mtnman82

I just got a set of Direzza Star Specs and wow, sticky tire fun! I'm just wondering how many miles I can expect out of these on the street (treadwear 200)? Will I get even 5K or 10K miles out of them? I bought them for my everyday tires but am wondering if I made a 'mistake'...

Dougs951S

ive got 15k miles on a set of michelin super sports, super sticky amazing tire but they're done...i'll be buying another set.

944Phil

I have the same tires (direzzas). I've done 7 track days over the last 3 years and a drag night. They're still going but they aren't as sticky anymore. Actually the fronts are almost due. I will buy them again. I really like them and they aren't super expensive.

mtnman82

Doug - are those all street miles? It came down to the Direzza's and the Super Sports (treadwear 300) for me, and I decided to try the Direzza's this time...

Phil - only track time on the Direzza's?

Dougs951S

15k street miles, zero track time, lots of hooning around and spinning the crap out of the rears

BTW treadwear is only helpful when comparing tires from the same manufacturer. in my experience the super sports are softer and stickier than the star specs and wont last as long, despite being a 300 vs 200 treadwear tire. I want to buy 4 new PSS but I'll be looking at well over 1k so I'll probably go with a slightly less sticky, cheaper tire up front. I NEED all the traction I can get in the rear so no compromise there.

mtnman82

Thanks Doug, that's what I was looking for. If I can get 15K, or even North of 10K out of these I'm good. I'm thinking I'll give the Super Sports a try next time around.

944Phil

Street and track. I have a set of pilot sport II's that I sometimes use for the street, but haven't had them on for a couple years. Those are 18 and I won't put them back on until I upgrade the a-arms.

jmj951

I've run R spec tires and various types of slicks on 18" wheels at the track many times using a stock 86 a-arm and stock hub, and I don't see any evidence of problems. I'm not sure that the a-arm is the source of the problem, but I do think the failures I have seen were preventable with proper setup and ball joint maintenance.

I used to be concerned about the stock a-arms after hearing about 'all the failures' and was convinced I would need to update them, but as I was able to see pics and get details of actual failures over the years, I've found two things that people do that specifically cause the a-arm problems:
1) Ball joints failed because they were not replaced when they wore out, or because the car was lowered. The pins and in some cases the a-arm material around the ball joint cracked or failed due to either a worn, loose ball joint that was not replaced when it should have been, or an improper ride height for the type of ball joint pin being used. (I understand that the ball joints on some aluminum a-arms are not technically serviceable, but that's not the case with mine.)
2) The drop-links for the front sway bar were mounted incorrectly, or the car had an inappropriate sway bar/spring combo, causing the middle of the a-arm to be overstressed and fatigued to the point of failure.

Porsche states that you need an updated caster block and a different, stronger eccentric mounting bolt for the rear of the a-arm when you mount 18" wheels. Porsche doesn't say anything about upgrading the a-arm. With those two required upgrades, I think you should be fine with those 18's on stock a-arms. Personally, I've upgraded the caster block, but not the eccentric bolt.

Aside from that, I think the following should also always be considered to prevent a-arm failures:
1) Make sure the ball joints are in excellent condition and that the ride height is appropriate for the pins you have. If a car has stock ball joint pins, then it must be set to run the stock height. If the car is lowered, height-correcting pins must be used.
2) Run a properly sized and mounted front sway bar. The point being that the sway bar shouldn't be doing disproportionately more work than the springs to keep the car level (with these a-arms). Stock springs allow the car to lean way over, so if you autocross or track the car and want to modify the front suspension, the springs (not the sway bar) should be the first thing that's replaced to level the car. Just upgrading the sway bar is a problem because it significantly increases the forces on the middle of the a-arm. If a car is set up to use a bigger sway bar to keep the front level but still running weak street springs or just mildly updated springs, the sway bar mounting point on the center of the a-arm is going to turn into a pivot point, and it will get overworked and fatigued at an autocross, track day or race.

For anyone who has a setup that conflicts with these two points, or if your car was lowered by a previous owner and you don't personally know what condition the a-arms and ball joints are in, you need to remove and inspect the a-arms. In many cases it needs to be cleaned up before you will be able to find any potential problems, and it's really not difficult to remove from the car so there's no big reason not to do it (you just need to leave the caster block mounted to the a-arm and remount the caster block exactly where it was so that the caster alignment is not affected). You want to look for a bent or loose pin, any evidence of the pin banging on the a-arm, cracks in the a-arm around the ball joint, and discoloration (in a specific pattern around the stressed area that would appear due to fatigue) around the ball joint pin and the sway bar mount. If you see anything that might be a crack, it needs to be analyzed by a machine shop that can use a process to find/confirm any cracks.

And I hate to mention it but I've seen it in pictures - if you don't have rubber bushings on both the top and bottom of the a-arm where the sway bar's drop-link is connected, you need to stop driving it now. Nothing should be bolted down solidly to the sway bar mounting hole in the a-arm, and it's probably not even a good idea to use polyurethane or anything other than rubber there. You can use polyurethane, delrin or another stiffer material for the inner sway bar mounts and the part of the drop link that connects to the sway bar, but the mounting point of the drop-link to the a-arm should always use OE-spec rubber with the stock a-arms, and you need to inspect those rubber bushings to make sure they're not significantly worn to the point of allowing the metal retainers to contact the a-arm.

Sorry this turned out so long, but I really think all of the alarm over the a-arms needs to be reigned in with facts and useful information about avoiding the failure. I mostly see generic nebulous claims about the weakness of the stock a-arm that never involve a real failure mode analysis.