as long as you keep tire OD under control that is true

245/40 x17 on a 9 works better than a 255/40 x17 on a 9 due to lighter weight, shorter OD and shorter sidewall

My 255/40's on the rear present no issues.

:rolleyes: I ddn't say that they present tissues, I did say that they suck up torque

a 255/40 diverts ~10lb-ft from acceleration to just spinning up the wheel tire compared to a 245/40 on the same 9" wheel, this broken into 2 sub categories, inertial cost and gearing cost. The more potent the engine the less this matters.

I use 255/40 on 9.5 x17 on mine but I also have a fairly potent breathed on 993nvram

but even w/ an even more potent 993 3.8 RS in there a 275/40 which sucks up ~30lb-more than the 255/40 just was not a good choice

going back further comparing oe 8x15 225/50 x15 tires that the car came w/ when new there is a a ~55lb-ft loss w/ the 275/40s

The point is you really need to watch the tire OD as it can extract a major toll in torque available for acceleration.

The tallest oes ever used were 215/60 x15s @ ~25.2" OD, I prefer to draw the line @25" max, the more under the better

Something I just discovered today. The 9s, at least the set I have here stick out a half inch further to the outside than the 8s. Wanted to run them on my track car but too much to the outside when running a slick. The hub flange is deeper which is why there is an additional recess at the lug bolt hole so as to have enough threads. I guess a strength concern by Porsche when going 1'' wider. Bob

That's really odd
What fender, what ET on the 9, what make and size slick, what ride height

Here mine 9.5x17 ET19 255/40 tires
http://forums.pelicanparts.com/uploa...1719496004.jpg

http://forums.pelicanparts.com/uploa...1719496758.jpg

wheel: f/s 4.35" b/s 5.85"(110mm/149mm)

tire: f/s 4.5" b/s 6"(114/152mm)

ride height 23 7/8"

stock Carrera 3.0 fenders w/ lips cklearanced for 275 tires, this is not needed for 255s

fuchs
 

These 9s (ET 15 911 302 119) ran on a street car with Bridgestone 245 with no clearance issue. Across the Bridgestone measures approximately 9 1/4''. The Hoozier 245 measures 10 3/4''. I run 9'' BBS 3 piece and a set of 3 piece Fuchs. Simply a matter of offset and I don't have the right combination on the 9'' one piece to make them fit. Bob
http://forums.pelicanparts.com/uploa...1719527337.jpg
http://forums.pelicanparts.com/uploa...1719527399.jpg
http://forums.pelicanparts.com/uploa...1719527449.jpg
http://forums.pelicanparts.com/uploa...1719527521.jpg
http://forums.pelicanparts.com/uploa...1719527576.jpg

There's something very odd going on w/ your car, obviously those tires and wheels do not fit

but I believe that the fault is in the car.

first guess the added on rear flares don't provide the clearance that oe's do
as I said i've run 275 tires that measure 11" across w/ 5.2" of f/s these did require a ride height restriction

current 255s measure 10.5: section width and fit fine tire f/s is 4.5"(114mm)

Try measuring from the inner wall to the lip it should be ~12+/-" for an SC/Carrera

Those pics remind me of putting early Turbo front 9x15s on back or a Carrera.

correct
the early 9x15 RSR wheels were ET3, they project 12mm further out than the late 9x16 ET15 wheels

She is a 78 SC with stock flares. I am running turbo arms, but don't think they cause the hub to project any further latterly than stock. Will take some measurements on this car and an 85 and an 87 over the weekend and compare. Thanks for the exchange. Bob

if the turbo arms are from '78 up they are the issue

from '78 up the 930 trailing arms push the wheel hubs out by ~19.8mm per side compared to 911 trailing arms

The relocated oil tank is interesting, I took it to be a '72 chassis like my first.

In the process of adding flares and 8ET10.6 x15s

http://forums.pelicanparts.com/uploa...1719586888.jpg
http://forums.pelicanparts.com/uploa...1719586888.jpg

7's work fine - on the back of my underpowered SC.
i love the light feel of the 6's and 7's.
full disclosure, i do not track the car - and i drive (more-or-less) responsibly.
the inboard 356 look? doesn't bother me. YMMV.
i tried out some spacers - looked like a dog mounting a football - no thanks.

It's true that very few really need more than a 225 rear, those that do really do.

that's why the 9 245 is so popular. it would be even better if Fuchs had a ET's a little bit more upgrade friendly.
weigh diff between a 7 & 8 is very minimal as long as you have the same radius

diff from 15 to 16 in the same size is more but the newest versions seem to be way lighter than the older versions

Bill you are correct. I measured a difference of roughly 1 3/4'' greater track distance between turbo arm outer hub faces and non turbo. So no way to make the 9s work with my present setup.

You can use 9s if the ET is appropriate

option 1
custom wheel w/ custom width and ET, that's going to be expensive

option 2
find a late 944 or 964 or 993 9x16, these have ETs 52 to 55 then space them out to suit, issue is you will need spacers