Ultimate offset of 968 (if you were creating a custom wheel)
 

So, if you were to pick the perfect set of wheels and then be able to spec the exact offsets (18"s) for your 968 what would it be. For example, the Speedline 3.6's are almost perfect, 18x8 ET52 and 18x10 ET61, but many people add spacers to them to get the wheels to fill in the rears.

I have a set of Carrera IIIs on a '94 968. They are 8ET57 and 10ET58 and are pushing the limit without any rubbing issues. Rear tires are 295 wide. 8.5s and 9s can work on the front as well. considerations might also include what tires sizes you plan on using for sidewall height and squareness (265 vs 275 vs 295 on the rear etc.)

Still a bit of a rookie at Offset. I think I get it, but sometimes wonder.

For example, the Speedline's referenced - 18x8 ET52 and 18x10 ET61. After asking Raj what his set up was I learned he added a 7mm spacer to the rear to provide a more aggressive stance. Making the 18x10 ET68...is that right?

The SSR GT3's are 18x8 ET49's and 18x10 ET 62 and they fit well also. But technically, the fronts could be pushed out a tad bit more...right?

I think that adding spacers takes away offset, so in the case of Raj and his 18x10 Speedlines the effective offset has changed from 61 to 54. Less offset causes the rim to stick out farther and closer to the outer fender.

Another consideration is what tire sizes are available for the rim size. Even though 18x10 Speedlines came with 265/35-18 tires I think they're stretched quite a bit and that 285/30-18 tires look much better. Now whether this still works with a 7mm spacer, I have no idea...so that's why I haven't bought spacers yet. :)

Also, do a search in the 944 Turbo forum here on Rennlist - there's a ton of archived info regarding offsets for 1987+ models which are the same as 968.

Offset is simply a distance measurement. The distance is that between the mounting hub of the wheel, and how far that is from the wheel's center (widthwise). Positive offset is towards the outside of the wheel/car, negative towards the inside. 0 offset is of course where the mounting hub is directly in the center. ET stands for the German word for offset, foget the word. Standard units of measurement for ET is mm.

The offset was changed in 1987 for the 944 (which carried through to the 968) to allow for sensors for the optional (at the time) ABS. Offset for the 911 was changed in 1989 with the 964-chassis Carrera 4 because the entire suspension geometry was revised (designed to allow for ABS). 1989 911 chassis cars' suspension remained unchanged. Excluding the 959, racecars, etc. etc..

928's from the start used a high positive offset. Perhaps Porsche was predicting a system like ABS (don't know if it was even thought of at the 928's introduction) Or perhaps the suspension itself takes up more width. 924's never had an offset change, but effectively uses a high offset (and narrow wheel) since it has less room in the fenders than a 944.

The respective offset's are commonly called "early" (low distance) and "late" (high distance).

On the 924-944-968 specifically, there are some things to watch out for. Watch out for your front wheel width. Eight inches in the front is pushing it for a car with stock struts; the tire and sometimes wheel will rub on the springs. Also - 285's are about as wide as you can go with stock fenders, and they typically require some alignment changes and maybe fender rolling. And keep in mind that Goodyear's 285 width tire is a different width than a Pirelli's, or Bridgestone, or etc. etc.. Supposed to be a set measurement, for some reason widths of different MFG's tires are all over the map, sometimes can vary up to an inch.

Take care!

There is disparity in the "perfect ET" debate. When I was trying to pick a tire / wheel combo for my 968 it became mind boggling and I'm an automotive professional with extensive knowledge on the subject. I finally did my own caculations and here's where I landed.

Front 8.5 X 18 ET 47 with 225 40

Rear 10 X 18 ET 62 with 265 35

ROW height - M 030 front spindles / hubs - Koni coil-overs - 1 degree negative camber on all corners
(Yeah I know the rear should have been set to 1 1/2 negative - I just decided not to)

Nothing is anywhere close to touching or rubbing and no tires appear stretched in my opinion. 968gene has seen / touched / driven car and can concur. Many other combinations have also worked well for others.

And two piece rotors...

...and Kokeln aluminum hats

Thanx for the reminder :)

Actually from a handling standpoint our cars should have a square set-up. The smaller width tire up front just contributes to understeer which is safer on the road. I am running 10x18" with 285-30-18 on the race car front and rear. That said the 285's are pretty wide for the front and you could do the 285's rear and 245/255/265 on the front depending on matching the overall height.

Mike, can you post your ET and camber numbers? Thanks, Gene

I would love to see those too. I've never done the calculations on fronts that wide but that must be the absolute max for front width.

My wheels are ET54 (all the way around). The camber alignment is between -3.0 and -3.5 depending on which side and what track I am setting up for). I run about -2.25 camber in the rear.

Thanks Mike.

Mike,

So do you think a 9.5 will fit (similar offset) with a -1.6 front camber? Seems crazy wide to me, but obviously you are making it happen. Currently have 17" Cup 2's running a neutral -1.6 all the way around. Did this for a compromise between street and DE's. Would moving to 18's require a change?

What wheels do you have for the rear? Try putting the rear on the front and see if it fits.

Fronts 245's on 8.5" wheels; rear 285's on 10" wheels. Wheels are CCW's. Have run with this combo since '06.

