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Chassis rake

501
319
sfo
Is there any consensus for ideal chassis rake for non-aero stock S550 PP1 splitter cars? I measure at the lowest point on the rockers.
 
501
319
sfo
In principle yes. I do not think the pp1 splitter or wing for that matter do anything aero-wise. I wish scca would at least allow the swing from the higher model mustangs in touring. But somehow in my T2 class they let in the bmw m2 clubsport factory racecar compete and the porsche 99x gets a $10,000 wing. Who do I have to bribe to get parity for the mustang gt?
 
Is there any consensus for ideal chassis rake for non-aero stock S550 PP1 splitter cars? I measure at the lowest point on the rockers.
I wouldn't say there is a 100% agreed upon consensus, but any time I was in the wind tunnel and we either gave the car rake (lowered front end or raised the rear) or gave the splitter itself rake (lower at the front) the results were a gain in Df, and surprisingly almost no change in drag, or even a small reduction in drag. But these were on cars with a real splitter. I wouldn't consider a PP1 car a real splitter but I'd bet the trend in results would be similar but to a smaller degree.
 
Hesitant to chime in on aero, but here goes...

I have a 2017 PP1 car that I've been slowly converting to a track car from day 1. Mine is a base GT, and had no rear spoiler of any kind. I decided to wait until I was ready for a wing on the rear to do anything. So, I added an APR GTC200 wing early this year, and have left it set to the 0* position. To balance up front, I made my own splitter out of ABS sheets (to make up for the expensive APR wing!).

I purchased +5mm longer screws to mount directly below the PP1 front lip. I had watched AJ's video about the front spoiler being at 0*, so when I went to measure it, I was surprised to see that it was pointing UP by >2*. I had expected it to be near-level, so surprised to find that. I use a digital level to set to about 1* down (to make up for any error) for track weekends, but since this is putting some force on the splitter, I loosen and let it "rest" between track events.
 
82
50
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
I find that as I increase rake (by increasing rear ride height), it makes the car less stable in entry and it makes the weight in the tail feel very high. The rear seems to be more of a pendulum and it tends to lack the defined 'set' I prefer in longer duration corners. It does reduce understeer, but it does so in a way which is difficult to use.
 

JDee

Ancient Racer
1,301
1,181
Exp. Type
W2W Racing
Exp. Level
20+ Years
halfway between Mosport and Shannonville
Hesitant to chime in on aero, but here goes...

I have a 2017 PP1 car that I've been slowly converting to a track car from day 1. Mine is a base GT, and had no rear spoiler of any kind. I decided to wait until I was ready for a wing on the rear to do anything. So, I added an APR GTC200 wing early this year, and have left it set to the 0* position. To balance up front, I made my own splitter out of ABS sheets (to make up for the expensive APR wing!).

I purchased +5mm longer screws to mount directly below the PP1 front lip. I had watched AJ's video about the front spoiler being at 0*, so when I went to measure it, I was surprised to see that it was pointing UP by >2*. I had expected it to be near-level, so surprised to find that. I use a digital level to set to about 1* down (to make up for any error) for track weekends, but since this is putting some force on the splitter, I loosen and let it "rest" between track events.

Same car as I have, except mine's a '16. My car's biggest problem is push (understeer) which IMHO is better than a loose car. It's not horrible push, it's quite manageable. Adding any aero to the rear is going to make that understeer worse so I'm not interested in that. Plus there's the loss of speed on the straights from aero drag, and the track I run most is a very fast track. I like it where it is, very forgiving car to drive with no nasty habits so I'm loathe to start fooling around with aero and potentially upsetting what I think is a very well balanced chassis.
 
82
50
Exp. Type
Autocross
Exp. Level
20+ Years
So Cal
Same car as I have, except mine's a '16. My car's biggest problem is push (understeer) which IMHO is better than a loose car. It's not horrible push, it's quite manageable. Adding any aero to the rear is going to make that understeer worse so I'm not interested in that. Plus there's the loss of speed on the straights from aero drag, and the track I run most is a very fast track. I like it where it is, very forgiving car to drive with no nasty habits so I'm loathe to start fooling around with aero and potentially upsetting what I think is a very well balanced chassis.

I agree with your understeer assessment. I think you're right on. Think about where the aero might help you, though. It will only be active in higher speed corners. In first, second and the bottom of third gears, it's influence is small. You'll only really feel it in higher speed corners (4th and 5th gear) and in braking. Chances are good that a little more rear security in these areas will be appreciated. I promise you that whatever drag penalty you pay for downforce will *always* be worth it unless you've massively unbalanced the car. Straightline speed is the least important variable to optimize unless you're on a super-speedway.
 
JDee: Agree with your points about the car understeering, and seems Ford (and most mfrs) set them up that way on purpose. For me, I know I'm not constantly on the ragged edge, but after several years with no aero, I decided to add some to expand the "car's envelope" and give me even more confidence in the read-end of the car. Still on the learning curve, but I'd say that so far the balance feels the same.

TeeLew: Agree with your points as well, and the ability to go faster in higher-speed turns was what I was looking for. I know I'm not getting all the possible gains yet, but will keep working toward it!
 
3,803
3,745
I agree with your understeer assessment. I think you're right on. Think about where the aero might help you, though. It will only be active in higher speed corners. In first, second and the bottom of third gears, it's influence is small. You'll only really feel it in higher speed corners (4th and 5th gear) and in braking. Chances are good that a little more rear security in these areas will be appreciated. I promise you that whatever drag penalty you pay for downforce will *always* be worth it unless you've massively unbalanced the car. Straightline speed is the least important variable to optimize unless you're on a super-speedway.
Yeah.. sort of. There will always be a trade off of drag vs cornering ability. As an example, a car that is running less wing, may mph better than a car with more wing.. but, if the car with more wing angle comes off the corner faster, it may get down the straight quicker. Throw in rake, which can unmask the rear wing, but potentially makes the car seem "bigger" to the air traveling over it. We run into this dilemma all the time in Porsche cup, as the cars are basically identical. So we are always farting around with rake and wing angle to try and get the car to set, throw in some funky requirements from Michelin, and you'll know why I'm glad to be returning to GS next year.
 

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