Z4M front camber: alignment pins vs camber washers

filtercoffee · 04-19-2021, 01:32 PM

Calling suspension geometry nerds

Does our macpherson strut front suspension gain negative camber during bump?
Does moving the strut mounting point on the shock tower inwards help with this dynamic camber curve? Should this be preferred over the camber washer method of getting additional camber?

Also, been geeking out about suspension geometry. Feel free to share good resources.

Steeler · 04-19-2021, 03:46 PM

Check out Chassis Engineering by Herb Adams

Steeler · 04-19-2021, 06:49 PM

filtercoffee

Free download here https://www.scribd.com/doc/157853842...is-Engineering

filtercoffee · 04-19-2021, 09:37 PM

Thanks. I gave it a quick read. Here's my interpretation.

First, a key concept and definition:
SAI = Steering axis inclination = the angle of the steering axis and the ground

The steering axis is the line from the upper ball joint to the lower ball joint. In our macpherson suspension, the upper ball joint is really the strut bearing within the upper strut mount.

Therefore, knocking out the alignment pins and moving the strut mounting point inwards increases SAI thus shifting scrub radius towards the negative. I don't yet know how this would change the dynamic camber gain if at all.

The camber washers do not impact the SAI or the dynamic camber gain, since the steering axis is not impacted.
The shims are at the lower strut mounting point which in our suspension has no impact on the steering axis.
^ at least this is my understanding.

filtercoffee · 04-19-2021, 09:50 PM

One thing seems certain, our front suspension has very minimal camber gain on bump, and that's not something that can be significantly changed by any modification. It's inherent in the macpherson design. I guess that's we focus so much on static camber angle.

Negative static camber + limiting body roll seems to be the theoretical way to get the most out of the front tires.

F360C · 04-20-2021, 07:44 AM

From my understanding to a point there is minimal camber gain on compression but if the roll center gets below the front suspension arms you actually loses camber. The camber lose is especially worse if the car is lowered

ANILE8 · 04-22-2021, 06:32 AM

You are way overthinking all of this.

Just get some camber plates and be done with it and call it a day.

If you ever get a decent set of coilovers then they should come with some camber plates in the kit.

Using washers will decreases the tire to spring clearance and limit how wide a tire you can run up front which will have more of an effect that the other things you are worrying about.

filtercoffee · 04-22-2021, 06:48 AM

I already have camber plates

and linear spring coilovers so plenty of clearance. this is more so for my curiosity. I appreciate the reply though.

F360C · 04-23-2021, 07:30 AM

Here is a good explanation and diagram of what I was trying to explain about camber loose after a certain point of suspension compression. Copied this from another forum...

"some MacPherson strut suspensions will develop positive camber from too much lowering. The reason is the angle of the control arm. If the chassis pick-up point for the control arm sits lower than the ball joint on the hub, further compression will pull the bottom of the hub inward. Here, I sketched something up right quick. Angles are exaggerated:"

"In other words, there is geometry that would cause positive camber from excessive lowering, but I don't know for sure that it does on the MINI. Check out the static angle of your control arm and you'll be able to tell. Donnos if the curve is drastic enough to matter, but it's certainly possible."

filtercoffee · 04-23-2021, 11:17 AM

Neat. I found this interactive calculator online that brings that drawing to life:
https://www.racingaspirations.com/ap...ry-calculator/

Whether the suspension gains camber on bump is dependent on the design
If it does, it can be either due to the strut mounting position being in board (SAI), or due to the arc of the control arm going from \ kind of angle to -. In our cars, I think it's the former, since the control arms are roughly level at rest (correct me if I'm wrong). The upward motion of the wheel causes the bottom of the spindle to move inboard slightly due to the arc of the control arm going upward, but the top of the spindle moves inward slightly faster due to the strut mounting point being inboard. At least until a certain amount of suspension travel where the effect of the arc of the control arm is greater. If we move the strut mounting point further inboard, the rate that the top of the spindle moves in increases. So changing the strut mounting point at the top, increasing SAI, does have *some* effect on the camber curve, not just the static camber.

