Trying to use the tool and not fully sure. Anyone ever run a +25 front and rear on 19x8.5f 19x9.5r. If it doesnt work does anything other than a +40 work?
The quick answer is 8.5+25 would be pretty flush, but I wouldn't go lower than 8.5+25. 9.5+25 is probably going to poke out a bit in the rear. 9.5+35 would be a better fit.
Offset is a function of width, it's the distance from the centerline to where the hub mounts to the wheel. The offset and width are the 2 primary specifications that dictate how close the rim comes to the fender and to suspension components.
OEM wheels are traditionally pretty inset to allow for things like tire chains and throwing mud and dirt across the door panels.
If you're not overly concerned, there's a pretty wide range of what will "fit" on the car. Most will look "pretty good". When you're trying to choose width and offset, you need to know what you're trying to accomplish first.
I would say the bar is set at around 9+30 (I would actually go for 9+32 if I'm being picky, 9+35 is very close to the suspension) in the front, 10+40 in the back. For every .5" added to the width, add +5 offset. For every .5" removed, drop offset by -5. (Technically it's 6.35mm offset, but you're not going to find exactly that from off the shelf rims).
Front: Be aware of the clearance between spokes and brakes (on Brembo cars) and between the rim and strut. There is no OEM camber adjustment up front.
8.5+25 to 8.5+35 (8.5+40 is wheel dependent and may not clear the brake).
9+30 to 9+35 (9+35 is wheel dependent, most will fit, but brake and suspension clearance is tight)
Rear: There is quite a bit of suspension clearance in the back, but most wheel manufacturers don't make high enough offset for us to take advantage of that. There is quite a bit of OEM camber adjustment in the rear. The lower end of the offset spectrum for each width will be very flush, the tire could possibly poke a little bit (which I think looks great, but YMMV). You're going to have a really hard time getting offsets higher than +50 in the rear so I stop there.
8.5+25 to 8.5+35
9+30 to 9+40
9.5+35 to 9.5+45 (I would stay closer to 9.5+35)
10+40 to 10+50
10.5+45 to 10.5+50
11+50
The next consideration for fitment is tire size, #1 priority is matching diameter between front and back, then making sure the tire width and profile fits (both of which are a function of overall diameter).
Our fenders are already "rolled" from the factory (i.e. there is no metal from the fender that protrudes into the fender well) which is a huge plus. However, our fender liners do stick out a little bit just inside the fender.
You can find my fitment in a previous post, I'm running an oversized diameter and personally love my fitment, it's exactly where I want it, but that little bit of liner that rubs out back under hard compression (which I'm hoping to fix by increasing my rear damping on my ECS suspension with the Mando ECS10, I've always found the ass end of the Stinger to be a bit floaty, so I'm hoping to fix that too). I'm planning on playing with -3 and -5 spacers up front to nudge it to right where I wanted it.