What's the best way to measure for tire size.

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MOA

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What type of Fixture?

I'm working on the back at the moment. I have some ideas, but better to ask those that have already been down that road.
 
"One test is worth a thousand opinions."
I have a rough idea what is going to work but with these cars, they all vary and asking what fits on yours doesn't do me much good when buying wheels and tires, unless I don't care about maximizing tire size.
 
I measured what I had so I had a baseline. Then I measured and added the space I had left. Make sure you measure both sides. They are usually different especially the rear. When I got my wheels, I was lucky enough to find a used tire the size I was planning to buy. I put it on the rim, tried it for fit on both sides. Then I ordered the new tires. If you pull the trigger and order new ones, you might not be able to return them if they don't fit.

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I got this at home depot.... notched it to fit the hub.... then used it to measure my clearances..... takes allot of the guess work out

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although i do have to add, prior to doing this i had talked to another member 72blu and told him my setup and his suggestions were 100% accurate :)
 
When I measured for slicks, I had a smaller tire on rim. Then strapped some ridgid foam board to tire and trimmed it to profile of slick I had wanted. Mounted that and rotated around wheel well to check clearance. Worked really well, but didn't take pictures then.
 
What type of Fixture?

I'm working on the back at the moment. I have some ideas, but better to ask those that have already been down that road.
I just did this on my 65 dart. I pull the tire and set the car on a jack stand under the axle leaving it at ride height. Get a yard stick and tape it flat to the disc or drum run it around in a half arch and find your maximum height. Then use cardboard over the end of the yard stick to find your maximum width. This will find the fender lip and or curve of the fender ( as in my case the fender curved inward minimizing my width) and be sure to clear the springs and spring clamps. Tape all this together and pull it out. Measure it for your max tire height and width and off set for your rim. Mine came out to be a 215 55 17 tire on the rims I chose
 
I came up with: Driver side, 6-11/16 from face to leaf spring, 4-3/4 from face to fender. Passenger side, 6-5/8 face to leaf, 5 from face to fender.

I'm putting 18x9 Bullitt wheels on the rear, I think the 265/35/18 will fit. The fenders are untouched stock, i have no problem w with modifying the wheel well.

What year Mustang had the right back space?
 
I came up with: Driver side, 6-11/16 from face to leaf spring, 4-3/4 from face to fender. Passenger side, 6-5/8 face to leaf, 5 from face to fender.

I'm putting 18x9 Bullitt wheels on the rear, I think the 265/35/18 will fit. The fenders are untouched stock, i have no problem w with modifying the wheel well.

What year Mustang had the right back space?

Looking at your other posts, this is for a '72 Swinger with a 8 3/4 and LBP axles right? And you're using a Dr. Diff 1/2" spring offset?

If that's the case your measurements make sense. Looks like the axle may be shifted a bit to the driver's side and the bodywork on that side is a little tighter. On my '71 with the stock spring locations and a BBP 8 3/4 I've got 5" on both side from the mounting face to the quarters and 6" to the spring on one side and 6 1/8" to the other, so that's pretty much in line with yours considering the 1/2" offset and some body variation.

On the tightest side (drivers) you've got 11.4" of space to work with. I try to figure on a 1/2" of clearance to the springs and the quarters. You definitely need a 1/2" to the quarters, you can run it a little tighter to the springs but it's nice to have a little wiggle room because section width specs and real life tires mounted on rims aren't usually exactly the same. So, that's only a 10.4" wide tire at the section width. 265/35/18's vary more by section width than any other size I've seen, from 10.3" all the way up to 11.1" depending on the tire. That's crazy, and I only looked at 4 different tires. Basically some manufacturers make a 265 that's pretty much the same as a 255, and others make a 265 the same as a 275. So, you absolutely have to check the section width of the tire you want to run. You could have a tire that fits all the way up to one that isn't even close. Most 255's are 10"-10.4" wide, most 275's are 10.9" to 11.1" wide.

