Proper offset for an 18x10 wheel

[Kevin369]

Can someone tell me what the proper offset is for an 18" x 10" wheel? I'm wondering if that will fit on my '99 Boxster and what the offset should be.

TIA

[HenryV]

You mean original 996 rear wheels? Or aftermarket?

Check the offset on the 18x10 wheels. Most rear wheels that are fitted for the 996 need about 14-25mm spacers to make them fit the boxster. I believe about 20mm should make it work on most Porsche OEM 996 18x10s. There is a little bit of play with camber/toe on the outside and you can get an add-on to pull the brakeline inwards, away from the rim to maximize the space.

(Front wheels 986/996 have similar fit - they should simply bolt on)

[ar38070]

You need an ET of about 40. I believe a 996 18x10 has an ET of 63 which is why you need a 20mm spacer. You could probably go as high as 50.

[hayaku]

You need an ET of about 40.  I believe a 996 18x10  has an ET of 63 which is why you need a 20mm spacer.  You could probably go as high as 50.

<{POST_SNAPBACK}>

18x10 996/993 turbo-look rims have a 65mm offset. the calipers clear fine, its the shock that needs the spacer...

if a 986 requires a 20mm spacer to wear the 18x10 turbo-look rim from a 996, then you need an offset of 45...

[HenryV]

From the Christophorus 310 issue (10/11 2004), page 63:

986 18" Carrera wheel: 9Jx18 - ET 52

996 (I) 18" Carrera wheel: 10Jx18 - ET 65

but

996 (II) 18" Turbo look II wheel: 10Jx18 - ET 47

(but - doublecheck the Christophorus numbers - last time they recalled them)

The 10J is 1" wider than the 9J, so it adds 1/2" to the offset (12.7mm)

Check the ET on your 10Jx18 wheel as well as the ET on your 986 9Jx18 wheel.

If your 986 ET is 52, I suggest you subtract (52-12=) 40 from that number:

e.g. ET 65 -> 25mm spacer (I)

and ET 60 -> 20mm spacer

and ET 55 -> 15mm spacer

and ET 47 -> 7mm spacer (II)

and so on.

You can be off by +/- 5mm for most fits, they will still fit fine.

If you want to make absolutely sure, get underneath your car and measure the shortest distance (plane to plane) from the wheel well to the outside tire/rim, and from the strut/shock and brakeline to the inside tire/rim. If both numbers are identical, you have the tire mounted dead center. If one of them is off, you can adjust the spacer by half that amount (if outside is larger than inside, you add, otherwise you subtract).

Be aware that the tire under heavy load (aggressive cornering) will tip inwards

Edited November 1, 2004 by HenryV

[ar38070]

One last note.

If you have not realized there is a range of acceptable offsets. If the offset is too high the inside of the wheel/tire will hit the strut (very bad). If it is too low then the outside of the tire will hit the wheel well.

Lower ET's will increase the track width of the car which can help with the handling. Also some people like the look of the car where the tires are even with the outside edge of the wheel wells. (The boxster 550 edition is like this as it comes from the factory with 5mm wheel spacers.)

Also the acceptable range of ET's will be less if you car has been lowered.

[Kevin369]

One last note.

If you have not realized there is a range of acceptable offsets.  If the offset is too high the inside of the wheel/tire will hit the strut (very bad).  If it is too low then the outside of the tire will hit the wheel well. 

Lower ET's will increase the track width of the car which can help with the handling.  Also some people like the look of the car where the tires are even with the outside edge of the wheel wells.  (The boxster 550 edition is like this as it comes from the factory with 5mm wheel spacers.)

Also the acceptable range of ET's will be less if you car has been lowered.

<{POST_SNAPBACK}>

Thanks for the feedback guys! I appreciate it. I test fitted an 18x10 on the rear of my stock '99 and the wheel will clear. There is not much space between the inside rim on the wheel and the shock body but there is clearance. It's close but clear.

[KevinC]

I believe that 18x10" wheels made for 993's (or 993 Turbo's?) have the proper offset to work on a Boxster.

[scherb]

z

Edited April 26, 2005 by scherb