General Cycling Discussion - Slipstream for cycling?

Race drivers make use of the vacuum behind the front car to reduce its own air resistance and sometimes even use it to over take the front cars.

I heard that this workd for superbikers, but what about cyclists?

Yep, it certainly does,

In Time trialing, it's against the rules to slipstream another rider.

One of my favourite hobbies it to slipstream buses..except in London that is... :D

Rich

I saw somewhere , can`t remember where, that even the cyclist in front has a slight air resistance advantage,

Don`t know how that works but seemingly it does

Originally posted by willic
I saw somewhere , can`t remember where, that even the cyclist in front has a slight air resistance advantage,

Don`t know how that works but seemingly it does
I heard that too. Something to do with the air scooting (I use scooting here as an extremely technical term) straight past the front rider rather than curving around behind the rider.

I don't know too much about that side of things but it sure makes a lot of difference when you're drafting behind another rider.

Especially if you were drafting behind me...I kick a$$! :D

Rich

DRafting cars can be pretty intense... but it can also be dangerous. You can't see hazards and obstacles before you're right on top of them, and cars do have a habit of stopping abruptly. At 50-60 km/h, that can be dicey. Better to have a professional derny driver who knows you're there.

As for the aerodynamics advantage to the guy at the front of a paceline, there is a very slight advantage over riding solo. The presence of a rider just behind reduces drag [very slightly] by interrupting eddies and turbulence and channelling them backward. Having said that, cyclists are imperfectly aerodynamic to start with and the advantage is minimal.

My best draft was for 3 miles behind an electric milk delivery cart going at an even 20mph.

Originally posted by willic
I saw somewhere , can`t remember where, that even the cyclist in front has a slight air resistance advantage,

Don`t know how that works but seemingly it does

The reason why is that there is less turbulence over the rear wheel of the front cyclist if there is another behind.

Originally posted by Spire


The reason why is that there is less turbulence over the rear wheel of the front cyclist if there is another behind.
I knew you were here for a reason.:D

That sounds so much more intelligent than my 'scooting' post. Thanks for the 'real' reason.

Can you also tell us what percentage difference it makes? The guy who told me that it makes a difference did mention a percentage but I've forgotten it and I'm not sure if it was correct or not.

Originally posted by MediaCreations

Can you also tell us what percentage difference it makes? The guy who told me that it makes a difference did mention a percentage but I've forgotten it and I'm not sure if it was correct or not.

I don't know what sort of percentage it is, but even if the guy behind is inches away, it probably is a couple percent at best.

Let's get technical and specific. It is generally acknowledged, confirmed through testing, that a cyclist expends up to 30% of his energy pushing the air out of the way. Still air, not a headwind. In a headwind, the difference is even more significant. What this translates to is that going 20 mph in someone's slipstream feels about the same level of effort as going 16-17 on your own. You can REALLY feel this in a paceline. You can breeze along at say 20-21 then suddenly it's your pull and that 20-21 isn't so easy. Obviously for more fit riders these speeds might be more like 25-26. The group I ride with on weekends cruises pretty steadily at speeds from 20-22.

The closer you can keep your wheel to the cyclist in front of you, the more pronounced the effect though you can feel the difference even 3-4 feet back. When first learning you should start off about 3 feet back. On successive rides, ease closer until you can comfortably stay within about a foot or so. Also, keep your tire slightly offset from the tire in front to give you some maneuvering room if a sudden stop is required. You definitely do NOT want to let your tire touch the tire in front of you. You WILL go down. Riding in a paceline can be fun, but it requires constant concentration. It is physically easier, but mentally intense. You don't want to get mesmerized by the tire in front and lose concentration. Observed the riders two or three ahead while watching the tire in front closely with peripheral vision. And when out riding alone, don't just hop on someone's wheel without asking. Some people get really testy about it, especially if it's someone who is not used to paceline riding. It doesn't bother me. I'm kind of flattered if someone finds my wheel attractive.
Regards,
Raymond

Originally posted by RainmanP
Let's get technical and specific. It is generally acknowledged, confirmed through testing, that a cyclist expends up to 30% of his energy pushing the air out of the way

I don't think this is accurate. When rolling at a constant speed of 20mph, I'd have to say about 80-90% goes to air resistance while the rest is rolling.

If air restistance is only 30% what accounts for the other 70%?

