Guest Anonymous Posted April 16, 2001 Share Posted April 16, 2001 I have recently bought and read a good book on braking systems, and also have scoured the web sites of Wilwood and Outlaw brakes. I have a question which hasn't been answered by any of these sources yet, and thought I would post here before contacting Wilwood directly. I'm planning to customize a complete racing brake system for my Z with 12.19" rotors on front and rear (17" wheels), but am wondering how folks decide what rotor width (vented) to use on the front vs. the rear. It seems natural to me to size the rear rotors a bit thinner because more of the braking will be proportioned to the front anyways, but there are still several widths to choose from. Has anyone been through this process who can offer up a rule of thumb? My take on this is that there are many ways you can get the results you want with brakes, depending on the rotor, caliper, master cylinder, and proportioning you choose (kind of a balancing act with trade-offs that overlap). I'm wondering if I am right here that the exact thickness of the rear rotors won't matter that much for my car since it won't be pounded to the absolute extremes of road racing. Anyone have experience with Outlaw calipers vs. Wilwood? From what I have read they both seem to be high quality products. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 17, 2001 Share Posted April 17, 2001 My understanding of brake systems has led me to believe that the rotor thickness has nothing to do with the actual pressure applied to the surface of the rotors. It is directly related to the cooling charactoristics of the rotor though. My opinion in the matter is that you would want equal heat build-up and dissapation between the front and the rears for them to remain ballanced for any given condition. In this sense, the rear rotor may need to be thinner, or of a different design, provided both front and rear rotors are the same diameter. But IMHO, for spirited street/slalom racing, stick with piston size, and rotor diameter differences between the two. Quote Link to comment Share on other sites More sharing options...
Guest scca Posted April 17, 2001 Share Posted April 17, 2001 i'm Back!... just got a new racecar anyway.. i usually use the 1.25" on the fronts and .81 rears, the 1.25 just plain LOOK better ask Mikelly, Blkmgk, and a few others what they look like.. some pics on the web too. ------------------ Mike mike@fonebooth.com http://www.outlaw-brakes raceparts and brake upgrades. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 19, 2001 Share Posted April 19, 2001 Hrm, my one comment - why size front and rear the same? The front does WAY more braking - is this a looks thing? I'm going to run a solid rotor in the rear and a BIG rotor up front. The rear rotor is 11inches or so from a 300Z I believe. Rotors are NOT custom so that replacing them later isn't a big chore. A prop valve will be plumbed if needed to get balance "right". Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 19, 2001 Share Posted April 19, 2001 BLKMGK- "Custom" in the sense that I will be engineering the brake system by picking from a wide variety of readily available race components (rotors, hats, calipers, etc.). "Custom" in the sense that I won't be trying to adapt an OEM component from another car. Not custom in the sense that when it comes time to replace a rotor (gosh, if I drive the car that much!) I will have to cast and machine a new one! I agree that for most street cars, I'm not sure why front and rear rotors would be sized the same diameter, except for design philosophy. i.e., if you start with four common rotors, it might be easier to tune front to rear bias, all else equal. However, if you are trying to equalize heat build-up, as indicated by blueovalz, then diameter and width sizing becomes more important. I am not by any means intimately familiar with full race braking systems, but from what I have read, it makes more sense to me to use equally sized rotors only on full race cars (Indy, Nascar, etc.) which are very low to the ground (low CG), and very little forward weight transfer occurs during braking. I suppose your braking requirements in general for this type of car would be -more- equal on all four corners. So far I am leaning towards getting the largest rotors I can fit on the front, and am looking for a good rule of thumb, or a more educated calculation for sizing the rear relative to the front. I do want to be careful and consider rotating weight and inertia, however. Extra mass not effectively used for braking will only slow acceleration. O.k., here is the killer question: Has anyone determined the CG height of their V8Z (much more difficult than f/r balance) ? Steve Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted April 19, 2001 Share Posted April 19, 2001 what book did you read? Puhn's? he goes through rotor sizing in quite a simple/quick manner to check out what mass of rotor you feel is needed I don't have