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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Sun, Dec-16-2018, 02:19:52 AM   #1
Volke
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Default Comprehensive BMW Steering Information Thread

I see a lot of misinformation regarding steering modifications being passed around Facebook groups and forums almost daily, so I’ve decided to put together this information thread to correct the many misconceptions, and to compile a comprehensive database for steering rack swaps and power steering modifications. The comprehensive steering rack database would not be possible with the community’s help, so many thanks in advance to those who read on and contribute!

Contents
  1. Understanding Steering Ratio
  2. How To: Determining Steering Rack Rates, Total Travel, and Linearity
  3. BMW Steering Rack & Knuckle Database
  4. Understanding Power Steering Operation
  5. DIY: Decreasing Power Steering Assist

1. Understanding Steering Ratio

What is steering ratio?

The term steering ratio refers to the ratio of the steering wheel rotation (in degrees) and the resulting wheel angle (in degrees). When written as 15.4:1 or 13.7:1, it tells you how many degrees the steering wheel needs to be turned to turn the wheels 1 degree. Smaller ratios make the steering feel more nimble and quick, and larger ratios make the steering feel more lazy and slow.

Is the manufacturer published steering ratio for another car model a good criteria for determining which steering rack to swap into my car?

NO!

Comparing the manufacturer published steering ratio for different models alone is not sufficient in determining the rate or “quickness” of the respective steering racks, and chances are it will not give the expected result. The only way to do an accurate comparison is to measure the steering racks directly. This is because the steering ratio is a function of the steering rack rate AND the steering knuckle design. In other words, swapping a steering rack from a 330 with a BMW published steering ratio of 13.7:1 into a E46 M3 will not necessarily result in quicker steering than using a steering rack from an E46 M3 ZCP with a BMW published 14.5:1 ratio. In fact, both the 330 and ZCP racks will result in a 14.5:1 steering ratio when installed on an E46 M3, M3 ZCP, or M3 CSL. This is because both the 330 and ZCP steering racks have the same rate. More details on this later.

What is steering rack rate and how does it affect the steering ratio?

The steering rack rate is the relationship between the left or right travel of the steering rack to the rotation of the input shaft or steering column. It has units of linear distance per angular displacement. For example, mm/rev or in/rev. A higher steering rack rate results in a lower(“quicker”) steering ratio. Assuming no changes are made to the steering rack other than the gear teeth, a higher steering rate also results in higher steering effort required.

It is also important to note that steering racks can be either linear or progressive. A linear rack has a constant rate across its whole range of travel while a progressive rack will have one rate for the first bit of travel to either side of the on center position and another, usually higher, rate on both ends.

How does the steering knuckle design affect the steering ratio?

The steering ratio is also affected by the steering knuckle geometry, or more specifically the distance between the tie rod pickup point and the steering axis. On the E46 MacPherson strut suspension the steering pivot axis is defined as the imaginary line passing through the center of the top strut mount and the center of the lower control arm ball joint, and the tie rod pickup point is the center of the tie rod ball joint. A shorter distance between the tie rod pickup point and steering axis results in a lower(“quicker”) steering ratio, and higher steering effort required assuming no additional suspension geometry or power steering changes. The E46 non-M knuckle has the tie rod ball joint closer to the steering axis compared to the M3 version, so it will always have quicker steering than the E46 M3 using the same steering rack.

Is there anything else I should keep in mind when choosing a steering rack?

Yes. Steering racks have limited left and right travel.

If the total travel of the new rack is less than your current rack, your turning circle will increase, and you will lose some maximum steering angle.

If the total travel of the new rack is more than your current rack, you may be able to get more maximum steering angle, or you may need to add some rack stops to prevent rubbing on the inner wheel well liner.

Is there any other way to get quicker steering without changing the steering rack?

Yes. SLR Speed sells an adapter that attaches to your steering knuckle and relocates the tie rod ball joint closer to the steering axis making the steering ~40% faster, but it requires machining your OE control arms to press in a new ball joint, or switching to aftermarket tubular control arms. The kit also provides bump steer and roll center correction. Provided you have the wheel well clearance, the kit will also allow you to go up to 60 degrees of maximum steering angle from the factory 40 degrees. More than likely, you will need to use some rack stops to prevent rubbing on the inner wheel well.

