Wheel and Tyre Fitment: Mounting

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Mounting

09.09

00:00	The final thing we'll discuss in this section of the course is how wheels actually mount to vehicles.
00:05	This is an area you'll no doubt already be familiar with, but there are a few special considerations and details here that aren't commonly known.
00:13	In almost all OEM vehicles, wheel lugs are used to secure the wheel to the hub.
00:19	In most cases, wheel or lug studs will be pressed into the holes in the hub of the vehicle and the wheel will be secured using lug nuts.
00:27	Alternatively, and more commonly used on European vehicles like VWs, Audis and BMWs, lug bolts will hold the wheels in place via threaded holes in the hub.
00:38	Either way, the wheel will have a number of holes around the centre bore.
00:43	In most performance cars, there's usually four or five holes or in larger SUVs and trucks it could be six or more.
00:51	These holes are equally spaced on a circle concentric with the centre bore.
00:56	The size of, which is called the PCD, standing for pitch circle diameter.
01:03	We'll cover this in more detail in its own module, but naturally the PCD of a wheel needs to match that of the vehicle for it to fit.
01:10	It can be argued that more studs are better for load capacity, but it might not be necessary and this also comes with a weight penalty.
01:17	It usually comes down to choosing the right wheels for our PCD while considering all the other factors we'll discuss of course.
01:26	But in saying that, certain PCDs are limiting when it comes to wheel selection so it is possible to change the hub to a different PCD, allowing us to fit different wheels or alternatively we could fit adapters that have two sets of holes.
01:42	One in the existing PCD to be bolted to the hub and the other fitted with studs into the new PCD.
01:48	This is something we'll be looking at in more detail in an upcoming module so we'll leave it there for now.
01:54	The other thing to consider is the size of the individual holes in the wheel compared to the studs or bolts.
02:02	The most common wheel stud and bolt sizes are 10, 12 and 14 millimetres or 7/16ths of an inch, half an inch or 9/16ths of an inch.
02:12	But the holes in the wheel will actually be larger than this by one or two millimetres in most cases, offering a relatively loose fit , which makes it easy to install the wheel onto them.
02:24	There's been a lot of different kinds of wheel studs, nuts and bolts that have been used over the years, but what's important to us is how they interface with the wheel, whether it's between a wheel nut or bolt, the same conditions apply.
02:38	The lug holes in the wheel will have a seat that matches the surface of the lug nut or bolt.
02:44	The most common in modern performance cars is the straight conical taper, sometimes called an acorn cone seat.
02:50	These will usually have a 60 degree taper, though sometimes we will come across a 45 degree taper.
02:57	This taper centres the lug hole in the wheel to that of the hub while also increasing the contact surface area between the hardware and the wheel as this will prevent the hardware from loosening.
03:10	Another common type is the ball or rounded seat where the surface is curved to increase the contact area further.
03:17	Older styles like the flat seat are less effective in both of these functions and mag seat or shank styles use the same theory, but with an extended section to lengthen the thread engagement.
03:30	The same idea applies to a conical ET lug nut where ET stands for extended thread.
03:36	These different types are mostly not interchangeable and it's important that we have the correct hardware for our wheels.
03:43	We briefly discussed how the centre bore can be used to locate the wheel on the hub using a spigot in the first module.
03:51	The lugs still hold the wheel firmly onto the hub, but it's the centre bore that locates the wheel.
03:57	Aftermarket wheels will often be made with a relatively large centre bore that will fit over as many vehicle hubs as possible and if it's not a perfect fit like the factory wheel then there will be a gap.
04:09	In this case the wheel will be centred on the lugs aka lug centric.
04:14	This is not ideal as it will stress the lugs and the face of the wheel.
04:19	Also any run out or imbalance in the wheel will disturb the contact patch, leading to a loss of grip and nasty vibrations.
04:27	Some wheels are designed to be lug centric and the hardware for these must be torqued with the vehicle on a lift or jack stands so the wheels are in the air and the lugs can centre the wheel without being forced off centre by the vehicle weight.
04:44	For demanding applications such as motorsport we should always have wheels that are hub centric and sometimes this means using an aluminium or plastic ring to take up the space between the wheel and the spigot of the hub.
04:57	For a street car the plastic ring is usually a better choice as the contact of dissimilar metals between the aluminium wheel and ring and the steel hub can accelerate corrosion.
05:08	Basically, this means if we leave the wheels on for long periods, they can get stuck and can be quite difficult to remove.
05:16	However, in motorsport applications, the severe heat of the wheels and hubs from the brakes and other functions can damage the plastic rings, so aluminium rings should be used in this case, just be sure to apply some anti-seize to the surfaces before installation.
05:32	The alternative to all of this is what's referred to as a centre lock , which is used in some high-end factory vehicles and certain forms of motorsport.
05:43	A modern motorsport style centre lock uses a hollow tapered shaft to centre the wheel on the hub through the centre ball, similar to how the centre ball works on a lug style wheel, but with a shaft that's much larger and stronger.
05:58	A large single nut is used to lock the wheel in place which will also be tapered just like our lug nuts and naturally this must match the taper of the wheel.
06:09	Older examples are commonly referred to as knock-offs due to the use of a hammer to strike the wings of the centre nut for removal.
06:16	The only place you're likely to still find these in use is on vintage race cars.
06:21	There's been various designs over the years from simple hexagonal nuts to what we now see in top tier racing like Formula One with a spline design to ensure that the socket of the tool used to do the nut will engage faster.
06:34	In any case a much higher torque is used to secure this nut at around 600 newton meters or more compared to around 120 newton meters for regular lugs.
06:46	The wheel is prevented from spinning relative to the hub and torque is transmitted through a number of pins that fit into pockets at the back of the wheel.
06:55	In some cases a locking pin or retention system is also used to prevent the wheel from coming loose.
07:01	The size and shape of the splines along with the threads of the centre lock nut are designed differently depending on the brand and system used in the interest of speed and reliability.
07:12	The key advantage of a centre lock system aside from the increased strength and security is the ability to change a wheel quickly, which is why we see them used in motorsport like Formula One or endurance racing.
07:25	For most of us though, the greater cost of these parts and specialist equipment, as well as the wheel itself is often not justified for certain types of vehicles that generally speaking won't need their wheels changed in a rush.
07:39	It should also be mentioned that in some types of racing, centre locks aren't allowed due to the regulations and in the interest of a level playing field and keeping the cost down.
07:50	OEMs like Porsche for example have patented centre lock systems that they offer on road going vehicles like the 911 GT3.
07:57	Further to this, for vehicles that weren't originally specced with centre locks, rather than undertaking a complete conversion to a centre lock hub, are sometimes fitted with adapters instead.
08:09	These are machined parts that bolt onto the lugs of the existing hub using the lug nuts and additional pins to transmit the torque to the wheel.
08:20	The rest of the adapter is designed just like a regular centre lock hub.
08:23	With that covered, let's recap the important points before moving on.
08:28	Traditionally, wheels are mounted to the hub via lug studs and nuts or bolts.
08:33	The design of the lug nuts and bolts, as well as the PCD needs to match that of the holes in the wheel.
08:40	Ideally, the wheel will be hub centric to help with strength and alignment and using aftermarket wheels, this usually requires the use of a plastic or aluminium ring.
08:52	Alternatively, centre locks are used where a large single nut will secure the wheel, with the key benefit naturally being around the ability to change the wheel quickly, but also providing a more secure and strong mounting solution.