ceboyd

...so I was hoping to be able to downgrade to 17" wheels for track duty (cheaper tires and I can get the very cheap kuhmo victorracers in 17")


Anyway.... I haven't actually tried to fit them yet (rear tire currently mounted TOO large anyway) but according to Fikse they won't work (Fikse says you can't put an 11" wide wheel on a narrow body 993)


..now I KNOW someone here put an 11" wide GT3 wheel on their narrow body 993 but I can't find that post right now.


So I measured the back spacing and came up with this:

17x8.5" front with 7" backspacing or ET62

17x11 rear with 8.25" backspacing or ET56


anyone have any concrete evidence of working or not on these before I try the hard way to fit them myself on the car OR give up and resell and give up on my brilliant downgrade idea...



What I hoped to do is eventually mount Kuhmo Victorracer 245 45 17 front and 275 40 17 rears (same exact ride height) --- I'd either sell my 18s or use up the expensive $1100+ tires with the knowledge that I can get the Kuhmo's for around $700 shipped next....


meanwhile... I know I don't have a chance in hell of making the exising hoosier 315 35 17 fit in my rear wheel well... (at least not on my narrow body)

Bill Verburg

I have been keeping track of what wheels fit what here 11" wide wheels w/ +ET 62-67mm have been reported to fit n/b 993.

Doesn't matter in the slighteest whether they are 17, 18 or 19. What does matter is dynamic loaded radius, which can be inferred from the revs per mile(~831 for a 993), static loaded radius is second best data and overall diameter if all other data is missing(~25.2")

simpateko

i did it.
11 x 18 et 63, gt3 wheels with 285 30 18 michelin n1.
car is lowered.
tried 295 30 first but they rubbed.
rolled fender lips, still rubbed on drivers side.
switched tires to 285 30 18, perfecto!
good luck
jeff

ceboyd

well, ET56 vs. ET63 is not what I wanted to hear.. I guess I can hope I measured the backspacing wrong and just get it over with and do my own test fitment and see if the wheel itself rubs on the rear suspension or not (trouble is I have to get a tire dismounted to attempt this test fitment)

Bill Verburg

The lower the ET the further outboard the wheel sits

Bill Verburg

p.s. you will want 9" wheels for the front

SwayBar

According to my calc:

(backspacing - (.5*width)) x 25.4mm = offset in mm's, or ET

I get:

08.5" rim with 7.00" backspacing yields an offset of 69.85
11.0" rim with 8.25" backspacing yields an offset of 69.85

ceboyd

well.. unless I measured my backspacing wrong.. which is entirely possible... but I checked and rechecked... (basicly a T ...straight edge across the back edges of the wheel and straight edge down to the back of the lug -- then got measurement of the line --- the I in T length is what I got for backspacing)

I guess my only thing left to do now is do an actual 'test fit' on my car and know for sure or not!

Bill Verburg

That formula doesn't work, you need to use the overall width not the bead width.

ET = backspace - .5*overall width

use this diagram to see where to measure

ceboyd

o.k. that diagram labled 'backspace' IS how I measured!!!!!!

Bill Verburg

Just as a data point, front space f/r 77/84 mm is getting close to the edge of what's usable on a n/b 993

ceboyd

ARG!!!!!!!!!!!!!

Bill Verburg

If it was easy everyone would be doing it

ceboyd

lol... yeah... true enough....

Cy

Here's something of very little value - ET is an abbreviation for the German word einpresstiefe . . . literally, pressed or pressed in depth, or offset as used in English.