offset vs backspacing...I KNOW A DEAD HORSE

[DrtyJack75]

ok Im talking to the tire guy and he says..

20x8.5 with a 14 offset is just a hair over 5.25
and
22x10 with a 1 offset is just a hair over 5.5

Make sense OR did I completely not understand what the heck he said?!?!? Im trying to get a 5.25 in front and a 5.5 BS in back.

Thanks!


I think Foose Legends are going on my baby soon....

[72BlckButy]

What year rearend do you have?

I'm running a the following on a stock '69 rear end and a disc brake/drop spindle upgrade:

Billet Specialties Vintec's
Front: 20x8.5" w/ 5.5" BS
- Center Bore: 3.430
- Bolt Pattern: 6 on 5.5"
Rear: 20x10" w/ 4.75" BS
- Center Bore: 4.250 (due to the center hub on the rear axle of my '69 [meas. 3.5"; BS only offered 3.43])
- Bolt Pattern: 6 on 5.5"

Toyo Proxes S/T ii's
Front: 255/40-20
Rear: 295/40-20

If I had chose to run bags, I would have increased the front BS to 5.75", and changed my rear to probably a 5.5" to account for getting the wheel higher in the wheelwell when aired out. 4.75" in the rear will work on bags but will require the rear inner fender mod found here.

[72BlckButy]

According to http://www.convertunits.com/from/mm/to/in

14mm = 0.5511811023628 in

I think you failed to post the rear BS measurement.

mm inches inches mm inches inches
1 - 0.04 0.63/16 26 - 1.02 1 0.38/16
2 - 0.08 1.26/16 27 - 1.06 1 1.01/16
3 - 0.12 1.89/16 28 - 1.10 1 1.64/16
4 - 0.16 2.52/16 29 - 1.14 1 2.27/16
5 - 0.20 3.15/16 30 - 1.18 1 2.90/16
6 - 0.24 3.78/16 31 - 1.22 1 3.53/16
7 - 0.28 4.41/16 32 - 1.26 1 4.16/16
8 - 0.31 5.04/16 33 - 1.30 1 4.79/16
9 - 0.35 5.67/16 34 - 1.34 1 5.42/16
10 - 0.39 6.30/16 35 - 1.38 1 6.05/16
11 - 0.43 6.93/16 36 - 1.42 1 6.68/16
12 - 0.47 7.56/16 37 - 1.46 1 7.31/16
13 - 0.51 8.19/16 38 - 1.50 1 7.94/16
14 - 0.55 8.82/16 39 - 1.54 1 8.57/16
15 - 0.59 9.45/16 40 - 1.57 1 9.20/16
16 - 0.63 10.08/16 41 - 1.61 1 9.83/16
17 - 0.67 10.71/16 42 - 1.65 1 10.46/16
18 - 0.71 11.34/16 43 - 1.69 1 11.09/16
19 - 0.75 11.97/16 44 - 1.73 1 11.72/16
20 - 0.79 12.60/16 45 - 1.77 1 12.35/16
21 - 0.83 13.23/16 46 - 1.81 1 12.98/16
22 - 0.87 13.86/16 47 - 1.85 1 13.61/16
23 - 0.91 14.49/16 48 - 1.89 1 14.24/16
24 - 0.94 15.12/16 49 - 1.93 1 14.87/16
25 - 0.98 15.75/16 50 - 1.97 1 15.50/16

[lolife99]

Here's a good offset chart that I use,...

[72BlckButy]

Right-click and save.

[DrtyJack75]

Originally Posted by lolife99

Here's a good offset chart that I use,...

So what he said makes sense...

I have a PB DM and trailing arm kit with what I think is a 67 rear end!

Thanks for the info guys....just wanted to run it by a 3rd party (alotta 3rd parties) before ordering!
Posted via Mobile Device

[BadaSs_Cal]

ok now im confused... :P

BS is how much room there is from the back flange to where the mounting surface is inside of the rim... check. (i.e 5 or 5.5 back space)

Offset is how the rim centerline is in regards to the whole rim right? has nothing to do with backspacing, just how dished the rim looks from outside?

Maybe I just got it all wrong..lol

Now for my stupid question...

(i.e. 5 or 5.5 in backspace) thats in inches?

I think Im just gonna find someone on the site that has 6x5.5 wheels... has drum brakes.. has a stance that I like.. then get the same exact thing he did.. that might be easier...

[LONGHAIR]

Originally Posted by BadaSs_Cal

Now for my stupid question...

