What’s The Best Suspension – Soft or Stiff Springs?

What’s The Best Suspension – Soft or Stiff Springs?


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

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  1. A big thumbs down. This is wrong. It doesn't cover important things like natural frequency and damping.
    The example is bad because the stiffer spring doesn't have enough travel. What happens if both springs have the same amount of travel? Then the stiffer spring will push down the tire even faster than the softer spring will and keep the vehicle from falling as much.
    I think the person that made the video should do a simulation first.

  2. I was a little disappointed in this video. You only considered the case when there was so little suspension travel that it bottoms out or becomes over extended over a bump. You also only considered a spring rate increase of 10x the stock rate! That's a pretty extreme. You should have considered a less extreme example, like springs that are 2x the stock rate.
    -Mike, PE.

  3. You should put down in description shortened version of the vid.
    Stiff:bad.. in this this this case
    Soft:good in thit this this
    ext ext.
    maybe its too much work but i think for people who don't get the numbers hit w that "oh, i get what this car nerd is talking about"… or maybe make another vids shorter idk

  4. Better is subjective based on the goal of the user. Suspension is not only to help maintain contact with the ground, but to affect how quickly or slowly the vehicle turns (provided the tires have stiff sidewalls) and the comfort of the passengers.

  5. I agree if you drive on a rough road like he shows. However on a smooth road like highway, it goes opposite, stiff spring give you more grip.

  6. I took physics and you still made this impossible to understand. being smart is about being able to explain something complicated to a child so that they will be able to comprehend it. im just trying to find a softer ride. explain your lectures more in layman's terms next time.

  7. Simple answer was reached in the early 1970’s by GM. The Chevrolet Z28 used moderate shocks, stiff springs and moderate sway bars for good (for its time) handling. Whereas Pontiac with the Firebird Trans-Am used softer springs, stiff shocks and large sway bars for a much more compliant ride but great control in cornering. Both worked.

  8. Ok so i got my wrx and he guy had it the stiffest and every bump bounces and feels like a roller coaster. So i gotta go softer and the car will bounce less?

  9. Hi very interesting…..I could suggest that what you said about the springs in a suspension system applies also to the profile of tyres. The higher the profile the more comfortable ride. Remember road races and your skinny tyres

  10. So if I am getting kicked in the testicles by my subaru forester everytime I drive over basic concrete joints at 25mph I may want a softer rate?

  11. Is there a "general" amount that race springs are stiffer than stock. ie. 50% stiffer, 20% stiffer etc? I realise this is a vague question and will require different answers for different vehicle setups etc, but I'm just trying to ballpark it. Also, do you suggest there's a maximum stiffness to go to? ie. never more than 60% stiffer etc? Thanks in advance, and love the channel!

  12. Wonderful presentation! Always thought shocks were mostly for a comfortable ride (as in a Cadillac) but finding out it's really about keeping tires on the ground is new to me but makes all the sense in the world.

  13. Okay so I suck at science and math or least dont know enough to not be confused by this guy. Can someone break it down for me in manner than you would explain it to someone who knows nothin.

    Ps. I do know quit a bit about cars. I am just still trying to understand more of the aftermarket and science behind the parts of cars so I am more educated before just throwing aftermarket upgrades on a vehicle and hitting the streets like a menace.

  14. I am wondering since i am getting coilovers. My vehicle is FWD. Should i set the rear to be stiffer than the front? Max is 36 clicks. Was thinking about 26 in the rear and 20-23 in the front.

  15. Another way to look at this: Drive extremely fast then you'll only ride the tops of the bumps creating a very smooth ride. In order to go extremely fast, I recommend either and Artic Cat for winter or a Gixxer for summer. Hope this helps

  16. I get the simplification of the weights for the calculations for the principle of showing the difference, but 100kg wheels?! Even steel rims with tyres full of cement wouldn't weigh that much lol.