Will changing the steering rack or modifying the knuckle geometry mess up the DSC?

Yes, but what extent depends on how different the new steering ratio is. The BMW DSC uses signals from the rotation sensor on the steering column, acceleration sensor and yaw sensor to determine when to intervene. Put simply, the DSC unit calculates the direction the wheels are pointing based on the column sensor output and some programmed information about the steering ratio, and if what the car is doing doesn’t match up, it will try to correct it. Steering modifications make the wheels point in a different direction than the car calculates they are, so it is more likely to intervene. The quicker you make the steering, the more it will intervene. Milder setups may work well enough to daily, but DSC will need to be turned off for track or autocross.

Ok, I understand how steering racks and knuckles affect the steering ratio along with the downsides. So which rack will give me the quickest steering?

Unfortunately, I only have information on a few of the BMW steering racks available. I need help from the rest of the community to complete the rack database further down below.

I have a steering rack not yet in the database, and I want to help. How do I contribute?

Follow the instructions in the section below to take measurements, or send the rack to me. I will take measurements and send it back.


2. How To: Determining Steering Rack Rates, Total Travel, and Linearity

Pictures from E46 M3 steering rack


Measuring on Center Rate
Step 1
Center the steering rack and use a paint pen to make an alignment mark on the input shaft and housing.


Picture Link

Step 2
Measure the distance from a fixed point on the housing to the end of the toothed shaft or tie rod.


Picture Link

Step 3
Rotate the input shaft 1 full turn. Try to be as accurate as possible with the alignment mark.

Step 4
Repeat the measurement from step 2. The difference between the two numbers is the on center rack rate.


Picture Link

Checking for Linearity / Measuring Progressive Rate
Step 1
Turn the steering rack all the way to one side and use a paint pen to make a new alignment mark on the input shaft and housing.


Picture Link

Step 2
Measure the distance from a fixed point on the housing to the end of the toothed shaft or tie rod.


Picture Link

Step 3
Rotate the input shaft 1 full turn. Try to be as accurate as possible with the alignment mark.

Step 4
Repeat the measurement from step 2. The difference between the two numbers is the rack rate.


Picture Link

If this number is equal to the on center rate, the steering rack is linear.

Measuring Total Travel and Turns Lock to Lock
Step 1
Make sure the inner tie rods are installed. They act as the rack stop and limit the side to side travel. Without these, the total travel and turns lock to lock will be inaccurate.

You can also use M18 drain plugs or bolts and washers, but you will not be able to measure total travel as easily.


Picture Link

Step 2
Turn the steering rack all the way to one side and make an alignment mark.

Step 3
Measure the distance from a fixed point on the housing to the end of the inner tie rod.

Step 4
Turn the steering rack all the way to the other side, and repeat the measurement from step 3. The difference between the two measurements is the total rack travel.

You can also center the rack, make an alignment mark, and take measurements going to one side, then repeat for the other side. The total travel is then the sum of the two sides.

Step 5
If the rack is linear, divide the total travel by the rack rate to get an accurate number of turns lock to lock.

You can also approximate the turns lock to lock by counting the turns using your alignment mark, but it’s hard to get an accurate value unless it’s a whole number.
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Last edited by Volke; Sun, Dec-16-2018 at 08:38:39 PM.
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Old Sun, Dec-16-2018, 02:20:24 AM   #2
Volke
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Default Re: Comprehensive BMW Steering Information Thread

3. BMW Steering Rack & Knuckle Database

Steering Racks

E46 M3 Steering Rack - Green Tag - BMW 2 229 395 - verified by me
Linear
Rack Rate = 47 mm/turn
Turns Lock to Lock = 3.19 (total travel divided by rate)
Total Rack Travel = 150 mm

E46 M3 ZCP Steering Rack - Blue Tag - BMW 2 282 640 - rate measured by a friend, needs verification on turns and travel
Linear
Rack Rate = 50 mm/turn
Turns Lock to Lock = 3
Total Rack Travel = 150 mm

