Proper alignment specs with new suspension set up

[dcaron9999]

Recently installed Swift Spec-R springs, Bilstein B8 dampers, and fresh Dunlop Direzza ZII Starspec tires a couple of weeks ago. Got the car aligned with -3.2* camber and 0 toe up front, and -1.8* camber with 3/32" toe in. I love the handling, and I shaved a few seconds off my best track lap times.

Last week, I had rear adjustable toe arms (with hard rubber bushings), custom made camber plate spacers to eliminate 20 mm rake I had, and got the car re-alignbed with following specs: -3.2* and 0 toe up front, and -2.2* with 1/8" toe in.

The rear end is definitely stiffer with the toe arms. But an odd behavior has developped at highway speeds and when braking hard at the track. The rear end seems to slowly wander or sway in a weird manner.

Perhaps my new alignment specs is not appropriate for my new suspension set up. Now that the car leans much less during high speed turns, and rear toe is now stable during hard accelerations, Im wondering if I should tone down my camber in the front and the rear, and maybe reduce my rear toe as well?

Perhaps something like -2.8* camber or less in the front, and -1.8* camber with a little bit less toe in the rear would help ...

Open to suggestions from owners with lots of track experience ...

Thanks.

[_Ryan_]

Are the arms decent? Everything torqued to spec? Doesn't sound like an alignment issue to me, assuming it's correct.

Also, How did you manage -3.2 up front? :O

[dcaron9999]

Originally Posted by _Ryan_

Are the arms decent? Everything torqued to spec?

Yes. Toe arms are well designed and solid. It made the alignment simpler to do.

I need more seat time to understand how and when the unsettling movement occurs. I may have described my issue incorrectly. The rear sway occurs at highway speeds on uneven pavement, and when braking hard on the track. I have become use to that in the front with high amount of camber, but not in the rear.

Originally Posted by _Ryan_

Doesn't sound like an alignment issue to me, assuming it's correct. Also, How did you manage -3.2 up front? :O

GC Camber plates + M3 FCA's, as listed in my signature

[_Ryan_]

Originally Posted by dcaron9999

Yes. Toe arms are well designed and solid. It made the alignment simpler to do.

I need more seat time to understand how and when the unsettling movement occurs. I may have described my issue incorrectly. The rear sway occurs at highway speeds on uneven pavement, and when braking hard on the track. I have become use to that in the front with high amount of camber, but not in the rear.

I run -2.4 camber, 1mm toe out front; -1.8 camber, 2mm toe in rear;
My front end does follow poor quality surfaces (as expected) but my rear grip is fantastic, quite stable and confidence inspiring.
Your 3mm total toe in rear seems OK to me.

If you brake from 120km/h to 20km/h on a smooth, then uneven surface with the wheel straight, what do you experience?
If you repeat this on a slight curve under control conditions on a flat road, what do you experience?

By sway, do you mean that the rear end is starting to step/swing out? Does this require intervention?

Originally Posted by dcaron9999

GC Camber plates + M3 FCA's, as listed in my signature

Vorshlag and M3 LCA maxes out at -2.4, i'm assuming I would need to space my top plate to clear the spool piece to hit the same numbers.

[dcaron9999]

Found this great piece on toe specific to street and race cars.

"The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.

With four-wheel independent suspension, the toe must also be set at the rear of the car. Toe settings at the rear have essentially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.

Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front. Likewise, when pushed down the road, a non-driven wheel will tend to toe itself out. This is most noticeable in rear-drive cars.

The amount of toe-in or toe-out dialed into a given car is dependent on the compliance of the suspension and the desired handling characteristics. To improve ride quality, street cars are equipped with relatively soft rubber bushings at their suspension links, and thus the links move a fair amount when they are loaded. Race cars, in contrast, are fitted with steel spherical bearings or very hard urethane, metal or plastic bushings to provide optimum rigidity and control of suspension links. Thus, a street car requires a greater static toe-in than does a race car, so as to avoid the condition wherein bushing compliance allows the wheels to assume a toe-out condition. It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system."

http://www.enginebasics.com/Chassis%...ing%20Toe.html

[_Ryan_]

Originally Posted by dcaron9999

Found this great piece on toe specific to street and race cars.

"The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.

With four-wheel independent suspension, the toe must also be set at the rear of the car. Toe settings at the rear have essentially the same effect on wear, directional stability and turn-in as they do on the front. However, it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.

Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front. Likewise, when pushed down the road, a non-driven wheel will tend to toe itself out. This is most noticeable in rear-drive cars.

