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MG TD TF 1500 - Guaranteeing a win at rocker box racing

This is for you applied physics guys out there. There's got to be a formula for guaranteeing a win at rocker box racing.
Here am I, a non scientist, racking my brains on the relationship between weight of rocker box racer, steepness of slope, length of track, affecting initial inertia, acceleration and terminal speed. And I suppose wheel bearing friction has to be a given, as good as you can get, but as for the wheel/ track interface ...
All this has been occasioned by our coming third in the rocker box racing at the MGC 50th Anniversary celebration at the weekend in the U.K. The winner was a monster length of an MGC rocker box and I apologise for ours coming from a midget!


David Wardell

Here you go:

Tim Burchfield

Its the Go Faster stripes that make all the difference!
Dave H
Dave Hill


One of the primary factors is the rotational energy (acceleration/energy storage) of the car. Look carefully at both the mass and moment of inertia of the wheels (not only the bearing frictional forces).

Don't waist any of the potential energy doing work that is not needed. Mass ratio of the body of the car to the wheels and maximum wheel rotation wins races.



And all along I just thought it was about the Vrooom Vrooom noise.
L E D LaVerne

Love it. Now working on the physics of long and short wheelbases. Completely forgot about psychological impact.

David Wardell

Moving the weight as far back as possible, just to the tipping point, will maximize the height the mass falls, the potential energy, which will then convert to kinetic energy with higher velocity.

There may be a phenomena if carried out to extremes, wheelstands. Looks more awesome with a smoke bomb mimicking "burning rubber."

Watch out as some organizers will concoct a rule that all wheels must be in contact with the track at all times because a wheelie is an unfair advantage.

Another tip is to have the rear wheels locked onto a solid axle so the racer will track straight. Go to as small an axle as possible with the lightest wheels available. You might even machine the wheels to the same exact OD, (but that's like picking the fly sh*t out of the pepper).


Along with what Jim said,cheaters in a Pinewood Derby would also slightly raise one of the four wheels so it did not make contact with the track (tilt the axle or reduce one wheels outer diameter). Imagine officials would watch for this for a fair race.

Meant to add; "Moving the weight as far back as possible, just to the tipping point, will maximize the height the mass falls." only really works if the car wheelies across the finish line. Otherwise, the total converted potential energy is mostly unchanged (this is affected by the curvature of the track).

A wheelie mid-track can affect acceleration along the track as the weight tips increasing kinetic energy (and the rate you apply kinetic energy along the track can be beneficial). Unfortunately, you also loose kinetic energy when the wheelie is finish and the wheels contact the track before the finish line (pushing the weight upward requires work).

Has nothing to do with wheelies.

basic physics mgh = 1/2 mv squared

The higher the mass, the greater the potential and thus kinetic energy and velocity.

The point is the racer is sitting on an incline at the starting line and having weight concentrated at the rear means it is at a higher elevation- the one with the center of gravity higher has more potential energy. The fact that they level off makes the vertical advantage possible.


In our scout troupe Pine Wood Derby we had an "Unlimited" class for the fathers. All Pine Wood cars have the dame wheels and they had rough nails as axles.

I machined the wheels and inserted miniature precision ball bearings. I took a chip off the OD of the wheels to be sure they were the same and had a rough surgace and I used a continuous solid axle with the nails pushed into a bore in the axle to keep the wheels on.

My son and I won in the unlimited class. There was one car made out of lead. The weight should cancel out but where its put can give an edge.

The potential energy is mgh. if its expended this results in kinetic energy of 1/2mV^2 Equate the two and the mass drops out. so adding mass should not help as long as the wheels do not slip. But if you can place whatever mass you have as far back its just a bit higher giving just a bit more energy

As noted you are then left with friction and the lost energy in rotating the wheels. The miniature bearings have low mass and very low friction.

Jim B.
JA Benjamin

See the four included diagrams (simple wedge diagrams to save time).

"The fact that they level off makes the vertical advantage possible."

Agree. And, that is why I clearly said: " Otherwise, the total converted potential energy is mostly unchanged (this is affected by the curvature of the track)".

Our races used a track designed to prevent this kind of advantage and give the kids more even competition.

"Has nothing to do with wheelies".

A wheelie at the finish line always produces more kinetic energy and a wheelie along different points of the track (but not at the finish) alters the rate of potential energy conversion (but not the total amount). See picture 2.

Geometries in pictures 1 and 3 produce equal amounts of kinetic energy.

As we agree, there is no advantage until the curvature of the track significantly flattens. See picture 4. This is countered by poorer aerodynamics and greater instability.



Diagram 2


I remember a race some years back where a car was disqualified. He had a weight system set up where the weights were back as described above, but the weight swung forward on the flat. Car beat out all others.
Bruce Cunha

There's no substitute for a good crew.


D A Provan

This thread was discussed between 13/06/2017 and 15/06/2017

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