McLaren MP4-28 Mercedes

[Pup]

The tyres are typically a lot less damped than the suspension itself, so the more you rely on them the less damped the "complete" (springs + tyres) axle seems to be.

So does that mean that the car would better damp the porpoising if the suspension were softer? Or would the car still bounce on the tires?

[Tim.Wright]

So does that mean that the car would better damp the porpoising if the suspension were softer? Or would the car still bounce on the tires?

Good question, its not immediately obvious to me. I think DaveW could answer this with some experience. My intuition would say yes it would help the damping. Mainly because you have a system with two elasticites in series (spring and tyre). As one of them increases in stiffness to the point of it being rigid, it mathematically starts becoming irrelevant to the overall response.

So in this case, the suspension is supposedly becoming rigid and that leaves a pretty underdamped tyre to control everything. I believe the tuned mass damper of Renault was primarily designed to better control these tyre oscillations.

The suspension damper has an effect on the "wheel hop" damping but its small and kind of a second order effect. The damper rates are chosen mainly to control the body and that usually leaves the wheel hop mode quite underdamped. If you increase the damping to better control the wheel hop, then you overdamp your body motions.

Anyway, to be honest I haven't been watching closely enough to see the porposing (you mean pitch oscillations?). If you could post a video it would help understand. If its a fast oscillation say 20-50Hz then its likely that its bouncing on the tyres.

Anyway, thats my take on it. I'm not a master on the frequency domain (unlike my anti dive skills!), so maybe someone will point out some flaws but I think basically what I'm saying is reasonably solid.

[trinidefender]

Just out of curiosity does anybody know the air pressures that different teams run? I am sure that pressures will have an affect on how the tires interact with the suspension in dealing with bumps

[Pup]

Tim...

[youtube]http://www.youtube.com/watch?v=52XGpW-1SRc[/youtube]

[ringo]

Looks all tyres to me, and a low tyre pressure.

[wesley123]

wouldnt the lower tire pressure in turn cause for a bit more tire deformation?

[Lycoming]

typically, lower tire pressure means lower tire spring rate, meaning more tire deflection. Agreed that all the suspension movement is in the tires, that's obvious to see. I wonder how much this particular property of the tire changed compared to last year, considering it looks like they added a significant amount of mass to them.

[Racer X]

wouldnt the lower tire pressure in turn cause for a bit more tire deformation?

When I read that the tires deform because of how they are engineered. I figured it will cause an irregular (more then already is) air flow. But with to youre question I add another; going into and out of the corners because of latteral g's Because of different speeds and corner types ext. I can see how together with a suspension that is new to McLaren they would have the unstable car we saw in China. (button).

I guess that's not really a question... Sorry about that... These tires wow but I hope we see the mechanical set up get better.

[Tim.Wright]

Tim...
http://www.youtube.com/watch?v=52XGpW-1SRc

Interesting, certainly looks like its mainly the tyres deflecting. But I think also there is a degree of aerodynamic self excitation (which I think is how porpoising was originally defined in the ground effect days). I.e.
Chassis moves down > downforce increases
Downforce increases > Chassis moves further down
Chassis moves further down > aero chokes or stalls
Aero chokes > downforce decreases
Downforce decreasess > chassis moves up
And so on...

I think a tuned mass damper was aimed at fixing this. Always thought it was such BS that it was banned.

The fact that its doing this on the entry to a corner is a bit unconcerting. At least the rear axle seems pretty stable.

[trinidefender]

Tim...
http://www.youtube.com/watch?v=52XGpW-1SRc

Interesting, certainly looks like its mainly the tyres deflecting. But I think also there is a degree of aerodynamic self excitation (which I think is how porpoising was originally defined in the ground effect days). I.e.
Chassis moves down > downforce increases
Downforce increases > Chassis moves further down
Chassis moves further down > aero chokes or stalls
Aero chokes > downforce decreases
Downforce decreasess > chassis moves up
And so on...

I think a tuned mass damper was aimed at fixing this. Always thought it was such BS that it was banned.

The fact that its doing this on the entry to a corner is a bit unconcerting. At least the rear axle seems pretty stable.

Well considering McLaren can't run the car as low as they want because the rub strip will wear down and they will be disqualified, it wouldn't make much sense that they can generate enough downforce to get low enough to choke airflow without rubbing the strip underneath can they?

