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Well, due to a complete lack of ability to get N-spec Cup 2s, Pirellis or Dunlops over here, I'm getting a set of K-spec's for my car - standard size 245/35ZR20 and 305/30ZR20. Hopefully this will not impact my handling too much. Kinda frustrating that we seem to be having persistent tire availability problems. Actually it was worse than that - I found a set, got them ordered, only for 1 of the rear tires to literally "go missing" - the shipper lost it irretrievably, so I wound up with 3 tires instead of 4, with no hope of getting the 2nd rear tire, at least in N-spec. So I took the conservative option - sent all 3 back, and am waiting for 4 K-spec tires to show up. At least they will be consistent in their stretchiness ...
Availability definitely seems to be regional.
Fortunately the local dealer ordered a lot of N-spec Cup 2s for themselves, but depending on the year that supply usually is gone by mid summer.
Completely agree that the tread width of the N-Spec tires (PS4S, P Zero, Cup 2) seems wider than standard tires, and other spec tires.
I would have done the same and sent back the 3 tires and gone with 1 version of the tire. What wheels will you be mounting them on?
Well it’s actually worse than that. Not only have i increased front by running N-Spec (Porsche) 265/35/20 front, I couldn’t get N-Spec rear. So I went K-Spec (Ferrari) 305/30/20 on rear. If you don’t know the difference between N-Spec and K-Soec, Porsche run 12 inch rim and Ferrari run 11 inch rim, and it shows. The K-spec look stretched.
So I have most likely decreased the rear and increased the front.
Mercedes Black Series have a 335/30/20.on a 12 and it looks flush. If I ran that, this time around, that would help?
It would be bigger than K-Spec anyway.
Yes its **** that you can get multiple 305’s all different sizes.
Since the K-spec is designed for an 11 it is most likely a 285 branded 305. Which means even if its a 30 it will have a smaller diameter than the N-spec one.
Agree that the K-spec looks like a 285 or 295 width.
Do you think this variation in rolling diameter may be contributing to any of your issues?
No idea if it does, but now I am wondering.
And yes the K-Spec 305 looks quite a bit smaller than the N-spec.
Yes, I do believe it is causing interference when i come onto the straight. I run full traction control OFF. But it appears something is still trying to intervene. If the car believes the rear is spinning due to increased front diameter and reduced rear, than perhaps it is applying rear brake.
I may try a 325/30/20 temporarily and see if it helps.
Once this set is done, I’ll return to stock, matched size and see if issue gone.
Originally Posted by enzotcat
Well, due to a complete lack of ability to get N-spec Cup 2s, Pirellis or Dunlops over here, I'm getting a set of K-spec's for my car - standard size 245/35ZR20 and 305/30ZR20. Hopefully this will not impact my handling
At least they will be consistent in their stretchiness ...
I think having K-Spec front and rear with stock sizes you will be fine. I’m N-Spec 265 with K-Spec 305. Front is most likely larger than rear due to K rear being smaller than normal.
This was never the plan. It has all been caused by lack of supply.
Yes, I do believe it is causing interference when i come onto the straight. I run full traction control OFF. But it appears something is still trying to intervene. If the car believes the rear is spinning due to increased front diameter and reduced rear, than perhaps it is applying rear brake.
I may try a 325/30/20 temporarily and see if it helps.
Once this set is done, I’ll return to stock, matched size and see if issue gone.
I think having K-Spec front and rear with stock sizes you will be fine. I’m N-Spec 265 with K-Spec 305. Front is most likely larger than rear due to K rear being smaller than normal.
This was never the plan. It has all been caused by lack of supply.
Hopefully going to a matched size set solves the issues.
Enjoy your informative posts
Took my 911 out of 'winter storage' today and went for a spin after work. Have an appointment to get my P Zeros replaced with Cup 2 and looking forward to trying them out. The cooler temps (right now) and the worn P Zero were not conducive for putting down the power.
Mines a GTS so it has 12 inch rear rims from stock like a GT3. What width are your rear rims?
Honestly a little hard to tell - when I got it, it did not have the wheels on it that were on the original sticker - they were spec’d as gloss black, these are platinum gray Carrera S wheels. Porsche’s tequipment site lists them as 8.5 front, 11.5 rear - while the wheel-size.com site gives them a possibility of either that or 9 front, 12 rear.
That said, I rather suspect that it’s 11.5, which would explain why they don’t look as stretched as yours.
I have similar upgrades to you (100/160 springs, Tractive, Giken mechanical LSD, big brakes, though the PFC cup challenge brake kit), though on a base carrera with the base ABS module. Just like in the PFC video that you refer to, if I don’t brake smoothly and just smash the brakes, with lots of camber I will get what feels like a “rolling” ABS, not shudder, which I believe to be reduction in brake line pressure in advance of lockup. I’m just referring to straight line braking, not traction control issues you describe while on throttle. This brake line pressure change is apparently a function of ABS module calibration, which is different in our lesser models than GT3 etc. As for your larger tires - it’s understandable if preemptive ABS would kick in more, as it does with better brakes - much better grip means faster increase in G forces during braking and turning, so you’re likely passing the lower traction thresholds that are baked into our ABS and TC modules.
I have similar upgrades to you (100/160 springs, Tractive, Giken mechanical LSD, big brakes, though the PFC cup challenge brake kit), though on a base carrera with the base ABS module. Just like in the PFC video that you refer to, if I don’t brake smoothly and just smash the brakes, with lots of camber I will get what feels like a “rolling” ABS, not shudder, which I believe to be reduction in brake line pressure in advance of lockup. I’m just referring to straight line braking, not traction control issues you describe while on throttle. This brake line pressure change is apparently a function of ABS module calibration, which is different in our lesser models than GT3 etc. As for your larger tires - it’s understandable if preemptive ABS would kick in more, as it does with better brakes - much better grip means faster increase in G forces during braking and turning, so you’re likely passing the lower traction thresholds that are baked into our ABS and TC modules.
How do the 100/160 springs feel/perform compared to your 80/130 setup?( I assume you did this for the track)
I have similar upgrades to you (100/160 springs, Tractive, Giken mechanical LSD, big brakes, though the PFC cup challenge brake kit), though on a base carrera with the base ABS module. Just like in the PFC video that you refer to, if I don’t brake smoothly and just smash the brakes, with lots of camber I will get what feels like a “rolling” ABS, not shudder, which I believe to be reduction in brake line pressure in advance of lockup. I’m just referring to straight line braking, not traction control issues you describe while on throttle. This brake line pressure change is apparently a function of ABS module calibration, which is different in our lesser models than GT3 etc. As for your larger tires - it’s understandable if preemptive ABS would kick in more, as it does with better brakes - much better grip means faster increase in G forces during braking and turning, so you’re likely passing the lower traction thresholds that are baked into our ABS and TC modules.
Nice. Thanks for the feedback. I haven’t had a chance to track in full anger as yet. Too much rain here. Next night track day is 3rd June. That should give me more information. Just to confirm, i run with full traction control OFF. But it clearly does not disable everything fully.
I am thinking of going 120/170 next, and changing the helpers to tenders. Tenders aren’t fully closed with body weight at rest. It is supposed to help with traction.
03-31-2022, 02:27 PM
