[Volke]

Originally Posted by mercedesc63

When I had my 02 E46 M3 I wanted to upgrade the steering rack.. i learned a few things first of all that purple tag zhp rack is linear whereas the e46 m3 comes stock with a progressive. In addition according to my research the zcp rack works fine on a MK20 which is a slightly faster rack 15;4 vs 14:5 both progressive. Also I reccomend that new dsc tune and i really do think it can settle the dsc down a lot in theory.

I discovered the cheapest and easiest way to run a purple label rack is by getting a racelogic TC (discontinued) wiring it in and fine tuning it. This system works off of the abs and detects slip and cuts power to regain traction. Whereas the dsc systems like mk20 or mk60 run a lot off of steering angle/speed of steering which is why these systems never really agree.

Bottom line the MK20 doesnt have some of the sensors or capabilities to adapt to a change like a steering rack swap especially a linear one. Swapping racks never really does work 100% even on a mk60 because lets face it you are messing with something that was engineered a certain way for a certain reason.

Both the regular and ZCP E46 M3 racks are linear...

[mercedesc63]

Originally Posted by Volke

Both the regular and ZCP E46 M3 racks are linear...

According to my research..

Competition ZCP/ Stock OEM = Progressive
Purple Label ZHP Rack= Linear

" On the topic of progressive racks, I think different racks were designed with different amounts of progressiveness. Its my theory that the unquestionably progressive 330 rack is "more linear" than the E46 M3 "quite progressive" rack. "

http://www.m3forum.net/m3forum/showthread.php?t=544445

[Obioban]

Originally Posted by Volke

There's nothing you can really do on the MK20 currently. The issue is that DSC uses the position and rotation speed readings from the steering column rotation sensor to calculate the angle of the front wheels based on a known steering ratio. It compares this information against the readings from the yaw sensor to determine if the car is in control or not. When you change to a faster rack, the wheel angle is greater than the DSC unit expects it to be, and the car experiences greater lateral acceleration than expected, so DSC kicks in.

On the MK60, you can change to the ZCP steering setting (14.5:1) or use NCS Expert/Dummy to fake a 12.8:1 setting. This minimizes the interference, but DSC will never work as intended with a 13.7:1 rack until someone finds a way to either flash the DSC unit and change the steering ratio, or scale up the output of the column sensor to trick the DSC unit by either modifying the column sensor directly or intercepting the CAN signal with a dual CAN.

Someone on this forum is working on a dual CAN, but it will be a while before it's ready.

The yellow tag ("ZHP") rack is 14.5:1 when installed in the M3 due to the different geometry-- the ZCP setting on the MK60 is pretty spot on for it. Terra did the calculation a while back.

[Volke]

Originally Posted by mercedesc63

According to my research..

Competition ZCP/ Stock OEM = Progressive
Purple Label ZHP Rack= Linear

" On the topic of progressive racks, I think different racks were designed with different amounts of progressiveness. Its my theory that the unquestionably progressive 330 rack is "more linear" than the E46 M3 "quite progressive" rack. "

http://www.m3forum.net/m3forum/showthread.php?t=544445

That guy's post has a lot of misinformation.

The "unquestionably progressive 330 rack" is unquestionably linear. I measured mine prior to installation. It has 50mm/rev, 3 turns lock to lock and 150mm total travel from side to side. I checked the 50mm/rev directly at center and on both ends.

The Z3 non-M rack is also fully linear. It has 53.5mm/rev, 2.7 turns lock to lock and 144.5 mm total travel. It's a little faster, but as you can tell from the total travel, it will hurt your turn radius a bit.

I'll go get my regular E46 M3 rack from PE on Monday and measure it.

Originally Posted by Obioban

The yellow tag ("ZHP") rack is 14.5:1 when installed in the M3 due to the different geometry-- the ZCP setting on the MK60 is pretty spot on for it. Terra did the calculation a while back.

Link? Remember any of the details?

That would mean that both the ZCP rack and the 330 rack are 50mm/rev, but the 330 steering knuckle has the outer tie rod location a little closer to the control arm bolt.

If that's true, saves me the effort and money of trying to find a ZCP rack.

[Obioban]

Originally Posted by Volke

Link? Remember any of the details?

That would mean that both the ZCP rack and the 330 rack are 50mm/rev, but the 330 steering knuckle has the outer tie rod location a little closer to the control arm bolt.

If that's true, saves me the effort and money of trying to find a ZCP rack.

From a bit of searching...

Originally Posted by terraphantm

Unknown since the steering ratio will depend on the suspension geometry as well as the rack, and no one's measured the effective ratio on an M3 w/ a Z3 rack. In their respective chassis, both racks are supposed to be 14.5:1.

Supposedly the rack of the Z3 unit moves 53mm per 1 revolution of the pinion. Though someone on the E36 forum says by his measurements it's 51mm at best. On a stock M3 rack, I measured ~46mm/rev (which results in a 15.4:1 ratio). On my ZHP rack, I measured ~50mm/rev (results in 13.7:1 on the non-M). No one's measured a ZCP rack and posted info, but it is supposed to be a 14.5:1 rack.

