Wobbly-web wheel
Encyclopedia
The wobbly-web wheel is a form of metal disk wheel
where the disk is 'wobbled' into spokes. This provides a stiffer, lightweight wheel.
Wobbly-web wheels are best known through their iconic use on Lotus
racing cars of the late 1950s and 1960s.
structure. Their materials are assumed to be inextensible, but flexible
. Such a skin is stiff against tensile loads in the plane of the skin, but flexible for loads perpendicular to it. A flat disk is thus strong for radial
loads in the plane of the disk and also for torque
s. It is flexible for axial
loads, perpendicular to the disk plane and also for nutation
, wobble of the axle at an angle to the main axis.
A coned disk also becomes stiff against axial loads, as the web is no longer purely perpendicular to the axis of the wheel. Unlike a flat disk, there is no direction where the whole of a coned disk would be perpendicular (and thus flexible) to it. A drawback of a simple cone is that the wheel now becomes wider, along the axis. The wobbly web effectively "folds" a coned disk wheel into pleat
s, making it narrower again, but retaining the axial stiffness. This pleated disk is also stiffer against nutating forces. A similar feature, a 'sine wave wall', is sometimes encountered in architecture where a straight wall is made stronger against sideways forces by corrugating it.
Key features of the wobbly web wheel are that they are designed as a modification of the disk wheel with additional shaping, rather than a spoked wheel with merged spokes. They can be manufactured by either pressing from sheet steel, or by casting
in light alloys. To avoid stress risers, the webs are formed into smooth curves, rather than sharply defined spokes.
When cast, foundries prefer a disk that has a consistent wall thickness, as this makes their shrinkage behaviour simpler to control. The Lotus wheel's peculiar shape was arrived at deliberately, by keeping this consistent wall thickness, for ease of manufacture, and folding it to achieve the varying stiffness distribution required across the radius, to meet the performance needs.
for his Cosmos
car of 1919. This pressed steel wheel used a disk with six spokes on alternating sides and three retaining bolts.
s use spoked driving wheels of cast iron or cast steel. A few makers have favoured variants of this, seeking a more weight-efficient design by using various forms of hollow or girder spoke, rather than solid oval-section spokes. One of the most successful of these designs was the Bulleid
Firth Brown or BFB wheel, often incorrectly confused with the Boxpok
wheel. This had some features of the wobbly web, being developed from a flat disk wheel with short, wide "spokes" formed in it by displacing teardrop-shaped sections of the disk into another plane. Except for a few small lightening holes, this disk wheel is consistently one wall thickness thick, all around the disk.
Like the Lotus wheel, the BFB wheel also displays wide shallow pleats at its outside diameter, with narrower steeper pleats towards the centre (see image).
Although superficially visually similar to the BFB wheel, the true Boxpok design is, as indicated by its name, derived from "box spoke". This is a spoked wheel, with square box-section hollow spokes. The wheel disk in section is either two skin thicknesses at the spokes, or zero (i.e. open space) between them.
. This basic design served with little change into the 1960s and the jet age
.
The first distinctly wobbled web appeared on the Convair CV-240 of 1948. This used a wheel cast with nine narrow radial spokes formed from a curved disk.
for their racing cars of the late 1950s and early 1960s. These wheels first appeared on the Formula 2 Lotus Twelve of 1957. A similar wheel was used by Vanwall
from 1958.
The wheel's design was, in typical Lotus fashion, intended to achieve the lightest possible weight. This is particularly important for wheels, as they are unsprung weight
and the cars intended to carry them were extremely lightweight. Their designer was Lotus' Gilbert 'Mac' McIntosh although, again in typically Lotus fashion, they are often credited to Colin Chapman
.
