Importance of Rake in setting suspension heights
#21
As others said, toe will change. But it's not hard to reset in your garage with a few boards and tape measures.
#22
As has been mentioned, there are a bunch of factors in play. My car does this too, but I can usually add more throttle or get back on earlier to come back to being neutral or oversteer (if I need it). Trying to find real consistency to compare small changes is incredibly difficult, as I'm sure you know
Also, since you mentioned numbers, I am 324mm / 318mm.
Penske DAs with 850lb / 600lb springs
Karcepts STR bars, one step off full hard up front, change the rear depending but I usually use the softest 3 pairs holes and this is all I really mess with at the track if I want the car to rotate more or less easily.
17x9 +45 w/ 255/40 square
DTC-60 stock rotors / HP+ Urge rotors rear
No aero
I have no idea where you live, but you're welcome to drive the car if we end up at the same event. Always good to compare notes.
Also, since you mentioned numbers, I am 324mm / 318mm.
Penske DAs with 850lb / 600lb springs
Karcepts STR bars, one step off full hard up front, change the rear depending but I usually use the softest 3 pairs holes and this is all I really mess with at the track if I want the car to rotate more or less easily.
17x9 +45 w/ 255/40 square
DTC-60 stock rotors / HP+ Urge rotors rear
No aero
I have no idea where you live, but you're welcome to drive the car if we end up at the same event. Always good to compare notes.
Some questions:
On suspension: Karcepts has different torsion tubes for their bars, which ones are you using. How did you modify to allow for more camber and how much camber are you running? Did you use lowering blocks (i.e. roll center adjusters) to get the additional camber? Which piston did you use in the Penske shocks (linear/linear, digressive/digressive, etc.)? Was any additional low speed bleed added? What are the reference points for you ride height measurement? Penske told me the 7500DA didn't have a lot of room for lowering.
On brakes; Are you using front brake ducts? Did you consider using the Girodisc or other two-piece floating front rotors, since the car now has 2-piece rear rotors?
On tires: Do the +45 rims rub the fenders? Why did you chose them over the +60s often used with 9" rims? Are you running under rules that limit your car to 9" rims or was there a different reason for not using wider rims and tires (e.g. a 265/35-18 or 275/35-18 on a 10" rim which would have about 1" more tread width)?
#23
While we're discussing ride heights, what is the consensus if it should be set with the driver (or equivalent weight) in the seat? I made some basic assumptions about where the driver's center of gravity would be relative to left/right and front/rear and it seems that for me (~180 lbs driving weight) that I add ~40 lbs more weight over the left rear wheel than the right (I'm assuming the left/right spit to be 1/3 to the right, 2/3 to the left) and the same front to rear. With 11kg/mm springs that would mean the left rear was compressed ~2 mm more than the right. Does this make much of a difference? My instincts say no, but curious if anyone has tried both approaches and can share if there were noticeable differences on the track.
#24
While we're discussing ride heights, what is the consensus if it should be set with the driver (or equivalent weight) in the seat? I made some basic assumptions about where the driver's center of gravity would be relative to left/right and front/rear and it seems that for me (~180 lbs driving weight) that I add ~40 lbs more weight over the left rear wheel than the right (I'm assuming the left/right spit to be 1/3 to the right, 2/3 to the left) and the same front to rear. With 11kg/mm springs that would mean the left rear was compressed ~2 mm more than the right. Does this make much of a difference? My instincts say no, but curious if anyone has tried both approaches and can share if there were noticeable differences on the track.
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DavidNJ (07-23-2018)
#25
To approximate the driver, I take the wheel weights with the driver in the car, then place dumbells in the driver's seat and the floor in front of the seat until the scales read the same.
Note that ride height and wheel weight are closely related. Making a ride height adjustment by itself will most likely put add wedge in the suspension.
Note that ride height and wheel weight are closely related. Making a ride height adjustment by itself will most likely put add wedge in the suspension.
#26
Great point that I hadn't thought about. I've been debating buying a set of scales vs. having a local race shop do a corner balance. I'm leaning towards the latter as I have my doubts that the stands I've created to do alignment in my garage are within 1 mm of each other in height. I leveled them with a long construction level but 1 mm (or even a bit more) is within the tolerance for reading the bubble over the width of the car. And with 11k springs, being 1 mm off means 22 lbs off - all else equal.
#27
Great point that I hadn't thought about. I've been debating buying a set of scales vs. having a local race shop do a corner balance. I'm leaning towards the latter as I have my doubts that the stands I've created to do alignment in my garage are within 1 mm of each other in height. I leveled them with a long construction level but 1 mm (or even a bit more) is within the tolerance for reading the bubble over the width of the car. And with 11k springs, being 1 mm off means 22 lbs off - all else equal.
With oval racing bias ply tires and stagger, scaling the car was a weekly event. With radial tires that may be less important, although tire wear may affect ride height and wedge.
Typically, ride was measured from the frame rail to the ground rather than a reference on the bodywork. In autocross, SCCA specifies the shock length as the ride height measurement.
This pictures shows a scale leveler attached to a platform, a raised stand that lets the tuner work under the car, two different hub stands that take the tire out of the picture giving a consistent reading and allowing more suspension access, and a stand with a roll-on, roll-off provision. There are also plates that let the stand slide to relieve preset. Not shown are a wide variety of ride height measurement tools that slide under the car to reach the frame rails.
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hybridb18
S2000 Brakes and Suspension
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08-05-2013 08:04 PM