The amount of toe-in or toe-out dialed into a given car is dependent on the compliance of the suspension and the desired handling characteristics. To improve ride quality, street cars are equipped with relatively soft rubber bushings at their suspension links, and thus the links move a fair amount when they are loaded. Race cars, in contrast, are fitted with steel spherical bearings or very hard urethane, metal or plastic bushings to provide optimum rigidity and control of suspension links. Thus, a street car requires a greater static toe-in than does a race car, so as to avoid the condition wherein bushing compliance allows the wheels to assume a toe-out condition. It should be noted that in recent years, designers have been using bushing compliance in street cars to their advantage. To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system."

http://www.enginebasics.com/Chassis%...ing%20Toe.html

Sure, but you've just fitted a stiffer arm, so your dynamic toe variations should be reduced...

[MPoweRo]

I do love suspension talk.

Are you sure it's not the front wandering under compression during forward weight transfer of braking? The front will toe out further when compressed. I run about 0.25 toe out and it does move around a bit during high speed braking.

[dcaron9999]

Originally Posted by _Ryan_

Sure, but you've just fitted a stiffer arm, so your dynamic toe variations should be reduced...

Totally agree, so one of my objectives is to reduce toe in the rear. Dont know what I was thinking when I got the solid toe arms installed and alignment re-adjusted, knowing there would be less deflection, hence less toe needed in the rear ...

I may slightly reduce camber in the rear as well, as in the front, if I can clear my fenders with my square 255/35R18 tire setup.

[dcaron9999]

Originally Posted by Ro1M

I do love suspension talk.

Are you sure it's not the front wandering under compression during forward weight transfer of braking? The front will toe out further when compressed. I run about 0.25 toe out and it does move around a bit during high speed braking.

It is possible as well, but I run, and have been running 0 toe up front for a while.

After I got the "solid" toe arms installed and alignment re-adjusted last week, is when I ended up with the rear wandering effect on rutted highways, under no acceleration as well. Went from -1.8* to 2.2*camber, and from 3/32" to 1/8" static toe. I wonder if the greatest impact is due to the reduced dynamic toe and cumulative reduced bushing deflection (M3 guide rods, hard bushings adjustable toe arms, diff pumpkin lock down bracket).

Im leaning towards 1/16" to 3/32" rear static toe per side, and -1.8* to -2.0* rear static camber per side...

[fe1rx]

Originally Posted by dcaron9999

Found this great piece on toe specific to street and race cars.

"...To maximize transient response, it is desirable to use a little toe-in at the rear to hasten the generation of slip angles and thus cornering forces in the rear tires. By allowing a bit of compliance in the front lateral links of an A-arm type suspension, the rear axle will toe-in when the car enters a hard corner; on a straightaway where no cornering loads are present, the bushings remain undistorted and allow the toe to be set to an angle that enhances tire wear and stability characteristics. Such a design is a type of passive four-wheel steering system."

http://www.enginebasics.com/Chassis%...ing%20Toe.html

Great summary. A few things I would point out:

1) rear toe in under cornering load (compliance steer) is an understeer effect, which stabilizes the car but reduces total grip available. The OE rear subframe bushings do this, as do likely the totality of the other suspension arm bushings at the rear. Passive rear steer is "always" designed for safety, not for performance. In a track application it is undesirable. Hence I take exception with the statement I have put in bold - I doubt this is either the motivation for, or the effect of such compliance.
2) the upper and rear guide form a virtual upper A-arm and the camber and trailing form a virtual lower A-arm. They each intersect the kingpin axis, which is the axis on which the rear would steer in the absence of the toe arm. It is difficult to figure out exactly where the kingpin axis is, because none of these arm axes actually intersect, but when viewed along the kingpin axis, they appear to intersect at a point. I have precise rear subframe pivot locations but don't have the pivot locations on the rear upright with sufficient accuracy to exactly state where the kingpin axis lies, but I have a pretty close approximation.
3) the rear kingpin axis appears to intersect the ground very close the center of the rear tire contact patch, which is to say zero scrub radius and zero trail. This minimizes any rear self-aligning torque in response to lateral load (although there is still pneumatic trail) and thus minimizes the loads in the toe link required to minimize the rear from compliance steering due to compliance in the toe arm.
4) this is interesting (maybe) except that there is compliance in all the suspension members (or their bushings) even with the M components installed. It is impossible to simply analyze how the rear will compliance steer in response to lateral, thrust or braking loads.
5) more compliance in any of the rear suspension arms is almost certainly going to provide worse handling. Selectively reducing compliance in one or a few of the arms may not measurably reduce understeer (this is my experience).
6) zero scrub radius also minimizes the rear wheel steering torque introduced by braking loads or thrust loads acting act the contact patch. Changing wheel offset from OE at the rear introduces a change in rear scrub radius which will increase such effects though. I believe you are using OE rear wheels, so this should not be an issue.
7) even with zero scrub radius, tire thrust does not necessarily act at the center of the contact patch. Camber will move it laterally (which is your apparent concern) as does any irregularity in the pavement (which may be what you are feeling at highway speed).
8) brake torque must be reacted in the suspension links. The guide and trailing links are oriented such that they will take braking loads primarily. The trailing link will be in tension and the guide in compression under braking. I have no doubt that BMW has arranged the compliances such that the corresponding changes in the effective lengths of these arms results in a toe-in effect when braking, as this stabilizes the car under braking.

