Hello everyone and welcome! In this video, we're going to be talking about soft versus hard springs and which one is better.
So you may think that because sports cars and race cars use really stiff springs that that's what's best
But in reality if you want the most maximum grip you want a softer spring, so why is there this differentiation?
Let's talk about that, and so what we've got here is
a depression in the road so we've got two cars driving. They're about to collide which is unfortunate, but that's irrelevant.
So we have these two wheels and they're traveling this one's traveling this direction this one's traveling this direction
and we have this twenty millimeter depression in the road now the only difference between these two vehicles is the spring rate and
so what we have on the left side is a
Spring, and we placed a thousand kilograms on it or about 10,000 Newtons of Force
Down on this spring and that compressed it a hundred millimeters so that gives us a spring rate of a hundred Newtons per millimeter
Ten thousand divided by a hundred- hundred Newtons per millimeter
This one on the right,
Spring B, basically what we have is we've placed that same load, ten thousand newtons on this spring, but it's only compressed ten millimeters
So a thousand Newtons per millimeter
So what's going to happen is these are going to travel over this depression
And we want to maintain contact with the ground
The whole point of a suspension is to keep tires on the ground so hopefully that much is understood
Seems pretty obvious cars can only do the things that they do if the tires are actually touching the ground
So, what we've got here is this car is about to leave over this ledge here
And then it's got a twenty millimeter gap to fill and it's got 100 millimetres of spring compression to do it
So if you look at this little graph right here
We've got our amount of spring compression., which is 100 millimeters, and then the force which is on that spring, so
10,000 Newtons at this point in time. So as it goes over this gap
you're going to have 10,000 Newtons pressing down on this wheel which we'll just say the wheel is a hundred kilograms and
So it'll press down on that
wheel and try and get it to contact this ground and it's got a 100 millimeters of compression to push that wheel down
Because it's been compressed that much from the weight of the car. So, as it travels over it
You've got 20 millimeters
So it's going to from a 100 down to eighty and so when it's at eighty
Now because we've got eighty millimeters of compression in the spring we've got an 8,000 kN force
So if we take the average of those 10,000 Newtons at the start, 8,000 Newtons pressing down at the end
Right when it hits contact, we've got an average of about 9kN, 9,000 Newtons
So we know that Force equals mass times acceleration;
Acceleration equals Force divided by mass; 9000 divided by a hundred kilograms. That's the mass of the wheel
We'll have about nine Gs
Pushing down on that wheel, so if you add gravity to that once this tire goes over this gap
It's got ten gs of acceleration acting on it, pressing it down towards the ground so it's going to hit that ground very quickly
Now this spring on the right what we've got is ten millimeters of compression and so you can see here
It's got ten millimeters of compression, and it's got a 10,000 kN
Force at that and so we want to fill this 20 millimeter gap well it only has ten millimeters of compression
so after that initial ten millimeters of
Pushing that wheel down it can't push it down any more and it just falls at the rate of gravity, so for those last 10
Millimeters, you've only got one g
Acting on that tire to bring it down and hopefully it does maintain contact at some point
Or you just skip over this bump entirely
But the point is you won't have contact so the wheel and tire can't be doing what they're supposed to be doing which is
maintaining contact, allowing the car to accelerate, turn,
whatever it's doing. And so because this softer spring presses it down faster
you're going to have more contact and you're going to have better contact, so
Therefore you're going to have, you know, the car reacting the way that you want it to
Same scenario if we move over here to a bump
so if we have
Tire A and that's about to hit a 10 millimeter bump, well, to compress the spring 10
Millimeters, 10 times 100 Newtons per millimeter it requires 1000 Newton Force to travel through that spring
So this will be a minor bump and the wheel will maintain
contact, tire maintains contact with the ground. Now for B, to compress that spring 10 millimeters, it requires a
10,000 Newton Force because of the higher spring rate, so the larger force could lift the car
physically into the air or it could just
unsettle it; you could have some load transfer occur and so it might slide out, and so obviously that's not ideal.
So that kind of explains why a softer spring makes more sense because it keeps the tire in contact with the ground. So why do
racecars have such stiff suspensions? Well, there's actually a lot of really good reasons,
they don't exactly apply to road cars though.
So you want to reduce body roll, body lean, that maintains a certain suspension geometry.
That's obvious and you can do that by stiffening the suspension. You also want to maintain
low ground clearance. Low ground clearance because you want a low center of gravity and so by doing that
you have low suspension travel because if you only have,
If you have a large amount of suspension travel and you have a little bit of ground clearance
And you're just going to be bottoming out and obviously you want your tires to be contacting the ground, not your vehicle. The aerodynamic efficiency
is at a specific ride height, so cars are set up for a very specific ride height, you want to maintain that ride height and
So you're going to have you know forces acting on this car that are going to be changing that so with the stiff spring you
can maintain somewhat of an ideal
ride height. Same goes for down force, you're going to have down force pressing down on that car
you don't want it to actually press down too much, you want to stay at a relatively similar ride height and
so by using stiffer Springs it won't press down as much.
And then also driving on tracks, tracks are often smooth, not all of them granted
but tracks are often smooth and so this allows for compliance with very stiff suspensions, whereas if the track was really rough,
you'd see very different changes in the suspension setup by the engineering teams
So thank you guys for watching and if you have any questions or comments, feel free to leave them below