Unlike earlier 'waved' wheels, the Lotus design and its distinctive 'wobbles' was a deliberate feature, even down to the way that the wobbles are deeply indented near the hub and soften outwards to the rim. For ease of manufacture by casting, the wheels were designed with a constant wall thickness. Their stiffness (force/area) was required to be highest aroudn the hub, so here the wheels were deeply and steeply folded. Towards the rim, distribution of this same force over a the greater circumference and metal cross-section thus required less folding and their profile became a gentle wave.
As for many other Lotus components, the wheels were cast from Elektron
magnesium-aluminium alloy. They were cast by Stone Foundrieshttp://www.stone-foundries-limited.com of Charlton
. Cooper
were already using magnesium wheels and apart from their technical advantages, Charles Cooper had found it highly profitable to sell drivers the many spare wheels required for racing, rather than having an external supplier take the business, something that Chapman was keen to emulate. McIntosh and Chapman also obtained foundry scrap, failed wheels from Coopers, and studied these failures to understand the failure modes of a magnesium racing wheel.
Lotus' team racing colours at this time were green and yellow, often small patches of each with the bodywork substantially of bare polished aluminium sheet. With the advent of the wobbly web wheel, rather than the previous wire wheels, the wheels were painted yellow and the car bodies green. This glossy bright yellow colour could be applied easily over the greenish-yellow zinc chromate
primer used on the wheels to prevent corrosion.
, whose Stout Scarab
would also inspire the Chapman strut
. The Formula Junior
Lotus 20
and Lotus 22
extended this to their front wheels, which used a 4-stud
fastening, compared to the previous 6-stud that was still used on their rear, driven, wheels.
At the 1963 Le Mans
Lotus entered the new, and somewhat unfinished, Lotus 23
, a widened version of the Lotus 22 two-seater. It was disqualified from competition before the race and did not take part. This was on the basis of its wheels, although not specifically due to the wobbly-web design. The car, as designed, used Lotus' typical 6-stud wheel at the rear but a 4-stud mounting at the front. The wheel rims were also wider at the rear, 6" vs. 5", with wider tyres of 5.50×13 rather than 4.50×13. www.examiner.com/auto-review-in-national/driven-1962-lotus-23-choice-of-champions As the rules for Le Man were still framed as a "sports car" endurance race, they required the carrying of a spare wheel. The 23 had such a spare, but obviously it could not be fitted to both ends of the car. The scrutineer
s rejected this and barred the car from competition. Matching 4-stud rear hubs were flown hurriedly from England, avoiding the incompatibility problem, but the scrutineers now objected that if 6 studs had been required before, 4 must be inadequately strong and still refused to allow the cars to compete. After this, Chapman
replied "We shall never again race at Le Mans.", a promise that Lotus kept until 1997, long after Chapman's death in 1982.
The following year's Can Am sports car, the Lotus 30
, switched from wheel studs to centre-lock wheels. This was mostly due to the far greater torque of its large V8 engine, but it also avoided this situation re-occurring, as the 30 also carried a single spare wheel.
alloy, corrosion of the magnesium was a problem for long-term service. Even though Lotus only used these wheels on its racing cars, not its road cars, they had a limited service lifetime. Lotus cars of the 1960s are still popular for historic racing, but these wheels are now no longer acceptable for competition scrutineering, no matter what their apparent condition. As the wheels are such a distinctive part of the car's appearance though, there are modern reproductions available.
Wheel
A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...
where the disk is 'wobbled' into spokes. This provides a stiffer, lightweight wheel.
Wobbly-web wheels are best known through their iconic use on Lotus
Lotus Cars
Lotus Cars is a British manufacturer of sports and racing cars based at the former site of RAF Hethel, a World War II airfield in Norfolk. The company designs and builds race and production automobiles of light weight and fine handling characteristics...
racing cars of the late 1950s and 1960s.
