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Discussion Starter · #1 ·
Hi gang,

As winter and snow tire season is upon us, I figured I'd do one quick double check (measure twice, cut once).

I know I asked some of these questions a long way back -- but I'm trying to see if my calculations are correct per my 987.2 2010 Boxster and ordering the correct wheel spacers for the rears. I think I figured it out, but it can't hurt to throw it out there before ordering.

In short, I'd like to reuse my former 987.1 winter tire rims. These are 235/40/18 square, ET 54, 8Jx18. They worked great in the snow many years ago, but I don't remember the rear spacer size that was originally on there that came with the car (likely 5mm or 10mm). A narrower rear is great in the winter, as it allows for greater downforce and traction on the snow.

Doing the math, to keep the outer rim positioned at essentially the same location as the summer OEM 265/40 18, ET43, 9Jx18, it appears that 20mm spacers would do the trick. Below is the diagram from the online calculator.

What do you guys think?

This seems to at least keep the wheel appearance per position visually close to stock (so the wheel wouldn't look sunken in and wouldn't potentially rub against anything). But would this significantly stress the suspension and mess up the handling by pushing things wider?

I could instead get something like 10mm spacers, which would center the weight distribution right exactly where the OEMs were and yet would still prevent rubbing. I'm guessing it won't make any major difference, but figured I'd ask here as I'm certainly no wheel expert.

Finally, as a weird bonus, the car strangely came with a single ECS 20mm wheel spacer with long bolts (per the aftermarket rims and tires, that I've since sold on) -- so I could save some cash and just order just a single
wheel spacer with 5x bolts -- assuming 20mm would suffice.

Thanks, everyone!


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Discussion Starter · #3 ·
Thanks, @Apex1 - I'm not going to lie, but I'm still not educated per camber and track setups (yet!). My guess is that pe the above diagram, this would keep the rear rim faces positioned closest to where they sit per OEM rims (not even flush).

It's just that it would appear to push the center of gravity on each tire just slightly wider (maybe 9mm further out), as these are 235s and not 265s on the rear and the rims drop from 9" to 8". I'm guessing this would be a negligible difference in terms of performance and wear on the bearings, etc.?

Finally, I'm not even sure how to clear the test for what you suggested:

You just do not want your tire shoulders hitting the upper fender lips under compression.
Any thoughts, I'm all ears. I'm guessing if they're positioned as above and the tires are the same height, I'm guessing it shouldn't be an issue?
 

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Discussion Starter · #5 ·
Oh wow -- you've got a beauty there and your wheels look fantastic.

To clarify, are you saying that we're both at 34mm (which I'm guessing is the stock ride height)? Or is this just the case in your situation? Just trying to figure out what I'd need to do.
 

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Discussion Starter · #12 ·
Thank you, @Kevin CS -- That's a huge help, especially given that returning a wheel spacer isn't an option. I generally like to "use what I already have" first, especially if it's invisible to the naked eye...and I have a perfectly good 20mm sitting here.

This has been a question that has bugged me since I got the car, and I really appreciate your taking the time to answer -- as nobody has seemed to be able to weigh in much about the effects of slightly shifting the center of mass.

Cheers and thanks!
 
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