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View Full Version : Questions about Z brakes & Rotational Mass

TEAMMiSCHiEFS14
08-15-2005, 10:20 PM
I've been thinking about this for a long time now and I've read previous posts about the advantages and disadvantages of Z32 Brake upgrades, but I still have a few questions unanswered..

Rotational Mass would be the mass that is being driven by the engine correct? So thus, on a 240sx, the engine drives the driveshaft, driveshaft drives the rear axles, rear axles drives the hub/rotors, hub drives the wheels/tires. Well actually the engine drives the flywheel that drives the clutch that drives the tranny then the driveshaft but let's just not include the tranny in this discussion for now.. So here are my questions..

1) If only the driving components are doing the driving or being driven (driveshaft, axles, hub/rotors, wheels/tires) than how come people say that when you install the Z32 calipers, you add more Rotational Mass? The only Rotational Mass I see that is added from the upgrade is the extra weight of the Larger Rotor because the calipers are stationary on the knuckle.

2) In addition, most 240sx owner only install the Z32 brake upgrades in the Front so therefore, no addition Rotational Weight is actually being added since the Rear is doing the driving. So since only the Rear is being driven by the engine, it wouldn't even matter if you upgrade the Front to Z32 brakes or not, right?

3) This brings me to my last question, since Rotational Mass seems to me to be the weight actually being driven by the engine and various components and in this case in the Rear. Then wheel/tire combo size and weight would only matter in the Rear, correct? Hence you see racers at the drag stripe only putting on smaller wheels in the Front (FWD) or Rear (RWD)..

The only disadvantage I see from installing Z32 brakes for the typical track user (road, drift) is that it adds Corner Weight to the car and that could cause an imbalance which is correctable if you have it done. I think the weight balance would be more even if someone decides to install the Z32 upgrade in the Front & Rear.
420sx
08-15-2005, 11:08 PM
i never heard of a disadvantage of a bigger breaking system. its not even that much heavier. if u do front and rear and a mc its a perfect upgrade no effect on cornerweight :ugh: . as far as rotation mass i dont think it add anything besides a bigger rotor. but then again its just what i think :goyou:
atom
08-15-2005, 11:21 PM
1. Brake caliper is unsprung weight,though you provbably won't notice it much. Brake rotor is rotational mass.

2 & 3. Front, rear or all wheel drive, it doesn't matter. You still need to accelerate/decelerate all four wheels. And drag racers might use smaller wheels to reduce rotating mass but mostly its so they can fit tires with larger sidewalls.
wootwoot
08-15-2005, 11:45 PM
1. Brake caliper is unsprung weight,though you provbably won't notice it much. Brake rotor is rotational mass.

2 & 3. Front, rear or all wheel drive, it doesn't matter. You still need to accelerate/decelerate all four wheels. And drag racers might use smaller wheels to reduce rotating mass but mostly its so they can fit tires with larger sidewalls.


Yeah thats about right.
DUDEIDONTHAVEA240
08-15-2005, 11:56 PM
have you guys ever seen Horsepower TV on spike tv? there was a great show that showed someshit about rotational mass. they had dynoed a car after some bolt ons and gained 15hp and they installed bigger brakes to compensate for the horse power and they dynoed again and lost that 15 hp. this is true, find that episode and check it out.
S14DB
08-16-2005, 01:07 AM
2 things with rotational Mass. Weight and distance from the center.
240sx rotor is 12.5 lbs and the 300zx is 17.5 lbs
Also another bigger issue is that the stock rotor is 10" and the 300zx is 11" moving the weight out further. A lot of the AEM brake kits weigh less than stock but cause the weight is out further they loose like 10hp on the dyno.

The Iron caliper weighs the same as the 240sx and the alum one weighs only 6.5lbs(3lbs less) so that's not an issue.
TurDz
08-16-2005, 02:11 AM
Original poster, what is the intention of the Z brakes? track? I think you should experiment with upgraded pads first....I know I did and I love the performance, and the benefits of keeping things stock. Pedal feel is awesome.

I like what the person above said, all four wheel STILL need to rotate. Think of putting 100 lb wheels in the front...with that example you can see how you will lose acceleration with the increased rotational mass.
OptionZero
08-16-2005, 04:27 PM
If it's rotating, it's rotating mass.

Tires matter for braking...and turning...and accelerating. Make sure you're running some decent compound tires.

Brake pads matter as well. Turdz has Porterfield R4 on stock s14 rotors; i have Porterfield R4-S on Q45 calipers, on an s14. His brakes felt like they had more bite (of course, when heated up, another factor).

so yes, on a street car that never sees the track, 3z's are superficial. On a track/street car, better tires and better pads probably still suffice. Only if u spend time on a track do you need 3z.

and if ur making huge, 500hp, skip the 3z and get some f50 brakes or some nutty stuff