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“The thing is... A strut bar is another spring, that is charged laterally when the towers flex to the inside. The strut bar act as a damper between the towers. allow them to move vertically but not against each other. When enough load is put on the other side of the car, the outer side is compressed against the inner side, making the inner tower closer to the outer. The bar dampens the movement.”

A “strut bar” is a chassis brace, by definition it isn’t a spring. It even less resembles a damper. A brace works to increase the rigidity of a structure by adding stiffness to it. The more stiffness it can add the more effective it is, so the less springy it is the better it functions.

Regards,
John.
 

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"To me, personally, 44 psi is too much on the rear, at least with the suspension setup that i have on the car, which is quite firm. The max i've used on the rear of the 156 SW was 40 psi (cold) and i've found it fun, but dangerous on the limit specially on the winter at medium to high speed corners"

In my experience the range of pressure which works well is very dependent on what a particular tyre ‘likes’, which seems to vary considerably from tyre to tyre. I’ve found that some tyres need quite a high pressure to work well (i.e. to NOT be soggy bags of unresponsive yuk), and other tyres work well with significantly less pressure. To find what a particular tyre ‘likes’ requires experimentation, and a given tyre may ‘like’ a different pressure if is fitted to different cars, and whether it is fitted to the front or to the back of the car.

As a rule of thumb it seems (to me) that the softer a tyre casing is the more likely it is that the tyre will work better at substantially higher pressures (i.e. than the car manufacturer recommends). The casing stiffness seems most important in the sidewalls. As a generalisation, tyres with stiffer sidewalls seem to need less pressure than tyres with softer sidewalls. As an example, 44psi may be too high for tyre X, but with tyre Y it might be in the sweet spot (or in the ‘sweet window’).

Of course the suspension set up may affect what pressure more suits a given tyre on a particular car. The damper / spring / ARB stiffnesses might influence the ‘ideal’ pressure for a given tyre (however we might define ‘ideal’, considering different drivers will have differing preferences for how they want their tyres to behave).

My car works well with 44psi (or nearabouts) in the rear tyres that are on it, being fairly soft cased tyres with softish sidewalls (cheap Achilles 2233). Other tyres may or may not need as much pressure. It isn’t perfect, the rear end is a bit ‘skatey’ on loose gravel surfaces, but it is quite controllable. Rear grip and stability is not a problem on sealed surfaces. The front tyres have much stiffer sidewalls and don’t feel to work better over about 38psi, the ride just gets harsher.

“Another thing i feel is that with higher pressures the road feel is firmer but less harsh. This sounds like a paradox but has a logic. Since there is more tyre damping due to the extra air, the vibrations dissipate more. So i feel more bumps, their vibration doesnt come through the struts and arms so much.”

I can’t account for your perception of “firm” vs “harsh”, or how you are differentiating between the two terms. It doesn’t match my experience in that I do find higher tyre pressures to be ‘harsher’, though I have a fair tolerance for a ‘harsh’ set up.

I have to disagree with your suggestion that the damping property of a tyre increases with increased air pressure. IMO higher air pressure doesn’t equate to greater damping in the tyre, the opposite is the case. The obvious analogy is an inflated ball. A ball that bounces well has relatively little damping, and a ball that bounces badly has relatively more damping.

Thought experiment;

From a given height, drop a highly inflated tyre and wheel (or a ball) onto the ground. How high does it bounce? It bounces quite high, because there is little damping effect to ‘absorb’ the bounce. Now take all or most of the air out and drop it again from the same height, how high does it bounce now? It bounces a lot less, because there is a lot of damping effect and most of the energy is absorbed (converted into heat rather than oscillation).

IMO a tyre with higher air pressure is less internally damped than a similar tyre with less air pressure. So, increasing tyre pressure reduces a tyres’ internal damping. How does this affect handling? That would be a good question with a complex answer that I would struggle to answer, but I think it is obvious that higher pressure makes the tyre react more responsively to forces acting on it. This may or may not cause grip to increase or decrease, depending on a lot of factors and interactions...

Regards,
John.
What i’ve noticed from the experiments i’ve did was the following.

