C4S tire wesr question

Bought a n '03 C4S with Yokohama neoADVAN08 tires with some wear on them. Now after 6 months of ownership there is a discrepancy in wear(as expected). Question is how much can I expect the all-wheel drive to tolerate before it starts complaining(how does it complain) resulting in me having to replace the rears? Sent from my iPhone using Rennlist

I'm not sure I understand the question. The AWD system is not going to know that your tires are worn. What condition are you imagining that would cause the car to detect a fault?

I think he is worried about differing diameters due to wear. I don't think the car will act up due to wear until the air starts to show through.

Hope this will help: Expect to get new rears at about 8k miles. If beyond you will experience some wheel hop and strange handling. Fronts should last about 10 or 12k miles. My advice is not to "cheap" out on tires. They are the only thing between the car and the road. get good ones, they're expensive but you'll not regret the obvious quality difference.

I've never experienced any AWD system issues, even when my rears were really worn compared to my fronts.

Running sanctioned tires on these AWD cars there should be no issue with any combination of front and rear tires from new to worn out on either axle. That is with brand new tires on the front and the rears down to the wear bars, or vice versa, or any combination, as long as the tires on each axle are matched in diameter with each other. More on this below. I have run the rear tires on my Turbo down to the wear bars with the front tires barely worn and not had any issues. By issues I mean mainly having a warning light come on indicating a problem with the ABS, traction control or PSM systems. Now if one runs non-sanctioned tires the tires could start out with diameters that are different from those of sanctioned tires and there is the risk that when it comes time to replace the rear set of tires the difference between front and rear tire diameters may cause an issue, a warning light to come on. There is the risk that even if no warning light comes on the difference in tire diameters between the front and rear tires means the viscous coupling is experiencing greater rotational speed differences and this overheats the fluid, causing the coupling to run hotter than it would otherwise and shorten its life. Consider this: At around 150mph the difference in speed between the plates driven by the transmission compared to the plates connected to the front diff differ in speed is enough -- due to the different sizes of tires between the front and back tires -- that 40% of the engine's torque is transmitted to the front tires simply because the fluid is hot enough and therefore viscous enough to transmit this much torque. (The fluid gets thicker as it gets hotter.) If the diameter difference is more, the rotational speed difference of these discs increases and the fluid heats up sooner and its peak temperature is greater. This occurs at slower speeds and there may not be enough air flow past the viscous coupling to remove this heat. One would hope that the thresholds of a warning trigger are such that the warning would be generated before damage occurs. Porsche does have guidelines for tires on one axle. A pair of tires can't have more than 30% difference in tread depth. IOWs, if a tire gets a hole and can't be repaired and has to be replaced, you do not have to replace the tire on the other side as long its tread depth is greater then 70% of the new tire's tread depth. FWIW, a mule deer impact ruined a front tire (along with some other things) on my car. The damaged tire was replaced by the insurance company. It also replaced the other tire even though there was just a 15% difference in tread depth.

5CHNELL, sorry for the clumsily worded question but the other guys did manage to get to the gist of it. Macster, thanks for the comprehensive answer. I have had PSM/ABS lights come on but that is related to my worn out brake light switch - new one is in the mail and will be replaced this coming week(both dealers in the area had none in stock). I just wanted to check and see if there weren't any other things to consider as well. Thanks again for the answers - very helpful.

I violated best practices by mixing tire brands. A new to me 03 C4S came with new rear sumitomos old contis and a dealer credit for new tires I spent elsewhere For my long distance daily highway commute I thought I'd just run them out while I decided on 19 inch wheel tire combo. Not the best experiences doing that. On a favorite high speed sweeper exit/on ramp if I braked very hard late into the apex both PSM/ABS lights would come on. Restarting reset everything. Yes they were the Correct tire sizes per mfg spec but very squirmy and not confidence inspiring. To drive aggressively I had to switch off PSM and plan braking and weight transfers in advance ! With new Potenzas the PSM/ABS light warnings are gone even well past my previous braking and weight transfer points. I'm finding that on these C4S to really enjoy it's performance and AWD systems it's even more critical to follow porsche recommendations. With new rubber and a full alignment it's a whole new car !