pp brakes

[Gudz2015]

Any of you guys know who makes a replacement rotor maybe a two piece that will be lighter? since it is such a massive size would be nice to cut down some weight.

Thanks guys.

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[scottpe]

You didn't specify GT or Ecoboost (the PP brakes are different between the two), but if you're referring to the GT brakes, they are believed by many to be the same 6-piston 15" units used on the GT500. If that's the case, there are 2-piece rotor options available already. A search will probably yield what you're looking for.

 

[Tim Hilliard]

Yes time will tell if the '15 has the same hub and off setts but they are currently available.
http://rehagenracingproducts.com/2013-14-MUSTANG-SHELBY-GT500-15-INCH-2-PIECE-BRAKE-ROTOR-PAIR-M-1125-MSVT15.htm

 

[Firepath]

DBA makes rotors for the current generation with / without aluminium hats, their 5000 and 4000 series I believe. I think I read American Muscle gave them a good review - quality vs price. I imagine with the car coming to Aus they will have plenty of incentive to make rotors for the 2016 (and probably the 2015).

 

[Gudz2015]

Yup GT, 1400 that's not much fun. Saving 10 pounds of rotating mass is equivalent to 30 pounds of the dead weight correct? Different wheels and tires will be purchased that's for sure but I might have to save up for rotors. Hope someone comes out with more or maybe a few hundred less than that.

 

[DHG1078]

I think its 4 pounds dead weight for every 1 pound rotational

 

[Firepath]

I think its 4 pounds dead weight for every 1 pound rotational

I think a good, conservative, leave some room to be surprised number is 1:3.

This is how I look at rotating parts:

Rotating mass to static mass equivalent depends on the radius at which the mass is being spun, so it can vary from about 1:1 to something like 8:1. Say you have a wheel that weighs 20lbs, with all the mass on the rim, and another wheel, looks identical, same dimensions except all the mass is in the hub, the one with the mass on the rim will have a greater moment of inertia (the object's tendency to resist being spun), which will be harder to accelerate.

Basically more mass removed from further out on the radius of a rotating object will give more improvement in the response to torque (angular acceleration).

So with something like a driveshaft, you don't get as much improvement as you might imagine. Even though you can knock half the weight off with a CF driveshaft, the diametre is usually slightly larger than the steel one it replaces. Since all the mass of the driveshaft tube is at the furthest point from its centre, it is in the worst spot with respect to rotational inertia. Couple that with the fact that reducing a driveshaft by 50% in weight is usually due to the fact that it was a two-piece with a static bearing holder that was not part of the rotating mass, and the rotating : static ratio just isn't that amazing. I'm not bagging (too much) on driveshafts for dropping weight, 12lb of any kind of weight gone is still a pretty good drop.

Obviously wheels have the greatest diametre and so potentially have a good chance at getting a good multiplier if weight is taken from the rim. Any weight off wheels is weight off the unsprung though, so wheels (and rotors likewise) are win-win when taking weight off.

Rotors lose most of their weight from moving to an aluminium hub. Performance rotors are usually larger (don't have to be, but usually are) and thicker. With most of the mass of brake rotors being midway to the very outer edge of their diametre, the lightweight hub is more of an unsprung benefit than an acceleration benefit.

So driveshafts I see about 1:1.5 ratio of rotating vs static, wheels depending on where the weight comes from (and what you're replacing) can be from 1:3 to 1:8, and rotors are more about 1:2 for just going to aluminium hats and more for dropping diametre or thickness (drag brakes).

 

[Grimace427]

Weight savings from two-piece rotors is almost entirely from the center hat so rotational weight reduction is minimal. The extra mass in the rotor itself(15" over the previous 14" Brembos) is additional heat capacity for track use. More heat capacity means you can work the brakes harder for longer before fade or complete failure so there is a tradeoff there.

 

[DHG1078]

I think a good, conservative, leave some room to be surprised number is 1:3.

This is how I look at rotating parts:

Rotating mass to static mass equivalent depends on the radius at which the mass is being spun, so it can vary from about 1:1 to something like 8:1. Say you have a wheel that weighs 20lbs, with all the mass on the rim, and another wheel, looks identical, same dimensions except all the mass is in the hub, the one with the mass on the rim will have a greater moment of inertia (the object's tendency to resist being spun), which will be harder to accelerate.

Basically more mass removed from further out on the radius of a rotating object will give more improvement in the response to torque (angular acceleration).

So with something like a driveshaft, you don't get as much improvement as you might imagine. Even though you can knock half the weight off with a CF driveshaft, the diametre is usually slightly larger than the steel one it replaces. Since all the mass of the driveshaft tube is at the furthest point from its centre, it is in the worst spot with respect to rotational inertia. Couple that with the fact that reducing a driveshaft by 50% in weight is usually due to the fact that it was a two-piece with a static bearing holder that was not part of the rotating mass, and the rotating : static ratio just isn't that amazing. I'm not bagging (too much) on driveshafts for dropping weight, 12lb of any kind of weight gone is still a pretty good drop.

Obviously wheels have the greatest diametre and so potentially have a good chance at getting a good multiplier if weight is taken from the rim. Any weight off wheels is weight off the unsprung though, so wheels (and rotors likewise) are win-win when taking weight off.

Rotors lose most of their weight from moving to an aluminium hub. Performance rotors are usually larger (don't have to be, but usually are) and thicker. With most of the mass of brake rotors being midway to the very outer edge of their diametre, the lightweight hub is more of an unsprung benefit than an acceleration benefit.

So driveshafts I see about 1:1.5 ratio of rotating vs static, wheels depending on where the weight comes from (and what you're replacing) can be from 1:3 to 1:8, and rotors are more about 1:2 for just going to aluminium hats and more for dropping diametre or thickness (drag brakes).

I understand how it all works. Just trying to remember what the "conversion ratio" was. I know I saw about a month ago somewhere said 4:1, but I thought it was a little hopeful.

 

[scottpe]

Weight savings from two-piece rotors is almost entirely from the center hat so rotational weight reduction is minimal. The extra mass in the rotor itself(15" over the previous 14" Brembos) is additional heat capacity for track use. More heat capacity means you can work the brakes harder for longer before fade or complete failure so there is a tradeoff there.

I think the biggest advantage to the lighter rotors with regard to weight is not in the reduction of rotational mass, but in unsprung weight.

As far as heat, don't most two-piece rotors have aluminum hats? Less heat capacity, yes, but higher rate of heat dissipation than iron too right?

 

[Firepath]

I understand how it all works. Just trying to remember what the "conversion ratio" was. I know I saw about a month ago somewhere said 4:1, but I thought it was a little hopeful.

I was just trying to point out there is no ONE conversion ratio, it all depends, but your number is more honest and realistic than the (wishful) numbers I see most people saying (1:10). Plus dynamics has always been very interesting to me throughout my life so I love discussing it.

 

[Firepath]

I think the biggest advantage to the lighter rotors with regard to weight is not in the reduction of rotational mass, but in unsprung weight.

As far as heat, don't most two-piece rotors have aluminum hats? Less heat capacity, yes, but higher rate of heat dissipation than iron too right?

From what I've seen, brake rotors with aluminium hats are usually bigger in diametre and have the same or more iron anyway, without being too much heavier, or even being lighter. I would think the design intention of these setups are that the iron part plays 100% of the role of the heat sink and the aluminium part contributes somewhat to drawing the heat out of it quicker (and into your wheels and hopefully not your bearings).

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