Weight reduction for autocross question

[M-Sport fan]

Wouldn't the delrin actually crack under those same conditions, even though it would not 'cold form' like poly?

 

[kevinatfms]

Wouldn't the delrin actually crack under those same conditions, even though it would not 'cold form' like poly?

Its a hinged joint at the rear beam(that has flex due to the rubber bushings). Remove side to side deflection and it should allow the beam to flex over the bushing binding into the mount. They may crack over time but ill be willing to test them out and see.

In the event they dont last i have a set of poly bushings to fall back on. If those fail, ill see about making solid rubber versions over the OE version.

 

[johnny5]

Its a hinged joint at the rear beam(that has flex due to the rubber bushings). Remove side to side deflection and it should allow the beam to flex over the bushing binding into the mount. They may crack over time but ill be willing to test them out and see.

In the event they dont last i have a set of poly bushings to fall back on. If those fail, ill see about making solid rubber versions over the OE version.

How does the rear beam flex since the pivots aren't parallel to each other? I always thought a solid bushing would cause a bind.

 

[ronmcdon]

for what its worth, could barely tell the difference after installing a lightweight battery that dropped close to 20lbs. Then again this was for hpde and not autoX, where I imagine its effects might be more noticeable.

With rear torsion beam bushing, I had the solid DNA installed around the same time I had miester coilovers and softer 5/3 rates, so hard to account for what did what, but I dont get the sense the car is any more twitchy on hpde course. The rear is a lot more planted for sure.

Only real con I can think of with DNA torsion beam bushing is cost at $300ish. Powerflex polyunI think is around $90

 

[kevinatfms]

How does the rear beam flex since the pivots aren't parallel to each other? I always thought a solid bushing would cause a bind.

They arent offset from each other in the mounting location front/back of the car. They still pivot vertically but are mounted off-axis horizontally from the mounting point. The beam still flexes as the car transfers weight to the outside corner just as a torsion member would.

The side load would be my worry and what M-Sport Fan brought up. With enough side load polyurethane will flex and bind; rubber will flex and bind; a spherical joint will rotate without bind. Delrin is extremely hard and may crack if that force is too much. If it can handle the stresses then more force is applied back into the beam(check my physics on that one).