SPD Tuning Service

Page down for detailed information. Suggestions, comments and questions are always welcome.

Why the US gets 15mm rear bars on the 2.5RS and the WRX has a 20mm rear bar.

Think of the larger rear bar as simply sliding the whole steering response curve over a couple of notches. Everything will happen with a little less steering input and the car will begin responding to your feet (brake and throttle) as well as your hands.

With the smaller bar the car needs much more steering input. It soon reaches terminal understeer, where no more steering will help. The larger bar reduces that dead (no pun intended) zone. ON the other end of the steering response curve, the small bar car will not respond to driver brain fade. A full lift or even application of the brake will not cause the car to rotate (or at least it takes much much higher speeds) or another way to put it is the car is much less sensitive (and much less responsive). This blind human reaction of trying to stop or slow down is not always what the chassis wants to see in a crisis, but since inexperienced drivers do it, you get a small bar.

We recommend the 18mm rear bar for automatic transmission cars and standard Impreza cars even if you are a smooth deciplined driver. If you have an RS with a manual transmission or use the Prodrive or STI suspension kits, then a 20mm rear bar is the other choice. We caution the average driver the the 20mm bar demands a certain smooth driving style. Please feel free to discuss this when ordering a rear bar.

Note that it is the proportion of the front to rear bar that is being changed. There are larger bars out there, but for a road car the 19mm/20mm combination has proven to be the magic bullet for experienced drivers. Owners of automatic RS and standard Impreza without up-rated shocks are recomended to purchase an 18mm rear bar. This is is more in keeping with your softer, less aggressive suspension setting.

SCCA Solo II stock class drivers should experiment with a 17mm front bar, as this is a legal combination with the existing 15mm rear bar.

Send mail to mshields@spdusa.com with questions or comments about this web site.
Last modified: May 23, 2000