Flat Springs vs Coil Springs
- Thread starter metroplex
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By flat, do you mean leaf springs?
Their bonuses are they're incredibly cheap, they position the axle without wishbones, control arms, radius arms, and all the assorted bushings and hardware.
The leaves scraping together work as a crude shock absorber/dampener.
One can increase the load capacity by adding a leaf. Great for plow trucks where the design is altered radically with additional weight.
Disadvantages are one usually winds up with cheap solid axles with the cheap leaf springs, with a lot of unsprung mass. One wheel hitting a bump on one side effects the wheel on the other. If power is being transferred through that axle and one hits a pothole that whole axle will shake and bounce like crazy.
Springs work better, packaging wise, in the front since you can have them further outboard. The wheel can turn for steering through where the leaf springs would be. Macpherson struts and double wishbones, 99% of car front suspensions, use springs. Springs in the rear are all but standard now too and in my cars they're struts, ie springs wrapped around shock absorbers for better packaging. These work better for independent rear suspension which rides nicer.
So you'll find coil springs on nicer riding vehicles but there are other design elements at work.
You'll find leaves on utility vehicles but it's for their utility, flexibility, and economy.
Their bonuses are they're incredibly cheap, they position the axle without wishbones, control arms, radius arms, and all the assorted bushings and hardware.
The leaves scraping together work as a crude shock absorber/dampener.
One can increase the load capacity by adding a leaf. Great for plow trucks where the design is altered radically with additional weight.
Disadvantages are one usually winds up with cheap solid axles with the cheap leaf springs, with a lot of unsprung mass. One wheel hitting a bump on one side effects the wheel on the other. If power is being transferred through that axle and one hits a pothole that whole axle will shake and bounce like crazy.
Springs work better, packaging wise, in the front since you can have them further outboard. The wheel can turn for steering through where the leaf springs would be. Macpherson struts and double wishbones, 99% of car front suspensions, use springs. Springs in the rear are all but standard now too and in my cars they're struts, ie springs wrapped around shock absorbers for better packaging. These work better for independent rear suspension which rides nicer.
So you'll find coil springs on nicer riding vehicles but there are other design elements at work.
You'll find leaves on utility vehicles but it's for their utility, flexibility, and economy.
A coil spring is actually a torsion bar wrapped in a spiral. The metal is stressed in torsion. A leaf spring is stressed in bending, tension on the upper half and compression on the lower half of each leaf. Which one is more durable? In theory, a smooth coil or torsion bar is better than a rough-finish leaf. The composite transverse rear leaf in the Corvette has a thoretically infinite life. Rates are still measured the same, force per distance of deflection (lbs per inch).
As mentioned above, in selection of a suspension design, other factors are more important than the type of spring alone. Packaging being the most critical in passenger car design.
As mentioned above, in selection of a suspension design, other factors are more important than the type of spring alone. Packaging being the most critical in passenger car design.
Woops I meant flat coil springs... as in, instead of a cylindrical coil, you have a flat piece of metal wrapped in a coil. Does this make sense? It's not quite used in vehicles but I always thought the standard coil springs were durable, otherwise they would not use them in HD commercial applications.
Kestas
Staff member
I often do failure analysis on coil springs. Not surprising, failure is typically by torsional fatigue. In theory, a coil spring with a square cross section just wouldn't have the long life a round cross section has. The corners would act as horrible stress risers.
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I know it's a bit off-topic, but since leaf springs and round and flat coil springs have been mentioned, I want to throw out torsion bars, which have been used over the decades in cheap cars like the original VW Beetle and Citroen 2CV, and in not-so-cheap cars like various Porsche models. A torsion bar suspension is pretty neat and eliminates much bulk.
Kestas
Staff member
Packaging... if there was some type of space constraint. Also if loading wasn't all that great or if the spring saw only a limited number of cycles, then perhaps a flat-coil spring would be considered.
Torsion bars and round-coil springs are pretty much the same thing, just packaged differently. One minor difference is that the round coil is more stressed on the ID surface, the torsion bar is more evenly stressed on the surface.
Torsion bars and round-coil springs are pretty much the same thing, just packaged differently. One minor difference is that the round coil is more stressed on the ID surface, the torsion bar is more evenly stressed on the surface.
sometimes they are used on rally and off road racecars in concert with a standard coil (coilover suspension, eg, 60mm coil diameter over a 2" OD damper).
Eibach, for one, make them so that they basically run in the coilbound state at normal ride height (it is a lower rate spring than the ride spring) and only comes into play at extreme droop, providing some 'push' onto the road surface over and above unsprung weight.
flat wire coil springs will be stiffer so you can get increased support in the same OA free length. The collapse distance is the same as the equivalent round wire coil spring.
When we design our coil springs, we try to go with round wire as much as possible, if the weight proves too much, we will substitute flat wire coils. They are quite a bit more expensive.
I believe the durability is about the same for round -vs-flat wire coils.
here's a site for some that we use:
http://www.danly.com/idanly/products/18123.html
When we design our coil springs, we try to go with round wire as much as possible, if the weight proves too much, we will substitute flat wire coils. They are quite a bit more expensive.
I believe the durability is about the same for round -vs-flat wire coils.
here's a site for some that we use:
http://www.danly.com/idanly/products/18123.html
just a factoid; "flat" wound coil springs are also known as "die springs"
I don't really have any more to offer.
I don't really have any more to offer.
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