Your Car 101 (Series) - BEWARE of the Impact Gun...when having others put wheels on.

More and more these days, people are beginning to do it correctly.  However, there are still some shops that continue to use an impact gun without reservations.  Let me explain.

Be Cautious.  Ask Questions.

Impact guns have a lot of power behind them.  Enough power to break wheel studs.

All too often have I observed tire shops who put the wheel on the car and just start synching the lug nuts down on the wheels.  Although, most still do follow the "star" pattern, there are still the possibilities of cross threading or tightening the lug nuts waaay too tight.  (Each wheel, whether a 4 lug, 5 lug, 6 lug, etc... has a specific pattern that optimizes the changes of centering a wheel correctly.  Cross threading is where a nut is put onto a bolt slightly sideways thus flattening out the threads...rendering the wheel stud useless.) 

Another problem is just plain over tightening.  Have you ever or seen someone struggle with taking lug nuts off with their spare tire kit?  Over-tightening can make it almost impossible to remove a tire without using an impact gun again. 

Today's Tech

These days, a lot more dealerships and tire shops are becoming more conscious of the torque (the amount of force applied to tighten) being applied.  The simple fact is that in the past, you did risk the change of breaking the wheel studs.  But today, manufacturers are cutting costs and making products right at the limits.  So over tightening has a higher chance of breaking than before. 

There are two different types of tools they can use.  First is a torque wrench.  Basically, lug nuts should be put on by hand initially (prevents cross threading), then with an impact on LOW torque, and in the correct pattern.  Once on the ground, a torque wrench can be set to the factory setting so that lug nuts do not get over tighten.  A torque wrench clicks and stops, telling the technician that this is as tight as the lug nuts need to go on.  A torque wrench should always be used when the vehicle is on the ground.

Second is to use what's called a torque stick.  Torque sticks are basically extensions that are manufactured to twist at a predetermined torque.  The technicians has to pay attention to the stick and the lug nut to make sure it's not accidentally overtightened.

They both work.  A tire shop should already have a reference guide to the torque settings of each vehicle and should always torque vehicles rather than just "throwing" wheels on with an impact gun.  Good luck!


- Bryan Lin | CEO, The Motorsports Authority, Inc. | www.MSAStore.com