All cold pressures, only driver on the car, 1/2 tank.
Factory pressures, 2.3/2.4 bar (33/34psi +/-) low speed the tyres seem to be softer with nice turn-in, but load transition is slowe and has a greater lateral bounce. Still good, but less responsive, at higher speed cornering 140kmh and above the car is planted on the ground and doesn’t roll on the tyres. (Nobody touches this subject but this is an issue as i will point after).
Higher pressures, 2.5/2.6 bar (36/37 psi), excelent lower speed initial turn-in and transition load is quicker, so better. Now the less nice part. The car feels less planted and at higher speed the car has a roll over feeling. Literally the cars is having body roll due to roll movement over tyres. I guess that higher speed naturally increases more the pressure, the warm tyre pressure is about 2.7/2.8 and probably the front tyres gets bulgier, making the tyre surface more round and allowing some roll. At the lower pressures the body roll is perfect. The car as i have now, simply corners flat.

In the end i guess it has to do a lot with the tyres. These cars come with P Zeros from the factory as far as i know. And P Zeros have stiffer sidewalls. With proper more sporty tyres, nobody would need such higher pressures to get the quick turn-in and fast transitional load change. And the tyres wouldnt bulge because the weight of the car is enough on the outer side to avoid the tyre to roll but flex instead.

I’ve experimented also higher pressures. The car wanted to oversteer badly. I’ve had the rear loose at 130kmh while driving hard and not while doing heavy lift off. Just subtle lift... so... i can’t recommend. This was with 2.7 bar cold (39 psi). At low speeds is a fun drive but as speeds gets higher, it gets dangerous. Its not 4C style oversteer. Its much much more unpredictable, because at cold pressure is all okay and when warm it has sudden loss of traction. With softer suspension its would be more driveable at those pressures since the softer suspension allows for greater mechanical grip.

What i’ve found so far is that the sweet spot on the 215/45/17 on these cars is around 2.2/2.4 bar, and to me personally that is 2.3/2.35 bar on the front and 2.4 on the rear. Its funny that Alfa revised the 2.2 bar to 2.4 lately but to me that is due to the reduced inner tyre wear. Raising the pressure to me also resulted in more even wear at the front, because probably raising the pressure at the center reduced pressure on the inner side and therefore it evens the band wear. 2.4 bar is okay but at high speed i still think it allows for a bit of roll, but that might happen more or less depending on the suspension compliance. On a less compliant suspension which is my case im preferring 2.35 bar at most on the front, more than that only with fully laden car.

Also having a great rear pressure, and since its still close to the sweet spot, helps the rear to rotate a little more without losing a lot of grip.

This setup works great but in my opinion to have the full advantage, stiffer sidewall tyres are mandatory to improve low speed response. Using higher pressures to solve that sincerely doesnt cut for me. Not so much because the car gets skatier but because the additional high speed roll just messes the whole driving experience. Higher pressure, yes but only for city driving or twisty roads at lower speed, below 100kmh, its a joy. Above that i would avoid it.
 

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I experiment with tyre pressures until the tyres behave as I prefer for a specific tyre fitted to the specific car in the general range of conditions in which the car is used. Unfortunately this doesn't include speed unlimited track laps. My car is used on public roads where the maximum local speed limit is never above 110kmh. I'm no angel and my snow isn't pristinely white, but my driving habit doesn't include speeds that are very substantially above the legal speed limit.

Does your car do many laps around Estoril or Algarve? If not then I'd suggest that the reasons you have put forward for sticking with lower pressures are irrelevant, and somewhat contradictory. Google informs that the general ex urban speed limit in Portugal is only 90kmh, and a more generous 120kmh on major highways. You imply that the relatively lower pressures you prefer are because you are "cornering 140kmh and above". If not on the track, when does that happen? The answer should be 'never'...

You say that higher tyre pressures are a "joy" for speeds below 100kmh, implying that higher pressures are better than lower pressures when speeds are not all that high. The vast majority of road cars will be driven at speeds below 100kmh the great majority of the time, including yours unless you are not particularly fond of your driving license. Logic says that if the car is near or below 100kmh most of the time, then you should be using tyre pressures that are a "joy" at those speeds.

