E36 Turbo "Special" REAR Alignment Specs

[NY98M3]

Bumping this for advice...

For high speed stability for the rear, Im thinking -1.0* (degree) camber but what about the toe-in settings? Car sees mostly straight line pulls with an occasional off ramp, but mostly straight line high speed pulls.

Also, what about the fronts, stock specs?

Going tomorrow, looking for some advice.

[NY98M3]

^^^^^^

[beeasy]

Bumping this for advice...

For high speed stability for the rear, Im thinking -1.0* (degree) camber but what about the toe-in settings? Car sees mostly straight line pulls with an occasional off ramp, but mostly straight line high speed pulls.

Also, what about the fronts, stock specs?

Going tomorrow, looking for some advice.

Factory front settings should work fine. For the rears I'm happy with .5-1.0 camber .2-.3 total toe in

[NY98M3]

Went this morning to a local performance shop this morning that has the newest Hunter machine. They knew what they were doing and a huge plus was the machine in sunk into the floor making it easy for lowered cars to get on to it.

Front
camber (not adjustable) -1.6
toe-in .05

Rear
Camber -1.5 (could not get it any tighter, the Bimmerworld arms were fully retracted.)
Toe in .10 (.20 total toe

Car seems to be driving nice, pretty stable at high speeds.

[BadBoostedBmwM3]

Went this morning to a local performance shop this morning that has the newest Hunter machine. They knew what they were doing and a huge plus was the machine in sunk into the floor making it easy for lowered cars to get on to it. Front camber (not adjustable) -1.6 toe-in .05 Rear Camber -1.5 (could not get it any tighter, the Bimmerworld arms were fully retracted.) Toe in .10 (.20 total toe Car seems to be driving nice, pretty stable at high speeds.

Nice!

[cdmbmw]

Damn that car looks good

[beeasy]

His car is one of the cleanest M3 I've seen in person

[e36ALPINE]

I'm not sure how I've overlooked this car for so long. That is one sexy sexy machine you have there.

[vollosso]

Went and got aligned yesterday with some fresh tires.

My eyeball alignment after rebuilding the rear was 5/8* positive camber and 1/32" overall toe in.
We set the rear up for -1 camber and 1/32" toe overall.
In the front we went back with -1.5* camber and zero toe.

Leaving/Entering the shop 82*f good pavement i had noticeably less traction. TCK SA, solid bushings, 350f/400r springs. I have a lot of squat, i will probably today mark the suspension and move it out to zero camber in the rear and see what happens.

I think overall this setup, soft springs/solid bushings, results in very good traction but the camber is critical.

Also my rear toe was biased left(driver side) after the alignment the car tracks even more straight under power.

[someguy2800]

Went and got aligned yesterday with some fresh tires.

My eyeball alignment after rebuilding the rear was 5/8* positive camber and 1/32" overall toe in.
We set the rear up for -1 camber and 1/32" toe overall.
In the front we went back with -1.5* camber and zero toe.

Leaving/Entering the shop 82*f good pavement i had noticeably less traction. TCK SA, solid bushings, 350f/400r springs. I have a lot of squat, i will probably today mark the suspension and move it out to zero camber in the rear and see what happens.

I think overall this setup, soft springs/solid bushings, results in very good traction but the camber is critical.

Also my rear toe was biased left(driver side) after the alignment the car tracks even more straight under power.

The answer lies in anti squat. Take a careful look at the pathway that power is transferred through the suspension of an E36.

[dburt86]

The answer lies in anti squat. Take a careful look at the pathway that power is transferred through the suspension of an E36.

After having this conversation with SG, and realizing how the rear suspension truly moves in these cars, i put a stiffer spring in the car and it changed everything for the better.

Cliff notes from our conversation- when the car squats, its not pulling the car down to the ground, its actually pulling the wheel up towards the trunk.

