Do Aerodynamics Matter on 250/300 Ninja Racebikes?

[tgold]

I have my thoughts, but I wanted to hear a few opinions first.

[jkv45]

No unless you are running consistently near top speed.

[tgold]

Originally Posted by jkv45

No unless you are running consistently near top speed.

Why only top speed? It takes power to push the air out of the way no matter what speed you are going.

[jkv45]

Originally Posted by tgold

Why only top speed?

That's where aerodynamics are most important.

[cbinker]

yes aerodynamics are very important due to the low power.

[tgold]

Originally Posted by cbinker

yes aerodynamics are very important due to the low power.

Exactly.

The first time you're in the middle of a big pack of riders in a bicycle race, you would understand the value of aerodynamics while you have a big smile on your face.

When racing a pregen 250 for the first time last month, I was doing the old flattracker's trick of taking my left hand off the bars and extending my arm back alongside my body while on the straights. I was still a little surprised by how much wind resistance I could feel when I would bring my hand back up to grab the bar before the next corner. I can't say that that was entirely the reason that I won the race, but when there were only 4 tenths of a second covering first through third at the checkered flag I'll take whatever advantage I can get.

I'll be doing quite a bit of smoothing sharp angles on my (newgen) bike's race bodywork over this winter. Basically free horsepower with no extra wear on the engine.

[csmith12]

^^^ We do that too Timm, every little bit helps. lol

The effects of wind drag is substantial on ANY bike.

[jkv45]

Originally Posted by csmith12

^^^ We do that too Timm, every little bit helps. lol

The effects of wind drag is substantial on ANY bike.

That depends on the amount of wind (speed).

The question is pretty open. It will always make some difference, just not significant difference unless speeds are high.

In Land Speed Racing it's going to be a bigger factor than sprint racing on a small road racing track. So it depends on the context.

[tgold]

Originally Posted by jkv45

That depends on the amount of wind (speed).

The question is pretty open. It will always make some difference, just not significant difference unless speeds are high.

In Land Speed Racing it's going to be a bigger factor than sprint racing on a small road racing track. So it depends on the context.

At some point the difference becomes significant and it has to do with your rate of acceleration in addition to top speed.

One thing that I've found to be true in racing: The faster your competitors are, the more the "not significant" things matter. The people who win are the ones who do more than others are willing to do.

[michvin]

According to my not too scientific observations, mpg increased slightly after installation of touring windshield.

[adouglas]

Easy to answer.

Go for a ride on the highway and make some passes while fully tucked, and while not.

I'm not even talking sitting upright. You can feel the difference between a mild tuck and a full race tuck, even at highway speeds.

So aero does matter overall. Not sure how much details like sharp edges really matter.

[psych0hans]

Originally Posted by adouglas

Easy to answer.

Go for a ride on the highway and make some passes while fully tucked, and while not.

I'm not even talking sitting upright. You can feel the difference between a mild tuck and a full race tuck, even at highway speeds.

So aero does matter overall. Not sure how much details like sharp edges really matter.

When I'm on the highway and just want to let it rip, I get into full tuck and gas the poop out of it... Then when I want to slow down I get on the brakes and at the same time I sit upright, hence becoming a sail and getting extra braking power... Works every time...

[tgold]

Originally Posted by adouglas

Easy to answer.

Not sure how much details like sharp edges really matter.

They matter very much.

Wind resistance increases with the square of the speed. Meaning if you double your speed say from 30 to 60 mph, the wind resistance at 60 mph will be four times what it was at 30 mph. At 120 mph the wind resistance will be 16 times what it was at 30 mph.

[Aufitt]

Aero matters more on a small bike than any other.

Recently been doing the Moto3 tuck bum on tail on the fastest straight and seen the speeds rise 3-4kph up top.
feels like you are higher, and have to learn a difficult transition into the braking zone in one fluid movement without unsettling the bike but its faster. picked it up from some fresh out of Juniors (Fast) racing 125gp/Moto3 & Production.

