Oger

Having a lighter car is almost always going to help. The biggest thing for me is being able to choose exactly where you want the weight to get you the minimum weight rather than just dealing with the stock distribution.

RogerM

Luckily for Lotus they didn't have to consider traction levels that could flip the car on it's roof at a milliseconds notice ;-)
In low grip lower mass is definitely better; less to accelerate, less to brake, less to influence direction change on.
The very high grip levels we get in RC mixed with the fact that we don't have the "seat of the pants" feedback on visual feedback mean that actually adding ballast low and central can make the car much more confidence inspiring which leads to better lap times.
Add to that most classes are over powered for the forward traction level they have available a few extra grams isn't going to make that much difference.

How much extra weight to use? Simple ... start light, add a little at a time to the appropriate place in the car, soon as it stops making an obvious improvement go back one step.
Where to add it?
Low and central is best if the balance of the car is otherwise good.
Towards the front axle if you want want less reactive feel, more mid corner tyre loading or there is a tendency for the front to lift.
Towards the rear axle if struggling for drive traction on a 2wd car (if the car starts to over rotate then either go back down in ballast or fix with geometry).
Never add it outside the wheelbase, doing so will definitely cause issues due to the increased polar moment of inertia.

toycardriver

iTrader: (41)

Someone may have tested this in the past.......you mean every race team in the history of motorsports. Lighter does everything better. Better polar moment in every direction. Its better in everything except durability.

staiguy

iTrader: (7)

Group B rally drivers pushed the limits of weight and power ratios at the cost of safety. It got to the point some drivers were scared of the car if they wanted to win.

obviously we don’t race at that level but a break can cost you the race and if the car is so fragile you can’t race competitively then what’s the point. The weight limit isn’t something that you really need to start skeletonizing or cutting parts. A majority of the car’s weight, before electronics, is coming from the chassis. The aluminum chassis are heavy but in a good way. It’s weight that’s as low as you can go. A carbon fiber chassis will get you to the point you start adding weight where you need it or if you need more durable aluminum parts.