AutoX Handling Issues (335i xDrive)

[Tallgeese179]

This weekend at autoX I noticed that I was having a lot of trouble getting the front end to turn in on long sweeping corners. I tried messing around with braking a little longer to scrub speed and transfer weight to the front. I also tried throttle induced oversteer, with mixed results since it's AWD and would just make the problem worse unless I really pinned it.

What I remembered is that the alignment printouts from BMW consistently have around 1 degree more camber on the rears (which also causes terrible camber wear on the rears). I'm guessing they do this since the majority of manufacturers try to bake in under-steer into cars since it's the safer of the two. However, I don't want this. I'd prefer a balance where I can more easily get the cart to rotate in (especially since its AWD).

I was thinking about having them reduce the amount of camber in the rear next time I go in or to at least discuss the problem with a service tech. I'd have no problem with more camber up front, but I don't want to have my tires get destroyed so quickly since it's a daily. Anyone have experience with this or have any recommendations?

Thanks in advance.

P.S. This is related to racing, thought with corners instead of roll racing. If it's in the wrong section let me know.

 

[doublespaces]

Hey I saw your AutoX video!

I have never driven a 35ix so I can't comment much on how they handle unfortunately. Are you understeering? I thought that was kind of one of the normal traits of AWD, perhaps due to the way the transfer case distributes power. But I don't know much about those things.

 

[Tallgeese179]

Hey I saw your AutoX video!

I have never driven a 35ix so I can't comment much on how they handle unfortunately. Are you understeering? I thought that was kind of one of the normal traits of AWD, perhaps due to the way the transfer case distributes power. But I don't know much about those things.

Yeah, it definitely feels like understeer. There I would distinctly feel times when I'm at the end of a sweeper and it just doesn't want to rotate. It was distinctly different from going into a corner too hot and turning, where I could hear the tires start to slide sideways. I'm still new to it myself so I'm trying to see if anyone has some experience with it.

On a similar note, I did notice that the steering rack is also relatively slow. Not sure if that's an xi thing, but there were def times when I just needed to add in more steering angle to get it to turn in.

 

[Mike335xi]

The xi steering rack is the slowest of the 3. The "i" rack is faster and the m rack is faster than both of them. The other racks have mounting tabs on the opposite side than the xi rack, so while you can interchange those, the xi can only use an xi rack.

 

[doublespaces]

I'm not an autox'er but I think part of the reason you get understeer, is simply because of the extra weight up front. There may be ways to cover this up, I'm sure there are, I just don't know how to do it properly.

 

[doublespaces]

The xi steering rack is the slowest of the 3. The "i" rack is faster and the m rack is faster than both of them. The other racks have mounting tabs on the opposite side than the xi rack, so while you can interchange those, the xi can only use an xi rack.

Nice first post Mike

 

[Tallgeese179]

The xi steering rack is the slowest of the 3. The "i" rack is faster and the m rack is faster than both of them. The other racks have mounting tabs on the opposite side than the xi rack, so while you can interchange those, the xi can only use an xi rack.

Haha, it's the story of owning an xDrive 3 series.

For every modification "...uh so does it fit xDrive...oh, of course it doesn't"

 

[doublespaces]

Haha, it's the story of owning an xDrive 3 series.

For every modification "...uh so does it fit xDrive...oh, of course it doesn't"

pssst N54 valve cover, cover

 

[1and1]

Want the front end to grip more/turn in faster? Or do you want the back end looser? If you're not sure yet you can make some quick tire pressure changes to help you decide- Raise pressure in the rear will get the rear to break loose easier for example.

Once you get an idea of what you want you can then attack the issue- happy with the rear stepping out easier, maybe go with a thicker RSB. Need more grip up front maybe try stiffer springs in the rear to keep weight up front, or raise your ride height in the rear which would also transfer weight but without a change in spring rate...

Anyway, bring some chalk, a tire pressure gauge and an infrared thermometer to your next autocross and play around with different settings on each run checking how different pressures react on the course along with how much the tire rolls over onto the side wall and what tread temps you get across the face of the tread.

FWIW, I spent a few years autocrossing an AWD Speed6 with pretty good results- Sure it had the benefit of double wishbone rather than mc-strut, but awd is pretty much always an understeering pig till you find the right balance for your car/mods/driving style...

 

[ASquared]

What are your toe alignment specs? Pretty sure toe has a lot to do with turn in as well. I'm sure it's not the be all solution but would be worth another look.