anyone have one of the above to get a fairly accurate weight??

Sorry for the smart allec reply as I don't have the numbers your looking for.

but when we built the new car last year we switched from rear vented to rear slotted solid. I don't remember the exact figures, but I know it was around 12-15lbs total savings.

brant

Mike,

I don't know the exact differences, but I've been toying with the idea of making swiss cheese rotors for autox. Problem is, changing front rotors is easy, but rears are more of a PITA, and that's where the weight savings would be best applied.

-Josh2

I have all the rotors handy, including one vented rotor I had the diameter reduced on. It will take a bit to weigh them up though.

QUOTE (brant @ Sep 30 2005, 09:07 AM)

Sorry for the smart allec reply as I don't have the numbers your looking for. but when we built the new car last year we switched from rear vented to rear slotted solid. I don't remember the exact figures, but I know it was around 12-15lbs total savings. brant

Hey Brent,

a 6 to 7.5 pound difference per rotor seems pretty excessive , however, maybe the vented rotors have a thicker hub section for the parking brake for when used with a 911 parking brake???

I'm trying to figure out the best cost to weight savings for a rear setup..

too many options:

solid or vented?

single piece rotor or 2 piece like my front setup?

brake caliper with intergrated parking brake or seperate parking brake?

if seperate calipers, mount the parking brake outboard or inboard?

QUOTE (davep @ Sep 30 2005, 09:17 AM)

I have all the rotors handy, including one vented rotor I had the diameter reduced on. It will take a bit to weigh them up though.

thanks Dave,

no big hurry, but it would be nice to have when you get it....

QUOTE (jhadler @ Sep 30 2005, 09:14 AM)

Problem is, changing front rotors is easy, but rears are more of a PITA, and that's where the weight savings would be best applied.

Cluelees noob here. Are you talking about available options for changing rotors ? For stock rotors, rear seem simple to R&R, whereas front ones have bearings to mess with.

Also, why is weight reduction more important in rear : trying to get more equal weight balance, or b/c they are the powerered wheels ?


Just curious.....

Mike,

I could be wrong on the numbers, and now I'm really curious to see Dave's numbers....


but yepp.
everyone uses the 911 rear rotors that were designed to have the 911 style parking brake and vestibule "drum" if you will.

that definitely adds some very unneeded, dead, and unsprung weight.


Jeff,
when racing a 914 it is common practice to try and balance the car better, by removing any rear weight and decreasing the rear weight bias the cars have. Especially if its a -6 cylinder car as the 6 motor adds about 130-to-150 lbs into the rear of the chassis.

QUOTE (jsteele22 @ Sep 30 2005, 08:50 AM)

QUOTE (jhadler @ Sep 30 2005, 09:14 AM) Problem is, changing front rotors is easy, but rears are more of a PITA, and that's where the weight savings would be best applied. Cluelees noob here. Are you talking about available options for changing rotors ? For stock rotors, rear seem simple to R&R, whereas front ones have bearings to mess with. Also, why is weight reduction more important in rear : trying to get more equal weight balance, or b/c they are the powerered wheels ? Just curious.....

Weight reduction in the rear for reduced driveline weight. I knew someone who built an EP rabbit that made swiss cheeze rotors for the front for autox use. Dropped something like 10 lbs of unsprung weight off the driveline...

Oh, and I guess I was crossed up there. The rears are not too bad to replace...

-Josh2

vented rear 911 rotor (290x20mm)
5.8kg or 12.75lbs

somebody weigh a stock-solid 4 lug (or 5 lug)

I'm really curious now

brant

BUMP>>>>>

I'm really curious.
anyone?

anyone know the weight of a stock rear rotor?

brant

QUOTE (Jeroen @ Sep 30 2005, 10:58 AM)

vented rear 911 rotor (290x20mm) 5.8kg or 12.75lbs

thanks Jeroen

someone at pelican/paragon would probably weigh one for ya...

reducing the mass of the rotor will allow faster acceleration {reducing the front will futher help} letting the engine rev quicker. smaller diameter rotors and wheels also help this. [btw rubber weighs less than aluminum] reducing unspung weight allows better chassis control, the and spings[and torsion bars] dont have to work as hard on the parts of the car not held up by the springs.

QUOTE (messix @ Sep 30 2005, 02:43 PM)

reducing the mass of the rotor will allow faster acceleration {reducing the front will futher help} letting the engine rev quicker. smaller diameter rotors and wheels also help this. [btw rubber weighs less than aluminum] reducing unspung weight allows better chassis control, the and spings[and torsion bars] dont have to work as hard on the parts of the car not held up by the springs.

Rubber does weigh less than aluminum, but tires still generally weigh more than the wheels they're fit on, probably because there's a lot of rubber in the tire than there is aluminum in the wheel, and there's more than a little steel in most tires. 25lbs is not an uncommon tire weight, which is a good bit heavier than anything but stock steel wheels among the wheels usually fit to 914s.

Also, for rotational inertia, the distance from the center of rotation makes a big difference, and nearly all of the tire mass is well outside the wheel mass. Reducing the mass of the rotor will help SOME in reducing inertia losses, but using a lighter tire would make a much bigger difference.

Where losing rotor weight matters is reducing unsprung mass, which is always beneficial. However, lighter rotors tend to overheat and warp more easily. There's always a tradeoff somewhere.

IMHO, the solution to brake overheating problems is to reduce the weight of the whole car, not to add heavier rotors. The lighter car will not only reduce braking loads from reduced mass, but will also allow higher cornering speeds, thus reducing the amount of braking required in the first place.

Everyone has their pet theorys, me included.

When I added S calipers to the front, I found that stock rear brakes were't up to the task of doing their share of the braking work. I found I needed bigger pistoned calipers back there.....Ms are what the 911s use, so that's what I went for...along came vented rotors. It's now a well ballanced system.....now my pet theory is : brakes are for braking, do whatcha gotta do to get em' right and the hell with the peripheral shit.

thickness dia lbs kg
911 rear 20mm 290 12.9375 5.87
911 rear 20mm 282 12.25 5.56
914 rear 9.5mm 282 9.56 4.34
914/6 rear 10.5mm 286 11.375 5.16
911 rear 24mm 290 13.6875 6.21