There are seven measurements to consider when attempting to measure wheel bolts on your car. Imports employ metric measurements, while domestic cars can feature standard measurement bolts or metric. Although measuring the wheel bolts would seem like a relatively easy task, if it is not done correctly, hazardous conditions can result. Because metric and standard measurements are somewhat similar, it is easy to apply the wrong sized lug nut to the wheel bolt when using an impact gun. The result would be stripped threads that would make removing the nut difficult or would prevent the nut from properly fastening to the wheel bolt.
- Skill level:
Things you need
- Jack stand
- Lug nut wrench
- Bolt pattern gauge
- Measuring tape
- Bolt and nut gauge (metric and standard)
- Thread pitch gauge (metric and standard)
- Wheel bolt torque specifications guide
- Torque wrench and suitable socket
Use the lug nut wrench to loosen the lug nuts on one tire of the vehicle. The first measurement to consider on the wheel bolt is the lug nut diameter size. Most imports use a 19mm or a 21mm lug nut. Domestic cars may use 3/4-inch or 11/16-inch. Light duty trucks and SUVs may feature 22-mm or 7/8-inch lug nuts. Lift the quarter of the vehicle with the jack and then support it onto a jack stand. Finish removing the lug nuts and then remove the wheel.
Use the wheel bolt pattern gauge to determine the size of the rim in comparison to the wheel bolts. This measurement is important when purchasing rims. The bolt pattern of the new rim will have to match the bolt pattern of the vehicle in order to fit properly. Since vehicles feature four, five, six, seven, eight or even 10 wheel bolts and nuts. The number of wheel bolts would be incorporated with the measurement between opposite bolt holes. In the event of odd numbered bolt holes--most commonly five--measuring the centre of the top bolt hole to the centre of the third in inches would determine the measurement.
Measure the length of the bolt shank using a measuring tape. The length of the wheel bolt is important because it has to be long enough to reach through the rim and then be secured by the lug nut properly. While OEM rims and wheel bolts are correctly measured to match one another, replacing the rims or replacing a wheel bolt can compromise the length and effectiveness intended for the mating of the nut to bolt. Keep in mind that the wheel bolt is pressed into the hub flange and the thickness of the hub flange needs to be applied to the wheel bolt measurement.
Place the bolt diameter gauge over one of the bolts. Since metric and standard sizes can interchange slightly, be sure to choose between the two for the proper diagnosis of the bolt diameter measurement. Some wheel bolt diameters will allow you to place the metric and standard size gauge over the bolt. One will fit more loosely than the other. The tighter the fit of the bolt gauge will determine the correct application. Other wheel bolts will not allow both metric and standard sized gauges to affix to them, which takes the guess work out of whether it is standard or metric.
Place the thread pitch indicator grooves into the threads of one wheel bolt. Again, wheel bolts can feature both metric and standard sized thread counts, depending on the make and model of the vehicle. Be sure the grooves align tightly to the pitch of the threads on the wheel bolt to determine the correct pitch count of the bolt. Check with both metric and standard gauges and apply the tightest fitting gauge.
Make sure the lug-nut threads match the thread pitch count of the wheel bolt. Impact guns can be unforgiving when applying the wrong sized lug nut. If you're replacing the lug nuts, make sure the nut fits snugly to the wheel bolt. Hand thread it on and then tighten with a torque wrench to the proper torque specifications indicated for the type vehicle. The diameter size of the wheel nut must also match the diameter size of the lug nut wrench in order to be able to remove them in the event of a flat tire.
Torque the lug nuts using a torque wrench set to the correct foot-pounds indicated for the vehicle in the torque specifications manual. While this may not be an actual measurement in inches or centimetres, it is a measurement in tightening. If not performed correctly, a wheel can fall off. Always tighten lug nuts in a star pattern, starting with one and then choosing the next one the farthest way from it. This will prevent the rim from being improperly mated to the surface of the hub flange and will eliminate vibrations.
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