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Xi Understeer Questions

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understeer xi
12K views 41 replies 6 participants last post by  fastjasonbmw 
#1 ·
I'm assuming that I am not the only person who has experienced this, but my 325xiT occasionally understeers on fast curves. It isn't very bad, although once I almost plowed directly into a curb. Luckily I was able to give it a bootful of power and make the turn thanks to the RWD biased system. However, I still don't like that I can't turn as fast as RWD. Can I do anything to help this? I'm thinking about adding a fender strut to help with the weight shift. Any ideas?
 
#8 ·
Tires- Michelin XSE 205/55 R16 (They are in need of replacement and I will be putting the new ones on ZHP alloys. Not sure on which type of tire just yet, but definitely all-season
Pressure- 38 psi front, 45 rear, just as my door jam says
Suspension- Completely standard, non ZSP. If I'm not mistaken, Xi models with sport pack didn't receive the sport suspension at all?
 
#14 ·
in many years of autoxing and tracking an E30 ix, which has the same torque split and similar weight distribution, I always had the best results running significantly higher pressures up front, rather than the other way around.

With hoosier slicks I'd start at 50 psi front, 38 rear (cold), and work my way down to 45-47 psi front, 35-38 rear (hot). With "normal" tires I found a similar bias worked but 5-psi or so less. in street trim I run a couple PSI more up front.
 
#9 ·
Try 35f/38r.

ZHP wheels are very heavy. Lighter is better- they will slow you down compared to 16s. If you want handling, spend money on summer tires, not all seasons. Keep the 16s and get some cheap all seasons used on craigslist and run them in the winter.

There is no sport suspension on xi's, but I think eibach and koni make springs and shocks for wagons.
 
#10 ·
Wow thats a lot of great information! I'm going to start with the tires since I have barely any tread. The suspension was very low on my list of future mods but now I am going to bump it up top. As for the tire pressure, the lower numbers make a lot of sense now and I'll try that immediately. In the meantime, I need a servicing so I'll ask about what BMW thinks of the suspension on it. I noticed it rides a little high on the driver's side (very weird, should be the opposite).
 
#11 ·
Wow thats a lot of great information! I'm going to start with the tires since I have barely any tread. The suspension was very low on my list of future mods but now I am going to bump it up top. As for the tire pressure, the lower numbers make a lot of sense now and I'll try that immediately. In the meantime, I need a servicing so I'll ask about what BMW thinks of the suspension on it. I noticed it rides a little high on the driver's side (very weird, should be the opposite).
Famous last words.
 
#15 ·
50 psi seems like a lot but I can understand why you would want so much at the front. I'll try it a few different ways to see what works. Luckily, I have the fact that it's a wagon on my side. That adds more weight to the rear getting closer to the 50/50 weight distribution. I've read that Xi sedans are 52% front, 48% rear.
 
#18 · (Edited)
To get the most grip from your tires, you need to maximize the contact patch. To do this, you chalk your tires along the outer rib of the tread down to the sidewall. You get the most grip when you roll the tire all the way to the rib of the tire without riding on the sidewall itself.

First you maximize grip at all four corners by determining the lowest pressure you can run without rolling on the sidewall. Then you figure out if the car is oversteering or understeering. If you are understeering, you add pressure to the rear to decrease the contact patch, until the car is neutral. If you have oversteer, you add pressure to the front.

Maximize grip at the front, then reduce rear grip to balance the handling.
 
#21 ·
Possibly one of the dumbest posts I've read in a while. How did you even come up with all those "solutions?" Did you just think if you buy something for your car and install it, it will fix a problem that you aren't even sure about?

Seriously, go learn how to drive. If you can't afford to go karting, autocross, or track days, then buy a playstation and gran turismo 5 and beat the game. Or even reading a book about driving would help so much.
 
#23 ·
Do you really want to start this? I'm not naming a bunch of solutions for an unknown problem. I know that I made the mistake of getting AWD, but there are ways to get around it. Basically, I want an AWD Touring with the performance and handling of an M3. I know of some very expensive and effective solutions, but wanted to see what others say first. Sometimes the best solutions are the simplest. Money isn't the issue, I just like to do a little research before I buy stuff.
And speaking of racing, yes I have done some. I would like to get a normal thing going with it but safety regulations won't let me use my Honda S2000.
Also, if you are insinuating that the understeer is my own fault, I think you will find it's not the case. Go to another forum to criticize.
 
#35 ·
Thanks for the compliment on wagons. I very recently got my S2000 and looked into track events. The organizers of the track told me that my car wouldn't meet the regulations of any of the clubs that raced there.
Also, I know all of the issues with the Audi's, that's why I don't drive one.
And, none of your last sentence is true, so allow me to break the trend.
 
#38 ·
^ I didn't say you were an idiot. I didn't like the suggestion to start with 50/38 based on e30 experience.

He should set the fronts low enough so they don't roll, and balance the car by setting the rear. Three hundred pounds is huge, yes I know a few ix's that are driven at the track, and setting fronts 10+ higher is not going to work well.
 
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