Originally posted by Spire


I don't think this is accurate. When rolling at a constant speed of 20mph, I'd have to say about 80-90% goes to air resistance while the rest is rolling.

If air restistance is only 30% what accounts for the other 70%?

Friction resistance from the tires and gravity.


:beer:

When rolliing at 20mph on a flat, you guyz are claiming that 30% of friction is from air and 70% from rolling (and mechanical)?

I found this website with loads of graph and formulae regarding specifics on cycling.

A lot of it is one guys opinion but he seems to know what he is on about.

Check it out at...... www.cptips.com/

I believe during the recent Tour de France coverage I even heard Phil Liggett mention the 30% savings in wind resistance figure. I've heard it before too and seen it in cycling related literature.

As a pointer I also read (and use it in my own drafting) is not to look down at the rider's wheel in front of you, but instead look up a bit and concentrate on the rider's hip in front of you. Easier to gauge your distance. Stay very attentive or as mentioned before if you touch wheels chances are great you will fall and probably take others with you.

A rotating pace line with other riders you trust and are familiar with is a blast and can really pick up the pace on a long ride. Rider in front stays out there for a just a brief moment and then peals off to the left and slides back to the end of the line. You really have to start pedaling fast slightly before you get to the end or you will get spit out the back of the line and you will watch your pace line buddies disappear off into the distance. Not fun getting dropped.:(

The resistence due to air increases with the square of the speed. Moreover, power is force * speed, which means that the power to overcome the air resistence is proportional to the cube of the speed. Rolling resistance, however, is purely linear (power of 1).

This means that, on a flat road I get the following values for power needed to overcome air resistance and rolling resistance:

10 kmh (6mph) = 5 Watts Air, 8 Watts rolling.
15 kmh (9mph) = 17 W Air, 12 W rolling.
20 kmh (12mph) = 40 W Air, 16 W rolling.
25 kmh (15mph) = 81 W Air, 20 W rolling.
30 kmh (18mph) = 141 W Air, 24 W rolling.
35 kmh (22mph) = 224 W Air, 28 W rolling.
40 kmh (25mph) = 335 W Air, 32 W rolling.

These values are for my weight and frontal area (your mileage may vary).

Note that it is the speed through the air that matters with respect to air resistance. So if you have a headwind, you have to add that to the air resistance (but not to the rolling resistance). Also note that gravity and your weight are playing a role in the rolling resistance (and in your acceleration). But, only on a hill do they play a significant role in the overall resistance (a 6% grade for me at 20 kmh would require 40 W for air resistance, 16 W for rolling, but a massive 245 Watts to overcome the slope.

So, as to the drafting question. The higher the speed the higher the benefit. I have seen numbers between 15-40%, but it is rarely stated at what speed these numbers apply. My guess would be that drafting in a peloton going about 35-40 kmh might give you about 20-25% reduction.

For the person in front, i have heard the benefits are around 1-3% Perhaps slightly more.

Cheers,
Jamie

The basic rule of thumb for slipstreaming is the guy(s) behind is using 20% less energy to maintain the speed of the leader

Originally posted by Rich
One of my favourite hobbies it to slipstream buses..except in London that is... :D

Rich
After being behind that bus for 20 minutes, doesn't your face turn black/gray from the nasty exhaust? I did it once and the air I breathed was worst than if I was smoking.

There is some downright Richard Cranium thinking going on here.

This idea of a drafting cyclist somehow "pushing" a leading cyclist is a bunch of *^%$*.

But go ahead and contiune to think it's true as long as I'm the one "on your wheel".....

You go ahead, I'll help out from back here, right.........

I had always thought that the lead cyclist gets a slight advantage. But I just read It's not About the Bike and Armstrong suggests that his teammates would draft an attacking cyclist to slow him down. Between that and this thread, I'm more confused than ever. Which is it?

Jupe, I haven't read the passage in Armstrong your are referring to, but I think that you might be reading him too literally. He might be speaking more broadly about tactics.

An classic tactic is for several team members to join a breakaway group, so that, when they take their turn at the front, they ride slightly slower than the other attackers. This slows the breakaway a bit. Even if the other attackers notice, they face the choice of pulling all the time, or allowing the slowing to work.

I doubt it has to do with aerodynamics.

With respect to Richard's comment on the aerodynamics, many sources claim that the front rider gets a 1-2% advantage. That's so small that you'll likely not notice it.

