987 Wheels on a 986?

[husker boxster]

Welcome to the world of offset - the amt of in & out a wheel sits on the hub. You need to pay attn to wheel width and offset when replacing OEM Porsche wheels. Thankfully, there are easy ways to figure out if potential wheels will work. The 1st item is knowing what a wheel's width and offset are. On Porsche wheels, they're stamped on the wheel right next to the valve stem. Then you take the current values and the potential wheel values and enter them in this offset calculator.

https://www.1010tires.com/Tools/Wheel-Offset-Calculator

It will tell you how far in or out the new wheels will sit on the hub vs the originals. Wheels that move too far inside may bump into suspension components, while too far out may bump fender lips.

Now to your specific situation...
Factory 986 18" wheels are 7.5" & 50mm Frt, 9" & 52mm Rear
Factory 987 18" wheels are 8" / 57mm F, 9" / 43mm R

You can adjust offsets with spacers. 5 or 10mm are common (my CSS came from the factory w/ 5mm spacers). You will need longer lug bolts if you use spacers. By eyeballing the above figures, the fronts will probably work w/o potential issues. The rears will probably need a 5 or 10mm spacer.

Chances are 911 wheels will not work, unless you want to go wild with massive spacers (the fronts probably would work but rears are too wide). Some forum members have made them work with 15mm spacers, but it's really not a good idea, esp if you want to do track days.

I have seen pics of 986s with 18" Cayman S wheels on them. Don't recall if spacers were required or not, but they will work. Search 'offset' for a lot of educational material.

[BoxMann]

Originally Posted by husker boxster

Welcome to the world of offset - the amt of in & out a wheel sits on the hub. You need to pay attn to wheel width and offset when replacing OEM Porsche wheels. Thankfully, there are easy ways to figure out if potential wheels will work. The 1st item is knowing what a wheel's width and offset are. On Porsche wheels, they're stamped on the wheel right next to the valve stem. Then you take the current values and the potential wheel values and enter them in this offset calculator.

https://www.1010tires.com/Tools/Wheel-Offset-Calculator

It will tell you how far in or out the new wheels will sit on the hub vs the originals. Wheels that move too far inside may bump into suspension components, while too far out may bump fender lips.

Now to your specific situation...
Factory 986 18" wheels are 7.5" & 50mm Frt, 9" & 52mm Rear
Factory 987 18" wheels are 8" / 57mm F, 9" / 43mm R

You can adjust offsets with spacers. 5 or 10mm are common (my CSS came from the factory w/ 5mm spacers). You will need longer lug bolts if you use spacers. By eyeballing the above figures, the fronts will probably work w/o potential issues. The rears will probably need a 5 or 10mm spacer.

Chances are 911 wheels will not work, unless you want to go wild with massive spacers (the fronts probably would work but rears are too wide). Some forum members have made them work with 15mm spacers, but it's really not a good idea, esp if you want to do track days.

I have seen pics of 986s with 18" Cayman S wheels on them. Don't recall if spacers were required or not, but they will work. Search 'offset' for a lot of educational material.

HB,

As usual, an excellent and thorough response and explanation. Thank you, sir.

[husker boxster]

Originally Posted by BoxMann

HB,

As usual, an excellent and thorough response and explanation. Thank you, sir.

You're welcome. It's not rocket science if you know the basics.

I should probably rephrase my comments on 911 wheels. The fronts generally work as the widths and offsets are similar between the 911 & Boxster. The rears aren't generally close. 911 rears can come in 10" and 11" variations. Both have a wild offset (I think 36mm IIRC). The offset is the reason 911 rear wheels are more difficult to use on a Boxster. People are always asking if the 11" rears will work on a Boxster. For a long time the pat answer was no, but a few members have somehow made it work. You just get into lots of hoop jumping to make it work. You're miles ahead by buying the 987 wheels and just slapping them on.

[BoxMann]

Originally Posted by husker boxster

You're welcome. It's not rocket science if you know the basics.

I should probably rephrase my comments on 911 wheels. The fronts generally work as the widths and offsets are similar between the 911 & Boxster. The rears aren't generally close. 911 rears can come in 10" and 11" variations. Both have a wild offset (I think 36mm IIRC). The offset is the reason 911 rear wheels are more difficult to use on a Boxster. People are always asking if the 11" rears will work on a Boxster. For a long time the pat answer was no, but a few members have somehow made it work. You just get into lots of hoop jumping to make it work. You're miles ahead by buying the 987 wheels and just slapping them on.

I understand the concept of offset -- distance from the centerline of the wheel to the mounting face -- just wasn't entirely sure how many mm's variation is tolerable, and how much isn't, and what exactly is done when the variation is too much. Also, don't fully understand how a variation in offset affects handling. Is it just a clearance issue?

Also, I understand that spacers increase offset, but how do you reduce offset if you're confronted with that? Like, the fronts on the 987 are 7mm more offset than current. Also, for example, what if in the 987 vs 986 the numbers on the rear were reversed where OEM was 43 mm and the wheels you wanted to install were 52 mm, or even, let's say, 57 mm?

And thank you for the further explanation on the 911 wheels.