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{{short description|Type of independent suspension}}
{{cleanup-date|February 2006}}
A '''Corvette leaf spring''' is a type of ] that utilizes a ] (FRP) mono-leaf spring instead of more conventional coil springs. It is named after the ],<ref>{{cite book |url=https://books.google.com/books?id=WsjanO7xW58C&pg=PA81 |title=Corvette - The Great American Sports Car - Staff of Old Cars Weekly |page=81 |date=1975-10-02 |publisher=F+W Media |isbn=9781440217647 |access-date=2016-11-14 }}{{dead link|date=October 2019|bot=medic}}{{cbignore|bot=medic}}</ref> the American sports car for which it was originally developed and first utilized.<ref>{{cite web|url=http://www.corvetteonline.com/history-2/the-top-5-technological-advancements-in-corvette-history/ |title=The Top 5 Technological Advancements In Corvette History |publisher=Corvette Online |date=2015-05-16 |access-date=2016-11-14}}</ref><ref>{{cite web|url=http://www.edmunds.com/chevrolet/corvette/history |title=Chevrolet Corvette History |website=Edmunds.com |date= |access-date=2016-11-14}}</ref><ref name=CompWorld>{{cite web|url=http://www.compositesworld.com/articles/composite-leaf-springs-saving-weight-in-production-suspension-systems |title=Composite leaf springs: Saving weight in production suspension systems |publisher=CompositesWorld |date=2014-02-03 |access-date=2016-11-14}}</ref><ref>{{cite web |url=http://www.autocomposites.org/composites101/history.cfm |title=ACMA: Automotive Composites Alliance - Auto Composites 101: History of Automotive Composites |website=Autocomposites.org |access-date=2016-11-14 |url-status=dead |archiveurl=https://web.archive.org/web/20170117063725/http://www.autocomposites.org/composites101/history.cfm |archivedate=2017-01-17 }}</ref><ref name=CB>{{cite web |author=Chris Longhurst |url=http://www.carbibles.com/suspension_bible.html |title=The Suspension Bible |publisher=Car Bibles |date=2016-10-26 |access-date=2016-11-14 |archive-date=2007-02-06 |archive-url=https://web.archive.org/web/20070206034707/http://www.carbibles.com/suspension_bible.html |url-status=dead }}</ref> A notable characteristic of this suspension configuration is the mounting of the mono-leaf spring such that it can serve as both ride spring and anti-roll spring. In contrast to many applications of ]s in automotive suspension designs, this type does not use the spring as a locating link. While this suspension type is most notably associated with several generations of the ] the design has been used in other production ] cars, as well as vehicles from ] and ] van. ] produced cars with a similar configuration, using a multi-leaf steel spring in place of the FRP mono-leaf spring.
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== Design ==
This is an article about ''']''' used on the ] ''']'''. While most other cars use ], the Corvette still uses leaf springs.
] rear suspension]]


The leaf-spring suspension configuration is ], because the movement of one wheel is not determined by the position of the other.<ref name=CB/> ]s are utilized to define the motion of the wheel as the suspension is compressed. The usual coil springs are replaced with a single FRP spring, which spans the width of the car. As in independent suspension systems using coil springs, and unlike the common leaf-spring supported ], the suspension ] are defined only by the control arms.
Multi-leaf springs suffer from friction between the leaves as the leaf flexes. The inherently flexible leaf spring is being asked to work as a spring AND a suspension arm. Springs (leaf, coil, torsion etc) are good at being springs. They are bad at being other things like rigid links. In those suspension designs the spring is being asked to hold the axle and be a spring. To it’s credit, the leaf spring does this much better than a coil spring. How well would a coil spring do that job? Think of a bobble head doll.


