c4s needs new tires?

Left work yesterday to find I ran over a nail.****! Luckily I had the pump in the trunk so that I could get home. Did not want to deal with that then. Question is being a c4s is it best to just replace all of them? The backs are in need and luckily thats what was flat, but the fronts look good. They are going to have to do an alignment,right? I know that will be a pretty penny. So I might as well just do them all? Any suggestions on tires? I have the pilot sport 2's on there now (I think thats what there called) Seem to be fine. Thanks

Just happened to me as well......OH THE JOYS OF BUILDING A HOME! Anyway, I just order 2 new rears. You will NOT need to do an alignment. Just replace the rears (same as before matching the fronts) and you will be good to go.

I'm due for new rears too. Right now I have S03s on and I was going to go with S02As, but it looks like the Michelin Pilot Sport PS2 are rated a little higher. Any problem with a different brand/tread on the rears in a C4?

How do your fronts look? On the 4WD versions you need to have the same rubber all the way around. On the 2WD versions it won't be as much of on issue.

I've still got at least 50% left on the fronts. I bought a whole new set last time around and would like to avoid it this time.

Dell, I wouldn't worry so much about having different front and rear tires for the sake of switching brands, as long as you replace both front or rears. Of course the tires need to be the same size, which is more important. I seriously doubt you would cause any degradation in ride quality or safety running different fronts for a while until they needed to be replaced. jmtc, Rob

I replaced the rears on mine in early April, got a spike in not one, but BOTH rear tires. On the BQE for you New Yorkers, during rush hour. What a pleasant memory.... Recently I changed tires then bought a set of Kinesis GT3 rims for the eventual "switch". I was running the SO2A's, which I liked alot. For the GT3 sized rims, moved to the Advans to see what they are all about. One thing is the Advan tires are HEAVY. This as the rubber is much softer than the SO2A's, so they give you more to start with in terms of tread depth. Have not tried the Advans on the track, but on the street they are nice, with a VERY stiff side wall. I think they will be good on the track.

Why no alignment? I always thought you had to do one every time you get new tires. When/how often should you do alignments?

Just do the rears. I picked up a screw on the bqe myself. I've always replaced rears/fronts at different intervals, never an issue.

Not sure...but I think you mean wheel balancing versus alignment. Wheels are always balanced with new tires. If Porsche need wheel aligments with new tires....then that's downright weird . thanks, Amir

NEVER mix and match tyres on a 911. If you have to replace then do it in pairs with the same brand, same model, same tread pattern. If you have less than 50% wear on the fronts then replace them as well. Failure to heed this advice will result in handling questions being asked on this forum when you crack between 45 and 60mph. If I had a dollar for all those who took the cheap option and then came back onto the forums complaining of handling problems I would be a rich man. A lot of effort goes into designing the best tyre combinations for the 911s sometimes in partnership with and sometimes not with Porsche. Speaking of Porsche, they write in many of their publications "Never mix and match tyres". Nobody ever said Porsche ownership was cheap, and if you want the best performance you have to have good properly matched and compatible tyres. I have never understood somebody spending large amounts of money to purchase a high performance sports car like the 911 and then penny pinching on the only thing that connects it to the road, the tyres!!!! Ciao, Adrian.

So what's the difference between alignment and wheel balancing?

Alignment is suspension Balance is making sure your wheels have perfect (near) weight distribution so they rotate cleanly without wobble or vibration.

Ok so it looks like I can't get S03s anymore. Just go w/the S02As? Anyone try the RE-01Rs?

Hey Rob, I have had two sets of Michellin PS2's on the rear of my 04 C2 Cab in 23K miles. I need to replace all four now and was thinking of maybe trying the Bridgestone S02A's. Did you like them and why are you thinking of going to the PS2's? The Michilens are great tires but they just seem to wear out rather quickly. I got 10K miles out of the factory rears and now 12K out of my second set on the rears. What type of treadlife have you experienced with the S02A's? Mike

Hey Mike Good to see ya here. I have the S03s on now, which I like a lot ( great in wet, wear longer then the P-Zeros I had before, very predictable ), but they're not N rated and it looks like they're discontinued. I looked on Tire Rack's ratings and the the PS2's were rated a bit higher then the S02As, but now enough people have convinced me that switching to the Michelins might be too drastic on just the rears. I'm still curious as to whether the brand has as much to do w/it as the different tread pattern.

