Question on weight distribution

[Caito]

There is a hole in my reasoning that I hope you can help me fix.

Let's take a non-aero RWD car as an example.Normal saying goes that you can move weight forward if you have understeer.

That statement would contradcit my understanding that if you put more weight you would have a higher maximum force, but you get diminishing returns due to tire load sensitivity. Aka, the front has 10% more weight, but can't generate 10% more lateral force. So the net result would be more understeer.

Can you help me point out the error? Maybe it's the simplification that the front weight is turned by the front wheels and the rear weight by the rear wheels.

Thanks!!

[Greg Locock]

Due to TLS the lateral force at the front wheels won't increase as quickly as the weight does, so more understeer. The idea that the front wheels laterally accelerate the front axle weight is useful and correct.

[Vyssion]

This post is purely from an aerodynamic standpoint and assumed to be acting on the centre of the vehicle. You could, by extension, apply similar logic to the front and rear bias but hopefully this helps add to "aero" side of the weight distribution discussion

Essentially, the generation of downforce is the way that allows for the car to simplistically "be heavier than it actually is, without the bad stuff that comes with an increased weight".

The downforce and the normal (weight) force of the vehicle is the simplified mechanism by which the tyres gain their grip. And again, over-simplifying things for a purely aero discussion, the more grip you have, the faster you can theoretically corner at.
(Can't display an actual 'mu' symbol so will refer to it as C_f from here)

The "N" denotes normal force which is made up of the vehicles weight force and any downforce currently being produced.


If you combine this equation with the formula for centripetal acceleration (which could be adapted to fit a corner if a constant radius)

and rearranged to give:


Then you get the following formula:


This then shows that for a constant coefficient of friction, that velocity is proportional to (meaning that an increase in the right hand side of the equation will increase the left hand side). If this is differentiated to get this in terms of time, it shows that time is proportional to (or simply that it is inversly proportional).

The important term here is this which is often referred to as the "specific downforce" of the vehicle. So if we are to increase this term, by means of increasing downforce or reducing the cars mass, the theoretical maximum velocity we can corner at will increase and hence the time taken to travel the corner will decrease. Add in that since you can carry more speed through the corner, braking time is reduced in the lead up to it and the acceleration beyond it begins from a higher speed, and you can begin to see the benefits.

By increasing mass initially, this would have the effect of decreasing this term, which would be counter productive.

[Tim.Wright]

Normal saying goes that you can move weight forward if you have understeer.

Who says that? As you've mentioned it's generally the opposite which is true.

[Greg Locock]

Tim's right, I misread your first sentence. As you move weight forward you'll often get more understeer.

I'll edit my first reply

[hardingfv32]

If you are more accurate in your statements by stating where you are in the turn you could find either statement correct.

More weight can improve turn in by increasing the tire temp at a faster rate. The tires will then be too hot for the balance of the turn.

Brian