Forgive me if I ask a stupid question. I have some rims and I'm looking to purchase for my 66 Coronet and I'm not sure about the technical side of backspacing. I am looking to convert to disc brakes and know that the backspacing should have something to do with that.i also know that backspacing also effects tire rub.
I have 17x7's W/1mm offset and 4" backspacing picked for the front. The rears will be 18x8 W/1mm offset and 4.5" backspacing. Will these work?

there are no stupid questions & this one makes VG sense (no one wants to make a blind purchase that turns out to not fit) & tires/rims ain't cheap. for a start what width/offset/tire size is on there now with the drums. what discs do you have in mind? EDIT & how much clearance do the present items have?

I have Factory tires and rims on the car currently. I would like to upgrade to the Wilwood brake kit that allows you to keep your drum brake spindles. However due to price I may have to go with your run-of-the-mill EBay disc brake conversion kit

if the one you have in mind is the 73-76 A body OE discs, there just was a thread on the increase, I forgot what it was. someone will know (& post)

I would like to think that the increase and rim diameter would give me all the room I could think I would ever need as far as the disc brakes go

Based on my 67 coronet ( same rear wheel wells as yours) your rears will not work

I have 8 X 15 on my rear with 5 1/4" BS...

Would it be a case of rubbing the inner Fender or outer fender?

Been 10 years since I have measured for this, so I will do my best..

I used 15 X 8 with 245/60/15 tires ( rear) I spent a lot of time with a couple of used Mags with different backspacing measuring and looking at tire width and aspect dimensions... I did not want any tire rubbing or "nobody can ride in the back" crap sizing.. I still feel I installed the max you can go without any mods.. I had some rubbing on the inside of one fenderwell ( trunk side) and had to install a 1/8" wheel spacer.. Most of that problem went away with the FF rear sway bar that stopped most of the lean in the car..

The fender wells slope towards the tire/wheel ( both sides) so the area for your wheel and tire get smaller the higher you get up into the wheel well..
I remember thinking that I would have gone 5 1/8 BS if I was to do it again..
Just isn't a lot of room.

Hope this helps

I've never converted to the metric system in my mind yet so I'm not sure exactly how wide 1MM is, that being said are you sure the rims are offset or inset 1MM? Inset would locate the rim center closer to the drive shaft and offset would move it away I have a 1966 Dodge Cornet Deluxe that I put a narrowed Dana 60 in and moved te rear leaf springs into the rear sub frames for more tire clearances, I put a set of 8x15 inch wide rims and a set of 275x60x15 tires on those rims. I did have the front fenderwells stretched, move forward, three inches and I used a set of the Mopar SS leaf spring that moved the rear end forward two inches also I should have measured better with those tires and rims before having the rear end narrowed, the front of the tires are really close to the front inner sides of the stock wheel tubs I ended up having to use a .500 inch wheel spacer on the rear end to get more room so the tires wouldn't touch to start with You may want to see if you can borrow, maybe give the wheel shop a refundable deposit to take two of the rims home and see if they fit with no tires on them to start with
Take time now to make sure what you end up with fits IHTHs

I'm not a fan of these big rims but for each his own. I also have no idea what 1 mm offset means.

What I can tell you is that I had 15 x 8 rims with 4.5" backspace with M/T ET Sreet Radials P255/60/R15 on my 67 Coronet 500. Around turns it would rub the quarter panel lip. Probably a 7" rim with 4 inch backspace would of worked as the section width decreases with the smaller rim, but I went with a 7 inch rim with 4 1/4 inch offset. No problems with that.

Not sure how this helps you with your selection.............

Do you have your tire specs yet? I just went through this for wheels n tires for the Challenger. The narrowed rear axle meant having to measure and confirm everything

You need to know the section width of your rear tires in order to figure out clearances.

Since your intended wheels are 1mm offset, that is basically saying 0 offset. So we know where your tire tread centerline is going to fall within the wheelwells. You can go off the hub face of the axle with a straightedge and eyeball the wheelwell arches for rub spots. Then youll be able to tell how far in to scoot the new wheels for clearance.

Remember: 0 offset means the tread centerline and the hub face are the same.

Are you with me so far?

my rears are 17x8 with 4.75 backspacing with 255/55-17 tires they will rub very little on the outside inner wheelwell when turning hard I do not have any swaybars yet and think if I at least added a front it wouldn't rub anymore. I think 5" backspacing would have been better.