mtnspeed

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.

968gene

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.)

mtnspeed

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?

PorscheG96

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.

FrenchToast

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!

chudson

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.

968gene

And two piece rotors...

chudson

...and Kokeln aluminum hats

Thanx for the reminder

mikew968

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.

968gene

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

chudson

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.

mikew968

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.

968gene

Thanks Mike.

mtnspeed

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?

mikew968

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