UMI Releases New Product: Bolt In Rear Coilover for the 1964-1972 GM A-Body

[UMI Tech]

Originally Posted by andrewb70

Ramey,

I see there are three locations for the LCA to mount at the rear end. Can you elaborate on that please?

Andrew

Certainly.

We always have the factory attachment point available. As you lower the car, the trailing arm can start to point uphill toward the rear. The top hole in our bracket allows you to get that arm back to a slight downward angle toward the rear. If you go super low, you can use the next hole to restore that angle. That's the simple explanation.

In side view, you can process the angles of the arms and come up with an instant center point somewhere in the front of the car (or within the confines of the interior). Simply a point in space. Knowing where you want that point in space is a big advantage and therefore having factory plus three options to tune that location is popular. Our brackets allow you to do that.

Without going into too much analysis at the moment, lowering the trailing arm normally improves forward traction but sometimes at the expense of a few other things like brake hop and excess roll steer...

ramey

[andrewb70]

Originally Posted by UMI Tech

....

Without going into too much analysis at the moment, lowering the trailing arm normally improves forward traction but sometimes at the expense of a few other things like brake hop and excess roll steer...

ramey

So basically this allow you to tune the anti-squat properties...

Andrew

[UMI Tech]

Originally Posted by andrewb70

So basically this allow you to tune the anti-squat properties...

Andrew

Haha, that's it exactly.

[andrewb70]

Ramey,

Another question if you don't mind...

Do the shocks themselves act as travel limiters in rebound? Can they handle that?

Andrew

[UMI Tech]

They aren't supposed to under normal circumstances. With that being said, the occasional high grip auto-x car can get out of sequence enough to lift an inside rear tire by topping out the shock. It doesn't seem to hurt anything when done on occasion. Each manufacturer has a different philosophy and I know some shocks are more delicate than others.

[andrewb70]

Originally Posted by UMI Tech

.....Each manufacturer has a different philosophy and I know some shocks are more delicate than others.

That's why I was asking...I know the stock suspension uses the shocks as travel stops and to keep the springs in place. Obviously this isn't a concern with coilovers, but I know some shock manufacturer explicitly state that bottoming the shock in compression or rebound will kill it in short order...

Would spring selection be better done by knowing the rear weight balance?

Andrew

[UMI Tech]

When designing a coil for the A-body for instance, we know some of the general parameters and don't deviate much from tried and true situations. For example, 130 lb/in works pretty nice. I can work in the 100 lb range safely and the 150 lb range safely. Beyond those numbers takes different tuning and balancing. Same goes for stroke lengths on the shocks. We follow the 60/40 rule where we like to have the shock shaft between 40 and 60% of its travel at ride height. Too much one way and we top or bottom the shock out. We also want to stay in normal situations like aprrox 5" stroke. 4 is a little low. 3 is really low. Extension is a little more forgiving where we can use 6-7 ish.

All of our stuff comes from driving, trying, re driving, re trying, racing, driving, testing then releasing product. Usually its' good, sometimes even the best plans need tweaked...

ramey