Drafting questions

[eboos]

I have read many times about racers purposefully positioning themselves in second (or in Jeff Wood's case 4th) place in order to catch the leader's draft and then shoot past them for the finish. I guess I don't quite understand how this is done. Assuming 2 bikes are equally powered, how would the second bike gain an advantage once it pulls out to make the pass?

Please be detailed.

[Pittenger5]

http://en.wikipedia.org/wiki/Drafting_(racing)

[s a x m a n]

haha, was just going to post that same link

The "slingshot pass" is the most dramatic and widely noted maneuver associated with drafting. A trailing car (perhaps pushed by a line of drafting cars) uses the lead car's wake to pull up with maximum momentum at the end of a straightaway, enters a turn high, and turns down across the lead car's wake. The combination of running downhill and running across the zone of lowest aerodynamic drag allows the trailing car to carry extra speed and pass on the inside of leader. [2]

[Degsy]

nesr at daytona

pay attention to 1:50 to 2:07 (a little drafting right at the beginning, but turns into late braking really)

When you come out of the slipstream, it's like hitting a brick wall (check out 1:04 in the video). If you sit right behind someone, you can stay behind them and even stay a gear up on them sometimes because you have less drag to worry about (especially if they are a donut-eating lard-o like Gman used to be). If you move back a little further, you hit some real bumpy air (worse than leading), but if you then move to one side, you get some smooth air again. The smooth air goes back behind the lead rider in a kind of arrow shape, but with bumpy air in the middle of the arrow head.

The very best Daytona guys (Russell, DuHamel etc) know just how to position themselves to get in the smooth air to accellerate faster than the person leading (less drag), then time it just right to dart out to the side at the last minute and pass the finish line before the extra wind resistance has a chance to take effect too much.

That's as best as I can describe it. Go race at Daytona and all will be clear. LOL

degs

[nt650hawk]

Drafting is how a 20 year old bike with 15 less HP and no race fairing can win at Daytona.

[eboos]

Yeah, both examples that were in my mind were from ASRA races in Daytona. Your pass, which was awesome, looked like you had a better brakeing point then the guys you passed. The draft looked like it got you into position, then you passed them on the brakes.

I never really appreciated how scary fast Daytona looked until seeing it in first person view.

[nt650hawk]

Yeah, both examples that were in my mind were from ASRA races in Daytona. Your pass, which was awesome, looked like you had a better brakeing point then the guys you passed. The draft looked like it got you into position, then you passed them on the brakes.

I never really appreciated how scary fast Daytona looked until seeing it in first person view.

Try being on it. and braking (in my case) from 149 mph.

[Paul_E_D]

Ultimately, the bike drafting generates more rpms. When they pull out, they now have a HP advantage over the leading bike, even though they both face the same wind resistance.

[RyanNicholson]

I never really appreciated how scary fast Daytona looked until seeing it in first person view.

uhhhh yup, same here. whoa.

The whole drafting thing was a new thing to me down there, I fell victim to it a couple times too.

[101expert]

Hello,
I was the one giving Jeff Wood his pit signals in that race. He did a great job of holding back at Daytona. If he had gone out of the last turn onto the banking in first place he would have lost that race. Datona is one of the few tracks where this really makes much difference. I got a frist place at Daytona in 1999 and had practiced for two days before the race. I have had a chance to draft in practice. In my first race I hit my brake marker into trun one at the usual place after drafting another rider and went right off the track. I had no idea I was going about 10 to 15 mph faster than in practice. I didn't loose a place and got back on the track and it took me a few more laps to figure out where I needed to move the brake marker to do it right. The speed on a superbike in the banking at Daytona are close to 200 mph. At Loudon for instance it is only about 140 mph. At london you hardly feel the draft at all. I also race a 50cc bike at Loudon on vintage days and can tell you on that bike it matters at Loudon. I had 3 hp less than another bike I was racing against last year and I could stay with him in the fast areas by drafting him close. I had him in the corners and won the race. Drafting is too close for comfort on the road and I do not reccomend that you try it there.

[nt650hawk]

In my first race I hit my brake marker into trun one at the usual place after drafting another rider and went right off the track.

Funny, I did the same thing.

[Crash Dummy Denno]

great thread!

[FireboltEric_MA]

Cool reading! Good shit to know right there.....

[nmendell]

Cool reading! Good shit to know right there.....

On that note:
The lack of wind resistance in the draft allows a bike to accelerate more quickly and also pull a taller gear/reach a higher top speed than it could otherwise. BUT . . . can a bike maintain that higher speed even after pulling out of the draft?

That was my impression from racing at Daytona, but my impression could have been misleading since I was usually pulling out of the draft either to take the checkered flag or while I was just into the braking zone.

So . . . can a bike maintain a particular speed out of the draft that it could not accelerate up to on its own?

[Degsy]

In theory, yes. In practice, it's tough to avoid starting to go backwards.

[CEO]

Wow... is this really a motorcycle-related, non-shitted-up, truly interesting thread on NESR?

I'm speechless.

So . . . can a bike maintain a particular speed out of the draft that it could not accelerate up to on its own?

No. You are using the momentum gained in the draft to give you a temporary advantage when you pull out of it.

In theory, yes. In practice, it's tough to avoid starting to go backwards.

In theory, no. There is a balance of forces of the bike's forward oomph and the aerodynamic drag (which goes with the velocity squared). There is a fixed terminal velocity for any given vehicle.


BTW degs that was a cool video, thanks for posting.

