[Dhillon92]

Hey guys, I only got my car a month or so ago and am still learning about the xdrive suspension and its components. It isnt my first car, that being said I feel it has more body roll than I am comfortable with.

After doing some readings/research, I've purchased the M3 rear sway bar, and am considering the rear subframe bushings as well (since I would be in there for the sway install anyway). My question is: Will upgrading just the rear roll bar and SF bushings cause any damage or more wear and tear on the rest of the stock suspension components? I plan on getting KWV1s, maybe after winter comes and goes though, I also have 19" staggered tires with 12mm spacers on the rear.

Just looking for some input and direction I should take with upgrading suspension components.
Thanks!

[ajsalida]

Umm, I would suggest you read some more. At the very least put on a front bar (UUC is the only one available last I checked).

The springs on XI are much stiffer than even OEM non XI sport, you are going to end up with a very tall car on stiff springs with a relatively very stiff rear roll bar.

I would suggest doing the suspension first (springs & shocks), after doing a great deal of reading. Then a front bar, then after digesting all the various opinions, the RSB and last (possibly with RSB) the rear bar. There are a ton of other bits (other bushings M3 arms etc.) you may or may not want.

Bottom line an XI with ONLY rear M3 bar (which one by the way?) and RSB's added could be a very scary car to drive, lot of oversteer and very twitchy, with hopelessly soft stock shocks.

I did the M3 rear bar (off the e92 M3) with RSB inserts, but only after sorting out the rest of the suspension pretty well (Koni/eibach and various springs for a year or so).

Even with the lowering and better shocks, rear was far too stiff roll-wise and immediately went for a front bar to even it out. I can't image what it would have been like with the tall and stiff stock springs, weak shocks, and limp front roll bar.

edit: I guess the point is the XI suspension is very tricky, not at all like the non XI. You would be better off and probably much happier starting with the suspension first (springs and shocks) get that all sorted out WRT ride height, stance, spring rates etc etc. Then see if it has too much roll, at which end, and why. Then if you feel the need, go after RSB's, bars (F/R) and all the other things you've found out by then about the car you want to change. M3 rear bar won't get lonely sitting in the garage in a box.

[Dhillon92]

Hey,thanks for the informative feedback, alright so I will save the rear sway and RSF bushings until I get a suspension in. Regarding the front sway bar, isn't the stock one 26.5 and the uuc 27? I understand the stock one gets smaller in the middle but is it a noticeable difference?

Im interested in the KWV1 for their adjustability since winter snow gets crazy over here, and I think the cost is similar to a good shock/spring combo.

Thank you very much for your input!

Edit: I got the non-vert m3 rear bar

[ajsalida]

There is a thread here in the XI section on the UUC bar, a good read. Yes the stock bar does have a taper to it, UUC does not. It is much stiffer than the stock bar. Lot of people here are pleased with the KWV1's, I have no direct experience with them.

As far as winter goes, be aware you'll need to get an alignment each time you raise and lower the car. Another solution is go with a moderate drop and not mess with it.

[Julian2485]

I have m3 rear bar plus rsb I put them on first and the car handled very well then later put on bilstein hd the car handles even better I don't have a upgraded front swaybar though

[ajsalida]

I liked it (m3 rear bar + RSB inserts, stock front bar) for a day or two but then when I started to push it a little it felt too twitchy for my tastes and driving style. Clearly there are other opinions.

[b-man]

I have v1s. They make a big difference in handling. But if you're looking for a comfortable ride, I'd say go with a more expensive coilover setup, or get shock/spring combo. My next upgrade is the ucc front sway bar. I'm not sure if I want to deal with the rear after that. A lot of work to change the rear sway bar

[ajsalida]

Quite a lot of the handling dynamics of the XI change substantially when the car is lowered and "stanced" or whatever you call it. You go from very tall with front higher than rear (wheel gap wise), to lower overall but more drop in front with wheel gaps equal F/R. This puts some more weight on the front and off the rear.

So I think it is a good idea to get your stance/drop/ride comfort etc sorted out with shocks/springs or coilovers and then decide on the bars and bushings. You drop the car using stiffer rear springs and you may have enough rear roll stiffness already to not need a big bar. Stiff rear springs + RSB + rear bar may knock all your fillings out or start something else wiggling and you replace ALL the other bushings trying to track it down.

Just about all these e9x cars XI and I seem to like a bigger front bar. Fortunately that is an easy DIY swap.

The rear is super complicated dynamically (~50 rubber bushings) and very sensitive to minor changes in various component stiffness, and seems to even be different for each car, owner, shocks/springs, age of car etc. Plus super hard to swap bars and RSB's so for all those reasons maybe good idea to wait.