Looking at your measurements, I don't think I'd actually try to put anything wider than a 255 on that car as it sits right now because of the clearance on the driver's side unless you want to trim the quarter lip back. Typically you can gain between a 1/4" to 1/2" by cutting the quarter lip back to the spot welds with the wheel tub. You also might try loosening up your U-bolts and shifting the axle on the springs to see if it'll square up a little better. Otherwise your driver's side is going to limit your tire size significantly. On my car I have 10" to work with and I don't have an offset and haven't cut anything.

Backspace to center an 18x9" on your car should be close to the 6" mark. Assuming a 1/2" clearance and a 1/4" of tire overhang past the rim lip (10.5" section width) the backspace for minimum clearance on the passenger side is 5.875". So I'd be looking for a 18x9 with a 6" backspace and not worrying about ending up at a 3/8" clearance on the inside. I tend to err on the side of slightly more backspace just because you can correct with a thin spacer if you need to. Obviously if you run a wider section width you'd need less backspace to clear the springs, but keep in mind that will push the tire closer to the quarters. On the driver's side you don't have any extra room that way, so I wouldn't go past a 10.5" section anyway.

So, if I were you I'd try to shift the axle on the springs and see if that helps any to balance the sides. Then I'd look at the quarter lips and decide if I really wanted to cut them, and how much. Then I'd see what that gets me for that spring to quarter lip measurement, and look for section widths that are about an inch less. Most 70+ Darts with a 1/2" spring offset can run a 275, but the way yours is measuring out right now I wouldn't go past a 255/40/18 unless you do some trimming.
 
Thanks. Ya,it has the dr diff offset kit.
LBP. 11" discs, 8-3/4. Rearend was modified to accommodate this plan.

I planned on shifting the rear end as much as I can, the way it sits is just the first time in,and the u bolts are only snug.

If I need to trim the lip,I'll trim the lip. I pretty much figured I would be doing that.

This car is nothing special really,it will be special to me but it won't be needed in the Smithsonian. Cutting and welding is a given.

Street car with handling in mind. As many Smokey burn outs as I can afford.
 
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Where to find the correct wheels?

Looking for bullit style wheel, 18x9, 5x4.5, 6" backspace zero offset.
Polished outer lip, anthracite center.
 
Well first, a 6" offset on an 18x9 isn't a 0 offset, it's a +25mm offset. Backspace and offset measurements are tied together, you can't change one without changing the other.

The '94-04 Mustang wheel is what you would be looking for, they have an 18x9 with a 5.95" backspace (+24mm) offset. Remember that with the Bullitt rims you have to open up the center register a bit to get them to fit over the hub on the rotor in the front.
18" Anthracite Bullitt Wheel 18x9 Rim Fits 94-04 Mustang® GT V8 V6 CP | eBay
 
OK, I see what you're saying.

Thanks
 
18x35x265 fit no problem on the rear.

Nitto 555 G2s
 
Get the Percy's Wheel Measuring tool. It works very well.
 
Most of the time it's guess work and head scratching or copy cat what others are currently running.

I've always been interested in one of these Percys tire measuring tool.
Just wondering how accurate they are.

I've mentioned this in earlier posts, I made my own gadget based on the Percy's tool. It wasn't too hard to do, and the bottom line is it worked perfectly and when my wheels / tires showed up they fit exactly as I expected they would. Just made another one for my son last weekend, as he is looking for new wheels/tires for his Suzuki Sidekick hunting wagon project. Takes out ALL the guesswork.
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I've mentioned this in earlier posts, I made my own gadget based on the Percy's tool. It wasn't too hard to do, and the bottom line is it worked perfectly and when my wheels / tires showed up they fit exactly as I expected they would. Just made another one for my son last weekend, as he is looking for new wheels/tires for his Suzuki Sidekick hunting wagon project. Takes out ALL the guesswork.
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That's pretty cool!
 
I have 3\4" clearance to the leaf spring and about the same on the fender side. Drivers side is a little tighter to the fender, I'll move it later when I get back to the rear end. New front end is next.
I was looking over muumuu's car at willow springs...
Muumuu's car is a lot tighter than mine but I have the offset and he doesn't, yet. I think He's using the same size wheels and tires.
 
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