Question

[Scarbs]

I was watching Tuner Vision this weekend. I know i shouldn't watch that stuff but i did. They put a big brake kit on a SRT Neon. There was a loss in horse power aftrer they did this. They also did a Cat Bac system and cold air.
They couldnt figuer it out why. Did some calling and there guys figuered that it was the brake rotor. Something about the larger Diamiter Rotor causeing a it. Has any one heard of this.

[II kings 9:20]

More rotational mass and more unsprung weight would make sense however + wheel/tire combos should have the same effect but you don't hear about that.

[todd tce]

Yup. All true. And much of it on the hush hush when buying wheels.

While rotor weight is part of it, it is also a bit hard to compare exacting numbers- so don't be fooled.

A stock rotor weighs 22lbs. ea
My kit replacements weigh 14.5lbs. ea
Add some hats however and the number get upward of 16.5lbs. ea

In the case of this vehicle the car will actually LOSE weight over the stock part. Now on your Honda....assume the stock rotor was of about 10.5" and was replaced with a giant 13" rotor. I promise you the total weight of the new part was a tick higher than the older one.

But.... more important than the total weight is the diameter of the rotor. It's rotational weight and more specific; the moment of inertia. Think the opposite of an aluminum flywheel and how it effects a vehicle- bit more hp and tq, but a faster rate of aceleration. Brakes to this too. Only in reverse.

Total weight or unsprung weight has no impact on this.

Luckily the parts on the market for the C are at or near stock. You'll be fine.

[james jefferson]

Originally Posted by Scarbrs

I was watching Tuner Vision this weekend. I know i shouldn't watch that stuff but i did. They put a big brake kit on a SRT Neon. There was a loss in horse power aftrer they did this. They also did a Cat Bac system and cold air.
They couldnt figuer it out why. Did some calling and there guys figuered that it was the brake rotor. Something about the larger Diamiter Rotor causeing a it. Has any one heard of this.

saw same show. the brake upgrade was lighter than the oem.

[II kings 9:20]

Originally Posted by james jefferson

saw same show. the brake upgrade was lighter than the oem.

Makes no sense to have lower HP with lower weight.

[todd tce]

If you mean that you don't understand why;

Most kit have a total weight redution to them. This has little impact on rotational weight which does rob power.

If I hand you a watermelon and you hold it at arms length you can do so while turning in a circle easy enough. Now if I put it on a stick that's five feet long... how long do you suppose you can turn in circles without becoming tired?

If you mean that you don't see the value in it; the value comes from the performance gains while in use as the trade off from what you give up. Suppose you lost 10hp. Under high speed or even acceleration you'd be giving up time. But under braking and REPEATED braking you'd make it back in spades over many stock brakes. Ten laps on a road course proves in a hurry that hp is not all that makes for a sprited drive.

* On the other hand... proof of the aftermarket weighing less on this car may well afford you some increase in HP! I'd be a fool to state the value of a BBK as "adds hp" but I'll wager $20 the numbers do go up slightly if we could measure close enough.

[Scarbs]

Yea thats right I forgot about the Lighter Rotors.
I know my 20 make me lose a little HP size wise but it i put a big brake kit there goes more. Ugh Math Is hard.

[james jefferson]

yes i understand, and the physics of it makes sense, the larger rotors cause an increase of centrifical force when spinning thereby requiring more hp to spin them. i agree that stopping power should be significamtly increased if on a track but i dont race mine. right now i think ill stay with stock brakes; if, however, i lived in a mountainous area might rethink that.

[DZeckhausen]

Originally Posted by james jefferson

saw same show. the brake upgrade was lighter than the oem.

But the distribution of weight on the Dodge Neon brake kit was different, since the rotors were larger in diameter and thicker than the stock rotors. The centers (hats) of the rotors were lightweight aluminum, which did drop the total weight over stock. But the polar moment of inertia for the new system was greater than stock.

Imagine you are a figure skater spinning in a circle. As you spread your arms out, you spin slower. As you pull your arms close to your body, you spin faster. In either case, your weight remained constant but the distribution of that weight changed - thus your polar moment of inertia changed.

As Todd correctly pointed out, the stock front rotors on the 300C are nearly as large as the aftermarket 355mm (14") brake kits from Brembo, StopTech, and TCE. So the end result is your polar moment of inertia won't change much, if at all and you won't notice a difference in handling due to any weird gyroscopic effects. Now if you were to install a brake kit with 380mm (15") rotors, you might have a different story. And a set of 22" wheels will have a much greater impact than even the 15" brake kit.

On a related note, I did notice a subtle improvement in ride and handling when I swapped the stock 300C wheels on my car to a set of Dodge Magnum RT wheels. The tires and dimensions of the Dodge wheels are identical. But the Magnum RT wheels are a few pounds lighter. Now I'm back to the 300C wheels because I have my winter tires installed on them. But I did like the difference. This may inspire me to buy a set of HRE wheels in 18" for next summer in order to shave some more weight.

[HaTaX]

Sounds like we have someone with a physics/engineering background in here. =)

Good info! And in my book, stopping faster is always better than going faster... No good going fast in a big car if it stops like a ship.