The wheel spacers designed for Audi A3 in the market are divided into four types, bolt-on and slip-on with different installation methods, hub-centric and lug-centric with different loading structures. Because Audi A3 is a European car, the wheel fastener used is to wheel/lug bolts to fix the tire, so the spacers used don’t have the pre-installed wheel studs.
First of all, what is the difference between bolt-on and lug-on of different mounting structures? The bolt-on wheel spacer is to fix the spacer on the vehicle’s own mounting pad first, then use one more set of wheel/lug bolts to fix the wheel to the spacer’s bolt pattern. This bolt-on design is mostly found in spacers that are more than 15mm thick, the reason for this design is that users can avoid the trouble of buying extended wheel bolts. If the original wheel bolts of the vehicle are not long enough, it is usually necessary to purchase additional extended wheel bolts to ensure that the wheel bolts can be used in the event of an increase.
Slip-on spacers are generally designed for spacers with a thickness of less than 12mm, because the thickness is relatively thin, there is no need to add another set of wheel bolts to increase the unsprung mass.
Second, what is the difference between hub-centric and lug-centric for the loading structure to distinguish? The hub-centric wheel spacer refers to a ring step structure in the center of the spacer, to form a stable and tight connection structure between the wheel hub and the axle hub of the vehicle, which is what the car manufacturer designed. In other words, the hub-centric wheel spacer does not change the load-bearing structure of the original tires. This is also recognized as the safest design structure of spacers.
The lug-centric wheel spacers do not have the hub-centric center ring step but use a large tolerance center hole to match a wider range of models. The advantage of this is that the range of potential users is greatly increased, and there is no risk of special data being overstocked. The real downside is that this causes the wheel/lug bolts to become the bulk of the load. This is very dangerous. The original design of the wheel/lug bolts is only to fix the wheel and maintain the wheel to rotate around the axle. The strength of wheel bolts is not enough for long-term load-bearing tasks, and in the long run, it will inevitably cause the tire to rotate off-center or even fall off. So, we generally strongly discourage the use of lug-centric spacers.
If you want to use 3mm-12mm spacers to avoid brakes or some bulky parts after modification, we recommend you to use the BONOSS Forged Lightweight Plus wheel spacers for Audi A3. This is an A3 spacer with a slip-on hub-centric design, which simplifies the installation steps and greatly reduces the weight of the wheel spacers themselves, which can keep the vehicle chassis light and flexible.
But on the other hand, if you want to use thicker spacers larger than 15mm to significantly improve the style and handling of your vehicle, then we recommend using the bolt-on hub-centric design of the A3 spacers. Because even if extended wheel bolts are used to hold the thick spacers, the strength of the wheel bolts is still challenging due to the increased length. So using the bolt-on installation method is very convenient and safe.