Point is you could swap the rear bar and RSB's and love it (or not), then you put on your springs/shocks and not love it, and be chasing that down for a while and $$$. It is not a simple XYZ recipe.

[Dhillon92]

Thanks again for the feedbacks! I understand where your going with the RSB and sway bar, saying it is the last thing I should do. I agree with you, I just didnt see myself buying a coilover set anytime soon, so I figured I could cheap out and just get the bushings/bar for some improved handling.

b-man, I had thought the V1s at a moderate drop would have been a quite comfortable ride over shock/spring combos. I guess I'm going to choose a suspension by the next couple months and have the set up ready to go as soon as winter ends. I see a lot of potential handling improvements on this car, and just itching to fulfill them.

thanks for the read and the feedback guys.

[ajsalida]

Just to beat a dead horse, the RSB + rear bar install cost is very expensive if you pay someone. Like on the order of 6 shop hours. So unless you DIY (and it is a huge job) the cost of parts and labor are going to be more than for a nice suspension.

An alternative to the RSB at least are RSB inserts, from either powerflex or whiteline. Cheap and vastly easier than full RSB R&R. Also reversible. Whiteline are only $50. I did the rear M3 bar and whiteline RSB inserts in my garage, it was time consuming but not difficult. Good results and noticeable improvement. You look at the DIY (in the DIY section) for full RSB it looks like open heart surgery.

[Julian2485]

Originally Posted by ajsalida

Just to beat a dead horse, the RSB + rear bar install cost is very expensive if you pay someone. Like on the order of 6 shop hours. So unless you DIY (and it is a huge job) the cost of parts and labor are going to be more than for a nice suspension.

An alternative to the RSB at least are RSB inserts, from either powerflex or whiteline. Cheap and vastly easier than full RSB R&R. Also reversible. Whiteline are only $50. I did the rear M3 bar and whiteline RSB inserts in my garage, it was time consuming but not difficult. Good results and noticeable improvement. You look at the DIY (in the DIY section) for full RSB it looks like open heart surgery.

Did you do anything to the front of your suspension. I just ordered a e90 m3 front bar

[ajsalida]

Originally Posted by Julian2485

Did you do anything to the front of your suspension. I just ordered a e90 m3 front bar

Better cancel that order, M3 front bar does not fit XI, no I front bar fits. I have the UUC bar, only one that fits XI as far as I know.

[gtaccord]

Originally Posted by ajsalida

Umm, I would suggest you read some more. At the very least put on a front bar (UUC is the only one available last I checked).

The springs on XI are much stiffer than even OEM non XI sport, you are going to end up with a very tall car on stiff springs with a relatively very stiff rear roll bar.

I would suggest doing the suspension first (springs & shocks), after doing a great deal of reading. Then a front bar, then after digesting all the various opinions, the RSB and last (possibly with RSB) the rear bar. There are a ton of other bits (other bushings M3 arms etc.) you may or may not want.

Bottom line an XI with ONLY rear M3 bar (which one by the way?) and RSB's added could be a very scary car to drive, lot of oversteer and very twitchy, with hopelessly soft stock shocks.

I did the M3 rear bar (off the e92 M3) with RSB inserts, but only after sorting out the rest of the suspension pretty well (Koni/eibach and various springs for a year or so).

Even with the lowering and better shocks, rear was far too stiff roll-wise and immediately went for a front bar to even it out. I can't image what it would have been like with the tall and stiff stock springs, weak shocks, and limp front roll bar.

edit: I guess the point is the XI suspension is very tricky, not at all like the non XI. You would be better off and probably much happier starting with the suspension first (springs and shocks) get that all sorted out WRT ride height, stance, spring rates etc etc. Then see if it has too much roll, at which end, and why. Then if you feel the need, go after RSB's, bars (F/R) and all the other things you've found out by then about the car you want to change. M3 rear bar won't get lonely sitting in the garage in a box.

I don't think the stock xi springs are stiffer than the non sport i springs. They are just taller and the shocks are valved differently.

If you do some reading, there are basically 3 camps. Leave the front sway alone and replace the rear with the M3, replace the front with the UUC only or replace the front with UUC and the rear with the M3. All of these assume that you have already modified the struts/springs and upgrading the rear subframe bushings go along with the rear sway upgrade.

There is a lot of suspension theory that supports the first option. A bigger rear bar only will reduce understeer and make the car more neutral overall. This will make the car feel more like a rear wheel drive car. This method is used on a lot of all wheel drive cars (subies go with equally sized f/r sways or bigger rears) and bigger rear bars with stock frontsare also used on a lot of front wheel drive cars to make the car "rotate" ie less understeer. Upgrading the front bar only will flatten the car out and make it "feel" better but it will not eliminate the understeering tendency of the car. In fact it will make it worse. Upgrading both bars should really only be done in extreme cases imo (racing/competition) when you can match them with a quality coil over suspension and good suspension tuning (corner weighting etc). This is probably a bit much for the street.

