Jerry Feather

This did not start out as the month for WRONG, but it sure seems to be ending that way. The wheels used on probably all Porsches are POSITIVE OFFSET. The amounts of positive offset are expressed as ET 65 or similar, but always ET. ET is the abrievation of einpresse tief, and the literal translation of that phrase is "pressed deep." I think that means that the mounting flange is pressed more deeply into the wheel from the back side. Many places online refer to "einpressetiefe" (or as two words) as translated to simply "offset," and I don't think that is correct, but one place I found has it more nearly correct in translating it to "inset." Inset goes with positive offset. It means that the rim is further inset from the mounting flange.

Negative offset wheels are very rare and often referred to as "deep dish." We do not ever see deep dish (negative offset) wheels on a Porsche. I cannot find just how negative offset wheels are or should be marked, but some I have found images that have things like "ET-46" or some other number with the minus sign in front of it. One image I found, of what was said to be a negative offset wheel, was marked IS 23. I have the feeling that that might be the correct way to express negative offset, but I can't find out what "IS" stands for or what it might be abrievating.

dr bob

Fixed, thanks!

Bertrand Daoust

Maybe this image will make everything easier to understand.

Vilhuer

IIRR AT46 where A is some other german language word. In any case xT46 meaning something else than ET.

FredR

Bertrand,

Nice diagram. I have no idea whether we have positive or negative offsets but if I were to make an educated guess I would refer to our wheels as having a positive offset as per your image.

All I have seen is ET65 or ET68. Doubtless ET means something in "Herman the German" lingo and maybe therein lies a clue.

Rgds

Fred

hacker-pschorr

Google:

James Bailey

Yes our wheels have more positive offset than most. Way more than early 911s.
When one tries to fit wider rims than stock it requires more positive offset or you will be moving the outer face and tire toward the fender lip by 1/2 of the amount of the extra width....
It is then made more difficult by the fact that tire width for a given size varies from one brand to another as they measure NOT tread width but widest point on the sidewall bulge and each brand may use what ever width rim they wish to make the measurement. Think about that one for a while

kmascotto

This is a good interactive website with a great calculator
http://www.rimsntires.com/specspro.jsp

FredR

Eric,

Good one- game set and match!

Rgds

Fred

Jerry Feather

Fred, if you are the referee in this, think your "call on the field" is likely to be overturned on review. If the word or phrase in question is only one word it would logically be abbreviated just "E." However, it it shown commonly as ET which suggests that it is the abbrievation for two words, "einpresse tief" and google translates that, as I posted before, as pressed deep or pushed in depth. Given that, I still think that ET might only be the proper abreviation for positive offset and that there is some other abbrievation for negative offset. I think that might be true even though it appears fairly common to express negative offset with ET and a minus sign in front of the applicable number. I think those uses of ET are based on the incorrect translation of the word or two words as simply meaning "offset." I don't think they do. I would expect something for negative offset that translates to "pulled out" or
something similar since I think that the whole concept of offset is in relation to the wheel centerline and not the inner wheel surface. If you start at the centerline you would not be "pressing" or pushing to get negative offset, only positive.

I still wonder what "IS," and now "AT," might be the abrievations for.

Vilhuer

Wheels where center is "more in than out" are rare. They were used in some Opel's in sixties I think but not much after that. Other than in some aftermarket wheels for eighties tuning cars which had really wide rear fenders and deep dishes on wheels. On those tuning cars possibly to comply with German TUV requirements without using spacers.

James Bailey

google chrome reverse wheels to see how odd they look but popular in some automobile cultures ...

FredR

Jerry,

The only thing I referee are sailing contests and not too many of those these days.

I have never seen a wheel on a car that had the mounting flange outboard of the rim centre line and if there was such a thing it would look very oddball indeed thus it would not be a surprise to me if there was no word to describe such an occurrence. Thus if there is such a thing as a vector quantity for ET it would make every sense to call the oddball one a negative value. Like you I might expect such to have a different name rather than a negative value which does not make a whole lot of sense.

Given front wheels with an offset of less than 65mm have no interest to me it is all rather academic but I enjoy being enlightened about such details whatever the origin.

Regards

Fred

Vilhuer

ATS 7051 7.0x15 ET -19 negativ mit 225/50R15
ATS 9051 9.0x15 ET -44 negativ mit 285/40R15

https://www.sat-autosport.de/html/ne...php?news_id=66

whiteNSXs

The subject does not need to be so complicated. The centerline for a given wheel is not a variable. All Porsche wheels have POSITIVE offsets as designated with a POSITIVE ET values. It is understood that the ET numbers are positive unless it specifically has a negative sign. Virtually, all modern road wheels have positive offsets. By saying a "more negative" wheel, it just means a wheel that is LESS POSITIVE and NOT a wheel that actually has a negative offset. I have yet used a negative offset wheel in my life but some old cars do have crazy negative ET wide wheels such as some custom 911 Fuchs wheels with added outer lips and ended up being negative offsets. I believe the older 15x11 wheels are also negative offset wheels.
So one more time. For a given width, say 8", a MORE POSITIVE offset(65mm) will tuck in more towards the body, so the centerline will also be drawn towards the median of the car. With a LESS POSITIVE ET, say 50mm, the wheel will stick outward 15mm more towards the curb as well as the centerline of the wheel. If everyone is clear on this, then we can talk about a related topic, the scrub radius. Please read up on Google before reading on.
As the old 911 up to 1989 had positive scrub radius, the using of a less positive ET wheel (more outward) would be OK. I am using a 16x7 ET 23mm wheel instead of the 16x6 ET 36mm for my 1989 Carrera 3.2. However, starting with the 964, the scrub radius was changed to negative just like the 928. This requires a more POSITIVE ET to make the wheels TUCKed in to maintain the negative scrub radius. The OP's wheels are for a pre-964 911. The offsets are just not POSITIVE enough, or "too negative".
Steve