mark kibort

I get that. However, it is interesting that thte older rotors are thinner in this area.

anyway, I was refering to Pcar post that there was going to be some dangerous situation without using the stock centerign for the rotor, or for that matter, the wheel on the hub, which because of most custom wheels chamfer, that really doesnt come in to support play.

pcar928fan

So, MK, let me get this straight... You are saying that hub centricity is just there for looks or roughly to center the wheels but that all the weight of the car is actually supported by the lug studs? I just want to be sure I have not misunderstood what you are saying here...

Sorry, but I don't buy it. If that were the case Porsche would not have engineered them that way. It would have been easier to not mess with that yet they did it anyway. You may say overkill, but I am not going to rely on the lug studs to take all the forces transmitted through the wheels in to my car...you are welcome to do that though.

mark kibort

I think you are underestimating the function of the lugs and studs.
Again, if you have aftermarket wheels, you can see that the ID of the rim, not only isnt that tight for alignment, (maybe off .25 to .5mm) AND, that the lugs have naturally certain capabilities to align the wheels to be centered. Look no farther than the rims distinct design. the forces and weight is on the bolt holes of the rim, not the center area. thats one of the reason the bolt holes are so built up with material. each wheel has 7-800lbs on it. 5 studs, puts a little over 100lbs on each stud and under braking or impact, double that. those 15mm studs are more than capable of holding that weight. anyway, there are a lot of of non hubcentric wheels out there that folks use succesfully.

Anyway, all you do is look at the kinesis wheels. look at the ID of the hub centric part. its chamfered, and a sloppy fit at best. you mentioned how important that it is, (emphatically) that all the hubcentric components are using their respctive hub centric elements. that isnt true either . the rotors are independent of the wheels. yes, like many things porsche designs, its over designed. the stock wheels use this as you say, but good luck finding an aftermarket wheel that fits like the OEM wheel, PLUS, dont take my word for it. look around the pits at any race track and see how many are hub centric.

Hey, its great to be careful, but your concern is a little on the **** side. what do you think is going to happen when you dont use the hub centric center? scot and I have been racing with non hubcentric front spacers , some as wide as 1/2" for over 10 years now. yeah, we are just risk takers!

VT928

I like the idea of this thread, when I upgraded my 1980 Euro S brakes the only option was early spindles and 993 rotors with S4 calipers. A solution that works great but was neither inexpensive or a simple bolton. This has the ability to be both. I did have a thought that you might want to consider, rather than use a modified "S" caliper you should consider utilizing the C5 Z06 Caliper front caliper. It is lighter, has a larger pad area, two pistons is designed for a rotor that is 320mm * 32mm, and are less epensive than the rotor you will be using (esp when purchased as widely available used). Given the popularity of the Corvette there is will be a far greator selection of brake pads for you to choose from. Since you are making adaptors anyway all you need is to design them formounting the Corvette caliper. I know that some will accuse me of Blasphmey but it is a race car and performance is what it is all about.

Paul

1980 Euro S Red /Blk Lea

VT928

Mark,

One more thing, the 993 turbo rotor is 322mm * 32mm and is a two peice unit with an aluminum hat. It is the same rotot that is currently used on the "Big Red" brake upgrade for early spindles. And it is almost a perfect fit for the C5 Z06 Corvette calipers.
Paul

1980 Euro S Red /Blk Lea

xschop

I'm still looking for the MC bore size info. I have them for all the 944/968. It will help me determine which 4-pot size to go with for the Wilwood superlites that have a larger pad surface than this 928 sliding calp pad....Anybody?
I'm also assuming 70-30 braking bias.

mark kibort

The turbo rotor, i would imagine, is more expensive, but I would use that on my S4 to GTS wannabe conversion, but the offset is wrong for the S4 calipers. I guess the adapter for the early models to use the GTS calipers, provides the right offset for the 993T rotors. anyway, too many unknowns. we have no idea how the corvette caliper is offset, AND i dont really trust the chevy brake system vs the porsche brakes, even if they are 2 piston calipers, lighter and bigger. unproven in my book. BUT, an interesting idea. certainly, later, a modification could be made to the adpaters we are making to accomodate the vet calipers and still use the cayanne rotors as they are 330mm.

pcar928fan

MK, LIVING ON THE EDGE!

VT928

Mark,

I understand you concerns about the Corvette calipers. But there is much to say for them, they are designed to stop that is 32 to 3450 lbs fron speeds that are quite high. They are used by a huge number of corvette racers with very few problems. The cost side of the issue is minimal and with all the Corvettes on the track even race pads are cheap. Not having to modify the caliper is also a good thing. For a street conversion where price counts they would win out if the adaptor can correct for offset issues. When I upgraded my Euro S I spent more on a single S4 caliper than two Corvette calipers cost.

Paul

1980 Euro S Red /Blk Lea

mark kibort

ha ha ha. what "Edge". Remember,I dont use the "Edge". . (or it isnt really even used)
Ill have to take a picture of what Im talking about. I remember being SO worried back when i did a spacer on my early race car 10 years ago. my dad, an ex mechanical, aero engineer, was jumping up and down about the forces not meant for sheer on those studs. but after looking at the design closely, he is right, to a certain point, but in actuality, the studs do all the work, especially up front where that lip is so small.

Hey Paul,

Interesting stuff. certainly worth considering as those calipers do look pretty beefy and do have a twin piston config, which would be nice. if they are cheap and mount the same way, heck, why not. as it is now, we want to spend 0 dollars to get an upgrade, very near a GTS set up, for the older 928s. this should do it. as far as pad costs, heck they are all about the same cost for a pagid black for racing . S4, GTS, 84s, alll cost about $200 a set.


thanks!

mark kibort

just measured the hubcentric-ness of the front and rear Kinesis rims. fronts have a 2mm gap. certainly is not being used for force relief off the studs, AND the rears are a little closer, more like 1mm, but not touching the ID. So, hubcentric, a misnomer, unless you have stock rims??? I dont know, but I dont think its a big deal, especially since almost everyone here has aftermarket rims and IM sure they dont fit tight like the factory stuff.

z driver 88t

Running factory rims on my 928, but my past cars Zs and VWs all have had aftermarket wheels that came with a properly sized hubcentric ring that provided a very snug fit to the hub = OEM. I don't know enough to say whether that was critical, but it has been my experience.

VT928

Mark,

The Corvette calipers differently, the abutment mounts to the spindle or in your case to the adaptor, the caliper then hangs on the abutment pins. The same caliper will handle any rotor fron 320mm to 340mm with only the abutment being changed. With all the Corvette guys going to 6 piston calipers from the C6 Z06 the base calipers are very cheap used, New they are like 100.00 dollars. Take a look at the photo mounting is a two bolt affair

xschop

I found the MC info on the Hybrids board.
That Vette caliper pad puts the 928 pad to shame. What are the S4 caliper piston size(s) and pad size?

The Vette caliper is 2 x 40.5mm pistons and @170mm pad width and ironically the input port is m10 x 1.0....It would be an upgrade for sure.
Find the eye 2 eye distance on that Vette caliper from the pics, it looks short enough lengthwise to drop on.

pcar928fan

Only problem w/ the Vette calipers is "CORVETTE" on them...guess you would have to grind that off!

MK, my Fikse wheels fit VERY snug to the hub... Just saying. In fact one of them fit so tight you could hardly get the damn thing off! Same for my stock wheels after having them repainted (they didn't bother to tape off the hub area of the wheels).