Theory
The theory of a disk wheel depends on their behaviour as a stressed skinStressed skin
In mechanical engineering, stressed skin is a type of rigid construction, intermediate between monocoque and a rigid frame with a non-loaded covering:...
structure. Their materials are assumed to be inextensible, but flexible
Flexible
Flexible may refer to:* Flexible electrical cable, also known as a power cord* Flexible electronics* Flexible response* Flexible mold* Flextime* Flexible-fuel vehicle* Flexible rake receiver* Flexible spending account, a tax-advantaged savings account...
. Such a skin is stiff against tensile loads in the plane of the skin, but flexible for loads perpendicular to it. A flat disk is thus strong for radial
Radial
Radial can refer to:* Vector , a line* Radius, adjective form of* A radial pattern is one that appears to radiate from a point, like the spokes from the hub of a wheel* A bearing from a waypoint, such as a VOR...
loads in the plane of the disk and also for torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
s. It is flexible for axial
Axial
Axial may mean:* Along the same line as an axis of rotation in geometry* A type of modal frame in music* One of several anatomical directions in an animal body* Axial age, the period from 800 to 200 BC in China, India and the western world...
loads, perpendicular to the disk plane and also for nutation
Nutation
Nutation is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behavior of a mechanism...
, wobble of the axle at an angle to the main axis.
A coned disk also becomes stiff against axial loads, as the web is no longer purely perpendicular to the axis of the wheel. Unlike a flat disk, there is no direction where the whole of a coned disk would be perpendicular (and thus flexible) to it. A drawback of a simple cone is that the wheel now becomes wider, along the axis. The wobbly web effectively "folds" a coned disk wheel into pleat
Pleat
A pleat is a type of fold formed by doubling fabric back upon itself and securing it in place. It is commonly used in clothing and upholstery to gather a wide piece of fabric to a narrower circumference....
s, making it narrower again, but retaining the axial stiffness. This pleated disk is also stiffer against nutating forces. A similar feature, a 'sine wave wall', is sometimes encountered in architecture where a straight wall is made stronger against sideways forces by corrugating it.
Key features of the wobbly web wheel are that they are designed as a modification of the disk wheel with additional shaping, rather than a spoked wheel with merged spokes. They can be manufactured by either pressing from sheet steel, or by casting
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
in light alloys. To avoid stress risers, the webs are formed into smooth curves, rather than sharply defined spokes.
When cast, foundries prefer a disk that has a consistent wall thickness, as this makes their shrinkage behaviour simpler to control. The Lotus wheel's peculiar shape was arrived at deliberately, by keeping this consistent wall thickness, for ease of manufacture, and folding it to achieve the varying stiffness distribution required across the radius, to meet the performance needs.
Fedden and the Cosmos
The first use of a wobbly web wheel was by Roy FeddenRoy Fedden
Sir Alfred Hubert Roy Fedden MBE was an engineer who designed most of Bristol Engine Company's successful aircraft engine designs.-Early life:...
for his Cosmos
Cosmos Engineering
Cosmos Engineering was a company that manufactured aero-engines in a factory in Fishponds, Bristol during World War I. Sir Roy Fedden, the company's principal designer, developed the 14-cylinder radial Mercury engine during this period...
car of 1919. This pressed steel wheel used a disk with six spokes on alternating sides and three retaining bolts.
Steam locomotives
Steam locomotiveSteam locomotive
A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...
s use spoked driving wheels of cast iron or cast steel. A few makers have favoured variants of this, seeking a more weight-efficient design by using various forms of hollow or girder spoke, rather than solid oval-section spokes. One of the most successful of these designs was the Bulleid
Oliver Bulleid
Oliver Vaughan Snell Bulleid was a British railway and mechanical engineer best known as the Chief Mechanical Engineer of the Southern Railway between 1937 and the 1948 nationalisation, developing many well-known locomotives.- Early life and Great Northern Railway :He was born in Invercargill,...
