16 x 9" fuchs backspace?
 

I'm trying to verify the backspacing of the 16 x 9" fuchs part # 911.362.119.

I've seen the backspace for 911.362.118.00 listed as 130mm.

I've also seen the backspace for 911.362.111.09 listed as 138mm

Unfortunetly I don't have access to the wheels, so can't measure for myself. Anyone know for sure what the backspacing is on the .119 wheel? Is it true that there are 2 or even 3 different 16 x 9" fuchs, or is 1 of the 2 measurements listed above incorrect?

Thanks a lot for your help,

Mike

There is only one 16x9 Fuchs, it has an offset of 15.

Agreed, everything that I've read says that the offset is 15mm. Its the backspace that I'm unclear on.

Backspace is 130 mm.

Not sure this helps....but I've been following and sometimes publishing Fuchs offsets and backspaces. Bill Verburg is truly "the guy" on this.

Nonetheless, the published numbers, some from credible sources...sometimes conflict and the numbers can be "off" by 5mm or more. I've come to a conclusion that exactly "where" the measurement is taken may be the key. The wheel rim has a certain material thickness, and it depends on if your focus is where the bead of the tire will end-up resting....or you take into account the outside surface of the wheel rim. There is only one offset/backspace of the 9" Fuchs, as was mentioned....so if that's what you want for your application, there is no additional check you need to make. Offset numbers are more understandable and consistent, as rim thickness doesn't vary much from wheel-to-wheel.

Thanks guys.I'm trying to buy a pair of minilites that will match my fuchs, but don't have access to the car to measure right now. If no-one can say for sure, I'll have to get to the car and dig out my trusty ruler. Thanks again.

Mike

If you measure wrong maybe,

here are the specs

Fuchs 9x16
bead width in 9.0
factory spec ET 15.0
ET calculated using these measurements 15.1, this is an indication of accuracy

Backspace mm 138.11
front space mm 107.95
total width mm 246.06
total width in 9.7, another indicator of accuracy, the flange width of all Fuchs has uniformly been measured @ .35in+/- using .7in as the total flange width the 9.7 agrees w/ the 246.06mm calculated from the measures

There is a school of thought(seems to be isolated to a small area of the Pacific NW) that does not include the flanges in these measure, it is in the minority and inconsistent w/ industry practice and it would be a grave mistake to rely on backspace #s that do not include the flange width. Those that need this # will need to know the total distance that the wheel extends

Wow thanks for the detailed response Bill. I really appreciate it.

Mike

So, Bill V.....to measure backspace or front space, you put a straight edge across either lip (bare wheel, no tire) and drop a tape to the lowest/furthest inside surface?

Also, can we get the definitive definitions?


ET (define the acronym) how to calculate?
Offset?
Backspace, same as offset?

Correct, as shown here, you need to be careful not to bend the horizontal bas and carefully rear the rule avoiding parallax errors
http://forums.pelicanparts.com/uploa...1298748158.jpg

http://members.rennlist.com/1976c38/...AQ-diagram.gif

Sorry, I didn't realize this guy didn't know what he was talking about: 911 Wheel Weights

Bill, you really need to brush up on your personal skills. :rolleyes:

OK....never saw that pic/diagram before. Backspace and offset are NOT the same, backspace and frontspace are not that difficult to measure.....ET on the other hand is a factory spec and not as easy to determine....

ET is a # that is calculated from the measurements, the result is only as good as the measurements
if all measurement is in mm

ET = backspace - .5* overall width

or

ET = .5* overall width - frontspace

In reference to the 16x9.

OK....my brain FINALLY figured out how ET is determined...it is determined by width 246.06/half, minus offset 138.11.

So, (246.06/2) - 138.11 = -15.08, negative offset, rounded off to 15.1....factory called it 15.0.

A number was missing when I was reading which was dividing the width by HALF...I suck at reading technical stuff on a screen. I gotta print it out so that it registers in my pea brain.