Also on Aero, three 250/300's can do a faster qualifying lap than out on your own if you time it right, oldest trick in the book,
everyone is guilty of it even though they pretend they don't. only takes 0.001 secs for grid position, sacrifice one lap for the next if need be.

Practice getting a tow at a track day out of the fastest corner onto the straight.
A 600 will quickly gap you, that helping hand makes a difference,
If they are on the same bike then you'll make a pass you never could have otherwise.

[jkv45]

Ok...you got me.

Here's the deal. To really know, you need to test before and after making your aerodynamic improvements. That's how you will know.

Your results will depend on your speed and the significance of your changes.

When I was racing Yamaha sprint karts we decided to install a driver's fairing. It blocks the wind from hitting your chest. Should make a difference with 15 HP - right? Depends. On the sprint track where speed were mostly in the 35-40 mph range, with minimal time at top speed (60 -65), there was no improvement in lap times. You would also get minimal draft passing until the very end of the straight.

Take that same configuration to a big track like Road America and it was significantly different. Where you couldn't feel much of a draft on the sprint track, it was huge on the big track when you were spending a good amount of time near your top speed (in the 80-90 mph range).

So, yes, it could. Or not.

[csmith12]

Originally Posted by Aufitt

Aero matters more on a small bike than any other.

Recently been doing the Moto3 tuck bum on tail on the fastest straight and seen the speeds rise 3-4kph up top.
feels like you are higher, and have to learn a difficult transition into the braking zone in one fluid movement without unsettling the bike but its faster. picked it up from some fresh out of Juniors (Fast) racing 125gp/Moto3 & Production.

Also on Aero, three 250/300's can do a faster qualifying lap than out on your own if you time it right, oldest trick in the book,
everyone is guilty of it even though they pretend they don't. only takes 0.001 secs for grid position, sacrifice one lap for the next if need be.

Practice getting a tow at a track day out of the fastest corner onto the straight.
A 600 will quickly gap you, that helping hand makes a difference,
If they are on the same bike then you'll make a pass you never could have otherwise.

[cbinker]

Originally Posted by jkv45

Ok...you got me.

Here's the deal. To really know, you need to test before and after making your aerodynamic improvements. That's how you will know.

Your results will depend on your speed and the significance of your changes.

When I was racing Yamaha sprint karts we decided to install a driver's fairing. It blocks the wind from hitting your chest. Should make a difference with 15 HP - right? Depends. On the sprint track where speed were mostly in the 35-40 mph range, with minimal time at top speed (60 -65), there was no improvement in lap times. You would also get minimal draft passing until the very end of the straight.

Take that same configuration to a big track like Road America and it was significantly different. Where you couldn't feel much of a draft on the sprint track, it was huge on the big track when you were spending a good amount of time near your top speed (in the 80-90 mph range).

So, yes, it could. Or not.

you are comparing cart racing to motorcycle racing? there is significantly more drag points on a cart then a motorcycle.

[Motofool]

Originally Posted by tgold

At some point the difference becomes significant and it has to do with your rate of acceleration in addition to top speed.

One thing that I've found to be true in racing: The faster your competitors are, the more the "not significant" things matter. The people who win are the ones who do more than others are willing to do.

What about hanging off the bike with that leg deployed trying to drag knee?

[jkv45]

Originally Posted by cbinker

you are comparing cart racing to motorcycle racing? there is significantly more drag points on a cart then a motorcycle.

Depends on the configuration of the kart.



I'm relating aerodynamics to speed.

[sharky nrk]

Besides body position and windscreen shape there are not many aero improvements you can make in most racing classes that require you to keep stock shape bodywork. Most rule books won't let you modify them up.

Anyone test different windscreens on their racebikes? I have a feeling something like the sport touring windscreen could actually be the better option depending on how big you are and how low you can get your body.