Cheers,
Jamie

Originally posted by jmlee
Jupe, I haven't read the passage in Armstrong your are referring to, but I think that you might be reading him too literally. He might be speaking more broadly about tactics.That's kinda what I suspected. Thanks a bunch.

Drafting works wonders...
Last week en route to work I drafted a bus for about 1/3 the ride, not recomended unless its 5 am...
I was able to maintain 44Kmph on a mountain bike for about 5k...
I was working hard, but It was much easier than trying to go along at 35 Ill tell you...

I agree with jmlee, the figures stated are what I have read also.

CHEERS.

Mark

Originally posted by willic
I saw somewhere , can`t remember where, that even the cyclist in front has a slight air resistance advantage,

Don`t know how that works but seemingly it does
The cyclist in back breaks up the vortex behind the lead cyclist. This reduces the the lowpressure point behind the lead guy and so reduces the amount of energy he has to generate to go at any given speed.

Sometime take two solid cones made of the same amterial say wood. mount them on each end of a bar, mount the center of the bar on a piviot. Now with the pointed end of one facing "out" and the othe facing "in" place them in the stream of air coming from a fan. The one with the flat side toward the breeze will have less air resistance than the other as wil be shown by which one moves with the air stream and which moves against it.

Joe
:beer:

Jupe,
It is more of an emotional drag. The attacker knows that the other rider is going to sit on his wheel and not do any work. Everyone knows that that is the guy's job in that situation. Look at what Roberto Heras did on the way to Plateau de Beille though Beloki wasn't attacking; he was chasing. Lance wanted to give Heras the win. When Beloki looked toasted, Roberto took off to try to bridge to Lance. When Beloki recovered and started closing on Roberto, his job was to drop back and sit on Beloki. Otherwise he was a target for Beloki to chase. He couldn't have caught Lance at that point, but Lance was trying to put as much time into Beloki as he could to build up a lot of insurance to allow for unforeseen problems on future stages like crashes, punctures or mechanicals.

There probably is a small benefit to the leader by the second and subsequent cyclists disrupting the vortices as someone suggested compared to riding alone.

If you ever get a chance to ride in a paceline you will see a very noticable difference. When you take a pull, don't overdo it; take very short pulls. If you toast yourself trying to match the stronger riders you may not have enough left to latch onto the last wheel, and you will get popped off the back. No one expects a new guy to take a long pull. They will suggest and respect a short pull.
Regards,
Raymond

Wind resistance increases with speed. I understand the increase is exponential. This is why averaging over 30 mph for a time trial is so difficult. At that speed, the cyclist is fighting a bunch of wind resistance.

I read somewhere that the draft you get is about 1% for every mph of speed. Of course, there are modifiers. At relatively low speeds in still air (15 mph and less) there is virtually no significant draft. And if you have a cross wind, getting a draft can be tricky. I have ridden a few times in large groups and I have the impression that the draft is much greater in this situation than normal.

Originally posted by unrelated
Race drivers make use of the vacuum behind the front car to reduce its own air resistance and sometimes even use it to over take the front cars.

I heard that this workd for superbikers, but what about cyclists?
Extreme slipstreaming.....

http://www.fredrompelberg.com/upload/algemeen/Fred_zoutvlakte_tijdens_record_achter_auto.jpg
Fred Rompelberg was 50 years old in 1995 (the oldest professional cyclist at that time) when he set the world record for an auto-paced bicycle at 166.9 mph.

Do you suppose the top fuel dragster experienced a 1-2% increase in speed from Fred's drafting?

Originally posted by bentrox!

Extreme slipstreaming.....

http://www.fredrompelberg.com/upload/algemeen/Fred_zoutvlakte_tijdens_record_achter_auto.jpg
Fred Rompelberg was 50 years old in 1995 (the oldest professional cyclist at that time) when he set the world record for an auto-paced bicycle at 166.9 mph.

Do you suppose the top fuel dragster experienced a 1-2% increase in speed from Fred's drafting?
:roflmao:

The lead vehicle can get a 2% increase in effective power if it is being drafted by a similar sized vehicle. The 2% increase in power will give 0.6% increase in speed.

You can also draft in echelon (behind and to the side of the lead). You can notice this effect if you drive in the lane next to a large truck at 60 mph with the front of your car almost level with the back of the truck. This is because the air is being sucked in behind the truck, and your car doesnt have to push its way through this air. This is how ducks and geese fly in formation.