RcTek : Information & Resources for the Model Car Racer

Model Car Plastic Bumpers - Curing the Droop

In a bid to either reduce weight, cost or comply with safety regulations, the bumpers on the front of some model cars droop down at their edges and trail on the track. This generally leads to problems with handling and breakage of other parts. In this article we offer our simple solution.

The Problem

Droopy front bumper

The image shown to the left clearly demonstrates what can happen to some model car bumpers when the material or design of the bumper isn’t correct.

Our Solution

Stiffened plastic bumper

Plastic bumper stiffener

After seeing a few different flawed solutions to this problem we came up with the idea of suspending a spring across the width of the bumper. An example of this is shown in the image to the left, a bigger version of which can be seen here…

The spring is an inexpensive coil spring that only needs to be strong enough to stop the bumper sides from sagging. It is connected to some short turned pillars that are shown on the right using two short lengths of piano wire. The grub screw in the post allows for the tension on the spring to be set. I find setting it with the bumper slightly curved up allows for better ground clearance in corners, etc..
Only one of the posts needs a grub screw in the top as the other piece of piano wire is simply bent over.

The countersunk washer on the underneath of the bumper is not an absolute necessity, it does however allow for the load of the spring assembly to be spread wider. A Flanged Headed or Pan Headed screw will probably suffice.

The piano wire does not want to be very heavy gauge as if it is it will bend and stay bent. The wire is being used in tension and so thin gauge wire is far better as it deflects well and is strong enough to not break.

Combining the Spring with Body Posts

Black Diamond with bumper stiffener

As the PB Black Diamond has it’s body posts on the bumper, we needed a solution that combined the pillars with the body mounting posts. The body posts were turned off-centre out of square stock to allow the spring holes to be drilled through.

A bigger version of the example shown is available here…

Alternatives

As mentioned at the top of this article, we have seen a few attempts at curing the droopy bumper problem and most of these involved fastening a piece of carbon fibre across the bumper. Carbon fibre doesn’t have sufficient impact resistance and is not flexible, so it generally breaks the first time that you hit something. Also, as fitting the carbon makes the bumper inflexible, there could be an issue of breaking the rules of the race organisation that governs your racing.

Another alternative tried by Serpent on some of its cars was to fasten the bumper to the front body mounting plate. Whilst this goes some way to curing the bumper droop, it is an inflexible solution that is broken in collisions.

Summary

We hope this provides either a solution or at least the source of some ideas of how to cure the problem of drooping bumpers on model cars. If you are a manufacturer who starts making a version of the above solution, don’t forget our 10% ;)

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© 2001, 2009 by Darren Burnhill