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YOUR RESEARCHOpinions on tire wear please....
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I can only assume that your issue is due to lowering it and the camber not being able to be put in spec.
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Mix this up so enough data is collected with the LF checked first, etc.
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My cars alignment specs were dead on perfect and the suspension was stock (coilover installed yesterday, wheels on order and fully adjustable control arm will be ordered in ths next few days).
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Check inboard, center and outboard tire surface temperatures
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Suggestion
At the end of a spirited drive (push hard - as much as traffic and road conditions allow) - check the inboard, center and outboard tire surface temperatures.
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My cars alignment specs were dead on perfect and the suspension was stock (coilover installed yesterday, wheels on order and fully adjustable control arm will be ordered in ths next few days).
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Need new tires too
. Seriously though, it was aligned actually twice during this period. All within spec except a a tiny bit of excessive negative camber
No doubt, a little of both. Does this look like a camber issue or toe issue? The extreme edge wear makes me wonder if it might be toe related, but I'm looking for expert opinion.
Thanks Scott, and others. I appreciate the input from those with experience with tire wear and alignment.
I wish I had kept the alignment printout to compare specs. I lowered the car, approx 30mm last winter before putting on these tires and realigning. I had asked for to be at the mildest end of the spec spectrum. With the lowering, negative camber could not quite be brought into spec, but was close to higher negative camber end of the spectrum. Toe was set to as close to zero end of spectrum as they could get (very mildly toed in), and well within spec. Since I have been trying to learn a little about alignment specs and 996 suspension to try to understand how it all works.
From what I've read, it would appear that 996 multilink rear suspension tends to toe out on compression, which seems to make sense looking at the arc of the links with the wheels off. This got me wondering if having almost zero toe in at static, might actually be creating a situation of excessive toe out under load, or accelerating? There is a very good chance I'm way off on this, but I throw myself to the collective of much smarter people than me here at Rennlist. Previous to lowering, tires also seemed to wear most heavily on inside edges, although not quite as bad.
Sorry, missed you comment while I was replying to others....first this is the rear not front. Fronts are wearing evenly. The other rear tire looks virtually identical.
Toe will remain consistent regardless of accel or decel (unless there is slop in the bushings/ ball joints).
Toe-out in compression, in the rear, usually induces oversteer. I doubt that is the way the suspension is designed.
You would do well to have it aligned to spec and have them take a little off the negative camber spec (go more vertical).
Oh - that's a whole different story. I thought this was the front.
It's actually so much different that the same things apply. Slightly more wear on the inboard side of the tire is much more common, and less of an issue, at the rear. Dialing out a slight amount of negative camber will help. Much less change than if this were at the front.
my tire wear isbasically identical to yours, and I got twenty thousand miles out of my Continental all season tires and I just replace them with some Michelin a few weeks ago. I would not be concerned
glad i asked
i agree w scott above - this is kinda normal
if u want less inside edge wear just dial out some rear neg camber, otherwise leave it if the car feels good to you on the move
Just bare in mind all the Porsche's recommended adjustments are a compromise. This includes tire pressure, alignment specs and all possible parameters. The fact that you lowered your car and perhaps drive a bit conservatively when it comes to cornering, the weight, load and how you take a line all have direct impact on the tire wear. I would start by decreasing tire pressure, because Porsche 911 rear tires are very wide and any more air pressure tend to load the outside more so than the average sedan.
Good point - especially when it comes to pressure. If that center rib is worn more than its neighbors, than your pressure has been a little too high. Would not account for the wear on the inboard, but it would provide more even tread contact (and wear). Tires, no matter what, are always a compromise. Finding the best compromise for the given task is what we are all after.
20,000 miles! Damn, I'd be thrilled if mine had that kind of mileage. I have yet to get more than 8000 miles out of any rear tire...and I drive like Miss Daisy.
Interestingly enough, I ran 40psi (44 recommended) in this set from day one. Every set I've had have worn the centre more than sides, as can be seen in the picture with the straight edge. I was concerned about going much lower in pressure with the low profile of the tires.
