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Track tyres for my Boxster GTS


Update: I've spoken to the dealership, and they told me that non N-rated tyres will invalidate the warranty (which still has a year to run).

However they have no issue putting 245s on the front axle, and since (with due thanks to Geoff for the suggestion) I can get N-rated Cup 2s in this size it looks like that's the way I'll be going. I'm presuming that the camber adjustment Ralph mentioned remains relevant so I will still look to raise it when I take the car in for a service on Thursday.

Thanks again for all the helpful comments and observations.
 


so you keep your warranty but loose your insurance !

So again shocked they will fit non oem size to your car as that changes the speedo and PSM etc etc as that will increase the front dia 6mm
Also it raises the front of the car so you will gain more lift and it will be more unstable at speed due to lift ! ALso less weight over the front so
while some might say a larger tyre might reduce understeer, this might increase it, as you do not have adjustable ride height to drop the front back down.



OPC are clueless !! and again why N spec is dangerous in the hands of OPC staff !!! that tyre size was made for a GT4 to match a 295 rear, but because it's N spec OPC will fit it to anything !!!!

SO now you would have to fine a rear tyre with 6mm increased size to bring every thing back in line ie a 275 rear and there is NO N spec in that.
on top of all this you are adding weight to rotational mass which again not good esp on tracked cars, as that means longer breaking distances etc etc.

don't fall for the invalidated warranty line, Porsche cannot do that. what they can do is refuse to renew your warranty but that's a whole new story.

on the plus side the MICHELIN PILOT SPORT 4 S might be in oem sies in March and N spec, I would give MICHELIN a ring as there are rumors of N spec 20" oem sizes due for your car.
 
This may be a useful resource for assessing inner and outer clearance and diameter effects of changing wheels and/or tyres.

http://rennlist.com/forums/tire_rim_calculator.php

I guess you are currently on 20" 8.5" front wheels running 235/35 tyres. I have moved from this to same size front wheels and 245/35 tyres with no issues from the electronics. Even with the standard 235/265 front/rear tyres I had understeer. I skipped experimenting with 245/265 and went to 245/295: I was able to tune out the extra understeer from the increased front/rear tyre width difference with more front camber using Powerflex camber bushing on the front and maybe extra grunt from the engine.

I tried 245/285 as part of my understeer management process but am reverting to 245/295 as the 285 on an 11" rim is too narrow to allow the tyres' rim protection to protect (as I recently found out).

I now run two set of wheels, one with Cup2s and one with MPSS.

Re Michelin and N rating, it would be good if they introduce a homologated MPS4S for Porsche but based on the frequent "it'll be soon" stories for 997 and 991, I would not hold your breath. But as long as you choose the non-Merc/BMW/Ferrari versions they will be good I am sure, but not N rated.

Re your Porsche Centre, it is nonsensical that they will not raise warranty as an issue if you fit a non-standard tyre type with non-standard width so long as it is N rated for another Porsche model.

I'd bite the bullet, get another set of wheels and fit the tyres you want and save the standard items for visits for warranty/service work at the Porsche Centre.
 
Thanks for the useful information / discussion ... this whole N `thing` has been the single most `pain` of my short ownership.

As above recommendation ... have now acquired a second set of OEM wheels and am using N rated fronts / non N rated rears (Cup 2`s).

Had heard that N rated tyres had a sidewall construction better suited to track work .... ?
 
I doubt it as you have 250 mph cars running on non N spec cup 2's all around the world.

I would not have mixed N rated and non N rated though , now you have a miss match in side wall if Porsche did say lets make N spec softer/harder etc !

(I did that on my last set though and they were fine, I just would not do it again)

I now run cup2 on my 987 car all non N rated and also PS4S non N rated.
in fact I won't run any N rated tyre as you have no idea what that tyres was designed for.

An N rated 265 MPSS rear is really a tested Carrera GT front tyre !
 
On the bright side, I don't have to worry about it for a few months: Anglesey is my first event on 20th May. Even so, it's proving to be a more convoluted exercise than I was expecting.

You don't need to be a rocket engineer to know this isn't my area of expertise, but what does baffle me slightly is why finding tyres to fit the brief is proving to be such a pain.

To be a little clearer about the dealership (and having thought about it a bit more) I'm not so sure they actually said they wouldn't honour the warranty, more that they simply wouldn't entertain fitting non N-rated tyres to the car. This in turn does make me a bit more inclined to look at an independent source for both wheels (if needed) and tyres. Also (not trying to be cheapskate, but) doing it through the dealer looks like costing me somewhere north of £5k, and in lieu of a bottomless well of financial wherewithal I'd quite like to bring that down a little if I can.

I'll look into some of the options and come back with a further update (and possibly some additional questions) in a little while. Thanks again guys.

 
I totally recommend Centre Gravity for a road/track suspension review and update. See my separate thread on "Suspension for Motorpsort" just updated today.
 
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