As in a coil-spring suspension design, the FRP mono-leaf spring supports the weight of the vehicle. However, the FRP leaf springs differ from steel coils and traditional steel multi-leaf springs in a number of significant ways. The FRP plastic springs have 4.3–5.5 times the ] storage per weight, compared to steel.<ref name=Yu>{{cite journal |last1=Yu |first1=W.J. |last2=Kim |first2=H.C. |title=Double tapered FRP beam for automotive suspension leaf spring |journal=Composite Structures |year=1988 |volume=9 |issue=4 |pages=279–300 |doi=10.1016/0263-8223(88)90049-9}}</ref> This results in a lighter spring for a given application. The single FRP mono-leaf front spring used on the ] is 33&nbsp;percent of the weight of an equivalent set of coil springs.<ref name=Lamm>{{cite book |last1=Lamm |first1=Michael |title=The Newest Corvette. Corvette from A to Z-15 |url=http://www.carbibles.com/images/fibreglass_spring.gif |date=1983 |archive-url=https://web.archive.org/web/20120219190009/http://www.carbibles.com/images/fibreglass_spring.gif |page=44 |edition=1st |publisher=Lamm-Morada Publishing |isbn=978-0932128041 |archive-date=February 19, 2012}}</ref> Comparing FRP to conventional steel leaf springs in similar applications, the weight saved is even greater. The ] offered an optional FRP mono-leaf spring as an alternative to the standard multi-leaf steel spring, the {{convert|48|lb|kg|0|order=flip|adj=on}} steel spring being replaced by a {{convert|7|lb|kg|0|order=flip|adj=on}} FRP spring.<ref name=McLellan>{{cite book |last1=McLellan |first1=Dave |title=Corvette from the Inside |date=2002 |publisher=Bentley Publishers |location=Cambridge, MA |isbn=0-8376-0859-7 |pages=86–87}}</ref> Volvo claims a weight savings of {{convert|10|lb|kg|0|order=flip}} by using a FRP spring in the rear suspension of its second-generation ], compared to designs using coil springs.<ref name=Volvo>{{cite web |title=Benteler-SGL mass-produces composite leaf springs for the new Volvo XC90 using Loctite Matrix resin from Henkel |url=http://compositesindustrynews.com/fullnews.php?ids=1298 |website=Composites Industry News |publisher=FRP Today |access-date=2015-07-30}}{{dead link|date=November 2016|reason=not at archive.org (as of May 2017)}}</ref>
First, the Corvette has double A-arm suspension like many other high end sports cars. The A-arms are used to fully control the movement of the wheels. The only difference between the Vette and other cars with A-arms is the Vette uses a leaf to pull the lower arm down rather than a coil spring to push it down. In both cases the spring is doing what it does best, being a spring ONLY.


The relative sliding movement of the leaves of a multi-leaf steel spring results in stiction-based hysteresis with respect to spring compression. This stiction reduces suspension compliance and can compromise both ride quality and handling.<ref name=Knowles>{{cite book |last1=Knowles |first1=Don |title=Today's Technician: Automotive Suspension & Steering |date=2010 |publisher=Cengage Learning |page=115}}</ref> Lacking individual leaves, the mono-leaf spring avoids stiction.<ref name=Lamm/>
The other problem was friction between the leaves of a leaf spring. Well the Vette uses a single piece leaf so there is no internal friction, just like a coil spring.


FRP springs are advertised as having exceptional cycle life and corrosion resistance.<ref name =Lamm/> A GM test comparing the third-generation Corvette springs found that failure of the multi-leaf steel springs was likely after 200,000 full-travel cycles. The replacement FRP leaf spring showed no loss of performance after two million full cycles.<ref name=McLellan/>
So what we have is double A-arm geometry just using a different type of spring.


Packaging is cited as both an advantage and disadvantage of the transverse FRP leaf spring, as compared to coil springs, depending on the application. The FRP spring is typically set low in the suspension, resulting in a low center of gravity. It also allows manufacturers to avoid tall spring mounts, thus resulting in a flatter load floor about the suspension.<ref name=Volvo/> James Schefter reports that, as used on the C5 and later Corvettes, the use of OEM coilover damper springs would have forced the chassis engineers to either vertically raise the shock towers or move them inward. In the rear this would have reduced trunk space. In the front this would have interfered with engine packaging. The use of the leaf spring allowed the spring to be placed under the chassis, out of the way, while keeping the diameter of the shock-absorber assembly to that of just the damper, rather than damper and spring.<ref name=Schefter>{{cite book |last1=Schefter |first1=James |title=All Corvettes Are Red |date=1998 |publisher=Gallery Books |isbn=978-0671685010}}</ref> However, in other applications, such as race car designs, the need to span the width of the vehicle resulted in significant design limitations. Coil and torsion springs present better packaging options for racing applications. FRP springs also have limited availability and selection as compared to coil springs.<ref name=Smith>{{cite book |last1=Smith |first1=Carroll |title=Engineer to Win |date=1984 |publisher=Motorbooks |isbn=9780879381868 |page=207 |quote=If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)}}</ref> Higher cost has also been cited as a disadvantage, when comparing FRP springs to coil springs on production road cars.<ref name="Edmunds-2014">{{cite web |last1=Edmunds |first1=Dan |title=2014 Chevrolet Corvette Stingray Z51 Suspension Walkaround |url=http://www.edmunds.com/car-reviews/track-tests/2014-chevrolet-corvette-stingray-z51-suspension-walkaround.html |website=Edmunds |access-date=2015-07-30}}</ref>


