Cars in Motorway Crosswinds handle better than others - Why??
My wifes car 'Pug HDI' is a beast driving on a motorway in a crosswind, but my ZX TD, I use for travelling to work has no problems at 70mph. I drove a Pug 307 HDI and a Skoda Octavia TD a few days ago and both of those are bad too.
Which car would you say is good in a crosswind travelling at 70mph??
|
|
The accord is pretty good but does have excellent aerodynamics all round IMO.
|
|
|
|
VW beetle was notoriously bad in crosswinds. Most rear-engined cars are quite affected by them.
|
>>Most rear-engined cars are quite affected by them.
Light weight rear engined cars like the Hillman Imp of the late 70's were notoriously bad in crosswinds. In mine I could not drive over 50mph in gusty conditions and even then you had to be very alert. An old trick was to put a heavy bag of sand in the boot at the front.
Most modern cars can handle crosswinds quite well, but heavier cars do it better.
--
Roger
A fine is a tax for doing wrong. A tax is a fine for doing well.
|
doesn't alot have to do with how much "updraft" (wrong word but don't know the technical one) there is under the car? hence why the faster you drive, the more "updraft" there is, the less downforce there is, the "lighter" your car becomes, the more it is affected by crosswinds.
I suppose some cars are more prone than others.
|
|
|
|
The original Sierra was awful in crosswinds. It was rumoured at the time that it was the main driver of the facelift which appeared a few years after launch. Certainly, the post facelift cars were better.
It always struck me as odd how a car which had aerodynamics play such a major part in its design struggled with even moderate sidewinds. I've ridden motorcycles that coped better.
The odd thing is, they got a lot of the aerodynamic stuff right - the wind noise levels on my 1983 example were incredibly low, as was the fuel consumption, especially considering it was a fairly big car, powered by an engine that even at launch was 15 years old, had barn door tolerances, and all the technical sophistication of an anvil. Someone clearly forgot to park it side on in the wind tunnel.
Cheers
DP
|
The original Sierra was awful in crosswinds. It was rumoured at the time that it was the main driver of the facelift which appeared a few years after launch.
Didn't they fit it with little plastic ears?
|
>> The original Sierra was awful in crosswinds.>> Didn't they fit it with little plastic ears?
>>
Yes. I think they were called strakes. They were fitted down each side of the rear window.
My Sapphire had them and they were a pain because leaves were trapped behind them and it needed a hose jet to wash the "compost" out.
|
It happens when the centre of downwards pressure is moved too far forwards or backwards by the aerodynamics of the car, Yes the sierra was too "aerofoylee" shaped with pressure too far back so they put the strakes on the rear side windows to break up the airflow. and create high pressure (and hence down force) further forward on the car. They actually needed to be behind the front door windows but there was no room, so it was still an evil side wind handler. The saphire didnt really need them that much.
The ran is good is side winds. Mainly becuase it has the aerodynamics of a fridge.
------------------------------
TourVanMan TM < Ex RF >
|
|
|
|
|
|
My Accord is not too bad, but SWMBO Shuttle used to be truly awful, that was until we changed the front tyres from P6000's to TZ200's, now it is a different car in crosswinds and not nearly so exciting to drive.
|
|
|
Something big, relatively heavy, wide, low, with suspension doing its job properly.
I used to have a Saab 9000 which was fairly immune to crosswinds, AFAIR.
|
One of the odd things about crosswinds is that more rounded cars are more troublesome.
The reasoning is that with a rounded car, the point where the airflow seperates isn''t well defined, and relatively small changes in either the wind, or the cars heading and attitude can have a large effect on the separation point. The forces acting on the car are dominated by the relative areas where the flow is attached, and where it is separated. So, for a rounded car, the aerodynamic drag, lift ,and side forces, pitching, yawing, and rolling moments can all change significantly, even if the wind or heading don't change much.
Then, if you have mkV Cortina, none of the above applies to you - the seperation points are remarkably well defined by the "smart" crease lines in the "neat" square body shape, and so, a Cortina will feel far less twitchy in a sidewind than a Sierra.
In effect, the "ears" on the rear windows of later Sierras were provided to give a well defined tripping point, to force the flow to seperate at a clearly defined point.
Number_Cruncher
|
The reasoning is that with a rounded car, the point where the airflow seperates isn''t well defined, and relatively small changes in either the wind, or the cars heading and attitude can have a large effect on the separation point. The forces acting on the car are dominated by the relative areas where the flow is attached, and where it is separated. So, for a rounded car, the aerodynamic drag, lift ,and side forces, pitching, yawing, and rolling moments can all change significantly, even if the wind or heading don't change much.
And for rounded cars, whichever way the wind is blown at them, it causes lift. With boxy cars you can get blown sideways due to the side area (like a sail), but you won't generate much lift.
Better aerodynamics and heavier cars that we have now are much better of course - with a 1950s car weighing only 750kg you might get 150kg of lift at the front at 70mph, add in another 100kg of lift from a crosswind and the suspension is on tiptoes! That's when it all feels very buttock-clenching!
|
|
Merc E-classes are good in crosswinds. Unlike the Merc-engined Smart For-Twos. Which are, unsurprisingly, terrible!
|
A big factor is the car's coefficient of yaw and this depends largely on the car's shape. Having a positive coefficient of yaw means that a cross wind turns the car away from the wind and the more the car goes off course the greater is the aerodynamic torque moving it off line, so it's a vicious circle. However, having a negative coefficient of yaw means that a cross wind turns the car into the wind and this results in the car being directionally stable. During my days of wind tunnel testing in the 1960s we learned that the most stable shape was one which had a conventional front and a boxy rear, such as a Land Rover or a small van of that era, i.e. not a forward control van. Steering and suspension characteristics also affect a car's directional stability and no doubt today's designers take that into account as well.
