A quick PSA for anyone that runs wheel spacers for the street or track - this quick test could save you from a LOT of problems in the future, money from repairs, and from possible disaster.
A proper hubcentric spacer slides over the hubcentric lip of the hub, which protrudes approximately 10mm. But the outside diameter of the hub the spacer is covering becomes the same outside diameter that the spacer must have to be hubcentric, so there must be a connector linking the spacer pad to the spacer’s hubcentric snout, which is in the form of a chambered feature. All wheels have a matching chamfer relief, but there is no standard dimension in wheel nor spacer brands for this dimension, and we see it even vary with production runs. And if you are using a spacer with a larger chamfer (typically used to give the spacer more strength) with a wheel that has a minimal chamfer relief, you are at risk of having a failure!
If using a large chamfer spacer with a small chamfer wheel, the wheel will rest against the spacer’s chamfer instead of the spacer pad itself causing the wheel to not be mounted flush. The wheel is never then seated flat on the wheel pad with the wheel studs or bolts providing only a clamping force. Instead, when hitting curbing for example, the hubcentric lip is not loaded as intended, and the load will instead transfer into fasteners, which may result in a premature stud failure. You can see if this spacer to wheel interference has occurred easily by looking for a witness mark along the spacer’s chamfer.
We strongly recommend testing all wheels and spacers you use with what we internally call "the paper test". Once the wheel and spacer are removed from the wheel, place a sheet of standard paper between the spacer face and back of the wheel mating surface and apply pressure. The paper should be captured by the wheel spacer and not able to be pulled out of place. If the spacer “rocks” on the chamfer in the hub then the paper will not be secured and the spacer and wheel have failed the paper test.
If the paper test fails, you should immediately discontinue use of that spacer/wheel combination, and evaluate potential fatigue on your wheel fasteners. When I have been at the track in the past with a small interference, I have used a barrel sander (or even a piece of sandpaper wrapped around a socket) to increase the chamfer relief on a wheel to fit properly - I wouldn't call this the correct solution, but it's gotten me out of a few jams. If you're not as pressed for an immediate solution, a different spacer is a good solution (10mm spacers have the most observed issues because of the more aggressive chamfer required due to the hub's 10mm lip extension - consider moving to a 12mm). If your spacer to wheel interference is excessive, you may have fatigued your wheel fasteners and accelerated replacement may be prudent.
Thank you for reading, and please do share with your track and race friends. The lack of standardized dimensions makes this an issue, but making the paper test a standard part of a fitment test for any new set of wheels or spacers (even if they are the same brand you already own), may save you some headache down the road.
#bimmerworld #safetyfirst #BMW
17 авг 2021
