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      01-09-2010, 09:19 PM   #1
JAJ
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Drives: 2014 Shelby GT500
Join Date: Apr 2008
Location: Vancouver, BC

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Suspension Upgrade Options for the M3

It’s winter and thoughts turn to the coming of spring – it’s time to think about suspension options!

I have to thank RLDZHAO for starting the survey thread of suspension kits. It would have been helpful before I started, but I was well into my analysis before it first appeared. This is the first of a number of posts. I’ll try to hold each post to one element of the suspension “situation” and focus on background rather than the merits of the various kits.

In the end, I built a set of motion analysis spreadsheets for the suspension and took four pages of notes and diagrams of measurements of the suspension itself. There’s a lot of misinformation out there on suspensions, and a lot of opinions. My goal is to just lay out the facts.

The most obvious fact about the M3 suspension is that the BMW engineers did a brilliant job. It’s going to be difficult to improve on it. You can re-prioritize your goals (handling, looks, etc) and improve one at the expense of the other, but there will be tradeoffs.

Before I dig into the M3 itself, I came to understand that there are three broad types of suspension kit for the E92 M3 and some interesting non-kit options as well.

The first broad type (let’s call it “Type One”) is “lowering springs”. Lowering springs drop the ride height of the car. They function on EDC and non-EDC cars, and while you can swap the dampers out, you don’t have to. They are usually form-fit-function replacements for the stock springs. Some (like Dinan) come with other replacement components; most don’t. You have the option to use replacement dampers from Bilstein (non-EDC cars only) to replace the stock dampers when you install lowering springs. The effect of lowering springs on handling is hard to predict – more on this later in another post.

The second broad type (Type Two) is “street-sport suspension kits”. These kits are essentially lowering springs matched with adjustable dampers. Examples are the Bilstein PSS-10 and the Moton StreetSport. They usually provide both adjustable ride height and adjustable damping rates. You can tell a street-sport suspension because it uses the factory upper spring and strut mounts – it doesn’t use race springs and it doesn’t come with camber adjustment plates.

The third broad type (Type Three) is “club-sport suspension kits”. These kits replace the stock upper spring mounts so that standard-sized (60mm or 2.5” ID) race springs and camber adjustment plates can be fitted. With this type of suspension, you can not only adjust camber, ride height and damper settings, you can swap out the springs to change the rate. The dampers are usually double-adjustable, which will demand some expertise to set properly. Examples of this type are KW Clubsport kits, Moton ClubSport kits, and products from TCKline and Ground Control.

The Type Four suspension is really the do-it-yourself “non-kit” kit. Buy dampers, buy hardware, buy springs and put it all together. Any of the club-sport units can be reinvented as Type Four suspensions just by changing your mind about a component. You can also buy racing dampers and build them yourself. Information on these is usually scarce – for instance, Bilstein makes a “VLN Suspension” for the E92 M3 that was aimed at the VLN racing series in Germany. It has to fit a stock M3, but beyond the fact that it exists, there’s no data sheet for it. Oh, for 2010, VLN’s governing body excluded cars over 3.5 liters, so the E9x M3 is no longer eligible. Of course, speaking of racing kits, Ohlins and Moton both make damper sets (just add springs and stir) for the M3 GT4. Buy those, you’re good to go. Pricey, finicky, but rewarding when you get them dialed in.

Next post will be on the challenges that the factory design presents for designers of each type of suspension.
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