Replacing C4 tires (can you do just the rears?)

Hi All, New to the forum and am currently looking at buying a 996. One is a C4 with the thought that the AWD would be nice for going up to our cabin in Tahoe (plus I am buying it for my wife so I like the idea of AWD for the rain). Based on my searches here it seems that rear tires wear out about every 20k miles, so my question is can you do just the rears with the AWD system on a C4? I know that there are a lot of AWD/4X4 systems that you have to be really careful with keeping the tires in the same ratios as they came from the factory even with different tires sizes front/rear from the factory (thus replacing all four at a time is necessary) is that true with the C4? With the rears wearing so much quicker than the fronts it seems that wouldn't be the case but better to ask than assume . Thanks all! Tim

My wild *** guess is I would think you could. The car doesn't explode when it goes from evenly matched (when new) to worn rear/less worn fronts. I don't see why it would go nutso when you then swapped that and had worn fronts/brand new rears. I had a Volvo S60R that they recommended keep the same tire wear all around but I think that technology was different in a way that mattered.

The AWD system on the C4 is a viscous clutch, as opposed to a mechanical clutch pack, and therefore can tolerate a difference in wheel rotation speed from the front to rear just fine. Also as DT points out, since the rear tires wear out at a faster rate than the front tires, there will be a difference in the tread depth within just a few thousand miles of replacing all four at once. Just try to match the brand and model of new tires to the set that is left on the car.

It doesn't matter if you're using factory-sized tires. Don't let any tire shops tell you otherwise, because it's bull****.

^^ Another vote for what the good Captain stated above. The only reason to replace all four tires at once is if you SOMEHOW manage to get them all to wear out at the same time. If this happens, you need to do one of two things: start buying lottery tickets or stop driving like a pansy.

We've had our C4 since the end of the 01 run. We've been told since day 1 that all 4 should be replaced at once, but we questioned it (especially when we saw what PS1s cost!). In the research that I've done for this and other similar AWD systems, it's not going to be a catastrophic failure if you run mismatched tires though it will shorten its life. By how much depends on the variation of the tires and how long you run it that way. Really this gets back to the same basic question as many of the "can I afford it" threads. If you are going to do it, do it right and don't cheap out. That said, there have been times when we've replaced just two at a time, but that was due to tire damage and having an insignificant amount of wear on the other set. As far as tire wear goes, there is rear bias so the tears will wear more, but unless you are constantly throwing it around and takin off at stop lights there won't be that much difference between the front and rear. I've never seen our fronts have more than 15% more tread left over the rears and at that point you might as well go ahead and do it all at once. Another thing I'd like to mention is your comment about the AWD in the rain for your wife. The tires you put on and how you drive are going to have a far bigger impact than the AWD system itself. It will do a lot for you, but it's biased towards performance rather than the traditional AWD tuning in more family centered vehicles. Additionally the PSM also plays a big role in this. It is standard (and can't be entirely disabled) on the C4, but it was a C2 option as well.

Most 996's won't go 20k on a set of rears. Some go 12k, some 15k. It does depend on driving style. If you swap out the rears and they are alot stickier than the old fronts you will get understeer and it will make your car less fun. If you are concerned about $500 of tires before buying a 996 you might want to consider another car choice. These cars are lots of fun to drive, eat rear tires when driven hard and maintenance isn't cheap unless you diy.

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Oh please, stop it with this bull****. Just because we can all afford a Porsche doesn't mean we want to throw money at it for no reason. Any car with an AWD drivetrain has built-in allowances for different rotational speeds for each tire, whether that reason is due to going around a corner, the tires wearing unevenly, or an inattentive driver who doesn't realize one his tires has been almost flat for two weeks. Even when brand new, the tires aren't they same size on a 911 from front to rear, they're "close enough". General rule of thumb across virtually all modern AWD platforms is that you have +/- 3% to play with when it comes to tire heights matching, the closer the better. When the tires aren't matching heights, it creates more heat in the system (in the viscous coupling in the case of the 996). If you create too much heat, you will ruin things. Running new tires in the rear and half worn tires in the front will not lead to this scenario. There's a big difference between "doing it right" and "spending a bunch of money you don't need to because you don't understand what's going on."

