Most factory or OE flywheels are made from cast iron (a.k.a. gray iron) to keep costs down. Cast iron is a very heavy and porous material and can be brittle when subjected to high stress loads. Steel is an alloy of iron where carbon has been added to increase strength and make the material more resistant to cracking.
(For more information on materials, please refer to the “Flywheel materials” section of our TECHNOLOGY pages…)
WHAT FLYWHEEL IS BEST; STEEL OR ALUMINUM?The choice between steel and aluminum performance flywheels is mainly a function of the vehicle’s planned uses and driver preferences. Either type of flywheel is a viable choice and improvement over cast OE units depending on what you are looking for in strength and performance, what type of vehicle you have and how you will be using it… Steel flywheels are designed to be stronger than OE ones and will deliver approximately the same weight (or in some cases more) than OE cast iron or nodular flywheels. This means they will deliver about the same inertia at rpm and driving characteristics as the OE unit, but will be less likely to break or explode under high rpm, high load conditions as seen in drag racing, etc. Steel flywheels are often SFI approved for race use. Steel flywheels are also a good choice for helping move heavy vehicles at lower rpms, such as in heavier trucks and for rock crawling, hill climb, etc. These flywheels are designed for use where extreme strength is the issue and not increased performance. Other considerations with steel flywheels are that they still require resurfacing when changing clutches and therefore have a limited service life, requiring eventual replacement, and that they do nothing to improve heat dissipation from performance clutches and therefore can not significantly improve clutch performance or longevity. Another drawback is that the ring gear teeth are often cut right into the steel flywheel, meaning any damage to even a few teeth from a starter mishap, etc. will often mean replacing the entire flywheel.
Billet aluminum flywheels are also designed to be much stronger than OE cast iron flywheels, but their lower weight will provide significant performance benefits by delivering faster throttle response, quicker acceleration, smoother shifting, easier vehicle braking and by freeing up additional horsepower to the wheels (by reducing parasitic driveline loses). Billet aluminum flywheels can also deliver OE equivalent inertia, but at increased rpms, and will require a slightly modified driving style. Billet aluminum flywheel equipped vehicles will provide a more responsive and “nimble” driving experience over vehicles equipped with heavy iron or steel flywheels. All Fidanza Performance aluminum flywheels are made from high quality 6061 T6 billet aluminum to deliver the optimum in strength and durability and are often SFI approved for race use just like steel flywheels. Our billet aluminum flywheels are a great choice for street performance vehicles, as well as, ones used in road racing, autocross, time attack, drift and drag racing; anyplace where increased horsepower and throttle response is desired. In addition, aluminum flywheels are much better at dissipating heat from your clutch, which can greatly improve clutch performance and life; and all Fidanza Performance aluminum flywheels feature a replaceable hardened steel clutch friction surface, which means they are infinitely re-buildable and will deliver years and years of exciting drivability.
Separating Fact From Fiction!So, what IS the best flywheel to use; steel, lightened chromoly or lightweight billet aluminum? Can you use a performance lightweight aluminum flywheel on a daily driven car? How about for drag racing? Can a factory dual-mass flywheel be replaced by a one-piece aftermarket flywheel? What are the trade-offs? These are just a few questions we hear every day at Fidanza Performance.
Unfortunately, there is a lot of misinformation out there about flywheels. We’ve all seen the conflicting posts on the multitude of forums about whether to use a steel or aluminum flywheel. Most often the posts are not really based on facts, just opinions or what other people have heard. Often, the majority of commenters have never even tried or used both types of flywheels to really know what the differences, benefits and trade-offs are, they’re just repeating an opinion they’ve heard from someone else (who often doesn’t have first hand experience either). It’s kinda like asking 10 people what to take for your headache… One will tell you asprin is always best, while another swears by ibuprofen and yet another says acetaminophen or naproxen or maybe just a cold washcloth. Which one really works? They probably all do, but to differing standards depending on your needs or likes and how they effect you personally. So before you make up your mind on what is the best “medicine” for your performance car, be sure to check multiple sources and find knowledgeable people that have actually USED the various products; if not, you’ll only get a partially informed opinion.
