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-   -   Car swaying on highway - Effect of crosswinds? (https://www.team-bhp.com/forum/technical-stuff/178869-car-swaying-highway-effect-crosswinds.html)

Hi All,

Recently, I completed a 800km round trip from Blr to Hampi and back. The machine of choice for this trip was my humble Alto K10 AMT - mainly because I had not taken it out on the highways and it needed a little "Italian" style tuning. :D Now, granted that the Alto K10 has a lot of body roll and bouncy ride, but what took me off guard was the lateral motion of the car while cruising on the highways.

One thing I noticed (probably a pattern) was that uneven roads cause the car to sway horizontally and I had to control this by micro adjustments from the steering wheel. This was particularly bad on the stretch from Hiriyur-Challakere-Rampura. If anyone has driven on these roads recently, one can observe that the roads have "sunk" in the place where wheels of heavy trucks move, sort of creating a very subtle, yet noticeable grooves on the highway. When I had to steer out of these grooves to overtake, the lateral motion was very noticeable. This was at speeds of 80-90kmph.

Another possible thing could be that there were a lot of gusty winds across and along the highway, but I'm not sure if winds can affect the stability so much. Again, I was maintaining 85-95kmph constantly.

On some stretches near Tumkur-Bangalore, the car was very well behaved, even at speeds of 100-110 kmph. Absolutely no movement and it was as planted as my Honda City generally is on highways.

On the other hand, when the roads got a little bad, like those sections of bridges/flyovers where the gaps between the joints get eaten away and all that's left is the gravel, or generally bad stretches of road - on the same NH4, the lateral sway was very perceivable.

Now, I dont know whether I'm used to driving the Honda City on the highways and whether comparing the rides of these 2 vehicles is even justified, but I thought that the lateral motion was sometimes too much - almost panic inducing (and I could probably have lost control) and I had to slow down to 60kmph.:eek:

I had my wheels rotated, balanced and aligned a week before the trip and the car behaves fine on city roads.

What could be the reason for such behaviour? The car is just close to 9-10months old and has done approx 7800 km on the ODO on stock tyres inflated to the factory recommended 35psi on all 4 tyres. There was no uneven (or unsafe) load distribution in or over the vehicle and no rooftop carrier is installed.

Crosswinds affect the cars a lot. I drive a WagonR which isn't aerodynamically gifted. I have faced lateral push and movements on very windy days or when HCVs overtake at high speed. Reduce the speed and roll down your windows in such conditions.

Driving in and out of grooves, at speed, also results in the wheels trying to change their direction on their own. Be it a car, a bike or your bicycle, you will feel the same thing. It is due to the tendency of the wheel to roll in the direction of the slope and it is very pronounced depending on the dept of the grooves. In areas where roads are worn out and have gravel only, you can feel some lateral movement due to lack of grip. This is very less and mostly goes unnoticed.

More than the grooves or ruts I think this is mostly due to crosswinds, happens on the route you took as well as the Chitradurga-Hospet road.
Moving out of a groove/rut will give a jerk and can be felt on the steering of cars like the Alto but that is different from the lateral movement.

The sway/lateral movement (a sort of "drift" if you will) is quite easily noticeable in the smaller hatches that are generally lighter cars, so I wouldn't worry too much. Your Alto K10 should be fine :)

Tyre problems, crosswinds. Have not noticed major (as in more than other light cars) tramlining issues in the Alto K10.
One thing I have noticed is a significant increase in wind noise at speed in a crosswind.

Regards
Sutripta

Strong winds do affect the car a bit. I guess the wind would make the car 'Lean' to one side and like on motorbikes leaning gives some turning action.

With respect to the grooves, its a phenomenon called 'tramlining' where the car tyre will grip a groove and move along with it. I used to notice it a lot when our Citys tyres were changed to a unidirectional V shaped tread. It almost felt like when the car was on the edge of a groove it would get sucked towards it then grip it and move along with it.

Also could be due to WB WA and suspension issues, play in steering, etc

Apart from the advice above, check cold tire pressure. If I am correct, the Alto uses 145/80 tires which means that the side profile of the tires is comparatively broad. If the air pressure is low, you would certainly feel it as a lateral movement due to thicker side profile and hence felt as sideways movement. It is just a general thought, may not apply to your case if the pressure is correct.

