Question About Negative Camber: More Negative Camber == More Grip at Corner?

[Zach3794]

Agreed with 7thgear entirely. Suspension tuning really is a black art.

You'll see lots of guys on the forums here going to crazy lengths to get precision handling; high spring rates, sway bars, crazy alignment settings. The reality is, these guys are track guys. They race on a frequent basis, whether competitively or not, and their cars are set up as such.

It sounds like you're just a normal guy, looking to have fun with his FR-S, like most of us out there. And honestly, the car is really well set up for this from the factory. Your best bet may be to enjoy the car thoroughly for the time being, and perhaps then start with a mild performance alignment to extract a bit more out of it when you're ready

[Figo]

Ithink I forget the recover case...

Originally Posted by Zach3794

The front and rear do NOT share the same camber curves; they're completely different suspension types.

Like Draco said, the whole point, regardless of your intentions with the car, is the maximize the contact patch of the tire in the corner with your camber adjustment. It is naturally different between front and rear, and different between drivers even because of their tendencies.

The point is that the general rule of thumb on this car is that more negative camber in the front will give you large improvements in cornering grip. Remember, even drift cars have extreme levels of grip, they would never be able to recover otherwise.

[Figo]

Originally Posted by Draco-REX

BTW, How to make your car handle, and Tune to Win by Carroll Smith are both excellent reads, if a little dated (ignore the aerodynamics chapters). They both cover roughly the same material, but with two different perspectives. I found reading both gave me an even better understanding than if I had just read one.

I actually hav both, hah. But it seems like How to Make Your Car Handle has more inset pictures in it. So I read that, hah.

[Zach3794]

Originally Posted by Figo

Ithink I forget the recover case...

What do you mean by that? I was trying to say that drift cars need crazy levels of grip to maintain control of the car at all times. Someone more into the drift crowd please chime in if I'm wrong but I don't think those cars are ever set up to oversteer at all. It's all initiated by the driver. They give those cars crazy front end grip so they can always get the cars pointed back in the right direction more easily.

Again, I don't know drift cars at all, and I'm probably digging myself a hole here :P

[Figo]

Originally Posted by Zach3794

What do you mean by that? I was trying to say that drift cars need crazy levels of grip to maintain control of the car at all times. Someone more into the drift crowd please chime in if I'm wrong but I don't think those cars are ever set up to oversteer at all. It's all initiated by the driver. They give those cars crazy front end grip so they can always get the cars pointed back in the right direction more easily.

Again, I don't know drift cars at all, and I'm probably digging myself a hole here :P

I meant u r correct. Drift car need some grip to recover.

[mav1178]

Originally Posted by Figo

So If i would like to build a car that can easily slide at low speed like 20mph, but grip at high speed like 50mph, I should run more negative camber at rear right? May be -1.5 front and -2 rear instead of -2 front and -1.5 rear.

You should seek the advise of a good alignment shop that specializes in suspension/alignment settings for track cars (or aggressive street use).

Unless you know what you are talking about, the only real way to benefit from alignment settings is to have someone set the car up according to how you drive. What works for others may or may not work for you, because some like to have a twitchy setup (see: BRZ guys trying to make their cars "slide easier" like a FRS), while others may prefer a bit more understeer at initial turn-in (myself).

When I set up my car previously for drift, I used a very reputable alignment shop in Los Angeles (West End Alignment), and asked Darin to set the car up for whatever road course I was going to run. It's not the extreme angle stuff others run, but it worked great and handling was never an issue for me.

Bottom line: don't figure out alignment settings on your own (or even with advice of others) if you don't know what changes in toe in/out, positive/negative caster, or positive/negative camber mean for the driver at turn in, mid-corner, turn exit, throttle, braking, etc etc.

Just leave the settings to someone that has experience setting up FR cars, and leave the driving to you to figure out.

-alex

[TheRipler]

IANASG: I am not a suspension guru

That said, even the suspension gurus will tell you, it's much easier to make a car handle worse than it is to make it better. This car is very tossable from the factory, even the "more" understeery BRZ.

Before you spend money on suspension changes (or even tires), see if there is some kind of Law Enforcement Driving School near you that will allow civilians to take classes. There used to be one in East TX (not sure if still there) that taught all the low/high speed low/high traction evasive/pursuit driving. It covered skid correction, but first you had to learn how to get there. Sounds like that would be perfect for you.

[Draco-REX]

Originally Posted by Figo

I knew wat u said.

But say if we set -2 front and -1 rear camber. At low speed, the camber might changed to -1.5 and -0.8, the rear wheels still have more grip.

Actually, the rear wheel will always got more grip until they go to positive camber.

so for a more negative front camber drift car, they always suppose to make rear camber go to positive at every corner?

Now we're getting into those messy details.

Fow what actually happens in a corner, you have to take the weight distribution, weight transfer, camber curves, and other things into account.

If we step up one level of simplification with our cars:
The front gets more negative camber because there are more things trying to push it positive. There's more weight up front, the steering angle makes it go positive, and if you're lowered without roll-center adjusters the suspension compressing adds more positive camber.

