E36 Steering Rack Ratios - The Facts

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E36 Steering Rack Ratios - The Facts

Post by Pooky » Tue Jan 10, 2006 5:13 pm

As there has been a lot of hearsay going around about the various steering rack ratios fitted to the E36 and the M3s I have spent some time doing some measurements (and have used some of M3 Compact's measurements) plus confirmed the data direct with ZF (I know someone who works there who can access drawings on their system).

The standard way ZF quote on-centre (straight ahead) ratio is in mm/rev, which is the travel in mm of the rack bar per revolution of the hand wheel. The higher the mm/rev the faster the rack.

M3 3.0 - 39 mm/rev- the slowest available rack. This is a variable ratio but it is slower than standard until 200 deg hand wheel angle

M3 3.2 and standard E36 - 45.5 mm/rev- the M3 3.2 rack has restricted lock.

Z3 rack - 53.5 mm/rev- by far the quickest rack you can fit.

E46 compact rack - 50 mm/rev- apparently this also fits the E36

Because the M3 3.0 has a variable rack it has the smallest lock to lock at 3.0 turns but don├óÔé¼Ôäót be fooled it is the slowest by a country mile. A worthwhile upgrade for any 3.0 M3 would be to fit a standard E36 rack which is what I did a year ago with a noticeable improvement.
Last edited by Pooky on Tue Jan 10, 2006 5:21 pm, edited 1 time in total.

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Post by pablo » Tue Jan 10, 2006 5:21 pm

is it a big job to swap racks and any other bits required?

nice info mate cheers :) I smell FAQ :P
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Re: E36 Steering Rack Ratios - The Facts

Post by Ringlapper » Tue Jan 10, 2006 5:27 pm

Pooky wrote: Because the M3 3.0 has a variable rack it has the smallest lock to lock at 3.0 turns but don├óÔé¼Ôäót be fooled it is the slowest by a country mile. A worthwhile upgrade for any 3.0 M3 would be to fit a standard E36 rack which is what I did a year ago with a noticeable improvement.
I was gonna say - have to admit to being shocked by the fact the 3.0 M3 has a cr4ppier steering ratio than a standard e36. Can anybody more intelligent than me explain the logic or the reasoning behind this seemingly mad fact? :? :?
Last edited by Ringlapper on Tue Jan 10, 2006 6:00 pm, edited 1 time in total.
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Post by Sport Coupe » Tue Jan 10, 2006 5:58 pm

Yeah I would be intrested also.

Going from my 328 into an M3 I have found the M3 one to have a huge dead spot in the middle ie small adjustments don't do an awful lot, but get the car sideways and the last part of the steering lock can be applied really quickly. Its taken me ages to get used to it :?
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Post by M3 Compact » Tue Jan 10, 2006 6:31 pm

Nice one Pooky, 8) just to add that the Z3 rack also has restricted lock. (Approx 7% less overall lock than a standard E36 rack, the same amount of travel as an M3 Evo rack.)

It's possible that the Z3 and M3 use 'lock limiting tabs' to restrict the rack, but this is seeming less likely from what I've read elsewhere recently. I'll check my Z3 rack to confirm 100% the next time the sumpguard's removed.

I've recently been driving two E36 Compacts regularly, one fitted with the Z3 rack and another fitted with the standard rack. Given the seemingly small 'on paper' difference between the racks, the difference between them in actual use is astonishing, the Z3 rack feels much 'quicker'. 8)

The Z3 rack I use is from a 1.9 Z3, some reports claim that the 6 cylinder Z3s use a slower rack.
is it a big job to swap racks and any other bits required?
The Z3 rack bolts straight in, one of the pipe supports is approx 50mm away from its position on the standard rack, a simple flat steel/alloy bracket with two holes in is all that's req'd.

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Last edited by M3 Compact on Tue Jan 10, 2006 6:39 pm, edited 1 time in total.
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Post by Ringlapper » Tue Jan 10, 2006 6:35 pm

O/T but what is the mm/rev 'measurement' for an e30 M3?
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Re: E36 Steering Rack Ratios - The Facts

Post by Pooky » Tue Jan 10, 2006 7:27 pm

Ringlapper wrote:I was gonna say - have to admit to being shocked by the fact the 3.0 M3 has a cr4ppier steering ratio than a standard e36. Can anybody more intelligent than me explain the logic or the reasoning behind this seemingly mad fact? :? :?
I can as it happens.