== Properties ==
==Types of leaf springs==
] model of a leaf spring under load. The initial, unbent shape of the spring is shown as a silhouette box. An upward deflection on the right side of the spring results in a smaller upward movement on the left side.]]


An advantage of the FRP transverse leaf springs—when supported with widely spaced, pivotable mounts—is the ability to replace the anti-roll bar. Typically springs that provide a sufficient ] need a supplemental spring (the ]) to increase the suspension ]. The coupling of the two sides of the transverse leaf spring across the vehicle results in an anti-roll bar like behavior. Corvette engineers have cited this property as enabling the use of a lighter anti-roll bar,<ref name=McLellan/> and even eliminating the rear anti-roll bar on some versions of the seventh generation Corvette.<ref name=Automobile>{{cite news |last1=Noordeloos |first1=Marc |title=Vette Engineering Manager Explains the C7 Chassis |url=http://www.automobilemag.com/features/news/2014-corvette-engineering-manager-dishes-on-the-c7s-chassis-206465/ |access-date=2015-08-01 |work=Automobile Magazine}}</ref>
===Model T style transverse leaf ===


When either wheel is deflected upward, the center span of the spring (the portion between the pivotable mounts) deflects downward. If both wheels deflect upward at the same time (for example, when hitting a bump in the road) the center section bends uniformly between the pivot mounts. In a roll, only one wheel is deflected upwards, which tends to form the center of the spring into an S-shaped curve. The result is that the wheel rate of one side of the suspension depends on the displacement of the other side.<ref name =Lamm/><ref name=McLellan/><ref name=Smith/> The extent to which the spring acts as an anti-roll bar depends on the distance between the pivot mounts and their rigidity.<ref name =Lamm/>
This model shows the transverse leaf used on a Ford Model-T. The suspension has two lateral arms that keep the front axle perpendicular with the chassis. Lateral axle movement is controlled by the spring. This system suffers from poor control of the axle’s movements among other flaws. I’m not aware of any production car that uses this suspension type.


]
===Conventional truck type, longitudinal leaf springs ===


A simplified flat, rectangular spring illustrates this principle. Deflecting the right side of the spring results in the left side rising. By comparison, a rigid central mount (2nd and 3rd generation Corvettes and other cars) shows no movement on one side when the other is deflected.<ref name=CB/>
This is the one we all love to hate. It’s also about the only type of leaf spring suspension still in use. It’s cheep, durable and handles badly. It suffers from friction between the leaves and from poor control of the axle’s location.