I tend to use higher pressures when I have softer cased tyres (typical of most cheaper tyres, but not necessarily) fitted to my modestly 'sporty' road car because I prefer the way it drives at road legal speeds compared to how it drives on such tyres when less inflated. I like the responsiveness and 'playfulness' that higher pressure imparts into the steering and handling.

For a 'sporty' car what matters is how the car feels, so long as safety is not significantly compromised. A 'sports' car, or a car with 'sporty' pretentions, doesn't need to be as fast as possible through a corner, it isn't a racing car, it just needs to be a lot of fun to drive on the road at the speeds it is driven at. I have driven quite fast cars which have had a great deal of grip, and I could drive through corners at very high speeds, but were actually rather boring to drive because the chassis was not very 'playful' and the steering rather 'numb'.

If I were tracking my car, then my criteria for tyre pressure would change, all that would matter is what pressure is fastest over a race distance. What would be fastest would be the pressure around which the tyre is grippiest at the temperature the tyre is working at over the race distance (a circular relationship). This is unlikely to be the pressure which feels more responsive and entertaining at reasonable road speeds, which is what I choose for a road car...

Regards,
John.
 

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I experiment with tyre pressures until the tyres behave as I prefer for a specific tyre fitted to the specific car in the general range of conditions in which the car is used. Unfortunately this doesn't include speed unlimited track laps. My car is used on public roads where the maximum local speed limit is never above 110kmh. I'm no angel and my snow isn't pristinely white, but my driving habit doesn't include speeds that are very substantially above the legal speed limit.

Does your car do many laps around Estoril or Algarve? If not then I'd suggest that the reasons you have put forward for sticking with lower pressures are irrelevant, and somewhat contradictory. Google informs that the general ex urban speed limit in Portugal is only 90kmh, and a more generous 120kmh on major highways. You imply that the relatively lower pressures you prefer are because you are "cornering 140kmh and above". If not on the track, when does that happen? The answer should be 'never'...

You say that higher tyre pressures are a "joy" for speeds below 100kmh, implying that higher pressures are better than lower pressures when speeds are not all that high. The vast majority of road cars will be driven at speeds below 100kmh the great majority of the time, including yours unless you are not particularly fond of your driving license. Logic says that if the car is near or below 100kmh most of the time, then you should be using tyre pressures that are a "joy" at those speeds.

I tend to use higher pressures when I have softer cased tyres (typical of most cheaper tyres, but not necessarily) fitted to my modestly 'sporty' road car because I prefer the way it drives at road legal speeds compared to how it drives on such tyres when less inflated. I like the responsiveness and 'playfulness' that higher pressure imparts into the steering and handling.

For a 'sporty' car what matters is how the car feels, so long as safety is not significantly compromised. A 'sports' car, or a car with 'sporty' pretentions, doesn't need to be as fast as possible through a corner, it isn't a racing car, it just needs to be a lot of fun to drive on the road at the speeds it is driven at. I have driven quite fast cars which have had a great deal of grip, and I could drive through corners at very high speeds, but were actually rather boring to drive because the chassis was not very 'playful' and the steering rather 'numb'.

If I were tracking my car, then my criteria for tyre pressure would change, all that would matter is what pressure is fastest over a race distance. What would be fastest would be the pressure around which the tyre is grippiest at the temperature the tyre is working at over the race distance (a circular relationship). This is unlikely to be the pressure which feels more responsive and entertaining at reasonable road speeds, which is what I choose for a road car...

Regards,
John.
Your point makes all the sense John.
But in fact, here, most of the time its easy to go above the legal limits. The reason is simple. I live close to the beach, if i go to the city nearby the closest access is a highway where the legal limits seems to be very slow. Doing 140kmh there its not a big deal.

I rarely pick my car to make 2km around my home, i use my bike instead. Everytime i use the car i pass through this short highway acess and most of my usage is on open sweeping roads which quite often, speeds, exceed 120kmh if i’m alone in the car.

I drive a bit fast, but not so fast to be considered a wreckless driving. Some of the times, the cars around me aren’t driver much slower. Its more about the roads configuration themselves. We have larger roads than in UK. Not USA large, but larger anyway.

Some of our roads are very similar to Autobahn, but with speed limits.
 
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