danglerb

Motorcycle petal brakes

BC

+1

dr bob

Herman, FWIW, when we were building prototype graphite brakes maybe 20 years ago, the brakes seemed most effective right about the time they started glowing. SCCA (and other racing groups) banned the graphite rotors because they were too fragile compared to metal. If a wheel comes off or something gets in there, he rotor would break too easily and leave you with no brakes. They would be awesome if used inboard, with an enclosure and forced ventilation. Rotors weighed less than two pounds.

Bill Ball

I bought a load of offset bolts before they disappeared from the market if anyone needs some.

hans14914

Here is something unusual, if you look at the drawings posted on the first page of the thread of the S4 rotor, it lists the overall "height" to be 77mm and if you look at the PDF posted on page 2, it says 76mm..... Which is correct, and is there that much variation between "OEM" manufacturing?

69gaugeman

Distances like that are usually +/-.250mm some are more, so 1.,000mm is large but .,500mm is normal.

Also, people sometimes just round up / down for these types of things. Figure they are going to use a tape measure to check

69gaugeman

These are done because the amount of heat dissipation is directly related to surface area. Because the rotors are solid this 'petal' design gives the rotor more surface area.

A car rotor has crap loads of surface area (inside with the fins) so the extra surface area that would be gained by 'petaling' is not worth the extra cost

mark kibort

why would you want to do this? save weight for what? how much weight could you drop out of a rotor by drilling holes. take that weight , and x 1.2 as if it was in the car. that would be its net effect. . Plus, the thermal mass is what you wouldnt want to remove.

mark kibort

so, let me see if I got this straight.

the new porsche 4x4 rotors are 8mm off the early 928s offset, to the inside, toward the tie rod. SO, could you just have a 8mm steel bar with 4 holes. 2 for the mount to the spindle and 2 for the old caliper. that would move the caliper inward by 8mm and walla, HUGE F40 (almost ) brakes!! alll you need to do his hog out some material of the caliper to match the new radius of the new larger 330 or 350mm rotor.

sounds real simple. I guess you could use some high quality aluminum, right?

mk

svp928

Spacing the caliper out radially is easy, you just make spacers as Mark suggests, and install with longer bolts. Getting the rotor located axially in the center of the caliper is what renders the Cayenne rotor un-usable for us. Any spacer that moves the rotor also moves the wheel, and our cars are space-challenged for wheel placement to begin with. To put larger rotors where they belong really takes a 2-piece hat-rotor combo. If a source for rotor discs in 13 and 14 inch dia. can be found, it would not be difficult to make hats to fit....

Mark Anderson

So Steve can you make a hat that can accomodate multiple diameter rotors or does each diameter require a different hat?

mark kibort

So, you are talking about us, being the S4 guys now. (as far as the spacers or use of hats for the bigger rotors ) But, for the early cars, since the rotor is offset more toward the inside, as long as 8mm of inside offset doesnt rub the tie rod ends, a spacer with just holes would work for the early calipers, wouldnt it? this way, you could get 330mm rotors (slightly bigger than GTS) and use the stock calipers with a spacer plate with 4 holes. 8.5mm of thickness would be strong enough, and all you would need to do is tap 2 of the holes that would hold the caliper further out.

I think the M3s use this size of rotor with their single piston calipers.

There you go, another GTS brake upgrade, for the cost of spacers and slightly more expensie rotors. 170 each for the 350s, what are the 330 rotors cost Mark???

Steve, we still have to make a run of the S4 hats so we can use those coleman rotors!

mk

F451

That pic looks like a dirt bike, or dual sport, in which case the petal, or wave shape , and drilled holes, are primarily for weight reduction and to allow for dissipation of dirt and mud.

A solid rotor does not work too good in a muddy environment. And dirt bikes are relatively light so do not need the massive brakes that autos do. They usually have one small, thin rotor up front, and a pretty tiny caliper considering how hard they stop. Modern dirt bikes are usually one finger stopping affairs.

It's also a bit of a fashion, hey look at me, statement as well I think.

svp928

I am not having much luck with Coleman responding to Q's about rotor availability- but, we can make a hat that fits the S-4 and takes a Stop-tech or similar inexpensive rotor, and bolts right on without mods. Or, we make hats that take a 13 or 14" rotor with the same center bolt pattern, that also fits right on to a stock S-4. Utilizing an adapter bracket, we can accomodate pre-87 cars for upgrade to S-4 or larger brakes.
Mark A, I believe you sell such an adapter now, don't you?

The main goal would be to make a setup that uses inexpensive rotors- the Colemans used to be about 120 bucks. I can make a hat to fit just about any rotor, so we just need to source some decently priced ones.

hans14914

I still nominate the Stoptech. I spoke with the guys over at Zeckausen - one of the Porsche oriented Stop-Tech dealers (they also sell other products, so believe it was an un-biased conversation) - and they said that the service life on the Stop-Tech rotors were very good, and often outlived the Brembo counterpart. While Coleman has been around a while, i have to imagine that they are using a lower grade alloy. Too bad ST doesnt make a 928 friendly hat, as they have some nice features, including vanes on the hat to assist cooling the outboard (hotter) side of the rotor for a more even wear and warm-up, which theoretically, should reduce fatigue and the cracking/crazing that appears on heavily used rotors.