What size tire using 15x6 wheel?

[72bluNblu]

Excuse me, I need clarification. Op says the wheels he wants to use are OFFSET 3.375 but doesn't state clearly whether that is positive or negative, or inches or millimeters . Everyone commenting here assumes he means backspace. If that is what he meant, then head on! But offset is a legitimate but entirely different method of describing a wheel.

On a personal note, I DESPISE wheel companies that use offset to describe wheels. I can't be simply measured, it has to be calculated, and it can't even be calculated if the actual width of the rim is unknown. Please, backspace only! It can be determined exactly with just a straightedge and a tape measure.
Okay, continue !

Offset can absolutely be measured. It's just the distance of the mounting surface from the centerline of the rim. The problem is that people don't understand that backspace is measure from the outside lip of the wheel, so when they try to convert backspace to offset they forget the extra ~1/2" of rim lip included in the backspace.

So, for example, a 15x8" with a 4.5" backspace. That's a 0mm offset, but people think that's wrong because the backspace is 4.5" not 4". Well, the 8" width listed in the spec is where the tire bead sits, not where the outside lip of the rim is. A 15x8" is actually 9" wide if you measure outside to outside, which is where the 4.5" backspace comes from. So the centerline is at 4.5" from the outside, which means the mounting surface is at the centerline.

And offset can be a very helpful specification. If you're changing the width of the rim, for example, you can just get a rim with the same offset. The additional width will be split between the inside and outside, if the offset is the same the centerline of the wheel is the same. If you keep the backspace the same and use a wider rim, all of the additional width is on the outside.

Another example- an 18x9 with a 6" backspace. If you remember that the 18x9" is actually 10" wide outside to outside, then you know that the centerline of the wheel is at 5". So if it has a 6" backspace, then it has a 1" offset, which makes is a +25mm offset (well, 25.4mm but it will be rounded down). Offset is always listed in mm, which also confuses folks.

but...... had you thought about 3.375 offset, on a 6" rim? is that even possible?
i do agree about listing backspace not offset. listing offset is about as useful as when people measure rear axles by the casing width, what about the variations in halfshaft size, brake drum/disc thickness etc. why not say wheel mounting face to wheel mounting face (or wmf for short). that's the measurement that you can work with.
neil.

Housing width is a lot easier to measure though because it's usually measured on a bare housing outside the car so there's nothing in the way and the tape measure will lay flat across the axle housing. Wheel mount-to-wheel mount on a fully assembled axle usually requires a couple of straight edges and an extra person to measure accurately. As long as you know what brakes are used you can calculate the WM-WM if you have the housing width.

 

[mygasser]

Offset can absolutely be measured. It's just the distance of the mounting surface from the centerline of the rim. The problem is that people don't understand that backspace is measure from the outside lip of the wheel, so when they try to convert backspace to offset they forget the extra ~1/2" of rim lip included in the backspace.

So, for example, a 15x8" with a 4.5" backspace. That's a 0mm offset, but people think that's wrong because the backspace is 4.5" not 4". Well, the 8" width listed in the spec is where the tire bead sits, not where the outside lip of the rim is. A 15x8" is actually 9" wide if you measure outside to outside, which is where the 4.5" backspace comes from. So the centerline is at 4.5" from the outside, which means the mounting surface is at the centerline.

And offset can be a very helpful specification. If you're changing the width of the rim, for example, you can just get a rim with the same offset. The additional width will be split between the inside and outside, if the offset is the same the centerline of the wheel is the same. If you keep the backspace the same and use a wider rim, all of the additional width is on the outside.

Another example- an 18x9 with a 6" backspace. If you remember that the 18x9" is actually 10" wide outside to outside, then you know that the centerline of the wheel is at 5". So if it has a 6" backspace, then it has a 1" offset, which makes is a +25mm offset (well, 25.4mm but it will be rounded down). Offset is always listed in mm, which also confuses folks.

View attachment 1715591872





Housing width is a lot easier to measure though because it's usually measured on a bare housing outside the car so there's nothing in the way and the tape measure will lay flat across the axle housing. Wheel mount-to-wheel mount on a fully assembled axle usually requires a couple of straight edges and an extra person to measure accurately. As long as you know what brakes are used you can calculate the WM-WM if you have the housing width.

as far as offset vs backspace i guess it's different strokes..... either works if you have a brain that can measure/work things out. me, i prefer backspace. it's the positive/negative offset thing that i've yet to fully grasp as i forget which is deeper dish looking and which is not when i'm on the spot looking at wheels.
as for axle i've never had a problem measuring total width on my own with a tape measure and a single straight edge. hell, you can get within an 1/8" with a tape measure and your eyes. again i guess it's different strokes and whatever you find easiest.
neil.

 

[33IMP]

So you MEASURED the backspace, and CALCULATED the offset, keeping track of what is positive and what is negative . Just what i dont want to have to do. And f*$k metric measurement.

 

[matthon]

Here's a real example.

67 Barracuda, currently has old Cragar14x6 wheels. I measured the backspace at 3.75 and the tire is a 215 70 14.
The offset must be +.25.

I want to put on 15" steel wheels: Wheel Vintiques 63 Series O.E. Chrysler Black Wheels 63-5654334

15x6, backspace 3.75, offset +6 mm.

It appears the backspace is the same on both wheels. My understanding is you don't have to consider offset when determining backspace on new wheels.

As the tire is already close turning the wheel lock to lock, my thought process is if I stay within the 215 70 14 size I'll be ok.

So, the closest available tire, Cooper as I already have them on the back, is a 215 65 15. It is within 0.1" in height, same width.

Did I do that correctly?

 

[33IMP]

Your +6mm And 1/4" offset is essentially the same. So, if the 215/70x 14s fit, so will the 15s you chose. Yep, you did it right.

 

[matthon]

Fit perfect, basically the same height and width as before, just a 15 inch wheel.
It is slightly taller, probably due to the tread, seriously.

Judging by the clearances, uca, front and rear lower fender sections, I would guess a bigger diameter wheel would fit, but the offset would have to be larger and the height of the tire would probably have to be about the same.
Just a guess, those Barracuda fenders leave little room for steering.

 

[512Stroker]

Fit perfect, basically the same height and width as before, just a 15 inch wheel.
It is slightly taller, probably due to the tread, seriously.

Judging by the clearances, uca, front and rear lower fender sections, I would guess a bigger diameter wheel would fit, but the offset would have to be larger and the height of the tire would probably have to be about the same.
Just a guess, those Barracuda fenders leave little room for steering.

View attachment 1715597060

215/65-15 correct?

 

[matthon]

215/65-15 correct?

Correct. Drove it all over as normal, no issues.

 

[69_340_GTS]

All front-driver wheels as well as all the new HP performance cars use wheels with very deep backspacing. Like a 2020 Mustang takes a 19x8.5 with 45mm offset (6.52" backspacing!). I guess on the new cars it is to make room for the big brakes.