Apex1.0

Doing research on new coilovers I came across this article.

http://farnorthracing.com/autocross_secrets5.html

Go toward the bottom and you will see a section regarding upper shock/spring mounts (top hats).

Obviously the OEM versions come with compliant rubber. Many better coilovers come with a spherical bearing. The GC design comes with a poly bushing that looks fixed.

Is the poly bushing a good design? Does the shock shaft need to pivot more?

gptoyz

I'm no suspension expert, but as the suspension compresses and gains camber angle, I would guess that the damper, where the top hat is located, would want to be able to articulate accordingly with the camber angle such that as the damper compresses minimal amounts of lateral force are working against the shaft. The poly bushing, to me, would resist the lateral pivot which would put lateral force against the shaft. That would be my guess.

I would go with spherical, if it wasn't a daily driver and sees mostly track/competition duty.

Interestingly, in another thread we were talking about top hats and apparently the Integra Type R DC2, which uses the same top hat components as the s2000 has a rubber bushing made of a harder rubber (durometer rating). It would be interesting to see if that bushing makes an appreciable difference.

FYI, GC also makes a spherical extended top hat that s2000 owners have adapted to all sorts of coilovers.

Apex1.0

You described it exactly. I would guess a poly bushing would bind ever slightly. Also if the upper mount is also the upper spring mount that means the spring will also be pushed laterally slightly.

User 121020

Tons of top hat options out there: HVT, ProParts, etc...

GC does make extended top hats, modification depends on the application -

devildust

Pretty sure ours cars wont benefit from spherical top hat bushings since we have a double wishbone suspension.

User 121020

Depends on how you look at it. Do the OE ones allow for enough range of motion? Yes. Do they have some rotational stiffness? Yes. I opted to use spherical top mounts for two reasons:

1. They swap a relatively soft spring (rubber bushings) for a very stiff spring (metallic bearing). By doing so, the dominant stiffness of suspension is closer to that of the coil spring. With springs in series, the softest spring is the dominant spring characteristic.

2. A good spherical bearing will reduce the rotational resistance vs. a rubber bushing top mount design. This reduces the moment load applied to the damper shaft/piston/body and in turn should reduce damper wear. With an OE damper that is designed to outlast the chassis, this isn't a big deal. When you slap on a set of high-end dampers that require much more maintenance, reduced moment loads could equate to longer maintenance intervals improved reliability.

Will you notice a huge change in performance with spherical top mounts vs. rubber? Nope. Also keep in mind, spherical bearings will add "clunks" and noises over time.

Cheers.

Aurex

I'm of the impression that a double wishbone suspension set-up does not have a rotational force to it like a macpherson strut would. On Mac strut cars, the strut turns with the knuckle and because of this, a bearing is needed in the top hat of the suspension.

Apex1.0

Good info...

What about the upper mount also acting as the upper spring perch? It seems like a flawed design because the spring perches on the shock should be exactly perpendicular to the spring centerline. As the suspension moves the lower mount will move laterally compared to the upper. The shock shaft must pivot inside the top hat (discussion above). This means one side of the spring will be loaded more than the other as the perch is no longer perpendicular to the length of the spring.

Slowcrash_101

But the shock shaft is not upright, it's slanted at an angle to have linear motion through suspension articulation.

User 121020

The angle change is less than it would be a McPherson strut suspension design, but there is still angular motion at the upper mount. A damper attached to a lever (LCA) that rotates about some point (in board attachment of LCA) will always undergo some amount of angular change for a given rotation of the lever. There is a window of LCA motion where the angular change of the damper is minimized, but it still occurs.

Apex1.0, you are correct. The OE perch perpendicularity does change as the suspension travels.

The angular change of the damper is not very large. That's why a rubber bushing is adequate for the upper mount. Small delta angle = small moment load applied to the damper shaft.