32 August 2015

FEATURETECHNICAL

PROPER WHEELINSTALLATION

We have all seen a technician in a shopor a tire technician in a tire service facilityuse a pneumatic impact wrench (gun) totighten every lug nut until they hear a clickingpoof poof sound of the gun as it tightens allthe way. However, not too many people knowor even understand that all that is happeningis the over-tightening of the lug nut. This isNOT something you should ever do. Tight isgood, but over-tight is NOT. Over-tighteningthe lug will stretch the stud and cause failurearound the rotor hub. Every OEM has a lugnut torque specification for each vehicle theyproduce. The proper way to tighten the wheellugs is to use a torque wrench to torqueevery lug nut to its recommended torquespecification when the car is on the floor.Some cars even require a more complex pro-cedure, which is hand tight first, then torqueto a specific lower torque while the car is upin the air, then torque to its final torque speci-fication when the car is on the floor. Afterthat, most OEMs require a one-mile driveand re-torque of the lug nuts.

There are a few different types of torquewrenches in the market. The most commontype is the “Click Type” torque wrench. Usingthis wrench is a simple process; just turn thetorque wrench handle until it reaches thetorque mark you are looking for, then starttightening the nuts slowly. As soon as the settorque is reached, you will feel a click aroundthe head of the torque wrench. Generally, itis recommended that you turn the wrenchone more time to ensure the nut is set properly. Do not turn it more, but barely applythe force one more time just to verify therewas a click. There is also the “Dial Type”torque wrench, which has a little meter onthe handle. You can see the torque gettinghigher and higher while you are applyingforce; you stop when you reach the desiredtorque. Some Dial Torque Wrenches comewith an electronic meter on the handle, whichallows you to read the exact torque. You mayalso find a Torque Adapter, which is a little

electronic device that goes in between a reg-ular wrench or a breaker bar and the socket.It will act like a torque meter, and these aremore affordable than the actual torquewrenches (which are very handy for homeuse, but generally not recommended for collision and/or mechanical repairs).

The general rule for steel wheel lug nuttorque is usually around 80ft/lb, and around100ft/lb for an aluminum wheel. But you mustcheck with the OEM for the exact torque forevery particular model before you start work-ing on the vehicle.

As always, we want you to do everythingproperly, so let’s look at the steps totorque the lug nuts. the following stepsare required to tighten the wheel lug nut:

1. Wipe every stud with a rag and airblow the inside of each lug nut toclean them.

2. hand-tighten each lug nut onto thestuds.

3. If you have an impact wrench, youmay use it to barely snug up each lugnut, if you first set the pressure to alower setting when you hear a coupleof clicks.

4. Set the vehicle under its ownweight; the car is on the floor.

5. Set the manufacturer recom-mended torque on the torque wrenchand tighten each nut according to it.

the right order to tighten the lug nuts isnot clockwise or counterclockwise; it isas follows:

1. If it is a four-stud wheel (rare setup to see on late-model vehicles),you should tighten them in a cross

order, which means first tighten thetop one, second the bottom one,third the left one, last the right oneand so forth.

2. If it is a five-stud wheel, then youshould follow an order of drawing aStAR.

3. If it is a six-lug wheel, then the firstto tighten would be the top one (12o’clock position), next the 6 o’clockposition, 1 o’clock, 7 o’clock, 5o’clock and finally the 11 o’clock.

4. If it is an eight-lug wheel, then thefirst to tighten would be the top one(12 o’clock position), next the 6o’clock position, 9 o’clock, 3 o’clock,7 o’clock, 1 o’clock, 5 o’clock and fi-nally the 11 o’clock.

We, along with Hunter and tirerack.com, recommend that you do not use impactguns or torque sticks when installing wheels.

Impact guns deliver torque as torsionalimpacts, made by internal hammers. Deliver-ing torque as torsional impacts can damagehardware, result in rotor warpage caused byover tightening and damage the wheel finish.Some vehicles, such as Porsche and Mer-cedes-Benz, require the use of special sock-ets to tighten the hardware without damagingtheir anodized coating.

