BLACK-BETTY

EDIT:
Ok I clearly made a mistake....


Here is where I'm at - BHCfarkas, am I on the money?

BHCfarkas

It appears you are on the money this time, sir! Great work

I also came up with the same combination of an outer lip of 3" and inner barrel of 7", which would put you roughly around ET+29. Granted, I worked backwards and estimated your backspace from the initial ET of +55 from your current setup.

BLACK-BETTY

Cheers mate,

But how come I get an ET of 32 then?!

Was really hoping for an outer lip of 4inch plus!

BHCfarkas

My +29 could be the difference of my estimation of your backspace working backwards, which isn't always 100% accurate, but very close! Also, there is a slight margin of error converting from standard and metric and the rounding.

Unfortunately, I'm not sure 4" of lip would be possible without mega camber or wide body. We don't call them narrow bodies for nothin' lol. We're simply limited by the design of the body and car and there's only so much room between the hub and fender for wide lips!

Anyhow, I'm glad you understand the calculations now and it will be proven invaluable to you... the least you could do is take me for a spin in that pretty 355 of yours lol

BLACK-BETTY

Well next time you're in London. The London 964 bunch are a great bunch.

Ok I have applied some man maths and I think I may have some simple equations to solve all the problems.

• Backspace = Inner barrel - Center dish Width
• Center Dish Width = Inner barrel - Back space
• Offset = ((wheel width ÷ 2) - Outer lip = Ans.) - Center dish width.

Let me know your thoughts.

STUARTQ

farkas, if you do ever come to London, I hope you look just like you avatar, otherwise we will be disappointed!

BLACK-BETTY

Some more BBS pictures to keep the ball rolling

Featuring: BBS - E88, E28, LM, RS

BHCfarkas

Frank, great diagram for everyone to see, and your equations are correct with the exception of your backspace equation.

You are using the front space to determine offset, rather than backspace, which is the direct measurement we take. It's easier to eliminate any extra measurements all together when you simply need two: Wheel Width(end to end) and Backspace.

To come up with an equation for offset in simplest form, I would set it up like this:

Offset = Backspace - (Wheel Width / 2)

Here's a good image I found online that shows the imaginary line you make through a wheel when you find the center line when you divide the wheel width in two. The offset is the space, positive or negative , in reference to that center line.


Without even disassembling the wheel you can still come up with that mounting pad height(center dish in your diagram) by simply taking the measurement of width of the inner barrel minus backspace.

Mounting Pad height = Inner Barrel - Backspace

For example:

Say we had a wheel of 10 inches wide bead to bead. Outer lip is 2" and inner barrel is 8". Backspace is 7". This means the mounting pad height(center dish) is 1".

Following me? Basically everything revolves around the measurement of backspace and wheel width. You can figure just about any dimension based off of those numbers.

I promise that's really me in the avatar, however, I won't be in my nerd costume. It is all too fitting though, right?

Rey Gunn

Ok. Did the measurements on my wheels.
Fronts: 9.5/2 = 4.75
6.5 (backspace) - 4.75 = 1.75
1.75 x 25.4 = 44.45 ET

Rears: 11/2 = 5.5
7.5 (backspace) - 5.5 = 2.00
2.00 x 25.4 = 50.8

So based on these measurements. The wheels should fit with minor adjustments! With the fronts, would it be possible to put a wider lip and still have it fit? If I did my calculations correct, a switch to a 1.5 lip from a 1.0 lip would give me a ET of 31.75. [(6.0 - 4.75) x 25.4]

On the rears, a switch to a 2.0 lip from a 1.5 lip would give me a ET of 38.10 [(7.0 - 5.5) x 25.4]. In my mind, the front wouldn't work, but the rear would? Am I correct in this estimation?

Another concern is with the centers deep lug nut holes. If you notice on my set, the lug nut holes are much deeper than those that I've seen in pics on this thread. Is that going to be a problem? I haven't seen any 964s with E28s with these deep a hole for the lug nuts. Thoughts? Thanks in advance for any input.

ThomasC2

I see the part number at 12 o'clock in the last pic. What does it say?

And can you also tell what the four digits at 2 o'clock say? The will give you the manufacturing date (week and year)

Thomas

BLACK-BETTY

Looks the same as mine Rey...

My numbers,
0226040
8&2 = 10J ET55

0228041
7.5&1 = 8J ET55

orp73

Hi Frank, any idea if BBS did/do make similar wheels as a centre lock fitment?

sorry yes they do

http://www.ebay.co.uk/itm/Genu-BBS-E...-/221399937830

BLACK-BETTY

I suppose my question is this then,

Can the backspace and mounting pad height be calculated if you have neither of these numbers but all the rest?

My point being that often we have the barrel lengths and offset but are missing the pad height and backspace numbers...

Forgive me if we're going round in circles. The idea is to be able to calculate all the numbers without having to even measure a wheel.

Here is my example,
How do I get my missing numbers and what would be the equation?

Backspace = Inner Barrel - Mounting Pad Height (assuming in this instance we know the mounting pad height)?

ThomasC2

Frank, I guess you mean 0228 and not 0226 for the rears. Your numbers says you have the centres made for 964RSR and then used for 993. They are same as I have.

Alls BBS motorsport rims are made for centre lock, afterwards they are drilled for log nuts depending on bolt pattern. This is why the edges around the holes are so sharp.

Thomas

BLACK-BETTY

Quite probable - I'm reading the number via a picture, harder to tell.