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  1. #1
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    Fixed vs. floating calipers (from old board)

    Serious race cars use fixed calipers exclusively whenever allowed by the rules.

    Manufacturers like floating calipers because they are much cheaper to manufacture, and their lack of positive location is actually a plus in a production application. The ability to float makes these calipers very forgiving of caliper misalignment and/or rotor run out. The downside is crummy pedal feel, as everything moves around and you have to take up the slack. This does not lead to linear brake application, and makes it much harder to keep the brakes on the edge of lockup - which is why you need ABS with floating calipers.

    The only functional disadvantage to fixed calipers, be they 2, 4, or 6 piston is that they are very intolerant of caliper misalignment and/or rotor run out. This means that in many cases you will have to shim the caliper and shim and/or true the rotor. What you will get is rock solid pedal with almost no travel. This allows you to "squeeze" the pedal and modulate the brake pressure in a very linear fashion. If you can't effect maximum, edge of traction braking with a properly set up fixed caliper brake system with no ABS, you probably should be playing golf instead.

    In subsequent posts I will address caliper dust boots (good if you don't like leaking calipers), fixed caliper weight/size/rigidity (sometimes cast iron is a good choice), thermal capacity (must be matched to usage), and how to put JL-8 brakes on a 68-69 Camaro (as detailed in "Untold Secrets..." (the real "cheap big brakes").

    keithq
    Registered User
    Posts: 321
    (4/16/02 7:46 am)
    Reply Re: Fixed vs. floating calipers
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    Can't wait to see the next post.

    I am in the process of doing a 60 Camaro right now.
    I made my own front suspension using early C4 suspension.
    I am not sure if I should run the Baer track kit or a Wilwood 4 piston set up. I can get the Wilwood calipers pretty cheap and I already have a good set of 13" C4 rotors.

    Any opinions?

    Keith Quinn.


    dsmerritt
    Registered User
    Posts: 2
    (4/17/02 12:46 am)
    Reply Re: Fixed vs. floating calipers
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    Didn't now about the 60 Camaro - obviously a rare and very early prototype. My Camaro is a 69 convertible, and I've been working on Camaros since the 67's came out in fall 66.

    I'm very impressed that you installed a variant of the C4 front suspension on your car on your own. The C4 front geometry is certainly far superior to the original 67-69 stuff, and probably to the best I can do by modifying the original 67-69 front end. However, I don't have the time or budget to do the C4 thing, and there are a few wrinkles against the C4 and for the modified early front end.

    Disadvantages of the C4 front suspension:



    1) Stock, it uses floating calipers. The Baer "Track" kit still uses floating calipers, so it will never have the pedal feel of a properly set up fixed caliper installation, making it much, much harder to hold the brakes on the threshold of lockup. The fixed calipers that you can get to bolt on to the C4 knuckle/upright are either very good and very expensive, such as Baer/Alcon and Porsche, or very good and not suitable for real street use, such as Wilwood.

    I do have hands on experience with the Baer Pro Alcon fixed caliper setup. One of my friends has a 94 Camaro on which we installed the Baer "Pro " front brake package, which consists of 4 piston Alcon calipers and 13.5 x 1.25" rotors on an aluminum hat. After psyching ourselves up to attack the 94 Camaro upright with a sawzall, the rest of the installation was truly a bolt on - big points to Baer for this. We did have to carefully align the calipers, since they are, after all fixed, but the results are everything you could want - rock solid pedal with no travel and completely linear modulation. Unfortunately, they cost $2,500 (for the front only) when he bought them, and are lots more now. He also needed more rotor mass than the stock 11" rotor, which would only make 2 1/4 laps at Texas World Speedway before going away. I'm sure these brakes would be equally effective on your car.

    The Wilwoods are much less expensive, but they are race car brakes. This means that they have no dust boots, and since Wilwoods have the actual seal on the piston, as is very common, the seal travels out into to grit filled outer portion of the bore as the pads wear. On real race cars, the calipers are disassembled and serviced regularly anyway, if done right, so this doesn't have a chance to become a problem. It is definitely not something to ignore on a street car.
    NOTE: if the seal is in the bore rather than on the piston, this is much less of a problem, but dust boots are still a good idea.

