Standard Wheel Sizes
Wheels are sized by two dimensions :-
The diameter of the wheel and the width of the wheel
Both are typically given in inches
The stock wheel is a 14" diameter by 6" width (6J14).
Standard tyres are 195/60/14.
The stock wheel is a 15" diameter by 7" width (7J15).
Standard tyres are 205/60/15.
The stock wheel is a 16" diameter by 7.5" width (7.5J16).
Standard tyres are 215/50/16.
What is 'PCD'
PCD (Pitch Circle Diameter) is the diameter of a circle that goes through the miffle of the wheelnuts
It is a standard measurement for aftermarket wheels, along with the number of bolts used to attach the wheel The Celica uses a 5 bolt wheel pattern. The PCD is 5/100 for ST165, ST185, and ST205.
What is 'Offset'
The Offset of a wheel measures the distance between the wheel centreline and the wheel mounting face and is measured in millimetres. It is extremely important that wheels of the correct offset are used in order to maintain the correct track of the vehicles. Offset can be Positive or Negative and is best illustrated in these two diagrams.
What is the offset required when ordering aftermarket wheels?
The offset is wheel and model specific. It is always worth checking that the wheels will fit, especially on the ST205 which has large brake callipers which may suffer with spoke interference on high offset wheels In general an offset of 35mm should work for most wheel styles.
What is Centre bore?
Car manufacturers use a central location collar on the stub axle hub in order to accurately locate the wheel. The wheel collar diameter varies, depending on the make of vehicle. The GT-Four uses a 54.1mm collar. Most replacement allow wheel manufacturers use an adapter (known as a spigot ring) to vary the diameter of the locating hole.
The wheel itself has a large diameter hole which is sleeved down to the appropriate size with the spigot ring
In this way, a particular wheel can be used on a variety of vehicles by changing the spigot ring The adapter/spigot ring arrangement is shown below
Should I use spacers with my wheels
It is a personal choice. Many feel that the 185 (particularly the wide body editions) look better with the wheels pushed out towards the bodywork. It is not uncommon to see 25mm spacers used in this case
The 205 generally will not require such extremes but again depending on wheel choice and offset some spacers may be required One thing to note on the ST205. With the standard wheel (ET45) brake caliper clearance on the backside of the wheel is a serious issue. There is perhaps 2mm of clearance. The wheels also look well pushed in to the centre of the car.
This is one of the factors governing minimum offset on the ST205 setup
An offset of 30 on a 7.5" rim will put the wheel almost exactly flush with the top of the wheel arch
The use of spacers will put additional strain on wheel bearings. While modern bearings are much better at dealing with this than the older versions you should still be aware that you are potentially reducing their life span