The amount of response you get from the car when you turn the wheel is governed by not just the steering ratio but by the amount of linear understeer in the car. By understeer I don't mean when the front wheels plough on at the limit of grip but a measure of how much extra you would need to turn the road wheel to acheive your intendend path. The chassis gets this understeer from tyres, bumpsteer and compliance steer and the more it has the slower the response.

Basically the amount of response you get is a combination of these two but they affect the car differently at different speeds. At low speed, less then 30 mph, the ratio is more influential, then between 30 mph and 80 mph the combination is important and then from 80 mph upwards the amount of understeer becomes important.

What BMW did with the 3.0 was remove a lot of the understeer, it doesn't have tyre differential as standard plus it has very little bump steer and compliance steer. The problem with this set up is that it makes the car seem slow and unresponsive at low speed but then a little too responsive and nervous at high speed (don't know how many 3.0 owners find this). So with the 3.2 they put the understeer back in with tyre differential as standard plus more bumpsteer (different front knuckle) and compliance steer (different bushes). This means the 3.2 generally feels more responsive at low speed and more stable at high speed plus a quicker ratio generally has the effect of making the straight ahead feel better.

The difference in the response in normal driving probably wouldn't be as big as you would think between the 3.2 and 3.0 but more obvious at higher speeds.

It also means that the best track set-up is a 3.0 but with the 3.2 (or Z3) rack which is what I've got so I would say that. :wink:

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Post by Pooky » Tue Jan 10, 2006 7:38 pm

Ringlapper wrote:O/T but what is the mm/rev 'measurement' for an e30 M3?
As far as I know it is slower than the E36 but you can't compare becasue the geometry of the steering arms and so on is different.

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Post by Ringlapper » Tue Jan 10, 2006 8:10 pm

Pooky wrote:
Ringlapper wrote:O/T but what is the mm/rev 'measurement' for an e30 M3?
As far as I know it is slower than the E36 but you can't compare becasue the geometry of the steering arms and so on is different.
Combined with your initial repsonse makes things a lot clearer.
Bit like looking at the bhp of a car without considering the weight, the gearing and the torque - in a way. The speed of the rack is only a small part of the story.

Ta. :wink:
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Post by =BA= » Tue Jan 10, 2006 10:45 pm

Good post.

However, what about the M3 racks are they of variable speed? Because mine seems to turn much lighter around town than on the highway. Or does the powersteering cut out at a certain speed?

BTW PaulGTR fitted a M3 3.0 rack on his 325 and he said it was faster?
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Post by enda320 » Tue Jan 10, 2006 10:49 pm

the powersteering assist does change, which might be what you can feel.
i personally prefered the m3 rack on an e36, even town driving was noticably better
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Post by M3 Compact » Tue Jan 10, 2006 11:24 pm

BTW PaulGTR fitted a M3 3.0 rack on his 325 and he said it was faster?
It could be when you're piling lock on as Paul likes too. :wink:

SundayJumper measured his E36 M3 3.0L at 160mmish travel and 3ish turns here, this puts it in the Z3 rack league for overall ratio.

Is it possible that the ZF ratio is calculated from the middle for Pooky's figures? This would make it a very interesting rack, with very high ratio steering when using a lot of lock. :idea:
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Post by =BA= » Tue Jan 10, 2006 11:40 pm

Possibly. I would like a lot of travel straight from the center, just linear.
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Post by Pooky » Wed Jan 11, 2006 7:46 am

Not sure what you are feeling as the power steering doesn't change with vehicle speed. The ZF system that does do this is 'servotronic' which is a vehicle speed proportional system and wasn't available on the E36 or E46. This sytem has a solenoid on the side of the PAS valve on the rack with a couple of wires going to it. It is controlled by an ECU which has a map of current supplied to the solenoid vs vehicle speed. This is still only an option on the 5 series and now E60 (standard on M5 and 7-series) and not available on the current M3. BMW may have fitted a falling flow PAS pump which would be proportional to engine revs, the faster the engine turns the heavier the steering would feel.

This is the measurement of the 3.0 rack:
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0 deg is the straight ahead position. It is not faster than a standard rack until 200 deg plus is never faster than a Z3 rack. This means it won't feel faster than a standard rack unless you are manouvering around a car park or something like that.

My rack only measured 141mm of travel.

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Post by M3 Compact » Wed Jan 11, 2006 8:28 am

Great info' Pooky. 8) 8) 8)

The graph answers my question about overall travel.

With 540 degrees in each direction obviously it has 1080 degrees/3 turns lock to lock, the graph shows an average of around 47 mm/rev for the 141mm travel, which adds up correctly. 8) (No good.)

Any info on 6 cylinder Z3s or breadvans? :?:
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