    So this leaves you with the Baer/Alcons, or perhaps something from Brembo or AP, or the adapted Porsche brakes - all very good, all very expensive.

    Furthermore, both my friends' 94 Camaro and your C4 front end use the late model sealed and non-serviceable front hub/bearing assemblies, and I much prefer the serviceable tapered roller bearing of earlier cars.

    The other possibility, given that you are determined enough to have installed the C4 suspension already, is to either add dust boots to the Wilwoods, or adapt some less expensive calipers, such as used Porsche, or Brembo takeoffs from a Viper, for example.

    On my budget I am using the Master Power reproduction JL-8 caliper brackets with 65-82 Corvette iron calipers and stock 12" x 1.25" rotors, which are unbelievably cheap and have adequate capacity. These also have pluses and minuses, but they're better than anything else I can afford and will do the job, I think/hope. Unfortunately, they won't bolt on to your C4 knuckles, so I'd go back to the used Porsche or Viper Brembo takeoff type solution.

    And please, please don't drill your rotors. I know that Porsche rotors appear to be drilled but the holes are cast in, not drilled.

    Rene Kooger
    Registered User
    Posts: 71
    (4/17/02 1:15 am)
    Reply
    Re: Fixed vs. floating calipers
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    "NOTE: if the seal is in the bore rather than on the piston, this is much less of a problem, but dust boots are still a good idea."

    That's why Willwood also sells spacers. Which can also be homemade offcourse.

    Rene


    keithq
    Registered User
    Posts: 327
    (4/18/02 4:42 pm)
    Reply Re: Fixed vs. floating calipers
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    Thanks for the great reply.


    As far as the drilled rotors go I would not attempt to drill, I had heard that the Porsche rotors were cast with the holes in them so as not to create stress.

    As far as the Viper caliper goes, that is something I had not considered, Do they use a Brembo caliper?

    I could check into some Porsche stuff also, I would assume the turbo brakes is the stuff to look for, any particular year?

    One more thing, I like the fact that the Alcons are radial mount, the Wilwood are not. Are the Porsche or Viper radial mount?

    Thanks

    Keith Quinn.


    dsmerritt
    Registered User
    Posts: 3
    (4/23/02 12:07 pm)
    Reply Re: Fixed vs. floating calipers
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    Keith,

    Having worked with the radial mount Alcons on the 94 Camaro I don't see that the radial mount offers enough of an advantage, if any, to worry about, as compared to the conventional mount. You still have to carefully shim it into position initially, which is no different than the conventional mount. The only plus I am aware of is that you can take the caliper off quickly and easily without disturbing the alignment or losing shims. So , although I have experienced the wonderfulness of Alcon, I wouldn't lose any sleep over having to use a conventional mount.

    As far as I know the Viper Brembos are all conventional mount, and there are different calipers as you go along the model/year progression. Can't tell which is which or if the mounting ears are different. Know people who are adapting them to a 90 Mustang and a 67 Mustang, but no Camaros.

    Porsches are also all conventional mount, I think. Don't know which ones are how big, the good ones come on more than just the Turbo, I think. If you win the lottery you could get a set of the Porsche ceramic rotors, which are still cheaper than the real trick deal, carbon rotors.

    As I said, I'm in the price range for $70 stainless sleeved factory 4 piston iron calipers with $70 12" x 1.25" rotors, hopefully with a later upgrade to J56 insulator pistons and the two pin racing pad conversion (pads are much stiffer due to lip at top).

    Nothing else will touch this for price/performance if your are on a budget.

    If you have a little extra the aluminum 4 piston calipers from Stainless Steel Brakes seem like a nice part in theory. They use BMW pads, a good thing, and although they do not have insulator pistons available, SS Brakes says that the stainless pistons (as opposed to the factory aluminum) which their calipers come with have much better, which is to say worse, performance on heat transfer.

    Bottom line, the 12" x 1.25" rotor is marginally adequate on a 3200 lb. car, but contrary to popular belief you want the smallest rotor that will get the job done, to minimize rotational inertia. Do the math - the extra inertia of a 13 x 1.25" rotor is a ton. The factors are:

    1) Thermal load. Determined by car weight, max/min speed, and duty cycle.