- - - Updated - - -

Also, i found 1.5 degrees of positive camber and 0 toe worked best with my spring rates and car. ON the leave the tire would be 0 camber.

[vollosso]

Agreed on both accounts guys. What kinda rates/dampers did you end up with?


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[Jaze]

After having this conversation with SG, and realizing how the rear suspension truly moves in these cars, i put a stiffer spring in the car and it changed everything for the better.

Cliff notes from our conversation- when the car squats, its not pulling the car down to the ground, its actually pulling the wheel up towards the trunk.

- - - Updated - - -

I have said this since 2011, this whole forum (Bf.c) and a hand full of people in this sub forum told me I was wrong. Some went as far to call me incompetent for it. There is more fine tuning besides just raising the spring rate to create maximum grip but raising rates is a good chunk of it. Glad to see this catching on, finally.

My whole business is literally built on this philosophy, and it has been good to me. I like to think most of my customers are blown away by our suspension, and never knew it could be what it is...considering everything they have heard "online" about what "works" will contradict what I am recommending.

[dburt86]

It was like a light bulb moment when i SG explained it to me. The problem you run into very quickly is getting a damper that can support those kind of rates (thats where Jaze comes in)

And through in the fact that most of you guys are stick shift, good luck lol.

[Robocop]

The answer lies in anti squat. Take a careful look at the pathway that power is transferred through the suspension of an E36.

i have an e30 so this might be different but don't you want the car to squat hard to keep max weight on the tires?

[someguy2800]

i have an e30 so this might be different but don't you want the car to squat hard to keep max weight on the tires?

nopety nope nope. I'll explain later

[MikeE36]

I started a thread regarding rear grip in the drifting section, but I think it is applicable here. I have been doing my own testing trying to increase my rear grip, and although I am drifting and not drag racing, the concepts are very similar to drag racing. I have recently learned how critical anti-squat is. I'll copy some text over from my other thread. I raised the rear of my car over 1" and the grip increased SUBSTANTIALLY with no other changes.

"I've been doing a lot of reading and learning lately - huge thanks to Chelsea for sharing a lot of his knowledge on the subject of making 36/46 rear grip. I have been searching for more rear grip for a long time now and have learned a few things. I would like for this thread to become a knowledge base so those that know more than me about rear suspension geometry can teach me things too.

Essentially I've been approaching the rear end incorrectly - I've always thought obvious rear squat = increased rear grip. That is not true at all. This introduces the concept of anti-squat, which is essentially a ratio of the total load transfer to the rear from acceleration that goes directly into the suspension linkage and bushings, rather than the spring/shock compression. 100% anti-squat means on acceleration, the rear does not squat at all. It will stay perfectly level, and the entire load transfer F-R on acceleration will be taken directly by the suspension linkage, pushing the tire harder into the pavement than with less anti-squat.

From what I understand, forces used to compress the rear suspension on acceleration are essentially "wasted" in doing so, as they could be doing a more effective job of pushing the tire into the pavement. That all sounds great, but how do we increase anti-squat?

-Raise RTAB front pocket mounts
-Raise ride height of the car
-Adjustable trailing arms that are not commonly available and would be custom race parts

Now, remembering Chelsea's E46... that thing was a monster truck. Really tall ride height, tons of anti-squat. Also if you watch old videos of him accelerating on the run up, there was essentially no rear squat. The front end would rise and the rear would stay where it was. Supposedly this is the key to everything in the back.

Now I had a higher ride height before with my old 16k rear springs. My 5" 10k springs are pretty soft and the car is very low with no adjusters in it or anything. I'm going to try raising the car substantially for Lonestar Bash next week and report if the grip levels change dramatically. If you guys have any input on this subject, I'd love to hear it. Studying drag racing suspension design, anti-squat is a huge deal and finely tuned for a perfect launch.

Let's also see some ride height numbers if you guys have access to your cars to measure:

Front: jack point with no jack pad to ground
Rear: jack point with no jack pad to ground

I'll post mine tomorrow and we can compare heights for the sake of learning more."