my calc's handy as a mech/engg student was using them for a project but I may have them back by next week so I can't recall what I assumed for centre of gravity but offhand depending on your motor height etc I'd guess it's a little lower than midheight of your engine/trans centre of mass given wheel/brakes/suspension/frame etc is all lower than this point and little weight above....make an assumption/walk thru calc's...change assumption and see how sensitive your results are to it to determine how accurate you should be with that number.... equal sized rotors for initial starting point is not warranted IMHO, braking bias on any of our rides would be to the front no matter how stiff our setup is so no point running that mass out back....you tune your bias with a prop valve and pad choices/not rotor choice, looking at OE systems on hipo cars gives a v. good starting point for decent balance IMO, handy since they're typically 3100-3500 lbs and slower than us that when we equate our faster cars to their systems they're pretty close to right on the money/C5 setups and others etc...lot of engineering into those/see how your numbers come out...... PS I decide on rotor width/diam depending on whats easily available for me to purchase in a pinch if I need a spare assuming the offerings meet my quality and minimum size requirements/bolt pattern/cost and ballpark offset.... ------------------ Of all the things I've lost, I miss my mind the most. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 19, 2001 Share Posted April 19, 2001 Boy, I hate to say this, but I do have the exact same size rotors on the front as on the back. NOW, with that said, the set-up worked well when I had 2" wider tires in the back than the front ones, and with the proportioning valve biased all the way. BUT, now that I have the same size tires all the way around, and with a slightly smaller piston caliper in back, and with the proportioning valve at full bias, it barely is balanced. My next big expense is the front (stage 3???) rotors SCCA has. Then I think I will be fully satisfied with the set-up. Front rotors really do need to be larger, or rear caliper piston a good bit smaller. Terry Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 20, 2001 Share Posted April 20, 2001 Terry, I've got that setup now and am owrking to bolt it all together - need bearings. Those front rotors are MASSIVE! Calipers are darned light tho' Lil2qwk - head to fonebooth.com and skip down to the Auto related stuff at the bottom. MikeSCCA has pics on his site of his offerings - I cannot imagine needing bigger up front than his setup. The rear on mine will be a Hybrid of 300Z and Outlaw with Wilwood spots for an E-Brake. Do not forget the E-brake as most "racing rotors" don't have them (or dust seals for that matter). I'll be running Coleman rotors up front with wipers and an aluminum hat that's been custom made. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 23, 2001 Share Posted April 23, 2001 Ross C- Thanks for the tip, I will check out other books on brake systems for sizing guidelines, and post the results. The one I got was published by HP Books within the past year or two or three, and while good, did not give numerical rotor sizing guidelines. As for calculations, I've got all the engineering texts as well. But as you may know if you have been out of school for a while, we could calculate all day and not come close to the guys who race the cars every day; experiment by trial and error. The calcs are only as accurate as the data and assumptions that go into them. This is why I need to know CG height as a bare min. starting point. Of course what makes this so tough is that I won't know my CG height and forces/masses involved until the car is built and I've tested it. A bit of an iterative process to perfect. I agree the rear rotors should be sized smaller, but to what degree. Perhaps a ratio of braking energy anticipated on front vs. rear to rotor mass - but something has to also be said for surface area (heat rejection capability). Perhaps some total measure of rotor heat absorbtion/rejection. On fonebooth.com, I have checked out this web site, but am concerned about hub mounting distance. i.e. I want to design my brake system for use with the same wheels front and rear, and definitely definitely without the use of spacers. It would be great if the owner of this web site could post some as-installed dimensions from the wheel mating surface of the hub to say the inner fenderwell, or even the stock fender lip for a reference. Also, I am a bit concerned about the rotor pricing at $120 each. Check out www.rebcoracing.com/outlawprod.html. They seem to offer a very similar if not identical rotor for $46.95 I'll give fonebooth.com the benefit of the doubt, but would not buy the product until an explanation of the difference was given. i.e. all else being equal, $120 vs. $46.95 is a no brainer. Steve Quote Link to comment Share on other sites More sharing options...