With the shape of the stock tank and bodywork, its pretty difficult to really get behind a stock or double bubble screen if you anywhere near 6ft I think.

[cbinker]

being 6'1" i really need to look into getting a taller wind screen.

[cbinker]

Originally Posted by Motofool

What about hanging off the bike with that leg deployed trying to drag knee?

that eliminates the need for brakes.

[tgold]

Originally Posted by jkv45

Ok...you got me.

Here's the deal. To really know, you need to test before and after making your aerodynamic improvements. That's how you will know.

Your results will depend on your speed and the significance of your changes.

When I was racing Yamaha sprint karts we decided to install a driver's fairing. It blocks the wind from hitting your chest. Should make a difference with 15 HP - right? Depends. On the sprint track where speed were mostly in the 35-40 mph range, with minimal time at top speed (60 -65), there was no improvement in lap times. You would also get minimal draft passing until the very end of the straight.

Take that same configuration to a big track like Road America and it was significantly different. Where you couldn't feel much of a draft on the sprint track, it was huge on the big track when you were spending a good amount of time near your top speed (in the 80-90 mph range).

So, yes, it could. Or not.

I agree that testing aerodynamic "improvements" is important. However, your method of testing is flawed because it depends on a driver exiting a given corner at the exact same speed in order to measure the results fairly. Doesn't matter who your driver is, they aren't going to be able to make their exit speed consistent enough to get good data.

So you either test in a wind tunnel or you test on something like a long runway where you can set up a speed trap and accurately measure your entry and exit speed. Some people are actually willing to do that sort of thing.

Here's one area (of many) where I think it matters: When you come out of a turn behind someone and you go down the straight working on passing them into the next corner. With "less aerodynamic" bike A you pull almost even with your competititor but your front wheel winds up about 6 inches behind his when you both brake for the turn at the same time. OR: Bike B with better aerodynamics you wind up with your wheel 6" in front of his at the same braking point. To me, option B is preferable both technically and psychologically. And it's not an unrealistic scenario at all.

Aerodynamics are not always intuitive. What is perceived to be aerodynamic often is not. However, there are some general rules that apply. Things like relatively sharp points and edges instead of rounded and smooth, gradually tapering trailing edges in stead of a sharp cutoff, small bodywork gaps instead of large ones.

[tgold]

Originally Posted by Motofool

What about hanging off the bike with that leg deployed trying to drag knee?

I've thought about that. Since you are slowing down all the way to the apex of the corner, it's ok to have your knee out as far as aerodynamics are concerned. That's kind of a part of your braking system. However, when exiting a corner I definitely get my knee up and tucked in earlier when on a 250 Ninja for that same reason.

[jkv45]

Originally Posted by tgold

I agree that testing aerodynamic "improvements" is important. However, your method of testing is flawed because it depends on a driver exiting a given corner at the exact same speed in order to measure the results fairly. Doesn't matter who your driver is, they aren't going to be able to make their exit speed consistent enough to get good data.

So you either test in a wind tunnel or you test on something like a long runway where you can set up a speed trap and accurately measure your entry and exit speed. Some people are actually willing to do that sort of thing.

Here's one area (of many) where I think it matters: When you come out of a turn behind someone and you go down the straight working on passing them into the next corner. With "less aerodynamic" bike A you pull almost even with your competititor but your front wheel winds up about 6 inches behind his when you both brake for the turn at the same time. OR: Bike B with better aerodynamics you wind up with your wheel 6" in front of his at the same braking point. To me, option B is preferable both technically and psychologically. And it's not an unrealistic scenario at all.

Aerodynamics are not always intuitive. What is perceived to be aerodynamic often is not. However, there are some general rules that apply. Things like relatively sharp points and edges instead of rounded and smooth, gradually tapering trailing edges in stead of a sharp cutoff, small bodywork gaps instead of large ones.

So how do you plan to test your theories?

I agree that the items you mentioned do affect aerodynamics. To what extent is dependent on the basic overall shape they are attached to and the speed at which that shape is traveling.

