in compliance with U.S. EPA Memorandum 1A, or this product has not been found, nor s believed to be, unlawful for use under the provisions of the Clean Air Act. Currently: This product is legal in California only for racing vehicles which may never be used upon a highway." Does anyone have a Dinan supercharger in CA, and, if so, what do you do at smog check time? -Chris > Date: Fri, 12 Jan 2001 16:59:44 -0800 > From: "Bora Akyol" <akyol@akyol.org> > Subject: Re: [E36M3] RE: Turbos > > FYI, > > RMS is NOT CA smog-legal, Dinan is. For those of us > living in CA, that is a > consideration. S/C comes in handy when the power is > out, I use my car as a > generator ;-) > > Bora > > ----- Original Message ----- > From: "Chad Armstrong" <caarmstrong@epicor.com> > To: "E36M3" <e36m3@bmw-m.net> > Sent: Friday, January 12, 2001 4:12 PM > Subject: [E36M3] RE: Turbos > > > > Date: Fri, 12 Jan 2001 16:02:48 -0800 > > From: Chad Armstrong <caarmstrong@epicor.com> > > Subject: RE: Turbos > > > > Scott Wrote: > > > > "I agree that some of these turbo systems are > relatively expensive, but > show > > me a better option." > > > > Sure Scott its called a Supercharger. Try RMS or > Dinan. > > > > Best Regards, > > Chad > > > > > > -------------------- 4 -------------------- > > Date: Thu, 11 Jan 2001 11:23:57 -0600 > > From: "Scott G Hemauer" <Scott.G.Hemauer@aexp.com> > > Subject: turbos > > > > > > I am thinking of buying one of these > systems......Please build and market > > this > > less expensive, better engineered and "fatter > profit margined" turbo > system. > > If it is in fact all three of these then I'm sure > it would sell very well. > > I > > agree that some of these turbo systems are > relatively expensive, but show > me > > a > > better option. > > > > Scott Hemauer > > > > >>>>>>>>>>>> > > You paid a lot of money or that system so you > figure > > that it's gotta be good. And it is good. But if > it > > had been properly designed the price could be much > > less - even with a fat profit margin. I'm not > gonna > > try to convince you of this because $10k+ out of > your > > pocket can support a lot of denial to convince you > > that you spent it well. So my words are directed > at > > people who are thinking about buying one of their > > systems. > > > > -Matt > > > > > > > > > > > > > ************************************************************* > > List Commands > > UNSUBSCRIBE - (in subject line) unsubscribes you > from the mailing list. > > DIR - sends a listing of files available in the > list's GET directory. > > GET filename1.ext,filename2.ext - sends the > requested file(s). > > > > To issue a command/request to the server: > > Send a message with the command you wish executed > as the > > subject of the message. > > > ************************************************************* > > > > > > > > -------------------- 10 -------------------- > Date: Fri, 12 Jan 2001 20:23:40 -0500 > From: "Paul Elliott" <pelliott@rcn.com> > Subject: : [E36M3] Stero Specialist Needed.... > > Sean, > > >>meaning you're gonna have to turn up the volume > alot (which is bad > too) you'll get more noise, and you'll be runinng > everything hotter.<< > > I've got a gain setting question for you....I have a > Kenwood Excelon head > unit driving my Excelon amp via 4 volt pre-outs. > I've always read that to > set the levels to best keep distortion at bay, you > should turn your amp > gains all the way down, and turn your head unit > volume up....Then, when your > get a comfortable listening volume, youre supposed > to slowly raise your amp > gains to provide you with the loudest listening > level you might ever use, > without distortion.. > > Now, here's my question. Are you more apt to > receive a clipped signal by > turning the Head Unit volume up high using 4 volt > preouts, or by turning the > amp's gains up high, producing the same ultimate > listening volume. ie, > there's 2 ways to get to the same loud volume: with > a relative higher HU > volume setting with a lower amp gain setting, or > vice versa. Assuming a > given high listening volume, is it best reached with > more HU volume and less > amp gain, more Amp gain and less HU volume, or a > mixture of both somewhere > in the upper middle? Thanks. > > _____________________________ > Paul Elliott > '99 Alpine White M3 <25000 mi Forged M dbl-spokes; > Rotex pads; Dinan Stage > II