malcolmd

These are 3 piece Simmons Wheels that I have had made for track use. The OEM hollow spokes will remain the daily driver wheels. I plan to fit MPSCs 235/40/ZR18 and 295/30/ZR18s to the Simmons Wheels.

As suggested by Simmons, the custom offsets are: 51.4 for the 8.5X18s and 39 for the 11X18s.

Before fitting the rubber, it was suggested I do a trial fitting to check clearances. Once rubber has been fitted, they tell me there will be no "returns".

The inner clearance seems fine. What do you tink of the outer?

Thanks
Malcolm.

Smindustries

It looks close, but it's deceiving when the suspension is at full extension. For what it's worth, I just ordered a set of Work Brombachers in 8.5- and 11-inch widths (albeit a 19-inch diameter). After much discussion, Work told me that the offsets they recommend and are willing to stand behind are +51 front and +38 rear. Your numbers are extremely close to theirs, so I suspect you're good.

malcolmd

Thanks - sounds encouraging. I must admit that I thought the +51.4 sounded excessively precise (smile)
Cheers.

bb993tt

Unfortunately I don't believe you're really going to know how good/bad the fit is without the tires on the wheels. I just went through this with Gert. Ordered a set of BBS race wheels, which came with the wrong offset, clearly noticeable with the wheels/tires installed. He argued that he'd checked them (without tires) on his own C4S and set us pictures to prove it. When we sent him pictures back with a Roock wheel+tire installed, with the proper offsets, he relented. Told us to send them back and he'd take up the issue with BBS. Promptly corrected.

Felix

As a data point people run 996tt wheels without issue; they're 11" wide and have a 45mm offset.

David in LA

You really need to test fit the wheels w/tires....with the car on a lift and the suspension unweighted your really can't tell for certain if a particular wheel/tire combo will fit. Since the 996TT 18x11 ET25 will fit without modification those rims w/295s should fit (reduction of 1/4"), and at worse may require a small amount of fender rolling.

JJayB

How much camber are you going to run? At stock setting it looks like a rub, at -3 deg no problemo.

malcolmd

Thanks for the feedback guys.
Jay: I have PSS-9s that have the car lowered by 25mm (1 inch) and with -2.5 deg camber (balance between street tyre wear and track wear/performance).
The "offset calculator" suggests that compared to OEM 10", the 11" with ET39 require + 12mm inner and + 14 outer clearance.
I'm a little confused about the 996tt OEM wheels as Phelix suggests they have an ET of 45 (+18mm inner and +8mm outer clearance required) whereas David suggest they have ET25 (-2mm inner and +28 outer clearnace required). If the latter were correct, the outer rim would extend another 14mm out beyond what is seen in the photos.
In any case, it does look pretty tight to me on the outer I must admit. Will see how it goes after tyre fitting.

David in LA

Oops..sorry, that's a typo...I meant ET45...

WHB Porsche

With the suspension compressed, the wheels will be farther outboard. Just sayin'...

Basal Skull

my bbs-lm are 11 x 18 et 56 +23 mm spacer = offset 33, with stock size tires fit nicely

malcolmd

Skull: H'mmm - an "effective" ET of 33 with stock (assume 285) tyres will fit......this looks encouraging!
There is an 18mm difference in section width between 285 and 295 in MPSCs when measured on 10 and 11 inch rims respectively. In your case the 285 on 11's will be about 5mm wider (2.5mm for every half inch variance from the designated measuring rim), so 13mm effective difference c.w. the 295 on an 11. So on this basis there will only be a 1-2mm difference between the outcome between your and my setup (accepting some variance in section width between different tyres of the same "size".

Guess I won't really know until we fit them, but the theory looks good. BB993tt and David's point about the geometry being deceptive between weighted and unweighted configurations became apparent when I paid attention during the re-fitting of the OEM wheel. Unweighted, it looked like even it would be a tight fit, but weighted there is 26mm clearence. So there's the answer - I suppose.

Thanks to you all.

Malcolm

David in LA

When the suspension is weighted the tires will camber and the upper part of the tires will lean in closer to the suspension while the lower parts "spread out" further apart. Keep us posted on how it works out...I'm looking for new wheels for the Turbo

Full Boost

David,

I have THE wheels for you.....

https://rennlist.com/forums/993-turbo-forum/421000-champion-speedline-wheels-other-tt-parts-for-sale-aussies-only.html

Simon.

malcolmd

So the answer to my initial question is.........."Yes and No".

To recap: PSS-9 suspension, lowered 1.25 inches, 2.5 degrees negative camber on rears, new 11X18 ET39 with 295/30s rear, 8.5X18 ET51.4 with 235/40 front. "Will they fit?"

The fronts were never going to be an issue, and predictably clearance is fine.

As for the rears, on the flat surface of my garage, there is about 5mm clearance from the inner aspect of the top of the wheel arch to the sidewall/tread of the tyre. I thought with the camber and the inward movement of the wheel as the suspension compressed would just allow me to "get away with it". Alas, it rubs just a little with stiff bumps in mid corner.

So my option I guess, are to a) raise the suspension say half inch which will give just that little more room for travel as the wheel moves in its suspension arc, b) increase the negative camber, or, c) roll the wheel arch sheet metal.

The car is booked in at the panel shop Tuesday for the latter as I suspect it will provide the most predictable outcome and will be cheaper than resetting the suspension and doing another corner balance. I hope the paint doesn't crack in the process.

Here ar some photos - initially of the clearance and then of the car itself.