Previously I was at 5.25" front and rear, now I'm at 5.75"/6.25" and the car is so much faster. It is planting the tire harder, the front end is lifting on acceleration and the rear is not squatting as much.



As you can see, if the trailing arm mounting point is higher, or at least higher relative to the base of the tire, you will have more anti-squat and press the tire into the ground harder via geometry alone.

Mike

[chikinhed]

When IRS cars squat the wheel alignment changes from good to bad and traction is lost. That's why high spring rates are preferred. As noted above, for drag racing, you may want the camber to be on the positive side just so when you launch the camber will be at the optimum of zero degrees. This of course will make your car totally suck for anything other than drag racing in a straight line.


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[BadBoostedBmwM3]

Multiplex found that out years ago with his c4 swap. ^^

[Robocop]

makes sense.
i guess the extra weight on the wheels when the car squats doesn't really matter.

my shit squats hardcore with like 280lb springs always thought that was a good thing.

[someguy2800]

There is more to it than just alignment changes but that is a big consideration. I will explain my thoughts on suspension geometry to go fast and not die when I have some time tomorrow.

[someguy2800]

I'm up with a sick kid so here is how to go fast and not die while doing it 101

We have all seen lots of videos of various high power bmw's where the rear of the car squats like crazy under acceleration and gets all squirly and burns the tires going 120. Like this

https://youtu.be/1LRJ83ylRec?t=2m15s

or this

https://youtu.be/frHsIOxmlpA?t=37s (don't mean to pick on donovan, this is before he got the car sorted out)

Now like was said above an IRS car is desgined to gain camber as the suspension compresses. This is so that during cornering the outside tire leans into the turn to maintain an even tire contact patch. The problem is when it does this during acceleration the tires gain camber and the tires loose pressure on the outside of the tread, and the toe of the rear suspension changes which makes the rear of the car try to steer itself.

So why does the car squat? There is actually alot more to this than meets the eye. The first thing people think is that because the car is accelerating so hard its transferring weight to the back tires and compressing the springs. This is partially true, but is not the major factor in what is causing the rear springs to compress. Think about it this way, weight transfers forward just the same as it does backward. When you hit the brakes on your car it decelerates at a way higher rate than it accelerates under power. If the car was squatting due to weight transfer alone wouldn't it bottom out the front suspension under heavy braking? Certainly the front end dips under braking but not by all that much. The reason is because the center of gravity in an E36 or an E30 is only a few inches above the height of the spindles of the car, so they there is some weight transferred from the G forces of acceleration, but not all that much.

The main reason the suspension compresses is due to the geometry of the rear suspension. Specifically anti squat. Anti squat is the tendency of the suspension to either push up on, or pull down on the car under acceleration forces. Positive antisquat mean the rear suspension pushes up on the body of the car under acceleration. Negative antisquat mean the suspension pulls down on the body of the car under acceleration. Now when looking up info on anti squat you will see a lot of info about how antiquat works in a solid rear axle car. You can forget most of that because the force is applied totally differenty in an IRS car. In an solid rear axle car the differential is allowed to rotate around the suspension points and as such the torque reactive forces can apply leverage through the rear suspension to push the rear tires into the ground. An IRS car cannot do this because the differential is rigidly mounted to the chassis. As such the power going through the suspension follows a different pathway to push the car forward.

First lets think about how the forces from the turning driveshaft are transfered through the car. Imagine you took the differential out of your car and sat underneath the car looking out toward the drivers side tire. Now you plug the axle shaft into a big cordless drill that you are holding. When you push the trigger the drill is going to try to spin in your hand right? Specifically the bottom of the drill is going to try to rotate toward the front of the car. Same thing happens to the diff. When you apply torque to the diff it will try to push the front of the diff up and the rear of the diff down. Since the diff is solidly mounted to the chassis its trying to raise the front of the car up using the whole car as a big lever. Imagine the tires of the car are sitting on scales. As you apply more force to the diff trying to rotate the car the scales in the front are going to read less since we are pushing the front of the car up. The weight must go somewhere so the scales on the rear of the car will read higher by the same amount. This is weight transfer through reactive torque.