Do some searches in this section on sway bars. Those posts cover the topic a lot better than I can. I will recommend that you proceed carefully when changing out the sways since they can significantly change the behavior of the car and not always in a good way. I have found this out the hard way in the past.

[ajsalida]

Originally Posted by gtaccord

I don't think the stock xi springs are stiffer than the non sport i springs. They are just taller and the shocks are valved differently.

They are stiffer, I measured them. They have the same dead length and # of coils, but thicker wire. Both front and rear. The fronts, if you've ever tried to compress them in a spring compressor, are very obviously stiffer. Than OEM non-XI ZSP or even Eibach pro-kit.

Furthermore, when you swap in OEM non-XI ZSP springs, the difference in ride height is substantial, for springs that look identical (except for wire thickness).

The shocks are valved differently, I am not sure how, but they are not very well matched to the springs. It could be that shocks are valved the same and the springs are so much stiffer they overwhelm the shocks, and that is why they feel so bad. Would need to put them on a shock dyno to compare but why. They suck.

As for the front bar, it is not as straightforward cookie-cutter as the theory implies (eg more front bar = more understeer). Due to McP front susp on BMW's the tire is not in optimal contact/orientation with the road under side loads. Bigger front bar will in many cases give you better grip in front and LESS understeer, as it keeps the tire more vertical WRT road surface under load due to less body roll. Then once you exceed that traction, sure.

But you are right about one thing, there are many camps and more reading is better than less. Quite a few people have put only the bigger front bar on and are pleased.

The nice thing about the front bar is it is so easy compared to other mods to do or reverse. 1 hr tops in your driveway with basic hand tools, nothing complicated or difficult. So you can do it and evaluate without too much trouble. Rear sway and RSB, forget it. You better 100% know you want it because reversing it is ugly and expensive.

[Dhillon92]

Thanks for more information! I think I'm going to just hold out on the sway bar and bushings I guess, atleast until I get in a new suspension. Labour is not a problem, but I dont want to waste $300+ on the subframe bushings just to "feel" if I want to keep it or not, so I'm going to put this whole suspension project on hold until I can make a final decision if I want to install just a rear sway bar, with the bushings. I dont really want to turn back after that point.

[Julian2485]

Originally Posted by Julian2485

I have m3 rear bar plus rsb I put them on first and the car handled very well then later put on bilstein hd the car handles even better I don't have a upgraded front swaybar though

I still have stock xi springs on as well I didn't want to drop the car due to bad roads and weather out here in ny

[gtaccord]

Originally Posted by ajsalida

They are stiffer, I measured them. They have the same dead length and # of coils, but thicker wire. Both front and rear. The fronts, if you've ever tried to compress them in a spring compressor, are very obviously stiffer. Than OEM non-XI ZSP or even Eibach pro-kit.

Furthermore, when you swap in OEM non-XI ZSP springs, the difference in ride height is substantial, for springs that look identical (except for wire thickness).

The shocks are valved differently, I am not sure how, but they are not very well matched to the springs. It could be that shocks are valved the same and the springs are so much stiffer they overwhelm the shocks, and that is why they feel so bad. Would need to put them on a shock dyno to compare but why. They suck.

As for the front bar, it is not as straightforward cookie-cutter as the theory implies (eg more front bar = more understeer). Due to McP front susp on BMW's the tire is not in optimal contact/orientation with the road under side loads. Bigger front bar will in many cases give you better grip in front and LESS understeer, as it keeps the tire more vertical WRT road surface under load due to less body roll. Then once you exceed that traction, sure.

But you are right about one thing, there are many camps and more reading is better than less. Quite a few people have put only the bigger front bar on and are pleased.

The nice thing about the front bar is it is so easy compared to other mods to do or reverse. 1 hr tops in your driveway with basic hand tools, nothing complicated or difficult. So you can do it and evaluate without too much trouble. Rear sway and RSB, forget it. You better 100% know you want it because reversing it is ugly and expensive.

Thanks for the info on the xi springs. I had never actually compared them directly to the i springs.

[ajsalida]

Originally Posted by gtaccord

Thanks for the info on the xi springs. I had never actually compared them directly to the i springs.

I wouldn't have noticed except I broke a spring compressor on the XI springs they were so friggin' stiff. Happened to have a set of OEM ZSP sitting there and compared them side by side (after I got a new spring compressor and cut the old one off).

They (XI) are also stiffer than Eibach pro-kit fronts, which is what I replaced the XI springs with at that time.