Evaluating Angle Kits

Usual disclaimer. I am not an engineer. Nor do I know everything about angle kits. This is a reflection of my current level of knowledge about angle kits. 

For most chassis, angle kits are narrowed down to either cut knuckles or Wisefab. In those cases, competition drivers will likely choose Wisefab and people with limited budgets will likely go with cut knuckles. In the BMW world (e30/e36/e46) options vary wildly and picking the right option is more than money limited. So if you’re in the position to actually pick your angle options, here are somethings to think about.

  1. Adjustable top hats

Angle kits generally come with longer control arms. The problem with longer control arms is that they give massive amounts of negative camber (-6 or more). General aftermarket camber plates will not give enough adjustment to dial this out. Some kits (wisefab pictured above) come with the option of fixed or adjustable camber plates. The camber plate on the left gives so much adjustment that the shock tower will have to be modified. The camber plates pictured on the right solve the same issue but will not be able to give camber adjustments since it’s just a fixed plate. It’s worth more to get the full adjuster plate. It is also worth noting that FD legal plates must leave the shock center point within the factory bolt holes in the shape of a circle.

2. Ackerman Adjustment

This one isn’t as much of a deal to anyone. Most kits these days 0 out ackerman and give no option to adjust it. If you’re a driver just getting into things, having the ability to try out various settings is a very good thing. For instance, the SLR kit for BMWs has 4 or more adjustment settings to go from 0 to close to stock ackerman.

 

3. Mechanical Trail (Caster)

There are 2(ish) factors that determine a car’s overall caster. The first is the actual caster in degrees the overall suspension components are angled to (what’s on your alignment sheet) and the second is the trail built into the physical knuckle via the control arm’s attachment point. The simplest way to explain trail is the picture above. It is measured by the distance between the wheel’s axis of rotation (blue) and the wheel’s physical attachment to the rest of the suspension (red). The farther apart, the more trail.

Tilting the suspension (caster) can add/remove this effect to an extent. But that will affect camber curves. The reason for wanting trail is that it helps the car’s self steer (IE wheel return). Shopping cart casters have no caster angle but the front wheels still have good self steer due to the mechanical caster.

Above is the SLR adapter bracket (an old version) that utilizes the factory control arm attachment point at the knuckle to maintain trail.

 This is the wisefab adapter. Notice that the yellow line is the actual control arm attachment point. This setup will rely on more caster angle to make up for the lack of mechanical trail. (Also notice the lack of ackerman adjustment)

4.  Actual Caster Adjustment

Most kits these days provide some form of caster adjustment. Either at the top had or at a lower control arm attachment point. But not every one does. Even then, the lower control arm adjuster is more useful than the top hat. It can also help relocate the wheel in the wheel well after the control arm changes its original location. This is one of the overlook ways to dialing in more self steer or other steering characteristics.

5. Back spacing

Quite a few angle kits offset the angle blocks from the knuckle itself. In my experience, this is to gain more realestate in order to properly locate the joints/nuts. The problem with this is that the point of articulation at the control arm is now farther away from the center of the wheels rotation. I don’t know 100% of the other down sides but at minimum, to maintain scrub radius, the wheel would need to be mounted the same amount inboard. Which, with some coilovers, may not be physically possible.

6. Roll center correction

Most kits offer some kind of roll center correction. The problem is that some offset roll center on the control arm but don’t do the same for the tie rod. At rest, suspension arms should be near parallel to the ground. If both control arm and tie rod aren’t on similar planes, suspension compression will cause uneven changes in geometry over travel. This can cause uneven steering feeling.

** Other considerations

  • Spherical bearings over balljoints
  • Parts availability for sections of the kit in the event of an impact
  • Welding/fabrication necessary to fit the kit on
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