If you are behind someone exiting a corner and plan to pass them on the straight shouldn't you be tucked in behind them in their draft until you have gained a significant advantage from the reduced drag to slingshot pass them? At that point (drafting) your aero drag is completely insignificant - it's just a fraction of what it normally is.

A brick with rounded edges will not show significant aero improvements over a brick with sharp edges. A motorcycle is a brick (especially a Ninja 250), and rounding the edges slightly isn't going to make a significant improvement in its aerodynamics.

Reducing the frontal area, smoothing the flow on the sides, filling the low pressure areas, and adding a tail, would.

I believe a "double-bubble" type windscreen may be your biggest aero improvement. Although it increases the frontal area, it reduces the turbulence over your helmet and back, which is a factor.

[Motofool]

Originally Posted by cbinker

that eliminates the need for brakes.

Originally Posted by tgold

I've thought about that. Since you are slowing down all the way to the apex of the corner, it's ok to have your knee out as far as aerodynamics are concerned. That's kind of a part of your braking system. However, when exiting a corner I definitely get my knee up and tucked in earlier when on a 250 Ninja for that same reason.

But the braking phase should happen before the turn-in point, not all the way to the apex.

In his books, Keith Code recommends going through a turn on the gas; that is, getting on the throttle as soon as possible and roll-on smoothly through the turn in order to achieve moderate acceleration that stabilizes the rear suspension and maintains ground clearance.

The faster the speed of the turn, the more drag that out-leg produces (as well as anything in the bike or your body or your luggage that induces drag).

Just to clarify the previous discussion, there is no point at which the aerodynamic drag becomes big.
As explained above, the drag, which is no more than a force pulling your bike back, grows with the square of the speed.
A curve showing that dependence looks like a half-parabola.

There is air turbulence downstream the main airflow around the bike, which is reduced by wearing a speed hump on racing suit, a full face helmet and a back pack.
Those things will move the zone of turbulence aft some, just like a water droplet shaped streamer.

The moving body has to separate the molecules of air first; then, after it passes by, the molecules have to fill the void by themselves.
A shape that helps those molecules to rejoin without chaos reduces turbulence and the time that the low pressure of the void volume is sucking the body in opposite direction to its movement.

The Cp shown in the picture below is known as Coefficient of Drag.
As you can see, different shapes have different CP's: you want to achieve the smallest Cp that is practical.

Any motorcycle is a bunch of parts with specific shapes and Cp's moving in formation and fast through more or less still air.
The total drag force is equal to the addition of the individual drag forces produced by each shape.
A radiator is a huge drag producer, reason for which, the P-51 Mustang had it hidden back and below the fuselage and had a damper that closed it when extra cooling was not needed.
The bigger frontal areas deserve more aerodynamic attention, as you can see in the formula of the schematic shown below.

[Racer x]

YES!!! Let's just leave it at that.

[Somchai]

It would be interesting to hear the opinion of @greenaero about this theme.

[csmith12]

Originally Posted by Somchai

It would be interesting to hear the opinion of @greenaero about this theme.

Me too, but it would have to be relevant to the OP context. A race is a race yes, some are an endurance, others are a sprint. So his knowledge may be less applicable.

If ya'lls don't think it matters much, refresh you memory on what the H2 looks like.



However, overengineering for anything over the max speed of the 250/300 would yield less significance vs the cost.

[alex.s]

think about it this way- aside from rolling resistance from tires (not much), air is the only thing stopping you from going faster (well aside from the rev limiter, but you could change that with gearing)... so yes, aero does matter.

[Racer x]

Racing land speed is all about aerodynamics. Power is easy. Just spend the money. Build a great engine and tune it for the environmental conditions.
The aero part is a more complex subject. After reading and studying aerodynamics I removed my fairings. I am running without them. It's to costly to do everything wrong. Without a wind tunnel I feel I'm just guessing.