    2) Thermal capacity. The rotor has to store the heat temporarily until it can be transferred to the atmosphere.

    3) Thermal transfer. The heat needs to be transferred from the rotor to the atmosphere, not into the other braking system components. Modern synthetic greases for the wheel bearings allow rotor temperatures that can more readily boil brake fluid, which becomes the limiting factor. The insulator pistons allow higher operating temperatures and therefore a smaller rotor.

    Again, the JL-8 conversion is developed for this application, more or less bolts on (housing ends and custom length axles are the least of your worries), and solves the parking brake problem as well. Furthermore, it fits in most/some 15" wheels, if you care, and has plenty of room for cooling in a 17" wheel.

    In short, it's cheap, it's easy to install, and it works.

    keithq
    Registered User
    Posts: 329
    (4/23/02 2:26 pm)
    Reply Re: Fixed vs. floating calipers
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    Thanks.

    I was considering radial mount just because it makes it a bit easier to make the mounting brackets in my opinion, the bracket is also smaller than a comparable conventional mount rotor.

    I realize that for my car the 13" rotor is alot of wieght to carry for probably more than enough braking for street use but the 12" rotor just gets lost inside a set of 17" wheels. I know this is a bit trivial but lets face it the "oohh ahh" factor also come into play with a car that sees mostly street use.

    I am looking into calipers made by a company called AP Racing right now, I should have pricing by tomorrow, not sure if you are familiar with thier products.

    Keith Quinn.


    dsmerritt
    Registered User
    Posts: 4
    (4/23/02 6:18 pm)
    Reply Re: Fixed vs. floating calipers
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    Keith,

    I'm not sure I understand how the radial mount is more compact or easier to make, although it may be. The caliper mounting bracket for both types bolts horizontally to ears on the upright/knuckle. The radial mount then basically turns a right angle corner and has two beefy studs extending radially from the bracket, at least on the Alcons. You still shim horizontally between the caliper mount and the upright/knuckle to square the caliper on the rotor. The advantage is that when you remove the caliper vertically this alignment is not disturbed, and exact positioning vertically is a non-issue. The downside, and the first rule of engineering by the way is "Everything is a compromise", is that you now have a mount that is less rigid than, or at least harder to make as rigid as, a simpler conventional mount. I doubt if the total radial mount is any stiffer in deflection from brake application, if as stiff. Caliper deflection, and caliper mount deflection, are very real issues at real world brake system working pressures.

    And just to start another controversy, stainless braid covered Teflon brake lines deflect/expand just as much as new fabric reinforced rubber lines. They have other potential advantages, but less give is a myth perpetuated by the vendors of Teflon lines. It's a shame they have to lie, since there are other valid reasons to use Teflon.

    Let me make myself clear on the rotor size issue. The 12" x 1.25" rotor is right on the ragged edge in terms of having adequate capacity for a 3200 lb. car being driven to the limit, and then only with the insulator pistons since the working temperature will by definition also be at the high limit. The 13" rotor gives a margin of excess capacity, and extracts the concomitant penalty in performance, i.e. 17.4 per cent more rotational inertia. That's not how you win if you're racing on the track or the street. Eons ago in the mid 60's when I was a teen-aged street racer, one of the comments about a car that traded performance for appearance was " If it don't go, chrome it." But then again, we were racing for money. Appearance stuff was also called "romance" and "eyewash". Looking cool is a very different goal than going as fast as possible - not bad or wrong, but different. Looking cool at the cost of going slower is simply does not compute for myself or the other hard core types I know. They would say "Why would you do that?" and be genuinely puzzled, not sarcastic, since we want to go faster than the other guy first, last and foremost. Of all my friends' cars, the car that is the most fun is a 66 Corvair - with a 350 (soon to be an LS-1) in the back seat. Not much to look at, but very likely to take your money.

    In short, if the car is going to be driven seriously on the track, let alone competitively, this drastically affects the compromises you make, if you're serious about it. If not, that's fine, too, but the guy who is serious is going to beat you, guaranteed.

