hard to say for sure but it seams maybe 2. My originals were pumped up to 40 psi so that probably helped them.
I didn't have the originals on very long either so I don't have a real good comparison...
But I can say I'm getting twice what my old truck got (2016 Colorado v6, right around 30 mpg...
I'm not sure what it is, they told me there was an alarm on it and it will cost me $600. I said no thanks, remove it. Well they did not and it caused a draw that killed my battery overnight. A different dealer ended up disconnecting it under warranty and now the draw is gone.