Im trying to determine which would be more beneficial.

Things to consider:

By lightening these, rotational mass is reduced. What matters most here is inertia.
Inertia=mass*(radius^2).

Driveshafts have relatively small diameters
Rotors, by comparison have a much larger diameter, but where is the mass actually being reduced with 2 piece rotors? Is it close to the axis of rotation , or is it on the pad contact area? Pad contact area would be much more beneficial.

Also worth noting that the rotation has to be transferred through the driveshaft before going to the axles. Meaning the rotational acceleration of the wheels is different than that of the driveshaft.

 

havent read the your statement, but i automatically say get the drive shaft! seen that thing in action man.. it really is a big difference! trying to have them make it for the AWD but they need a prototype to build one.

 

Im trying to figure out what would be better:

This kit: http://www.racingbrake.com/Brake-Pac...1-p/g37s-p.htm

Or

this kit: http://www.conceptzperformance.com/C...1969.156.48.66

+ a carbon fiber driveshaft

 

id go with CZP

and an aluminum driveshaft.. dont know how durable a CF shaft would do

 

This is a tough one as you are comparing apples to oranges. You are comparing losing unsprung weight to losing rotational weight. The lighter driveshaft will help you put just a bit more power to the ground while the lighter rotors will technically make better use of what you already have.

I don't have time to go into this, here's a good read on this stuff - http://www.w8ji.com/rotating_mass_acceleration.htm

I would go with both. If I had to choose one, I'd go for the rotors. As for which rotors, I'd go for the one with the most surface contact for better braking.

 

dofu always so technical!

i DOFU, dofu!

 

I forgot about the additional important difference that the rotors are also unsprung weight, in addition to rotating weight.

I think rotating mass is analagous to an inductor in a circuit. Lightening the driveshaft and the brakes will give benefits to acceleration and braking, you have to get the thing rotating to accelerate, and you have to stop its rotation while braking.

I have found that the 3.7 gears means that for every 1 wheel rotation, the driveshaft spins 3.7 times.

The OEM driveshaft is also 2 piece, and the radius is larger where the 2 pieces meet, but I cant imagine that a large portion of weight is carried at the joint, so Im not sure if that has a significant effect.

 

If you want speed your money would be better on some FI first

 

F.I. is in my future as well.

 

Ah, I have found something interesting!

If we are to look at the inertia from the point of view of the transmission, the total intertia is J(driveshaft)+Jwheel*(1/3.7)^2

This means [AFAIK, this is definitely true with the wheels suspended in the air (not actually accelerating the car)] essentially means that reducing the inertia of the driveshaft is 13.69 times more effective than reducing the inertia of the wheels! (With 3.7 gears, as I have).

Keep in mind though, that this is easily negated by the radius of the rotational mass in question. J=mass*(radius^2)!

Hope this is educational for you guys, this is actually helping me study for my exam in systems & simulation tomorrow.

Based on this, I can see why people enjoy their driveshafts so much.

 

Im going to relate driveshaft weight loss to wheel weight loss.

Im going to assume that the rotational centre of mass is located at 4/5 of the circumference of a wheel. I have 19" wheels so 19"*4/5=15.2" diameter -> 0.19304 meter radius

(15 lbs)*13.69*(0.0381 meter radius)^2=(4 wheels)*(x lbs) *(0.19304)^2

Solving for x, we have x=2 lbs

Therefore, with the assumptions I have made, and with a 3.7 gear ratio, removing 15 lbs from the stock driveshaft is equivalent to removing 2 lbs from the wheels. Which is big.

Im now going to relate it to the 2 piece rotors. I havent gotten any answers for this, so I am going to assume that the rotational center of mass LOST on the 14" rotors on akebonos is around the hub. Im guessing this because having 2 piece rotors enable you to use a different material for the hubs as you do for the pad contact area, meaning you could make the hub lighter than usual. Because of this Im guessing that the center of rotational mass LOST is a ring of radius 4" around the hub. 4" ->0.1016 m.

Im only looking at the CZP option. Given what I have found so far, I am no longer considering racing brake. With CZP, you save 7 lbs on each front rotor IIRC.

(15 lbs)*13.69*(0.0381 meter radius)^2=(2 wheels)*(x lbs) *(0.1016)^2

x=14.43 lbs.

With the assumptions (Im trying to be as realistic as possible) I have made, a 15 lb driveshaft reduction is equivalent to shaving 14.43 lbs of both front rotors. (28 lbs total), compared to the CZP bbk which shaves 7 lbs of both front rotors (14 lbs total)

Remember though, that rotors also have the advantage of reduced UNSPRUNG weight as well.

After doing these calculations, I think I will go for the CZP big brake kit along with a carbon fiber driveshaft.

I would get aluminum, but I dont trust it, since it isnt used by any OEMs from what I've read. I feel that the aluminum driveshaft is a liability.

 

Speak English Please^^^^lol

 

I bolded the important parts...the rest of it is just showing how I came up with it.