windy drive home tonight

[peanut]

coming home to Somerset tonight from Bristol there were 40mph speed restrictions due to the wind. I was travelling at about 55mph and the S2 was weaving all over the road even with new shockers adjusted to max hardness[8|]
there were idiots in beemers and 4x4's passing me at 80mph + All I can say is either they are totally insensitive or they must have a handy change of underwear.....

 

[Diver944]

It's funny you should say that as I have often thought my car wanders more than it should during high wind.

If huge 4x4's are blasting past, I wonder if their weight and/or softer suspension enables them to soak up the gusts of sidewind [&:]

Is there a scientific reason why a low slung sports coupe copes with gusts worse than a big 4x4?

 

[pauljmcnulty]

Is there a scientific reason why a low slung sports coupe copes with gusts worse than a big 4x4?

Sounds totally contradictory. I can understand why my van is a little, shall we say, interesting in severe cross-winds, because it presents a huge, flat side profile. The Legacy is unbelievably stable, but with Japanese wind tunnels and 4WD it should be.

I'd have thought that a 944 would be less well developed aerodynamically because the technology was less advanced at the time. I'd be very surprised, though, if it performed less well than a modern 4x4 with a high centre of gravity and soft suspension.

 

[Peter Empson]

I think that a lot of the problem with 944's and cross winds may be suspension related, I certainly suffer from this a lot less now than when it was standard. I cannot say if its due to the settings or just the stiffness of the setup but this problem has effectively disappeared for me. The latest setup (track settings, v.stiff springs and with solid bushings wherever possible) is even better at reducing this effect than the previous less extreme setup. However throw some bumps and cambers into the equation and I'll be a road block for everything out there bar the slowest tractor []

 

[zcacogp]

I echo Paul's comments ... I'd have thought that a slippery (streamlined) shape should mean that high winds pass over the top of it more readily, and the car is lesss affected by it. Hence, I'd have thought that the 944 should do pretty well ... despite the aerodynamics not being that advanced, it's a pretty low, streamlined shape.

In which case, maybe it is suspension-related. But then, even with standard (and 126,000-mile-old) suspension my S2 was never anything other than stable on the road, so I'd be possibly suspecting something else again.

As for the 4x4's going quickly despite the wind, that may well a result of other factors altogether ...


Oli.

 

[hamzamian]

Couple of important factors that have been overlooked, weight & tyre contact area

Although the 4x4 have greater surface area side on they are also heavier so need greater force to move them laterally.. not sure but they generally also have pretty wide tyres so again need more force to move them laterally... in fact the same goes for most modern cars....

The 944 by comparison however, although relatively small side on is quite light by comparison to modern cars

 

[zcacogp]

Sure, but weight has two effects, which would cancel each other out, I'd have thought. Yes, it makes 4x4's harder to push off course, but it also makes them harder to get back on course when they are blown around. (i.e. 4x4's don't handle well, which is something we all know.)

Tyre contact area - you're talking about grip on the road, and knobbly 4x4 tyres are designed to grip mud, not roads. They actually have very little grip, as there is not much rubber touching the road at any one time.


Oli.

 

[Mark Elder]

ORIGINAL: zcacogp

Tyre contact area - you're talking about grip on the road, and knobbly 4x4 tyres are designed to grip mud, not roads. They actually have very little grip, as there is not much rubber touching the road at any one time.

Yes, but when did you last see knobbly tyres on a 4x4? (except a Defender) - annoys me that I buy a 4x4 because I want to use it for its purpose and it comes with tyres that won't grip on damp grass[8|]

 

[hamzamian]

yep precisely... most 4x4 dont actually have knobblies, they have road tyres...

agree with the weight being harder to put back when moved but if it doesnt move in the first place.......

 

[zcacogp]

Yes, but look at the stopping distance of a 4x4 and the stopping distance of a similar-weight car - the 4x4 will take a lot longer to stop, largely because the tyres simply won't grip the road as well. They aren't road tyres on most 4x4's - they are cross-over tyres, which offer compromised off-road performance and compromised on-road performance.

Greater weight will not stop the vehicle from being affected, it just will be affected less, leaving you with the job of getting athat great weight back on course. F=MA works in both directions.


Oli.

 

[hamzamian]

hmm.... yea good point about the stopping distance...

i dunno then ![&:]

 

[appletonn]

ORIGINAL: zcacogp

Yes, but look at the stopping distance of a 4x4 and the stopping distance of a similar-weight car - the 4x4 will take a lot longer to stop, largely because the tyres simply won't grip the road as well. They aren't road tyres on most 4x4's - they are cross-over tyres, which offer compromised off-road performance and compromised on-road performance.

Greater weight will not stop the vehicle from being affected, it just will be affected less, leaving you with the job of getting athat great weight back on course. F=MA works in both directions.


Oli.

The other impact on the braking distance is obviously the momentum and energy contained in stopping 2.5tonnes from 80 mph....[&:]

Did you see 5th Gear with sexy old VBH throwing that Porsche Cayenne around the Anglesey race track - it lapped faster than an Astra VXR[&:]

 

[George Elliott]

I find that Un-aerodynamic cars behave better, (are less affected) by Cross-winds than an aerodynamic car.
The reason is the "Brick" shape is smashing its way thru the air on a calm day or a windy day - its little different. But the aero shape is cutting thru the air and in a crosswind the air its cutting is very different to a calm day.
Proof is the way an aeroplane behaves in cross-winds - really bad.
On top of that you get differences in the Balance (mass location) of the car.
An old (1983/4) 5 cylinder audi with a blunt profile (like the early 80 quattro) was amazing on a wet windy motorway. It had narrow tyres, was front heavy, and was pre the slippy body shape.

I have not tried one, but I imagine the front splitter (Promax for example) should improve the front downforce and behaviour of the 944 at speed/in crosswinds.

George
944t
964

 

[pauljmcnulty]

I find that Un-aerodynamic cars behave better, (are less affected) by Cross-winds than an aerodynamic car.
The reason is the "Brick" shape is smashing its way thru the air on a calm day or a windy day - its little different.

Having driven my little van today I can understand why they close bridges to high-sided vehicles in strong winds...I was not a brick moving forwards...[]

Still reckon that the Legacy is even more stable on the motorway than anything since our Volvo 740 Turbo, so the evidence is that large estates, preferably 4WD, are the safest cars. []

 

[George Elliott]

Paul,
Vans and lorries are another matter. I agree the 4wd comment you make.
George