Guest scca Posted April 24, 2001 Share Posted April 24, 2001 the rotors that are $47 are a winters rotor and they are let me say not the best... they will crack within 3 months- those are for dirt track cars and not meant to withstand the heat in a street/pavement car.. they may work ok- i have some here but i wont suggest to use them.. if you want 5 lug you must use some sort of spacer- ifyou want to stay 4 lug the offsets dont change... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 24, 2001 Share Posted April 24, 2001 SCCA- Do the rotors at fonebooth conform to a specific SAE grade for gray iron automotive castings (ref. SAE J431) ? If so, which grade? Can you provide any alloying / chemical comp. details? Are the rotors heat treated and/or annealed? Heat checking is usually due to material issues and of course can be compounded by not following proper application guidelines with regards to sizing. I have some limited experience with this in heavy equipment. I am not sure of the details on the $47 rotors, but I would be interested to find out, and will look into this. Any quality manufacturer which conforms to the latest industry quality standards / ISO certification should be able to provide some level of detail on the material so that a fair comparison can be made between competitive products. The $47 rotors might be absolutely fine for a performance street car, but might not hold up under a 24 hour road race. Certainly the material and manufacturing details would help shed some light. With the SAE standard referenced above, one can make an educated guess on what is being used by GM / Ford. Or, could call Bendix or other aftermarket manufacturers. As to the 4/5 lug conversion, I'm planning on 5 lug, but am counting on machining my own hubs from 4140 or treating a lower grade, to keep away from spacers. The boundries here are the limits of my imagination (and pain/wallet threshold? ) Steve Quote Link to comment Share on other sites More sharing options...
Guest scca Posted April 25, 2001 Share Posted April 25, 2001 YGWYPF... you get what you pay for... first of all--last i checked the $47 rotors were NLA. i have 1 here but no match for it. they had too many problems with cracking and dropped the supplier- ( i havent looked into them for over 6 months tho) Man! your asking a lot of questions..your expecting WAY too much from a $47 rotor. a stock rear 280 zx rotor costs $40 so what kind of quality can you expect in a 12"x1.25" for the same money?? you dont need that kind of detail just looking at the cheapo dirt rotor and comparing to the heavier one its easy to see the difference. i used the liteweight ones on a GT2 Mazda and they cracked in 20 minutes.so this isnt a 24 road race issue.. are you talking making front hubs or rears? rears have room to drill- i dont believe the fronts have this room. if you want to avoid spacers just get 3 pce wheels...or make rear stub axles. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 25, 2001 Share Posted April 25, 2001 O.k., I'm going to have to plead ignorance on your acronyms YGWYPF and NLA, but I think I get the context clues. But as for asking too many questions and demanding too much for $47 let me just say this. Back when I was researching a 12" brake upgrade for the front of my Buick Regal, Camaro 1LE 12" rotors were $49 each, and they include special machining for bearing races to be pressed in. All we are talking about here is a plane jane rotor made to bolt to a separate hat. There is no center section to speak of, and hardly as much machining as OEM rotors. Certainly not as much as the $37 rotors I just bought for my Neon. If I can expect the material of the $47 race rotors to be equal to that of the Neon rotors, then I think they would work fine for my application (high performance street, occassional autocross). I don't usually buy into the hear-say thing unless I know and trust the source well (no offense to you). It's your right to know what you are getting for your money. And it is easy to tell what bare minimum you SHOULD be getting by reviewing the appropriate SAE standard. Incidentally, there are also SAE standards on brake tests which many OEMs use as a benchmark. For a $120 rotor, I would expect special alloying and annealing over a typical OEM piece, or at least much tighter control and tolerances on material quality and machining. If the vender can't confirm this to some level of detail, he doesn't get my business. There are simply too many "high performance" venders out there who do nothing more than price gouge. On the hubs, I was considering machining new front hubs for use with the race rotors/hats, and to keep the wheel offset the same as on the back. If I can just re-drill the rear hubs, adapt race brakes, and keep a common wheel offset that would be great! I keep hearing about these three piece wheels, but have never seen one. Thanks for the tip! Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 25, 2001 Share Posted April 25, 2001 I'd suggest that you look at the Brembo rotors in thesize Mike sells in order to get an idea as to pricing. Yup, Mike might be a bit higher but realize that you're also paying for the fact that he's already puzzled all this stuff out. As for the backspacing - by virtue of the fact that you'll wind up with 300Z hubs up front your backspacing WILL change - I'm not sure you'll be able to compensate with a machined adapter for the rotor as I believe the hub moves the rotor in a direction that cannot be compensated for with the rotor's hub. You'll also complicate the issue of mounting the caliper to the spindle when you do this IF you can move the rotor to were you want it. I've got Mike's setup for my car now - it's VERY beefy. I'm still waiting for the pads and hoses - no biggie. He's also working out a setup for the rear of my car using an OEM rotor with Outlaw calipers and Wilwood stuff, as I believe I stated above I don't think the rear rotors are as critical a piece. Can you duplicate Mike's stuff and possibly pay less? Sure that might be possible but what's your time worth? If you're really interested in a cheaper rotor maybe check into some of the roundy round boards and see what their experiences have been. For $120 I honestly don't expect I'll be replacing this rotor for many years to come ! Oh, and I wouldn't suggest redrilling the front hub. I'm not sure there's enough material but I DO know that the front hub appeared to be MUCH softer when I drilled it for larger studs. The material on the rear hubs is some serious stuff - tough as nails. Front hubs felt more like soft cast iron. Drilled like butter! Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted April 25, 2001 Share Posted April 25, 2001 Well, you give lots to chew on Steve and don't take offense by any of this but my typing time is limited so I'll try to convey my points quickly. "But as you may know if you have been out of school for a while, we could calculate all day and not come close to the guys who race the cars every day; experiment by trial and error. The calcs are only as accurate as the data and assumptions that go into them." Being qualified to practise eng. one must understand on what assumptions and basis any formulae you aply are derived from. The book isn't made applicable by using original heat transfer/absorption equations derived decades ago. Puhn's book included braking surface and some other data for MANY existing cars and their weights for some comparison including racing setups. I felt my post briefly incorporated both his calc's and observations of real world scenarios as any eng. approach should. " Of course what makes this so tough is that I won't know my CG height and forces/masses involved until the car is built and I've tested it." What? Your only roadbloack at present IMO is not having some calculations to chew on. Do you feel your cars final weight is going to vary a few hundred pounds? Obervational eng. method will see you at a solution easily and fairly quickly. Assume your best and worst and see where this sits..and revise if variance is great as more info becomes available/if variance is negligible/ie. all fits one design then progress as is.. CG can be easily guesstimated and sensitivity checked as can be your weights from info of other builds and looking at your own planned mods. " but something has to also be said for surface area (heat rejection capability). Perhaps some total measure of rotor heat absorbtion/rejection." something yes but not as a factor in your ONE max braking scenario as the time frame involved is negligible as are other factors to assume any cooling, the cooling is an integral part of your overall rotor temp...keep your overall track ave. temp low enough and during this MAX braking zone you won't exceed your design maximum temp This is where some more recent brembo designs have moved away from 'vented/vaned' rotors into ones with only small 'spikes'/like stalactites/stalagmites/pillars with narrow centres which vent far better with greater surface area of actual rotor exposed, less airflow impedance and some improved metallurgy. " i.e. I want to design my brake system for use with the same wheels front and rear, and definitely definitely without the use of spacers. It would be great if the owner of this web site could post some as-installed dimensions from the wheel mating surface of the hub to say the inner fenderwell, or even the stock fender lip for a reference." As Mike mentioned/rotors_hats non slipon as seen on his site don't alter your hub geometry/wheel relation. I think most are running same wheels all 4 corners and those with altered f/r combos aren't limited due to brake choices. I'd like to hear your reasons for 'no' spacers just for curiousity as you never know when you may raise new issues to broaden discussion. Kudo's to you on making your own alum. hubs, I only know of one other (a local) who's done this and it is impressive Is this for the challenge or your overall weight intentions? My front much enlargened brake/wheel combo (13s/16x8's)weighs in at stock setup's weight (or less) so I'm sure alum. hubs could only improve that more! I was v. glad to be able to do the upgrades without increasing the