The lack of knowledge about tyres still surprises me. There is a comment about replacing tyres and doing a wheel alignment is this necessary? The answer is: It all depends on the wear patterns on the tyres. When you remove your old tyres you have them checked. A tyre expert can tel you if you have been running overinflated, underinflated, with incorrect camber or incorrect caster or toe settings. If there is any evidence of irregular wear on the tyres then a "proper" wheel alignment is necessary. Remember this is all mechanical, it gets knocked out of its original settings over time. An critical area ignored by most Porsche owners is corner balancing also known as weight distribution over each wheel. The 911 in particular is very sensitive to weight distribution. The amount of weight over each wheel can be adjusted. Get it right and the wear patterns improve along with the handling. Corner balancing is especially critical after a 911 has been lowered. Tyre brand; this one surprises me the most I have to admit. I read on these forums all about Porsche Excellence yet people canot seem to relate this same topic to tyre technology. All the tyre manufacturers use different designs, construction methods, rubber compounds etc to produce their products. When different brands of tyres are installed on a 911 they react differently to given situations. This is not good. You want tyres that react the same under load. If you have tyres reacting differently you have uneven grip "traction" on each corner. Believe me this is NOT good. The same applies to matching tread patterns. In modern tyres many have assymetric tread patterns designed for specific purposes. Mixing up these patterns away from the original set up in my opinion is the same as using generic parts to replace Porsche parts. I do not advocate using "N" rated tyres as the only solution, however I do advocate using tyres using a set of rules I wrote many many years ago which clearly 996 owners have not read. X4 tyres of the same brand. X4 tyres of a matched tread pattern. X4 tyres that have been tested on the car type they are to be fitted to using the same tyre tread pattern mixture. X4 tyres that are not more than 6 years old. This time includes time in storage. When tyres reach 6 years old they should be replaced regardless of condition. Where does all this lead? Simple answer: The Porsche 911 is capable of very high speeds not only in a straight line, but also around the twisty bits. If you drive at 90kph (55mph) and never any faster you might get away with mixing and matching tyres (however I have seen handling problems kick in with mixed tyres at lower speeds). If you are going to drive at 260kph or higher you might want to consider that all that is between you and disaster are those round black bits wrapped around the wheels called tyres. But in the end it is up to each and every Porsche owner to decide what they want to do with their own money. Many here on this forum (as with the others) are first time 911 owners. That is why these forums exist. The problem with the 911 is that even a badly handling one is still better than most cars out there on the road. Another problem is that if a badly handling 911 is purchased (say with mixed and matched tyres) the new owner does not know any difference. Then they tend to make comments like I have seen on Rennlist over the past eight years or so. I will write a 996 book like my 964, 911SC and 993 versions, but not right now. I cover this subject over and over again. I still recommend that NOBODY mixes and matches tyres on their 911 regardless of model or version. Ciao, Adrian. PS: This is a Porsche 911 forum. Treadlife is always going to be low on ANY 911. If you want high treadlife out of your tyres then drive very slowly in straight lines only or find something else to drive. The treadlife has not really changed nor improved on the 911 series since 1964. I have heard the same comments about tyre life since I have been involved with Porsche products. It is something you have to get used to as a 911 owner. Right foot down= low treadlife. Corner balancing and the occassional wheel alignment can help though.

Hi Adrian, I think your being a little hard...the tyres on my 914/6 are nearly as old as the car and wonderfully hard. I can get drfits and oversteer that you wouldn't think possible with 110 PS. Old tyres need love as well they bring new excitment to life !!! Cheers, P.S. next slalom Sunday 16th Cannstadter Wasen, Stuttgart. one after that, Sunday 30th July, Solitude, Stuttgart. you should come north of the border some time !!!

Since the original question is about C4s, let me ask my question here. I know that the C4s are suseptible to differneces in tire circumference, since that is used to dictate the amount of fore/aft lockup in the center diff. My 99 C4 came with 225/40/18 fronts, and 265/35/18 rears. Later models used 285/30/18 rears, which is a different circumference ratio front to back (actually smaller in the rear). Can I change to the 228's? Or did Porsche do something in the diff logic to accommodate this tire size change on later models? Another alternative is to go to 275/35/18 rears and matching that to 235/40/18 fronts, which would maintain the same circumference ratios front to back. Comments. Thanks Tony

There is no centre diff in a 996. There is a viscous coupling mounted behind the front differential. The drive transfer is made through plates rotating in a silicon based fluid inside the viscous coupling. The viscous coupling is connected via a drive shaft to the gearbox for the rear wheels and by a hollow shaft assembly to the front differential and the front wheels. Drive transfer and the viscous coupling is purely mechanical. There is no differential logic or any other form of control. When the rear wheels as a pair spin faster than the front wheels, the plates connected to the rear drive spin faster, the viscous fluid heats up and starts to harden. As the fluid hardens it grabs the front set of plates effectively connecting them to the rear set and drive or torque is transferred forward to the front differential and the front wheels. It's as simple as that. When the rear wheels slow down the fluid cools, returns to a fluid and releases the front set of plates. In the 993 the viscous coupling was mounted in the front of the transmission case, but it worked exactly the same way. To keep 100% of the drive on the rear wheels under normal circumstances the rolling diameter of the front wheels and the rear wheels has to be the same. If you have tyre with a lower ratio this will cause the rear wheels to spin faster than the fronts and some drive will be permanently transferred forward. This does not cause any problems by the way because the amount of drive sent forward is low. Ciao, Adrian.

Adrian, Thank you for clearing that up.

Excellent description, thanks Adrian

Adrian, It's also my understanding that the C4 and C4S always have some drive to the front, 5% to be exact, so you never achieve 100% RWD on either car. Rob

A very common misunderstanding based on the not so well written statement on page 60 of the owners manual. If the front wheels and the rear wheels are rotating at the same speed you have 100% drive to the rear and that is how a standard Viscous coupling works. The only way to get permanent drive forward on the 996 is by tyre ratio selection to create a permanent wheel speed differential. Inotherwards less rolling diameter on the rear as compared to the front to make the rear wheels turn faster to cover the same distance. I actually do not recommend this because it is unecessary and it introduces understeer. Ciao, Adrian.

Adrian, I've been driving a C4 since 2001 and was always under the assumption that the C4, or my C4S ever achieved 100% RWD. Thanks for the clarification. Puzzling why Porsche would document it as such. Thanks, Rob

They don't document such. They say the amount of drive transferred forward varies between 5 and 40%. They don't say it starts at 5%. This is typical of Porsche explanations which dates back to when they first started writing owners manuals in the Marketing department. Similar vague explanations appeared in the 964 owners manual which caused confusion for years. If you ever read a 993 manual it says nothing at all about drive movement. A Viscous coupling only start to work (harden) at 160C (320F). This would cause the front luggage compartment to get awful hot awful quickly and stay super hot. This is one reason I recommend you do not create the situation by doing the tyre trick. Ciao, Adrian.

Adrian, PM sent........

Received and answered. Nothing to worry about the transmissions are almost identical. Ciao, Adrian.

Adrian....