It’s obvious under tightening your wheel nuts is dangerous since they are liable to come loose when driving, but overtightening wheel nuts can be just as dangerous.
All cars have a specified torque value for their wheel nuts which are usually in the region of 100Nm for the average car. Tightening the bolts over the specified value stretches them, and when they are stretched past their yield point this can cause them to shear, since the force they can withstand is greatly reduced. Having said that, don’t let this stop you changing a flat tyre if you’re out on the road, just make sure you bring in to us afterwards and we’ll check the wheel torques for you with a torque wrench.
For a more comprehensive guide take a look at the government info leaflet: Careless Torque Costs Lives .