== Applications ==
===Golf cart style transverse leaf spring===
A number of manufacturers have produced vehicles or concepts utilizing independent front or rear suspensions supported by transverse leaf springs that have an anti-roll effect.
* Chevrolet Corvette: ] 1984–1996 (front only, centrally mounted rear spring did not have the anti-roll effect)<!-- this article is specifically about versions of this suspension that use the twin, widely spaced spring mounts, not the single central mount such as used on the C3 and C4 rear suspensions -->, C5–C7, 1997–2019 (front and rear).
* ] cars: first generation (Lumina, Grand Prix, Regal, Cutlass Supreme).
* ] cars: (Eldorado, Toronado, Riviera, Reatta, Allante).<ref name=PopSci>{{cite news |last1=McCosh |first1=Dan |title=Luxury coupes: $24,000 a seat |url=https://books.google.com/books?id=zQAAAAAAMBAJ&q=GM+E-body+leaf+spring+transverse&pg=PA42 |access-date=2015-07-30 |work=Popular Science |date=April 1998}}</ref>
* ] (from model year 1995) renamed to S90 (sedan)/V90 (wagon) from model year 1997 to 1998.<ref name=Schulon>{{cite news |last1=Schuon |first1=Marshal |title=Behind the Wheel/1995 Volvo 960; A Box That's Well Rounded |url=https://www.nytimes.com/1994/10/23/automobiles/behind-the-wheel-1995-volvo-960-a-box-that-s-well-rounded.html |access-date=2015-07-30 |work=The New York Times |date=Oct 23, 1994}}</ref>
* ] and ] (second generation).<ref name=CandD>{{cite web |last1=Stoklosa |first1=Alexander |title=10 Things You Need to Know About the 2016 Volvo XC90 |url=http://blog.caranddriver.com/10-things-you-need-to-know-about-the-2016-volvo-xc90/ |website=Car and Driver |access-date=2015-08-01 |archive-date=2017-12-29 |archive-url=https://web.archive.org/web/20171229021116/https://blog.caranddriver.com/10-things-you-need-to-know-about-the-2016-volvo-xc90/ |url-status=dead }}</ref><ref>{{cite web |language=en |url=https://www.materialstoday.com/composite-applications/news/volvo-xc90-features-polyurethane-composite-leaf/ |title=Volvo XC90 features polyurethane composite leaf spring |author=Amanda Jacob |date=15 October 2014 |access-date=2018-02-02 |archive-date=2018-02-02 |archive-url=https://web.archive.org/web/20180202190441/https://www.materialstoday.com/composite-applications/news/volvo-xc90-features-polyurethane-composite-leaf/ |url-status=dead }}</ref>
* ] vans (front only, Hotchkiss in rear).<ref name=CW>{{cite web |last1=Wood |first1=Karen |title=Composite leaf springs: Saving weight in production suspension systems |url=http://www.compositesworld.com/articles/composite-leaf-springs-saving-weight-in-production-suspension-systems |website=Composites World |access-date=2015-08-01}}</ref>
* ]: 1969–1973 (Front only), Trailing arm with coil springs, panhard bar (Rear).
* ] Mk1-Mk3 (used with MacPherson Struts).<ref name=Smart>{{cite web |title=The Smart Fortwo Evolution |url=http://www.fq101.co.uk/data-a-reference/61-the-smart-evolution.html |access-date=2015-08-01}}</ref>
* ], prototype.<ref name=AutoIntel>{{cite web |title=Volkswagen : The 1-Litre Car |url=http://www.autointell-news.com/european_companies/volkswagen/vw_marke/volkswagen-concepts/volkswagen-1-liter/volkswagen-1-literauto-02.htm |website=Automotive Intelligence News |access-date=2015-07-30}}</ref>
* ], a Swedish made, low volume roadster. Due to the anti-roll properties of the transverse leaf-spring, the car does not employ a separate front anti-roll bar.<ref>{{cite web |url=http://www.lakritz.se/nyheter/INDIGO.PDF |title=The Successor: Indigo 3000 | archive-url = https://web.archive.org/web/20081216074553/http://www.lakritz.se/nyheter/INDIGO.PDF |archivedate=2008-12-16}}</ref>
* ], which used a similar system with a more traditional multi-leaf steel spring but configured with two pivots to provide the anti-roll effect.<ref name=Unique>{{cite web |title=How it Works: Suspension |url=http://www.uniquecarsandparts.com.au/how_it_works_suspension.htm |website=Unique Cars and Parts |accessdate=2015-08-01}}</ref>
* Some later models of ] and ] used rear transverse steel leaf springs with anti-roll pivot mounts.
* ].