Supercharger; Stygar Short Shift kit and Clutch > Stop; Skaggs Pedals; > X-brace; Sound by Kenwood Excelon, Polk, JL Audio > > > > > ************************************************************** > Digest Commands > UNSUBSCRIBE DIGEST - (in subject line) unsubscribes > you from the digest. > DIR - sends a listing of files available in the > list's GET directory. > GET filename1.ext,filename2.ext - sends the > requested file(s). > > To issue a command/request to the server: > Send a message with the command you wish executed as > the > subject of the message. > ************************************************************** > __________________________________________________ Do You Yahoo!? Get email at your own domain with Yahoo! Mail. http://personal.mail.yahoo.com/
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#9. Negative camber: Possible to have too much? - from Rob
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Date: Sat, 13 Jan 2001 13:04:29 -0700 From: "Rob" <motor@cadvision.com> Subject: Negative camber: Possible to have too much? My car will be going in for some new bushings, upper mounts and an alignment and I'm starting to wonder about alignment settings. Is it possible to have too much neg. camber in terms of contact patch? The way I see it, we all run so much neg. camber because when the car rolls into a turn we want the tire to be as close to 'flat' on the ground as possible. If you are running stock ///M suspension you will need tons of camber to compensate for all the body roll, but if you were to remove the springs and weld the shock (yeah I know....just for example!) then the car wouldn't really roll at all and the -3deg. of static camber you set into the suspension wouldn't allow all the tire on to the ground. Right? So, even with really stiff suspension (coil-overs & big bars) do you still want as much neg. camber as possible or is -3deg. too much? Probably not but I have to ask :-) Rob
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#10. [E36M3] Acceleration of Wheels (was Unsprung Weight) - from LoweSeaton@aol.com
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Date: Sat, 13 Jan 2001 15:23:05 EST From: LoweSeaton@aol.com Subject: [E36M3] Acceleration of Wheels (was Unsprung Weight) Matt writes: [Sorry for the long <snip> I tried to cut it down as much as possible. My comments to follow.] > The kinetic energy of our wheel is going to be equal > to the energy due to translation + the energy due to > rotation. > > K=1/2Mv^2 + 1/2(MR^2)(v/R)^2 > > Where > K=Kinetic Energy > M=Mass of tire/wheel > v=linear Velocity > R=Radius of the wheel/tire > > We can reduce the rotational energy (second half) of > the equation to 1/2Mv^2 since the R's cancel out. > This gives the total kinetic energy as > > K=1/2Mv^2 > > which is twice the energy due to translation. Every > sprung part of the car has a kinetic energy of 1/2Mv^2 > so my assumed wheel/tire requires twice the energy for > a given mass or, conversely, the mass of the wheel > requires a maximum of 2 x the energy as the sprung > weight. Matt - Thanks for the physics lesson. I always enjoy a little calculus in a discussion. <grin> However, I think your second equation has a typo? 1/2 + 1/2 = 1. So the second equation should be: K = Mv^2 Right? This mathematic derivation may help explain a little fact: Here is a trick question for the List. If a car is moving down the highway at 60 mph, how fast is the top and bottom of the tires moving? Answer? Give up? Since the bottom of the tire is in contact with the ground and the ground is not moving, then the bottom of the tire is going zero mph!! Yeah. There are always 4 points on your car that are stationary no matter how fast you go. And the tops of the tires? They are traveling exactly 2X as fast as the car or 120 mph in this example. But my real reason for posting is I think the question is about ACCELERATION of wheels and flywheels. I hate to mention it because now I will be expected to do the math. :) The commonly bantered about figures that reducing wheel weight 1 lb is equal to reducing total weight 4-5 or more lbs is due to the effect of ACCELERATION and the amount of energy it takes to accelerate the wheel. Matt - I don't think your equations above take into account acceleration. You would need a term with rate of change of velocity per unit time. I'd have to do some research to come up with an