By Staff Writer
Korman Auto Works
(336) 275-1494
kormanautoworks.com
We have so many tech tips for the BMW 2002 that we couldn’t fit them all in our upcoming issue of Classic Motorsports magazine. Subscribe now to Classic Motorsports to get this issue and the whole set of tech tips in your mailbox!
Geometry If you’ve installed some high-performance shocks and lowering springs, they’ll function well for normal driving. If you’re going to autocross the car or enjoy some club on-track events, however, some relatively inexpensive changes to geometry can greatly improve the handling of your 2002.
Consider the front suspension. In the original design and ride height, the front lower control arm sits at a downward angle toward the hub. When the outside-front corner is depressed in cornering, the angle pivots in a circle toward parallel to the ground. Thus, the more the corner drops, the more negative camber is produced. This keeps the tire flatter to the ground and minimizes load on the outside edge of the tire.
But when you lower the front end, the control arms will be nearly parallel to the ground. Then when you corner, the control arms will point upward and produce a decrease in negative camber. When you corner and the angle goes upward, it produces more positive camber—not what you or your tires want.
Changing the inner pivot point is done on serious race cars. On a more modest level: A machined, hardened aluminum spacer is inserted between the lower ball joint and the control arm that restores some of the downward angle. There is a limit to the correction that can be made here. Too thick a spacer will have the control arm cutting into the wheel. The original rivets must be drilled out and replaced–not with standard 8.8 metric bolts. Use stronger 10.9 metric bolts and lock nuts, and torque to 23 ft.-lbs. Note: Cadmium-plated bolts require 30 percent less torque.
There are a few geometric problems that need to be addressed when lowering the rear suspension. When you lower the rear, you get more negative camber. A little more is good for cornering. When you lower a lot–say 1.5 to 2 inches–you get too much negative camber, which wears the tires on the inside and prevents it from making full contact with the pavement.
Correcting camber for a lowered stance is heavy work that involces careful measurements. Then you must cut and weld to the subframe trailing arm mounts in order to install adjustable pickup assemblies. Large changes in camber will pull the rear toe out of spec, so it is paramount to alter both pickup points. The inner adjustable mount is installed for vertical movement to set camber, and the outer mount is installed horizontally to adjust toe. We are looking at modestly improved street machines here, not race cars, so we won’t go into those mods. Assuming your springs lower the car just .5 to 1 inch, our focus will be on the trailing arm angle.
The rear trailing arms are mounted with them trailing downward from the chassis pickup point on the rear subframe toward the hub. With the hub lower than the forward mount, the torque of the rear wheels presses downward, giving the wheels more traction. If the forward point is lowered, as happens when you install lower springs, you have a less favorable angle. If you lower enough so that the front pickup point is lower than the hub center, you’ll have more wheel spin than a championship drift car.
You can make a modest but worthwhile improvement by modifying the rear subframe mounts. This will entail some heavier work than up front, as you must remove the subframe mounts. Typically, the bolts are corroded in place, and you’ll need your biggest wrench and a little help from Godzilla to remove them. Have spares available. The old ones may break.
When you remove the mounts, you’ll see that the center bushing is offset. By reversing it, you’ll move the subframe closer to the chassis. You can also cut off most of the shorter protruding end to get even closer. For racing, we use solid mounts here, but they would be harsh for street use. You can get more stiffness from the rubber mounts by driving some hard rubber or even wood dowels into the open spaces in the rubber mount. Yes, this is a small improvement, but in an autocross, 0.1 second can be the difference between first and fourth!
Now look at what we’ve done: We’ve moved up the subframe, but note that the front of the differential is mounted to the subframe, and this increased angle of the diff will not make the drive shaft and rear U-joints happy. To compensate, we’ll raise the rear differential mount.
Remove the rear diff mount. This is the steel plate with two rubber bushings. Push up this plate so the top edge is moved to the bottom of the trunk floor. Then mark and drill two new holes. It is good to weld a big washer around this hole, as it’s just a sheet metal box section. With the mount installed in this higher position, you’ve compensated for the change at the subframe. Oh, did we mention you’ll need to remove the diff to reach up and do all this?
For racing, we use offset Delrin mounts here so we don’t need to drill a new location. But the amount of diff noise that this will transmit through the chassis will astound you. I’ve had customers who were convinced the diff bearings had gone out. We had them put the rubber mounts back on, and the noise was gone. Diffs make more noise than you realize, but the rubber does effectively damper it.
We don’t recommend a solid mount–or even polyurethane–for any street use. Again, you can get a bit more stiffness out of the rear rubber bushing by driving some material into the open spaces in the rubber. This is not sufficient improvement for a serious race car, but it’s worth the effort for a daily driver that’s looking for another .1 or .2 second in an autocross.
The 2002 has always been a great car to autocross. With the right little tricks, it will out-corner many two-seat sport cars. In the mid-’60s, I autocrossed the predecessor of the 2002–the great 1800 TI. It came from the factory with stronger springs than a 2002 and bigger 14-inch wheels and tires. With the above changes to my daily driven 1800 TI, I cleaned up at many autocrosses.
The most memorable one was an SCCA event where I had concern about being classed with a bunch of two-seat sport cars. I was told in a rather disdainful way that “this was a sports car club event,” as in take it or leave it. That got me going.
I walked the course three times, carefully studying my entry and exit to each corner. I made my practice run a bit slowly, concentrating on how I was going to drive the course. I nailed my first timed run, and the official came over and informed me that something must have been wrong with the timing device and I could take another run. My next run was a half-second quicker, and they realized the timer was not faulty. Their appreciation of a BMW was just inadequate.
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