Firth Brown or BFB wheel, often incorrectly confused with the Boxpok
Boxpok
A Boxpok is a steam locomotive wheel that gains its strength through being made of a number of box sections rather than having traditional solid spokes . Being hollow, they allow better counterbalancing than conventional drivers, which is important for fast locomotives...
wheel. This had some features of the wobbly web, being developed from a flat disk wheel with short, wide "spokes" formed in it by displacing teardrop-shaped sections of the disk into another plane. Except for a few small lightening holes, this disk wheel is consistently one wall thickness thick, all around the disk.
Like the Lotus wheel, the BFB wheel also displays wide shallow pleats at its outside diameter, with narrower steeper pleats towards the centre (see image).
Although superficially visually similar to the BFB wheel, the true Boxpok design is, as indicated by its name, derived from "box spoke". This is a spoked wheel, with square box-section hollow spokes. The wheel disk in section is either two skin thicknesses at the spokes, or zero (i.e. open space) between them.
Aircraft
Aircraft with cast light alloy wheels appeared in the 1930s. A common form in British military practice used a single-thickness disk, displaced sideways in sharp-edged segments and joined by radial webs. Such wheels were fitted to, amongst others, the SpitfireSupermarine Spitfire
The Supermarine Spitfire is a British single-seat fighter aircraft that was used by the Royal Air Force and many other Allied countries throughout the Second World War. The Spitfire continued to be used as a front line fighter and in secondary roles into the 1950s...
. This basic design served with little change into the 1960s and the jet age
Jet age
The Jet Age is a period of history defined by the social change brought about by the advent of large aircraft powered by turbine engines. These aircraft are able to fly much higher, faster, and farther than older piston-powered propliners, making transcontinental and inter-continental travel...
.
The first distinctly wobbled web appeared on the Convair CV-240 of 1948. This used a wheel cast with nine narrow radial spokes formed from a curved disk.
Lotus racing cars
The best-known example of the wobbly-web wheel was that used by LotusLotus Cars
Lotus Cars is a British manufacturer of sports and racing cars based at the former site of RAF Hethel, a World War II airfield in Norfolk. The company designs and builds race and production automobiles of light weight and fine handling characteristics...
for their racing cars of the late 1950s and early 1960s. These wheels first appeared on the Formula 2 Lotus Twelve of 1957. A similar wheel was used by Vanwall
Vanwall
Vanwall was a Formula One motor racing team that competed in the 1950s. Founded by Tony Vandervell, the Vanwall name was derived by combining the name of the team owner with that of his Thinwall bearings produced at the Vandervell Products factory at Acton, London...
from 1958.
The wheel's design was, in typical Lotus fashion, intended to achieve the lightest possible weight. This is particularly important for wheels, as they are unsprung weight
Unsprung weight
In a ground vehicle with a suspension, the unsprung weight is the mass of the suspension, wheels or tracks , and other components directly connected to them, rather than supported by the suspension...
and the cars intended to carry them were extremely lightweight. Their designer was Lotus' Gilbert 'Mac' McIntosh although, again in typically Lotus fashion, they are often credited to Colin Chapman
Colin Chapman
Anthony Colin Bruce Chapman CBE was an influential British designer, inventor, and builder in the automotive industry, and founder of Lotus Cars....
.
Unlike earlier 'waved' wheels, the Lotus design and its distinctive 'wobbles' was a deliberate feature, even down to the way that the wobbles are deeply indented near the hub and soften outwards to the rim. For ease of manufacture by casting, the wheels were designed with a constant wall thickness. Their stiffness (force/area) was required to be highest aroudn the hub, so here the wheels were deeply and steeply folded. Towards the rim, distribution of this same force over a the greater circumference and metal cross-section thus required less folding and their profile became a gentle wave.
