Correct wheel offset for 986 cars

[Cloudsurfer]

I searched a bit online and on here, and I cant really find a clear answer to this. I'd like to get a set of factory 18x8 and 18x10 hollow spoke turbo wheels for my 02 S. I am told that the 993 turbo wheels fit perfectly without spacers, while 996 wheels require a rear spacer. I am very against the use of spacers (mostly for convenience as I change wheels/ tires frequently and lug bolts are a PITA enough by themselves without gettingi spacers involved in the equation).

986 cars ideally want about 55ET front and 50ET rear, yes?

Any input from those who know would be greatly appreciated.

Patrick

[dcporsche99]

Hi,

I recall when I was contemplating new rims and wheels last summer, from what I have read,...I don't recall if it was on this forum or PCA, but after 9.5, spacers are best to put on. This may be especially true if you have lowered your ride. I, too, didn't want spacers, but not for the reason that you described....anyway, I went w/ staggered rims (re: 8 X18 in the front and 9.5 X 18 for the rear). They haven't caused me any grief yet (knock on wood).

Intererstingly, the Bentley Service Manual 1997-2004, p. 44-1 states that the approved tire combinations for 18 inch wheels are:

Front 7.5 X 18 (ET50) 225/40 ZR18
Rear 9 X 18 (ET52) 265/35 ZR 18

-OR-

Front 9X18 (ET52) 225/40 ZR18
Rear 10X18 (ET 65) 265/35 ZR 18

BTW, I am sure you know this, but our tool kit has an aluminum guide rod (re: threaded wheel centering stud) that you screw into the hub to make for an easier re-install of the wheels. If you don't have one, you might want to invest in one....I know Performance Products (I think that's the company) has them for something like 20 bucks. You may also want to check what our sponsors might have to offer.

Anyway, maybe some of the more knowledgeable guys out there can help out!

Good luck with your decision!

[blinkwatt]

I used to have 993 Turbo wheels on my Boxster. The rears were 18x10 w/ a 45mm offset,they fit perfectly with no problem. That is the biggest wheel size you can fit on a Boxster w/o spacers.

[Cloudsurfer]

That looks correct, the 10x18 ET45 rear, vs what the Bentley manual states with the 65mm ET.

If the 993 Turbos are good thats what I'll be looking for.

Patrick

[Cloudsurfer]

Just found a dandy chart on rennlist:

http://members.rennlist.com/911pcars/WheelWts.html

Apparently there were two versions of the 993 10x18 hollow spoke rears, one with a 40mm offset and one which is 65mm. Blinkwatt, do you know which version you used?

The fact that the Bentley manual suggests 65mm rear offset would mean you can use either the 65mm 993 turbo or the 996 turbo rears, which in that case would both be 18x10 at ET65.

So, for the 986 do we want 40 or 65 MM of rear offset?

Patrick

[ray986s]

Per the Tequipment Boxster catalog it lists the 18x10 rears at et47 for both the Turbo look II and the SportTecho. The fronts are at 18x8 with et 50.

[silver-S]

[LAP1DOUG]

Long dead thread resurrection?

[Dubaday]

seen a website that calculates wheel fitments, thought I'd share.

Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

[bwdz]

I just picked up a set of Cayman wheels I want to put on the 986, they are 18s. Fronts are 8 with an ET57 and rears are 9s with ET43 I believe that is the numbers stamped on them. These are factory wheels so I would imagine they fit fine but anyone have any guesses as to how they will look? I couldn't pass up the deal, guy bought them for a 928 and they did not look good, he put new tires on them and drove a few blocks and they rubbed on the front, I got the wheels with $700 worth of tire on them for $400.

IN TERMS OF THE WIDEST WHEEL/TIRE SETUP FOR A PORSCHE BOXSTER 986 CHASIS...

INTRO:
For all-around performance and looks, go with 18x8.5" Front Wheel/Tire and 18x10.5" Rear Wheel/Tire setup. This 18" wheel/tire combination with good tires and suspension components amazingly allow the car to handle as if it's sitting on train-track rails! No spacers needed with this setup and they fill in the wheel well perfectly.

Hence, although 19" wheels work and look great, they don't perform as well, not even close. However, if you want to go with 19s and you're going to keep your car, I highly recommend that you replace all of your suspension components with race quality parts (from control arms to struts).

If you rub with either of the 18" or 19" setups I have mentioned, then you may own a car that has had front-end impact, and may require you to figure out what needs to be pulled out.

The positive aspect with going with a 19" setup is that your car ends up being a higher, which slightly helps reduce driveway/speed bump scrubs, until you need new tires.

CURRENT WHEEL DIMENSIONS (No Rub Issues):
:: Front: 19x8.5" (45 offset - 2" lip)
:: Rear: 19x10.5"****(43 offset - 4" lip)

CURRENT TIRE DIMENSIONS (No Rub Issues):
:: 
Front: 235/35/19 (25.48” Diameter)
:: Rear: 275/30/19 (25.49” Diameter)

FUTURE WHEEL DIMENSIONS (L+4" - R+4" Steel-Super-Wide-body Fabrication):
:: Front:19x9.5" (3" lip)
:: Rear: 19x13.5" (7" lip) +1" Spacers OR 1" Arm Extensions (alleviates spacers)

FUTURE TIRE DIMENSIONS (L+4" - R+4" Steel-Super-Wide-body Fabrication):
:: Front: 275/30/19 (25.5” Diameter)
:: Rear: 355/30/19 (27.4” Diameter)

THE SCIENCE BEHIND WIDER/STAGGERED WHEEL SETUPS:
In short, you typically want to stay within a 2" difference between the front and rear tires to avoid understeer/oversteer.

Based on this methodology, I should go with a 10" wheel up front; however, I would have to rework the entire steering and front end suspension system. And even then, for those who have driven a Viper with 10" wheels in the front and 13" i the rear, its challenging to turn. For cars that aren't setup for it, a similar wide-body setup would quickly wear-out relevant front and rear-end components.

Obviously, I am extending the fenders to accommodate the new wider wheels and tires; however, I sincerely do not recommend you doing what I am unless you have the funds to do it correctly (GT/RS specs).

Please be sure to also note that going larger and/or heavier will wear-out your bearings a lot quicker, but that goes for any sports car.

CONCLUSION
I truly hope this information helps one of you in some way. Such R&D knowledge doesn't come cheap and not many people I know or have ever met have produced such conversions unless they have large budgets to play around with. Personally, such R&D has cost me a few "million pennies" (so to speak), and what's left is pure knowledge, experience, and how to do things better each time around.

Best wishes,

MoMo
Self-taught Coach-builder/Industrial Engineer