== Recent patents and related research ==
I couldn’t find any pictures of this but it basically looks like a double A-arm where the leaf spring is one of the A-arms. The geometry is probably OK under vertical loads but lateral loads would defect the spring and cause camber changes. Not an issue for golf carts but bad for sports cars.
Several automotive companies have filed patents for suspension designs using a transverse composite leaf-spring supported in a fashion similar to that of the Corvette.
* Ford Global Technologies, 2006, patent #7029017, ''Wheel suspension for a motor vehicle with a transverse leaf spring''.<ref>{{cite web |url=https://patents.google.com/patent/US7029017 |title=Patent US7029017 – Wheel suspension for a motor vehicle with a transverse leaf spring |access-date=2015-08-03}}</ref>
* Porsche AG, 2000, patent # 6029987, ''Front Axle for a Motor Vehicle''. Describes a strut suspension system supported by a transverse leaf-spring system largely the same as that used by the Corvette. The Porsche patent mentions the beneficial stabilizing effects of this arrangement.<ref>{{cite web |url=https://patents.google.com/patent/US6029987 |title=Patent US6029987 – Front axle for a motor vehicle |date=1997-05-26 |access-date=2015-08-03}}</ref>
* Honda, 1992, ''Transverse leaf spring type suspension'' patent #5141209.<ref>{{cite web |url=https://patents.google.com/patent/US5141209 |title=Patent US5141209 – Transverse leaf spring type suspension |date=1988-11-30 |access-date=2015-08-03}}</ref>
* DaimlerChrysler, 2004, patent #6811169, ''Composite Spring Design that also Performs the Lower Control Arm Function for a Conventional or Active Suspension System''.<ref>{{cite web |url=https://patents.google.com/patent/US6811169 |title=Patent US6811169 – Composite spring design that also performs the lower control arm function for a conventional or active suspension system |access-date=2015-08-03}}</ref>
* ] released a concept rear suspension design, in October 2009, using a composite spring-based rear suspension. The strut-based suspension uses a transverse leaf spring to function as both ride and anti-roll spring. The ZF concept differs from the system used on the Corvette by using the leaf spring as one of the suspension links.<ref>{{cite news |last1=Buchholz |first1=Kami |title=Composites take prime chassis roles at ZF |url=http://articles.sae.org/7840/ |access-date=December 22, 2016 |publisher=Society of Automotive Engineers |date=March 31, 2010}}</ref><ref>{{cite web |title=Lightweight Construction: Fighting the Fab |url=https://www.zf.com/corporate/en_de/magazine/magazin_artikel_viewpage_22131368.html |website=ZF Company corporate website |publisher=ZF Company |access-date=December 22, 2016}}</ref>


===Leaf with links=== == See also ==
* ]


==References==
There are variations on this suspension:
{{Reflist|30em}}


]
* Miller Indy Roadster and (on top of the front axle)
]
*Jaguar MkII rear suspension
]

Like #3, these suspensions uses a combination of links and the leaf spring to support the axle. The Jaguar set up looks similar to a 4 bar solid axle rear suspension except the lower link is the end of an inverted leaf spring. The other end for the leaf is attached to the chassis under the passenger compartment. The middle of the upside down (frown rather than smile) spring presses against a rubber block. The end connects to the bottom of the axle. This system offers better handling and axle control than #2 but is still suffers from friction between the leaves of the springs and compared to multi-link live axles, poor control of the axle’s location.

==Leaf springs on the Corvette==

To be honest, I have no idea how GM got started with the transverse leaf spring. The used to use coils in front but in 1984 they switched too leafs front and rear. I suspect it’s a tradition they maintain for the same reason Porsche keeps their engine out back even though the platform mate Boxster moved it to the middle.

===Advantages===

This is an article written around the time the C4 was released. It covers a lot of the reasons why GM retained the leaf suspension

http://web.telia.com/~u60113742/misc/suspension/fiberglass_spring.gif

The big advantages are:

-It weights A LOT LESS than coil springs. One leaf replaces two coils. The two coil springs weigh 3 times as much as the one leaf. Additionally the leaf is placed at the bottom of the car. In addition to removing weight you lower the CG.

-It acts as an anti role bar. The article above explains how this works so I won’t. The advantage is you can run lighter anti-role bars because the springs are taking care of part of the job for you.

-The leaf springs never wear out. The vendor of these springs has never had to replace one due to fatigue failure. Coil springs to were out but you typically don’t notice on smaller, lighter cars. You do see it more on old, heavy Caddies and such. The improved fatigue life was really evident compared to the C3’s steel leaf spring. Thus this is an advantage over coils but not a big one.

===Drawbacks===

They are expensive. We normally don’t think of leaves as the expensive suspension, but in the case of the Corvette, coils would be cheaper. Coils are usually easier to install as well. In the C5/C6, the lower ball joint must be popped on one side for the spring to be pulled out. It's also impossible to run stiffer springs left-to-right, so a transversely leaf sprung car would be a poor choice for oval tracks.

The Vette already has all the parts a coil sprung double A arm suspension would use. Pull the leaf off, replace the shock with a coil over and you’ve converted the Vette. Since the rest of the system is the same, the cost comes down to the price of 2 coils or one spring. Well if it was a steel leaf spring it might be cheaper (remember truck suspension is cheaper because the leaves also act as links).

