Air turbulance

[DebK]

Apologies if this has been discussed before but did a quick 'search' & couldn't find a thread of the like.

I'm interested to know how your bike handles sitting behind different vehicles. I've been experimenting this week by sitting behind different vehicles (not absolutely behind, for safety reasons).

Today on the way to Tawa I spent time trailing an ambulance. It was the worst I've been buffetted around so far. My helmet was starting to lift off my head & the scoot at 105 was hard to keep in a straight line because of the extreme turbulance. Very uncomfortable ride.

Yesterday I was behind an Isuzu Irmsher and at a short distance I was actually being 'towed' along with little throttle & easily doing 100. Also very little air displacement. I find any similar 'truck', as owners seem to call them these days, acts the same way.

Any car with a boot spoiler/wing buffets me around.

What are your experiences? Is it soley down to the weight of the bike & rider or is it the aerodynamics that your bike may or may not have?

[Two Smoker]

I find sitting behind trucks to be good for a wind breaker, but at certain distances the turbulance heads back down and can start too buffet you.... MR (when he is on his TZR) slip stream each other on the road (aaahhhhh, cough cough, eeeeerrrrrrmmmm, track) at 140-180kmh.....

[badlieutenant]

I get the same sorta thing as well. I prefer to get on an empty lane on the motorway for that reason, oh and its safer. In the oppisite direction the same thing seems to apply, weird thing is different trucks (the real ones) have different effects. Went past one going the oposite way once up near whangarei and it felt like someone had punched me in the chest, and i have a full fairing which you would think would help.

[Zapf]

coming from an automotive modification point of view, trucks / ambulance's have a very bad drag, as the end of the car is just abruptly cut off and that creates a massive hole that air will circulate around.

Hatch backs will be better cause they are smaller, then sedans / hatch backs and lift backs (fast backs) should be best.

[Mr Skid]

Hey Debs,

I'm sure someone more intelligent will come along shortly and correct me, but I understand that on a big non-aerodynamic box such as an ambulance will create alot of turbulance, as the airflow detaches from the vehicle, and your've been stuck in all that turbulent air.

Something slightly more aero-dynamic like the izuzu would do most of the hard work of pushing the air out of the way for you, and create a low pressure zone behind it. This has the effect of sucking you along behind it.

Roughly speaking the energy used to keep you moving forward at a given speed is split between overcoming the friction between your tires and the road, bearings etc and the resistance of the air. As you go faster you spend more energy overcomming the air resistance, which is why slipstreaming is more efficent at higher speeds.

As for the cars with spoliers / wings / ironing boards on the back, I understand they create drag in creating downforce, and that would then mess with the airflow..

I'll now sit back and wait for someone that knows what they're talking about to give you a real explaination

[thehollowmen]

Ok - from what I remember from first / second year physics...
You're thinking along the right lines...

But a big car / truck has a burble behind it... a nice calm spot that you can sit in, and it also a very wide wake which passes out into the lanes either side of it. Watch an oncoming truck in the rain, it has a huge wake of swirling water in either lane beside it about 3 seconds after it passes...

Yes spoilers create downforce by laminar airflow, however the corners at either end pose some problems and cause turbulent airflow

[dangerous]

When it come to oncomming trucks (big suckers) I take note of weather they have the air ducts on the frount corners as the later models do, these ducts are desined to curl some of the air that builds up infrount of the rig to be directed down the side of the truck and not straight out the sides and into little road users like us.
Older cab over trucks can be very rough on bikes were as long nosed are usually less turbulant.

This dosent real help with your question Deb but similer situations go for the following of cars aswell.
You will notice the closer you get to a car the smother it gets and you will be sucked along with it and the further behind the rougher it gets till you are out of its turbulance.
The same goes for a light aircraft taking off after a 747.... it has to wait for a couple of mins for the air to settle again.

[Aleph]

Hi,
If I sound knowledgeable enough no-one will question the answer even though in reality I am an accountant.
The answer is a factor of all of your questions.
The vehicles you are following have different aerodynamics and will produce different amounts of turbulance and suction. If I have got it right, rear wings should be disruptive to the airflow to reduce the lifting effect of the air, this disruption will generate more turbulance for you following. No doubt various wing designs will work differently due to the car shape.
Wagons and vans will suck you in more due to the squared off rear shape. Some trucks put out an enormous frontal blast, some suck you along. 25 years ago I used to be able to get my 125 sucked along by riding close alongside the trucks. Gave that up before I became temporary.
The heavier you and your bike are the less you will be affected but that is probably just due to the mass being harder to move. Ride an old 900 and they sit pretty solidly on the road.
Your bike aerodynamics will have an effect as some shift the airflow better so turbulance will simply be pushed around you. Of course, one style will work better in certain situations and be crappy in another.