weight from OE (that's my knock on the 4x4 calipers HEAVY)Ahh, a ways down my priority list I'm afraid. "Also, I am a bit concerned about the rotor pricing at $120 each." rotors you compared to were far smaller and of lesser quality AFAIK, as well those camaro cheapies you mentioned are produced in HUGE quantities so cost isn't so surprising. Decent (ie. for street/track to last a year or two) rotors do not run much less than $120US for anything 12"+. Some cheaper aftermarket OE's will be cheaper but YGWYPF. Myself and others have cracked rotors in a day as Mike has in minutes and those lessons have been learned [ April 25, 2001: Message edited by: Ross C ] Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted April 25, 2001 Share Posted April 25, 2001 A few points are no longer worth beating up on the calcs. I do need to get this Puhn's book though, as it seems he provides more information than in the book I've got. For my comments on spacers, see the other post "billet spacers". If it ends up that I can't get the rotor where I need it with a custom machined front hub, then I'll end up using the 300Z hubs as well, and suffer with different front/rear wheel offsets vs. going with wheel spacers. On the rotor cracks, lets be fair and compare apples to apples, not apples to oranges. Who has cracked a $47 12" front rotor on a Z car? Under what circumstances, what pad material, etc. etc. This is why I ask for material details. All the rest is hearsay (sp?). As for production quantities, I agree costs go down with volume, but to a point. $120 vs. $50 is still a big margin. Lets find the difference between the $120 rotor material and OEM, and the $47 rotor material and OEM. It's easy to look at price and think you are getting better quality. That's not always true. Steve Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted April 25, 2001 Share Posted April 25, 2001 quote: Originally posted by lil2qwk: On the rotor cracks, lets be fair and compare apples to apples, not apples to oranges. Who has cracked a $47 12" front rotor on a Z car? Under what circumstances, what pad material, etc. etc. This is why I ask for material details. All the rest is hearsay (sp?). It's easy to look at price and think you are getting better quality. That's not always true. Steve I never buck up more unless I truly am convinced I'm getting more. Friends have cracked cheap and not so cheap 12 & 13" rotors on new cobras and camaros at lesser use than I (yes/they're heavier but I was going faster in an hour and less of track use. Both NAPA stuff and Ford OE stuff. Ford made some changes and switched to brembo in latter 90's and this seemed to correct it as a common cobra upgrade is the rotors for track and race use. they'd warp in a day on the street. For cheap OEM Z rotors I haven't had troubles with cracking but warpage was fairly soon. The OE camaro/ford stuff is only $50-60 per rotor in 13" sizes in aftermarket 'cheap' stuff but true dealer/brembo stuff doubles in cost and the wear seems to reflect the metallurgy improvements. When a few dozen cobras and the 4th gen fbody buds replace stuff hand over fist till they get good stuff I like benefitting from this and paying a little extra for piece of mind that my $ invested in a track day is well spent and I don't have any maintenance/serviceability related concers. I never even thought of playing with the cheap large rotors for my brake conversion after enough hijinks experienced from others with similar size/mass/brands. Rotor wear and warpage frequency are my main concerns and led me to the higher $ rotors. Hopefully someone can comment more on your q's for 12" rotors and smaller. On the spacer issue/I thought most use spacers to optimize wheel placement outboard or to clear larger wheels with both 4 lug and 5 lug patterns, not for rotor positioning. That's typically handled I believe by caliper spacing or the hat offset. Their are many wheels that can greatly improve rotor cooling as well as you'd know that are great lighten the unsprung weight/or balance larger tires Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted April 26, 2001 Share Posted April 26, 2001 Just a point - putting on the 300Z 5lug hubs changes the offset up front I believe. Since this isn't a slip on rotor changes you make to the rotors aluminum hub won't change the wheel mounting surface. IF you stick with 4lug stuff then this isn't an issue however I believe you'll find wheel selection limited. Go price out the BREMBO 12X1.25 rotors. Or maybe the Coleman stuff - that's apples to apples I believe. Another possibility for those who are warping and cracking rotors - look into cryro treatments. Some of the stories I've been hearing about improved life are incredible! Unfortunatly this adds to the cost. Toyota 4X4 calipers are indeed HEAVY. A pair of Outlaw calipers weigh less than a single Toyota caliper I'd wager. However the 12X1.25 rotor is seriously beefy - overall I'm not sure you really save any weight there. Hrm, oh yeah - MikeSCCA races much of what he sells.... Quote Link to comment Share on other sites More sharing options...
