k-vic

Would like to see the spec sheet but need the bumpsteer reading also

I think that the role that negative camber plays in traction under lateral g's is not a HS physics problem. I mean that in the sense that there are some complex interactions occuring. I'm sure that there are models that predict this behavior well, but they must be complicated.

Which is a long winded intro to this idea: "There's a lot more going on then just the role of body roll". Was that a pun? There is a force vector going thru the car's center mass to the center of the traction patch. Under significant lateral g's, there's a hell of a horizontal component to the force vector. If the load is more then a g then there's more horizontal component then vertical. And since the force of friction is a function of the vertical (assuming flat road) force, that means that tires shouldn't be able to hold more then a g of lateral force. Yet we know that they can. Just one example of how tricky the dynamics of suspension is.

When talking friction, that vertical force is called the "normal" force. Normal means perpendicular to the surface.

Thought experiment:

Consider what is happening to a car's traction patches when it travels around a 45deg banked corner and is pulling 1 g. Intuitively we know that the banking provides additional grip. In this case the vertical vector associated with gravity and the lateral vector associated with turning, are both equal at 1g. Since they are equal the sum of the horizontal and vertical acceleration components is a 45deg acceleration vector. Since, in this example, the banking is at 45deg, the sum of the acceleration vectors are exactly perpendicular to the track. Therefore the entire force is pressing down on the track's surface and there's no horizontal component of acceleration left that the tire's traction patch has to fight.

Ok, now transition from that thought experiement to the word of camber. I read somewhere the other day that camber can be thought of as a taking turns and bringing your banking with you. There's some weaknesses in that analogy, but it's got some charms too.

I'd attempted to wax poetic on the weaknesses of the "bringing your banking with you" idea, but it seems that they've been trumped by 2 beers.

Hopefully that made sense. If it didn't, have another beer.

Oh, and I'm running AD07's with 30/36. Rear wear looks good, but I think that the fronts can roll over a couple millimeter more. So Fri-Sun I'm going to be experimenting with 29/36.

I found your post interesting and like to make my point.

It’s been mention that there is negative camber but the tire wears on the inside so I don’t see camber as the problem.

(I read somewhere the other day that camber can be thought of as a taking turns and bringing your banking with you. There are some weaknesses in that analogy, but it's got some charms too.)

This comment intrigues me. I believe Camber should be set to maximum the footprint width on maximum load conditions for best traction while providing the correct toe to minimize friction.

This comment has a lot more analogy than weakness.

But at this point we are talking about why tires wear on the inside.

Tire pressures can cause problems when low because the sidewall can collapse but with high tire pressure the tire is supported. I have a problem believing that tire pressure can force a steel belt to buckled.

One reason I believe for center tire wear is the tire construction and can easily been seen by bring your eyesight level down to the footprint and looking for air gaps between the road surface and footprint. You should see the tire centre sits higher and the main friction area for tire wear.

Your banking method is great and would love further discussion maybe the correct cambers for banking?

Interesting theory panameras

Im guessing its got more to do with inducing understeer, tire wear wouldnt be their main concern.

Porsches generally turn to this for the safety factor but honestly I find a little more oversteer to be more comfortable.

Vehicle manufacturers don’t make tires and normally recommend the minimum tire pressures for a vehicle. The tire manufactures gives you the maximum tire pressure for a tire and sometimes you can see the recommended maximum pressure on the side wall.

Tire pressure is about the amount of air needed to keep the sidewall from collapsing on turns. Check out the load tire on a car turning. As far as the recommended tire pressure I go for 2/3 the maximum allowed for safety when driving hard and slow and to provided good driver feel and handling and for optimum tire wear .

02 boxster S 19x8.5 front 235/35/19 19x10 rear 275/30/19

hi all, im getting uneven wear ( cupping) on all 4 tires (inner) , was told the alignment was off by tire shops. however my mechanic says its the suspension. any thoughts???

also i was asked to rotate the tires around so inner becomes outer before doing alignment to prevent/ correct the problem. now why would that matter if the alignment is good that should take care of the uneven wear isn't it?

i heard the best for porsche is the laser type alignment, called some shops they all use infrared, does it make any difference?

thanks for ur help

anyone know good alignment place in vegas??

Sounds like the tires to me. If the cupping is on the edges inside or out then the tire side walls are not holding up under harsh driving and may need more pressure or just slow down on corners. If you run your hands over the cupping and you can feel it in one direction but not in the opposite direction then this is call feathering.

If it was suspension or wheel alignment then how are all the wheel affected the same

But poor quality tires do the same

I agree with Highlander. And I would also say it's a real bonus to have a guy who actually knows what Akerman and Castor are. If he can fix your bump-steer problem we want to know more.

The comment about letting the car settle reads backwards to me; the car is settled with the full weight on its tires, not on the jack. In fact, at least on my 928, you have to pull the car down to its correct ride height in between adjustments before you can take a measurement. For me I always liked to roll the car forward and backward a car length to make sure we had everything settled back down.

There should be some alignment guys in your area who have Porsche experience and some good references. And getting it done right is worth a bit of extra cash. Especially the silly details like getting the steering wheel centered (-: Be sure to ask for the 'before' and 'after' settings report so you can see what changed and where it was out.

And if you're really interested in alignment, Carroll Smith's book, "Tune to Win" is worth a reading.

Most cars are built without the ability to make changes to the wheel alignment. But you have mention the one thing that will check your wheel alignment problems and that’s bumpsteer.

I was going over the option list and noticed that 17mm is a factory option on the cayenne. Are those for all 4 wheels? What are the benefits of using them besides a wider track? Do you need longer wheel bolts?

The factory option shows that a spacer is bolted to the hub, then the wheels are bolted to the spacer with stock lug nuts. You can also buy aftermarket up to 25mm.

Don't like spacers but if you are going to use them check the most important thing of all. The wheel thread must turn a minimum of 10 turns depending on the pitch before tightening . This means that you must make sure there is enough thread holding the wheel

Background: I just put on a set of Michelin PS2s (235 40/18 front, 295 30/18 rear) on my 03 TT. I figured after seeing how my last set of rear tires wore down on the inside of the tire, I best get a wheel alignment.

I just picked up my car after the alignment and I swear, the car feels different. The steering wheel just doent feel as stiff and I'm starting to wonder if anything with the alignment might be impacting my drive feel. Can anyone tell me, am I halucinating or could this be the problem? Maybe its simply the feel of brand new tires too. I dont really know what all goes into alignments on these cars. (It was a laser alignment.) Thoughts?

:huh:

k-vic

I have been in the wheel alignment industry for years and have come across your problem many times.

Steering can feel different after new tires are fitted as the old tires are stiff, new tires will make the steering wheel feel lighter but this should get better over 5000km. The problem with the wheel alignment pulling is most likely caused by the wheel alignment set poorly.

When a vehicle is new the manufactures wheel alignment specification may work fine but over time the geometry design changes. This means that the suspension changes shape and the wheel alignment settings need to change to optimize the wheel alignment balance.

The wheel alignment industry just make changes to the wheel alignment back to the vehicle manufacture settings. But for your tires to wear poorly on the inside means that there is a change to the geometry design and the wheel alignment settings need to change with the change in geometry design for corrected driver feel and tire wear.

The old tires drove straight because they wore on the inside and track your vehicle straight but with flat tires your get a different feel.