As for many other Lotus components, the wheels were cast from Elektron
Elektron (alloy)
Elektron was a magnesium alloy developed in Germany during the First World War between 1914-18 as a substitute for aluminium alloy. Elektron is unusually light and has a specific gravity of about 1.8 compared with the 2.8 of aluminium alloy. Elektron was used to make incendiary bombs: the B-1E...
magnesium-aluminium alloy. They were cast by Stone Foundrieshttp://www.stone-foundries-limited.com of Charlton
Charlton, London
Charlton is a district of south London, England, and part of the London Borough of Greenwich. It is located east-southeast of Charing Cross. Charlton next Woolwich was an ancient parish in the county of Kent, which became part of the metropolitan area of London in 1855. It is home to Charlton...
. Cooper
Cooper Car Company
The Cooper Car Company was founded in 1946 by Charles Cooper and his son John Cooper. Together with John's boyhood friend, Eric Brandon, they began by building racing cars in Charles' small garage in Surbiton, Surrey, England in 1946...
were already using magnesium wheels and apart from their technical advantages, Charles Cooper had found it highly profitable to sell drivers the many spare wheels required for racing, rather than having an external supplier take the business, something that Chapman was keen to emulate. McIntosh and Chapman also obtained foundry scrap, failed wheels from Coopers, and studied these failures to understand the failure modes of a magnesium racing wheel.
Lotus' team racing colours at this time were green and yellow, often small patches of each with the bodywork substantially of bare polished aluminium sheet. With the advent of the wobbly web wheel, rather than the previous wire wheels, the wheels were painted yellow and the car bodies green. This glossy bright yellow colour could be applied easily over the greenish-yellow zinc chromate
Zinc chromate
Zinc chromate, ZnCrO4, is a chemical compound containing the chromate anion, appearing as odorless yellow solid powder. It is used industrially in chromate conversion coatings, having been developed by Ford Motor Company in 1920s...
primer used on the wheels to prevent corrosion.
4 stud wheel controversy at Le Mans
Lotus' main design principle at this time was Chapman's famous maxim, 'Simplicate and add more lightness'.A quotation that is widely attributed to Chapman, although it actually originates with Gordon Hooton, a designer for the aircraft maker William StoutWilliam Bushnell Stout
William Bushnell Stout was an inventor, designer whose work in automotive and aviation fields was notable. Stout designed an aircraft that eventually became the Ford Trimotor and was an executive at the Ford Motor Company.-Early years:William Bushnell Stout was born March 16, 1880 in Quincy,...
, whose Stout Scarab
Stout Scarab
The Stout Scarab is a unique 1930s U.S automobile produced in small numbers by Stout Engineering Laboratories and later by Stout Motor Car Company of Detroit, Michigan...
would also inspire the Chapman strut
Chapman strut
The Chapman strut is a design of independent rear suspension used for light cars, particularly sports and racing cars. It takes its name from, and is best known for its use by, Colin Chapman of Lotus....
. The Formula Junior
Formula Junior
Formula Junior is an open wheel formula racing class first adopted in October 1958 by the CSI . The class was intended to provide an entry level class where you could use inexpensive mechanical components from ordinary automobiles...
Lotus 20
Lotus 20
Lotus 20 was a Formula Junior car built by Lotus for the 1962 season as a successor to the Lotus 18.The chassis was a spaceframe, clothed in fibreglass bodywork. It had front double wishbone suspension, but the rear had a lower wishbone with the driveshaft being fixed length and therefore used as...
and Lotus 22
Lotus 22
The Lotus 22 was a racing car built by Lotus cars in 1962, and a total of 77 cars were built. It was developed from the 1962 Lotus 20, with the major differences that it had disk brakes all round, had a top link to the rear suspension, and had a dry sump engine that was canted over to lower the...
extended this to their front wheels, which used a 4-stud
Wheel stud
Wheel studs are the threaded fasteners that hold on the wheels of many automobiles. They are semi-permanently mounted directly to the vehicle hub, usually through the brake drum or brake disk. Lug nuts are fastened over to the wheel stud to secure the wheel...
fastening, compared to the previous 6-stud that was still used on their rear, driven, wheels.
