Wheels
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- Last Updated on Saturday, 17 September 2011 20:36
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Here we are going to look at some of the factors you should take into consideration concerning wheel choice if you should happen to stray from factory items.
Pitch Circle Diameter (PCD)
The wheel P.C.D. can be defined as the diameter of an imaginary circle drawn through the centre of the stud holes on the wheel and/or the vehicle wheel hub. PCD is measured in millimetres and also indicates the number of studs or bolts the wheel will have.
One of the most common car fitments has 4 studs and a PCD of 100mm, hence the fitment 4x100. Land Rovers (except 101 FCs) generally have a five stud PCD.
When new wheels are required, it is essential that they have the correct P.C.D. for the vehicle you are fitting them to. However, just because a wheel from one vehicle has the same PCD and offset as the wheel from another does not mean they are interchangeable - the centre bore of the wheel and hub must also be the same to ensure correct centralisation of the wheel, and the shape of the spokes must ensure clearance of the brake calipers. Many manufacturers use the same wheel fitments as others, but some are unique.
Offset
Wheel offset is the distance between the imaginary centreline of the wheel and the inside face that bolts up against the wheel hub on the car. Fitting wheels that alter the track of your car (the distance between the centre of the left and right wheels, either front or rear) by more than 20mm may void your insurance policy, so check before making this sort of change. Altering the track will also affect your car's handling.
Negative Offset wheels have their mounting face toward the rear of the wheel - powerful rear-wheel drive cars often have wheels with negative offset.
Zero Offset wheels have their mounting face even with the centerline of the wheel.
Positive Offset wheels have their mounting face toward the front face of the wheel. Front wheel drive vehicles usually have positive offset wheels.
Spigot or Centre Bore Size
The center bore of a wheel is the size of the hole at the back of the wheel which the hub's spigot fits into. To help the wheels to seat properly this hole needs to be an exact match to the size of the spigot. The spigot is the bit in the centre of the hub that you rest the inside centre of the wheel on whilst aligning the studs and screwing back the wheel nuts. On generic after market wheels, the spigot hole inside the wheels (centre bore) is a lot bigger than the spigot on the car. So what you need to do in this case is fit spigot locating rings. Spigot rings are just rings of aluminium or hard plastic, that fit over the spigot on your car and then have a proper snug fit with the spigot hole on the wheel. If you don't have the spigot taking all the weight of the car, chances are you'll break one or more studs when you drive the car hard or have to brake hard. Usually the wheel nuts are simply there to hold the wheel on, NOT support the weight of the car. Also, as there is nothing to centre the wheel, you'll notice the wheels go in and out of balance because as you drive around, the wheels will move around on the hub.
Wheel Size
Examples of typical wheel size designations are 5.5J16, 7J17 or 6.5J15. Other combinations of numbers and letters are available. In these cases the first number (before the letter) refers to to the width of the rim where the tyre fits measured in inches between the rim flanges. The second number (after the letter) refers to the diameter of the wheel and is again measured in inches. The letter J specifies the height of the rim edges above the bead seating area. J is the normal designation for many modern car wheels, but other letters are possible as shown below.
| Height of Wheel Rim Flanges | ||
|---|---|---|
| Letter | Inches | mm |
| J | 0.68 | 17.3 |
| JK | 0.71 | 18.0 |
| K | 0.77 | 19.6 |
| L | 0.85 | 21.6 |
It is quite normal to alter the size of wheel when fitting alloys. Most cars are fitted with 14" to 16" steel wheels. When changing to alloys - you can replace with the same size of wheel, and keep the same size tyre, or move up to larger diameter wheels.
Upsizing the wheels means you would need smaller profile tyres to keep the overall tyre diameter (rolling radius) the same, which helps keep your odometer and speedo accurate. The larger the wheel and the smaller the tyre profile the more impact the wheel chosen will have on the overall look of the car. Upsizing also has an effect on the handling of your car. Each step will decrease the proportion of flexible tire sidewall to rigid wheel. On-road, this could improve response, help keep the tyre tread square to the road and would improve your car's 'feedback'. However - tyre inches are often lighter than wheel inches. upsizing can make your overall wheel/tyre package heavier. Reducing the profile of your tires will also decrease your car's damping deflection under compression, so the ride quality will get worse.
Changing your wheels
Before you do anything, make sure that you have the right sort of fixings for your new wheels - Bolts and studs have various diameters, threads and settings, your wheel supplier should be able to advise on this. Also double check to see that you get any spigot rings you need to match the wheel to the hub.
Next you need to jack your car up; do this in a secure way, and be sure to use axle stands, chock wheels still in contact with the ground and apply the parking brake. Offer a wheel up to the car and check that the bolt holes line up (correct PCD), that the wheel locates on the hub properly (correct centre bore) and that there is wheel arch, suspension strut and brake caliper clearance. If you have upgraded your brakes be sure to seek advice and measure everything thoroughly before you order.
The wheel bolts or nuts must be tightened to the manufacturer's precise torque recommendations. Be sure to re-torque after 50 miles or so as they will compress slightly. When fitting the bolts, tighten them increasingly till they're 3/4 tight then lower the car and complete the process.
Fitted new Alloys? Take care of them!
There are lots of specialist wheel cleaners on the market, all designed to help make the job of cleaning your new alloy rims that little bit easier, But here's some tips to make those alloys last.
Before you fit your wheels, give them several coats of good quality car polish back and front. This will help prevent the road salt, brake dust and dirt keying to the surface on first use. Be sure to treat the surface of your alloys as well, if not better, than you would your paintwork. Remember they're going to be subject to the harshest conditions of just about any part of the car!
Alloys prefer frequent washing with mildly soapy warm water; and remember to hose all the loose abrasive grit off first. This is the best way to keep these wheels clean. Do not use abrasive cleansers, electric buffers or wire wool pads on your wheels. Where it is possible let your wheels cool before cleaning them and keep away from car-wash wheel-cleaners at all times.
Land Rover PCDs, Offsets and centre bores
| Model | Year | PCD | Offset | Centre Bore |
|---|---|---|---|---|
| Defender 90 | 1992 on | 5×165 | 33 | |
| Defender 110 | 1992 on | 5×165 | 33 | |
| Discovery 1 | 90-98 | 5×165 | 33 | 70.1 |
| Discovery 2 | 1998 on | 5×120 | 55 | 70.1 |
| Freelander 1 | 97-05 | 5×114.3 | 35 to 38 | 64.1 |
| Freelander 2 | 2006 on | 5×108 | 35 to 50 | 63.4 |
| Range Rover 1 | 86-95 | 5×165 | 33 | |
| Range Rover 2 | 94-02 | 5×120 | 55 | 70.1 |
| Range Rover 3 | 2002 on | 5×120 | 55 | 72.6 |
| Range Rover Sport | 2005 on | 5×120 | 55 | 72.6 |
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