[Bodean FZR1]

I have seen alot of superbike races where a second or third place rider pulls in front and wins a race on the last straight away, because he tucked in behind to ride the draft, then pulled out in front at the last few feet. I have a basic understanding of the principle of the negative air space behind a moving object, I can't quite grasp how that negative air pressure can slingshot a bike ahead of the leader . Any Ideas?

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[AZ Scott]

When you are in the pocket of air behind another bike, you are not having to push the air in front of you out of the way, so your bike is able to go faster than it normally would. This essentially gives you a "running start". You can carry that extra speed for a few seconds, as you pass the guy, until the air causes your bike to slow back down to its normal speed. But by then, you've made the pass, if you timed it right.

Picture two bikes, side by side, topped out at 150 mph. Assuming all else is equal, they will remain side by side the whole time.

Now, imagine all of a sudden, one of the bikes has a wind-blocker in front of it. That bike will surge ahead drastically. That's what happens when you're in the draft.



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I'm not joking. And don't call me Shirley.

 

[R6Racer]

I'm not an expert in fluid dynamics, but if I'm not mistaken, riding in someone's draft also causes them to slow up slightly by creating additional drag. I could be wrong, but I'm pretty sure I read that somewhere. I'll check with my brother, he's a mechanical engineer (I'm electrical ). But in either case, the largest advanage comes from the reduced wind resistance anyway.

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[Scooter]

Right you are. When sitting in the draft, you can actually reduce the throttle a little and maintain the same speed as the bike (or car) you are drafting. At the most opportune moment, roll into the throttle all the way, and accelerate past your opponent.

In a drafting battle, the one place you DON'T want to be is leading the race going into the last turn on the last lap. I have even seen riders/drivers allow the second place bike/car to pass, then draft and repass right before the line. It works.

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"After all, we ARE professionals, here."

 

[AZ Scott]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by R6Racer:
...if I'm not mistaken, riding in someone's draft also causes them to slow up slightly by creating additional drag...
<HR></BLOCKQUOTE>

Actually, it's the opposite:

When two bikes (or cars, or whatever) are drafting, both of them end up going faster than a single bike.

Here's why: At speed, two things cause aerodynamic drag -- the air hitting the front of the bike is responsible for most of it. But there's also the air coming back together behind the bike. This turbulence forms a vacuum that essentially is trying to suck the bike back where it came from.

These two effects are constant for any given speed.

Now, think of the two bikes, nose to tail, drafting. Obviously, the bike in the rear doesn't have much of the air in front to deal with, so he can certainly go faster than normal.

But at the same time, the lead bike doesn't have the normal vacuum area behind his bike, since the air is continuing to stream past the rear bike, rather than swirling around directly behind his own bike. This actually gives him (the leader) a slight speed increase as well!

Now, of course, the difference is not nearly as apparent as the one the drafting bike is experiencing, but it's there. This is why a pack of riders freight-training together can almost always catch a lone rider on the faster tracks. It happens all the time at places like Hockenheim.

This effect is even more noticeable in Stock Car racing. Because of the shape of the stock cars, when they get up on somebody's rear bumper, the turbulence between the two cars is virtually eliminated, so two or more cars, nose to tail, can run much faster than a single car...



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I'm not joking. And don't call me Shirley.

 

[Bodean FZR1]

Thanx guys --very informative!


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[R6Racer]

Yeah, thanks for the correction Scott

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[auger]

OK,AZ lets assume that the rear bike has ram air.Would he lose the effect of ram air?Doesn`t ram really come onto effect above 100mph?Its interesting because the rear bike would have the advantage of the slipstream but would lose the advantage of positive air pressure in the airbox,would he not?

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[AZ Scott]

Yes, I would think that the drafting bike would lose a little ram-air power, but the lack of air resistance in front of him is more significant to his overall speed capability.

And think about this: As soon as he whips over to go around the lead rider, not only does he have more speed, but now he has his ram-air effect back WITH that extra speed, which shoves even MORE air down the ducts! Double bonus!

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I'm not joking. And don't call me Shirley.

 

[mashuri]

There are other things to consider as well. The rear bike will start to run hotter due to less air flowing through the radiator. This also can hurt power and reliability if done for a long time. I've seen some races where the drafting bike will pull out of the slipstream briefly just to cool the engine a little.

Drafting has an even more pronounced effect on cars heavily utilizing aerodynamic grip (i.e., wings and ground effects) like Formula 1 and CART. The big wings on those cars punch a big hole through the air and cause a lot of turbulence behind them. This really upsets the handling of the car drafting them because they lose a lot of downforce as a result. You can still draft and pass on the straights but you have to be careful following into corners. CART cars still have enough "mechanical" (i.e., through the tires) grip to draft and pass into a corner. F1 is suffering because of the rule requiring all cars to use grooved tires with less traction. They have become so reliant on aerodynamic grip now that it's virtually impossible to pass another F1 car. It makes for boring, parade-lap races and is currently the subject of much heated debate.

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1999 Blue/White YZF-R1: 2 Bros. C4 exhaust, Dynojet jet kit, timing tricker, dyno-tuned by Graves
2000 NBM/Lt Oak int/Blk top C5 Convertible - MN6, Z51, A&A Exhaust, C/R X-pipe, Corsa tips, !CAGS

[This message has been edited by mashuri (edited June 28, 2000).]

 

[SpeedPhreak]

that exact thing happend at ppir on fathers day irl race. i dont know names or numbers but 1 car was drafting, dropped down off of 3 to pass under.. the car got goofy & the front car blocked, now the rear car is all unsettled & cant make the turn & drives it right in the wall.

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[R6Racer]

F1 cars have enough downforce from aerodynamic effects that if they drove in a tunnel they would have enough grip to drive upside down!

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[Mattrazzo]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by R6Racer:
F1 cars have enough downforce from aerodynamic effects that if they drove in a tunnel they would have enough grip to drive upside down!<HR></BLOCKQUOTE>

I think the numbers I heard were 3,000 lbs of downforce and the car weighs 1,600 lbs.

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- Dan

 

[Bodean FZR1]

I love those F1 cars-when they are running on circuts not ovals. Mawybe when I pay off my R1 I'll get an F1----I Wish!

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[SpeedPhreak]

cool

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[Mattrazzo]

Coolest thing I've seen was at some track in Germany you can have a day where they train you to drive an F1 car. You start out with a little classroom instruction then you get to drive an F3 car for a few hours. When you come back from lunch you get to drive the real shmeal.

Whats real cool is that the cars are equipped with GPS and a track side computer tracks your progress. If you go off the "correct line", the computer automatically applies your brakes to keep you from going off track. It applies the brakes more aggressively the more you go off the line. Pretty cool.

The day costs $3,000. Money very well spent IMHO. I know plenty of people that would think it's insane to spend that much money, but me? It's a bargain...

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- Dan