==Competition==

If it’s so good why don’t other people use it?

It’s legitimate to ask, does GM know something that Ferrari, Porsche etc don’t know or are the people at GM just being pig headed and sticking with “outdated” technology.

===Street cars===

#You must design them into the car in the first place. This seams obvious but consider these springs span across the bottom of the car. In the front they have to clear the engine oil pan and in the back they have to stay out of the way of the differential. Basically, you can retro fit coils on the Vette because the mounts can be shared with the shock mounts. For the most part you can’t retrofit Corvette style leaves onto other cars because you would have to add mounts that don’t exist on the regular car.
#GM and their supplier spent a lot of time and money developing the Vette’s composite spring. Currently they are the only manufacture with the knowledge and understanding to make the springs work. On the other hand, coil springs are common and well understood. Lots of vendors can make them in a wide variety of configurations. It’s easier for the other manufactures to stick with what they know. Other manufactures would have to study the design and manufacture of composite leaf springs before they could pop them on the next Supra-NSX-Type-GT. GM did that work years ago. Toyota could certainly afford to develop their own composite springs if they wanted. The same may not be true for smaller companies like Ferrari and Porsche.
#Engineers like to stick with what they know. Lots of suspension engineers are familiar with using coil springs. They could experiment with leaves if they wanted or they could stick with coils and get the job done. See the point about undertaking a research project.
#Coils are cheaper. This automatically keeps them off lower cost cars (Miata, Civic) and cars that share platforms with lower cost siblings (Audi TT). Porsche isn’t worried about saving every last dollar but there suspension and chassis design may not allow packaging a Corvette type leaf. The same is probably true of Ferrari. Even if packaging isn’t a problem they still have to pay for tooling to make the springs. Unlike the GM who spreads that cost over 30,000 Vettes a year, Ferrari would spread that over maybe 2000 cars a year. Porsche would be somewhere in between. Conversely I can get coils made with relatively low setup cost and a cheaper per part cost. So not only would they have to spend more per car, they have to spend a lot more up front.
#Perception. Just like pushrods, the leaf spring as a stigma attached to it. The reasons for the stigma are legit (key component to heavy and typically poor handling suspension). However the reality is the sum of the older parts was the problem, not a specific part of it.
#Some Do! Volvo used a transverse leaf spring on the 960.

===Race cars===

To start off, not all race cars use coil springs. Some F1 cars (Ferrari and others) use torsion springs instead. Years ago Indy and F1 cars DID use leaf springs but those days are long past.

The current design of open wheel racecars places great restrictions on suspension packaging. The Corvette’s transverse leaf spring must span from one side of the car to the other. Also, to be most effective the links between the spring and suspension arms should be under tension. This makes a bottom mount spring most effective. This packaging doesn’t work well on an open wheel car because the spring would have to pass though the gear box around the dif (or the gear box would have to be raised and hurt the car’s CG). At the front the driver’s legs would get in the way. Additionally the spring is wide and would have to extend past the body work where it would hurt the car’s aero package.

NASCAR rules dictate coil springs on the rear axle. They probably originally used leaves but given the option any car designer (modifier back in the day?) would have replaced the leaves with a multi-link set up. As I said before the multi-link offers better control of the rear suspension.

Another good reason is only a few companies understand the technology necessary to make the springs. Hypercoil is currently the top race spring manufacture. They can make very precise, matched spring pairs. The level of precise spring rate control and matching may not exist in the composite bow springs.

Coil race springs are not car specific. You select rates, diameters, length etc but you don’t have a specific spring for a specific car. If you want to order a custom spring Hypercoil will wind it to your specifications on the same machine they use for the next custom spring. A custom Porsche, Formula Ford and LMP car spring can all be made on the same machine. By the time the C6 evolves into a C6-R (they don’t start off with a production Corvette) the suspension geometry is so different that they couldn’t just mount a C6 leaf spring. It’s far too expensive to have a few custom leaf springs tooled up (you would have to buy the tooling as well as the springs) so they use readily available coil springs.

This type of universal tooling isn’t availible for the composite leaf spring. Only the Vette currently uses the spring so you are making a Vette only part. This seriously reduces the market for aftermarket composite leaf springs (still there are after market leaf springs available for the Vette). The business case for custom equipment to make Vette springs is harder to justify since it’s a smaller market.

