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      04-23-2010, 07:02 AM   #1
UncleScottie
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Z4 3.0si coupe vs 3 series.

It seems that in these forums a lot of the blame for the Z4's poor steering feel and poor ride quality gets put on the run-flat tires and Electric Power Steering (EPS). However, new 3 series models, which have both EPS and run-flat tires, get high marks in most reviews for both ride and steering.

Is this simply BMW starting to get a better handle on EPS and run-flat tires? Or is there more going on such as significant front suspension geometry differences for things like caster and trail? I know run-flat tires are slowing improving, but I believe I also read BMW switch to Sachs struts and shocks on recent 3 series cars.

I guess what I'm getting at is whether or not any of the things that allow the recent 3 series cars to get good marks for steering and ride be applied to ours cars and at what cost?

Last edited by UncleScottie; 04-23-2010 at 07:15 AM..
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      04-23-2010, 11:49 AM   #2
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I don't have the TIS for the E90's, only for the E85/86 but a little searching on RealOEM could shed some light on the mechanical..
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      04-24-2010, 02:41 AM   #3
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Quote:
Originally Posted by UncleScottie View Post
Is this simply BMW starting to get a better handle on EPS and run-flat tires? Or is there more going on such as significant front suspension geometry differences for things like caster and trail? I know run-flat tires are slowing improving, but I believe I also read BMW switch to Sachs struts and shocks on recent 3 series cars.
A couple of thoughts, just my opinion. First, having owned a 2003 Z4 with run-flats and EPS, I always felt BMW was simply lying their asses off when they claimed they'd tuned the suspension for the RFTs. The car was too bad with them and too good without them for me to believe BMW simply got it that wrong - they fudged. I've heard the facelift cars are a bit better on the RFTs because by then they were common on the 3-series, but I've never sampled one.

I would concede that they got better with EPS on the 3-series after the over-servo'd versions on the Z4. That was just straight-up technological progress. However, because the ECUs are vastly different, I don't see that tech transferring to old Z4s.

And our front suspension has much shorter travel/length, making any kind of 3-series swap improbable. Much simpler to drop the run-flats and get nicer tires and a flat tire kit.
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      04-24-2010, 09:03 PM   #4
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don't forget the wheelbase length and it could be softer bushings considering they are different markets. Also ours are based on a modified e36 front design, which could be a good or bad thing depending on what you prioritize
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      04-26-2010, 07:27 AM   #5
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Quote:
Originally Posted by epbrown View Post
.....And our front suspension has much shorter travel/length, making any kind of 3-series swap improbable.....
Wasn't thinking as much swapping of parts as just knowing the differences in geometry and if things like caster, trail, camber, toe could optimized. It may very well be that our cars are handicapped by the suspension design and thus could never achieve the steering feel of the 3 series.

What it really comes down to for me is whether or not it is even worth attempting to remedy the things I don't like about the car or just get another car that already has the qualities I feel the Z4 3.0si Coupe is missing.

I was really hoping this thread would get into more technical details than just broad generalizations and opinions.
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      04-26-2010, 02:32 PM   #6
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Is this what you want? Attached is a printout of the alignment specs for the car. Non-M I think...

I am beginning to get the feeling that you need to trade your car in and get something you like.

The Zed is not for everyone, and based on your comments to date, it might not be the car for you. You might be better off in a Z4M since is does not have electric steering. Barring that, a 1,3 or 5 series.
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      04-27-2010, 06:35 AM   #7
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Quote:
Originally Posted by Shipkiller View Post
......You might be better off in a Z4M since is does not have electric steering. Barring that, a 1,3 or 5 series.......
Yes, the Z4M does not have have electric steering, but my point is that EPS is not at fault here. The 3 series has electric steering, yet it gets rave reviews for steering and ride (the 3 series also has run flats).


Thanks for the info.

Your right the Z4 is not the car for me in stock form, hence this thread. Unfortunately it has put a bad taste in my mouth. If I go with something else it won't be a BMW. I would either go back to a marvel of engineering, the S2000 or a Cayman S.
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      04-27-2010, 12:50 PM   #8
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Just try non runflats...I have a e90lci and have had a s2000 and a 997 before coming to the e85 platform and I love it The couple hundred in tires will save you the hit from trade in.
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