Quote:
Originally Posted by Lonestar
Anyone without any commercial interest wanting to add to the "technical" part of the discussion? 
Paul
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Interesting thread as I've been pondering this after returning to the RC world after stopping in 1996.
Basic science says the lighter car will be faster. In all forms of motorsport there is a minimum weight, and teams spend a fortune lightening their cars to get to the weight limit. Reason being that more energy is required to move the greater mass, in any direction, and on top of this are inertial effects which increase the energy required to accelerate the mass, or to put this simply for the mass to change from one moving state to another.
In practice it is not so simple as the car has to contend with bumps and make use of the grip available from the tyres.
In a tractive and braking sense the tyre's grip is primarily controlled by the mass it's carrying, so a heavier car will have more traction, or a more rear weight biased car the same. So in a low grip scenario the extra energy needed to accelerate the higher mass could be much less significant than the improvement in available traction.
In a cornering sense the tyre's grip is not a simple function of mass, infact carrying more mass could reduce it's capacity depending on it's properties. This is very long and complicated to explain but F=muR does not apply simply because the tyre is rolling and flexible. In a 1/10th sense different foam inserts will produce different cornering properties (as different tyres pressures do on the big stuff). A heavier car will need bigger/stiffer inserts to allow the tyre to produce more cornering force and these same inserts could then reduce cornering force on the lighter car. This is also the reason why high unsprung mass on a light car could not be desirable.
As for the bumps well whether the car behaves itself or not is a function of mass, unsprung and sprung, spring rates, mass distribution, damping properties (at different damper speeds) and tyres. Mass is only part of it.
1/10th damper technology is archaic and this means that it is impossible to seperate the performance between large bumps at high speeds, or rough ground, or handling and so on. It may be that a heavier car has a larger window of performance and the dampers are better at dealing with the variety of what's thrown at them.
My observation is that weight gets put on regardless at the moment but as the sport moves forward those that can find a way of making the set-up work with a lighter car are going to be faster, just basic physics.