Why don’t other cars retrofit leaf springs? Well they also don’t retrofit torsion springs despite the fact that F1 cars use them. Put simply it would be VERY difficult. The Vette was designed to have them. It has mount points under the car where the springs fit to the suspension sub frames. It’s not easy to just add that to a car that was designed to use a coil spring. All of the cars you mentioned would have to be re-engineered to add leaf springs. Replacing the factory spring with a racing is easy by comparison.

The other VERY significant reason is racers will use what they know. They will put effort into learning about new technology (torsion springs in F1) but ultimately it is too there advantage to stick with what they know.

==Coil springs==

Would the Vette be better with coil springs?

Well that depends. As I said before, there are a lot more options available in coil springs. If I want to substantially change the Vette’s spring rates then I will need to go to coils. Also, if I want to totally get rid of the Vette’s anti roll I need to dump the leaves because they provided some roll resistance.



BUT…

If for some reason I just lost my leaf spring (maybe someone stole it to make a very strong bow and arrow) and had to replace it with coils. I want the same ride quality, the same spring and roll rates etc. Basically I want the car to be the same as before but with coil springs. Assuming you didn’t change anything but the springs (same tires, shocks, ride height, same spring rate and effective roll rate, etc) the Vette would unquestionably be SLOWER with coils instead of the leaf setup. Basically if all else is equal, the coils are heavier and raise the CG of the car. One other small advantage is the shocks on the leaf sprung car will move more freely than the car with coilovers. When used as a coil over, coils impart a bending load on the shocks that cause them to bind a bit. On a street car you will never notice but on a race car it can cost a tenth of a second or so. (Hypercoil markets a pivoting spring perch to reduce the effects of side loading in coil over shocks).

Again, if I decide I really want to race I will likely dump the leaves because I have more options with coils. For a reasonable (in racing terms) price I can get custom coils made. The same isn’t true of the composite leaf spring.

]
]

Latest revision as of 16:59, 9 June 2024

Type of independent suspension

A Corvette leaf spring is a type of independent suspension that utilizes a fiber-reinforced plastic (FRP) mono-leaf spring instead of more conventional coil springs. It is named after the Chevrolet Corvette, the American sports car for which it was originally developed and first utilized. A notable characteristic of this suspension configuration is the mounting of the mono-leaf spring such that it can serve as both ride spring and anti-roll spring. In contrast to many applications of leaf springs in automotive suspension designs, this type does not use the spring as a locating link. While this suspension type is most notably associated with several generations of the Chevrolet Corvette the design has been used in other production General Motors cars, as well as vehicles from Volvo Cars and Mercedes-Benz Sprinter van. Fiat produced cars with a similar configuration, using a multi-leaf steel spring in place of the FRP mono-leaf spring.

Design

The C5 Corvette's rear suspension

The leaf-spring suspension configuration is independent, because the movement of one wheel is not determined by the position of the other. Control arms are utilized to define the motion of the wheel as the suspension is compressed. The usual coil springs are replaced with a single FRP spring, which spans the width of the car. As in independent suspension systems using coil springs, and unlike the common leaf-spring supported Hotchkiss rear axle, the suspension kinematics are defined only by the control arms.

As in a coil-spring suspension design, the FRP mono-leaf spring supports the weight of the vehicle. However, the FRP leaf springs differ from steel coils and traditional steel multi-leaf springs in a number of significant ways. The FRP plastic springs have 4.3–5.5 times the strain energy storage per weight, compared to steel. This results in a lighter spring for a given application. The single FRP mono-leaf front spring used on the fourth-generation Corvette is 33 percent of the weight of an equivalent set of coil springs. Comparing FRP to conventional steel leaf springs in similar applications, the weight saved is even greater. The third-generation Corvette offered an optional FRP mono-leaf spring as an alternative to the standard multi-leaf steel spring, the 22-kilogram (48 lb) steel spring being replaced by a 3-kilogram (7 lb) FRP spring. Volvo claims a weight savings of 5 kilograms (10 lb) by using a FRP spring in the rear suspension of its second-generation XC90, compared to designs using coil springs.

The relative sliding movement of the leaves of a multi-leaf steel spring results in stiction-based hysteresis with respect to spring compression. This stiction reduces suspension compliance and can compromise both ride quality and handling. Lacking individual leaves, the mono-leaf spring avoids stiction.