“You can’t run an aluminum flywheel for drag racing, you need a steel flywheel for drag racing, it has more inertia.”This is one we see all the time. Truth of the matter is, there are drivers who run; and swear by, aluminum flywheels in their drag cars. Including some multi-year national champions. They love the extra horsepower they get from using a lighter aluminum flywheel, as well as, the fact the flywheel friction surface can be easily changed, allowing them to put a new clutch in ad get right back out on track if needed. Many also say the lighter flywheel doesn’t shock the tires as hard at launch and allows for better traction. He bottom line is that inertia is a math equation; mass X rpm = inertia. If you have a lighter mass, you just need to add some rpm to get the same inertia; it’s all in how you drive the car.
“Aluminum flywheels are just for racing, not for the street.”That is another comment we hear all too often. Who says and for what vehicle or what type of driving? There are tens, if not hundreds of thousands of cars on the road today with aluminum flywheels, and they work great! If you are changing from a heavy iron or steel flywheel to a lightweight aluminum flywheel the car WILL drive differently, but most people get used to the differences and adapt quickly, some people say they don’t notice anything other than the faster acceleration, quicker throttle response and an overall lighter, nimbler feel to the car.
“An aluminum flywheel is noisier than a stock or steel flywheel.”
“A lightweight flywheel will be louder than a stock/replacement dual-mass flywheel.”We’ve heard this a few times too. While this can be true in some instances it is not a significant difference in sound over stock flywheels in most cases; and if the flywheel is going on a performance car with say a high performance exhaust system and aftermarket intake system, the sound difference might not even be noticed. Keep in mind that the whole reason for heavier stock flywheels, and especially dual-mass flywheels is to help dampen noise and vibration in a car’s driveline. When you go to a lighter flywheel, some noise and vibration may return, but if the flywheel and clutch assembly is balanced correctly as a unit, it is usually minimal. In any case, the performance gains in liberated horsepower, faster acceleration and quicker throttle response are often considered more than adequate trade-offs for any minimal increase in sound or vibration.
Looking for more outside input on these subjects? Then check out some of these links to see what others are saying, or check out our Customer Testimonials under the COMPANY tab here on our website:
Automotive flywheels can be constructed out of several different materials including cast iron, nodular iron, steel or billet steel, chromoly steel and billet aluminum to name the most common.
Most OE or stock flywheels are made out of cast iron (commonly called “grey iron”) similar to what cast iron frying pans are made of. Heavy and relatively inexpensive, cast iron is a material that dates back to around the 5th century BC.
“Grey” cast iron is formed with graphite flakes in the casting material that help it resist straight-line cracking as you would find in “white cast iron,” but also makes the material more brittle. Grey iron has less tensile strength and shock resistance than steel, but a comparable compressive strength to low or medium carbon steel.
(Ok for a stock flywheel, but will not take much additional stress or impact, also does not have the tensile strength to endure high rotational stress – high rpm. Can be re-surfaced a few times in most cases, except in the case of Dual-mass flywheels, before requiring replacement.)
Nodular cast iron (also referred to as ductile iron) is the next common step-up in material and is characterized by having the graphite content of the iron form nodules during casting rather than flakes, this nodular formation of the graphite further inhibits the formation of stress cracks and strengthens the material against impact and fatigue but does little for tensile strength, surface wear or heat dissipation.
(Better for a flywheel, but will still not handle impacts or high rotational stress well. Can be re-surfaced a few times in most cases before requiring replacement.)
Steel is an alloy of iron when combined with carbon and other trace elements. The amount of carbon in the mix can vary the hardness, ductility and tensile strength of the steel and can improve the iron at an atomic level to overcome what makes pure iron so ductile and weak. Steel therefore is stronger than cast iron, but only by sacrificing ductility and thereby requiring significant making and handling. The quality and characteristics of steel can also vary widely dependent on the mix of carbon and trace materials, as well as, how the steel is heated, mixed and cooled as it is formed. The term “billet” steel, actually refers to the form the steel is created in. A billet is a long square or round bar of material than is then cut into “slices” before machining. The primary benefits of “billets,” are that they are more consistent in metallurgy and that their outer material is often machined away removing stress areas from the metal and creating additional strength. Weighing in at about the same as a cast iron counterpart, the benefit of a steel flywheel is its increased tensile strength and reduction in brittleness.
