You die in a flaming ball of fire! Well, actually, it's not a good idea to drive for a long time with less than what the engineers designed into the car, but typically it won't cause a problem or be noticeable. Chances are you won't find a mechanic or shop owner who says that because of liability concerns. They have to cover their butts because customers are lawsuit-happy.
Broken studs can be replaced. If just the nut is missing, take one from a rear wheel and put it on the front. There's a lot less weight on the rear, and if the worst happened and a tire fell off, losing a rear one is inconvenient whereas losing a front one is scary.
Lug nuts must always be tightened with a torque wrench. Do-it-yourselfers forget this step or are not aware of the importance. The reasons are to be sure they are tight so the wheel doesn't come loose, to be sure they aren't over-tightened and wreck the threads or break the studs, the clamping forces are even all the way around, and a 90 pound driver can get them loose to change a tire.
Uneven clamping forces coupled with lots of city driving and splashing through puddles is a common cause of warped brake rotors which leads to a pulsing brake pedal when stopping. Of course do-it-yourselfers blame the mechanic who did the brake work or the manufacturer of the rotor.
Over-tightened lug nuts will damage the treads but that will not usually show up when it is done. The problem becomes apparent the next time you have the tires rotated or try to take one off. You blame the mechanic who is trying to take the tire off, when in reality you should be blaming the person who over-tightened the nuts the last time or even two times ago.
There are huge wall charts in almost every shop listing every car model and the correct torque for their lug nuts. A typical value for front-wheel-drive cars is 95 foot pounds with regular studs and 80 foot pounds for anodized studs. Larger wheels means larger diameter studs and higher torque values.
Some people put grease on the studs to prevent rust. NEVER, NEVER, EVER use anti-seize compound. The nuts WILL work loose. Any mechanic found doing that deserves to be fired. A little bit of axle grease is acceptable, but then air tools should not be used to run the nuts on. The grease could build up on the rounded contact surface of the nuts as they are run down and the centrifugal force will distribute that grease around the friction surface that is needed to hold the nuts tight. Grease should never be used on anodized studs. Those are the ones coated with an electroplating and look silver, light blue, or light yellow. That plating IS a lubricant and can be dissolved by some greases.
When all the nuts work loose while driving, the wheel is usually ruined from the holes getting stretched out. Even though you retighten the nuts, the rounded contact surface on the wheel no longer conforms to or matches with the surface on the nuts. That eliminates the friction surface that holds them tight. In those instances the wheel and nuts must be replaced.
Friday, December 3rd, 2010 AT 3:20 PM