Technical Wheel Offset For Dummies Like Me (Up Date)

Who stock’s anything anymore?

 

Maybe this'll help. This is where I ordered the wheels/tires for my '54. They have all the wheel measurements in millimeters. The same with tires too. I just use an online millimeter to inches calculator so I can comprehend better. Never could grasp the metric system!
https://www.performanceplustire.com/buy-wheels-online/cragar-wheels/61c-s-s-chrome-w-alum-ctr/

 

12mm is 1/2 and 14mm is 5/8 give or take a mm.

 

dividing or multiplying by 25.4 is pretty difficult...

 

15 x 10, 3-1/2" backspace.

10 inches is 254mm.

The center line is at 127mm.

3-1/2 inches is 88.9mm

127 - 88.9 is 38.1mm.

Since subtracted number is lower than the center line number, it a negative offset.

If the backspacing was 7", or 177.8mm the number is greater than the centerline number, it is positive offset.

In that case 177.8 - 127 is a 50.8mm positive offset.

It's just that easy.

 

Yup.

 

I've always known negative as back and positive as forward this would be negative in my book



And positive on this set



Why is the world all backwards nowadays

 

The last pair of wheels I bought were from Summit, I called the order in. I was asked about the offset, I said “I don’t know, but here’s what I want”. The guy took it down and they were what I wanted.
I’ve no reason to “know” what’s what with offsets, I don’t order wheels often enough to remember.

 

"I was told there would be no math today"

 

With a tire it has the illusion of deep
8-10 inch deep ,
Only 7 total .

 

And 25.4 isn't approximate, it's exact. It's how the units are defined relative to one another.

 

Then your book is wrong....

 

Backspace vs offset - the easy way.
Backspace is the measurement from the inner most part of the rim to the wheel mounting surface in inches.
Offset is how far the wheel mounting surface is away from the wheel's center line in millimetres. (25.4mm = 1")

If the backspace is exactly half of your TOTAL wheel width you have 0 offset.
The wheel mounting surface is exactly on the center line of the wheel.

If the backspace is less than half of the TOTAL wheel width you have negative offset.
The wheel mounting surface is inwards from the center line of the wheel. "MORE DISH"

If the backspace is more than half of the TOTAL wheel width you have positive offset.
The wheel mounting surface is outwards from the center line of the wheel. "LESS DISH"

Or you can just do it using this......



www.americanlegendwheels.com/wp-content/uploads/2018/10/alw-offset-backspace-conversion-chart-2.jpg

 

what is it you're try'n to do???? it's pretty simple... are you still changing the wheels on the 57??? do the wheels on it now fit proper, but you want a differant look... if so, just measure what you have..

 

all you have to do is pull the wheel, put a straight edge on the wheel mounting surface, measure in from that edge and that'll tell you how much positive room you have.. then measure out from that edge and that'll tell you how much neg room you have..... remember... possitve offset is less bearing load... and neg is more bearing load...reverse rims put a lot of neg. load on bearings. so it's called a neg off set

 

my 2 pence
if thinking you fancy some 4.5 by 16 inch genny 4 slot wheels on the front and you
think you want to run modern 175 75 16c commercial / van tyres
you cant - as the wheels dont have a snap bead and the valve stem hole is larger for a tube.
the next size up is a 6j by 16
6j is inner rim wall to inner rim wall
150mm - so you can run a 175 and have 12.5mm sticky out each side - or 185 OR 195
anyways the 6J wheel is actually 7 inches outer rim to outer rim
rear backsplashing is listed at 3 3/4 inches
the wheels 'actually' have a POSITIVE offset of 1/4''
which is ET6.35


just for laughs
IF you run a 10 inch wheel on a non c -clip axled car with a 10 inch negative offset, you will pull the collar off the shaft and lose the axle shaft
i think that is why they invented floating axles

 

It's hard to get proper information on bead profiles, but I understand that while it's not a good idea to run temporary spare tyres instead of ordinary tyres, temporary spare wheels have a normal J bead profile. Though, the range of available temporary spare wheels is narrower than you might think, but there might just be a 16" wheel narrower than a 6J. It is possible to get the centres knocked out of those and have early centres welded in — it's legal here; it might not be everywhere.

Edit: it seems 4J x 16 is a common space-saver spare wheel size: a tad narrow for a 175/75R16. Another option is the rim off a generic trailer wheel: 5.5J x 16 is common.

 

Kinda hard to put a straightedge on the inside of the lip

 

What I have learned lately is that people don’t know how to use tape measures either. I have been looking for some wheels and asked multiple people to measure backspacing even sending them an image of how to do it. Thus far, no one has measured it correctly that I have found at least trying to buy used wheels on marketplace. Also, I don’t think in “offset” dimensions, only backspacing.

 

it never was measured from the inside of the wheel... that rumor started with a few guys drinking beer in their buddy's garage... then it spread like wild fire... that and calling reverse rims positive off set because it was positively what they wanted

 

I “simply” want to know where the centerline of the tire is from the axle flange. Not much to ask for.

 

Got to love those 90 gallon rolling trash bins. Perfect for painting parts on

 

Then what you are wanting to know is the offset.......
You need to do this. It will work whether tires are on the wheels or not.
Lay the wheel on a flat floor, outside of the wheel to the bottom.
Lay a long straight edge on the inside edge of the rim across the middle (or the inside of the tire if mounted).
Measure from the straight edge to the floor. Divide by 2 to get the center line.
Measure from the straight edge to the wheel mounting surface.
I'm sure you can take it from there.......

 

Correct me if I’m wrong. Isn’t that in the title of this thread?

 

Yes it is, but you don't seem to know exactly how to measure it or define it.
It really isn't that hard.... although there seems to be a lot of people that don't understand it.
Some of the info here is way off the mark and just downright confusing.

 

In today’s Cragar SS offerings. It’s as follows for 15 8’s.

4” back space @ 13mm negative offset
4 1/4” back space @ 6mm negative offset (match’s your catalog)
4 3/4” back space @ 6mm positive offset

All of which are non reverse wheels and a compilation of both direct fit and uni-lug.

 

Inches X 25.4 = millimeters. Therefore millimeters / 25.4 = inches.

Liters x 61 = cubic inches. Therefore cubic inches / 61 = liters.

You might want to use the calculator on your desktop, laptop or cell phone, but you don't need an internet connection.