--
L\'escargot.
|
Wife's Xantia seems virtually unaffecyed by strong croswinds - is that the shape or the suspension or both?
"most stable shape was one which had a conventional front and a boxy rear" - sounds like a Berlingo - but mine is affected by crosswinds, though not too badly cosidering its height and slab sides.
Wonder what a new Disco is like?
--
Phil
|
"unaffecyed by strong croswinds "
Oops, sorry about typos
"unaffected by strong crosswinds"
--
Phil
|
I should have added that aerodynamic forces are also proportional to the car's direction and speed relative to the direction and speed of the wind, but it's all a long time ago and my memory isn't what it used to be.
--
L\'escargot.
|
Here's a bit more about the subject. tinyurl.com/26sr23
--
L\'escargot.
|
|
My x-father-law's Morris Ital was a delight to drive in crosswinds. Not.
|
|
>>proportional to the car's direction and speed....
I think you mean speed squared.
Number_Cruncher
|
>>proportional to the car's direction and speed.... I think you mean speed squared. Number_Cruncher
I purposely didn't put directly proportional because I couldn't remember the exact relationship.
--
L\'escargot.
|
|
|
|
sounds like a Berlingo - but mine is affected by crosswinds, though not too badly cosidering its height and slab sides.
Yes I agree and I'm surprised. Given the height, weight, and flat sides of these things you'd think they would be a nightmare, but they are not. However the Porsche Boxter that passed us on the M6 at the weekend was clearly quite a handful.
|
|
|
|
|
My 1996 2.0 ltr Vectra was designed with a for want of a better word a dead spot in the strait ahead position,I found this prevented me from having to make frequent and unessesary corrections and thus the effects of side winds was nullified.
ndbw
|
|
Focus hire car yesterday had me scared. The bonnet on this wobbled alarmingly - it was 500 miles old.......doubt whether anything had happened to it. Tyres were spot on.
|
Focus hire car yesterday had me scared. The bonnet on this wobbled alarmingly -
>>
Relax dear it is not a Clio.
|
My old Pug 205 used to sway a bit in exposed areas of the M40, mind you it was quite a tall slab sided car for its size.
--
Its not what you drive, its how you drive it! :-)
|
One important factor is the relationship betweentthe vehicle's centre of gravity (COG) and the centre of wind pressure (the point at which all the forces can be resolved into one; let's call it the COWP) in a side wind. This is a point at which all the forces could be said to act as one.
If the COG is in front of the COWP, then a gust of wind from the left will blow the car sideways to the right and at the same time will rotate the car to the left (the car will tend to rotate around its COG , which is in front of the COWP). Thus, the car will to some extent self-correct. As it's blown to the right, it turns to that it steers back to the left. The further ahead the COG is of the COWP, the more this effect will show.
Contrast this to a situation where the COG is to the rear of the COWP. A gust from the left will blow the car to the right, but also rotate the car to the right. Thus, the car will swerve right thanks to the wind and will add to this by steering to the right.
You can see that a rear-engined car (Beetle or Imp) will tend to have its COG to the rear; result, poor sidewind handling. A car with the engine in the front and a slab side at the rear (Landy as mentioned above) will have its COG to the front and its COWP far to the rear, hence the nice handling.
There are planty of other factors at play, but this bit of physics is pretty crucial.
V
|
There's actually a bit more to it than that Vin - especially for the low frequency limit of behaviour.
The relationship between the centre of pressure, and the neutral steer point is what determines which direction the car will yaw in - the neutral steer point is influenced by the position of the c of g.
If you imagine a car running along the road, and someone on a another vehicle running along side. If that person applies a side force to the car - by simply pushing it aside, in general the car will be both deflected and it will yaw.
As you vary the point along the length of the car where this side force is applied, you find there is one point which does not produce any yawing motion, the car simply moves away without altering course - this is the neutral steer point.
Whether the centre of pressure is ahead, or behind the neutral steer point determines whether the car reacts in a stable, or unstable way -ideally, the centre of pressur should be behind the neutral steer point, to make the vehicle turn into the wind, as you described.
The neutral steer point is, among other things, a function of the position of the c of g, and the corrnering stiffness of the tyres - so, you can move the position of the neutral steer point by changing the relative front/rear tyre pressures, for example.
Number_Cruncher
|
|
The Smart 2 x 2 must be brilliant- probably flies well above the speed cameras line of vision.
|
|
|
N_C,
I like that explanation a lot. Now I see why tyres, etc, make a difference. I had wondered about that before. Seems there a lot to be thought through in car design. No wonder they get it wrong sometimes!
V
|
Hi Vin,
I like the concept of the neutral steer point - it's so simple and intitive an explanation.
Taking the neutral steer point idea, its position relative to the c of g determines whether a car oversteers or understeers. BTW, I'm not talking about the on limit behaviour when you have gross sliding of a tyre a la Clarkson, but more the underlying, more fundamental, behaviour.
Number_Cruncher
|
|
|
|
|
|
>> Focus hire car yesterday had me scared. The bonnet on this wobbled alarmingly - >> Relax dear it is not a Clio.
Theres nothing wrong with the Clio bonnet catch if its maintained correctly
|
>>Theres nothing wrong with the Clio bonnet catch if its maintained correctly<<
How do you maintain a bonnet catch ?
There just there aren't they ?
|
|
|
|
|
|
Thanks for your replies.
The purpose of the topic was to find on average which car you think performs well in a crosswind, without mind boggling theories.
Its either bad or good!!!!!!!
If you think your 'BMW Mini One or Audi A4' is good.
or
If you think your 'Mazda 3 or Ford Mondeo' is bad, then say so.
thanks
|
|
|
