Air turbulance

[Blakamin]

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.

One of the main reasons I no longer have a Zeal!
had to drop back a gear and rev the life out of it to get 110 in a headwind... then reach for 6th again

[Hitcher]

One of the main reasons I no longer have a Zeal!
had to drop back a gear and rev the life out of it to get 110 in a headwind... then reach for 6th again

Did your Zeal have a flatspot at about 6,500rpm? Mine did, as do most Zeals, which was particularly irritating as this was about 100kmh in top. In the case of passing manouevers as described above, I generally had to come down into fourth or even third and wring the poor thing's neck out to the redline to generate "go" on demand. The more confident I got with the Zeal the more time it used to spend at about 12,500rpm where it was quite happy.

[jrandom]

had to drop back a gear and rev the life out of it to get 110 in a headwind...

Join the club.

I try to think of it as character-building.

[vifferman]

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.

Not surprising, I guess.
Last week I was reading about the "200 Club", and attempts to break 200 mph (and various records). Apparently much harder than it seems, due to drag, which increases exponentially with speed. If you don't have at least 225hp, then you will be struggling to achieve it.
Getting back to turbulence, buffeting and the like, the reason the EyeAbuser is so ugly is aerodynamics - it's much more aerodynamic than the Kawasaki, because the Big K opted for looks before optimum aerodynamics.
How much you are buffeted around in various conditions depends on the overall package too, not just screen, fairing, etc. I found my VF500 was badly buffeted (half fairing and 16" front wheel didn't help), the VFR less so, and the VTR is the best, apart from the front wheel being affected more by gusts through the railing of the Harbour Bridge when the wind comes from the Southwest. I think it's due to the shape of the front mudguard, and results in the bike weaving a bit. The VF was least affected by this, due to a very vented front guard.
However, the VF had the most turbulence-producing windscreen, due to its shape and a rubber bead on the edge, which I removed. Most shields have this moulded in now, for extra strength, but from an aerodynaics point of view it's bad. Similarly, riders who opt for higher screens will often find they produce more turbulence and/or shift the wind blast up so that it buffets their helmet around rather than just striking their chest or shoulders. On my VFR, the wind stream was directed at shoulder level (chest level on the VTR) and this created a lot of wind noise from the collar of my jacket creating turbulent flow around the bottom of my helmet!

[pete376403]

Getting back to turbulence, buffeting and the like, the reason the EyeAbuser is so ugly is aerodynamics - it's much more aerodynamic than the Kawasaki, because the Big K opted for looks before optimum aerodynamics.
However, the VF had the most turbulence-producing windscreen, due to its shape and a rubber bead on the edge, which I removed. Most shields have this moulded in now, for extra strength, but from an aerodynaics point of view it's bad.

Surprising about Kawasaki, I understood that, because of the aircraft division of KHI, they had a better idea of aerodynamics than the other makers (except perhaps Agusta, do they still make helicopters?) Perhaps just another example of marketing trumping engineering.

Another reason for the bead on the edge of the screen is to prevent an otherwise thin plastic edge from slicing open riders in the event of a crash

[Paul in NZ]

This is actually pretty interesting...

Just a couple of observations..

Not all squared off back ends are un aerodynamic. In the '60 a lot of vehicles pioneered this style utilising work done by Professor Kamm. Cars like the Ford GT40 and Lola / Maclaren etc were influenced by his work. However, introducing the Kamm Tail on cars like the Alfa Romeo Sypder made little or no difference other than to the look of the thing.

Moto Guzzi spent a lot of time and money figuring out how fairings etc work on a bike. They were one of the only companies to have their own wind tunnel and the fairing on the Mk2 and the amazingly fugly barn door one on the contemorary SP were a direct result of this.

Sadly, the nose section are also bar mounted fairings and while I find the Mk2 a great bike to ride in the rain (apart from the cast iron disks that spew rust all over the show) it does not like a strong gust coming in from the front 3/4 angle. You really feel it in the bars and once I nearly rode off a bridge because we could not come about in a strong gust (150kph wind gust day - bloody stupid to be riding at all)

Cheers

[jrandom]

Surprising about Kawasaki, I understood that, because of the aircraft division of KHI, they had a better idea of aerodynamics than the other makers (except perhaps Agusta, do they still make helicopters?) Perhaps just another example of marketing trumping engineering.

