UDim2 Resize Help?

So you are making a bar that changes size depending on the amount of fuel?

Here is a better way of doing what you were doing:

Hierarchy

• ScreenGui
  • BarHolder (size of the bar)
    • Bar (what you resize)
  • Script

LocalScript

local maxFuel = 100
local fuel = maxFuel

while wait() do
    script.Parent.BarHolder.Bar:TweenSize(UDim2.new((1/maxFuel) * fuel,0,1,0),"InOut","Quad",0.1,false) -- this is for a bar on the X axis, not the Y, to have it on Y, simply change the first argument to 1
end

This is for a length wise bar , not height wise. To change, simply swap the first argument of UDim2.new() with the third.

Tweens change the size/position of a gui smoothly.