OK, to get to a (perhaps) useful conclusion:
1) I believe reducing your camber is unlikely to eliminate the characteristic you have observed. If you are convinced though, you can test your theory with a re-alignment. I wouldn't bother with the front though as the instability is almost certainly coming from the rear.
2) If you have a GoPro, aim it at your rear wheels (both sides) and observe what is happening before you change anything. If you can actually see any toe change, I would suspect some of your suspension bushings are failing.
3) Instability under braking could also be due to excessive rear brake bias. If you can log your abs activity, have a look and see where it is working. Generally you would want the front ABS to activate first. The simplest way to change your brake bias is to run different front and rear brake pad compounds (e.g. DTC70/60 is a common split on our cars).
4) Is the handling you are describing a flaw or a feature? If you get to the point where you can't figure out what to try next, consider whether you can actually live with the characteristic even though you don't like it.

[Kgolf31]

With the tires you have, at 0 toe...the front will walk on ruts on the highway. However, the rear, makes my head scratch.

I run -1.9* at 14 minutes total toe (which IIRC works out to be 1/8")

If the rear wants to wander under braking it would appear you don't have enough toe for stability. Which doesn't make sense unless the alignment is god awful, and I doubt that

[andrey_gta]

Originally Posted by dcaron9999

Last week, I had rear adjustable toe arms (with hard rubber bushings), custom made camber plate spacers to eliminate 20 mm rake I had, and got the car re-alignbed with following specs: -3.2* and 0 toe up front, and -2.2* with 1/8" toe in.

What is this spacer? is it to raise the front?

[dcaron9999]

Gentlemen, thanks for the amazing input as always. I'm sitting at an alignment shop now, and the senior tech found a loose bolt on the rear toe arm, and toe was massively out of wack. Camber in front had moved a half degree apart. This is four days after I got my toe arms installed, camber plates spacers installed, and alignment done!

The senior tech verified all front+rear camber and toe bolts for proper torque tightness.

After a quick discussion with him, I opted for - 3.0* & 0 toe Front, - 2.2* & 1/8" total toe Rear. This is from -3.2* & 0 toe (front) and -2.2*& 1/4" total toe (rear).

[Kgolf31]

This would make sense. Good to hear you caught it

[dcaron9999]

Good that it didn't catch me as I lapped the car for half a day in this state. Could have been a more dramatic conclusion.

Not particularly impressed by first shop who installed my parts and did my alignment right now.

Will try to get them to pick up the bill for 2nd alignment.

[dcaron9999]

Originally Posted by andrey_gta

What is this spacer? is it to raise the front?

I wound up with 25 mm rake after I installed my Swift Spec-R springs, attached to my Ground Control camber plates. The Swift springs were likely designed for stock BMW top hats, which are thicker than GC Street camber plates.

I had a friendly and knowledgeable 1addicts member, get me out of trouble. He proposed a design, and fabricated the 22mm spacers, with a modified GC bolt plate (welded longer bolts). This member had a professional approach, offered great service, and great turn around time for the whole process. He did all this at a very affordable price considering he provided the design drawings, parts fabrication and modification, and shipping. He obviously does this out of passion, and not for a large profit. He would rather not advertise, does this to solve issues, not for esthetic purposes.

PM for details ...

[MPoweRo]

Originally Posted by dcaron9999

Gentlemen, thanks for the amazing input as always. I'm sitting at an alignment shop now, and the senior tech found a loose bolt on the rear toe arm, and toe was massively out of wack. Camber in front had moved a half degree apart. This is four days after I got my toe arms installed, camber pates spacers, and alignemtn done!

