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      04-09-2012, 05:46 AM   #11
Billy_BMW
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Drives: E90 318i LCI
Join Date: Feb 2012
Location: UK

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The reason for 5mm spacers not being safe is due to the fact that the BMW rotor hat (the place where the wheel rests) has a 10mm lip for the wheel to rest on. This lip, in combination with the bolts makes the wheel 100% true and allows the whole system to maintain its strength and integrity. A 10mm spacer or more carries a hubcentric ring which extends the BMW original lip to allow the wheel to rest onto (the circular part above a 10mm spacer). With a 5mm spacer and stock bolts, not only does any spacer below 10mm not have this crucial hubcentric ring, but also using stock bolts can allow the entire wheel to rest essentially on the wheel bolts. Obviously not a safe and desirable solution in the least as the whole weight of the wheel and rotor is being borne by the wheel bolts.