Driving - Smooth is fast (why?)

It's a phrase that is thrown about a lot in the racing world. "Smooth is fast"

A related phrase is "the slower it looks, the faster it is"

Why is this true? And how?

Well you see it has all to do with the transfer of weight (also known as load) whilst you are driving, commonly referred to as weight transfer. 

When a car is completely still, the weight is evenly distributed across the four wheels of the car, or distributed in the way the manufacturer designed it. In this state of rest, each tyre has an equal amount of avaliable grip, as they have equal load on them. 

This changes when the car is in motion. Let's start with moving forwards (and backwards). This is longitudinal weight transfer. When you accelerate, the weight of the car is transferred to the rear, pushing the rear down. This extra weight on the rear pushes the tyres into the circuit, generating more grip on the rear, but less on the front because the tyres are not being pushed into the surface - they are now unloaded. During braking, this is reversed - the front is pushed down, forcing the front tyres into the circuit, allowing them more grip. Again, the rear end would have less grip because they are unloaded.

It is important to note that whenever there is any weight transfer, the overall grip level for the total 4 tyres on the car is reduced. 

This Corvette will have more grip on the left side tyres, even though it is turning right.

For example, imagine that each tyre has a numerical value of grip, the total grip possibly avaliable being 100.

When the car isn't moving, the tyres have a value of 25 grip points each, totalling 100 - maximum possible grip. 

When the car is accelerating (in a straight line) and weight transfer takes effect, pushing the rear down, the total amount of grip points is reduced, let's say to 90. The two rear tyres will have more grip than before, due to being pushed into the ground, whilst the front two tyres will have less grip than before, due to less load being on them.

So let's say 15 and 15 on the front tyres and 30 and 30 on the rear tyres, totalling 90 grip points.

When the car is braking (in a straight line), the weight is transferred onto the front wheels, so they now have more grip, whilst the unloaded rear tyres have less. Let's swap the grip point values for the front and rear end, so the front tyres now have 30 grip points each, the rear 15, once more totalling 90 grip points.  

This all changes again when the car turns for a corner. Longitudinal weight transfer is no longer a priority. The main focus is lateral weight transfer. 

Just as longitudinal weight transfer was load being transferred when travelling forwards and backwards, lateral weight transfer is load being transferred when travelling left and right. 

Practical exercise: You can feel load transfer in your own car and see it visually on the sim. Drive aggressively left and right and feel or watch how the car will lean the opposite direction from which you are turning - lateral transfer. Accelerate and brake harshly to feel or see how the car will dive backwards and forwards - longitudinal transfer. This will happen in any car, the suspension setup will not matter. Weight transfer is often confused with body roll. Body roll is simply the suspension reacting to weight transfer.

Let's go back to our grip point example and imagine a right turn. All the weight transfers onto the left side, forcing the left hand side tyres into the circuit. The right side tyres are unloaded. Because weight transfer is still present, the maximum number of grip points is still 90, except now the left front and left rear have 30 points each, whilst the right front and rear have 15 points each. Again, it is crucial to remember that the tyres that become less-loaded lose more grip than the loaded tyres gain, which is why the maximum grip points achievable are 90, not 100. 

Flip it for a left hand turn. All the weight is on the right side, forcing the right tyres into the circuit, and unloading the left side. So, the right front and rear have 30 points each, with the left front and rear having 15, once again totalling 90 grip points.  

Okay, now you understand how the weight transfer works, you need to know how this ties into smooth being fast:

More weight transfer equates to less total grip. The smoother you drive, the less weight transfer you cause, the more grip you maintain. If you maintain more grip, you will be faster. 

So, now you fully understand how weight transfer works and why it means that smooth is fast. The example I created is a perfect example of smooth driving leading to maximum grip.

If you do not drive smoothly, it is likely you will only be extracting say 80 grip points out the of the 90 used in the example.

(Note: Grip points and the numbers are only example numbers, and discount other external factors. It's just to understand weight transfer.)

To be smooth, try to look as far ahead as possible, so you know what you need to do when you arrive at a certain point, and try to be smooth and progressive with your inputs. 

Practical exercise: Go onto the sim, pick a car and track and head towards a corner. Do it once being aggressive; turn in quickly, slam the brakes on, throw the weight around. Then go into the replay cameras and look at just how much the car "leans". You will also likely notice and hear the tyres scrub along the track.  Do this same exercise again, but this time drive smoothly; turn in slowly and progressively, trail brake, be mindful of where the weight is. Again, go into the replay cameras and look at the body language of the car. You will see less "leaning" and hear and see less tyre scrubbing as there is more grip. Do not confuse weight transfer with body roll. Body roll is simply the effect of the suspension reacting to weight transfer.