Well this is more complicated than you may think and with the emergence of Amazon, UPS and other shipping providers have had to adapt their policy on how shipping is calculated and to be quite honest its not in your favor.
For many year boxes were based sheerly on weight, but when companies started shipping small, lightweight items in huge boxes these carriers implemented what's know as dimensional weight.
A UPS truck in this instance only has a set amount of cubic volume, so they now value boxes based on their size more than their weight.
What this means to you is shipping is very hard to have a computer calculate accurately as it can't understand the size of the box only how much it weighs. We have our store to provide shipping cost if the order meets the following:
* Does not contain oversized items like tires, wheels, seats and bodies
If the above are included in any capacity other than smaller tire and wheel orders, we have the shipping module not display the normal ground shipping option as in most cases it won't be accurate and could overcharge or undercharge depending on the situation.
That is the reason you see the shipping option state "Shipping Calculated Once Order Is Received". When the order is received we will calculate the correct shipping and associate it with the order and complete the transaction in store where your card will be billed with a final total including shipping.
If you see that shipping looks wrong or you want a shipping quote first, Message,Chat or Text and we will get you a shipping quote first. if its a time sensitive order you can add a comment to the order to call as soon as we receive the order and quote shipping prior to the order being shipped.
All the above is mainly for ground transportation, if your order requires expedited shipping, there is Next Day and 2nd Day Air available but its needs to be for very small items and is reserved for orders weighing 10lb. or less for the option to be displayed in checkout.