Your skateboard trucks are the part that connect the wooden deck to the wheels.
Skateboard truck sizes are often quoted from the length of the hanger: 129mm, 139mm, and 149mm are pretty typical for modern street skateboarding.
Here is a truck with the parts labeled:
Turning with the truck
The truck is designed to allow you to turn while riding on the skateboard. When rolling you can turn the skateboard by shifting your weight to one side of the board or the other. When you shift your weight the bushings on the truck will compress on the one side. This allows the hanger to pivot from the pivot bushing and rotate around the kingpin. This happens on both the front truck and the back truck and causes the board to turn and lean to the direction that the weight is applied.
By adjusting the kingpin nut to make the truck either tighter or looser you can make the board turn more or less. The tighter the truck is the less that it will turn. The looser it is the more it will turn.
You can make the skateboard trucks so tight that they don’t move at all or so loose that the board is unstable and hard to stand on. This is based on personal preference and skating style.
Tight trucks are more stable at high speeds. For beginners it is good to have your skateboard set up pretty tight. This lets you get used to being on the skateboard without having it lean side to side all the time. Once your balance improves your can loosen the board up to give you more control.
Loose trucks give you a lot of control. They allow you to turn quickly but can be unstable.There are few draw backs; speed wobble and wheel bite and it is tougher to balance in a grind.
Speed wobble is scary. When you are going fast on your board the vibration of the wheels on the road can cause the skateboard to start wobbling in an uncontrollable fashion. The skateboard trucks will start turning quickly from side to side on their own. This is called speed wobble. It is a strange and dangerous thing. This can easily throw you from your skateboard. That is the last thing you want to have happen when you are going really fast. Try and avoid going really fast until you build up good balance.
Wheel bite is when the hanger turns so much that the wheel rubs against the bottom of the deck. This happens often and leaves a burn mark on the deck as seen in the photo here.
Sometimes the wheel bites hard enough to stop the board dead and throw you to the ground. Again, not good.
Somewhere in between
I like to ride with my front truck looser than my back truck. Both skateboard trucks are moderately loose but not really loose. This lets me turn pretty good when riding normal. It adds just a little more control when riding switch. It is the best of both worlds for me. I find if I make them too loose then my bushings get pinched when I do grinds and it is harder to land them.
Eventually we all get the most annoying skateboard break of all. The kingpin breaks.
Session over. It can be tough to replace the kingpin. They are hard to get out of the baseplate, and hard to get back into the baseplate.
I have come up with a few tips to make it easier.
You need a few tools to do it:
With all those tools changing the kingpin will be easy.
As things work in you may need to adjust the tightness again. Have fun and hopefully you won’t need to do this too often.
Very often the axle will get smashed and bashed around and start to move back and forth in the hanger. When this happens one side or wheel will seem to be way to tight, well the other will be very loose.
Don't worry, all you need to do to get rolling again is to smack the axle like a hammer down on something hard like a curb.
This should re-align the axle in the hanger. Keep an eye out for when the axle shifts again. Use the metal spacers that come with your bearings to help prevent the shifting.
Most trucks will shift once in awhile. Just keep adjusting when needed.
Skateboard Trucks last longer than any other part on your skateboard. Learn how to maintain and adjust them and spend your money of a fresh deck whenever you can.
When working in a set of new skateboard trucks when I tend to hold on to my old bushings and put them on the new skateboard trucks. This helps with the working in period.