FRP springs are advertised as having exceptional cycle life and corrosion resistance. A GM test comparing the third-generation Corvette springs found that failure of the multi-leaf steel springs was likely after 200,000 full-travel cycles. The replacement FRP leaf spring showed no loss of performance after two million full cycles.

Packaging is cited as both an advantage and disadvantage of the transverse FRP leaf spring, as compared to coil springs, depending on the application. The FRP spring is typically set low in the suspension, resulting in a low center of gravity. It also allows manufacturers to avoid tall spring mounts, thus resulting in a flatter load floor about the suspension. James Schefter reports that, as used on the C5 and later Corvettes, the use of OEM coilover damper springs would have forced the chassis engineers to either vertically raise the shock towers or move them inward. In the rear this would have reduced trunk space. In the front this would have interfered with engine packaging. The use of the leaf spring allowed the spring to be placed under the chassis, out of the way, while keeping the diameter of the shock-absorber assembly to that of just the damper, rather than damper and spring. However, in other applications, such as race car designs, the need to span the width of the vehicle resulted in significant design limitations. Coil and torsion springs present better packaging options for racing applications. FRP springs also have limited availability and selection as compared to coil springs. Higher cost has also been cited as a disadvantage, when comparing FRP springs to coil springs on production road cars.

Properties

FEA model of a leaf spring under load. The initial, unbent shape of the spring is shown as a silhouette box. An upward deflection on the right side of the spring results in a smaller upward movement on the left side.

An advantage of the FRP transverse leaf springs—when supported with widely spaced, pivotable mounts—is the ability to replace the anti-roll bar. Typically springs that provide a sufficient ride rate need a supplemental spring (the anti-roll bar) to increase the suspension roll rate. The coupling of the two sides of the transverse leaf spring across the vehicle results in an anti-roll bar like behavior. Corvette engineers have cited this property as enabling the use of a lighter anti-roll bar, and even eliminating the rear anti-roll bar on some versions of the seventh generation Corvette.

When either wheel is deflected upward, the center span of the spring (the portion between the pivotable mounts) deflects downward. If both wheels deflect upward at the same time (for example, when hitting a bump in the road) the center section bends uniformly between the pivot mounts. In a roll, only one wheel is deflected upwards, which tends to form the center of the spring into an S-shaped curve. The result is that the wheel rate of one side of the suspension depends on the displacement of the other side. The extent to which the spring acts as an anti-roll bar depends on the distance between the pivot mounts and their rigidity.

A transverse leaf spring with a central rigid mount. The two spring halves are effectively isolated. Movements of one half of the spring do not affect the other half.

A simplified flat, rectangular spring illustrates this principle. Deflecting the right side of the spring results in the left side rising. By comparison, a rigid central mount (2nd and 3rd generation Corvettes and other cars) shows no movement on one side when the other is deflected.

Applications

A number of manufacturers have produced vehicles or concepts utilizing independent front or rear suspensions supported by transverse leaf springs that have an anti-roll effect.

Recent patents and related research

Several automotive companies have filed patents for suspension designs using a transverse composite leaf-spring supported in a fashion similar to that of the Corvette.

  • Ford Global Technologies, 2006, patent #7029017, Wheel suspension for a motor vehicle with a transverse leaf spring.
  • Porsche AG, 2000, patent # 6029987, Front Axle for a Motor Vehicle. Describes a strut suspension system supported by a transverse leaf-spring system largely the same as that used by the Corvette. The Porsche patent mentions the beneficial stabilizing effects of this arrangement.
  • Honda, 1992, Transverse leaf spring type suspension patent #5141209.
  • DaimlerChrysler, 2004, patent #6811169, Composite Spring Design that also Performs the Lower Control Arm Function for a Conventional or Active Suspension System.
  • ZF released a concept rear suspension design, in October 2009, using a composite spring-based rear suspension. The strut-based suspension uses a transverse leaf spring to function as both ride and anti-roll spring. The ZF concept differs from the system used on the Corvette by using the leaf spring as one of the suspension links.

See also

References

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  10. ^ "Benteler-SGL mass-produces composite leaf springs for the new Volvo XC90 using Loctite Matrix resin from Henkel". Composites Industry News. FRP Today. Retrieved 2015-07-30.
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  13. ^ Smith, Carroll (1984). Engineer to Win. Motorbooks. p. 207. ISBN 9780879381868. If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)
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