  17. My friend's car has a problem. The car's steering wheel gets a bad hitting on it (we could feel the hit on our hands) when we drive through a road full of potholes. Jason, is this a problem with the suspension…? What should he do?

  18. Do you think changing to a lowering springs from H&R to replace a stock spring from a cayman is a good idea? the purpose is to let the car sit 20mm lower, look better and not to be like hard to drive, does it work?

  19. But you also have dampers which prevent the movement, and if you have stiffer springs, the dampers should take that into account. My new, stiffer springs (just because my old ones were worn and this is what I got) make much better contact when I go over speed bumps. I don't think there is much difference between 350 lb per in springs vs 310 lb per in springs, especially if you factor in the dampers, yet cornering and braking are better with the stiffer springs. I think there is a sweet spot, softer than that is worse, and so is stiffer.

  20. there is not everything in springs, big deal is in shock absorbers that can have variable sensitivity in bump and rebound, with same spring it could be softer or harder on bump or /and rebound so there are many possibility to adjust suspension for some demands

  21. who makes soft suspensions components ? majority sport, heavy duty, off road application, never see in description "this will make your ride softer"

  22. My head still feels the "race suspension" from s friends car. I dont know why anyone wants a race suspension on a daily car

  23. Would putting hard springs on my rear wheels reduce sag when towing? Is it even a good idea to have soft fronts and hard rears?

  24. Thanks for this. What happens when the suspension is used for many many miles in both soft and hard setups?

  25. All I wanted to learn was can I get my car suspension springs changed for a softer ride than a very hard one? Got a Suzuki Ignis 4×4 and where I live the roads are bad and it's like horse riding. Need something smoother, less bump exagerated.

  26. Why the hell does Honda Insight have very stiff suspension, if it definitely isn't a performance car?
    Every city bump is a real pain in the back.
    😡🤬

  27. With coilovers, what is considered too soft and too stiff spring rates? Usually off the shelf coilovers are 8k spring rates front and 6k spring rates rear.

  28. Slower speed / lighter vehicle / longer suspension travel = softer springs. Higher speed / heavier vehicle / shorter suspension travel = stiffer springs. Relatively.

  29. The one going the fastest will win so speed up before you hit like a falling elivator jump before it hits bottom so you dont hit hard lol

  30. Thanks to you, I finally know what im doing when im tuning my cars in Forza 4 Horizon. Cheers mate!

  31. Good explaining here, but the example spring rates are a bit extreme. No one goes for a 10x stiffer spring in real life.

  32. You're a smart guy, tell me from your experience and mathematical /physics background what vehicle comes with an absurd ride height from the factory and no consideration was given to the dimensions of math or physics…

  33. How would the shocks effect the performance of the coils? If you had the same strut and changed the coils what would the result be? I am currently having this issue with a 2018 car I bought new. The manufacturer changed the dampers and bump stops but the ride is dreadful. Really feel every little bump…. I believe the coils were never changed or altered.

  34. another great video explained very well. I understand the math and ow the science behind the math. Makes so much sense in racing and now I get it for the street too.

  35. so, i bought these maXpeedingrods coilovers from ebay. all the videos on youtube review it as not a noticeable difference compared to more expensive coils. however, the ones i bought, i can't change the damper nor camber(not relevant.) I want to know if i can soften my springs (in case they're too stiff to my pleasure) without the ability to change my damper? meaning what if i change my preload? i dont need an explanation on what damper and preload is. i just wanna know if i can soften my springs without a damper knob and if there are other ways to soften my springs to my desire

  36. Imagine a car fully packed with your friends, and has a soft suspension, the ground clearance will reduce drastically and even a small speed breaker will be like an obstacle… Whereas hard springs require more power to press, so don't worry about speed breakers you will have enough ground clearance even when your car is full… I don't agree with the fact that cars have springs to maintain contact with the road, anyhow gravity ensures that… The main purpose of springs is to reduce the instantaneous effect of a bump by slowly going down and coming up, thereby spreading the effect of jerk over a longer period of time… Hence, our back remains safe…

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