[BLACK SQUIRREL]

On that note:
The lack of wind resistance in the draft allows a bike to accelerate more quickly and also pull a taller gear/reach a higher top speed than it could otherwise. BUT . . . can a bike maintain that higher speed even after pulling out of the draft?

That was my impression from racing at Daytona, but my impression could have been misleading since I was usually pulling out of the draft either to take the checkered flag or while I was just into the braking zone.

So . . . can a bike maintain a particular speed out of the draft that it could not accelerate up to on its own?

I found on my Own I Could not hit the ReV limiter in 6th, As I was drafting it would rush me forward I would hit the limiter for about 1/2 Second then The wind would catch me and keep me out of the limiter until I drafted again.

[Paul_E_D]

I say YES. You can get your revs up higher while in the draft. When you pull out next to another bike and you have 1-200 more revs, your bike can push through the wind better as it's making more HP. Drafting battles on the 125 are a perfect example. When I would pull out into the wind, I could just slowly motor past on the revs.

[nt650hawk]

I love this word and what it is all about.


Terminal velocity


Granted it is used in a verticle format. Instead of gravity hp comes into play and can work in a similar fashion. HP is the force propelling the object horisontaly rather than pulling. Other things come into play....


From Wikipedia
Based on wind resistance, for example, the terminal velocity of a skydiver in a free-fall position with a semi-closed parachute is about 195 km/h (120 mph or 55m/s).[1] This velocity is the asymptotic limiting value of the acceleration process, since the effective forces on the body more and more closely balance each other as the terminal velocity is approached. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on. Higher speeds can be attained if the skydiver pulls in his limbs (see also freeflying). In this case, the terminal velocity increases to about 320 km/h (200 mph or 90 m/s),[1] which is also the terminal velocity of the peregrine falcon diving down on its prey,[2]. And the same terminal velocity is reached for a typical 150 g bullet travelling in the downward vertical direction — when it is returning to earth having been fired upwards, or perhaps just dropped from a tower — according to a 1920 U.S. Army Ordnance study.[3]

Competition speed skydivers fly in the head down position reaching even higher speeds. The current world record is 614 mph (988 km/h) by Joseph Kittinger, set at high altitude where the lesser density of the atmosphere decreased drag.[1]

An object falling on Earth will fall 9.81 meters per second faster every second (9.81 m/s²). The reason an object reaches a terminal velocity is that the drag force resisting motion is directly proportional to the square of its speed. At low speeds, the drag is much less than the gravitational force and so the object accelerates. As it accelerates, the drag increases, until it equals the weight. Drag also depends on the projected area. This is why things with a large projected area, such as parachutes, have a lower terminal velocity than small objects such as cannon balls.

[CEO]

When you pull out next to another bike and you have 1-200 more revs, your bike can push through the wind better as it's making more HP.

The increase in power over the rpm range is a linear increase, whereas the aerodynamic drag increases quadractically. You will slow down, it's just a question of when

Anyways I didn't mean to argue. My point was that the advantage is only temporary. Obviously drafting works, it's a common technique... but it's mere strategy. You can't overcome the physics / fluid mechanics.

edit: Gino that's sort of what I was getting at. Paul does have the point that as your speed increases the bike is making more power due to the higher RPM... but again that can't overcome the fact that the aerodynamic drag increases faster. So yes, terminal velocity applies here as well

[Paul_E_D]

My point is that your bike overcomes MORE resistence than the bike next to you. Yes, you are slowing, but the guy next to you slowed before you. It's like he's on the brakes earlier. We all know what the result of that is.

[CEO]

My point is that your bike overcomes MORE resistence than the bike next to you. Yes, you are slowing, but the guy next to you slowed before you. It's like he's on the brakes earlier. We all know what the result of that is.

Yes, for a short (but often long enough, i.e. in Gino's case) time, you're right.

I was answering this question:

So . . . can a bike maintain a particular speed out of the draft that it could not accelerate up to on its own?

And the answer is no.

[Degsy]

edit: Gino that's sort of what I was getting at. Paul does have the point that as your speed increases the bike is making more power due to the higher RPM... but again that can't overcome the fact that the aerodynamic drag increases faster. So yes, terminal velocity applies here as well

Yeah. When I said 'in theory' I meant, temporarily, you get a boost, but you do end up slowing down. Watch my dayton clip again and watch me try to pass Gerard 3 times between 1:00 and 1:17 . I hit 'the wall' every time. i could feel myself gaining on Gerard, but as soon as I moved over to hit the wind resistance, the wall hit me. I have much to learn about drafting (but not much to learn about late braking).

Also, check out what missing one gear coming out of the chicane does to you. The two guys in front tear away and gerard re-passes me.

Another interesting thing to note is the engine pitch changing coming from the banking down towards the start-finish line. That's the tire circumference changing according to lean angle and consequentially, the engine revs changing.

BTW, flat out there, with Daytona gearing, my F4i reached 12.5k RPM and I THINK I was doing about 155mph.

degs

[Kitt]

There is a balance of forces of the bike's forward oomph and the aerodynamic drag (which goes with the velocity squared). There is a fixed terminal velocity for any given vehicle.

is "oomph" a technical term?

Terminal velocity involves gravitational force and drag force due to wind resistance.

A bike will go as fast as the power and gearing will allow... essentially, there is no "terminal velocity" for a powered vehicle.

Velocity can be defined as a function of power and drag force.

[CEO]

Cool stuff degs. It's amazing all of the other things that come into play when you get to a track with different features than we are used to (long sustained high speeds, long bankings, etc etc...). A whole different ballgame.