What size wheel spacers

[SilverZed]

When I put rear wheel spacers on my Z3 it really enhanced the look of the car.

It would appear that the Z4 would also benefit from some widening of the rear track. Anyone know what size is best? I have the 108 split rims.

I was going to go for either 15mm or 20mm.

Any advice appreciated.

 

[GazHyde]

I think my suggestion would be either 12mm or 15mm, but wouldn't go any more than that. Supposedly the more you space, the more load you put on the bearings.

Keep looking at mine and thinking I need some spacers on the rear. I have some 15's on my Z3, but I couldn't get them off when I tried so will probably have to buy some more!

 

[SilverZed]

After taking some measurements I have odered 15mm Hubcentrics. I think 20mm may also be OK for wheel arches too but there is a bit of negative camber on the rear so I'm mindful of pushing the bottoms out too far.

Regarding increased load on bearings etc. I think there is a load of flannel posted on most car forums about this. Often posted at length using language from text books suggesting they know what they are talking about. They usually don't. For a start the existing wheel fitment offset is usually never even mentioned! Without knowing this starting offset you cannot draw any conclusions with regard to the impact of a spacer. Most spacer fitments will in fact typically result in a more centralised wheel in relation to hub bearing.

I think talk of increased stress on the bolts is codswallop too. The engineering theory behind this is that in fact it is the frictional resistance between the two contact faces that resists the forces created under driving conditions and not the bolts themselves. The bolts act in a totally different plane to effectively create one structural member from the two faces of the hub and the wheel by holding them together under compression. The bolts are subject to some stress but only that conferred from being under tension at the correct torque setting within their design parameters.

I would not worry at all about fitting up to 25mm spacers. I reckon other things will get your bearings before any effects from spacers will.