Not the post I was looking for, but verifies he measured the yellow tag ("ZHP") at 50mm/rev.

Yellow tag is supposedly more feelsome than the ZCP rack, as well.

If you want further details, PM him a link to this. I can't seem to find it.

[Volke]

Originally Posted by Obioban

From a bit of searching...

Not the post I was looking for, but verifies he measured the yellow tag ("ZHP") at 50mm/rev.

Yellow tag is supposedly more feelsome than the ZCP rack, as well.

If you want further details, PM him a link to this. I can't seem to find it.

Thanks! His measurement of the 330 rack matches up with mine.

If the regular E46 M3 rack is 46mm/rev and that results in a 15.4:1 ratio and we assume that the ZCP rack has the same total rack travel as the regular M3, we can calculate the mm/rev of the 14.5:1 ZCP rack since we know they both use the same steering knuckle. Doing so yields ~48.9 mm/rev. That tells us that the 330 rack is faster than 14.5:1 when installed on the E46 M3. In fact, we can calculate it to be be ~14.17:1.

Of course, all this depends how accurate that 46mm/rev measurement is. If that number is actually 47mm/rev, then the ZCP and 330 racks would come out about even and I'll be very happy I don't have to try to find a ZCP rack. I'll take some good measurements off my M3 rack next week to verify.

I'll start a new thread to solicit measurements from the community once I have the measurements off my E46 M3 rack. The community should be able to populate the the info for each rack pretty quickly. That way we can have a definitive guide for rack swaps on the E46.

Also, I'm not really concerned about the torsion bars and feel. You can offset the effect of a smaller torsion bar by lowering the power steering system pressure which I've already figured out how to do.

[Obioban]

Originally Posted by Volke

Also, I'm not really concerned about the torsion bars and feel. You can offset the effect of a smaller torsion bar by lowering the power steering system pressure which I've already figured out how to do.

Assist level is separate from feel, imo. A car can have light steering and be extremely feelsome, or heavy and dead isolating (most modern cars).

I can't imagine lowering the power steering pressure increasing feel-- just adding weight/decreasing assistance.

[Volke]

Originally Posted by Obioban

Assist level is separate from feel, imo. A car can have light steering and be extremely feelsome, or heavy and dead isolating (most modern cars).

I can't imagine lowering the power steering pressure increasing feel-- just adding weight/decreasing assistance.

There are a lot of variables that affect feel. Decreasing assist won't do anything to increase feel if your suspension geometry is poor, but I think decreasing the pressure would compensate for the "over-assisted" feel people complain about with a smaller torsion bar. I'll find out for sure when I get a chance to test with a lower pressure.

The torsion bar is effectively a torsion spring that controls how much torque needs to be applied to the steering column to open the valving inside the steering rack and send pressure to the steering cylinder. The power assist reduces how much of the load from the tires is transferred back through the column to the steering wheel. If you remove the power steering all together, there's no reason a rack with a smaller torsion bar would have worse feel than one with a larger bar, so decreasing the pressure should help reduce the difference in feel between the two. If the torsional rigidity of the column was that much of an issue even without power assist, then an aluminum steering guibo should improve feel greatly.

This place has a pretty good explanation of how power steering works.

http://www.agcoauto.com/content/news/p2_articleid/214

[M3 dude]

fwiw,

i found the 330 rack to offer abit less in terms of feel, compared to std.
the rack was also tighter, and i dialled in a tad of toe in up front to save my tyres.
so that could have influenced the outcome.

[terraphantm]

Originally Posted by Volke

That guy's post has a lot of misinformation.

The "unquestionably progressive 330 rack" is unquestionably linear. I measured mine prior to installation. It has 50mm/rev, 3 turns lock to lock and 150mm total travel from side to side. I checked the 50mm/rev directly at center and on both ends.

The Z3 non-M rack is also fully linear. It has 53.5mm/rev, 2.7 turns lock to lock and 144.5 mm total travel. It's a little faster, but as you can tell from the total travel, it will hurt your turn radius a bit.

I'll go get my regular E46 M3 rack from PE on Monday and measure it.



Link? Remember any of the details?

That would mean that both the ZCP rack and the 330 rack are 50mm/rev, but the 330 steering knuckle has the outer tie rod location a little closer to the control arm bolt.

If that's true, saves me the effort and money of trying to find a ZCP rack.

I don't know if my measurements were accurate enough to say for sure whether or not the ZHP rack is 49mm vs 50mm or M3 rack 46mm vs 47mm. I also never had a ZCP rack on hand, I can't confirm or deny whether there's a measurable difference there.

Edit: In this post (which I believe was closer to when I actually changed steering racks and did the measurements), I said the M3 was ~46.5 mm/rev. http://www.m3forum.net/m3forum/showp...0&postcount=13