It's comments like this that make me feel like something isn't right. There was a new set of BS S04s on car when I got it. Inside edge to cords in 5000 miles. Replaced with Falken FK453s and had it realigned. That set of rears lasted about 7500 miles. Another set of Falkens, alignment and about 8000kms. Michelin PSS, alignment and this wear and mileage (6800 miles). First sets I stick with factory recommended tire pressures (44psi rear), Michelins I dropped to 40 psi. No drag racing, no significant high speed runs, three track days each year. Majority is city, back road and highway.
My cars alignment specs were dead on perfect and the suspension was stock (coilover installed yesterday, wheels on order and fully adjustable control arm will be ordered in ths next few days). Tire pressures are exactly what the factory calls for (36 and 42 if i recall). My rears are perfect and my fronts have very very very minimal feathering.
I can only assume that your issue is due to lowering it and the camber not being able to be put in spec.
Here is my right rear, the left rear looked just like it and my two fronts were not worn at all. These were Continental DWS all season tires. They were on the car for about 18,000 street miles, I run about 34 PSI or so. When you looked at the rears without getting under the car, they looked great....but go under the car and you'll see the inboard shoulder is completely worn compared to the outboard shoulder. I put some Michelin Pilot Sport 4S's on them. They are sticky! But the car is in hibernation.
I was just thinking about tire pressure yesterday.
What's the lowest one can safely go?
I know the front is light and could use less than the tire manufacturer suggest.
Commuter car with nice twisty roads to and from work, down hill in the morning and uphill home makes for a great end of the day.
I'm not going to touch the - how low can you go question. However - I will offer some ideas.
Use an IR temperature gun (or better yet, a tire pyrometer). At the end of a spirited drive (push hard - as much as traffic and road conditions allow) - check the inboard, center and outboard tire surface temperatures. Do this as quickly as possible after stopping. Log the data over several trips and look for trends. Hopefully your drive will have an equal number of rights and lefts. If not, try to look for a mid-point stop that is close to the balance of direction and severity. You can also focus on just one side at a time - take what is learned and apply to the other side.
Once a decent set of data are captured, analyze for ways to equalize the readings. I.e. if the center is warmer than the sides, you can drop pressure. Any changes should be in small increments (unless temp deltas are large). If one side or the other is hotter, than camber change should be considered. It's unlikely you would ever get temps uniform, even after much testing and refining. Just getting things closer will be a good step.
Surface temps will drop quickly. Be sure to note the order in which each tire was checked. Mix this up so enough data is collected with the LF checked first, etc. Then move to a different corner as first up, for additional data-sets. It will probably take a lot of trials - but the more data you have to work with, the more likely a good picture will emerge. Some data sets will be ruined for any number of reasons (rain, cold, speed, etc). Keep the data - but be sure to note what happened and why it should not be used for any calculations. Consistency in testing is key.
I've had two in the back seats of my 996 once.
2 12 year old girls who weighed almost nothing.
I don't think a couple of normal sized adults could fit back there.
I wonder what weight passenger they considered being in the back.
Most people don't have a tire pyrometer. Though this one is inexpensive:
https://www.summitracing.com/parts/l...iABEgKOcPD_BwE
For a trial such as this, a cheap infrared thermometer will work fine. I think you can get one at Harbor Freight for about $15.
JTT:
The fact that your car is lowered makes it hard to know all of the variables you have added to this question. My car is stock for ride height, but I experienced excessive rear tire wear on the inside rib when I was at the end of the useful life of my first set of shocks. New shocks all around and some refreshed bushing and one tie rod (up front) and the wear pattern returned to what I think of as normal - approx. 12,000 miles on a set of rear Super Sports before the inside rib shows threads. Are your shocks in good shape? Do they match the lowering springs you are using?
Brand new Bilstein B8s all round, with new H&R lowering springs. I can't feel any play in any of the bushings, either with hands or with pry bar. All rubber bushings are visually good with no cracking, still feel firm.
Thanks Scott, I will try to track temps come spring. I already have an infrared thermometer.
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