E46 330 Steering Rack Starting 9/2001 - Yellow Tag - BMW 6 757 650 - measured by me on a BMW re-manufactured 330 rack with no tag sold as 6 757 651, could use another data point from an original yellow tagged 712 rack
Reman Part Number: 6 757 651
Linear
Rack Rate = 50 mm/turn
Turns Lock to Lock = 3
Total Rack Travel = 150 mm

Z3 2.5L - Silver Tag - BMW 1 092 031 - measured by me, didn’t have inner tie rods handy for lock to lock or total travel measurements
Linear
Rack Rate = 50 mm/turn
Turns Lock to Lock = ???
Total Rack Travel = ???

Z3 1.9L - part number? - claimed figures posted around the internet with no real proof, realOEM says part number should be the same as 2.5L above
Linear
Rack Rate = 53.5 mm/turn
Turns Lock to Lock = 2.7
Total Rack Travel = 144.5 mm (calculated from 53.5 mm/turn and 2.7 turns)

Z4 M Roadster - found on another forum, needs confirmation
Linear
Rack Rate = 51 mm/turn
Turns Lock to Lock = 2.7
Total Rack Travel = 137.7 mm (calculated based on 51 mm/turn and 2.7 turns)

Z4 M Coupe - Green Tag - 7 838 790 - found on another forum, needs confirmation
Reman Part Number: 7 838 794
Linear
Rack Rate = 54.5 mm/turn
Turns Lock to Lock = 2.5
Total Rack Travel = 136.25 mm (calculated based on 54.5 mm/turn and 2.5 turns)

Steering Knuckles

Section for anyone interested in knuckle swaps or knuckle modifications. Included some bonus information on camber impact. Negative number means it add negative camber. Positive number means it adds positive camber.

E46 M3
Tie Rod Distance from Steering Axis = ~130 mm

E46 M3 CSL
Tie Rod Distance from Steering Axis = ~130 mm - Measurement
Camber Change from E46 M3 = -1 degree (approximate)

E46 non-M
Tie Rod Distance from Steering Axis = ~126 mm - Measurement
Camber Change from E46 M3 = +1 degree (approximate)

SLR Speed E46 M3 Race Kit Adapter
Tie Rod Distance from Steering Axis = ~90 mm - Measurement
Roll Center Correction = 28 mm with matching bump steer correction
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Last edited by Volke; Sun, Dec-16-2018 at 08:56:33 PM.
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Old Sun, Dec-16-2018, 02:20:55 AM   #3
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Default Re: Comprehensive BMW Steering Information Thread

4. Understanding Power Steering Operation

How does hydraulic power steering work?

Without getting into too many details, hydraulic power steering uses a positive flow, fixed displacement oil pump and pressure regulator to build pressure and help the steering rack move left or right. On the E46, the pressure regulator is built into the pump itself, and the pressure setting of the regulator is what determines how much power steering assist you get. The stock E46 M3 pump regulates to 120 bar pressure.

Whenever the steering rack is not moving, such as driving straight ahead or maintaining a constant steering angle, 100% of the pump output flow goes through the pressure regulator and recirculates back to the pump inlet side. The pump is doing zero useful work under these conditions, and is just robbing engine power and heating the power steering fluid.

When the steering rack is moving left or right, some of the flow goes to the steering rack to help it shift, and the rest goes across the pressure regulator to maintain the desired pressure. Faster steering inputs require more pump output flow to be able to maintain the power steering assist. The pump must always output enough flow to have at least a little go through the regulator, or there will be no power assist.

My steering feels too light. How do I make it heavier?

See the first part of this guide to make the steering ratio quicker or follow the instructions in the DIY below to decrease the power steering pressure. You can also remove the pump or pressure regulator and send it to me for modification.

Can’t I just install an underdrive power steering pulley?

No. Underdrive pulleys just spin the pump slower and decrease the amount of pump flow available. This just makes it more likely you will lose power steering assist all together if you steer too quickly at low RPM.