(Better choice for a performance flywheel – can be SFi approved, but still very heavy. Does not dissipate heat well and still requires resurfacing when changing clutches. Can be re-surfaced a few times in most cases before requiring replacement.)
Chromoly (aka. Chromoly steel) is an alloy of steel created primarily by the addition of chromium and molybdenum to high carbon steel. The addition of these two materials makes the steel stronger by weight, which in turn allows for a lighter flywheel to be made by removing some material from the dimensions of the part or creating “lightening holes” where sections of metal are completely removed. Re-dimensioning or adding these “lightening holes” to the flywheel design must be done carefully though to avoid creating any weak spots or stress points that may fail at high rpm or aggressive clutch engagement. Chromoly also often has a higher surface hardness or durometer that may be sacrificed when re-surfacing is required.
(Better choice for a performance flywheel – can be SFI approved, but still heavy. Lighter weight than OE these flywheels can add some performance, but still do not dissipate heat well and will require resurfacing, if possible, when changing clutches. Can be re-surfaced a couple times at most before requiring replacement.)
Aluminum (aka billet aluminum, 6061 T6 aluminum) is a non-ferrous metal that is lighter weight than iron or steel alloy and has a higher rate of thermal dissipation allowing it to cool and transfer heat more quickly. Aluminum also has higher ductility and is more easily machined and formed than steel alloys. “6061” aluminum is a hardened aluminum alloy containing magnesium and silicon to give the metal a higher tensile strength, making it stronger and able to handle higher rotational and impact stresses. The T6 reference in “6061 T6” refers to a tempering process that further increases the aluminum’s tensile strength to at least 42,000 psi. Since aluminum is malleable, and will not hold up well to direct contact with friction materials (as used on clutch discs), most aluminum flywheels incorporate a replaceable wear surface or friction plate made of high carbon steel and mated to the flywheel’s friction surface area with bonding material, rivets or bolts. Aluminum flywheels also usually feature a separate hardened steel ring gear/starter ring mated to the aluminum flywheel body by various means including interference fit, lock bolts or welded tabs.
(Much better choice for performance flywheels – can be SFI approved, and is much lighter in weight providing additional performance, quicker throttle response and faster acceleration. Aluminum also dissipates heat better allowing for increased clutch efficiency and longer clutch life. Replaceable friction surface means flywheel is re-buildable and will not require periodic replacement with a new flywheel once re-surfacing tolerances are exceeded, just simply replace the friction surface.)
What all this means in the case of our Fidanza Performance aluminum flywheels is that they are much lighter than any of the iron or steel flywheels on the market, without the need to eliminate material or possibly weaken the flywheel’s design or construction. That lighter weight reduces some parasitic loss through the driveline, delivering more of the engine’s horsepower to the wheels! The reduced rotational mass also provides faster throttle response, quicker acceleration, smoother shifting and reduced stress to the engine. Our design featuring the bolt on friction surface and replaceable ring gear also means our flywheels can be easily re-built to allow years of trouble free use. And unlike some of the other aluminum flywheels on the market that have bonded or riveted friction plates that must be replaced back at the manufacturer, ours can be easily done in the field with simple hand tools. No need to send a flywheel out and pay to have it resurfaced, a simple bolt on kit allows complete replacement of the friction surface in minutes. In addition, the bolt on hardened ring gear means that should you have a starter failure or issue that damages the ring gear teeth, the ring gear can be replaced also, saving the cost of replacing the entire flywheel for just a few chipped or broken teeth; can’t do that with an iron or steel flywheel with integral teeth (teeth cut into the actual flywheel). For more information on the construction of our flywheels, check out the aluminum flywheel page in the PRODUCT area of our website!