Demon Performance Rotors for Road Courses

[DGatzby]

I remember the rotors, did those pads nearly melt?

 

[Finface]

When talking about rotor weight differences of about 7-8 pounds between these makes how much does that really affect performance? Four wheels equals 28-32 total car weight pounds that must be accelerated and decelerated - a relatively small weight difference that equals having about 5 gallons of gasoline in the car.

Is the discussion limited to this total gross weight difference of the car, or are their other forces in play?

 

[2ndgen]

A brief google search reveals that for a miata, it has weight : effective HP gain ratios of
- sprung: 7-10:1 (about 1HP effective gain by losing 7-10 lbs of sprung weight)
- unsprung: 1:6 (about 6HP effective gain by losing 1 lb of unsprung weight)

How that translates exactly to a heavy LX platform I'm not sure, but the ratio is what stands out. 1lb of unsprung weight is worth as much as 60+ lbs of sprung weight on the Miata. Probably a much lower ratio on the heavy LXs, but very likely still over 1:10 since a challenger doesn't weigh 6x a Miata.

 

[BULL]

A brief google search reveals that for a miata, it has weight : effective HP gain ratios of
- sprung: 7-10:1 (about 1HP effective gain by losing 7-10 lbs of sprung weight)
- unsprung: 1:6 (about 6HP effective gain by losing 1 lb of unsprung weight)

How that translates exactly to a heavy LX platform I'm not sure, but the ratio is what stands out. 1lb of unsprung weight is worth as much as 60+ lbs of sprung weight on the Miata. Probably a much lower ratio on the heavy LXs, but very likely still over 1:10 since a challenger doesn't weigh 6x a Miata.

Depending on where uou look, "Rotational mass" will have different multipliers, 1.5 to 3.0x compared to non-rotational mass.

In simplistic terms, not only do you have to accelerate the mass down the track, but you also have to accelerate it up rotationaly.

Some of the variables come about from the diameter differences, it's easier to spin a driveshaft than a brake/wheel/tire assy.

 

[SIXGUN]

That is a Dba T5 rotor. It earned it, I ran these hard for several track weekends on Sebring and other tracks. I think there were 3 cracks in the outer portion of that rotor, the the one on the other side had one crack. You can feel the crack when they get to the outside edge as you probably know. I think I was at Road Atlanta when it happened so ended up driving it home to FL.

These pic is one of the first Girodisc front rotors I ran, and although the grooves are gone, you can see the difference in the cooling "paws" on the Dba discs vs the curved cooling vanes on the Girodisc rotors. I think they cool better/more evenly so lessen the likelihood of cracking. Wore all the grooves off the rotors (there are still traces of portions of the grooves) but not cracks. Seems the Dba rotors are harder, so don't wear as much, but they end up cracking. Again, this is with me in my WBRE that weighs 4700+ lbs with me in it, and I drive it pretty hard on track. The rear original set of DP rotors I have on back have held up well, although those grooves are almost completely gone. They have held up well given they have outlasted two sets of front rotors and I am now on the third set of front rotors not counting the OE rotors that I originally replaced. The OE front rotors seem really soft, and are exoensive.
Either Girodisc, DP, or Dba front rotors are a great choice. I just installed a new set of Girodisc front rings and have a new set of Girodisc rings to go in the rear, although they are still working will even with the grooves gone. Long answer to a short question.
Interestingly, the OE front rotor hats are still black, whereas the DP hats are now purple from heat.

Sorry, it's unclear which rotor it is in the first picture (the cracked one).

 

[SIXGUN]

...and yes, on the autocross course and 3S at MOPARTY, hotlapping last year...the front Girodisc rotors got really hot, but were up to the challenge with no cracks. Same rotors as the rusty ones in the pics with no grooves. Drove them home and replaced soon after.

 

[Christian Dionne]

That is a Dba T5 rotor. It earned it, I ran these hard for several track weekends on Sebring and other tracks. I think there were 3 cracks in the outer portion of that rotor, the t
Either Girodisc, DP, or Dba front rotors are a great choice. I just installed a new set of Girodisc front rings and have a new set of Girodisc rings to go in the rear, although they are still working will even with the grooves gone. Long answer to a short question.
Interestingly, the OE front rotor hats are still black, whereas the DP hats are now purple from heat.

All of my Girodiscs on several of my cars have purple hats after a few sessions. I think it's the anodizing they use.

 

[DGatzby]

...and yes, on the autocross course and 3S at MOPARTY, hotlapping last year...the front Girodisc rotors got really hot, but were up to the challenge with no cracks. Same rotors as the rusty ones in the pics with no grooves. Drove them home and replaced soon after. View attachment 116690 View attachment 116691

Autocross? Okay how did you do?

 

[SIXGUN]

Oh, this year with year old PS4Ss? Terrible! I had no traction in the dry, then it rained and it was like I was on ice. Barely ran any laps as I was helpful. With those tires it was off a half second on the drag strip, so serious traction issues. Totally my fault!
It is a Grand Champion competition, which I won in the inaugural year in 2020. Next year, I tied for the win with Johnee Brown's 392 Chally autocross racecar and he had the tie-breaking better autocross score, so he won. Last year a borrowed, track prepped Viper with Yokohamas won (couldn't do anything with that), then three track prepped Vipers showed up, so that was that. Johnee Brown got on the podium with his racecar, so he drove it well. He has the car down to about 3300lbs so it is purpose built.

 

[GNBRETT]

Ur confused with sprung weight and unsprung weight. 30 lbs of sprung weight isnt that much. 30 lbs of rotating mass is about 250 lbs of dead weight removed.

30 lbs of rotating weight off ur wheels makes a HUGE difference bro..... HUGE!!!! I had this discussion with an NHRA dragster tech one day at the track. He was the head crew mechanic of this car going 280 mph. I asked him about the rotating mass and how it applies to dead weight and he told me it was 7-8x compared to non rotating mass.

That wasnt something I read on the internet that was right from his mouth! I said 7-8x? He replied yes 100%.

When talking about rotor weight differences of about 7-8 pounds between these makes how much does that really affect performance? Four wheels equals 28-32 total car weight pounds that must be accelerated and decelerated - a relatively small weight difference that equals having about 5 gallons of gasoline in the car.

Is the discussion limited to this total gross weight difference of the car, or are their other forces in play?

 

[BULL]

Well CDT rotors are set to take 60lbs off of a Challenger/Charger...

I'm going to dare claim 400-500lbs equivalent, but take it for what it's worth.