Comprehensive Steering Information Thread

[terra]

From what I measured I think its a mistake..I specifically measured multiple z3 racks from multiple cars (couple 1.9, 2.5). They were all the same. The real puzzling one to me is the z4m coupe vs roadster rack. I measure both and again they were identical (50mm\rev), but in this case I believe even BMW reports the coupes as having a quicker steering ratio. Not sure what that's about.

The OP of this thread needed photos to update the post and avoid misinformation but I didn't take any at the time.

Yeah that one is a mystery to me. BMW claims 13.7:1 vs 12.8:1 for the roadster vs coupe. As far as I know suspension is otherwise identical between the two so a geometry change wouldn’t explain the steering difference.

A hypothetical 53.5mm rack would get you to that ratio difference (assuming 50mm = 13.7:1)

More confusingly, the first post indicates the tie rod to control arm distance on the Z4M is the same as the M3 (and longer than the non-M), which means a 50:1 rack should result in a 14.5:1 ratio.

[bigjae46]

You could just put on an underdrive pulley

Not the same. An underdrive pulley doesn't do anything to lower the system pressure. It spins the pump slower and increases the likelihood of cavitating the pump at low RPMs. The PS pump is a PD vane pump and those do not tolerate cavitation.

I'd have to do some math but I'm pretty sure the pump reaches the operating pressure fairly quickly. The shims lower the operating pressure by opening the pump pressure relief/regulator at a lower PSI which increases effort but avoids the low RPM cavitation.

[duracellttu]

I've always wanted to drive a car with a yellow or purple rack and see if it feels any heavier. My blue tag is pretty light.

You could just put on an underdrive pulley

[Ubaderb]

Send a PM to Volke (OP of this thread).

OP hasn't been on since March of last year.

[Obioban]

I've always wanted to drive a car with a yellow or purple rack and see if it feels any heavier. My blue tag is pretty light.

Shim it?

[D-O]

Anyone know where to source the power steering shims?

Send a PM to Volke (OP of this thread).

[lapoune]

53.5mm/rev stated in this thread post #3? Maybe it’s erroneous

From what I measured I think its a mistake..I specifically measured multiple z3 racks from multiple cars (couple 1.9, 2.5). They were all the same. The real puzzling one to me is the z4m coupe vs roadster rack. I measure both and again they were identical (50mm\rev), but in this case I believe even BMW reports the coupes as having a quicker steering ratio. Not sure what that's about.

The OP of this thread needed photos to update the post and avoid misinformation but I didn't take any at the time.

[9kracing]

I've always wanted to drive a car with a yellow or purple rack and see if it feels any heavier. My blue tag is pretty light.

[digger]

Placebo effect is one hell of a drug.

As far as I'm aware, nothing faster than 50mm/rev has been identified thus far.

53.5mm/rev stated in this thread post #3? Maybe it’s erroneous

[terra]

thanks for confirming, i just wondered why you hear people say the z3 rack (2.7 LTL) is more twitchy than the 3 turn LTL racks e.g. purple tag on the highway when they are geared the same.
I did note the 2nd post it says one is 50mm/rev vs 53mm/rev so actually not geared the same unlike stated on other resources.

Placebo effect is one hell of a drug.

As far as I'm aware, nothing faster than 50mm/rev has been identified thus far.

[Lavatoad]

Anyone know where to source the power steering shims, or the dimensions?

[digger]

The ones I measured I checked if linear, so e36 m3\z3m = progressive...z4mc\roadster, standard z3s, zcp = linear

thanks for confirming, i just wondered why you hear people say the z3 rack (2.7 LTL) is more twitchy than the 3 turn LTL racks e.g. purple tag on the highway when they are geared the same.
I did note the 2nd post it says one is 50mm/rev vs 53mm/rev so actually not geared the same unlike stated on other resources.

[sapote]

Has anyone measured the linearity of the rack travel just off centre?

The rack/pinion ratio is fixed so the rack travel should be linear to the wheel rotation, the whole range.

[lapoune]

Has anyone measured the linearity of the rack travel just off centre?

All measurements seem to be based on 1 full rev when i would have thought you'd need to do various incremental measurements at 1/8, 1/4 turn etc to establish this

The ones I measured I checked if linear, so e36 m3\z3m = progressive...z4mc\roadster, standard z3s, zcp = linear

[digger]

Has anyone measured the linearity of the rack travel just off centre?

All measurements seem to be based on 1 full rev when i would have thought you'd need to do various incremental measurements at 1/8, 1/4 turn etc to establish this