Pipe size up to connection at fixture

[55tbirdfan]

I am installing a new tub faucet for a standalone tub. The faucet is attached to the floor. The faucet I purchased connects to the plumbing with braided hoses similar to sink supply lines and ½" threaded hose style connectors.
I am disappointed and surprised at the supply line size on the faucet. I assumed it would have ½ supply line. I had thought there would need to be much larger pipe size to deliver more volume. Or is it strictly higher pressure because of supply line size.

The sales person told me to make sure I have a ¾ pex line all the way to the point of connecting to tub. He said keep ¾ all the way and connect ½ threaded fitting at the faucet..
If the fixture only has ⅜" inside diameter supply line does it matter when I switch to ½? I ran ¾ thinking I would need ¾ supply line for oversized (72×34 Soaking) tub. But if I reduce to ½" after the tee from vanity, does ¾ help volume for the last 10 feet?

My other concern is the flow rate of the faucet. It claims to be 7gpm if I remember correctly. That doesn't seem likely.


Thanks

 

[wwhitney]

If the fixture only has ⅜" inside diameter supply line does it matter when I switch to ½?

Yes.

I ran ¾ thinking I would need ¾ supply line for oversized (72×34 Soaking) tub. But if I reduce to ½" after the tee from vanity, does ¾ help volume for the last 10 feet?

Yes. The way water volume and pressure works is that if you have a constant pressure supply (like the water main in the street, for practical purposes), the rate of water flow to an outlet is the exact amount that causes all the pressure drops along the route to add up to that source pressure, so there is 0 pressure left at the outlet (or at least just after the outlet, when the water is falling through free air).

Each segment of the piping contributes to the pressure drop due to flow, and a bigger pipe gives you less pressure drop for a given flow and given length. So increasing any pipe size on the route from the water source to the outlet will give you slightly better flow at the outlet. As would shortening the length of the pipes, if that is possible.

Cheers, Wayne