Spacers: General Info
>>I have a set of 21mm rear wheel spacers but before I install, can someone
>>tell me if the standard studs will work with these. Don't want a wheel to
>>find it's freedom while travelling at speed.
>>Thanks, John McDermott
>>1982 928 AT
Nope, they won't work, assuming that you have the 50 mm studs now. With
the spacers, you need 72 mm studs. Sorry.
'84 928 S
There are two kinds of spacers. One is just a slotted plate that fits over the studs. Porsche uses a 17mm spacer which they correctly call a "washer" on Club Sport and GT from 1987. They also use longer studs to ensure adequate threads. There are several sources of hub-centric spacers in varying widths from 15mm up to 2.0" but these come with lugs also.
On my 1982, I recently upgraded my rear rims to S4 8" slotted rims for appearance and so I could use a wider tire. I measured the remaining threads and using the standard suggested here of 9 threads, calculated I could safely use a 5mm or .25" washer. These can be bought for around $6.
However, wanting a little more offset, I ordered and received 15mm spacers from Troutman. These center on the hub. In fact it was a very tight preset that will probably be very difficult to remove should the need arise. The 15mm spacers have their own wheel lugs. A quality piece. Now the offset is just right with enough clearance for the tires. I wouldn't do this if I ever intended to mount chains.
For the stock 7" wheels, I would use the 1" spacers from 928 International or others. These would move the wheel and tire out for a wider track and better appearance. If you just want to fill out the space for appearance, this is the way to go. It is a lot less expensive than a wheel and tire upgrade.
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