And tram lining as others have said and as per my experience too, is more pronounced in cars with wheels with shorter radii as they fall for smaller ruts/ slope formation due to surface irregularity etc. Wheels with larger diameter cope better with irregularities on road. I don't think what you have experienced is abnormal.

Regards,
Saket.

Yes - the effect could be felt specially when a big lorry or a bus passed me on the oncoming lane (this was a highway without any median/barricade) and the car just shook a bit every time this happened; but it wasnt as bad as the times I tried to change lanes / overtake.

Thanks - I guess the entire region is blessed with good strong winds (hence the windmills at Chitradurga) and the monsoon/current weather conditions made it very windy.

The noise within the cabin was quite high - wooshing sound when winds hit the car and constant tyre noise, thanks to the non existing tyre well cladding and poor insulation! I could barely listen to music from the ICE and putting it on at high volumes didn't help either - there was just too much noise, specially rolling tyre noise.

Yes - while overtaking or changing lanes, the car swerved very badly from side to side and was literally getting pushed/pulled sideways depending on the road. This is when I had to slow down to prevent loss of control.

Thanks - the K10 uses 155/65 R13 tyres. May be you are referring to the 800cc Alto tyres. I think the body roll + tiny tyres + bad roads + tramlining were contributing factors to the lateral movement of the car. Plus, I had WA and WB done recently and if it were something persistent, then I should have felt the same on the newly laid NICE road - where I was able to cruise at 100-110 kmph without any significant lateral movement.

Should I get the tie rod ends /control arms / bushings / steering assembly checked at the upcoming service just to be sure things are OK under the hood?

I have some footage from my dashcam but I'm not sure if it would help as the camera is attached to the car and that would pretty much cancel all relative motion. Let me see if I can find something interesting anyways..

The others have covered most of the points. Just wanted to add that some cars don't appear to be as affected by crosswinds as others. As an example, my C220 was built like a tank and didn't get nervous in a crosswind. The wafer-light 1st gen City Vtec however would severely lose its composure under expressway crosswinds.

Crosswinds even affects big cars. I drove a lodgy 83PS from Chennai to down south and whenever there was heavy winds(I could see the trees and bushes shaking very badly) my car would sway. Almost like a drift where the whole car will move from side to side. All this drama is at speeds around 120. If I reduce my speed to 90 the swaying stopped. I did not know that lowering the windows will help till now. Next time I travel, I'll try the same and get back with the result. Thanks a lot :)

I own a chevy beat, and during storms and high winds it shows a bit of horizontal swivel (very little but quite noticeable) on its suspensions, even while standstill. It does not move horizontally, remain planted, but just a bit of suspension movement, as if someone is pushing it from the side.

Very common I guess, esp on highways where the relative motion of air between, above and below vehicles vary greatly - both in speed and in direction/thrust.

Of course, weight and height of vehicle can accentuate that

I maybe wrong, But i have felt crosswinds in my XUV 500, Both current and previous generation, But NEVER in the VW Jetta, I really haven't, Something related to the built quality?

To some extent, it could be the tyres. Stock tyres are narrow. I used to experience this in our A-Star when I was on stock 155-section tyres. The car is now on 175 section Yoko's, and I have not seen the problem since.

Surprised !

(my Storme is happy even in cross-winds. Of course, it is heavier than the XUV).

All other things being the same, a tall vehicle will surely be more affected by crosswinds as they'll provide more resistance.

The Storme or the Safari don't get affected by crosswinds when moving. However a parked Storme oscillates a bit when a truck or a bus pass by at high speed in close quarters. Bikes on the other hand are a handful to control in crosswinds or when in close proximity to heavy vehicles.

My analysis:

The rough roads with exposed gravel generate lateral forces on each tyre, as a component of traction force. The car sways laterally in the direction of the resultant force of all these lateral forces on each tyre.

The crosswinds what we usually come across, can make the car roll on its suspension but it cannot make it drift laterally. Rubber (tyre) has fairly good amount of grip on the road (co-efficient of friction at least 0.5). So a lateral force of at least half of the car's weight will be needed to displace the car laterally. With ambient air density of around 1.2 - 1.25 kg/cu m, very high crosswind speeds will be needed (more than 200 kmph for Alto) to displace the car laterally.