BHCfarkas

Backspace, absolutely. Pad height is a little harder.

Just like any equation, you can solve for any missing number by working backwards or solving for the missing measurement.

So let's say the only information you have about a wheel is that it's a 10j wide wheel with an offset of ET +55 (these are typically the only measurements we're giving when a wheel is sold.). This is all I had to go by when you listed your wheels a page back and I had to find the backspace myself before I could figure out what size barrels and lips you could resize to, to tell you if your work was correct or not. I didn't have either your backspace measurement nor your pad height.

So, we have the width and we have the offset. No idea what the pad height is or the backspace. I like simply plugging in numbers until I can come up with the missing part of our equations:

18x10 ET 55 - let's play with numbers:

First guess: 6" backspace. Let's see if it comes out to ET 55
11 / 2 = 5.5
6 - 5.5 = .5
.5 x 25.4 = ET 12.7 - way off

Second guess: 7.5" backspace.
11 / 2 = 5.5
7.5 - 5.5 = 2
2 x 25.4 = ET 50.8 - really close, but not quite. just need a little more!

Third guess: 7.625" which is 7 5/8ths inch
11/2 = 5.5
7.625 - 5.5 = 2.125
2.125 x 25.4 = ET 53.97 - Bingo! about as close as we're going to get(within 1mm)

So, by plugging in backspace numbers, I was able to find from your ET of 55 your measured backspace should be about 7.625 inches.

Now, the ONLY way I see that we can possibly find pad height is by knowing barrel width. If we don't know barrel width, there's not enough information for anyone to find it. You could have multiple barrel widths and pad heights and still come up with the backspace we found.

Since you indicated the barrel was 8J, that made it much easier for me, so:
Barrel Width - Backspace = Pad height
8J - 7.625 = .375
.375 x 25.4 = ~9.5mm, correct?

BHCfarkas

You nailed it buddy, great job!

Fronts with 1.5" lip would not fit, but the rears with the 2" lip will work with a little camber! As of right now, without touching them, they will for sure work.

I'll share a cheat with everyone:

There are 25.4mm in one inch, right?
Divide that by two we get 12.7, that's a half inch
Divide that by four we get 6.35, that's a quarter inch
Divide that by eight we get 3.175, that's an eighth inch.

So in your example you wanted to change out a 1" lip for a 1.5" lip. The half inch difference is roughly 12.7mm

If you take the offset, which was 44 and subtract 12.7 you get 31.3... basically what you estimated with your calculation

I didn't want to share this right away because it can be confusing if you're not careful when making lips bigger or smaller, or barrels bigger or smaller. You have to understand how those changes affect the offset before you can cheat! It's safest just to do all the math the long way to be sure.

BHCfarkas

Just to keep this thread on topic:

964Lovac

Love the gold centers... lookin' good!

mfinanthony

What is the going rate for BBS RS nowadays?

Rey Gunn

Looks like the part # is 0228231 all the way around. Different from Franks. Since they're different, does that mean I have the wrong centers? The four digits on the wheels differ. 2 have 3103, 2803, and 3703.

Ok Thanks BHCfarkas. I guess it will save money in the end not having to change out the front barrels and just do the refinishing. Rears I will change out to 2" lips.

Rey

Undutched

I have a narrow body 964 and wanted to know if the rears can fit 18x11 ET40. I do not mind working the fenders a bit.
Reason is I'm looking at 2 sets of BBS wheels, both magensium.
The 18x11 ET40 are about a grand cheaper.

One is a RE-Mg and the other look like LM, but are magnesium.

ThomasC2

Not "wrong" in the sense "doesn't fit". But they are probably made for another model/car with an matching offset for that set up. But with other inner/outer rims they can fit your car.

The four digits mean that they are built during week 31, 28 and 37 year 2003.

Thomas

robt964

As much as I adore the look of the BBS wheels, unless you get very lucky with a good 2nd hand set, they're a serious investment.

I was discussing this else where when I was provided a link to a UK manufacturer called Image Wheels. No association etc but they do look pretty good and proper billet aluminum light/strong too.

LM ?



E28 ?



Cost wise it appears to be approx £484 for an 18x8 and £535 for an 18x9.5 (ex vat I assume)
You can even have them in 17s if you fancy it!

All custom made to your dimensions. You also get the choice of having the wheel centres front mounted or sandwiched (sandwiched for me - gives a greater dish appearence) I know its not the real mccoy BUT for the price and weight advantages I'm giving this some serious thought.

Image Wheels

BLACK-BETTY

Yup image look good - in fact I believe they manufacture the Fuch wheels which are seen on Paul Stephen's back dates.

However.... That's still expensive! I bought my E28s for the same price as those you quote (assuming VAT needs to be added) and the Cargraphics for much less...

Just keep an ear to the ground and wait, second hand sets do pop up...

That being said Image do a wheel design that's similar to HREs 454s....

Keep us posted with what you do. Sure lots of interest would be had if you went with a set of custom image wheels.

jotaking

Deeeeep Dish!!

Rey Gunn

Ok thanks for the info Thomas. having my wheels built by Brian over at Rotiform. So I'm sure they'll turn out great and will fit perfectly.

911Thrasher

Soi ordered the E88 gold from BBS in Germany a little over a month ago for my 964RS, so shouldnt be much longer now (2/3 weeks at most i would think).

Which tyres should i go for? and what size?
Michelin Cups? I use to run them on my 997.1GT3RS and thought they were quite good.

The BBS will come in 18" x 8J (52) and 18" x 9.5J (47)

KarlSpackler

Love me some BBS split wheels

BLACK-BETTY

Shame you didn't go with a wider set. Anyway 8J will take a 215 or 225 and 9.5J will take a 255 or 265. Tyres, obviously depends on your use. Why don't you do a little search - surprising but there's lots of info here.