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YOUR RESEARCHwheel and tire size quandry
Leading reported evidence
Run 235 and 295
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Suggestion
I now run 225/255 as i like my car to be adjustable on the throttle on the road.
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Suggestion
The spacers you have now will work and you can run 225/40 on the front and 285/35 in the rear without rubbing.
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Suggestion
You will find people running their cars at the track running anything from stock sizes to 245/315 depending on wheel and offset choice.
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Suggestion
The current wheel/spacer setup sounds less than ideal for a number of reasons, and it is certainly odd that the previous owner was running two different spacer thicknesses from right to left.
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Suggestion
The 996 is super sensitive to the geometry of the rear suspension, so make sure that is set to a known quantity before testing your current tires and then making any changes.
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Recently I bought a car that came with a set of Fikse FM10 wheels. They are 18" and as best I can measure they are 9" wide in the front and 10" in the rear currently wearing 235 and 265 tires. Since there are no offset markings I measured it at roughly 41.25mm F and 44.5mm R. There are 5mm RSS spacers up front, and 15mm in the rear. Inspection revealed there has been some rubbing on the inner rear of the right front fender liner.
The plan is to put on PSS10 coilovers, and setting the car up for track days.
Since these are neither the OEM staggered widths for 996.1 nor .2 nor GT3, nor other
Fikse 996 NB fitments
I found via search. What is my best option for tire size and spacer size front and rear?
I would confirm 100% actual size and offset. If your planning on setting up for track your going to want to maximize the contact patch and you really won't know what your getting yourself into fitment wise unless you know the specs...
I would recommend either:
A: Sell the Fiskes and replace them with factory lightweight wheels. The spacers you have now will work and you can run 225/40 on the front and 285/35 in the rear without rubbing.
B: Dismount the tires you have now, get actual width and very importantly offset numbers... You will find people running their cars at the track running anything from stock sizes to 245/315 depending on wheel and offset choice.
Are there no markings on the Fiske ? that's a bummer.
I�d like to fit the widest set of tires that with be balanced front to rear. I found this
recommendation for 996 tire and wheel sizes
, but my wheels don�t match any of their pairings in width or offset. Stock wheels are 7.5 or 8� front and 10� rear, and they pair 9� fronts with 11 or 12� rears.
I guess my question is:
Is there a tire width and offset combo with a 9� front and 10� rear that will fit and be balanced.
My guess is 9� and whatever offset they are is too wide up front without increasing the spacers to 10 or 12mm to eliminate rubbing inside. If I do that with a 235 or 245, I might start rubbing the outside.
Maybe they would fit with a 225 tire and 5-7mm or no spacers, but then I would be limited to 265 in the rear because of the reduced front contact patch, and would 225 tires be over stretched on a 9� wheel?
NB C2
that was what I got by measuring from the hub to the inside bead (6.75�) and subtracting 5� (10�/2) which left 1.75 to the centerline or 44.45mm. I will double check that in the morning.
My factory sport techno wheels r 8x18 et 50 front and 8x11 et 63 rear. I run a 235 and 295. Front will work with an additional 8mm spacer. Ride height and camber will also determine how wide u can go.
Tires are a very personal thing. I suggest you run the car on the tyres it has to determine what you want it to do differently before you buy a set. The 996 is super sensitive to the geometry of the rear suspension, so make sure that is set to a known quantity before testing your current tires and then making any changes. I have had 235/265 on my car in an attempt to kill understeer and it was only after I made several rear geometry and damping changes that I finally dialled it out. I now run 225/255 as i like my car to be adjustable on the throttle on the road. If going on the track I would go for 235/285, but as I said, it's a very personal choice.
Also, if you scroll toward the middle part of this thread, there is a helpful tip on how to mold the fender liners to deal with minor rubbing issues:
https://rennlist.com/forums/996-foru...it-review.html
While I can't tell you the specs of your current wheels, I'm happy to help. In order for anyone to give you good advice, we'll need a little more background information.
How often will you track the car?
Will you want to keep this same set of wheels and tires on the car for street use as well?
What tire compound(s) do you currently have track experience with?
Beyond the PSS9 coilovers, do you plan to dial in negative camber through adjustable camber plates and/or GT3 lower control arms?
- Ryan
Thanks Ryan,
7-8 HPDE weekends about 21-24 days
Yes, same wheels and tire for street use. I will eventually switch to slicks once I am more comfortable with the car overall.
I've been using Direzzas, RE-71Rs, and RS4s since my car has been dual purpose.
Yes, I plan on installing GT3 LCAs.
I have also discovered that the left rear wheel has a smaller spacer (~7mm) than the right (15mm). I don't know whether that was a mistake or this means the rear end was hit at some point, but so far everything looks normal back there.
Thanks for the supportive info. The current wheel/spacer setup sounds less than ideal for a number of reasons, and it is certainly odd that the previous owner was running two different spacer thicknesses from right to left. Ideally you would have 9" front / 11" rear width wheels in the correct offsets so that spacers are not required. While 10" rear wheels work just fine for street cars with 265 or 275 tires, they are not going to properly support track compounds in 285 - 315 sizes
From what you've told me, I think the ideal solution would be as follows:
F: 18x9" ET46 - 235/40-18 Yokohama Advan A052
R: 18x11" ET60 - 295/30-18 Yokohama Advan A052
If you wanted to re-use your existing wheels, I would remove the spacers to get an understanding of why they are being used in the first place. An 18x9" wheel with an offset in the low 40's (assuming your calculation/measurement was correct) does not need spacers for inner strut clearance, so unless they are there for brake caliper clearance I would remove them. In the rear, an 18x10" wheel with an offset in the mid 40's does not need a spacer to sit flush with the fenders, so I would remove those as well. With these wheel widths you will have to stick with a slimmer 265 or 275 tire, or pinch a 295 on them and deal with a little sidewall flex.
- Ryan
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