[Pup]

Tim...
http://www.youtube.com/watch?v=52XGpW-1SRc

Interesting, certainly looks like its mainly the tyres deflecting. But I think also there is a degree of aerodynamic self excitation (which I think is how porpoising was originally defined in the ground effect days). I.e.
Chassis moves down > downforce increases
Downforce increases > Chassis moves further down
Chassis moves further down > aero chokes or stalls
Aero chokes > downforce decreases
Downforce decreasess > chassis moves up
And so on...

I think a tuned mass damper was aimed at fixing this. Always thought it was such BS that it was banned.

The fact that its doing this on the entry to a corner is a bit unconcerting. At least the rear axle seems pretty stable.

I agree, and of the rumors from the pit lane, this is the one that I've seen repeated the most and which I think makes the most sense.

With the flaw in the theory being that in testing, it was supposedly when they ran the car illegally low that it worked the best. My guess is that it isn't to do with the floor/diffuser height, but rather an inconsistent sealing of the diffuser edge by the exhaust. That accounts for the bobbing into the braking zone, ties in the rumor about tire deformation, and seems reflected in the work that they've done to date on the car: changing the profile of the floor around the tires and moving the exhaust forward.

[Coefficient]

Tim...
http://www.youtube.com/watch?v=52XGpW-1SRc

Interesting, certainly looks like its mainly the tyres deflecting. But I think also there is a degree of aerodynamic self excitation (which I think is how porpoising was originally defined in the ground effect days). I.e.
Chassis moves down > downforce increases
Downforce increases > Chassis moves further down
Chassis moves further down > aero chokes or stalls
Aero chokes > downforce decreases
Downforce decreasess > chassis moves up
And so on...

I think a tuned mass damper was aimed at fixing this. Always thought it was such BS that it was banned.

The fact that its doing this on the entry to a corner is a bit unconcerting. At least the rear axle seems pretty stable.

I agree, and of the rumors from the pit lane, this is the one that I've seen repeated the most and which I think makes the most sense.

With the flaw in the theory being that in testing, it was supposedly when they ran the car illegally low that it worked the best. My guess is that it isn't to do with the floor/diffuser height, but rather an inconsistent sealing of the diffuser edge by the exhaust. That accounts for the bobbing into the braking zone, ties in the rumor about tire deformation, and seems reflected in the work that they've done to date on the car: changing the profile of the floor around the tires and moving the exhaust forward.

This all sounds very plausible which is great because I really want Mclaren to improve so if you guys have sussed their issues out by discussing it in here it gives me confidence that Mclaren will have done likewise and will show better in Barcelona. Fingers crossed!!

[marcush.]

The tyres are typically a lot less damped than the suspension itself, so the more you rely on them the less damped the "complete" (springs + tyres) axle seems to be.

So does that mean that the car would better damp the porpoising if the suspension were softer? Or would the car still bounce on the tires?

why ?
you got two springs in series (tyre and suspension spring(s)) making one of them rigid will take that one out of the equation
But you cannot make the tyre rigid as there is a finite amount of pressure capacity tied to grip as well ...So this approach will only make the whole suspension even softer.

You may be able to trade in some camber for vertical stiffness as lots of camber will lead to the tyre just working the inside shoulder decreasing its springrate...

BUT at the end of the day the STIFF setup is not the cause of the porpoising it´s the mend to keep it in manageable amplitudes! So first solve the problem of steeply rising downforce with decreasing rideheight -make it less rideheight sensitive near the ground and half the problem is gone .
A wild guess would be the lack of rear downforce /constant rear downforce leads to sudden massive forward movement of
Cof P as the leading edge of the splitter will always create a downforce peak .Fluktuating pressure decrease at the rear will play havoc with your front downforce percentage as well ..so less front downforce will help the rear and apparently that´s what Macs are doing and they suddenly find themselves in the same mudhole MGP may or may not have just left...

[Pup]

why ?

Because you're eliminating any damping. The question is which is the worse of two evils, or rather if they have a choice at all. McLaren seem to have chosen controlling the severity of the porpoising over the duration. My question was if it mattered. That is, if, because of the aero oscillations, the car is going to bounce on these goofy front tires regardless, then it makes the decision less of a tradeoff and more of a given.

[PlatinumZealot]

Tim...

[youtube]http://www.youtube.com/watch?v=52XGpW-1SRc[/youtube]

Very interesting indeed. It looks as if they have said sod all to the suspension movements and instead attempted to prioritise getting a consistent contact patch. ??? Because the rideheight surely aint stable in that little video there.

Hmm.. The front tyre contact patch..