    The 13's may be the right choice, and are certainly the safe one, but from a performance point of view "filling up the wheels" is the wrong reason, and bad for brake cooling, too. The fact of the matter is that a mounted 245/55-16 @ approx. 26.6" tall is probably lighter than a 245/50-17 also @ approx 26.6" tall, since most street wheels like my OZ Competitions are relatively heavy so they'll hold up to chuck holes and the like, while modern tires are lighter than an equivalent amount of street worthy wheel. Who'd ever have thought - but that's the whole point. Very few people think, fewer analyze, and fewer still question. Remember, since in hindsight the conventional wisdom frequently wasn't (the world probably isn't flat), that means that the current conventional wisdom is, very probably, just as wrongheaded.

    On the other hand, the goal for my car is to have the Porsche Club tell me not to come back to their events at Texas World Speedway, then go to the drag strip in Baytown and run 10's at 130 plus (with slicks, of course - 11's at 120 plus on street tires). Through the mufflers, on pump gas, with power steering and air conditioning. At that point, I'm not going to care if the wheels don't look full. Our idea has always been that we don't care if you're impressed with our car or how it looks. As long as we're faster, we'd rather impress you with that.

    By the way, Alcon was founded by a former AP guy who broke away from AP and started Alcon, seems like about 20 years ago or so. Now they are direct competitors. Both have web sites, by the way, and "Race Car Engineering", a British racing technology (not fan) magazine has had articles on both AP and Alcon. Unfortunately, I believe you'll find the AP's just as expensive, as well as just as good.

    keithq
    Registered User
    Posts: 331
    (4/25/02 12:31 pm)
    Reply Re: Fixed vs. floating calipers
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    dsmerritt.

    Thanks for the info in the AP Racing stuff, I am waiting for a response from them.

    As for the radial mount bracket, I have taken some measurements of the mounting location for moth styles of brackets, with the radial mount I have much less distance brtween the mount on the upright and the mount on the caliper, this to me may translate into less flex in the bracket. Also since the bracket will be smaller I can afford to make it out of a thicker material and still be as light, in fact the ones that Bear sells for the 4 piston Alcons are aluminum I beleive.
    But as you say there may not be much difference in the fabrication required.

    As far as the look of the rotor in the wheel. I know what you mean about not doing stuff just because it looks good, but that also comes down to the compromise, I have to be happy with the apprearence of the car, afterall it is mainly a street car. I, as I am sure you did, picked a car that was asthetically pleasing to the eye when I bought my 69 Camaro. I am sure from an engineering standpoint, where you make descisions based only on how fast it will make your car the Camaro may not win out as the body style to choose. You mentioned a Corvair above that is very fast, this may be a better choice but for appearence reasons I prefer the Camaro.

    "Looking cool at the cost of going slower is simply does not compute for myself or the other hard core types I know. "

    Do you think that you would still have chosen the Camaro if you made no choices that would make you go slower?
    You pick something you like and that is what you work with.

    I will post when I get pricing of the calipers from Brits.

    Keith Quinn.



    keithq
    Registered User
    Posts: 333
    (4/26/02 1:42 pm)
    Reply Re: Fixed vs. floating calipers
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    Just heard back from Brits regarding the 4 piston AP Racing caliper. I can get a 4 piston radial mount caliper with pads for $1000.00 for a complete front set, that seems like a great deal to me. The guy I talked to said that the AP Racing stuff is superior to the Wilwood and about par with the Alcon stuff, sounds good to me. I think the price is much better than the Alcon also.
    He sent me a PDF of the dimensions so I am going to do some research and see if it will fit.

    I will let you know what I find.

    Keith Quinn.


    dsmerritt
    Registered User
    Posts: 6
    (5/14/02 4:58 pm)
    Reply Re: Fixed vs. floating calipers
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    Keith,

    Sorry about the delay in getting back to you. Have been very busy at work (we do computer stuff - data recoveries and computer forensics) and most of the time we don't get to paln ahead but have to respond on short notice. I'm not complaining, glad to be busy - more money to spend on cars.