Well, *I* heard that Kawasaki did initial design prototyping on the '12 based on aerodynamics research, and the result was, more or less, a green Hayabusa.

So they hacked it around so that it looked different, did what they could to boost the ponies so that it would be as fast as the bus, regardless of the fact that it now had bookcase-like aerodynamics, and released it.

A marketing decision, indeed.

[Blakamin]

Did your Zeal have a flatspot at about 6,500rpm? Mine did, as do most Zeals, which was particularly irritating as this was about 100kmh in top. In the case of passing manouevers as described above, I generally had to come down into fourth or even third and wring the poor thing's neck out to the redline to generate "go" on demand. The more confident I got with the Zeal the more time it used to spend at about 12,500rpm where it was quite happy.

That was EXACTLY the way it was!!!
thats why i wanted more power... was just too difficult getting around things in the wind!

[vifferman]

Surprising about Kawasaki, I understood that, because of the aircraft division of KHI, they had a better idea of aerodynamics than the other makers (except perhaps Agusta, do they still make helicopters?) Perhaps just another example of marketing trumping engineering.

I'm not saying the Kawasaki was unaerodynamic (it does have things like the 'winglets' on the fairing, after all), but it's less aerodynamic than the Suzuki, according to the article I read (on Sport Rider, I think).

Another reason for the bead on the edge of the screen is to prevent an otherwise thin plastic edge from slicing open riders in the event of a crash

Other reasons too - apparently Aaron Slight had a bead on the edge of his RC45's windscreen so he could see it, as otherwise he kept banging his helmet on it.

[Pwalo]

Other reasons too - apparently Aaron Slight had a bead on the edge of his RC45's windscreen so he could see it, as otherwise he kept banging his helmet on it.[/QUOTE]

Yep I've noticed this on my Givi 755 screen. It's great but really easy to head butt as it doesn't have a bead on the edge. Must admit that the screen really helps, especially in the cold and or rain. It seems to deflect the wind blast on to my chest/shoulders area. No helmet buffeting, but a bit noisier.

Funnily enough it seems to make a difference to streamlining. If I'm really keen and tuck behind it (you know elbows, toes in) my revs can drop by .5k for the same speed. Can see why a properly designed fairing really helps.

The good thing about the GS is that it's not really affected by side winds too much. The only thing that's a bit scary is a rear 3/4 gust.

Cheers

Paul

[Gasman]

It's all to do with "Flutter". Flutter is the action of the ocillations of airflow over a concave aerodynamic surface! Oh shit, no that's not right, thats to do with aeroplanes!
Cocked up again. Anybody want to go flying instead?

[dangerous]

When I got up alongside the cab doing about 115kmh I remembered that there was a stiff headwind...

True and the other thing that I notice on a lighter bike (VTR1) is as you near the frount of a bigger car/4x4/truck is the suction that pulls you into the car/truck which has me pulling back in frount of them much closer that I plan to.

[bgd]

So last night I sat behind a van (ambulances being in short supply) but I didn't notice anything. Probably because it was pretty windy.

So tried again this morning at motorway speed (about 80mph) and still didn't detect any difference. I get so much dirty air from my screen that I think any change in turbulance is probably being masked.

I didn't come across any trucks that were going fast enough for me to sit behind (they were all jugging up hills) but I'll keep a lookout.

[Motu]

When I first got my XLV750 I couldn't believe how much I was getting smacked around,it seemed every day I rode it was really windy,but when I stopped it didn't seem that bad.I was using an MX helmet - it was taking all my strength to stop my head doing a 180,I'd get off the bike with my head locked at 45deg from centre,I'd have to turn my body to look at things.Bloody hell,been riding all my life and never had anything like this.Brian,a previous owner had made a screen and I fitted it,the improved things heaps.I've taken the screen off again,and I don't seem to find it a problem anymore - just a phase I was going through I guess....it's ok,I'm alright now,no lasting effect...but sometimes I look sideways at things.

The XLV750 goes into a wobble behind a B train,just a head shake - move up closer so you've got no room to stop and it goes away.