(i.e. 5 or 5.5 in backspace) thats in inches?

Yes, backspace is measured in inches, but for whatever goofy reason, these charts are refering to the off-set in millimeters?
Why? I have no idea.....seems stupid to me.
Most people in the U.S. do not use metric measurments with enough frequency to deal with it. So you use one chart to get a number, then another chart to convert that mm to inch.


Think of the difference like this.
BS does not change with with wheel width, it is a constant.
An 8" wheel with 4.5" BS will look exactly the same as a 10" when viewed from the back, the "addition" is all out the front.

Now, if you have a an 8" wheel with zero off-set and another that is 10" wide with the same zero off-set, you will see the difference on both sides. It will be 1" wider on each side.

[BOZO]

Next time somebody throws some of them millimeters at you, just whup out the old cellphone, punch up the calculator, and divide by 25.4. You'll get your answer in good old complicated American inches. Also, some calculators nowadays have a unit conversion built in.

[lolife99]

Originally Posted by LONGHAIR

Yes, backspace is measured in inches, but for whatever goofy reason, these charts are refering to the off-set in millimeters? Why? I have no idea.....seems stupid to me.
Most people in the U.S. do not use metric measurments with enough frequency to deal with it. So you use one chart to get a number, then another chart to convert that mm to inch.


Think of the difference like this.
BS does not change with with wheel width, it is a constant.
An 8" wheel with 4.5" BS will look exactly the same as a 10" when viewed from the back, the "addition" is all out the front.

Now, if you have a an 8" wheel with zero off-set and another that is 10" wide with the same zero off-set, you will see the difference on both sides. It will be 1" wider on each side.

That's why I like that offset chart that I post above.
The red numbers at the top,... are the "backspace" numbers in inches.

Like you posted,... backspace numbers are real numbers.

Offset numbers mean nothing,... unless you know the rim width.
example: a 14mm offset on a 8" wide wheel is totally different than a 14mm offset on a 10" wide wheel.

[lolife99]

DrtyJack75,... your truck is BADA$$!

[BadaSs_Cal]

Originally Posted by LONGHAIR

Yes, backspace is measured in inches, but for whatever goofy reason, these charts are refering to the off-set in millimeters?
Why? I have no idea.....seems stupid to me.
Most people in the U.S. do not use metric measurments with enough frequency to deal with it. So you use one chart to get a number, then another chart to convert that mm to inch.


Think of the difference like this.
BS does not change with with wheel width, it is a constant.
An 8" wheel with 4.5" BS will look exactly the same as a 10" when viewed from the back, the "addition" is all out the front.

Now, if you have a an 8" wheel with zero off-set and another that is 10" wide with the same zero off-set, you will see the difference on both sides. It will be 1" wider on each side.

I keep reading it waiting for something to click, but nada.. HAHA

Does that mean I should just find wheels that have No offset as opposed to ZERO offset?
Im going to keep reading your post and that Diagram until I get it.

later:

GOT IT!!! Now what you were saying makes sense.. You just thought you were telling someone with a brain..lol

Here are some crib notes for figuring out backspace, centerline, and offset.
* Step 1: Measure the room in your wheel wells relative to the wheel hub.
* Step 2: Backspace = The distance from back of the wheel to the wheel's mounting space, in inches.
* Step 3: Centerline = The wheel width divided by 2, in inches.
* Step 4: Offset = Backspace - Centerline, which will be positive or negative, in inches.
* Step 5: Offset in Millimeters = Offset x 25.4.]

from:
http://www.truckinweb.com/tech/suspe...equations.html

[lolife99]

http://www.tirerack.com/wheels/tech/...jsp?techid=101

[Mike Bradbury]

Originally Posted by BadaSs_Cal

Here are some crib notes for figuring out backspace, centerline, and offset.
* Step 1: Measure the room in your wheel wells relative to the wheel hub.
* Step 2: Backspace = The distance from back of the wheel to the wheel's mounting space, in inches.
* Step 3: Centerline = The wheel width divided by 2, in inches.
* Step 4: Offset = Backspace - Centerline, which will be positive or negative, in inches.
* Step 5: Offset in Millimeters = Offset x 25.4.]

from:
http://www.truckinweb.com/tech/suspe...equations.html

Your getting it but #4 you wrote that "Offset = backspace" which is not accurate and might tend to confuse you more if you think of it that way.
Offset is Offset, and Back space is Back space.