At the 1963 Le Mans
24 Hours of Le Mans
The 24 Hours of Le Mans is the world's oldest sports car race in endurance racing, held annually since near the town of Le Mans, France. Commonly known as the Grand Prix of Endurance and Efficiency, race teams have to balance speed against the cars' ability to run for 24 hours without sustaining...
Lotus entered the new, and somewhat unfinished, Lotus 23
Lotus 23
The Lotus 23 was designed by Colin Chapman as a small-displacement sports racing car. Nominally a two-seater , it was a purpose-built for racing with a driver alone. The 23 used a wider version of the Lotus 20 space frame, with the same suspension, clothed in a fibreglass body...
, a widened version of the Lotus 22 two-seater. It was disqualified from competition before the race and did not take part. This was on the basis of its wheels, although not specifically due to the wobbly-web design. The car, as designed, used Lotus' typical 6-stud wheel at the rear but a 4-stud mounting at the front. The wheel rims were also wider at the rear, 6" vs. 5", with wider tyres of 5.50×13 rather than 4.50×13. www.examiner.com/auto-review-in-national/driven-1962-lotus-23-choice-of-champions As the rules for Le Man were still framed as a "sports car" endurance race, they required the carrying of a spare wheel. The 23 had such a spare, but obviously it could not be fitted to both ends of the car. The scrutineer
Scrutineer
In general, a scrutineer is a person who observes any process which requires rigorous oversight, either to prevent the occurrence of corruption or genuine mistakes. It is most commonly known as part of voting in an election, where the scrutineer observes the counting of ballot papers, in order to...
s rejected this and barred the car from competition. Matching 4-stud rear hubs were flown hurriedly from England, avoiding the incompatibility problem, but the scrutineers now objected that if 6 studs had been required before, 4 must be inadequately strong and still refused to allow the cars to compete. After this, Chapman
Colin Chapman
Anthony Colin Bruce Chapman CBE was an influential British designer, inventor, and builder in the automotive industry, and founder of Lotus Cars....
replied "We shall never again race at Le Mans.", a promise that Lotus kept until 1997, long after Chapman's death in 1982.
The following year's Can Am sports car, the Lotus 30
Lotus 30
The Lotus 30 was a racing automobile, Colin Chapman's first and only attempt at a Group Seven / Can Am racing machine, and was first built in 1964, designed by Colin Chapman and Martin Wade. It was most notable for its curvaceous fibreglass body work and "pickle fork" backbone chassis design first...
, switched from wheel studs to centre-lock wheels. This was mostly due to the far greater torque of its large V8 engine, but it also avoided this situation re-occurring, as the 30 also carried a single spare wheel.
Spoked wheels
A drawback to the use of a disk wheel, particularly for front wheels, is the lack of airflow through the wheels, which is important for cooling the brake disks. The rear wheels of single-seat racing cars are driven by driveshafts from the transaxle and the brakes are usually mounted inboard anyway, away from the wheels. Later Lotus designs, from the 26 onwards, used spoked wheels anyway, although this was more about the shrinking diameter of racing tyres, especially fronts, rather than brake cooling. With an open-wheel racing car, any shrouding from the wheels was never a serious limitation anyway.Alloy problems
As for many articles made from ElektronElektron (alloy)
Elektron was a magnesium alloy developed in Germany during the First World War between 1914-18 as a substitute for aluminium alloy. Elektron is unusually light and has a specific gravity of about 1.8 compared with the 2.8 of aluminium alloy. Elektron was used to make incendiary bombs: the B-1E...
alloy, corrosion of the magnesium was a problem for long-term service. Even though Lotus only used these wheels on its racing cars, not its road cars, they had a limited service lifetime. Lotus cars of the 1960s are still popular for historic racing, but these wheels are now no longer acceptable for competition scrutineering, no matter what their apparent condition. As the wheels are such a distinctive part of the car's appearance though, there are modern reproductions available.