Next lets look at what happens to the tire. As we first start to apply torque to the tire the rear suspension is basically sitting slack on the springs. As we apply torque to the tire the tire is going to want to roll forward, but the hub is held in place by the trailing arm. Now being that this is an IRS car, all of the torque reactive torque of the tire is absorbed by the diff. Since the no part of the suspension is connected in any way to the rotating part of the tire nothing in the suspension has any torque or leverage applied to it. The only thing the suspension has to deal with is the hub of the tire pushing forward parallel to the ground. Now imagine you took the tire, the brakes, the rear spring and the rear shock off your car so that the trailing arm was free to swing up and down at will. Now you grab the rear hub with your hand and shove it forward. The force of your push goes through the trailing arm to the front trailing arm mounting point and pushes the car forward.

But what would happen if the trailing arm was not parallel to the direction you were pushing? Say for example if the trailing arm was at a downward angle with the front mount lower than the hub? The trailing arm is going to swing up when you push forward on it. This is called negative anti squat. The more force you push forward on the hub, the more force is trying to pivot the trailing arm up




Now if the rear trailing arm mount is above the hub, the trailing arm is going to want to swing down when you push forward on it. This is called positive anti squat.




If the rear trailing arm mount is directly inline with the hub the trailing arm will not push up or down, it will just push the car forward. This would be neutral anti squat.




Now here is the thing, an E36 from the factory has the front trailing arm mount close to neutral, but when you accelerate the torque reaction of the diff wants to raise the front of the car and compress the rear springs. Once the car starts accelerating the center of gravity of the car transfers some weight to the rear and compresses the springs. Now the rear trailing arm mount is well below the rear hubs so we are in a negative anti squat situation. Now the force of the tires pushing forward against the road is actually pivoting the trailing arm up. So it is not the power of the car pushing the rear end down. Its actually the suspension pulling the body of the car down!

So why is this a bad thing? Well imagine you are standing on a bathroom scale and holding a 50 lb weight at chest height. If you drop the weight down to your knees the scale is going to momentarily read lower while the weight is dropping and then level out again when the weight stops moving. Likewise if you raise the weight above your head the scale will read heavier while the wieght is being raised.

Same thing happens to the car. When the suspension is pulling the body of the car down its actually lifting the rear tires up off the pavement at the same time that we need the traction the most. Once the suspension stops moving and the car is fully squatted out the force on the tires will go back to normal, but by that time your already turning tire into smoke. Now add to that the fact that your rear suspension was designed to change the camber and toe while the suspension is compressing and suddenly you now have two rear tires being pulled up away from the ground and putting all there pressure on the inside of the tread, and trying to steer themselves. Worse yet the effect is the worst at just the worst time, on the initial hit after releasing the clutch on a launch or gear change, just when you need it the most.

Now if you want to accelerate a car efficiently you need to find the right balance between using the energy coming from the motor to push the rear tires into the ground, and pushing the car forward. I'm going to steal an analogy I read from somewhere back when I was planning out the suspension in my car.

Imagine you are trying to push a fridge across a floor. When you push on the fridge the force is being transfered from the soles of your feet to wherever you push on the fridge. If you grab the fridge by the top and push your are wasting most of your energy lifting the fridge up. You will transfer alot of the weight of the fridge to the soles of your feet but the fridge will not slide across the floor much and will probably just fall over. If you push right on the bottom of the fridge you will not apply any force to the soles of your shoes and you will just slide backwards and lose traction. But if you push on the fridge in just the right spot you will apply enough force to your shoes to keep traction, and the fridge will slide across the floor easily. Its actually pretty easy to predict the correct location to push. You just need to draw a line from the center of gravity of the fridge to the soles of your feet and push where that line intersects the side of the fridge.




