eLTwerker

Do progrssive rate springs experience changing spring rates due to how fast and/or hard they're compressed? Or does their rates change in the same manner regardless of the forces acting on them?

How are progessive spring rates achieved? By having the spacing between coils change through the spring?

I ask in regards to QA1 rear coilovers which can be used with a variable(same thing as progressive?) spring rate of 100-200. I want to know how it varies. On hard launch is the spring rate less to allow weight transfer and harder on slower acting forces such as some cornering loads?

chupr0kabra

iTrader: (10)

It's not so much a matter of how FAST the spring is compressed as it's how MUCH the spring is compressed.

The more a progressive spring compresses, the higher the rate it pushes back. A linear spring (say 300lbs) would exert 300lbs of force throughout the range of oscillation. A progressive spring (like the QA1 springs you mention) would exert 100lbs as the first coils compress, then exert progressively more force as more coils are compressed. In actuality, the softest coils are already compressed somewhat when the car is at rest, as the weight of the car has already "activated" them.

This is achieved by the spacing of the coils. The farther apart the coils, the softer the rate. Springs achieve their vertical oscillation through torsional (twisting) energy. As the coils compress, they get closer together.

Mark a point on a coil, then measure the outside diameter to that same spot on the next coil (around the outside of the spring). As you get to the coils that are farther apart, there is more distance to cover. Since the spring isn't as compressed in these areas, it doesn't take as much force to compress it.

It's all about converting energy. Whatever is compressing the spring is expelling kinetic energy to do so. That kinetic energy gets stored as potential energy in the spring. When the spring pushes back, that kinetic energy is being released. Remember Newton's First Law? For every action, there is an equal and opposite reaction.


-Mike

eLTwerker

What, then would be the advantages of using a progressive rate spring vs. linear rate for road racing, drag, and street handling and vice versa?

chupr0kabra

iTrader: (10)

Progressive rate springs - when paired with adequate dampers (shocks) - generally offer better ride comfort. I say generally because it depends on several factors: shocks, rims, tire sidewall stiffness, swaybars, etc. The suspension on cars works as a system. This is why if you just change out the stock springs for higher rate lowering springs, but don't upgrade the shocks, the ride worsens tremendously. For the street, the idea is ride comfort. If your kidneys are sore after driving long distances, your suspension combination should be evaluated (or you need to re-cushion your seats).

For drag racing, the objective is weight transfer. You want the rearend to squat, then push the car forward. Any twisting motion should be minimized, as the energy wasted could have gone to acceleration, instead of twisting the car back to straight. This is where your torque arm, lower control arms, and rear swaybar help. The springs' job is to let the rearend squat without bottoming out. Generally, drag springs and shocks are softer, to aid in weight transfer.

For road racing, the objective is to minimize body roll and keep the wheels planted to the ground during a turn. Again, the energy wasted in rolling the car back to level should be minimized. Additionally, having a lower center of gravity aids in handling, so the springs tend to be shorter, but higher rate.

The progressive vs. linear argument is less about which type of spring is best for which application, and more about how the springs (and spring rates) interact with the other components in the suspension. You might see two road racers take different approaches, but get similar results. Maybe one uses a coilover kit with linear springs while the other uses progressive rate springs with adjustable shocks. As long as they know how to drive their cars and know how they will react in certain situations, there really isn't one setup that's better than the other.

Of course, this is all just information I've gathered while researching what components to buy for my own needs. If you REALLY want to know about road racing and suspension, go lurk at http://www.frrax.com/rrforum/. The bottom line is, you want to pick components that will work together for YOUR driving style and YOUR goals for the car. A call to Sam Strano's tech line might do you a lot of good when you're ready to buy parts. Just don't call him and ask for all kinds of advice, then buy from someone else. That's just shitty.


-Mike

trackbird

iTrader: (4)

Bravo Mike. Well done sir!

Edit:

One correction:


You've got that flipped. The more coils in a given area (wire diameter, spring diameter and such being equal), the softer the spring will be. Consider a piece of spring wire that's not wound, it's just a metal pole standing straight up, it's very stiff (won't compress at all unless it kinks). As you add coils (and make them closer together), the spring becomes softer. Otherwise, you've taken very good notes and explained things quite well.

BlackHawk T/A

iTrader: (3)

Actually, you don't want the rear end to squat much. The more it comes down the more energy you are losing that could have been used (by the suspension) to push down on the rear tires.

trackbird

iTrader: (4)

I agree with this and a proper drag suspension will lift the rear and not squat at all. That's due to the instant center that's built into the geometry of the rear in a proper drag setup.

However, I suspect that the soft rear spring approach works (even though it's not ideal) because the cars just land on the bumpstops. So, it takes a second to compress the spring (ok, a fraction of a second) and then you have pretty much a solid contact point (damped by the "non rebounding" 4th gen bumpstops, 3rd gens are rubber and will "bounce" when they hit the axle, the 4th gens are a high internal loss foam and they just make heat out of most of that energy). Again, this is my theory as to why the soft rear spring guys are still claiming it works so well (and I've seen results where it seems to work). I could always be wrong.

chupr0kabra

iTrader: (10)

I wasn't 100% sure on that, but thanks for the correction. It makes sense, though, now that I think about it further. There's more metal (a longer section of the "wire" that makes up the spring) to displace.


-Mike

chupr0kabra

iTrader: (10)

That's likely true. I know from watching people at the track, on TV, and talking to people in forums that "softer springs work better for drag racing". Maybe that's more a reference to the front springs?

Does anyone have a link to that website where all the manufacturers' spring rates are posted? I'm curious now.


-Mike

soulless

iTrader: (3)

Here ya go: Link

Damn good post by the way. Thanks for the info!

eLTwerker

I was suggested 150lb rear spring for a drag set up. That link show OE rear spring rate at 110lbs. I don't get it??

chupr0kabra

iTrader: (10)

Per the discussion earlier in the thread, the rearend will want to squat, but it should be controlled. Blackhawk T/A and Trackbird are correct that this should be countered, though not at the expense of weight transfer. Are the springs you were suggested lowering springs? If so, that makes a lot of sense, as shorter springs are going to want to have a higher rate, to keep you from riding around on your bumpstops.


-Mike

eLTwerker

They are the springs in a QA1 rear coilover from Hawk's Third Gen Parts. They're 2.5" i.d. coil-over springs. I assume i.d. means interior diameter? I don't know how long they are or if they're shorter than stock.

trackbird

iTrader: (4)

There's the trick. Countering squat will help weight transfer. If I drop a bowling ball on my foot....it hurts. The ball hits my foot with maximum force, or maximum weight transfer. Imagine this is the car with stiff springs (though stiff shock valving can also handle much of this load transfer). Now, put a basket ball on your foot, now drop the bowling ball on that. The ball will absorb most of the shock and it probably won't hurt as bad. The car will put less peak weight on the tires with softer springs. If we pull the front wheels off of the ground, we have 100% of the weight on the rear end. The car won't care much what spring rate is in it, it will still have 100% of the weight on the rear. The springs and shocks can only control how it acts when it is asked to deal with that weight. Even if the rear doesn't squat at all, but we pull the front wheels, we still have 100% weight transfer.

Or, do an experiment. Go get a bathroom scale. Grab something heavy. Stand on the scale and read the weight (you plus the heavy object). Then, rapidly lift that object over your head and watch the numbers on the scale. You'll see that the scale shows that you weigh more when you are lifting the object even though your total weight hasn't changed. By building a suspension that can lift the rear of the car upwards during the launch, you can put even more weight on the tires (during the launch event) and the car won't squat at all. That's why squat and a proper launch are not as related as many people assume.