Is there any point in installing an underdrive power steering pulley?

Yes. For a car that spends a lot of time at high RPM, underdrive pulleys will help keep the power steering fluid a little cooler and free up a small amount of engine power. The slower pump speeds and cooler temperatures increase pump life. Underdrive pulleys are not recommended for drift cars due to the super quick, large, and frequent steering inputs required.

Are there any other benefits to decreasing the power steering pressure?

Yes. Lower pressure also helps prevent blown out or leaking power steering lines, keeps power steering fluid temperatures lower, and frees up a little engine power.


5. Decreasing Power Steering Assist

Tools and Items Required
27 mm socket or wrench
11 mm socket
A collet vise (preferred) or soft jaw vise with round grooves
Shims
22 mm socket or wrench
Drain pan
Magnetic pick-up tool
Banjo bolt washers
Power steering fluid

The ID and OD of the shims are critical. If the OD is too large, it will rub on the spring and cause it to fail, sending debris into your power steering system which could damage your pump and steering rack. I had to work with a local company to get some shims made up with the proper ID and OD. I have some left, and I can always get more if anyone is interested. I can sell them for $15 for a pack of 10 plus shipping. I can ship them for free in a basic envelope via USPS, but there will be no tracking.

For those that want to source their own, the factory shims are 10 mm ID, 13 mm OD and 0.4 mm thick. The shims I can supply are 10 mm ID, 13 mm OD, 0.5 mm thick, and hold the OD to very tight tolerance to prevent rubbing on the spring. You can also steal some factory shims off other E46 pumps if you have any laying around.


Picture Link

Step 1
If you’re doing this on the car, you will need a 22 mm wrench or socket to remove the banjo bolt and disconnect the high pressure power steering line. Place a drain drain pan underneath for any oil that comes out. I haven’t attempted it on the car, so I’m not sure how quickly it will drain out.

Step 2
Remove the 27 mm hex plug on the pump output.

You will need to use an impact or a vise to secure the pump if you’re doing this off the car.

Step 3
Use a magnetic pick-up to remove the pressure regulator and the spring behind it.

If you’re doing this off the car, you can just turn the pump upside down and both will come out.


Picture Link

Step 4
Secure the pressure regulator in a collet vise and remove the 11 mm hex plug. Be careful not to lose the small ball or spring hidden behind it, or any shims that may be on the plug.

If using a normal vise, be sure to use soft jaws and be careful not to damage the regulator or you will need to buy a new power steering pump.


Picture Link

Step 5
Add additional shims to reach desired assist level and reinstall the plug being careful to keep the shims as centered as possible. They can rub on the spring if they get pushed too far to a side which will cause the spring to fail. Also make sure the tiny hole in the center of the hex is not plugged.

If you’re using the shims from me, each 0.5 mm shim will reduce the power steering assist/pressure by ~12.5 percent.

1 additional shim = ~12.5% reduction
2 additional shims = ~25% reduction
3 additional shims = ~37.5% reduction
4 additional shims = ~50% reduction

You can go up to 6 shims for 75% reduction, but I don’t recommend it because it will start decreasing the total thread engagement of the plug which could cause it to back out. If you must do this, I suggest cleaning the parts of oil and using some thread locker(ex. Loctite). Be sure to let it cure overnight before putting it in oil again.


Picture Link

Step 6

Installation is opposite of removal. Be sure to use new washers for the banjo bolt and top off your power steering fluid.

Closing Comments

Big thank you to bigjae1976 for volunteering his car and pump to try this modification. I reduced the pressure by ~50% on a pump he supplied, and he has been running it since September/October with positive feedback. He previously tried doing a power steering delete and found that it was too heavy, and made it too difficult to hit the apex, so his feedback was very valuable to me in figuring out how much reduction is good with minimal trial and error.

This is what he had to say about it. Sorry, it's kinda written like a review which isn't what I had in my mind, but maybe it's more helpful like this.

Quote:
Originally Posted by bigjae1976
I started out deleting the entire PA system and using a crossover block on the rack. This wasn’t acceptable for track use since it takes too much effort to get the car to the apex in slower, tighter turns. I ended up turning in way earlier so I can make it to the apex.

