Do I have to change my stock studs to use 7mm spacers in ther rear?

[PSportoVeloce]

I found a pair of 7mm spacers in my dad's garage (yeah free stuff!) and was wondering if I can stick them on the rear of my Carrera 3.2 without having to replace the stock wheel studs. The car is wearing 8" fuchs back there. Yes, I tried a search and it seems that it will work but want to ask explicitly to be sure.

TIA,

Derek

[IROC]

A good rule of thumb is to always ensure you have at least one diameter of threads engaged. In other words, if the studs are 14mm in diameter (I think?), then you should have at least 14mm of threads protruding with the spacers installed to ensure adequate thread engagement.

[3.2 CAB]

I believe that I have also seen 1.5x the cross-sectional diameter, for thread depth capture ratio published for safe torquing and anti-shear strength.

[IROC]

Originally Posted by 3.2 CAB

I believe that I have also seen 1.5x the cross-sectional diameter, for thread depth capture ratio published for safe torquing and anti-shear strength.

We used the "one diameter" rule of thumb in the aerospace industry, but I would not argue with 1.5, for sure.

FWIW, I used some cheapo spacers like these (I seem to recall mine being 6mm) and I swapped over to steel lug nuts at the same time just to add a bit of extra strength...

[Steve@Rennsport]

7mm spacers need longer studs to be safe. I would never do otherwise here in the shop.

[Paulporsche]

PP parts catalog states 6 and 6.5mm are the two widest spacers that can be used w/ the original studs. I used 6s on my 6x15" Fuchs for years.

[Superman]

Originally Posted by Steve@Rennsport

7mm spacers need longer studs to be safe. I would never do otherwise here in the shop.

I would never second-guess Steve's experience or judgment, but am surprised by this. When I prepared to install 21mm spacers I noticed the lug nuts did engage the threads of the original, stock studs. Of course, they did not engage enough so I installed longer studs but since they did engage, more than 14mm (21mm - 7mm) of original-stud threads would be engaged when installing 7mm spacers.

Again, always dismiss my input when it does not agree with Steve's. One more thing: Some folks are not impressed with stock, 'alloy' lug nuts. So, I use steel nuts. I don't ever want to see my wheels while I'm driving.

[Fleming]

Derek, check in your tool kit for a steel open top lug nut, or borrow one, put the spacer on and the wheel, tighten up the steel nut and if you have 1 to 1.5 threads standing proud of that nut - it is fine. If the threads are short of the outside of the nut that space plus 1.5 thread will be the measurement for the additional length for your replacement studs.

If the stud and nut are flush it should be ok, but most folks who push there cars (even on the street) like to have a safety zone on such items.
Bob

[PSportoVeloce]

Originally Posted by Fleming

Derek, check in your tool kit for a steel open top lug nut, or borrow one, put the spacer on and the wheel, tighten up the steel nut and if you have 1 to 1.5 threads standing proud of that nut - it is fine. If the threads are short of the outside of the nut that space plus 1.5 thread will be the measurement for the additional length for your replacement studs.

If the stud and nut are flush it should be ok, but most folks who push there cars (even on the street) like to have a safety zone on such items.
Bob

Bob,

Thanks for the suggestion...this is where I am already without spacers though:
Does this mean I need new studs regardless of the spacer size that I use?

[3.2 CAB]

From looking at what you already have, I believe that you would have to install longer studs. Your appear to be just about flush right now, and adding a 7mm spacer behind that would not be something that I would try nor hope anyone else would either. Good luck!! Tony.

[javadog]

There's no question that you need longer studs for the spacers.

JR

[Wil Ferch]

I would generally agree about the 100%+ engagement...but look at the 996 and 997 that use bolts. Same 14 mm size... but "stock", the receiving plate it threads into... is only about 7 mm thick !!!!

So how can you get 100% ???

Answer...you can't.

Which begs the question...why is it then imperitive on our older cars?

[jpkelly3]

Thanks for allowing me to utilize this thread. I have an 82 SC want to put on Cup II's and do know I need 1" on the front and 1.5" on the rears. What size wheel studs do I need for the rear? 67mm 72mm?

Thanks in advance!!

John

[fredmeister]

Here is how the "rule of thumb" works:
Maximum strength thread engagement is based upon the principal that the bolt will break in tension before the threads will shear on the bolt.
Thus if you have a steel stud of 14mm diameter you need 1x for a steel wheel nut of thread length.
2x for an aluminum lug nut (in our case of the expensive black anodized OEM ALUMINUM wheel nuts) because of the difference in material properties of aluminum and steel.
In general the steel lug nuts should have 1-2 threads of the stud sticking out past the end of it for safety. If you don't meet these conditions, get longer studs.

[nameisbauer]

some numbers for those guessing:

I installed 13mm spacers on the front (81 SC) with LONGER 52mm (45mm is stock) studs and steel open end lugs. I only get 1/2 way through the steel lug. About 5-6 threads engaged with about 5 threads until the end (flush)
I installed the 6.5 mm(1/4 inch) spacers in the rear with STOCK 45mm studs and steel open end lugs and get 1/3 the way through, with about 3 threads to the end (flush)

It looks real sketchy so I am going to get longer studs for the front and move the 52mm studs to the back. Hope this helps someone.

[francesconyc]

Originally Posted by nameisbauer

some numbers for those guessing:

I installed 13mm spacers on the front (81 SC) with LONGER 52mm (45mm is stock) studs and steel open end lugs. I only get 1/2 way through the steel lug. About 5-6 threads engaged with about 5 threads until the end (flush)
I installed the 6.5 mm(1/4 inch) spacers in the rear with STOCK 45mm studs and steel open end lugs and get 1/3 the way through, with about 3 threads to the end (flush)

It looks real sketchy so I am going to get longer studs for the front and move the 52mm studs to the back. Hope this helps someone.

I know this is old thread but maybe someone can help me understand.

are you saying that for the 13.5 spacer you can use a 52mm stud?
i bought 14mm spacers that came with 66m studs (71mm full bolt length) and they seem to long in fact...

[Noah930]

No, just the opposite. He said that with a 13.5 mm spacer, 52 mm-long studs were NOT long enough. The open steel lugnut would NOT thread down all the way. Instead of lug protruding out from the center of the lugnut, there was a concavity.