On the subject of fiberglass bumpers

On the subject of fiberglass bumpers

Well, I have a composite front bumper now.

The stats:

Material: Fiberglass impregnated resin
Weight: 7.3 pounds naked
Aluminum bumper support weight savings over stock bumper shocks: 3 pounds
Total installed weight savings over stock bumper (also weighed naked): 46.7 pounds

I could drone on about how to refinish a fiberglass part, but I’ll just hit it lightly and give you all some pictures, since there are literally thousands of how-tos on prepping and painting fiberglass. There’s no secret: Make sure the part is clean, use lots of body filler, and sand until your arms fall off.

I prepped and painted mine at home, in my basement, with Duplicolor rattle can product from the parts store. I think it came out just fine.

First scuff Primer
Lots of putty went into this thing. Wet sanding after paint
Finished with lights installed New lightweight aluminum bumper supports
Finished!

Now, the big question? Why?

Weight is the enemy. The more mass the more energy it takes to move it, and once it’s moving, it takes even more energy to change it’s direction. On top of the simple question of mass, the position of the mass on the car makes some mass removal more effective than others.

In this case, I had 46 pounds of mass hanging two feet ahead of the front axle. Go to the gym. Pickup if a 45lb dumbbell, and hold it close to your chest, and twist your torso back and forth. Sure, the dumbbell is heave, but you can move pretty easily.

Now extend your arm with the dumbbell still in your hand and try to move it. The difficulty level goes up quite a bit, and the period, the amount of time it takes for you to move that mass from one side back to the other increases, just like a pendulum. It’s the same concept as a figure skater spinning.

So getting this much weight off of this particular location is going to be extremely noticeable. That 46.7 pounds of mass 24″ from the front axle actually gets multiplied in terms of the force it imparts on the front axle. By removing just 46.7 pounds from a lever arm that’s dangling two feet in front of the axle, I’ve removed possibly a hundred or more pounds of load from the springs and reduced the amount of force required to change the direction of the front of the car by a lot.

Andrew

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