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 21.12.2010 at 08:02
 How does the wake behind a car lead to slipstreamimg?
 
I've been thinking a lot about that article by Gordon McCabe and vorticity but there is something I can't get my head around.

I get that there is turbulent air flow behind a car but I don't get why following a few yards behind a car makes it very difficult to overtake and is damaging for the following cars' engine and tyres but yet a few yards further back again there can be a slipstream effect.

At what point does the wake change from being a hinderance to a benefit to the following car and why should that be, I mean, why isn't it just a neutral effect rather than a benefit?

Confused...


  
 
      


 
 21.12.2010 at 11:00
 Re: How does the wake behind a car lead to slipstreamimg?
 
As far as I know slipstreaming is happening on both the situations you mention (just after the car and a few meters further), in fact the effect should be stronger the closer you are to the front car.

The problem of the engine heating is because the exhaust air of the leading car is too hot to refrigerate effectively the follower. If the car would be (for example) electric they could follow each other without any problem of that kind.

As for the tyres and the difficulty to overtake, a F1 depends a lot on aerodynamics to keep a decent level of grip (the car "weights" several times its weight at 200 kmh). On a straight line this is not a problem and you can draft the front car as close as you dare, but as soon as you need to turn the loss of grip is too much and it's better to be cutting more laminar air.

The problem of F1 cars with this is that they are too delicate in terms of refrigeration and aerodynamics, in NASCAR for example drafting is 100% advisable.


  
 
    
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 21.12.2010 at 18:20
 Re: How does the wake behind a car lead to slipstreamimg?
 
Saltire said:
I get that there is turbulent air flow behind a car but I don't get why following a few yards behind a car makes it very difficult to overtake and is damaging for the following cars' engine and tyres but yet a few yards further back again there can be a slipstream effect.

Turbulent air from the car in front affects the wings and stops them working as well as they should.

Because wings produce both downforce and drag, this has two effects : the reduction in downforce means lower cornering grip, while the reduction in drag means higher straightline speed.

If the straight is long enough, the driver can take advantage of the lower drag and overtake before the corner and before the lower downforce becomes a probem for him, but the problem is when circuits - particularly the newer ones - have a lot of corners linked by short straights and there simply isn't enough space to take advantage of the slipstream effect before the corner, and then the lower downforce hurts him too much that he can only get so close. Because of circuit design the downsides (lower grip) usually outweigh the upsides (higher straightline speed) by a massive margin, and overtaking is impossible.

Note that on circuits like Monza (long straights, few corners) then slipstreaming happens a lot more - there is room on the straights to do it, and because there are so few corners the penalties are reduced. This is why newer circuits - with the Tikle-clone long pit-straight but also with lots of tight corners linked by short straights - have problems. Because there are so many corners the effect of losing the downforce is multiplied, and the single long straight is not enough to make up for it.

It is this "only getting so close" that is the problem that F1 has tried to tackle in recent years with repeated rule changes (plus proposed new ones, see here), but most people say circuit design is the bigger problem.

Some say it's the wing settings that are the problem, but it's the circuit that dictates the wing settings. If there's a lot of corners then teams will crank on the wing and the problem is made worse - note how F1 never saw as much overtaking as they hoped when they raced at Indy : the tight, twisty infield section made teams increase the downforce, so they couldnt slipstream as much as the Indycars could on the straight.

So to answer your question, when the car is far behind the guy in front, he gets the benefit but not the downside. When he gets closer, the gets the downside, and this more than cancels out any benefit.

Glacierre makes a great point about NASCAR - although they have small wings and front splitters, they are more about highspeed stability than downforce, plus they race mainly on ovals, so slipstreaming happens a lot more.

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 21.12.2010 at 18:36
 Re: How does the wake behind a car lead to slipstreamimg?
 
Too much emphasis is put on the cars aero side. The tyres and the driver are the key areas for overtaking. In an overtaking situation the 2 questions are; is there the grip to overtake (ie. will the car stop in time) and is there the will (Do I want to risk the car, with Kobayashi its always a yes. Which is why he is exciting to watch). If both those answers are yes then we have overtaking.

Kobayashi said if the Pirelli tyres aren't as durable as the Bridgestones he may have to curb his aggressive style.

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 21.12.2010 at 23:18
 Re: How does the wake behind a car lead to slipstreamimg?
 
Pitmonster said:
This is why newer circuits - with the Tikle-clone long pit-straight but also with lots of tight corners linked by short straights - have problems.

Circuits are a big part of it but I wish people would stop pointing the finger at Tilke.
Silverstone is awful for overtaking.
Shanghai is great for overtaking.

There's a fashion for street circuits and bringing the racing close to the people - and we've always known that Monaco brings little in the way of overtaking to the party so does it matter who designs the street circuits? We'd be better off placing the blame on the guy who keeps signing deals with cities to host races.

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 21.12.2010 at 23:19
 Re: How does the wake behind a car lead to slipstreamimg?
 
kimster said:
Kobayashi said if the Pirelli tyres aren't as durable as the Bridgestones he may have to curb his aggressive style.

:-) Well we can't allow that can we, Bernie?

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 21.12.2010 at 23:51
 Re: How does the wake behind a car lead to slipstreamimg?
 
Maverick said:
Circuits are a big part of it but I wish people would stop pointing the finger at Tilke.
Silverstone is awful for overtaking.
Shanghai is great for overtaking.

There's a fashion for street circuits and bringing the racing close to the people - and we've always known that Monaco brings little in the way of overtaking to the party so does it matter who designs the street circuits? We'd be better off placing the blame on the guy who keeps signing deals with cities to host races.


Woo!! Common sense. Silverstone tends to be boring. Definitely the last 2 years have been dull as hell. Shanghai is good because of rain, 08 was terrible.

Tilke is restricted in terms of the plot of land he is given and what the people who own the place want. But insulting Tilke is fun...

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 21.12.2010 at 23:53
 Re: How does the wake behind a car lead to slipstreamimg?
 
Maverick said:
kimster said:
Kobayashi said if the Pirelli tyres aren't as durable as the Bridgestones he may have to curb his aggressive style.

:-) Well we can't allow that can we, Bernie?


My guess is that the Pirelli's will be very similar to the Bridgestones. Judging from what people were saying after the Abu Dhabi tests. And with fixed weight distributions for 2011 (only) I think that does take the excitement away..

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