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BMW E30 Sway Bar Modifications
 
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Pelican Technical Article:

BMW E30 Sway Bar Modifications

Robert Bowen

Time:

3 hours3 hrs

Tab:

$30-$120

Talent:

***

Tools:

wrenches

Applicable Models:

BMW E30 3-Series (1984-93)

Parts Required:

Sway bar

Performance Gain:

better handling and performance

Complementary Modification:

New shocks
The CarTech BMW 3-Series Performance Guide

Whether for on-track duty or simply improved street performance, the E30 series cars have proven to respond to well-chosen upgrades. The CarTech BMW 3-Series Performance Guide offers current and future owners a wealth of important information, including a buyer's guide, year-by-year upgrades and changes, and more. This book is a valuable addition to every BMW owner's library, and Pelican is proud to present you with the excerpt below.

Sway Bars

The more you can reduce body roll, the better your car handles. The stiffer the springs, the less roll, but of course this also impacts the ride quality. A larger sway bar increases roll resistance, but since sway bars are connected to both wheels, they do not add to the wheel rate (spring rate when measured at the wheel) when going over a bump with both wheels.

Therefore, the springs effectively determine ride quality, while the sway bars come into play during a corner. For a street car, it is generally most practical to run the largest roll bar you can get away with to avoid making the ride too harsh. Use the springs to tune the ride and suspension travel.

Sway bars offer another way to fine tune suspension behavior as well. The stiffer the sway bar on an axle, the more likely that axle is to lose grip before the other one does. In other words, the smaller the bar, the more grip. So a larger front bar promotes understeer and a larger rear bar promotes oversteer. On a 17-inch wheel, the maximum tire size is 215/40R-17 in front and 225/40R-17 in the rear on 7-inch-wide wheels, with around 25 mm of offset, although more offset still clears the struts. A safer choice is a 215/40R-17 in front and rear.

Most cars that share the E30 wheel bolt pattern of 4x100 mm are front-wheel drive; they also require more offset than E30s do. Since so few wheels are designed specifically for the E30, most aftermarket wheels in the required bolt pattern have too much offset and allow the tires to interfere with the struts. Wheel spacers are the solution to this problem and allow you to choose from a much wider selection of wheels.

Because of the design of the wheel and hub, only certain spacers can be used. The wheel actually is supported by the center of the hub. The 57.1-mm bore of the wheel fits the hub very closely. If you add spacers thicker than 3 to 5 mm, make sure that they are hub-centric with a lip that fits both the wheel center bore and the hub. If you use non-hubcentric spacers, expect to have vibration issues and possibly broken wheel studs and/or bolts.

With thicker spacers you have to convert your hubs to studs or it is very difficult to get both the wheels and spacers mounted. The best spacers come with pre-installed bolts so that the factory wheel bolts don't have to hold both the spacer and the wheel onto the hub. This is the safest setup.

Tire fitment is easier with a lower, stiffer suspension. The negative camber gain from lowering the car pulls the top of the wheel inboard, which increases fender-to-wheel clearance. Also, stiff springs are less likely to bottom out and cause the tires to rub the inner fenders.

A spring adapter setup lets you run rear rates that are stiff enough to allow controllable oversteer without using a large rear bar that can reduce traction on corner exit
Figure 1

A spring adapter setup lets you run rear rates that are stiff enough to allow controllable oversteer without using a large rear bar that can reduce traction on corner exit. (Photo Courtesy Vorshlag Motorsports)

An adjustable front or rear bar is the ideal setup for any dual-purpose or track car, because roll resistance needs to be increased for sticky race tires
Figure 2

An adjustable front or rear bar is the ideal setup for any dual-purpose or track car, because roll resistance needs to be increased for sticky race tires. If you set your car up for street tires, when you bolt on a set of R-compounds, the front to-rear handling balance is totally different, and you have to stiffen the rear bar to avoid understeer. (Photo Courtesy Ireland Engineering)

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Page last updated: Wed 12/7/2016 02:24:50 AM