CKit

Hi guys, would like some opinion on a '14 Cayman S:

1. How much does running same outer diameter tire size (i.e. 25.6") affect ABS, PTV, etc. Can I get away with it? With PASM kicking in when ABS is engaged, I don't want to get into ABS way early with the different-than-factory heights.

2. I'm going to probably order 18" CCWs as the OZs don't have the proper rear width to do -1" sizing from the OEM 19s. Any thought on what offset? I have 6mm to play with by stock rules. And I'm likely to cram tires that bulge outward a little so I'd like to plan my clearance.

Thanks in advance. Any and all opinions welcome!

CKit

This would be for SCCA "street" class for next year.

Audii-Dudii

For the record, I know nothing of 2014s, but with my 2006, I am finding that .4" of stagger is fine (versus .9" OEM), but less than .2" causes problems with the ABS, at least when braking from higher speeds ... say, 60 mph or faster. Strangely, when I'm braking from less than 50 mph or so, everything appears to be okay ... weird, to be sure, but this is what my intial troubleshooting/testing has shown. (Yes, I'm still pondering the reason(s) why this happens, but as of now, I have no definitive answer. It also appears to explain why track folks are almost militant about the importance of preserving the OEM tire stagger, whereas autocross folks seem not to have any problems even when running same-size tires front and rear.)

While it's true that OZ does not offer its Alleggerita wheel in a 9.5" width, they do offer two 10" wide versions, one with a 40mm offset and the other with a 58mm offset. They also offer an 18x8.5 front wheel in two versions, one with a 53mm offset and the other with a 40mm offset.

Apparently, not many people are aware of this, but the optional Carrera Sport wheels measure 19x8.5 ET57 and 19x10 ET42, which means that if the SCCA's proposed +/- 1" wheel diameter allowance is passed for 2014, then it will be legal to run OZ's 18x8.5 ET53 and 18x10 ET40 (or ET58 plus a spacer) Alleggerita wheels in the Street class. Given their lightweight and (relatively) modest price, I would recommend these over the CCW wheels, unless you're also planning to use them on the track, in which case, I'm a little bit leery of the OZs, due to them being a cast wheel.

Is Porsche still offering the optional 5mm spacers for the 2014s? If so, then you actually have 11.35mm of offset allowance to play with (1/4" + 5mm), not 6mm. I have no idea how changing track width will affect the handling of the 2014 Cayman chassis, but I do take take advantage of the ability to adjust this for each course by using different thickness spacers with my 2006...[/QUOTE]

Hope this helps and, as always, YMMV...

CKit

That would be excellent, but the Carrera sport wheels are not listed as an option from the web site (or manual). The 19x9.5 is the only rear 19 that I see. I would absolutely love to get the OZs though. I'll check with my dealer and see what they say. Thanks for bringing it up!

Audii-Dudii

I could have sworn that I saw a 19x8.5 / 19x10 wheel combo offered as an option at some point, but apparently not, as I just checked Porsche's website and you are correct: The largest 19" wheel combo offered for the 2014 Cayman S is 19x8 / 19x9.5. I'm not aware of any lightweight 18x9.5 wheels available in a Porsche bolt pattern, but if you don't mind running a spacer/adapter and mis-matched wheels, you could make a 1997-2003 N73-option Corvette wheel work: 18x9.5 ET65, made of magnesium alloy, and weighs just over 18 lbs. Alas, the matching front wheels were 17x8.5, which won't work for a Cayman...

Interestingly, even the 20" Carrera S wheels are now just 8" wide in front, so it appears the 8.5" front wheel option has died with the Gen. 1&2 cars ... whether this makes any significant difference in the Cayman's competitiveness remains to be seen, of course, but it certainly can't help any, as these cars have historically benefitted from stuffing as much tire as will fit up front for autocross purposes.

Audii-Dudii

While I was eating my lunch this afternoon, I pondered about Porsche's rationale for using narrower front wheels (8" v. 8.5") and wider rear wheels (11" v. 10") with its 2014 Cayman chassis than it did with its 2006-12 chassis. Where there previously was a maximum 1.5" difference in wheel widths front to rear, there is now double that ... a whopping 3" difference! I haven't driven a '14 at speed yet, so I can't speak to its ultimate chassis balance, but this certainly does seem to suggest that it will understeer with a vengance, at least on the typical autocross course. Hmm...

CKit

There is a factory 8.5x20f and 10x20r wheel option. But no top tier street tires in those sizes.

Can I ask what offsets you'd pick for a custom wheel?
With the 8 and 9.5 combination, factory offset is +57f and +45r. I reached through the wheel and there's really not a lot of space inboard to the shock body.

