Tuning suspension for a noob (rear roll axis & antisquat)

[darkostoj]

Hey guys, I'm building my first racecar. Its a 1977 Rolls Royce with a Viper Drivetrain.

The rear suspension is an offset 3 link with an adjustable upper arm and adjustable watts link.

I am taking the car out in a couple weeks to get the suspension dialed in, and there is scarce info out there in regards to how to get the rear roll axis and anti squat dialed in.

Any body care to help out a noob?



Thanks!

[79T/Aman]

I assume by roll axis you mean rear roll center, roll axis is the relationship of the front RC to the rear RC, the first thing you will need to do is make sure you have the car at full weight in order to figure out the CG.
as for anti squat and roll axis there is no general pre-set to shoot for, those are things that will need to be adjusted to give the drive the feel that matches his driving, provides the fastest lap times and doesn't eat tires.

[jetmech442]

I'm heading to Blackhawk farms for my first track event this Saturday. I'm going in with my antisquat set to 100% as a baseline. I've been doing a lot of street driving and the 100% setting gets a good launch without locking the rear brakes on decel. granted, I've got EBC red stuff currently and the track day will have Wilwood BP-20 pads, so that may change-not sure. If I start to lock up the rears, I can drop the antiaquat to the 70% mark(next lowest setting). Not even sure I have enough experience or guts yet to be braking that hard repeatedly on the track, so we'll see I guess lol.

My Rear roll Center is centerline of my axle. That setting on my car gives me just a little understeer without throttle input. this is something I might change depending on how the car feels on track. I'm more focusing on learning the lines of the track, tire pressures...you know, all the newb stuff, but if a simple Watts change helps make the car more stable, then I might adjust in between sessions.

This is just my thought process, obviously don't have any track experience yet, so grain of salt and such.

BTW, I love your car! What an absolute beast!

[Chad-1stGen]

I'm heading to Blackhawk farms for my first track event this Saturday. I'm going in with my antisquat set to 100% as a baseline. I've been doing a lot of street driving and the 100% setting gets a good launch without locking the rear brakes on decel. granted, I've got EBC red stuff currently and the track day will have Wilwood BP-20 pads, so that may change-not sure. If I start to lock up the rears, I can drop the antiaquat to the 70% mark(next lowest setting). Not even sure I have enough experience or guts yet to be braking that hard repeatedly on the track, so we'll see I guess lol.

My Rear roll Center is centerline of my axle. That setting on my car gives me just a little understeer without throttle input. this is something I might change depending on how the car feels on track. I'm more focusing on learning the lines of the track, tire pressures...you know, all the newb stuff, but if a simple Watts change helps make the car more stable, then I might adjust in between sessions.

This is just my thought process, obviously don't have any track experience yet, so grain of salt and such.

BTW, I love your car! What an absolute beast!

Do you have power brakes?

[jetmech442]

Do you have power brakes?

Yeah, I have the standard a 12'' booster with CPP slotted rotors(11.x'') and D52 Calipers up front(wilwood factory repalcements), the rears are the GM metric stuff that comes in the standard disc brake conversion--nothing fancy--and the winter project might be upgrading brakes or adding AC, not sure yet.

Why do you ask? Is there something wrong in my setup? I'm all ears if so....

[Chad-1stGen]

Yeah, I have the standard a 12'' booster with CPP slotted rotors(11.x'') and D52 Calipers up front(wilwood factory repalcements), the rears are the GM metric stuff that comes in the standard disc brake conversion--nothing fancy--and the winter project might be upgrading brakes or adding AC, not sure yet.

Why do you ask? Is there something wrong in my setup? I'm all ears if so....

Without power brakes you might of not enjoyed the pedal effort required with BP-20's on the road course. With them you will be fine. I actually like BP-20's on autocross for the increased effort (harder to lock up with my manual brakes).

[jetmech442]

Just as a follow up for my suggestions above: hard on the brakes at the top of 4th(107mph) (turn1) nets some serious wheel hop...like serious. same story for turn 5 at the top of 3rd. I didn't want to change anything on my first track day so I left the antisquat at 100%-next time I head there it'll start at 70%. Now, mark has coached me several times that I need to be running an adjustable shock front/back...and I agree, it's just a budget issue right now, so I might be able to leave it at 100% and eliminate the hop with shock tuning. He also cautioned me prior to the event to be smooth on the brakes to prevent possible hop, but when your chasing down that 4th gen in front it sure is enticing to wait that extra 50 feet lol.

My rear roll center at axle height was dead on though. I wouldn't change a thing, the car cornered flat, didn't push or kick out on me at all, even at the end of the day. I know our roll axis will be different, but just wanted to follow up on my thoughts from above. Good luck man.