The senior tech verfied all front+rear camber and toe bolts.

After a quick discussion with him, I opted for - 3.0* & 0 toe Front, - 2.2* & 1/8" total toe Rear. This is from -3.2* & 0 toe (front) and -2.2*& 1/4" total toe (rear).

Yikes. Well that explains it!

Feed back to the shop that could have caused you to crash.

[_Ryan_]

Originally Posted by dcaron9999

Gentlemen, thanks for the amazing input as always. I'm sitting at an alignment shop now, and the senior tech found a loose bolt on the rear toe arm, and toe was massively out of wack. Camber in front had moved a half degree apart. This is four days after I got my toe arms installed, camber pates spacers, and alignemtn done!

The senior tech verfied all front+rear camber and toe bolts.

After a quick discussion with him, I opted for - 3.0* & 0 toe Front, - 2.2* & 1/8" total toe Rear. This is from -3.2* & 0 toe (front) and -2.2*& 1/4" total toe (rear).

Glad to hear you got this sorted!

[E82MSport]

Originally Posted by dcaron9999

I wound up with 25 mm rake after I installed my Swift Spec-R springs, attached to my Ground Control camber plates. The Swift springs were likely designed for stock top hats, which are thicker than GC Street camber plates.

I had a friendly and knowledgeable 1addicts member, get me out of trouble. He proposed a design, and fabricated the 22mm spacers, with a modified GC bolt plate (welded longer bolts). Great service and great turn around time for the whole process, at very affordable price for the design, parts fabrication and modification, and shipping.

I had a discussion recently with Ground Control in regards to their Street plates with use of the race perch. When I mentioned the measured stack-up height as compared to the OE top mount they were slightly confused that it was shorter. I'm not stating it's a bad thing because without that height difference my ride height would have been roughly 20mm higher that it is now and I had actually taken that difference into consideration.

My problem is similar to yours and I also need to raise the front by ~5-8mm but also reduce my spring preload by roughly the same amount. With my current lower perch height within 3 threads of highest setting (i.e no more adjustment to raise the vehicle) I found the engagement of the internal bump stop was happening more often under very hard compression loads on the track. The only way I found to both increase ride height and reduce spring preload was a two step approach. First I needed to raise the damper in the spindle by way of a spacer and the second was a smaller spacer on top of the camber plate. Because of the additional spacer on top of the camber plate I needed the corresponding length (like you mentioned) of the studs in the attachment girdle. Ground control was able to install longer studs into two new girdles for this purpose based on my specs.

Like you I also had help from a very knowledgeable forum member that I'm very thankful of.

I'm glad you sorted out your issues, I enjoy reading your posts.

[dcaron9999]

Originally Posted by Ro1M

Yikes. Well that explains it!

Feed back to the shop that could have caused you to crash.

I sent a note to the indi shop, and they apologized profusely, paid for my second alignment (done at another shop), and offered me a rebate on my next visit (which I will likely pass on).

This is the second screw up for this shop, this season. First time, was probably due to a test drive (joy ride maybe?) with my 135i that ended up badly. Cannot prove the incident, but after a discussion with Harold @ HPA, about the sequence of events, I have my doubts about what the claimed has happened. My car had to stay at this shop for a week, while they scrambled and replaced bent rear suspension arms, a destroyed OE wheel, along with some body work on my passenger side rocker panel.

[dcaron9999]

One thing I notice with alignments, and any suspension mods, is that it does not hurt to revisit the settings once or twice per lapping season. Parts will settle, shock towers will absorb large impacts, leading to alignment getting thrown off a little. I notice this to be the case in the front a little more than in the rear.

Another thing is that following a change in your suspension components, specs should remain stable or sway much less after you do your second alignment ...

[MPoweRo]

Originally Posted by dcaron9999

I sent a note to the indi shop, and they apologized profusely, paid for my second alignment (done at another shop), and offered me a rebate on my next visit (which I will likely pass on).

This is the second screw up for this shop, this season. First time, was probably due to a test drive (joy ride maybe?) with my 135i that ended up badly. Cannot prove the incident, but after a discussion with Harold @ HPA, about the sequence of events, I have my doubts about what the claimed has happened. My car had to stay at this shop for a week, while they scrambled and replaced bent rear suspension arms, a destroyed OE wheel, along with some body work on my passenger side rocker panel.

At least they admitted liability for the second time. The first indiscretion though...