iX 2 Door to 4 Door Swap?

[nando]

The trans tunnel fab should not be difficult. Don't let that stop you.

The strut towers are, I think, very much open for debate.

My iX has power steering disabled (belt's been gone he entire time I've owned the car). It doesn't bug me, but what it does is give me *much* better contact patch feel at the limit of tire grip.

The iX, because of its very small caster angle has very poor feel for when a contact patch is about to break loose. There's essentially no change in load on the steering wheel between full grip and sliding.

That being said, the extra caster of the RWD body would *certainly* help contact patch feel.

However, would AWD with that caster angle induce torque steer? I don't know. I suspect not, but I haven't built such a car... yet. I'm also not sure why BMW built the car with so little caster. Did they make a mistake because of their lack of experience with front wheel drive?

Did they feel like the drive torque + caster would muddy steering feel? I can't see that as being their motive because what they did in response certainly muddies steering feel.

In your shoes, I'd do the swap. Please let us know how it turns out.

ETA: Another point: the AWD crossmember bolts to different locations on the body than the RWD crossmember. I've been told that the front bolt holes of the RWD crossmember are in the same location as the rear holes in the AWD crossmember. If that's the case, just bolt the AWD crossmember up to the front two locations in the RWD body and then weld steel in until you have the other two bolt holes. You may also need to notch the front frame rails a little bit for axle clearance.

There's no torque steer on an ix. That's mainly caused by unequal length halfshafts (from center of joint to center of joint), common on FWD cars.

The caster angle wasn't a mistake. It was done to optimize traction on slick surfaces for both acceleration and braking - it's all about weight transfer. They didn't do this on later AWD cars but they also came with crummy open center differentials and fake limited slip controlled by the brakes (E46 I'm looking at you). Cost comes before performance these days when it comes to BMW.

I wonder if it would actually work just fine to have the ix drivetrain with the RWD strut towers - it may in fact handle better, albeit on dry surfaces (the extra dynamic camber would be nice). The important part would be the ix subframe, which you'd definitely need to swap over. I think on later cars the frame rails are basically the same and you can bolt it on, on earlier cars you'd have to extend it.

Otherwise, if you want more caster angle get the M3 offset bushings and run the GC camber plates. It's good for a couple more degrees, which is a lot considering stock is about 1.0-1.5.

[The Dark Side of Will]

The caster angle wasn't a mistake. It was done to optimize traction on slick surfaces for both acceleration and braking - it's all about weight transfer.

Where'd you hear that?
I'm not sure I buy it... weight transfer doesn't care about geometry. Weight's going to transfer based on wheelbase/track, CG height and g forces.
The geometry just controls how much of the weight transferred goes into the springs vice the suspension pivots.

I wonder if it would actually work just fine to have the ix drivetrain with the RWD strut towers - it may in fact handle better, albeit on dry surfaces (the extra dynamic camber would be nice). The important part would be the ix subframe, which you'd definitely need to swap over. I think on later cars the frame rails are basically the same and you can bolt it on, on earlier cars you'd have to extend it.

Especially if the ostensible reason they built the AWD cars with no caster was traction on snow and ice, I think that an AWD powertrain in a RWD shell would handle much better than an original AWD car, at least as far as the items we've identified: contact patch feel & caster induced camber gain. However, such a beast would gain some bump steer because the extra caster would raise the outer tie rod end. The rack could be spaced up, but that would probably interfere with engine position. Might as well just make some bespoke hub carriers to fix the bump steer ;-)

It would make sense that once BMW started to build the AWD cars, they would have used the AWD frame rails across the lineup in order to simplify supply chain and manufacturing, but Germans are generally not good at simplifying things.

[nando]

There was a discussion about it a long time ago, now lost, on E30tech.

I doubt the increase in bump steer would be significant from the caster changes. It's not very noticeable even on a very lowered ix with the maximum caster possible. It could be a problem if the ball joints don't have enough travel though due to the extra angle involved.