    Hope things work out with the AP brakes. $1,000.00 for a complete front set is an incredible deal. As I said, the 4 piston Baer/Alcons were $2500 several years ago, and are supposed to be lots more now. Not only is this 2/3rds the price of even the Stainless Steel Brakes kit (which has stainless pistons), but it is close to the cost of a JL-8 conversion with J-56 calipers (with insulator pistons and dual pin pads). If this works out I may have to finds a home for my JL-8 stuff.

    I believe I mentioned that Alcon is basically an offshoot of AP in that the founder of Alcon was a senior person at AP before he went out on his own. I have no doubt that the AP stuff is every bit as good as the Alcon, some would say that the AP stuff is the original. They have a long history in formula and sportscar racing.

    Have some more comments on the "looks good/goes fast" trade off, but will have to wait till later. Partly it comes from a very warped perspective. Quick example: yesterday I drove a C-5 Corvette again (belongs to one of my oldest friends - since age 5 - and high school street racing buddies from '65-'67) and confirmed what I remembered, and what he thinks also. Which is to say that although it is a very nice car, and very fast by any reasonable standards, it isn't very fast to us. And the stupid floating caliper brakes are really numb and dead, not that they won't stop the car very effectively, but the feel sucks. My friend's going to fix the horsepower problem, by the way - he thinks one of the 550 horsepower packages would be about right. He doesn't intend to change the appearance of the car at all. With sticky tires it ought to go 10's at 125 in the 1/4, and they top end around 170mph stock (no 155 mph limiter like the Nazi-mobiles) so I doubt he'll ever top it out with the new engine.

    If the AP's turn out to be so incredibly cheap, maybe we'll put some on the C-5, but inside the stock wheels.

    Looking forward to good news.

    David Merritt

    davidpozzi
    Moderator
    Posts: 383
    (5/14/02 8:21 pm)
    Reply
    Re: Fixed vs. floating calipers
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    David,
    You refer to the early vette rotors as 12" but they are actually 11.5".
    I agree the 13" rotors are huge and heavy! Another thing, the late vette calipers don't cover the whole machined surface of the rotor. The 13" rotor almost appears to be made for some other car! What's the deal?
    Any thoughts on how they reduced the venting and increased the rotor "cheek" thickness? Looks like they increased the mass at the expense of venting. What's the proper balance for rotor mass to venting?
    How much is the benefit of curved vanes?
    David

    *****ncamaro
    Unregistered User
    (5/17/02 2:38 am)
    Reply AP model and part number
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    Sounds like a nice system! What is the model and part numbers for the AP set up ? Does the $1000 price include rotors+ hats?

    Kevin

    keithq
    Registered User
    Posts: 346
    (5/17/02 3:45 pm)
    Reply AP Racing?
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    Just got a look at the PDF file for the AP racing caliper.
    Although it does not include a measurement from the centre of the rotor to the outside of the caliper it does give me a measurement to the mounting holes. These look like they are about half way to the outside of the caliper. If that is correct the caliper is about 4" from rotor centre to the outside of the housing, this will never fit in my wheel with a stock C4 13" rotor.
    Looks like the caliper will be about 8" wide.

    Dsmerrit, as far as putting new fixed calipers on the C5, I have been told that it can me a challenge with stock wheels because of how shallow the rotor is. There is very little room between the rotor and the inside of the wheel, adding more rear spacing on the rotor is out of the question too because of steering arm interference.

    Let me know what you think.

    Keith Quinn


    davidpozzi
    Moderator
    Posts: 398
    (5/20/02 6:37 pm)
    Reply
    Re: AP Racing?
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    I wonder what the C-5 Lemans vette uses?
    David

    dsmerritt
    Registered User
    Posts: 7
    (5/20/02 8:00 pm)
    Reply Re: AP Racing?
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    Whatever hard core brakes (AP, Alcon, Brembo) Pratt & Miller (the builders of the "its really a production car, honest" C-5 race cars chose to install. I'd guess AP's, but I can't tell from their web site (www.prattmiller.com) and my March 99 Race Car Engineering with the article on the car is packed away. Anyone else know the specifics?

    davidpozzi
    Moderator
    Posts: 399
    (5/20/02 9:44 pm)
    Reply
    Re: AP Racing?
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    I found my R&T article on it. They say it uses AP Monoblock F&R, 15" front, 14" rear.
    David

    dsmerritt
    Registered User
    Posts: 8
    (5/20/02 10:31 pm)
    Reply Re: AP Racing?
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    Interesting - the mystery deepens. I found a website about the cars (www.c5motorsports.com) that says the cars are equipped with Alcons. Maybe the "fitment" (as the Brits say) has changed. I believe some of the AP and Alcon calipers have the same mounting points and can be interchanged.

