Okay, so I have good tires on my car which is probably going late this week or early next week to a "we buy cars" type place.

My mom's car could use some new tires and Id like to swap her old

P215 R16s for my newer/more expensive
P225 R16s

Does this work? I know that my tires are a "size bigger" whatever that means, there shouldnt be any problem with this right? I mean except for the fact that my car doesnt run and Im going to have to put it on blocks to get my wheels off then take them somewhere to get the tires off.

what is the height of the tires? 225 means your tires are just a bit wider than her 215's, but there is also the sidewall height to consider.

you left out the aspect ratio. there are 3 measurements on a tire. width, aspect ratio, and rim diameter. aspect ratio is basically the sidewall height. it's listed as a percentage of the width of the tire. so a 200/50/16 would be 200mm across, 100mm tall, and would fit a 16 inch wheel.

you can fit a wider tire, but the aspect ratio will have to be smaller. otherwise the tire will be too tall, and that will throw off your speedometer and final drive ratios.

Okay I will have to check that now that it has stopped raining here in Dallas.

If you have 215/65/16's then you could go to a 225/60/16 just fine in the vast majority of cases. This is called "plus zero" sizing your tires.

use this to calculate different sizes

http://www.discounttire.com/dtcs/infoTireMath.dos

Assuming the new tires fit, you can use this calculator to see what the difference will be: http://www.net-comber.com/tirecalc.html.

my calculator is better than your calculator.

Well they are both 60 in the middle, I went to the local tire shop and they said it would be fine, so Im going to do it. Im selling my car for less than 1k$ and my tires are newer than 2 years with only daily trips from my apartment on Harvey to Zachry/Wiesenbaker on them, so another 70k miles the way my mom drives (shes old).

Yes, this will work fine. You can be off a little either way.
Most people don't understand the tire numbering anyhow.

It works like this

First number is total amount of rubber.

Second number is percentage in the sidewall. Something like 40/45 usually for more performance oriented cars so that it doesn't flex as much in turns, 70/75 for cars and trucks since they will absorb more road bumps.

Third number is the diameter if the wheel.