Mech33

Side question: how do you get *over* a 2x multiplier vs. straight weight difference of PCCBs vs the cast iron? Would love to see the math. At best I can see 2x if the weight was concentrated at the outer tire radius, and it's obviously much lower inertia than that since the weight is more concentrated towards the center of the wheel.

Brosef

thanks. still interested if there are any like for like comparisons

GT3

Petevb

You're quite correct, my mistake and thanks for that. I rushed through it, used radius where I should have used diameter and managed to overstate the kinetic energy from rotation by a factor of 4. Revised I get only a 25-30% increase in energy due to the rotation vs simply accelerating the same mass in a straight line. This means specing PCCBs is equivalent to removing 44 lb from the chassis according the the numbers I have (96 lbs for iron rotors, 56.2 for PCCB, small weight difference in the calipers and pads). So only 7 hp. Hopefully you get similar numbers...

drdonger

Petevb

Very impressive. Looks like that RS is running steel, so the equivalent of a 14 hp swing from the other way vs the previous race. Add in ~15 additional hp from lower losses through the transmission and within a gear you're up the equivalent of 30 hp- in this case apparently enough to keep it nearly even until drag begins to dominate, at which point the 3 begins to walk the RS. Also impressive shifting- the manual's only losing a foot or two with each flat shift.

fxz

Someone told it to Waxer?? A GT3 is a GT3
Henry Catchpole was absolutely rigbt

mac10

So what have we learned here ? After splitting hairs with 2 great cars, the new GT3 may be as fast as an RS(with steel brakes) in a strait line with all the appropriate variables as the video. Sounds to me like after all the back and forth the RS is still faster(in a strait line) assuming it has PCCB's, and faster yet in corners with the added downforce.

SCCAForums

Thanks guys, I posted a new thread, with a few more runs. Great cars indeed!

Best Regards,
Dave

fxz

RS is more stable at track at very high speed
otherwise useless
that' s why they have always built GT3 as well

signes

FWIW, the wing on the RS in that last roll race looks to be in max downforce setting.

Anybody have frontal area for both cars?

Petevb

2018 GT3 RS 2.14 M^2 x .36 cd = .77 cd x A
2018 GT3 2.036 M^2 x .33 cd = .672 cd x A

So the RS has 15% more drag.

Touring splits the difference:
2.36 M^2 x .35 cd = .713 cd x A, 6% more than the winged GT3.

SCCAForums

Both cars had rear wing in 'low downforce/as delivered' setting.

Best Regards,
Dave

drdonger

IPSA

What exactly is the point of this kind of roll race ?

The extra drag of the RS is very likely a bigger penalty than the extra 20hp. Parasitic drag is also a penalty for the pdk car.

Number of shifts in the manual is relevant as well and favors the pdk until the drag overcomes the hp difference.

If you want a drag race start from zero.

If you want a track race do that. The RS should win that assuming both well driven, although the difference may not be as big as some may think absent a mistake shifting/braking with the manual car which after enough laps will occur.

So I don't get the roll race comparison.

Happy to be educated .

Cheers