[uucdigest] Monday, June 23 2003 Volume 03 : Number 6496
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Send 'em to [EMAIL PROTECTED] |__________________________________________________________________ In this BMW UUC Digest: RE: [uuc] Brake upgrades for E34 525 Re: [uuc] Brake upgrades for E34 525 RE: [uuc] <e36><m3> Track Pads [uuc] FS: 1997 328i ---------------------------------------------------------------------- Date: Mon, 23 Jun 2003 09:39:28 -0400 From: "Money, Jack (J.J.)" <[EMAIL PROTECTED]> Subject: RE: [uuc] Brake upgrades for E34 525 - -----Original Message----- From: Michael McCoy [mailto:[EMAIL PROTECTED] Sent: Friday, June 20, 2003 2:50 PM To: [EMAIL PROTECTED] Subject: Re: [uuc] Brake upgrades for E34 525 <<you don't change suspension setup to adjust for braking. suspension setup is to optimize cornering speed. (and sometimes straight line speed in some cars, based on ride height.) and balancing brake bias isn't for better pad wear.>> I know, that's what I was getting at. This is why I can't believe people run the same pads front and rear on a track car....I don't see how they can balance the brakes (well, except if they're using a proportioning valve which stock class cars are not allowed to do). <<so in your situation the brake bias was too rearward. if the calipers were smaller in the rear than what you were using, then perhaps the pads would not have been so problematic? no? or perhaps the pads and forces generated were ok, but the rotor temp was not right in comparaison to the fronts. coefficient of friction changes with temp a little with most pads. they all have their *happy range* and if you go above or below that, their not so happy in one way or another.>> Yes, I'm well aware of that and the problem was using a pad in the rear which was not able to operate in it's appropriate temp range. I was using stock calipers, I did not have too much rear bias, simply the wrong pad. <<also, based on you saying it had a terrible push, that makes me think the rears were doing less than they should have, and when you went to the more agressive fronts, it put the rear pads back in their happy place. cars with too much rear brake bias tend to be *twitchy* and want to swap ends. cars with too much front brake bias push.>> No, this is not correct. Perhaps I should have stated it more clearly. I switched pads and went with the same pad front and rear. I found the cars handling to be terrible in heavy trail braking situations and tap and go/high speed transition maneuvers. I then went to a lighter compound on the rear and kept the fronts the same (I knew they were working properly and well) and this immediately sent my car back to neutral handling. The initial switch to the same pads all around was already an "upgrade" from my previous set up so I did not go to a lighter pad in the front as my email suggested. The problem is that the rear pads were never able to get to their operating temp range. Although I will have to admit that my conclusion that they were not getting up to temp is not based on experimentally measured evidence. Rather it was by my experiences with different pads, track conditions, countless hours of track time in my car, and of course engineering understanding of the situation. To clarify further, the pads, Hawk HT-10's, are very sticky when they're not up to normal op temp. I have felt this in the front as well. The initial bite is VERY sticky, very nonlinear. This is what happened in the rear and that is why it was so push prone and tail happy. I wouldn't say there was too much bias, since that is not adjustable, other than via pad compound, but rather the pad was the incorrect choice for the application. <<currently BMW seems to like the 70% front bias for my car. this is indeed the "safe" approach as the car will lock the fronts first in a panic and thus go straight. same reason that FWD's are marketed as safer cars... people don't like it when cars swap ends. even if it is driver error. apparently people think that hitting things head on is better or something... I dunno. (how many skid marks do you see go straight into concrete walls along interstate on ramps and off ramps? lots.)