How do I get the fronts lower?

[Alpine003]

Holy cow! that's some crazy stuff right there. I like how you kept part of the front bumper to be legal. haha.

Since you seem to be more into racing, you should sell off those Euro Corners for extra cash for race parts.

[Mannix]

Heh, yeah, the bumper ends are back on - they have to be.  I am allowed to cut fenders, bumpers and hoods for tire clearance - at the time of that picture, the fenders had been trimmed, but not the bumper ends - had to take about 2" off.  

I have to have the bumpers on to be legal (in class, I can't say I care about street legality with that car - but the lights work, it has insurance & legal registration;), as well as the turn signals.  

So, they'll stay:).  I did not know they were cool - they were on the car when I got it.



Iain

[b318isp]

Even on the E30 H&R Race springs?  Most of the ones I've seen do have several dead coils at the bottom of the spring.

Both H&R springs that I have used up front weren't like this. Maybe more hard core race springs are - I'm not familiar with them.

A spring is simply a torsion bar in a coil; when the spring compresses, the wire actually twists.  There are two things that affect spring rate - length of the torsion bar and diameter of the wire.  

But there is also a bending force too.

Two things - negative camber does not kill tires, toe does.  I've run as much as 3.5 degrees on the street; my inside edges _absolutely_ wore faster than the outside edges, but by the time the insides were done, the rest of the tire was close behind.

I don't think you can say that camber doesn't eat tyres - but I agree that poor toe can also accelerate wear. When you see excessive inner (or outer) tyre wear, then the camber is not optimal for the type of driving being done. -3.5 degrees would be fine for track use, but the inner part of the tyres are taking a disproprtionate load most of the time while on street.  You also loose sensitivity around the steering centre which is not always ideal for the road. You can get very close to the legal limits on thread depth before the outer edges catch up too.

Secondly, MacPherson Strut suspensions _lose_ negative camber (gain positive camber) as soon as the control arm goes beyond parallel to the ground - if the control arm is pointed "up" to the wheel from the body, it has less negative camber than if it were parallel.

That depends. If the front is in squat then you will increase negative camber. It also depends on the roll angles you get, back to springs and ARBs again. The possible target is to have zero camber at maximum roll.

So, the difference is .76" shorter.  Not bad.  .38" difference in wheel gap (divide difference by two to figure out how much the car was lowered by the wheels).

Compared to a 205/55/15 it is 109mm shorter in circumferance or 6.3% out.

Using a shorter diameter wheel can be _very_ good for handling - it reduces gear ratio, center of gravity, etc.  

Agree on using smaller wheels for handling but gearing will be dictated by the tyre circumferance.

[Mannix]

That depends. If the front is in squat then you will increase negative camber. It also depends on the roll angles you get, back to springs and ARBs again. The possible target is to have zero camber at maximum roll.

No.  Geometrically, if the suspension compresses on a Mac strut car, and the control arms go past horizontal, it is losing negative camber.  No two ways about it.  The outer ball joint travels a circular path around the pivot point of the control arm, and all else being equal, the car will have the _most_ negative camber when the arm is perfectly parallel to the ground.  Anything beyond that, the bottom of the steering knuckle gets proportionally closer to the body of the car (it has to), which reduces negative camber.  The strut is fixed, there's no way to compensate at the top.

It is an inherent "flaw" in MacStrut cars - they have lousy camber curves.  Think about what happens when both front wheels are off the ground - it gets about 8 degrees positive camber.  

It is not as dramatic a change as, say, a swing axle, due to the pivot at the ball joint and the strut, but by default, a macstrut car simply loses negative once beyond parallel.  

Take a spring out, get a level/smartcamber gauge, start jacking and measuring - unfortunately, it is true.  

Double A-arm cars are a different story; they typically gain camber under bump, which is why so many Hondas have 5 degrees negative.  

Have the springs you've cut broken?  



Iain

[b318isp]

No.  Geometrically, if the suspension compresses on a Mac strut car, and the control arms go past horizontal, it is losing negative camber.  No two ways about it.  The outer ball joint travels a circular path around the pivot point of the control arm, and all else being equal, the car will have the _most_ negative camber when the arm is perfectly parallel to the ground.  Anything beyond that, the bottom of the steering knuckle gets proportionally closer to the body of the car (it has to), which reduces negative camber.  The strut is fixed, there's no way to compensate at the top.

Can't follow you with this one. I understand the balljoint moving in an arc, but I don't understand your connection to camber. Aaccept the point on the steering knuckle moving closer to the car reducing negative camber.