Whether these numbers are big enough to have any material impact, I don't know. But it's fun to speculate.

04-19-2021, 01:32 PM	#1
filtercoffee I like Coffee & Z4s. 106 Rep 366 Posts Drives: 2007 Z4MC Join Date: Feb 2019 Location: New York, NY iTrader: (1) Garage List 2007 BMW Z4MC [0.00]	Z4M front camber: alignment pins vs camber washers Calling suspension geometry nerds Does our macpherson strut front suspension gain negative camber during bump? Does moving the strut mounting point on the shock tower inwards help with this dynamic camber curve? Should this be preferred over the camber washer method of getting additional camber? Also, been geeking out about suspension geometry. Feel free to share good resources.
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04-19-2021, 03:46 PM	#2
Steeler Colonel 2429 Rep 2,704 Posts Drives: Built not Bought 04 Z4 VF Join Date: Feb 2013 Location: Kitchener Ontario Canada iTrader: (2)	Check out Chassis Engineering by Herb Adams __________________ W2A Intercooled Vortech V3Si, custom ducting, Alpha N, 60# Bosch,2.62 pulley, multi port WMI, Severn Tuning(pokeybritches), Tial, magnaflow,SS race muffler, 42 design,3.91LSD, H&R, Hotchkis,ST coils,Konis, Megan camber arms, AKG SS, Nylon mounts, Poly bushings, Carbon interior, CF Aero.APEX
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04-19-2021, 06:49 PM	#3
Steeler Colonel 2429 Rep 2,704 Posts Drives: Built not Bought 04 Z4 VF Join Date: Feb 2013 Location: Kitchener Ontario Canada iTrader: (2)	filtercoffee Free download here https://www.scribd.com/doc/157853842...is-Engineering __________________ W2A Intercooled Vortech V3Si, custom ducting, Alpha N, 60# Bosch,2.62 pulley, multi port WMI, Severn Tuning(pokeybritches), Tial, magnaflow,SS race muffler, 42 design,3.91LSD, H&R, Hotchkis,ST coils,Konis, Megan camber arms, AKG SS, Nylon mounts, Poly bushings, Carbon interior, CF Aero.APEX
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04-19-2021, 09:37 PM	#4
filtercoffee I like Coffee & Z4s. 106 Rep 366 Posts Drives: 2007 Z4MC Join Date: Feb 2019 Location: New York, NY iTrader: (1) Garage List 2007 BMW Z4MC [0.00]	Thanks. I gave it a quick read. Here's my interpretation. First, a key concept and definition: SAI = Steering axis inclination = the angle of the steering axis and the ground The steering axis is the line from the upper ball joint to the lower ball joint. In our macpherson suspension, the upper ball joint is really the strut bearing within the upper strut mount. Therefore, knocking out the alignment pins and moving the strut mounting point inwards increases SAI thus shifting scrub radius towards the negative. I don't yet know how this would change the dynamic camber gain if at all. The camber washers do not impact the SAI or the dynamic camber gain, since the steering axis is not impacted. The shims are at the lower strut mounting point which in our suspension has no impact on the steering axis. ^ at least this is my understanding.
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04-19-2021, 09:50 PM	#5
filtercoffee I like Coffee & Z4s. 106 Rep 366 Posts Drives: 2007 Z4MC Join Date: Feb 2019 Location: New York, NY iTrader: (1) Garage List 2007 BMW Z4MC [0.00]	One thing seems certain, our front suspension has very minimal camber gain on bump, and that's not something that can be significantly changed by any modification. It's inherent in the macpherson design. I guess that's we focus so much on static camber angle. Negative static camber + limiting body roll seems to be the theoretical way to get the most out of the front tires.
	Appreciate 0 Quote

