no u cant,selina needs to get by http://www.xt660.com/images/icons/icon14.gif

Good point :sleep01:

I used to use the trick of sticking out my windward knee in high winds on the motorway and can confirm that it does actually help. Reading the OP was helpful in understanding why and where it did not.

With my knee out it helped in how much the bike lean towards the wind (or how much I countered depending on how you want to view it) which meant I felt a little bit more in control than I would otherwise. You still need to correct the bike from veering away form the wind however (ie getting blown across the carriageway) but overall the riding experience is improved.

Forecast 50mph gusts were the limit I would ride in (about 30mph constant winds) and it was these gusts than sticking my wind-side knee out helped most with (tree lined motorways rarely have constant strong winds but I suspect it would help lots there too)

Now here in Guernsey riding more in built up areas than a motorway this is much less useful as the direction of wind can change far too quickly (and I'm not going over 35mph legally anyway).

Tried this theory a few years back when I had the Africa twin. Like many theories, it sounds good but for me at least, I just increased my fuel consumption and I got a cold knee! But hey, if it works for someone then stick with it.:laughing7:

all these headwinds, sidewinds, crosswinds and technical bla bla went right through my helmit and gave me a bj deluxe...
i tried sticking my leg out and i hit a car ...
gb.

Runs to toilet in floods of tears

So to recap, if my cat is running at 50 mph following a good scalding and it has a 30 mph crosswind it can stop itself falling over by acting like a dog having a pee..

Or do I just lean my bike into the wind to stop it being pushed into the bushes ?

You need to also consider forward movement. It's all there in the earlier posts.

One thing I absolutaly agree with you, it's easier with a whiteborad, and being in the same room!

------

I have infront of me a number of crude sketches depicting various windflows over a symetrical (assuming the bike is symetrical - which it isn't, well not perfectly anyway), and I'm still happy that the OP is correct, regarding the flow of air over the bike.

What has perplexed and vexed me over the weekend is the relationship of the headwind to the sidewind, given that the headwind isn't actually a moving force, it's just the realionship to the bike that has the effect of an oncoming wind. I can safely say it gave me a headache just thinking about it!

At some point, where a sidewind exceeds the 'power' of the headwind then things are going to go wrong, so this might as well be ignored for now. Lets concentrat on a relatively small sidewind force of 9 meters per second (about 20mph) , against say a 27 meters per second (about 60mph). To further simplify this, I'm going to take a sidewind at 90 degrees to the bike, the results change as the asngle of incidence becomes smaller than 90 degress and greater than 90 degrees.

You'll have to forgive the rough drawings.

Under normal (no sidewind) riding the bike would part the oncoming air (headwind) in a nice equal pattern


http://www.smokingtailpipes.com/Gallery/Headwind.jpg


Assuming the bike is stationary, the sidewind would part something like this.


http://www.smokingtailpipes.com/Gallery/Sidewind.jpg



But when both are present, the sidewind, having less velocity than the headwind would not be able to pass around the motorcycle in the same way due to the velocity of the headwind being greater than the sidewind, as airflow is easily defelcted, the result would be that the sidewinfd flow would pass to the rear of the bike, this is what would cause the lower pressure on the widward side of the bike

http://www.smokingtailpipes.com/Gall...26sidewind.jpg

Therefore you get higher windflow down the side of the bike on the windward side, thus lower atmospheric pressure.

I've looked at the possibility that the power of the sidewind is somehow expelled as energy, but there is no other energy that is being shown, the scrub off the tyres isn't really evident (you don't get black line down the road) and the bikes dont move in the direction of the wind anyway, there is no noise (but that is difficult to demonstrate or prove due the the windnoise being created around your helmet), no heat is being created, so I can't see any evidence of the winds power being converted to energy. Therefore I can only conclude that the wind is still there and being deflected. Of course a bike isn't a 2 dimensional object, so wind can deflect over and under the machine, I haven't even thought about the complications a 3d view would give.


Another thing that strikes me, this topic is 4 or 5 pages long and other than the OP there has been no other attempt to describe why a bike moves in the way it does when in a sidewind....... lots of disagreements, but no alternative theory.

I'm waiting for a windy day - my gut feeling is still that a bike *doesn't* lean into the wind without any input from the rider. I'm also not sure you can sit on a bike in a crosswind without either falling off the top of it, or putting some steering input through the bars or pegs.

I'm not going to try and explain something I don't believe happens, until I know it happens ;)

Back to your flow diagrams...I don't think that's how the air flows. You mentioned having some trouble figuring out the relationship of headwind to sidewind...

The thing you need to figure out is what frame of reference (point of view) you are operating in, and stick to it. The obvious one is to sit yourself on the bike, as that is what we are interested in.

The bike doesn't know that it's moving. Take the cross wind out of the equation, and all the bike knows is there is a 27m/s air flow coming from straight ahead.

Alternately, just considering the cross-wind, all the bike knows is there is a 9m/s air flow coming from 90deg to the way it's facing.

Combine the two, and you have a wind direction which is the resultant of those two components. There is no difference* between a bike moving at 27m/s with a 9m/s cross wind, and a stationary bike in a 28.5m/s wind which is coming from 18.5degrees off straight ahead.

(or if you're feeling clever, a bike in a two wheel drift at the speed and angle above on a perfectly still day).

Which brings us back to this flow diagram...

http://upload.wikimedia.org/wikipedi...attack.svg.png

with alpha in this case being 18.5deg. And that will, undoubtably result in 'lift' towards the downwind side.

Your point about what happens when the cross wind starts to approach or exceed the headwind is an interesting one. Aerofoils will 'stall' and stop producing lift if the angle of attack is too great, so if you take a bike which is a fairly efficient foil (not many of them) then there might be a 'worst' speed to ride at for a given cross-wind speed - speed up or slow down from that speed and you'd be affected less. Hmm.


*well...aerodynamically. And strictly speaking the stationary bike would have to be on some sort of treadmill with both wheels spinning at 27m/s, because wheels do affect airflow.