hey guys before you start bashing, yes ive checked the tech archive and did a search buy nothing yeilded an answer to what im looking for. so here the question, i have a 73 chally with stock length axle and disk brakes, whats the widest tire i can fit being 28" tall ? or how can i go about measuring to figure that out with the back spacing for a rim. i think i can fit an 11" or so wide tire with a 6" backspace. thanks guys any and all help is appreciated.

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how can i go about measuring to figure that out with the back spacing for a rim

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Make or buy a plumb bob. Drop a line from the inside of the wheel house on whatever the tire will rub on first. Usually it's the leaf spring. Don't forget to correct for wheel travel if there is anything the tire will rub when the suspension is compressed. Make your first mark on the floor where the plumb bob lands.

Now drop a line from the surface the rim seats to. Brake drum, rotor, whatever. Mark a line on the floor parallel to the first mark.

Now drop a line from the outer wheelhouse correcting for anything that the tire will rub when the suspension is compressed. Make your third mark on the floor parallel to the first two marks.

The outer marks are the maximum section width tire you can stuff in there. Section widths of the tires is usually posted on the tire mfg's website. Subtract 1" from the section width to allow for 1/2" clearance on the inner and outer edges of the tires.

For backspace measure from the center mark to both outer marks and subtract the smaller number from the larger. That number is your backspace positive or negative depending on which way the wheel needs to shift to be in the center of the wheel well.

Do the same on the front and account for the turning of the wheels. I mock up a cardboard wheel and attach it to the wheel mating surface. Use a ruler during lock to lock turning to see what will fit in the front.

It's surprising how much rubber you can stuff in there using custom backspace wheels. I was able to get 255/45/18" tires on all four corners of my 66 Coronet. The car sticks to the asphalt real nice with the sticky new tire compounds available.

Great answer, I'll use it this week.

Billet Specialties 18x8 w/ 5.5" backspace. Tires are 255/45/18 Nittos w/ 10.2" section width. Front tire on driver side rubs the frame slightly on full left lock, not a problem however.

Forgot to add - Make sure you check BOTH sides for backspace measurements. The numbers will be different.

I'll tailor my response not towards your question but rather to what I found given we are dealing with the same car.

I'm speaking about the rear tires. My car is a '73 Challenger with the factory 8-3/4" housing, stock leaf spring location and the factory drum brakes. I have a 15"x10" w/5.5" bs wheel riding on BFG 275-60-15 tires which are 28" tall tires.

From my experience, a 15"x10" & 5.0" bs wheel will not clear using the same size tire w/o interfering with the rear fender's wheel lip. Likewise, I don't think a 6.0" bs wheel will work either since you are likely to encounter interference with the leaf spring since a 5.5" bs wheel with a 275 tire is only about 3/8" clearance from the springs.

I mocked up a 15"x10" with a 5.0" bs wheel firsthand and it did not fit as well as the 5.5" wheels on my car. I was hoping that it did since I like the look of the deeper dish however, from my experience, the 5.5" bs was the perfect fit on my Challenger.

Each car is slightly different and you are best served by measuring and test fitting. Perhaps you can borrow a set of wheels and tires or go to the place you are considering purchasing them from and let them make the call. Another option is to use the spring relocation kit which will likely allow you to use a 6.0" bs wheel. Perhaps you may consider ordering a custom sized 10" or 11" wide wheel with a specific size backspace to work on your setup as well. If you like I can supply you with some detail photos of my clearances.

I'd be into some pics.
I have a 71 Challenger that I would like to get as much tire as i can without body mods.