Torque sticks are designed to limit ap-plied torque by absorbing input torquethrough torsion deflection, or twist. Theycome in multiple colors to represent differenttorque values. However, many variables canaffect the torsional deflection (absorbedtorque) and the applied (delivered) torque.These can lead to inaccurately appliedtorque or variations in applied torque.

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Some of the variables that can cause inaccurate torque are as follows:

Type of impact used (air, electric, cordless)(Some identical ones are stronger than others.)

Power (air pressure, air volume, length ofhose pipe, length of hose, size of the fittings,battery power, battery age, electric cord length,power to the facility)

Impacts per second

Size of internal hammers

Possible use of additional adapters, such asextensions

Socket size, weight, length

Operator grip strength

Weight of the impact

Applied angle during use

Attempting to fully tighten hardware withimpact guns/torque sticks also prevents usinga click-type torque wrench to confirm the speci-fied amount of torque is present. This is thereason a click-type torque wrench should beused, as it can identify when the selectedtorque has been reached. (It cannot diagnoseexcessive torque.)

Once you have the right tools, use the appropriate crisscross sequence (mentionedon the previous page) for the number of the ve-hicle’s wheel-attaching hardware positions untilall have reached their specified torque value.

Once all the original wheels that were removed are tightened, it is now time for a testdrive. Most OEMs say the vehicle should betest driven for one to five miles. Any collision-damaged vehicle requires a safety test drive,but you may also need to test drive the vehicleto relearn computer controlled componentsand navigation position. Another reason to testdrive is to make sure clamping loads havechanged following the metal compression/elongation or thermal stresses. Once the testdrive is complete, go and re-torque the wheelsonce they have cooled off.

When installing new OEM wheels, theyshould be re-torqued after the first 50 to 100

miles of driving. This is due to the fact thatafter the initial installation, the metal compres-sion/elongation or thermal stresses affectingthe wheels are different than those affectingthe original wheels as the new wheels arebreaking in. Additionally, re-torque of thewheels will verify the accuracy of the originalinstallation.

When rechecking torque value, wait forthe wheels to cool to ambient temperature(never torque a hot wheel). Loosen andretighten to value, in sequence using thetorque procedures listed.

Remember that it is your liability, andchecking the torque of the wheels on your cus-tomers’ vehicles can save lives. We cannot tellyou how many cases we have been involved inwhere there was wheel separation. Eighty-fivepercent of the time, the cause was fracturedstuds, generally from overtightening. Too looseor too tight is never good; the tightness mustbe as per the values set by the OEM.

We hope this article has explained theproper way to torque wheels. Please feel freeto contact us if you have any questions. H&D

Larry Montanez III, CDA is co-owner of P&L Consultants with Peter Pratti, Jr. P&L Consultantsworks with collision repair shops on estimating, production and proper repair procedures. P&L conducts repair workshops on MIG & resistance welding, measuring for estimating and advanced estimating skills. P&L also conducts investigations for insurers and repair shops for improper repairs, collision repairability and estimating issues. P&L can bereached by contacting Larry at (718) 891-4018 (office), (917) 860–3588 (cell), (718) 646–2733 (fax) or via email at larrygoju@aol.com. The P&L website iswww.PnLEstimology.com.

Jeff Lange, PE is president of Lange Technical Services, Ltd. of Deer Park, NY (www.LangeTech. net).Jeff is a Licensed New York State Professional Engineer who specializes in investigating vehicle andcomponent failures. Lange Technical Services, Ltd. isan investigative engineering firm performing forensicvehicle examinations and analysis for accident recon-struction, products liability and insurance issues. Jeffcan be reached at (631) 667-6128 or by email atJeff.Lange@LangeTech.net.

33August 2015

Nuts and bolts, tips and tricksfrom our resident industry experts.

By lARRy MoNtANez III, CdA & Jeff lANge, pe

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