Thanks everyone for the quick replies! You all confirmed what I was assuming but figured no harm in asking (there are manufacturers where it actually will do damage) . No, I'm not concerned about spending the extra $500 for the fronts, it was just based on some threads it seemed people were at 50% up front when they needed rears but it sounds like that may not actually be the case. I wasn't seeking out a C4 for wet/snow performance but figured it may be a perk. I'm looking forward to getting my hands dirty on one of these! In a past life I was a ASE certified mechanic (at a dealership that isn't Porsche) but I changed careers when I no longer enjoyed working on my own cars so I've been scouring a lot of the DIY threads.

After buying many many tires for my C4, you will go through rears twice as often as fronts.. Ensure you replace the rears with exact make and model tires, and do not vary from the size recommended by porsche. Also don't buy cheap tires, you would be saving the wrong buck.. Michelins have been my favorite Great car, I had mine for seven years..

I agree with the comments in this thread about the ability to change the rears. I've done it several times on my C4S. For my driving style, I tend to get about 15K out of a set of rears. Sometimes it's a little more, but usually not. As noted above, the 996 C4 AWD system utilizes a viscous coupling. In normal driving, it sends 5% of the power to the front wheels and 95% to the back wheels. In the event that the front wheel(s) rotate faster than the rear wheels, the viscous coupling will send up to 40% of the power to the front wheels. Realistically, the only time that this scenario will take place is driving on the track, or perhaps aggresively driving on twisty roads. In a lack of traction situation like snow or rain, the PSM will intervene and "correct" the wheel slippage before the AWD system ever reacts. Your best bet for driving in rain or snow is proper tires with good tread. I drive my AWD 996 in almost all conditions, and it is very good.

Went through this last year with my car Rears were worn and fronts looked really great Got exact replacement rears and it was terrible Loose feel in rear After contacting the factory to discuss I learned That the tires change over time, not just from Visible tread wear but also from Heat/Cold Cycles, Storage Temperatures I bought a new set of michelins and it felt like I had replaced the entire suspension !

Same issue here, rears were corded on inner tread, fronts at 80% of new. Aggressive camber for track days doesn't help. 2003 Carrera 4S Speed Yellow / 1955 356 Continental 1500 Rust Red

You think the 911 goes through rear tires, get yourself a Corvette with line locks. I can go through a set of tires faster than KrazyK goes through a barrel of DT40. I am due for another set of rears on the 996 too. Every so often I get the urge to find some 6" or 8" wide wheels for the 'Vette and some nice hard tires and find myself a parking lot.

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I remember doing that with a friends old Mach 1. We mounted the spare and he started doing donuts. The problem was, the wrong tire was spinning. We couldn't stop him because of all the noise and laughing.

The old wives tale that you can't mix tire brands is BS. No one in five years of watching this thread will present any data to the contrary.

^^^^^Says the guy that thought the ABS light came on when the ABS was activated sorry couldn't help it....

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This is sound advise. Installing a set of like rears will probably not cause a differential problem, but it is likely to adversely affect the way the car handles. New fresh rears when mated to a fresh front set will handle differently. I have had many people buy rears, only to have them installed and immediately turn around and buy a set of matching fronts because they don't like the way the car handles anymore. You can replace in pairs, try it. Worst case scenario is you have to buy a set of fronts to match if you don't like the way the car handles as a result.

I think the age of the tires impacts this as much or more than the remaining tread. Rubber compounds used in tires oxidize over time. You might have a set of tires with 70% of tread remaining that look great, but if they oxidize and the compound stiffens or becomes brittle, then the handling will be adversely impacted. You have to conisder tire age as well as tread.

Thanks again everyone! It's good to know that it won't do anything to the drivetrain itself. Definitely if after putting a new set of rears on the handling is adversely affected, a new set of fronts would also be in order (otherwise I shouldn't be looking at a 996 ).