The rear is designed to gain *negative* camber as the suspension compresses, so that's helping you counteract the body roll. And the rear doesn't have to deal with steering angle either.

Also, you have to take into account that while we're talking negative camber like -3 degrees, at the limit the body is rolling MORE than that. You're still seeing positive camber even after all the negative camber we're putting on the car. So once you see more body roll than the rear can compensate for, the front has more grip. The reason why you don't see MASSIVE amounts of negative camber on anything short of a dedicated race car is because you lose straight-line grip which hurts braking and acceleration.

[Draco-REX]

Originally Posted by TheRipler

IANASG: I am not a suspension guru

That said, even the suspension gurus will tell you, it's much easier to make a car handle worse than it is to make it better. This car is very tossable from the factory, even the "more" understeery BRZ.

Before you spend money on suspension changes (or even tires), see if there is some kind of Law Enforcement Driving School near you that will allow civilians to take classes. There used to be one in East TX (not sure if still there) that taught all the low/high speed low/high traction evasive/pursuit driving. It covered skid correction, but first you had to learn how to get there. Sounds like that would be perfect for you.

SCCA Regions will also offer similar courses. Really though, go to an AutoX! There is nothing better than AutoX to teach you how your car behaves at the limit.

[TheRipler]

Originally Posted by Draco-REX

SCCA Regions will also offer similar courses. Really though, go to an AutoX! There is nothing better than AutoX to teach you how your car behaves at the limit.

Also a good idea. Auto-X is cheaper, I forget about it.

I just thought about the LE training stuff first because you get wet courses, and are encouraged to learn general hooliganism. Sounds like that's what the OP is interested in.

[ZDan]

Originally Posted by Zach3794

The front of these cars utilize a macpherson suspension, and as such, their camber curve sucks. They actually tend to gain positive camber under compression.

You have to go a long way into bump before you stop gaining negative camber. So far that the LCA becomes perpendicular to the line of action of the strut.

That's why the front needs a lot more negative camber than the rear. The rear, being a multilink design, gains negative camber rather easily, and should have less than the front.

Other FR cars with double wishbone front suspensions have optimal setups with more front camber, it is the norm for FR cars, as roll stiffness is biased to the front to allow the rears to get better drive traction on corner exit. Struts may need a little more static camber, but not necessarily a tremendous amount more.

Model I made of the FR-S front suspension (from link to geometry I found on this site, accuracy not validated, but not too dissimilar from my 240Z strut models) has it gaining negative camber at the rate of 0.6 degrees per inch of bump travel from static. At 3" of bump travel, it's still gaining 0.3 degrees per inch of travel. Camber gain doesn't stop until 4" of bump, at which point it's gained 1.45 degrees.

To the OP, at the camber levels you're talking about (-1.5/-2), more is going to pretty much be better for ultimate lateral grip, up to something on the order of 3 degrees.

Really, anything in the ~2-2.5 degree range is going to be OK for a street/track/autoX compromise setup.

[Draco-REX]

Originally Posted by ZDan

You have to go a long way into bump before you stop gaining negative camber. So far that the LCA becomes perpendicular to the line of action of the strut.

Other FR cars with double wishbone front suspensions have optimal setups with more front camber, it is the norm for FR cars, as roll stiffness is biased to the front to allow the rears to get better drive traction on corner exit. Struts may need a little more static camber, but not necessarily a tremendous amount more.

Model I made of the FR-S front suspension (from link to geometry I found on this site, accuracy not validated, but not too dissimilar from my 240Z strut models) has it gaining negative camber at the rate of 0.6 degrees per inch of bump travel from static. At 3" of bump travel, it's still gaining 0.3 degrees per inch of travel. Camber gain doesn't stop until 4" of bump, at which point it's gained 1.45 degrees.

To the OP, at the camber levels you're talking about (-1.5/-2), more is going to pretty much be better for ultimate lateral grip, up to something on the order of 3 degrees.

Really, anything in the ~2-2.5 degree range is going to be OK for a street/track/autoX compromise setup.

I'm having trouble picturing how a MacPherson strut design can be gaining Negative camber after the LCA passes horizontal. Once above horizontal, the LCA is effectively shorter so it should be pulling the strut inwards, tilting it towards positive. And as the strut shortens, this should increase in rate.

[Dimman]

Originally Posted by Draco-REX

I'm having trouble picturing how a MacPherson strut design can be gaining Negative camber after the LCA passes horizontal. Once above horizontal, the LCA is effectively shorter so it should be pulling the strut inwards, tilting it towards positive. And as the strut shortens, this should increase in rate.

I drew this a while back while ZDan was helping to explain why a MacStrut isn't exactly a 1:1 motion ratio, but it also shows camber effects.




The discussion is in the 'Ask RCE and CSG Mike suspension question tag-team' thread.

[7thgear]

Originally Posted by Draco-REX

I'm having trouble picturing how a MacPherson strut design can be gaining Negative camber after the LCA passes horizontal. Once above horizontal, the LCA is effectively shorter so it should be pulling the strut inwards, tilting it towards positive. And as the strut shortens, this should increase in rate.

here ya go... a buddy of mine made this a long time ago.