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      02-22-2020, 06:51 PM   #1
Redd
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Suspension Tuning - Dialing out Secondary Motions

When I got my 2010 M3, I felt that the chassis was very sloppy after my last car which was a 2010 RenaultSport Megane RS250 with Cup chassis. My M3 had Competition springs and H&R antiroll bars, but the chassis felt 'loose', like it had a lot of secondary motions and took a long time to settle after a bump. I didn't like that feeling.

Then I got solid rear subframe bushes (I used Turner Motorsports) and instantly the chassis felt like it was one generation newer and tighter with zero additional NVH. The solid subframe bushes got rid of the rear end wiggle that I felt when going over road imperfections like bridge joints. I then realized that our cars have many large rubber bushings throughout the suspension system. These rubber bushes act like small springs, but, more importantly, they were undamped. These large rubber bushes are the source of a lot of the secondary motions - the sloppiness and looseness - you feel in the suspension.

Next I got the Ohlins R/T kit, and there's enough stellar reviews of this mod out there that I won't repeat them. Safe to say that all the comments are true. The Ohlins were firmer than my Comp springs, but at the same time more comfortable because it dialed out some more of the secondary motions with excellent damping. I realized that the undamped secondary motions created a sense of instability in the chassis that had a negative effect on ride comfort. So, softer wasn't always more comfortable.

With the success of the solid rear subframe bushes, I then tried front subframe rigid collars. These did absolutely nothing for the M3 cos our front subframe mountings already had very tight tolerances. Luckily they were a very cheap mod to do.

Next I got Dinan rear toe links and a rear strut bar. The strut bar I added to get rid of a creak from my rear parcel shelf during chassis flex (it worked). These added some extra stiffness to the rear end but did not have a major effect on the secondary motions. I add these here as I think they contributed to the overall change I felt in the chassis which I will talk about later.

After that I go GAS front monoballs. This was another excellent mod with zero NVH and some added firmness in the front suspension. The monoballs greatly improved steering feel and front end steering response. There was also improved stability under braking. It also dialed out some secondary motions by helping the front end to settle quicker after a bump.

The big surprise to me came when I swapped out my differential bushings for Powerflex Purple polyurethane units. I did those as part of my rear diff and LSD rebuild, and it had the unexpected benefit of dialing out a significant amount of secondary motions from the rear end. I guess the original rear diff bushings were soft enough that the rear diff was 'bouncing' slightly on them and that motion was felt in the rear suspension. The harder rear diff bushes did contribute some NVH in the form of diff whine at certain speeds. It didn't bother me much though.

The nett effect is that all of the above has transformed my chassis. I was surprised at how solid the M3 chassis feels now, without being crashy or harsh. It feels as if the entire car is now one solid block of aluminum with zero flex in the chassis. I can actually feel the springs working now when going over bumps, and I can tell that they are the only suspension components moving (as it should be). The dampers now do a great job of damping this spring motion and the car settles much more quickly after a bump. When driving fast, the car takes a set quickly, and becomes less unsettled by road imperfections or roughness. It's much more confidence inspiring than before and reminded me a lot of the RS250 Cup chassis which I dearly missed. The ride is definitely firmer than stock but it's not uncomfortable or crashy, and I have rough roads where I live. A few weeks ago, I had the chance to drive my friend's M3 with stock EDC suspension and it was a night and day difference. The EDC was stiffer, crashier but the chassis felt loose and sloppy. My friend who took my car immediately commented on how planted my car felt, and how responsive the steering was. Also, another effect is I can now feel the rear power delivery much better. Not sure if this is due to the stiffer rear diff bushes or my new OS Giken LSD, but I can feel exactly how much grip I have left in the rear axel and this gives me much more confidence in applying power.

So now I'm on this quest to dial out suspension secondary motions without compromising ride quality (my car is also my daily driver). I'm going to try Bimmerworld Rear Camber Arm Bearings next as these replace a large rubber bush in the rear subframe with no additional NVH (reportedly).
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      02-23-2020, 10:50 AM   #2
wyatth
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Good stuff, Redd. Keep us posted!

Which rear strut bar did you get? Never seen one for this chassis.
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      02-23-2020, 04:40 PM   #3
Redd
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Quote:
Originally Posted by wyatth View Post
Good stuff, Redd. Keep us posted!

Which rear strut bar did you get? Never seen one for this chassis.
Got a cheap Ultra Racing one and sprayed it grey to match the trunk interior. The UR one is mounted higher up closer to the parcel shelf so it doesn't take up much trunk space and you can't see it unless you really duck your head down.
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      02-23-2020, 05:32 PM   #4
rhyary
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Nice report. i am getting my car back from the shop after Turner solid rear bushings. I can't wait to drive it
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