Gearing changes the rate of acceleration but won't help top speed. Sure the wrong gearing will hurt it . But only more power will make you faster.

The guys with more power than you can imagine 300+ Hp are hitting a serious wall at 250 mph. Actually the wall is about 225mph. At that point the acceleration has deminished. The weight is now balanced. So the rear tire is not weighted by the acceleration. So unlike 1/4 mile racing bikes, the weight shifts forward. The "wall" begins to push down on the front of the bike. This allows the rear tire to spin. Something that hurts acceleration and is not fun at over 200 mph.
The other option is aerodynamic bodywork that causes air to go under the front end. This lifts the front wheel off the ground. Again not fun at 200+ mph.

Any bodywork that is made to counteract these forces becomes a nightmare if the wind is blowing sideways. Even a 2mph crosswind will cause the bike to turn into the wind.

Motorcycle aerodynamics is not well understood above 250 mph. I see only computer controlled wings front and back that fly the bike. And they must react in milliseconds.

I am fascinated by aerodynamic forces. But terrified to watch my friends go into the unknown. This is serious stuff.

For small power bikes it makes all the difference. Any headwind will drop 10% off my top speed.
On a bicycle at 25 mph. It takes 30% less effort if there is another bicycle rider in front of you and with a rider behind it takes even less.

[Motofool]

Originally Posted by Racer x

............ The guys with more power than you can imagine 300+ Hp are hitting a serious wall at 250 mph. Actually the wall is about 225mph. At that point the acceleration has deminished. The weight is now balanced. So the rear tire is not weighted by the acceleration. So unlike 1/4 mile racing bikes, the weight shifts forward. The "wall" begins to push down on the front of the bike. This allows the rear tire to spin. Something that hurts acceleration and is not fun at over 200 mph............

That is very interesting, Eric.

For deep analysis that is still easy to understand, I recommend these books, which are available from most public libraries:

"Illustrated Guide to Aerodynamics" by Hubert Smith

"Model Aircraft Aerodynamics" by Martin Simons

The donuts shape of the motorcycle front wheel, plus the circular shape of the forks, plus the frontal area of the radiator (or engine's fins if air cooled have a huge coefficient of drag compared to the frontal area of the bike that is above the center of mass (streamliner and tucked rider).

Since the beginning of last century, when airplane races became popular, exposed landing gear proved to be a huge problem.
Any modern airplane has a way to hide those wheels away from the air stream.
When you are flying in a commercial plane, you can notice the huge deceleration that deploying the landing gear for landing induces: you can feel that G force like a deployed parachute pulling you forward.

[Racer x]

Old Burts bike looks cool but never went over 210 mph also the design is totally Illegal for any competition. The thing is just not safe incase of a crash or engine fire.
Also his record is cursed but that is a different story.

One thing I have found is the aerodynamic requirements to get the lowest coefficient of drag change dramatically as the speed changes. I other words. Something good at 150 mph is not good at 300 mph.

One thing learned from the golden age of airplane racing is the cable has 10x the drag of a strut.

[tgold]

Originally Posted by Motofool

But the braking phase should happen before the turn-in point, not all the way to the apex.

In his books, Keith Code recommends going through a turn on the gas; that is, getting on the throttle as soon as possible and roll-on smoothly through the turn in order to achieve moderate acceleration that stabilizes the rear suspension and maintains ground clearance.

The faster the speed of the turn, the more drag that out-leg produces (as well as anything in the bike or your body or your luggage that induces drag).

Just to clarify the previous discussion, there is no point at which the aerodynamic drag becomes big.
As explained above, the drag, which is no more than a force pulling your bike back, grows with the square of the speed.
A curve showing that dependence looks like a half-parabola.

There is air turbulence downstream the main airflow around the bike, which is reduced by wearing a speed hump on racing suit, a full face helmet and a back pack.
Those things will move the zone of turbulence aft some, just like a water droplet shaped streamer.

