More and more sports racers and formula cars are showing up equipped with single wheel nut assemblies that hold the wheels on. Not only are these neat to look at, they make wheel changing a lot easier than dealing with up to 20 or more individual lug nuts or bolts. However, there are a few basics that should be considered when tightening, and loosening, these wheel nuts.
A little history: Ralt Atlantics and Super Vees have long had a problem with stub axles breaking. When this happens the wheel assembly leaves the chassis and pursues a path of its own. Obviously the results may be disastrous. It was not that the axles were poorly made, for they were not. It was more to do with misuse and abuse. While an axle should be crack checked any time there is a wheel banging incident or the axle takes a sharp blow (as in falling off the chassis stand), there is another area of abuse in which the driver/mechanic actually thinks he is doing his job conscientiously.
First of all, know the proper torque specifications for your car and type of assembly. Use a good torque wrench that has been calibrated within recent history. Use the proper socket and range/size of torque wrench. If you insist on using the torque wrench to remove the assemblies make sure it is designed to be used in both directions. Most torque wrenches are not designed for removal.
Scenario: conscientious driver/mechanic diligently torques the wheels and installs the safety pins before going out for the first session. After the session he brings the car in to the pits, leaps out, takes off his gear, and grabs the torque wrench. His intention is to make sure the wheels have not loosened during the session. How? By checking to see if they are still tight. If he can tighten them at all using the installation torque specifications then they must have backed off. Right? Wrong!
What should he do? One of two things. Leave the wheel assemblies alone or loosen them. Why? The entire wheel/axle/nut assembly is designed to be tightened to a specific torque under normal, non-racing, temperatures. When the appropriate torque is applied under average temperatures (which include temperatures far colder and hotter than we will ever see) the units get appropriately snug with each other. As Emeril says, they are “happy, happy.” Part of the design considers what happens to these individual parts, which have differing metallurgical properties, when they reach racing temperatures. Normally the nut and axle are made of steel, the wheel is aluminum or magnesium, and the wheel nut conical spacer/washer is aluminum. Obviously they will expand and contract with temperatures at different rates and to differing degrees.
So, we come in off the track with a car that has hot wheel assemblies. In fact, they are probably getting hotter as there is no airflow to cool them. So they sit there and heat soak for a while. Imagine what happens to them if they are re-torqued. In the case of the failing Ralt axles, it was surmised this was a common practice which led to the stretching of the axle beyond the design parameter. While the axles were not snapping under this load, they were being weakened and their life was shortened considerably. So, the best thing to do is to allow the individual items to normalize in temperature, either by leaving the wheels alone until they have completely cooled, or by loosening the wheel nuts. If you think there is a possibility of going back onto the circuit within a short period of time simply leave them alone. If you are concerned about your wheels loosening then find someone with a reversing torque wrench, wait for the wheels to normalize, and check the removal torque. It won’t be exactly the same as you used to tighten the nuts but it should be close.
Care should be taken when installing and tightening the nuts. Cleanliness is obviously important. Most of the smaller bore formula/sports racers use a solid stub axle with a large fine thread nut and the torque values will range from 120 ft-lbs to 150 ft-lbs. These will all be normal right hand threads. The larger cars (F1, GTP, F3000, CART) use a much larger axle which is hollow and uses a monster nut, usually put on and off via an air gun. These will be left-handed or right-handed, often different colors for different sides. These nuts should still be tightened with a ¾ inch torque wrench and special socket after the nuts have been snugged. The torque values can easily exceed 300 ft-lbs for these units. Alternatively, calibrate your air gun for the proper torque settings under a known air/nitrogen pressure.
The smaller nuts are normally put on dry. Whenever you feel a little slop in the assembly it is time for new units. Normally the nut wears before the axle, but always check both. The larger nuts are specially shaped to fit into the wheel, with no conical washer or spacer. They are designed to have a small amount of anti-sieze put on the threads only (due to the fact the nuts are usually aluminum and the axles steel.) If the anti-sieze gets into the conical mating area all torque values are negated. I have seen units that were coated with anti-sieze and then torqued to 350 ft-lbs. It took over 1000 ft-lbs of torque to remove them as the anti-sieze had allowed the nuts to turn far more than they were supposed to.
A little care can go a long way. Understand how the units do their job and what you can do to preserve and protect them. As in most things, the proper tools and the proper knowledge are invaluable.
Charlie Warner
Fatto Gatto Racing
Administrator