04-20-2021, 07:44 AM	#6
F360C Major 366 Rep 1,373 Posts Drives: E86 S54 Join Date: Apr 2006 Location: Hoboken, NJ iTrader: (2)	From my understanding to a point there is minimal camber gain on compression but if the roll center gets below the front suspension arms you actually loses camber. The camber lose is especially worse if the car is lowered __________________ 07 Z4 M Coupe AW/IR
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04-22-2021, 06:32 AM	#7
ANILE8 Captain 180 Rep 700 Posts Drives: Z4 M Coupé - Carbon Black Join Date: Mar 2008 Location: The Dark Web iTrader: (0)	You are way overthinking all of this. Just get some camber plates and be done with it and call it a day. If you ever get a decent set of coilovers then they should come with some camber plates in the kit. Using washers will decreases the tire to spring clearance and limit how wide a tire you can run up front which will have more of an effect that the other things you are worrying about. __________________ Nitron NTR R3 \| StopTech Trophy Sport STR-60 380x32mm / StopTech Trophy Sport STR-40 355x32mm \| Bridgestone RE-71RS \| ADV.1 \| CDV Delete \| TMS Rear Camber Arms \| RE Diablo's \| 4.10 Gears \| Euro Headers \| RTD REVO1 Short Shifter
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04-22-2021, 06:48 AM	#8
filtercoffee I like Coffee & Z4s. 106 Rep 366 Posts Drives: 2007 Z4MC Join Date: Feb 2019 Location: New York, NY iTrader: (1) Garage List 2007 BMW Z4MC [0.00]	I already have camber plates and linear spring coilovers so plenty of clearance. this is more so for my curiosity. I appreciate the reply though.
	Appreciate 0 Quote

04-23-2021, 07:30 AM	#9
F360C Major 366 Rep 1,373 Posts Drives: E86 S54 Join Date: Apr 2006 Location: Hoboken, NJ iTrader: (2)	Here is a good explanation and diagram of what I was trying to explain about camber loose after a certain point of suspension compression. Copied this from another forum... "some MacPherson strut suspensions will develop positive camber from too much lowering. The reason is the angle of the control arm. If the chassis pick-up point for the control arm sits lower than the ball joint on the hub, further compression will pull the bottom of the hub inward. Here, I sketched something up right quick. Angles are exaggerated:" "In other words, there is geometry that would cause positive camber from excessive lowering, but I don't know for sure that it does on the MINI. Check out the static angle of your control arm and you'll be able to tell. Donnos if the curve is drastic enough to matter, but it's certainly possible." __________________ 07 Z4 M Coupe AW/IR
	Appreciate 0 Quote

04-23-2021, 11:17 AM	#10
filtercoffee I like Coffee & Z4s. 106 Rep 366 Posts Drives: 2007 Z4MC Join Date: Feb 2019 Location: New York, NY iTrader: (1) Garage List 2007 BMW Z4MC [0.00]	Neat. I found this interactive calculator online that brings that drawing to life: https://www.racingaspirations.com/ap...ry-calculator/ Whether the suspension gains camber on bump is dependent on the design If it does, it can be either due to the strut mounting position being in board (SAI), or due to the arc of the control arm going from \ kind of angle to -. In our cars, I think it's the former, since the control arms are roughly level at rest (correct me if I'm wrong). The upward motion of the wheel causes the bottom of the spindle to move inboard slightly due to the arc of the control arm going upward, but the top of the spindle moves inward slightly faster due to the strut mounting point being inboard. At least until a certain amount of suspension travel where the effect of the arc of the control arm is greater. If we move the strut mounting point further inboard, the rate that the top of the spindle moves in increases. So changing the strut mounting point at the top, increasing SAI, does have some effect on the camber curve, not just the static camber. Whether these numbers are big enough to have any material impact, I don't know. But it's fun to speculate.
	Appreciate 0 Quote