I was planning on running 275 / 295 Rivals on 8 and 9.5 inch wheels respectively. With the extra bulge of the crammed tire (0.5 narrower wheel than recommended for those tire sizes per Tire Rack), I'm worried about inboard clearance.

I wonder how much outboard space I'll have. I'd rather rub a little on the strut than chew the fender.

So was thinking of building a set of CCWs with just 1mm more offset.
Factory offset is +57f and +45r, I was going to build +56f and +44r.

Could I do a +55 / +43 without chewing the fender with those size tires?

Audii-Dudii

I'm not surprised such an option exists, but I am surprised my search of Porsche's website for the new Cayman didn't turn this up...

Sure, but because my experience is limited to the Gen. 1 & 2 cars in general, my 2006 in specific, and a 15-minute test drive of a 2014, I certainly wouldn't make any purchase decisions for your car based upon anything I have to say...

With that said, because most cars today understeer on an autocross course, I personally like to widen the front track and narrow the rear track as much as the rules allow, although I also like the ability to tune the amount of this adjustment to suit each course by using spacers.

Because a 5mm spacer was available as a factory option on the Gen. 1 & 2 cars (I have no idea if this is also true of the Gen. 3 cars), any offset that falls in the range of +11.35mm and -6.35mm is legal per the SCCA's rules. With the OEM offset of 55mm for the 19x8.5 front wheel and ET42 for the 19x10 rear wheel, this means any offset between ET43.65 and ET61.35 for the front wheels and ET30.65 and ET48.35 for the rear wheels are legal (note: if you do include the extra 5mm for the optional spacers, then you must do so at all four corners, not just two.)

Accordingly, I spec'd my front wheels at ET49 (6mm less than the OEM ET55) and one pair of rear wheels at ET36 (6mm less than the OEM ET42) and the other at ET58 (16mm more than OEM), which I then fine-tune with spacers.

For instance, if a particular course emphasizes slaloms, then I will run the front wheels without a spacer; if it has sweeping corners, then I'll further widen the front track by running a pair of 5mm spacers and narrow the rear track by running 10mm spacers (for a net ET48) instead of 25mm spacers (for a net ET33), etc. (Yes, running spacers does add some extra weight, but I believe this is a fair tradeoff for the ability to tweak the car from course to course. YMMV...)

At the moment, I'm running Yokohama AD08 tires, 255/30-19s up front and 275/30-19s in back, and I have no clearance problems at either the fender lip or strut body with any combination of legal offsets.

Going forward, I have acquired two sets of 18" OZ Alleggerita wheels, with the front 18x8.5 wheels having an ET53 offset and one pair of 18x10 rear wheels having an ET40 offset and the other an ET65 offset, so I will be running some thickness spacers up front and in back at all times.

FWIW, it's my experience that street tires, unlike Hoosiers, don't like to be pinched onto narrow wheels, but I have no experience yet with the BFG Rivals, so who knows? Personally, I believe 255 is about as wide as I'm willing to go with an 8.5" wide wheel and at least with my car, a 275 seems to be adequately wide in back (in retrospect, I think a 275/35 tire would have been a better choice than the 275/30 I went with, because the additional diameter may be necessary to prevent the ABS problems I'm experiencing). As much as I would like to try the Rivals myself, it doesn't appear the range of available sizes will work well with the Cayman, so I'm instead going to run 255/35-18 / 275/35-18 Dunlop ZIIs instead and cross my fingers that the upcoming AD08R (which will be availble in the same sizes as the AD08) can compete with the ZII and Rival once it's released.

Beats me! I'm afraid that you'll need to get under the car with a tape measure and a ruler, and see for yourself.

CKit

It's hard to tell the outside edge limits without suspension compressed fully. From your specs, I'm probably okay. I'm going for 1mm less offset in the build so I have leeway with 3mm and 5mm spacers and still be within the stock offset allowance.

I'm glad that Porsche has lug studs so I can see what I need and get longer studs and spacers as I need them.

I have new gen street tires pinched on other cars and just like stock class on Hoosiers, the trade of ultimate grip over steering feedback usually winds up worthwhile. I have run 255 Z1s on a 7 inch wheel before. Also 265s on an 8.

allen_skillicorn

I haven't noticed anything except less understeer on my 986S on 245/40/18 BFG Rival's. I have about 1500 miles and 3 autox's on them. They even work well in the rain. ABS functions fine. I do wish they were shorter, I get some very minor fender liner rub while pulling out of my steep driveway.

CKit

Good to know. Got the car aligned today and it seems like very similar alignment-ability to the 987s.