>> Yup. <<less front bias means more rear brake usage, which in turns means more total braking force. think of it this way, if the fronts were on the edge of lockup, thus contributing maximum braking force, and the rears were at 50% utilization in terms of grip... you're quite far from the car's max potential braking force. if instead when the fronts were in that situation again, the rears were closer to 90% utilization of grip, then the car is stopping much faster. that to me is safer. to repeat, if given the choice between stoping quickly, or not stoping quite as quickly but guaranteed to be still pointed perfectly straight, I'll take stopping quickly...>> As I'm sure you understand, just because you can use rear brakes more does not meant they will be more effective....weight transfer is the key here. If your dynamic weight is 70% front and 30% rear under heavy braking then more braking in the rear will not necessarily help the situation. Now due to all the suspension changes, addition of roll cage (chassis stiffness), weight reduction, tire change, brake pad bias, and other environmental factors, my car does not utilize the braking force available near the same as a stock street car. And of course I'm only interested in optimizing it for track use. <<I did the math based around G forces of braking, as it made things easier. (weight transfer becomes extremely easy to calculate.) the big wild card in the brake calculations was maximum adhesion between the tire and the road. Gotta try to find that piece of paper now... I think I assumed *max* would be somewhere between 1.1G and 1.2G, and then *normal* braking to be closer to 0.6G. (0.7G also happens to be the decelerative contribution of sliding tires. so even a locked tire could generate this.) then kinda averaged the data. (biased the data torwards the upper end of the specturm though, but I did look at lower numbers for consideration to make sure it wouldn't be too tail happy. tail happy is what the long thin pedal on the right is for.)>> Pick up any modern vehicle dynamics book, they will at least have a place to start as far as tire adhesion limits. As I said, it's been years since I've done the math but I do recall doing braking force diagrams. And you will still need suspension characteristics to properly calculate weight transfer. <<anything less than 0.6G, and balance isn't too important as none of the tires will be near the limit of adhesion. (yes even in the wet.) wet stopping distances on modern street tires are disturbingly close to their dry stopping distances. the 60-0 stopping distance of my 525 according to the literature is around 130 feet. which equates to ~0.9G. for reference 0.6G would be stopping around 200 feet from 60 mph.>> I'm not interested in deceleration rates of that low magnitude. ; ) <<for center of gravity, something around 20 inches seemed like a reasonable number for a street car. (H&R springs with bilstein sport shocks, so the car is ~0.75 inches lower than stock. supposedly.) 108 inch wheelbase. so +- a couple inches in CG won't make the weight transfer numbers that horribly different. couple percent here or there is probably less than the difference the tire temps or pressures as well as brake temps would make.... or say the 0 to 4 extra people in the car with stuff in the trunk... :o)>> If you're that interested in being accurate with your calculations and set up, I'd be corner weighing that car to get exact numbers. To go through all the trouble to do the calcluations and pick exactly the set up you want, this is a very important piece of information which factory numbers will not give you....unless you already have a catalog of different weights based on options, etc. Jack Money '89 325iX #86 JP M3 Elephant Motorsports ------------------------------ Date: Mon, 23 Jun 2003 09:55:29 -0400 From: "Gary Derian" <[EMAIL PROTECTED]> Subject: Re: [uuc] Brake upgrades for E34 525 The way I see it, only wheelbase and CG height affects steady state weight transfer under braking. How quickly the weight transfers under dynamic conditions is affected by anti-dive and damping. A large amount of anti-dive transfers weight immediately with brake force. Less anti dive causes the weight to transfer more slowly, as the car pitches forward. Gary Derian > Pick up any modern vehicle dynamics book, they will at least have a place to > start as far as tire adhesion limits. As I said, it's been years since I've > done the math but I do recall doing braking force diagrams. And you will > still need suspension characteristics to properly calculate weight transfer. > ------------------------------ Date: Mon, 23 Jun 2003 09:53:57 -0400 From: "Money, Jack (J.J.)" <[EMAIL PROTECTED]> Subject: