Rims: What You Need To Know
12/08/2016




Singaporeans love toying with their cars; there’s just no question there. Whether it’s with stickers or spoilers, chrome bits or body kits, the abundance of aftermarket options make it a temptation that’s hard to resist; ESPECIALLY for first time car owners.

And usually, the rims are the first to go. Whether it was right out of the factory alongside the new car or inherited from the previous owner in a used car, sports rims are always the first thing car owners would choose to meddle with.

But before nose diving into this relatively expensive accessorising game, we believe there are a few important aspects of a rim that most consumers aren’t aware of, to take note.

 

Pitch Circle Diameter

It’s more commonly known as PCD in street, workshop or petrol head lingo. What is this you wonder? So we all know a car’s wheels are held together by bolts that’s locked in with nuts. To make it sound simpler, some rims require you to unlock FOUR nuts, some FIVE and in rare cases, even SIX.

Now, often time when buying a new set of rims, you’d come across dimensions like 4x100, 4x114.3, or 5x120 and so on. First off, take 4X100 for example, possibly the most conventional size found in most cars, the first number in this case, four, represents the number of “holes” the rims have and this should be matched with the number of bolts on your car’s wheel hub – some cars have four, some have five. Simple right?

 

Credit:dnamotoring.com

And this is the slightly trickier bit, the “100” in 4x100 represents the distance from the centre of one hole in the rim to the centre of another hole that’s directly opposite of it as you can see in the illustration above. If the PCD measurements on the rims are different from what is prescribed for your car, they simply won’t fit.

 

Offset

Typically, there are Three Types of Offset – Zero Offset, Positive Offset and Negative Offset. Offset is expressed with ET followed by a number, for e.g. ET38. ET is derived from the German word “Einpresstiefe” which means “insertion depth”. The number on the other hand, determines the distance in millimetres (mm) between the centre line and the mounting surface.

With the rim in upright position, the offset is determined from the middle of the rim. At Zero Offset, the hub mounting surface (which is the surface on the wheel that is locked in to the wheel hub) is aligned dead centre with the middle of the rims.

 

Credit: lesschwab.com

Positive offset is where the hub mounting surface is placed further out towards the road from the centre line of the rim. This set up is typically found in factory rims. Negative offset is where the hub mounting surface is placed further inside the wheel arch from the centre line of the rim as the illustrations show. These Negative offset rims are more commonly known as Deep Dish rims.

 

Centre Bore


Credit: driveaccord.net

The Centre Bore is the diameter of the hole behind the rims that fits into car’s wheel hub. For most rims, the centre bore fits tightly onto the hub, transferring the load of the car to the hub. These are knowns as hub-centric rims. This is a more common set up where the bolts and nuts of a car do nothing but merely lock the wheels onto the hub.

That being said, there are also lug-centric rims where the bolts and nuts are the ones that withstand the load of the vehicle because the centre bore does not always fit properly onto the hub. However, these are less common and they require the bolts and nuts to be replace in order to fit the rims.

 

Width

Before we forget, you’d also need to put the width of the rim into consideration. Again, with the rims standing upright, the width is measured from the inner circle of the rims to the outer circle. Usually, they’d appear as 5J x 15-inch or 7J x 16-inch where the 5 or 7 would indicate the width of the rims in inches and the 15 or 16-inch would indicate the diameter of the rims.

 

                                                                                                                                                                                                                                                       

Now that you’re better off with some basic knowledge, we recommend to first find out the PCD, centre bore and other aspects of your original rim set up first and compare with what’s available in the market to know what fits your vehicle and what doesn’t.

Stay tuned for our next article where we discuss the benefits, the disadvantages and the things you should know before changing or upsizing your rims.

 

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