[pete376403]

My Suzook is a heavy old pig and has a full (barn door type) fairing. Nonetheless I can feel the turbulence even when riding behind another bike - the guys I ride with have F650/Aprilla Pegaso/and SV1000. I have to drop back to about 20 - 30 metres before the turbulence is not noticeable.
Have never tried tailgating an ambulance. As others say, big trucks coming the other way at open road speeds are probably the worst.

Its amazing how little things affect the air flow. The BMW system III helmet has a couple of small ridges on top, not much bigger than paint runs, yet they are enough to completely stop the wind patter that my previous lid was really bad for

[bgd]

Interesting thread. I've never really noticed any turbulance (or lack of) when following vehicles. The GS is pretty heavy so probably doesn't get effected as much as a lighter bike. Also there is quite a bit of buffeting from the screen at about 70mph and upwards (which I'm used to) so it might get disguised in that.

I certainly notice the turbulence when overtaking trucks - that blast of air from the side.

Must experiment on the way home tonight, although I tend not to sit behind vehicles, espcially ones I can't see over, if I can help it.

[Mongoose]

Interesting thread. I've never really noticed any turbulance (or lack of) when following vehicles. The GS is pretty heavy so probably doesn't get effected as much as a lighter bike. Also there is quite a bit of buffeting from the screen at about 70mph and upwards (which I'm used to) so it might get disguised in that.

I certainly notice the turbulence when overtaking trucks - that blast of air from the side.

Must experiment on the way home tonight, although I tend not to sit behind vehicles, espcially ones I can't see over, if I can help it.

My experience of trying this sort of thing out is this. All of what has been said is true, how ever what people have NOT said is to get the "slip stream" effect from following a truck you have to be a farkin sight closer to the back of a truck than I am comfortable with. Maybe this is the real reason you have noticed it before, just not following close enough.

[scumdog]

The side-to-side type buffeting you get when follow some trucks is caused by the "decaying vortex phenomina" - but you all knew that already, right?

Worse 'blasting' I get is from a truck going the other way when there is a cross-wind blowing from the trucks side of the road to mine, dang if it don't have make your bum suck the buttons off the seat when your day-dreaming and a truck goes past like that!!

[Pwalo]

Don't forget buffeting is also affected by the vehicles speeds, both independently, and combined.

On the GS it's amazing what a difference traffic makes. Being fairly light almost any other vehicle in front causes buffeting. It's certainly a bit better (if noisier) with my screen.I never follow too close behind trucks. Like to see what's coming up. Curiously I've also found that 4WD/SUV thingies (Ngaio mother's taxis) don't seem to upset the bike as much.

And they are so easy to overtake. On acceleration, on the brakes, on the outside around corners, on the inside around corners, bugger it anywhere. (Hate the things in urban areas ).

[Dodgyiti]

Don't forget buffeting is also affected by the vehicles speeds, both independently, and combined.

On the GS it's amazing what a difference traffic makes. Being fairly light almost any other vehicle in front causes buffeting. It's certainly a bit better (if noisier) with my screen.I never follow too close behind trucks. Like to see what's coming up. Curiously I've also found that 4WD/SUV thingies (Ngaio mother's taxis) don't seem to upset the bike as much.

And they are so easy to overtake. On acceleration, on the brakes, on the outside around corners, on the inside around corners, bugger it anywhere. (Hate the things in urban areas ).

No.. lets not slag off the lovely 4WD's. People need ground clearance and 4WD for umm...ummm.. parking an stuff

[Hitcher]

Ahh, the vagueries of chop and buffet (sounds like a meateaters' smorgasbord). Big square vehicles are the worst. Tankers too cause a lot of swirl. I am too cautious to follow close enough to slipstream but have experienced this effect while overtaking. The worst was on my Zeal overtaking a Fonterra tanker on the Takapau plains. When I got up alongside the cab doing about 115kmh I remembered that there was a stiff headwind... The tanker driver smiled and waved as I valiantly searched for enough horsepower to complete the manouever.