If we ignore the effects of roll of the car and steering angles for the meantime, starting from horizontal, as the control arm moves up the balljoint moves inwards. The strut compresses (and pivots slightly at the top) so the top of the tyre will have moved inward more than the bottom - so increasing negative camber.

If the arm could swing 90 degrees upwards, the tyre would be nearly parallel to the ground!

As the arm descends it continually increase positive camber - as you say, the wheels will have a very high positve camber when jacked off the ground.

Have a look at this : http://www.miracerros.com/mustang/t_animate_mps.gif

[Mannix]

The strut compresses (and pivots slightly at the top) so the top of the tyre will have moved inward more than the bottom - so increasing negative camber.

Yup.  It did not make sense to me either, until I took a spring off and jacked the wheel through the travel, as limited by the strut.  

Don't trust me, trust the camber gauge.  There might be *slight* (incremental) camber gain at 0-1degree beyond horizontal, but I never looked at it _THAT_ closely - as the wheel begins to truly move through the available travel, it loses measurable camber.  The strut can only pivot "so" much - the top of the wheel can only deflect inward (negative camber) a small amount, but the distance from the control arm pivot to the balljoint changes fairly quickly.  I think you might be forgetting that the lower balljoint is going to move with much less resistance than the bottom of the strut moving toward the centerline of the car - the strut is going to stay relatively fixed, the balljoint is going to pivot outward as the c-arm moves upward - but the overall distance will not change appreciably; the outer pivot point is fixed.

If I have the spring out of the 2002 anytime soon (far, far more likely than the 318), I'll measure camber loss & post it, in degrees per inch of wheel travel.  It is substantial.  Look at the picture of my car above - not much lean, right?    Look at tire deflection - the car is pretty fully loaded in that photograph.  

The car has ~4 degrees of negative camber at rest in that picture - the wheel looks pretty much vertical in that picture.  It also has a fair bit of caster, but the wheel is not turned very much.  It is losing a bit of camber through roll, and the rest is going away through the suspension.

We could theorize for days.  I'm not inclined to, I know what really happens when the c-arm goes past horizontal - it loses camber (the good kind).  


Iain (want another brainteaser?  If you have coilovers, and you want to redistribute weight to the rear of the car through ride height adjustment, would you raise or lower the rear ride height?)

[b318isp]

How would this explain why lowering a car increase negative camber? The more you lower, the more negative camber you get.

Also I have to think about your pivoting idea of the control arm as it is limited by the rear bushing. Perhaps the combination of all these things in an E30 gives rise to relatively controlled camber changes. The E36 has it slightly better again.

Your '02 seems to have a little bit of negative camber left!

I like these conversations as there is opportunity to learn something.

[Mannix]

How would this explain why lowering a car increase negative camber? The more you lower, the more negative camber you get.

The control arms are not parallel to the ground when stock - they're pointed down from the body to the wheel.  The more you lower, the more negative camber you get - until the control arm goes beyond parallel.

Also I have to think about your pivoting idea of the control arm as it is limited by the rear bushing. Perhaps the combination of all these things in an E30 gives rise to relatively controlled camber changes. The E36 has it slightly better again.

The two pivots effectively act as one, as far as the balljoint is concerned.  Depending on how the c-arm is attached to the car, the balljoint may move up and back, or up and forward as the c-arm rotates.  Not all Macstrut camber curves are the same, and the E30/36 may well be better than a Dodge Neon, but no matter how it is sliced, macstruts lose negative camber once beyond horizontal - they all do (barring  weird eccentric bushings which create an ellipsoid type curve - I've never seen that on a production car).  

Your '02 seems to have a little bit of negative camber left!

I like these conversations as there is opportunity to learn something.

I like them, too.  The 02 is set up just about right; still tweaking rear spring rates, but it is close.  Unfortunately, the rules prohibit me from fixing the rear camber issue, but stiff springs cure that problem:).



Iain

[b318isp]

I like them, too.  The 02 is set up just about right; still tweaking rear spring rates, but it is close.  Unfortunately, the rules prohibit me from fixing the rear camber issue, but stiff springs cure that problem:).

When set up right, the '02 seriously handles. On the tracks days over here, there is a fairly scruffy race prep'd  '02. The things hangs on like something you wouldn't believe (well I wouldn't :p). It has something like 127bhp but will lap faster than an E30 M3.

http://www.bmwcarclubireland.com/gallery/displayimage.php?album=random&cat=8&pos=-2567
http://www.bmwcarclubireland.com/gallery/displayimage.php?album=159&pos=31

Here's me not showing much negative camber!
http://www.bmwcarclubireland.com/gallery/displayimage.php?album=47&pos=191