How to: Choose #Wheels for your Car.

Following on from yesterday’s story about buying my first set of wheels, I have created a guide to help you make sure you get the right wheels for your car.

Below I have constructed a checklist to ensure you don’t end up in a situation like mine.

Taste

Whether you plan to add Ronal Turbos or Ronal Teddy Bears to your vehicle, you will need to consider how to make sure they fit and how to
a) give them that stanced look, or
b) get the largest width for drag racing.
The best option is to buy new wheels from the manufacturer or a re-seller, however you can often find a bargain by searching the classifieds, and facebook groups. Either way, this checklist will help you to get the best for your vehicle.

It is often said that it is the wheels that make the look of a car.
In the image above, the luxury appeal of an old Toyota has been revived simply by adding BBS Mesh wheels that give it a sophisticated look.
Steel wheels are increasing in popularity and are often used to give a vehicle a bad-ass look, like on the Liberty Walk Kenmeri.

If you want to go for the steel wheel look, it can be as easy as removing your hubcaps. Job Done!
If you want a different look, or aftermarket rims, then I suggest you keep reading.

Size/Diameter

The wheel size is often the first consideration made when deciding to buy new wheels.
Standard wheels are usually between 14” and 16” in diameter, however some newer cars offer up to 20” wheels.
Again, wheel size is all down to taste. Tuners usually go for 18” or 19” wheels, while old Toyotas and Datsuns owners usually choose 13” or 14” wheels.
If you don’t know the size of your wheels, you can measure across the lip of the wheel. If your wheels have tyres on them, you can check the numbers on the side - my car is running 235 40ZR18. The last two digits tell the wheel size; mine are 18”.
If you are going larger, then make sure the wheels will not hit any components inside the wheel arch, such as the upper A-arm.
If you are going smaller, make sure that the inside of the barrel can clear the brake calipers.

PCD

Pitch Circle Diameter, or stud pattern, is the distance between the studs. If the wheels you want to buy have a different PCD from your vehicle, don’t buy them.
Common diameters are 100, 110, 112, 114.3 and 120mm. These are measured from the centre of one stud to the centre of the opposite stud.
Next count the number of studs. If there is an even number of studs, measuring is straightforward. If there is an odd number of studs, then you need to draw a circle that runs through the centre of each stud.
The trick to measuring 5-stud wheels is to measure from the centre of one stud to the outside of the opposite stud.

The wheels above fit RWD Toyotas and Nissans. It is a 4-stud wheel, and the PCD is written as:
4x114.3
A 5-stud wheel with the same diameter, like on my car, reads as:
5x114.3

So far we can tell the size as 18” 5x114.3

Width

After we find out the offset of the factory wheels we can find a width that will fit - this can be done either in a Google search, or by measuring it yourself (see next section).
Wider wheels usually look better and have more grip making them better for racing and take-off, however they will force the car to use more petrol.

Width is usually measured in inches, however it is usually rounded to the nearest half-inch. Tyres often have a marking that tells us the width in mm. My tyres are supposed to be 245mm wide (however I got stretched tyres so it runs on 235-40ZR18).
Convert this to inches and it gives us 9.6”. We can round this to 9.5”.
Sometimes width is followed by the letter J, or JJ.

Now we have the size of my wheels as 18x9.5J 5x114.3

Offset

This is an aspect that confuses many people, and as such it means it must be important.. right?
Correct; however it is not crucial.
The offset is how far pushed out your wheels are. Typically, factory wheels are a lot thinner than they need to be and have a lot of clearance on either side.

Offset is measured from the middle of the wheel to the back of the mounting pad (where the wheel bolts into the hub). The easiest way to measure offset is to measure from the mounting pad to the closest lip. Subtract this measurement by half the wheel width.
If the closest lip is the inside, then offset will be negative.
For example, my wheels are 245mm wide (9.5”) and I measured 105mm from the hub to the outside lip of the wheel. Divide the wheel width by 2 and that gives us 122.5mm. Subtract the 105mm I measured, and that leaves us with 17.5mm. Round it to the nearest multiple of 5, and that gives me an offset of +20.
Sometimes offset is followed by the letters ET.

My wheels can be read as:
18x9.5J 5x114.3 +20ET
This is the number I will use when l look for new wheels.

Most wheels have a positive offset. The higher the offset, the further in towards the car they will be. However, too high an offset can mean that you will scrape components of the car, like the suspension.
A low offset means the wheel will be pushed outwards from the body. Negative offsets are used for dished wheels, and the fenders will often be modified to house the pushed-out wheels.

Clearance

This is not an official measurement, however it is just as important as offset. I made the mistake of installing flat-backed wheels onto my R33; they touched the brake caliper and the car would not move.
To ensure your wheels will clear your brake calipers, you need to measure the difference between the highest point of the caliper and the hub. Then you need to find a set of wheels where the back of the spokes is higher than the caliper.
The image above shows my front wheels with only 1mm between the spokes and the Nissan logo.

If the wheels you wish to use don’t have enough clearance, and you want to use them, you can use spacers to push them out. Some wheels allow the use of spacers, like the XD9 above, while others did not consider it. If your wheels fall into the latter category, then your spacer must be wider than the length of your wheels studs (usually 1” long).
If you only need an extra 5mm of clearance then you can use a slip-on spacer.

Fitment

Using the width and offset we can now calculate fitment. If you plan on using spacers, then take them into consideration also.

Now we must measure from the wheel hub to the lip of the wheel arch like in the photo below. Our goal now is to find a set of wheels that will fill this space. If you are looking at 10” wheels, divide that by 2 and subtract the offset (two negatives make a positive). This will tell us how far out they will sit - you want to match this to the distance between wheel hub and wheel arch.

Consider the situation below:
A 245mm (9.5”) wide wheel with a +20 offset will fill 102.5mm outwards from the hub.
A 255mm (10”) wheel with +45 offset will fill 82.5mm outwards from the hub.
In the photo above I measured 110mm from the hub to the wheel arch. In this situation the +20 offset will fit it better, even though it is a thinner wheel.
If you wish to run stretched tyres, then add an inch to the measurement between wheel hub and wheel arch.

18x10 5x114.4 +45 on left.
18x9.5 5x114.3 +20 on right.