Tyre advice

Hey Sorry if this has been asked and covered before, however still quite new to 996 ownership...my 2000 C4 Man Coupe needs some new rear boots as 1 has a slow puncture and while they both have loads of tread they are an unknown brand and definitely not N-rated... So question I have two tyre width choices for my Porsche 18inch turbo look wheels 265/35-18 285/30-18 Why?? what are the benefits of each width and what is the preferred brand for a car that will be used as my daily driver in the U.K. With some fast road trips/ sustained U.K. Motorway speeds... Any thoughts?? Cheers Dai

I'm in the market for new tires too, so I'll be interested to hear where this goes. In terms of rear size, it'll depend on what width wheels you have.

Personally I go for higher profile, more resistance to dings from pot holes. Also IMHO N rating is just to mark up stuff, plenty of good rubber out there that isn't N You misspelt tire

Michelin Pilot sport PS2 - get the 285/30 size

I'm using Pilot Sport A/S 285/35-18 rears. 500 tread wear rating should last you several summers & they're under $300 a tire. They grip well from my experience and shouldn't hydroplane as bad when the roads are wet.

At the moment its on the 265/35 - 18 and they look stretched. The side walls are not square to the rims the tread part looks is narrower than the rim. Will price up some 285/30 and report back.

Its on Conti's at the front some may go this route...

Go for 18/285/30 not 285/35. It is a better match to the original tire size. There are some tire calculators out there that will allow you to compare. Volkert

I have the Continentals above on my street wheel set, they are nice tires.

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I'm curious if I'm just a moran or if there are some material problems with running the 35s in back. The fitment is fine from my perspective and there's no AWD to mess up. My speedo runs about 3mph above actual with the 30 profile rears, so I don't see any major problem. The P/S all seasons are really durable & grip well for spirited driving, so I'm a bit of a fan of running this setup. Anyhow, appreciate any insight you might offer. I couldn't find any big issues prior to buying new rears last month.

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Where are you located? Never mind I see U.K.

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With the C4 and its AWD system the front and rear tire sizes need to be selected to keep the revs/mile the rear tires turn compared to the fronts in some ballpark relationship. I advise you get a tire/wheel brochure from Porsche -- these may be available online -- and from this you can see what wheel/tire sizes Porsche sanctions for use on your model and year of car. You should probably stick with these tire sizes/combinations. If you want to use different sizes then use a tire calculator and plug in the front tire numbers and note the revs/mile number then do the same for the rear tires. The rear tires want to make more revs/mile than the fronts -- this difference in revs/mile means the rear axle driven discs in the viscous coupling turn faster than the discs connected to the front axle. The difference in speed heats the viscous fluid and this is what transfers torque to the front axle. If the speed difference is too great this can subject the viscous coupling to too high operating temperature. (The working temperature of the fluid is already in the 300F range.) This can result in a viscous coupling bearing failure or because the coupling is inside the front diff a front diff failure. If the revs/mile numers are flipped, IOWs the front tires make more revs/mile than the rear tires, there is no torque transmitted from the rear axle to the front. A braking action is instead created. As long as the wider (or narrower) tires meet with the diameter requirements which I coverd above, wider tires have some pluses and minuses. Same goes for the narrower tires. Wider tires put more rubber on the road but can be noisier, more prone to tram lining or hydroplaning in the wet. They can cost more. Narrow tires of course put less rubber on the road but still as long as one stays with sanctioned tire sizes put more than adequate rubber on the road. They can be quieter. Less prone to tram lining or hydroplaning. They can cost less. I can't comment on the cosmetic pluses or minuses. Beauty is in the eyes of the beholder. The preferred brand of tires for the car are those tires Porsche sanctions for the car. The brands: Possibly Pirelli, Michelin, Bridgestone, Continental. These are the brands that are listed for use on my 996 Turbo which has the AWD system similar (identical) your C4. I've run Continental and Bridgestone tires and can't tell the difference. (I've run Pirelli and Michelin tires on my Boxster and for all intents and purposes can't tell the difference.) This is as it should be and tends to in my opinion lend some weight to the value of Porsche and its N-rated tire system. Might as well cover this while I am here: Porsche does not sanction using non N-rated tires, mixing brands of tires even if they are of the same N number, mixing N numbers of even otherwise identical tires. If you elect to ignore or worse go in opposition to what Porsche has to say on this subject -- the only authority in my opinion -- then you are free to I guess buy any tire based on what someone other than Porsche told you will work. I can't tell you to go against what Porsche says. I can only second what Porsche says and recommend you do as Porsche says.

Macster, "If the revs/mile numers are flipped, IOWs the front tires make more revs/mile than the rear tires, there is no torque transmitted from the rear axle to the front. A braking action is instead created." Are you sure about this? Would that be the reason why PS2 N3 was never "certified" on porsche's tire recommendation documents? http://www.porsche.com/usa/accessori.../tyreapproval/ I try to understand the AWD feature, the effect of rear vs front rotation speed, of the car (2000 C4) since I have it, no one could really explain me how the permanent 5% to the front are achieved (difference of tire rotation front to rear? / rear wears faster.. so more than 5% on worn tires?) Another one funny thing is slip of rear required to have more than 5% to the front but PSM kills power when it sense slip on the rear?? Talked to various sales, tech, Werkstattschef etc, many different opinions, no one really convincing.

So I went with a set of Conti's in the end to match the fronts some before and after pictures...the 286/30/18 fit the wheels so much better... Old tyres Old tyres, seem stretched New Conti's Wheels looking dirty... New Conti's tread pattern looks great not sure how long the colour bands will last...