IcemanG17

the 245/45 16 is 24.7" diameter....the 285/30 18 is also 24.7".....so its perfect!!! Just wider with way more grip!!

Jeff928S4

I was a tad thrown off because my new front tires are a 225/40/18....and with the back tires being 285/30/18, I thought the front should also be in the "30" series....(as, from the side, the front look bigger than the back) but I suspect that the 225/40/18 is similar to the original size 16' tire size?

...and I have noticed a lot of cars now having different 30/40/50, etc. series tires front and back....now that I am looking.

Jim bailey - 928 International

The series 30,35,40 simply means the sidewall is 30% .40% ,50% of the width of the tire at it's widest point not the tread but the bulge of the sidewall. So a narrow tire MUST be a higher % if the sidewall (diameter of the tire) is to match the wide rear tire

Garth S

For anyone interested in the specifics, Jeff now has a set of 993 wide body 18" techno twists on his S4 ... from my C4S as donor. The fronts are 8x18ET52 .... a drop in fit, and the rears are 10x18ET40 .... custom fitted with a 33 0z. Lousiville Slugger. The rear fender rolling was done in multiple passes to avoid wrinkles and paint cracking - and came out looking as if it was that way from the factory. The narrow body 993 rears 10x18ET65, and would fit a S4 without rolling .... but the visual impact of the WB (ET40) wheels on the rear is stunning.
As far as tire sizes, practically all Porsches use an ~ 25" diameter: once the wheel width and ET are selected ( or fitted), a tire of the necessary width is selected by its aspect ratio to achieve this diameter.

PS ... spellcheck is dead - I now have to proof read my own crap

AJK

I forget what the exact numbers are, but the factory 16 inch Phone Dials are a very light rim. Far lighter than any one piece 18 inch wheel.

AO

Garth

Not to be picky but... I thought all 10" wheels were considered Narrow Body and the Wide Body were the 11's like what I have.

Jeff928S4

Garth.....do you have that pic of the new "wide look"??

mark kibort

circumference is related to diameter, and the speedo is generally off. my 305 35s are correct for calibrated speeds off the spedo and verified with radar. what this means, is that our cars are conservative speed indicating-wise
thats 26.5", so i wouldnt worry about diameter much if i were you.

mk

Garth S

Andrew,
AFAIK all 993 18" rears are 10" wide: only the ET varies between the NB/WB cars (65/40) - this applies to both solid and hollow spoke versions IIRC.
The 11" hollow spoke rears, ET45, which I have on the C4S were from the 996TT ..... perhaps the source for yours. I think that there was also an 11" solid spoke version from the 996, but am not certain offhand.

Garth S

Poor pics Jeff, but here's the before/after from the side - too much shadow to capture the rear view.

AO

Sorry, I missed the 993 reference. I believe your information is correct.

Jeff928S4

Thanks Garth!

Ahhh yes....the ol' "Hercules" tires. Had them for 2 years and I believe they GREW tread.

Those tires had to be made of plastic.