My 575 starts to float at 135-140

If you are going to drive that fast on a regular basis, I would check tire pressures. You may not have enough air, causing your contact patches to deform somewhat at speed. Less tire on the road will give you a floaty feeling. I'm sure someone on Fchat will give you some specific advice but I am reasonably sure that the appropriate amount of air in your tires will go a long way to getting high speed stability, absent any other mechanical issues like worn worn or loose suspension components.
As an aside, where in Newport Beach do you get the car over 130MPH?

 

hahahhahaha.. I can see a new LIDAR thread in the near future.

 

I'm not sure what the problem is, but sumthang is wrong. Not that I will admit to have driven a 550 at speeds in excess of this on public roads; but I do remember an occasion where I had to tell Rob Lay that I probably should pay more attention to what was going on than chatting.

Dale

 

my 2003 575 is rock solid at 177mph.

 

Don't drive that fast on a curve. Tire pressures will affect straight line stability also. I had a similar issue with my 348 and getting the pressure right helped very much. I had one rear tire that was about 6-8 pounds low.
BT

 

That is why you are still alive.

 

I have driven 165 mph on a public road (legally), and my 550 from 2000 is steady as a house at that speed, like 68rcodemustangs 575.

On fairly twisty highway sections I have done over 140 as well and it did not feel unsettled at all. And yes, I'm still alive, Mbutner. I know my limitations and the car's were way above them.

So I would say there is something wrong, probably suspension wise. Get it checked out, it might be serious enough to affect you when you are NOT doing 140 if left unattended.


Onno

 

Is the FHP too stif?

 

Does anybody know what the downforce is on a 575M at each end at 140mph?

 

The car should not feel unstable at those speed at all. I've had a 550 at over 180mph and all was well. 140-160mph are fine "cruising" speeds for a 550, just as well for a 575. I've kept those speeds comfortably for relatively long periods of time on long trips (no, not in the US!). Check tires for pressure/wear and look at the steering, something might be amiss.

Good luck,
RS6bird

 

As well it should be. I, also.

 

Ouch! I won't even drive down the street without checking tire pressure. If you are going to roll on, be ready for it.

 

what the miles on the car now ?

who did the alignment last time ?
TOE settings ?
Camber settings ?

what tires are on the car now ?

when cornering what is the car doing, on initial imput what is the car doing ?

also when you were tempting to do ***mph how much gas was in the tank at the time ? .25/ 1/2 / Full ?

 

There is a specific bulletin on Fiorano alignment settings. VERY fiddly to do, but worth it. Can lower ride height about 20mm without much problem, and I always ran rear spacers with max. spec negative camber in front, careful toe settings with me in car.
Bad shocks can also do this, so check the actuators and wires to them. My Superamerica had the most atrocious alignment new of anything I've ever bought, even with HGTC on it.
Sharks should be planted at 175. They tend to get a bit light in the rear at above 180-185, I'm on roughish pavement usually, and dips can be amusing, usually trigger ASC a little. Only float I've had. A significant dip (i.e. one that gets near full jounce and rebound is a bit weak on these cars) can do it too.
I would look at shocks, alignment, and ride height. Any missing underbody panels can cause lift senters in the low pressure under the car, so another thing to look for if a shield is peeling back between 130-150.
Use it like a light aircraft.
PS, +1 on fuel load. Makes a big difference acutely. IIRC, the bulletin suggests 1/2 fuel.

 

get it gone over. i had occasions to have my 550 at speeds above that and the only scary thing about it was how damn stable and glued it was - it was otherworldly in that regard.

doody.

 

if possible go to a very very very good alignment shop. Bushings can you take a look under your car next time it up on a lift and look at the bushings for the steering rack + also the control arms as well if you see any thing broken or cracked get it replaced asap !

have some one turn / left and right while the car is up on the lift - look at the steering rack there should be NO movement between the collars that hold the steering rack in place , and just use a process of elimination to sort out any problems.

is the car a daily driver or a weekend driver ?


I don’t know what others may feel what Im about to suggest is this

1mm toe "in" the front
1.5mm negative camber front

rear toe setting -0-
rear camber 2mm negative

as for height I would do a 1.5 inch - 2inch drop on the coil overs you have on the car
and from there start making the constant adj that make you feel comfortable with the handling of the car

again----I want to stress ever one has a different idea and option for suspension and some might not like what I recommended but its a start and check all of those items out.

 

I had the same issue with my 456GT. Too much float at speeds over 250km/hr.
Here was my remedy:
1) changing the worn out bushings: Major help.. really.
2) Tire camber and toe adjustments (I ll check mine and write them for you tomorrow)
3) Tire Pressure
4) Check if the little metal air guide fins that cool the brake discs are loose..
Dont forget though the under carriage is open unlike 360, 430 or 599GTBs , We will always have more float than others unfortunately..
But once I did the above.. I had nice control up to 290km/hr. .Did 305km/hr quite a few times... well first of all I was just glad I could reach that speed.. but it was scary a little due to the float