E46 handling?

I have a 2001 330ci with Koni orange shocks and struts with KYB mounts, OEM sports springs. I squeal my tires going around medium sized round-abouts at 25. I also get a pop from the rear occasionally when going around one. I'm on 225 and 245 all year continental DWS tires.
Is my handling really just this bad? Or is something wrong? I heard about the RTAB going bad and causing handling to decrease at some point. Could that be it? Thanks!

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What tire pressure are you running?

Squealing tires doesn't mean bad handling, but the pop concerns me. What would you estimate as the diameter of this roundabout you speak of? If you are around 0.75-0.8g at that point the tires will definitely be squealing on any normal car.

New RTABs would definitely help to settle down the rear. Especially if they are original, or haven't been replaced in some time. Same goes for the rear ball joints and lower control arm bushings. These items also might be causing the popping noise you hear.

In reference to the pop, you might also want to get the rear subframe mounts and mounting points looked at. As to the squealing, different manufacturers tire compounds start to squeal at different load points. Some start at lower loads to give you early feedback before breakaway, some give you almost none.........

Pressure is fine. RTABs have never been replaced as far as I know, nor any of the bushings in rear.. at 164k miles. Haha. I can't turn as hard as my buddy's civic if that gives you anything..

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+1 on rtabs! I just changed mine at 56,000 miles and they were 100% blown out. The center spacer was seperated from the bush and the TA was knocking side to side on heavy shifts. I blew threw 1 set of Pilot SS tires in 7k and almost wasted my replacements already. When people say Bmw bushing need to be changed at 60k they aren't kidding.

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Originally Posted by Weste46

Pressure is fine. RTABs have never been replaced as far as I know, nor any of the bushings in rear.. at 164k miles. Haha. I can't turn as hard as my buddy's civic if that gives you anything..

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well you car weights 3400lbs and you buddy's civic is probably 2400lbs or less.
besides DWS is not for its grip at limit.

Originally Posted by HiHoBrian

+1 on rtabs! I just changed mine at 56,000 miles and they were 100% blown out. The center spacer was seperated from the bush and the TA was knocking side to side on heavy shifts. I blew threw 1 set of Pilot SS tires in 7k and almost wasted my replacements already. When people say Bmw bushing need to be changed at 60k they aren't kidding.

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I would imagine M3s are a lot more punishing on RTABs. But good job at replacing them anyway. they needed it for sure. I just did a friend's E36 M3 rtabs at 160,000 miles and they were completely blown out. center torn away.

I had dws' as my last set of tires and they squealed like crazy! Most all season tires squeal a lot. My car handled just fine on them, they were just loud.

Max lateral tire force increases with applied weight so the mass doesn't really affect the maximum lateral acceleration as much as you think. The BMW should be able to turn with the civic. If you want to see if it really isn't turning as hard as it should, set up a large diameter skidpad (about 150 ft diameter). See how fast you can go around it until you can't keep the radius any longer. That is your max lateral acceleration (a = (v^2)/R) where R is half the diameter of the circle and v is your velocity. Convert your speed into ft/s and your radius into feet then divide a by 32.2 to get your estimate in G's. If you are good at graphs look at the one attached. It is a computer sim of a G35. Should be similar.

Originally Posted by WDE46

Max lateral tire force increases with applied weight so the mass doesn't really affect the maximum lateral acceleration as much as you think. The BMW should be able to turn with the civic. If you want to see if it really isn't turning as hard as it should, set up a large diameter skidpad (about 150 ft diameter). See how fast you can go around it until you can't keep the radius any longer. That is your max lateral acceleration (a = (v^2)/R) where R is half the diameter of the circle and v is your velocity. Convert your speed into ft/s and your radius into feet then divide a by 32.2 to get your estimate in G's. If you are good at graphs look at the one attached. It is a computer sim of a G35. Should be similar.

well the civic is heavier in the front so more front grip also shorter wheel base.

Originally Posted by jasonbimmer

well the civic is heavier in the front so more front grip also shorter wheel base.

More weight on the front actually induces understeer. The additional vertical force applied to the tire increases the cornering stiffness of the tire, but this is almost always offset by having additional mass to accelerate. Basically, even though the front tires may be capable of providing greater lateral force, the force is wasted on the additonal mass of the front of the car. A front heavy car will be understeer all other things being equal. So, the civic probably has more understeer than the BMW.

To break it down a little more: If I add 10 lb of load to the front axle, the maximum lateral force of the tire will not increase by 10 lb. I have attached two more graphs. They are based on the Pacejka tire model (look it up) which is quite accurate and interesting to look at.

Ca vs Fz shows the Tire Cornering Stiffness (Side force per slip angle, y-axis) vs the vertical load (Vertical force on tire). Note the peak of the graph. After a certain point, adding downforce will actually decrease the cornering stiffness (though the max lateral force continues to increase).

Fymax vs Fz shows the maximum lateral force the tire can provide versus the vertical load.

The wheelbase affects the yaw moment of the vehicle. Given two vehicles with the same weight distribution, the one with the longer wheelbase will have larger yaw moment. All other things being equal, the shorter car will have a higher peak lateral acceleration in stead state cornering. The length affects other things though. The longer car will be more stable at higher speeds. The shorter car will become unstable at a lower velocity, so there is a balance you want to reach between keeping your yaw moment low and your critical velocity (the speed at which the vehicle becomes unstable) high. There is a reason Formula 1 cars are so long.

I have a ton of other graphs for this stuff and I can make more on my home PC with almost any variables. If you want to see more just ask, I love writing about this stuff.

How did you guys do your RTABs? I don't wanna have to buy the tool to press them out.. thanks!

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Originally Posted by Weste46

How did you guys do your RTABs? I don't wanna have to buy the tool to press them out.. thanks!

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I just order the parts to do mine from BimmerWorld. They have a tool you can rent. It is $99.99 and you get $60 back upon return and they include return shipping. $30 for the right tool is worth it IMO.