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How to calculate the right spacer size?

Discussion in 'Wheels & Tires' started by Vikas76arya, Mar 19, 2017.

    • Member

    Vikas76arya

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    I have a 2012 e92 M3 with Competition Package and I am planning to run a Apex 19x10 wheels all the way around but only at the track. The Apex wheels have 25mm offset which is the same as my ZCP rear wheels but my front stock wheels are 31mm offset.

    What size spacer do I need to make the Apex wheels work on my car for track application?

    Thanks.
    • Member

    MGarrison

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    I think apex has a good knowledge base as to what fits and clears, easiest thing is probably just call them. BMW these days fits narrower wheels on the front (stock) to make the cars inherently understeer. Run a square setup, same wheel diameter, width, & offset on all four corners of the car, and you take out some of the understeer bias, and you can also swap wheels around to even out wear, which is certainly handy for maximizing your tire life at track weekends. Reducing understeer will make for more balanced handling, although the risk is having an oversteer skid happening more quickly and unexpectedly vs. the stock setup. Most experienced drivers on a racetrack find too much understeer to be less-than-desirable.

    If you're running stock front wheels, realoem.com says comp. pkg. front wheels (31mm offset) are 19x9. Your offset difference is because of the narrower front wheels. You could use spacers to make the stock fronts match the rear offset number, but it doesn't work the other way around. Making the apex 25mm offset 10x19's be 31mm offset would mean shaving width from the mounting side of the wheel hub, or, impossibly, moving the wheel hub outboard towards the outer wheel edge/lip. Apex can confirm fitment, but I doubt they'd need spacers, I think much of the point with apex wheels is fitment without the nuisance of spacers.

    Separate track wheels are not a bad idea, but the stock setup is fine when beginning - if you're just starting with track days, do yourself a favor and skip the full r-comps for something like some max-performance summers, you'll learn more, more quickly.
    • Member

    Vikas76arya

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    Thank you for the input, this is very helpful. Your suggestion to call Apex is the most logical, given that they should know the best way to support their product.

    In reading many opinions on the topic of square vs. staggered, I came to the conclusion that a square setup significantly reduced understeer in the e46 M3 but not so much in the e92 M3. At this moment, I have no practical experience to confirm whether this is true but having completed several track days last year with the BMW stock setup, I will be able to draw comparisons after a few runs in the coming months. I did not find a lot of options for track tires in the size I wanted (275/35/19) so I ended up buying TOYO PROXES R888 in 265/35ZR-19.

    I'm really looking forward to the experience of driving a dedicated track tire and comparing them to the performance of my Michelin Pilot Super Sports. After seeing the wear that they incurred after just 4 sessions at Summit Point, I realized it would be more cost effective to save those tires for the 70 miles I driver per week and purchase wheels and tires dedicated to the 8 or so track events I'm planning to do every year.
    MGarrison likes this.
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    MGarrison

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    Yep, if you're going to be at the track that frequently, & with some experience under your belt, that's a good plan. Have fun @ the track once the season gets rollin' here!
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    slewis245

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    I'm in same boat. I am saving my pilot ss for summer and put on ps 3 for winter. cheaper than new wheels/tires. considering its my third track at VIR 3/31/18.
    • Member

    CSBM5

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    I'm sure you've found by now that the ET25 10" width wheel works fine all around on the E9x M3 with the proper tire size. I have a set of Apex 10x18 ET25 with RE-71R 275/35-18 tires I use for autocross with no issues/plenty of clearance. In 19" diameter, you'll need to not run anything larger in diameter, up front, than a 255/35-19 or 285/30-19 due to fender well rubbing against the face of the tire. Pay attention to the diameter first as there is plenty of "width room" -- you need to stay at/under 26.0" diameter.

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