I was looking for something in between the OEM feel and Ps delete feel.

I tried Volke’s modification which would increase effort. I also deleted the cooling loop and expansion loop. It’s just straight hoses from the reservoir to the pump to the rack and back to the reservoir.

On the street, it adds some effort but I’m not sure I’d consider it transformative. It was better and I think it is acceptable for DD.

On the track, I loved it! It provides most of the feedback that I got with no PS. The wheel gives you a tug over every bump or surface imperfection but doesn’t overtax your forearms. Whereas the feedback was telepathic with no PS but wears your arse out after a couple of laps.

I’d say this is a great mod for a track car or canyon carver. Not sure I’d do it for an endurance racer. You will feel it a little in your forearms if it’s a twisty track at the end of the day.

Overall...FANTASTIC!!!
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Last edited by Volke; Wed, Dec-19-2018 at 02:53:28 AM.
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Old Sun, Dec-16-2018, 02:29:01 AM   #4
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Default Re: Comprehensive BMW Steering Information Thread

Hope you find this useful because it sure took a while to write up!

I'll add some pictures for the measurements and DIY soon. I have them on my phone, but need to upload and link them all.
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Old Sun, Dec-16-2018, 02:41:35 AM   #5
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Default Re: Comprehensive BMW Steering Information Thread

For whatever it’s worth, yellow tag steering rack (the so called ZHP rack) appears to be 2.7-2.8 turns lock to lock with the same 50mm/rev ratio.

This video appears to show < 3 turns lock to lock, and that’s pretty similar to what I see on my own car with the zhp rack


Also I was wondering if you had any thoughts about possible Ackermann angle differences - would the steering racks effect that or is that purely a function of the suspension geometry?

Last edited by terraphantm; Sun, Dec-16-2018 at 02:45:36 AM.
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Old Sun, Dec-16-2018, 03:01:49 AM   #6
Volke
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Default Re: Comprehensive BMW Steering Information Thread

Sounds like we need someone to measure a yellow tag rack off the car. That's precisely why I wanted to start this thread.

Steering racks don't affect Ackerman. It's a function of suspension geometry, more specifically the tie rod ball joint location and distance from the centerline of the car. The SLR Speed kit adjustable Ackerman just moves the ball joint farther or closer from the center of the car.
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Old Sun, Dec-16-2018, 03:08:09 AM   #7
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Default Re: Comprehensive BMW Steering Information Thread

Given coding data on the various non-M E46s, I’m fairly confident it’s 50mm/rev regardless.
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Old Sun, Dec-16-2018, 03:20:00 AM   #8
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Default Re: Comprehensive BMW Steering Information Thread

I think it's probably 50 mm/rev too, but it's possible it has some additional rack stops to keep the tires from rubbing on the inner wheel well with the narrower track and the quicker steering knuckles on the non-M. You would need to look under the boot and see if there are any washers or C-clips before the inner tie rod hex.
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Old Sun, Dec-16-2018, 03:27:49 AM   #9
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Default Re: Comprehensive BMW Steering Information Thread

Thanks for posting this. Trying to decide between the ZCP and ZHP racks.

I tested out a ZHP rack in a M3 recently, and at higher speeds or engine revs, it felt like it was biased slightly towards the right (less effort to turn right than left off center). It was a used rack with about 100k on it. I'm thinking a rebuild would be recommended for any used steering rack.
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Old Sun, Dec-16-2018, 03:36:33 AM   #10
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Default Re: Comprehensive BMW Steering Information Thread

Quote:
Originally Posted by Volke View Post
I think it's probably 50 mm/rev too, but it's possible it has some additional rack stops to keep the tires from rubbing on the inner wheel well with the narrower track and the quicker steering knuckles on the non-M. You would need to look under the boot and see if there are any washers or C-clips before the inner tie rod hex.
I don’t remember seeing anything like that when I installed my rack (I replaced inner and outer tie rods at the time of install), but I might not have known what to look for.
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Discussing Comprehensive BMW Steering Information Thread in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)