Guest scca Posted April 26, 2001 Share Posted April 26, 2001 OMG!!!!!!!!! thats Oh my god.. for those acronym challenged.. per Ross's post.. YGWYPF was "you get what you pay for" if you missed it.. NLA is (i thought very common) NO LOnger Available.. i am used to old mustangs/camaros and lots of parts are NLA , try to buy some new nissan stuff and thats what you get/ this is where NOS comes in NEW OLD STOCK. this is new parts someone is holding on to for resale... a few points.. been in the garage working on the race car soon time for sleep.. 1) the $47 rotors i will sell those to ANYONE who wants them, (as i am a rebco/outlaw dealer) if they work for you great- but dont complain to me at all if they do not suit the intended purpose or if you replace them within 2 years. 2)the rotors i sell ARE Coleman racing, price out their stuff - no $47 rotor there.. 3)while making front hubs is very nice, i have seen 2 Z's with billet alum hubs, (both race cars) the cost would seem HUGE.. yes if you make front hubs in the SAME offset as the 4 lug i have everything to BOLT on the big front conversion..you could easily sell the hubs - but what you are missing is more important. 4) you WONT find wheels to fit your new front hub! at least not cheaply . all the 5 lug stuff is now the newer FWD offset so making a custom hub is a WASTE of time IMO... (in my opinion). what you need to make is a rear hub adapter in order to equalize the offset when you change the car to 5 lug. you NEED that offset, not changing the offset is pointless. why go 5 lug then? to use OLD mustang wheels? not a lot of selection in 5 on 4.5" with the kind of backspace you will need...all new cars mustang/nsx/rx7/supra/300 will be the newer offsets making a hub to match the old z 4 lug offset will cause you to need $$ rims. i might have gone overboardhere but i hope i made my points clear... Mike Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 2, 2001 Share Posted May 2, 2001 scca- Thanks for your response. If I understand you correctly, you are saying that a 4.5" BC wheel is not commonly available for older American RWD car offsets (which if I understand is what suits the Z in stock form). I was not aware of this, but have not checked out rim/wheel availability yet. If it's easier to make a rear hub adaptor and stick with an "off-the-300ZX" front hub, then I'm just as happy! I am not partial towards machining new front hubs, just towards having wheels with the same offset front to rear, and staying away from wheel spacers. On the rotors, I also appreciate your feedback. When I do finally get around to researching rotor material/ processing with the individual manufacturers, I'll post my results to this group. I may end up buying the Coleman stuff as well and/or buying more of your kit parts than I originally thought! As you can probably tell, I am more of a researcher (stubborn?) than many who choose to just blindly do what others are doing. As for YGWYPF, I agree that quality costs money, but you can easily NOT GWYPF as well. Been there done that! Steve Quote Link to comment Share on other sites More sharing options...
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