What speed to create air pocket behind

[hcjg1]

Hi i would like to know how fast does a cyclist have to be going to create air pocket or vortex so that the rider behind can benefit from the slipstream. I tend to chase buses (not recommended) and you definitely feel the pull when you are within an area of about 3 metres or so. anything outside that and I dont feel it but you get resistance and find you have to work harder to keep up.

The reason why this has been coming up for me is because on quite a number of occasions when I have been cruising / napping on my put-together commuter bikes and some wannabe Lance Armstrongs would overtake. I they drop you, its fine but when they realize that not only am I able to match their speed but can outrun them if i want to, the attitude changes and they start weaving and complaining that you're sandbagging and you can see the aggression. Now its ok if they just pass and leasve you for dead but how dare a guy on a makeshift bike keep up with Lance. My commute is 15 miles one way and i do a return 5 days a week but they wouldnt know that.

Now my point is that I dont think the cyclist is traveling fast enough to create slipstream for the rider behind because I have never felt the effect of it whether I am in the front or behind, so I am wondering if these guys just spend too much time watching bike racing dvd's or Formula 1 and this might all be some sort of mumbo-jumbo but please let me know from a scientific point of view I am wrong because I am only talking form my experience.

[RobAR]

hcjg1, I think you already know the answer. Your use of 'vortex' proved it.
Unless you're drafting behind a 340 lb Sumo Wrestler who is spinning at 92 rpm and averaging 18 mph on the flats, stick with the bus. They have Brake Lights.
In Road Racing, a Team will often 'Pack' to allow a strong/refreshed team-mate from the rear to advance forward to 'carry' the team. If running into a head- or quartering-wind from the front - the pack tightens to block any wind as needed. No "I" in the word Team.

"so I am wondering if these guys just spend too much time watching bike racing dvd's or..."
Yep. If the pros do it; I need to practice it!

Trust me. One rider has to totally trust another before wheel-hugging becomes even acceptable. Wheel-kissing is for Emergency Use Only. And it usually results in a serious skin abrasion.

Some people watch too much Television.

Rob

[JohnV]

It's been my experience that posers usually think that when they are in their complete team kit that they are getting ready for the TdF and no one else is allowed to show them up. I see it happen at least once in every charity ride I attend. I guess they haven't figured it out yet that neither the kit or the high dollar carbon bike will make them faster. And to really see them get upset, let the person passing them turn out to be a 65 year old.

[Joe_W]

(02-21-2012, 03:37 PM)JohnV Wrote:  And to really see them get upset, let the person passing them turn out to be a 65 year old.

And overweight. Yup, happens to me, I get passed by older, much heavier guys. On the other hand: I don't really care (plus my bike is at the lower end of the spectrum, ok, but definitely not top material).

Regarding the actual topic: We tend to practice drafting or the Belgian thing every now and then. At high speeds (and with headwinds) the effect is very noticeable. Also on organized rides there are usually packs forming that are 10 or so strong. However, usually those are mainly cyclists from one club who know each other well. You are welcome there if you know how to behave in a tight pack (and do your share of the work). I tend to be careful when drafting: The guy in the front should at least be able to ride in a straight line and have a smooth cadence.

Experience (eg. yesterday's cross duathlon = drafting event I participated in) shows me that as soon as you have a noticeable headwind drafting can make a huge difference. I teamed up with one guy on the trail and we rode most of the distance together, especially in the open fields we could pass many who were trying to solo this (or were unlucky with finding a pack). Average speed was... not that high (cross event, 50 minutes for 20 km including both transitions = 2x300m running, some of that pusing the bike, and picking up bike and helmet and stuff).

---

Oh, and from a scientific point of view: This does depend on the shape of the object pulled through the air, so I guess Chrissie, Norman or Macca on their carbon wonder weapons create a bit less of turbulence at the same speed than eg. me (even though I look more aerodynamical in horizontal cross section due to affinity for good food and drink).

Any aeronautical engineers around? What I usually find in the cycling and tri rags is numbers for the total drag of bike + rider but no pictures of vortices forming though it would be interesting to see (at least you get nice pictures).