With regard to where you finish your braking, I'd say that you should look at Keith Code's comments in the context of trail-braking. Yes, you do most of your hard braking while upright, but you can gradually taper off all the way to the apex if you're good. I don't quite do it that far but I do consider some level of trail-braking necessary to win even at the club level.

Back to the aerodynamics discussion though, I am talking about racing, so a backpack isn't something I'd normally have with me on the racetrack. But your mention of the aero hump is an excellent example of the sort of things that matter in racing terms. There are aero humps, and then there are AERO humps. Some sort of vestigial aero hump that you see on many suits isn't going to do much of anything, but just take a look at the size of the aero humps on a MotoGP rider's suit and you'll see what I mean.

It was asked how I plan to test any aerodynamic improvements that I want to make. Short of building my own wind tunnel, (which I have considered) I plan to do the old-fashioned method of short pieces of yarn attached all over the bike and taking video so I can look at airflow.

A speed advantage matters not just in getting in front of your competitors, but it also means that you don't have to work as hard in the corners to stay in front of them. Less taxing mentally and less taxing on the bike means that you have more left for the end of the race when it really matters.

When you want to win, you look at details because they make a difference. Aerodynamic details absolutely can make a difference.

[choneofakind]

Aero always matters. Look at videos from Specialized bicycles about their wind tunnel (humorously referred to as the Win Tunnel) and all he tests they do to debunk aero myths.

One thing they keep reinforcing is that all the shapes that offer aero improvement at high speeds also apply to low speeds. And we can see this in the math: there is no velocity component in the drag coefficient, C_d. Yes, drag force is a function of the square of speed, but drag is always a factor in moving bodies.

Is it worth chasing for speeds under 60? Nah. It's it worth chasing for land speed numbers? Heck yeah. What about for a road course...? Not sure. I'd hazard a guess that your biggest improvement from a single modification will come from adding teardrop tail to the backside of the rider/tail, but I'd assume that's not legal in your racing class.

[SLOWn60]

So from what I get from the charts & discussions; I should be as fast as a speeding bullet or maybe a sphere! No wonder there's always riders right behind me...until the sprint to the finish!

[choneofakind]

Lol. Round is a shape! Good sense of humor about it.

[Racer x]

I have a very close friend that did land speed racing for years. He then switched his focus to vintage road racing . He builds his own bikes and pays very close attention to aerodynamics. Things like cables and riding position are just as important as engine power. When he first started racing he was not great at the turns. But because he was so fast on the straight. He had low lap times. When he entered novice class. He won or placed top three a lot. So I would say it matters in road racing.

[Sirref]

I'd say yes, I didn't run a windscreen for a while but I put one on at summit point raceway

I gained 5mph at the end of the straight and dropped 1.5s/lap instantly (it's a horsepower track so there's a lot of time in 6th gear on the ninjas)

[tgold]

Originally Posted by choneofakind

Aero always matters. Look at videos from Specialized bicycles about their wind tunnel (humorously referred to as the Win Tunnel) and all he tests they do to debunk aero myths.

One thing they keep reinforcing is that all the shapes that offer aero improvement at high speeds also apply to low speeds. And we can see this in the math: there is no velocity component in the drag coefficient, C_d. Yes, drag force is a function of the square of speed, but drag is always a factor in moving bodies.

Is it worth chasing for speeds under 60? Nah. It's it worth chasing for land speed numbers? Heck yeah. What about for a road course...? Not sure. I'd hazard a guess that your biggest improvement from a single modification will come from adding teardrop tail to the backside of the rider/tail, but I'd assume that's not legal in your racing class.

Interestingly, WERA rules allow just about any bodywork for the 250 Ninja superstock class.

The race organization that I race with (Motoseries) is a little less clear about that. However, there will now be a combined 250 superbike/ 300 superstock class for Motoseries, so I'm thinking of going a little aero-crazy.

Here's a little device to get some brains working overtime:
http://www.rynofender.com/