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

:party0030:Hey guys.

Iv seem some people run -2.5 or even -3 camber.

Im confused that does "More Negative Camber == More Grip at Corner" correct?
"=="means "Always Equal to".

Iv read <How to Make your Car Handle> by Fred Puhn, and I remember that in the book he said more negative camber does not always equal to more grip. Factors like Speed and G-force affect the change of camber alot.

For example, I am thinking that -2 camber may not be as gripy as -1 camber at the corner when speed is only 30mph, and might be more gripy when at 50mph?

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.


But it does not make sense that some drift car run -3 front but -1 rear.

:cheers:

i'll write something intelligent later

but for now,

http://darklygaming.com/images/brainsmeet.png

Iv seem a lot of people said:"more negative camber front and less negative camber rear make you car oversteer."

So Im confused. I dont think more negative == more grip. And doubt that -3 front and-1 rear can make a low speed drift car.

There might be a range..

I don't really wanna get too into it...but "reducing understeer" is not always the same as "increasing oversteer". 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. 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.

I know a lot of people on this forum say this car oversteers like crazy, and I thought that way for awhile too, but really that's the driver. In reality, once I improved my driving, I found that at the limit the car had a strong tendency to understeer. Smoother input and throttle control will really help you make leaps and bounds in controlling the car.

As far as alignment, camber is just the tip of the iceberg, and I'm sure more knowledgeable folks will chime in here soon enough :)

GRIP is the end result of a number ofthings



The tire



It’s contact patch



Force acting on itvertically (more vertical load = more grip, this is vehicle weight and aero)



Force acting on itlaterally ( weight transfer during cornering, once you exceed the tire’sability to grip the surface laterally, you start to slide)



Force acting on ittorsionally (power delivery, too much power and you start to spin)





You have a wholebunch of things at your disposal to control and modifyi these parameters…



Adjust camber isjust one of them.



So it’s not that Xfront camber and Y camber will give me grip, and if I deviate from thatmagically start to slide. It’s simple one of many adjustments you could do.



A car going straightwill always grip so long as the road surface doesn’t change and that the forceacting down on the car is higher than lift.



A car going turningwill grip until it doesn’t. You can adjust that.



So knowing all this,can you make the right conclusions?

So I kinda get it. macpherson earn camber at the corner easier than multilink....Is that wat u mean?

For example, someone set the car to front -2, rear-1.5. At a corner the camber of outter wheels might change to around -1 and -0.8.

I actually like oversteer car. Lots of fun. And thats the reason why I bought an FR-S.

Super simple explaination:
Tires grip the road.

Tires grip best when they are vertical (0 camber)

When you turn your car, it leans to the outside which tilts the tire away from vertical (positive camber).

If you lean the tire inwards (negative camber) when going straight, it'll be closer to vertical when the body leans (positve camber cancels out the negative camber, i.e. -1 + 1 = 0)

The trick is figuring out how much negative camber you need to offset body roll and other sources of camber change. That's where all the complexity comes in.

Thank you. lol.
I knew there r many factor. I might try the camber first.

I think @Zach3794 is correct. Its all about camber curve.

If the front and rear have the same camber curve, I dont think for the front -2 rear -1 setting, the front will earn more grip before the rear go to positive.

If you read racecompengineering's sticky in this forum, it'll go into motion ratios and that explains why the macpherson's have a different camber curve than the multilink setup.

I think what you mean is that you like the rear end of the car to come out. As I said before the FR-S and BRZ both naturally understeer, but with driver input, yes, you can get the back to come out rather easily. The point is that engineering understeer into the car will make recovering from that slide much easier than a car whose design is to simply keep letting the back out at the limit.

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.

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.

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?

no

camber and camber control helps maximize the contact patch of the tire. However it's effect is very limited in normal applications.

what determines of whether you grip or not is WEIGHT transfer. This is dictated by the springs, car weight/dimensions and driver input.

camber is just a small part, and it most definitely doesn't correlate to grip in the linear fashion that you are thinkging about.

it's not like the front has more grip because it is -1.0 camber vs -0.5 in the rear. NOT AT ALL.