Here are two slow motions I took of my car launching. Pay special attention to the height of the rear fender compared to the top of the tire. Keep in mind I have a 4 link suspension that allows me to put whatever properties I want into it.

This first one is early last summer on my drag radials. A drag radial needs to dead hook to work so I found I needed to hit the tires really hard and plant them into the track by putting a lot of anti squat in it. Notices how violently the whole car raises on the launch. And even with 100% of the weight on the rear the back of the car is still higher than when sitting still. Now the caveat, because I'm using so much energy to raise the car in order to plant the rear tires, the front tires don't come off the ground till the car settles and its 20 feet out

https://youtu.be/AYzj3_MJ_Qc?t=2m59s

This video is the second run after switching to a bias ply slick. This is on a no prep day. A bias ply slick will tolerate a lot more wheel slip than a radial will and so I didn't need to plant it quite so hard, so I actually reduced the amount of anti squat in the rear. Now you can see when the car hits the car is not raising up anymore but its rotating the whole car around the center of gravity. Now because I'm not using so much energy to lift the back of the car up it picks the front tires up almost instantly and puts 100% of the availible weight on the back. As the car moves out and the clutch is starting to lock up the reactive torque going through the 4 link extends the rear suspension applying more force to the rear tires to keep it from breaking loose as the power is rolled in.

https://youtu.be/JLbHWU7bYE0?t=44s

Now you may think thats fine and great for a drag car but I don't do that. Well every time you roll into the power this same thing IS happening, its just more dramatic when launching the car. If the geometry is wrong for the launch it will be wrong anytime you roll into the throttle at any speed and on every gear change.

Okay you say but my car doesn't have a 4 link and I can't move the rear trailing arm mount so what am I to do about it? Well there isn't much you can do about anti squat other than that you need the front trailing arm mount to be up off the ground as much as tolerable by raising the rear of the car, and you need to keep it as high as possible under acceleration. Remember that the geometry gets worse as worse as the rear compresses, so if you allow it to squat on the hit the problem just gets worse. This means you need a relatively stiff rear spring and a shock that can control that stiff spring. Because of my solid axle I can use the reactive torque of the diff to apply leverage to the rear suspension to create anti squat, so I only need to run a 125 lb springs in my car. You will often hear drag racers talk of using as soft a rear spring as possible. The reason for this is it allows the shocks to work better and allows you to use the inertia of the car to push against to gain traction. This does not apply to an IRS car at all. On an IRS car with a non adjustable suspension geometry you have to rely on the springs and the shocks alone to control the squatting and keep your alignment.

As far as the actual alignment numbers I can't help much there but keep in mind everything in the back of the car is bending and deflecting under power so you may need to keep this in mind and preload a bit for it. You will never get positive anti squat in an E36 so you may need to start with positive camber like Dburt said so that you end up with neutral camber one the suspension loads up. Same thing with the toe. Under acceleration the trailing arms will be pulling on the lower control arms and because the trailing arms are a U shape they are going to bend somewhat under power. Add to that deflecting bushings and sheet metal and the rear end is going to toe in under power. You may be best off starting with 0 toe or even very slightly positive toe in the back to keep the rear from trying to steer.

Okay so that go straight fast and not die 101. I'll let chikinhead or Juggernaught write go fast and turn and not die 101.

[TheJuggernaut]

You can also get dampers with separate low and high speed compression. In the road racing world, low speed compression is known as the tire temperature knob for the same kind of reasons you describe above. I'm not a drag racer but I imagine if you dial up some low speed compression it could go a long way to getting you traction while leaving the car compliant over bumps.

[Butters Stoch]

Well then, I guess my simple "put stiffer springs in and have people hang on the bumper " while setting up the rear is wrong.

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[dburt86]

thats not wrong at all, its essentially what you need to do.