equation but maybe I can explain it? Mass does not really matter if you are at a steady speed. In fact, heavy wheels would be good if you wanted to maintain that steady speed. This is the "flywheel" effect. A heavy car with big heavy wheels would coast much farther than a light car with light wheels given everything else the same (i.e. rolling resistance, aerodynamic drag, frontal area, etc.) Another example. Ever watch science fiction movies set in out space? In outer space, it takes very little energy to move objects because there is no gravity i.e., no weight. A man could pick up a bulldozer. However, what does not change is mass and acceleration. Once that bulldozer is moving, it would take a lot of energy to rapidly slow it down and stop it. Hence, you see these movies with space stations crashing into each other and Jedi fighter pilots shooting bullets that destroy enemy fighters. A fired bullet in outer space will cause the same kind of impact damage as on earth even though a bullet does not have any weight in outer space. OK, back on earth what does this mean. Basically, it means that the more rapidly you accelerate any object, the more energy it requires. Pretty simple. That is why we are always concerned about keeping our cars as light as possible. Less weight to accelerate. But why are wheels more important? Why do wheels have 4X maybe even 10X the effect? Because wheels and the flywheel are also spinning. They have a rotational or angular acceleration factor too. Matt - I think we need to look at the equation for ACCELERATION energy, not kinetic energy. Do you know what this equation is? I don't think you can give a blanket statement that reducing 1 lb of wheel weight is equal to X amount of vehicle weight because it all depends on how rapid you accelerate. That may be the reason we see figures all over the board. For example, if you accelerate you M3 from 0-60 mph in 6 seconds and then do another run where you accelerate from 0-60 mph in 30 seconds, which run do you think you used the most gas? Obviously the faster run even though they both ended up with the same kinetic energy - i.e., 60 mph. It too more energy to rapidly accelerate the M3. So the end result that you see in your particular case will be different from the next guy. Putting lighter wheels on a slower car will have less effect than a faster car. And probably the initial weight of the wheels is a factor. If you already have light wheels, perhaps reducing the weight will not have as big effect. That is going from 30 lb wheels to 24 lb wheels will be more effective than going from 23 lb wheels to 17 lb wheels? I don't know? I'd have to see the equation to determine if mass has an effect or just acceleration. OK, flywheels. The flywheel has a much larger effect than wheels for the reason above. It accelerate MUCH FASTER than the wheels. The flywheel can go from 2,000 rpm to 7,000 rpm in 2 seconds say in first gear. In second gear it might take 10 seconds to go from 2,000 rpm to 7,000 rpm. Third gear might take 20 seconds to go from 2,000 rpm to 7,000 rpm. I'm just guessing at these numbers. I've not recorded the times for fixed gear acceleration runs on my M3. But bottom line is the engine winds up faster in lower gears and attains much higher rotational speeds than the wheels. Speaking of which, I can tell you how fast the wheels are spinning. If you assume 24.7 in diameter wheels, then at 30, 60, and 90 mph respectively the tires are spinning 408 rpm, 816 rpm, and 1225 rpm. 30, 60, and 90 mph are roughly equal to 7,000 rpm engine speed in 1st, 2nd, and 3rd gear. So during a 0-60 mph acceleration run, the wheels go from 0 to 816 rpm while the engine goes from 2K to 7K back down to 4K and then up to 7K again. The flywheel accelerates much MUCH more rapidly than the wheels so a smaller weight reduction has a larger overall effect. I'm sorry this is long :) I hope this helps explain why reducing rotating weight is effective and why you hear different numbers - it depends on the rate of acceleration. And why flywheels are more critical - they accelerate faster than the wheels. If anybody does want to do the math, try to pick a realistic situation for an E36M3. Say use 22 lb stock wheels and 0-60 mph in 6 seconds. I don't know the diameter of the stock flywheel but I think we all agree it weighs about 20 lbs. Good luck! Lowell Seaton '95 M3 BMW CCA #131505