RE: [uuc] <e36><m3> Track Pads Donn, I find it surprising that you want to move DOWN in pad compounds but I suppose I don't know your situation so I can't say for sure. But, to answer your question, if you think the Blues are too much pad I would highly recommend trying the Porterfield R4. It's a great intermediate to advanced level pad. However, depending on application, I would not race on it, I just don't think it's strong enough personally. And frankly, a T2/IS M3 is a heavy car as far as race cars go. The HT-10's that many have recommended are the cat's ass I think (haven't tried the HT14 or HT15, I think my car is too light for them and I don't have much downforce to speak of) but they're a step above the Blues, both in torque and temp range. If you feel the Blues are too much pad now you certainly don't want the HT10's or higher, you'll wear them out faster and they'll kill your rotors. My suggestion is to reevaluate your braking technique. Are other racers in your class consistently outbraking you? What are others running for pads? I would check with your competition, assuming they're friendly on info sharing, and figure out where you're at compared to them. Are you running a biased pad set up...meaning a lighter compound in the rear vs. the front? What happens when you go into a corner too hot...do you push or does the rear end want to come around? What about high speed transition corners where you require just a tap of the brakes....does it cause the car to be very unsettled? Perhaps brake pad bias can help you. How about some more info about your tracks, your car set up, etc. Good discussion, I'd love to continue it! Jack Money '89 325iX #86 JP M3 ----> brakes just fine for a stock class car Elephant Motorsports - -----Original Message----- From: Donn Vickrey [mailto:[EMAIL PROTECTED] Sent: Sunday, June 22, 2003 12:40 AM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: [uuc] <e36><m3> Track Pads Acck. I always forget at least one question. I'd also like to get some opinions on track pads. I'm currently running Hawk Blues. I've run them for years on other racecars but am not completely crazy about them as they are pretty hard on rotors. Unfortunately, they were the only thing that worked consistently on Spec RX7s. What other pads have M3 racers had good luck with. The tracks around here are pretty easy on brakes. So, I probably can go with a slightly milder compound than the Blues. Thanks in advance. Donn Vickrey Scottsdale, AZ 98 IS/T2 M3 race car 02 996TT daily driver 03 Navigator tow vehicle and tot hauler ------------------------------ Date: Mon, 23 Jun 2003 09:09:14 -0500 From: "Randy Reeves" <[EMAIL PROTECTED]> Subject: [uuc] FS: 1997 328i 1997 328i Bright Red/Sand Interior 88,000 miles VIN WBACD3323VAV20806 5 Speed w/PS, PB, PW, PL, A/C, Cruise Control, Sunroof, SRS, Full Function On Board Computer Excellent condition, interior and exterior as defined at Edmunds.com and KBB.com UUC short shifter w/ERK and Delrin bushings Dinan Stage II Suspension Dinan Front and Rear Strut and Shock Tower braces. BMW Motorsport Crossbrace BMW Accessory GPS Navigation BMW factory alarm w/ keyless entry. Homelink Garage Door Control Autodimming rear view mirror. Xenon Headlights Nokia Hands Free Car Phone Kit w/ Nokia phone included-integrated with BMW car radio 100w Kenwood powered Subwoofer Rockford Fosgate 300w Amp BMW 6 Disc CD Changer Alpine 14 Band Graphic Equalizer w/ Sound Field Processor 17" BMW Style 32 wheels VDO Oil Temp, Oil Pressure, and Voltmeter Gauge Package All records and operating manuals. Engine Oil changed every 3K w/ Mobil 1 Synthetic Oil Transmission and rear differential serviced w/ Redline products every 25K miles Pictures are available on request. $15,000 Car is located north of Dallas Texas I can be reached at 214-674-0019 or [EMAIL PROTECTED] Include BMW in subject line to avoid spam filters. _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail ------------------------------ End of [uucdigest] V3 #6496 *************************** | | In memory of Michel Potheau - friend, enthusiast, founder of the BMW CCA. |________________________________________ | Please visit these UUC-approved BMW parts vendors/service providers: | (listed alphabetically) | | Autoscope-Motorsports - http://www.autoscope-motorsports.com | |==================================================== | | Koala MotorSport . 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