I just wasn't reading Bill's post correctly. Thanks for the illustrations....they helped.

You are either reading or typing wrong

the factory measuremants are far more precise than anything we get with a ruler

the ET of a 9" Fuchs is 15, the ET calculated from owner measurements is going to be only as good as the measurements, the closer to 15 the calculated result, the higher the confidence one can have in the measurements themselves

using the formulas I gave above returns the correct sign of the ET as well as it's magnitude.

Bill is correct, Scooter....and accounts for the variations I've seen posted over the years. People keep on re-posting other's published numbers ( I've been guilty to do the same thing when quoting credible people like Jim Pascha and Bruce Anderson....they make mistakes too, and so does the factory).

For ( hopefully) clariity..... ET = Einpress Tieffe in German...or "pressed-in depth", its the difference from the backside mounting "plane" to the actual 1/2 wheel width dimension....or in Englsih terms, "offset", which should be self-explanatory, if we consider this as the variation from 1/2 wheel width. Typically stated for most wheels as "negative" offset, such that the wheel gets "sucked-in" toward the center of the car more... than if the mounting plane was truly at 1/2 wheel width. Poistive offset would go the other way, ...and the wheel would be "pushed-out" toward the outside of the car more, as compared to measured from 1/2 wheel width.

Wheel width/2 + (neg) offset = backspace.

JoeBob ... a mis-cue here in what you say... " OK....my brain FINALLY figured out how ET is determined...it is determined by width 246.06/half, minus offset 138.11.

Should read.... " OK....my brain FINALLY figured out how ET is determined...it is determined by width 246.06/half, minus backspace 138.11. Notice that ET would, in this example....be "negative", as is correct.

Should have used the second calc...(width/2) - frontspace

(246.06/2) - 138.11 = -15.08

(246.06/2) - 107.95 = +15.08

Thanks for the explanation Will. And thanks for being polite about it.

Here is another source (see the chart). It appears he got his information from PET. Can we assume PET is wrong in its calculations? http://forums.pelicanparts.com/porsche-911-technical-forum/324902-fuchs-wheel-all-part-numbers-offset.html

I'm not trying to be argumentative, just trying to make sense of things.

Scooter. ...look at my Rennlist post on the same topic a number of years back. Now that I see it., I notice the 0.35" variability that Bill notes here, and that must be the reason. Perhaps Bill's assessment that only NW coast guys ignore wheel rim thickness may be somewhat incorrect...and maybe other people do this too. If they do, it does us all a dis-service for the reasons Bill stated.

Remember, Fuchs wheels are forged aluminum with a certain resulting rim thickness,.... some other wheels are cast aluminum ( presumably thicker rim material) and steel wheels ( presumably thinner rim matrerial )...all perhaps conspire to make some people simply ignore rim thickness in the calcs....and *hope* you know to add YOUR rim thickness "as measured", at the end of your calcs. If so....this is a dangerous approach and precedent to take and I much prefer Bill's method as it accounts fully for the possible mechanical interference of the rim thickness when using the ruler/straight-edge method.

BTW.....when measuring "front-space"......don't forget.....it's still measured to the "backside" of the wheel where it mounts to the mounting hub of the car...otherwise, here too we must account for material thickness at that point, if erroneously measured to the front-face where it doesn't mount to the car. No one, it seems, would measure this way if they can avoid it anyway.

Here too is my years-ago posting on Rennlist, giving reference sources for the info. At that time I couldn't explain the 0.35" differences, and I say so....now it makes sense---> http://tech.rennlist.com/911/pdf/FuchsSizes.PDF. Scooter...at that time I was also trying to make sense of this and although I got "close".... I could never get it to match with all published sources. Now we have a clue.

the part #s and ET may have come form PET but not the other #s, It was because of things like that that I took the time to collect as many measurements as I could to find out the real specs. Measurement is tough so I also try to take the time to double check and correlate the data for errors, something that some others could profitably do too