    I will measure one of my nominally 12" rotors tomorrow. You're right about it not being quite 12", but its more like 11.8 than 11.5. Thickness is nominally 1.25" but I'll measure that too.

    One more advantage of the factory cast iron 4 piston caliper is that it is really compact. The extra stiffness of cast iron allows a very rigid caliper with minimal bulk. In my case, the OZ Competitions (17x10) are going to require a major spacer to position the wheel correctly, or in our case a custom hub/hat with a Vette brakes bolt on rotor. This also requires having the maximum steering stops in the steering box, ala Impala SS. Crummy turning circle - like I care. And Keith is right, they may look lost in the 17's, but there ought to be plenty of cooling.

    I can believe the AP is wide. My only experience with installing aftermarket calipers was on my friends' 94 B4C Camaro with the 4-piston Baer/Alcons, which is also a chunky caliper. On this car he uses 17x9.5 OZ Monte Carlos, and in fact when we tried the 17x10 OZ Competitions there was very slight interference between the wheel spokes and the caliper. On mine the clearance will be measured in inches.

    Haven't paid any attention to the 13" rotor construction, so don't know about mass versus venting ratio. Comparable sized racing rotors should be a good point of reference. Curved vanes do seem to pump air more efficiently. The very latest racing rotors have curved vanes with an airfoil cross section.

    Words to live by:
    "Going fast IS looking good."

    Edited by: dsmerritt at: 5/21/02 10:46:36 pm

    dsmerritt
    Registered User
    Posts: 9
    (5/21/02 8:26 pm)
    Reply Re: AP Racing?
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    Measured a rotor - one of those wonderful $70 replacements which are readily available - and it is approx. 11.75", or maybe it is 11.8 more or less, since that's less than a 1/32" larger radius (or less than .03125" for the fractionally challenged). My resolution with eyeball and tape measure, not to mention production tolerance, falls within that, I'm pretty sure. Sure hope it turns out to be enough rotor at TWS.

    davidpozzi
    Moderator
    Posts: 404
    (5/24/02 5:39 pm)
    Reply
    Re: AP Racing?
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    the road and track David Kimble cutaway illustration shows AP on the calipers too.
    11.8 rings a bell in diameter. Are those 1.1" in width?

    The old cast iron vette calipers are darn good for stiffness for sure. The phenolic insulators are a good way to go too.
    David

    jon sikora
    Registered User
    Posts: 218
    (5/26/02 11:05 am)
    Reply 13's
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    i was speaking to daryl at precision brakes and metioned my concern about the additional weight of 13's vs. 12's.he countered with the idea that unsprung weight is important as a percentage of sprung weight,on a heavy car the difference is nominal.any thoughts?

    andrewb70
    Registered User
    Posts: 68
    (5/26/02 8:41 pm)
    Reply Re: 13's
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    Jon,

    Daryl put together my brake system for my GTO using the Wilwood calipers and a 14X1.38 rotor with an aluminum Wilwood hat. I have not weighed those new rotors, but I can tell you that they weigh less then my all iron C4 13X1.1 inch rotor that came with my Baer kit. I am no expert, but I would tend to agree with Daryl on his point. If I was building a 2000 pound race car, then I would care about extra unsprung weight. As it stands, I am putting together a car that will be close to 4000 pounds and frankly I don't think that an extra poung or two will make any difference in handling.

    Andrew

    davidpozzi
    Moderator
    Posts: 408
    (5/26/02 9:34 pm)
    Reply
    Re: 13's
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    Jon,
    Yes it is the relationship of sprung to unsprung weight that is important for good ride, or good contact tire to road over bumps.
    David