I c, thank you, hah.
:cheers:

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 :)

Ithink I forget the recover case...

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.:party0030:

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. :cheers:

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

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.

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.

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.

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.

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.


http://i1283.photobucket.com/albums/...ps35169005.jpg

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

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



http://i5.photobucket.com/albums/y16...herson_001.gif

This would be true only if the line of action of the strut were vertical. It's not, it is canted inward at ~12 degrees or so. The wheel will gain camber until the LCA is perpendicular to the line of action of the strut, about 12 degrees beyond LCA-horizontal.

Thanks guys, that makes a lot more sense to me. I was missing the perpendicular to the strut angle thing..


Hmm... Need to do some thinking.

ALso, here is a MacPherson design used in a Lotus racing car.

I can guarantee you that under compression these thigns gain an ample amount of camber :)

i'd say pre-aero days this would have been a fantastic design.

http://upload.wikimedia.org/wikipedi...suspension.jpg-

I only drive around on the street but even then I can appreciate a better setup suspension than stock. optimal static camber for maximum lateral grip level of the stock tires; more front roll stiffness from springs and less from sway bars will make steering response more linear and feel more supple. Having more bump travel in the rear will make taking bumpy corners so much more confidence inspiring. I've had quite a few instances on the street where the rear momentarily lost traction in the middle of a corner when hitting a bump, not to mention when the rear hits the bumpstops full-on, the chassis bounces off the bump stops and the whole car wiggles left to right.

there is so much I can improve on the stock setup that will make the car better without upsetting the balance and I only drive on the street... I see most bad setups start at very low ride height with not stiff enough spring rates or the use of too big sway bars...

Excellent gif. It took me a second to realize what I was looking at. I think the pause in the animation threw me off a little because it looks like I'm looking at the rebound effect rather than the compression effect.

Based on this animation, one can infer that macpherson struts gain negative camber under rebound when the LCA and strut are past the perpendicular point. Not really useful when you're cornering since you want the outside wheel to gain negative camber and not the inside wheel.

So all else equal, if you lower the front of the car, you'd want to increase spring rate to minimize the LCA and the strut from being perpendicular under compression.

Assuming @ZDan's suspension model is accurate, the front keeps gaining negative camber up until 4'' of compression. However, that doesn't take into account body roll, which changes the angle of the strut. That 4'' of bump travel is actually less when you take into account body roll, right?

Then you also have to take into account caster, which can change the amount of camber when cornering. More caster equals more negative camber under bump. I'm sure there are other variables as well.

Correct me if I'm wrong, but it appears you want the front to be as stiff as possible when tuning macpherson struts (ignoring all other factors). From a pure performance standpoint (ignoring cost, packaging, etc), double wishbone appears to be the superior design. I guess that's why Formula One still uses it.

no, if you lower the car, the LCA angle will change period, upping the spring rate will do nothing for that because it is a function of mechanical geometry.


F1 uses the design because it packages better

but otherwise, F1 suspension design laughs and farts and throws beer bottles in the general director of production vehicle suspension theory.

so you should NEVER draw any conclusions of F1 design and production cars. If you want to immitate a racing body.. watch what the rally guys do.

So by adding camber plates and adding negative camber, you're essentially changing the angle of the strut. This means you increased the negative camber bump travel to greater than 4", right? Let's assume zdan's model is accurate.

yes, but do it too much and wonky things start happening during steering

There's some debate about whether it's better to add camber at the topmounts (camber plates) or at the lower strut mounting point (camber bolts). Using plates pushed in gives you a higher roll center and can improve camber curve. However, it also increases the SAI which has a negative effect on camber when you turn the steering wheel.

- Andy

Wow, this thread was very informative and exactly what I needed!

So since FR-S engineers added less negative camber to the front, this helps break out of a slide easier? (harder to oversteer?)