Another post in my series 'Myth Busting How stuff Works'. You can also contribute by suggesting topics that you want to get covered or clarified. Send me your suggestions! Thanks.
Wheels spacers have been a hot topic probably since the first one hit the market. A lot of people consider them ‘unsafe’ and belittle everyone that considers running them. The truth is, that wheel spacers are not any different as mounting a wheel with the same effective offset.
As you can see in the Image, a zero offset wheel with a spacer results in the same back spacing as the equivalent negative offset wheel. Your wheel bearing will see the same amount of load, your wheel will see the same amount of load, and the wheel studs or bolts will see the same mount of load.
Wheel spacers are actually stock equipment on front axles of dual-rear-wheel pickup trucks!
A potential issue arises, if you don’t know how to properly torque a bolt. Most common mistake is to tighten wheel spacers to higher torque. The studs (or bolts) will get microscopic stress fractures and then, eventually, snap. This is not the fault of the spacers, but the weekend warrior handling the wrench.
And then there is also one problem that wheel spacer users create themselves. They apply thread lock to the threads for the wheel spacers. This can turn an easy 30 minute brake job into a day long ordeal and increases the parts bill significantly. Again, not the spacers fault and to state this clearly: thread lock should not be used on wheels or spacers.
Here is a quick introduction to what makes bolts hold things in place: The tension in the bolt.
Rotating the nut on the thread stretches the bolt, which creates the clamping force needed to affix 2 pieces together, and also to keep the bolt locked in place.
Please note that torque on the bolt (and nut) does not directly translate to tension in the bolt. Equal amount of torque applied to a rusty thread (high friction) would not result in the same amount of rotation of the nut as compared to a pristine thread (low friction). As a result the tension would be less and the bolt might come loose or parts could move. The best way to control friction in the thread and achieve proper and repeatable bolt tension, is to clean the threads and then apply grease. Torque the greased bolt or nut to the lower end of the recommendation of the manufacturer and you will never have a problem with spacers or wheels or anything else.
For more information please see ASME PCC-1-2019
For now, we will leave it at that. Feel free to contact me if you have any questions.