Hub Centre Bore and wheel hub size

[bteoh]

Hi,
Just wanted some info on centre bore hub and wheel hub size. I am in the process of getting some wheel spacers made up for my Alfetta GTV (4 x 98 PCD) and GTV6 (5 x 98 PCD). The later front wheel drive Alfas have a centre bore size of 58.1mm whilst the older rear wheel drive ones have a centre bore of 58.6mm. So they have a difference of about 0.5mm but that is enough not to make the spacers fit (Found out the hard way after ordering them). However, if I put the original wheels (With bore size of 58.6mm plus onto a centre bore hub of 58.1mm , is there a safety issue? Obviously it is easier to get more diverse wheels with a 58.1mm wheel bore. The engineering place is still waiting for me to specify what centre bore size I want on the wheel spacer. If using original wheels, I should go for 58.6mm. But if I am going to fit later GTV or 156 wheels, then I need to go for 58.1mm. Would a difference of 0.5mm represent a huge safety risk?
Cars are mainly street use and not for track or racing.
Thanks for any info.

[aggie57]

You should not rely on the wheel bolts / nuts to centre the wheel; the hub spigot is designed to do that.  All a wheel bolt / nut is intended and designed to do is apply clamping force between the face of the wheel and the face of the hub.  Once clamped the wheel-hub assembly works as one unit and carries the vertical load.

So yes, you need to match the wheel bore to the hub spigot.  If there is a gap, well that's what spigot rings are for.  And many spigot rings are plastic because unlike wives tales they do not carry a burden.

In summary:

- spigots to centre
- wheel bolts / nuts to clamp. 

[aggie57]

Here's one plain English explanation:

http://machinedesign.com/fasteners/what-s-difference-between-lug-centric-and-hub-centric-wheels

[bteoh]

Thanks Alistair,
I shall specify as per original with spacer having a hub centre of 58.6mm. Can anyone confirm that is the correct size hub on an Alfetta GTV / 6 ? Should be the same on Alfa 75's too?
🍻