Our friend Pablo is currently racing on 285's all around (like Mike's set-up). I may try Mike's suggestion of putting the rears up front just to see if 285's will fit without flairing, etc.

The car is dramatically different with 285's all the way around!!!

Hi Mike,

Did you have to flare the front fenders?

As Richard stated, +1 for square setup. And credit to Mike Ward and Scott Good who convinced me to take the plunge! Best thing I ever did from every angle...

I run the Enkei Nt03 Wheels 18x10 which have a 60 offset and 285 Hoosier R6s. I do run a 5-7 mm spacer in the rear to prevent the tire barely rubbing the inner fender-well under heavy loading and 2.4 camber which I had been running (2.3 seems to be my sweet spot for me now).

I never had issues with the front rubbing the fender lip. On full lock, the tire does rub the wheel well cover and barely rubs the one brake line .... Nonetheless, I try to keep the full-lock drifts to a minimum! LOL

My 968 has standard non M030 brakes/spindles.
I am in process of installing Moton Clubsport coilovers/new coil springs/minimal torsion bars/M030 stabilizers.

Will there be any clearance issues with the above with either of these wheel selections ?
- 17in x 7.5/9.0 Cup2
- 18in x 8.0/10.0 MY02 (50/65 offset).

I would think you would be fine in either case

So, back in the game on this after deciding it was too complicated to create a set of custom wheels. Found a set I am very interested in. These will not be track wheels as I will save my Cup II's for that, granted I like mikew968's square set up

These should be about perfect, with the rears filling out the fenders well...right?
18x8.5" 46 offset fronts
18x10" 54 offset rears

I bet these will be just fine - just as long as there's no spacer in front. I needed a front 7mm spacer for my 18x8 et50 in order to clear dust cap. Everything fits barely with 225-40-18 tires.

I also have the 18x10 et65 (with 295-30-18 tire) setup in the rear. I still have room for a ~10mm spacer.

Still looking to put coilovers in front so I get wider wheels in front.

Good Luck!
-Robert

They arrive today
 

So, I guess I will see if they fit. My expectations are they are going to be perfect. Stay tuned, and I will let you know. No space planned for the front at this time. I suspect these will have a very flush fitment to the fenders. Now, I just wonder if moving from 17's to 18's will really change my camber adjustments made last year. My expectation is with the same tire diameter, it shouldn't affect the set up?

So, new tires and new wheels on today. HELP
 

RH 3.6's

8.5x18 - 46 front tires 235-40-18
10x18 - 54 rear tires 285-30-18

Sumitomo HTZII's (they were free)

Couple of things to consider. The difference in profile is REALLY obvious. Looks like I am driving a "Big Wheel" from my childhood as the front are noticeable larger. They clear at full lock by mere hairs... The rears look stretched. The tire's rim saver doesn't even come close to saving the tire.

So, I am wondering if I moved to a 235-35-18 in the front and a 295-30-18 in the rear if that would work well. Thoughts? I am not even sure if I can find matched tires at these sizes, as the 295 is not a common size. All I know now...it simply doesn't look right. I assume it could be the tires as well.

Thoughts from the team of experts? I will have photo's up soon.

What tires are you running?
 

I have these size wheels on and my 285's look a little stretched in the rear. The 8.5 with a 45 offset does fit in the front, but the 235-40's look silly compared to the rear 285-30's. One looks stretched and the other one looks fat...

Assuming you have rolled fenders front and rear you can run some pretty wide rubbers. I am currently running 245/40/18 fronts and 305/30/18 rears on a 951S. Looks a little bit ridiculous but in a good way. A good/flush fitment I can recommend on stock MO30 set up would be 225/40 with 7mm spacer to clear front bearing caps with 50 ET, and 295/30 in the rears with parking brake cable zip tie to the trailing arm- no spacer needed in the rear.

No rolled fenders..
 

No rubbing or any issues, but it is tight in front. Think I am going to move down to a 224-40 vs. the 235. Rears with a 54 offset and 285-40's could actually come out a bit more if I wanted. Pretty sure 295 would fit, but don't see the need.

mtnspeed, I also have RH's on a late offset 951, with the same offsets as your 3.6's. My car is not lowered. You need to get 225/40's on the front. The 245/40's are too tall for a 285/30 rear combo. If you move down to a 225/40 and a 295/30 rear, they will be almost identical height... now the $64k question is will a 295/30/18 fit on a 10" ET54? That is where I am at right now, as I am contemplating putting on 295's, but I am afraid I will rub under boost, even at stock height. I am undecided on if I should pull the trigger on them or just replace them with the current 265/35's although I can get the 295/30's much cheaper right now.

Thanks Mike!

Has anyone tried using a square setup of MY02 18 x 8 wheels? This would be for a 968 with stock engine and suspension. Would this increase balance or be a step backwards in the handling department?

Interesting topic.

I just picked up a square set of 18x10 with 265/35/18 tires off a fellow Rennlister. Even with 21mm spacers the rears were no problem as you can see below. I'm pulling off my front spacers Thurs and will test fit the front to see if it clears. My concern is not so much the outer lip but the inner fender liner at full lock.