*Original guide rods were made to deflect under load, a bad thing for good handling and traction(in of the the product images you can see where the stock 335i guide rod can deflect and bow under cornering and acceleration loads)
*Aluminum guide rods are made of all aluminum, a lightweight component thereby reducing wear and tear on other, more critical parts (rear subframe, control arm bushings, etc) Each guide rod weighs just over 1.5 lbs making for a total of ~3 lbs for both parts (stock guide rods weigh 2.1 lbs each or 4.2 lbs for both). A weight savings of over 1.2 lbs from the rear suspension.
*Bushing with a rubber material at one end is replaced by a sealed joint for deflection and noise free operation. Bushing deflection is unwanted because it leads to excess suspension movement. This is bad for handling and traction due to constant alignment changes. Plus, any power from the engine can take longer to get to the ground because it has to windup the bushing first.
The traction link is no brainier. You will have better traction and braking and more stability and you will feel this under acceleration. The traction link is actually a tuned spring so it is designed to deflect a lot under load which is really bad for the suspension control. This is the most important link to replace.
Retail: $412.80
$359.13
Order here:
http://www.hpashop.com/BMW-Rear-Guid...kit-e9x-m3.htm
We now have the TRW version of these guide rods.
$445.89
Order here:
http://www.hpashop.com/BMW-Rear-Guid...de-Rod-TRW.htm