How far back you can be to still get a tow?

LittleGreyCat · Post by **LittleGreyCat** » 30 Sep 2021, 7:25pm

Watching F1 from last weekend reminded me.
They kept on about how having a car at the other end of the straight was enough to give a speed advantage.
A distant tow.

Now in TdF most cyclists who are being given a draft to get them back on the peloton are so close to the rider in front that they are practically engaged.

Riding in a group always seems easier if you are fairly close, but it feels hard to catch up if you fall back too far.

So how close do you have to be to get a decent tow/draft? Enough to significantly reduce the energy required to maintain speed.

CyberKnight · Post by **CyberKnight** » 30 Sep 2021, 7:37pm

Jdsk · Post by **Jdsk** » 30 Sep 2021, 7:58pm

The size of effect for a bike behind a motorbike:
https://link.springer.com/article/10.10 ... 20-00332-z

I'll look for bike behind bike the next time I'm near my copy of the bible.

Jonathan

thirdcrank · Post by **thirdcrank** » 30 Sep 2021, 8:16pm

Watching F1 from last weekend ....

What you learn from that is that the higher the speed, the greater the benefit. What I think is different about cycling is the psychological effect whereby even when climbing at relatively slow speeds, riders gain an advantage from holding wheels and the support of team mates. I'm no runner but I believe there is an element of this in distance running events.

Jdsk · Post by **Jdsk** » 30 Sep 2021, 8:19pm

thirdcrank wrote: ↑30 Sep 2021, 8:16pm
Watching F1 from last weekend ....
What you learn from that is that the higher the speed, the greater the benefit.

The dominant effect in F1 at the moment isn't that following close to another car promotes passing. It's that it slows cornering.

And no-one can find a solution...

Jonathan

[XAP]Bob · Post by **[XAP]Bob** » 30 Sep 2021, 8:32pm

There are two effects - with a long straight it absolutely allows passing, with twisty sections it pushes you back, hence the DRS option to hopefully give you that little boost to get you back alongside for the next corner.

Yet to see a DRS line painted at the right place though.

And F1 are looking at solutions, all the aero changes from next year are designed to massively reduce the loss of downforce from following a car closely - the curved wings, and overwhelming reliance on underfloor downforce should make a huge difference.

thirdcrank · Post by **thirdcrank** » 30 Sep 2021, 8:39pm

I forgot to mention that my interest in motorsport is less than zero.

kylecycler · Post by **kylecycler** » 30 Sep 2021, 8:58pm

Just my purely empirical experience, but...

Cycled from Inverness to Gairloch with a group on the first day of a trip as far north as Kylesku Bridge, stopped at this viewing point...

,,,then set off behind one of my pals. His bike had drop bars and a bikepacking setup; mine, flat bars and rear panniers. Mine had 'bar ends' either side of the stem to get narrower and lower when descending, though. There's a long descent after the viewing point and when he was freewheeling I found I had to pedal in top gear (48F/11R) right up until I got to within a bike's length then I could freewheel and stay with him.

What might sound ridiculously obvious but wasn't to me until that moment was that the point at which I was able to stop pedalling and still stay with him was the point at which I could no longer hear the airflow (because there effectively wasn't any!) - *silence* - it really was as simple as that.

From Jonathan's link, though, I think one answer would be 'a lot further than you might have thought,' at least behind a motorcycle, although as the study shows, motorcycles produce a lot more drag (and therefore shelter) than a bicycle. Cars maybe not so much; they have a larger frontal area but a lot less drag than a motorcycle with two upright riders and panniers (unless the car has a roof rack full of bikes!).

MikeF · Post by **MikeF** » 30 Sep 2021, 10:10pm

CyberKnight wrote: ↑30 Sep 2021, 7:37pm

28 mph is somewhat faster than I cycle on the flat.

CyberKnight · Post by **CyberKnight** » 1 Oct 2021, 7:33am

Indeed

i find if you lose more than a couple of bike lengths you are off the back and your not getting back on if you were on your cruising limit to start with

iandusud · Post by **iandusud** » 1 Oct 2021, 7:35am

I know this might be stating the obvious but it is very much speed dependant, that is to say that the faster the bike in front is going the further back the draughting effect can be exploited. IME there's not much to be gained below 20kph but at that speed draughting close up is definitely beneficial. As speed increases so the "hole in the air" gets bigger and you don't need to be so close. Also the size of the rider in front makes a difference. I'm quite tall at 6'1" and sometimes end up behind petite riders one club runs where the draughting effect is negligible. Of course if you can get behind a tandem at speed then you really do get a free ride. We have dragged solos for miles on our tandem in the right conditions!

thirdcrank · Post by **thirdcrank** » 1 Oct 2021, 7:46am

Stating something else which may be obvious, this is illustrated in time trials where some riders are significantly better than others at riding without shelter. I don't think this is just about strength and technique but a state of mind. Also in time trials, where sitting on a wheel is outlawed, some riders get a psychological boost from chasing the rider(s) who started immediately before them. In races like the TdeF, the top riders on GC who are the last to start are separated by bigger gaps, partly to minimise this.

Audax67 · Post by **Audax67** » 1 Oct 2021, 8:28am

According to the report of a study I read ~20 years ago, the rider in front benefits from draughting as well: the turbulence that would normally hold him back moves to the back of the "bubble", so that the leading rider gets less drag and the back one less frontal resistance.

Jdsk · Post by **Jdsk** » 1 Oct 2021, 8:44am

Jdsk wrote: ↑30 Sep 2021, 7:58pm The size of effect for a bike behind a motorbike:
https://link.springer.com/article/10.10 ... 20-00332-z

I'll look for bike behind bike the next time I'm near my copy of the bible.

Bicycling Science has an analysis of the physics but no answer to this specific question.

Jonathan

Stradageek · Post by **Stradageek** » 1 Oct 2021, 8:46am

I once followed my stupidly fit brother who was doing just over 30mph on the flat. I could only stay with him (on his spare racing bike) by keeping my front wheel almost touching his rear, pretty much 'track pursuit' style. This was OK until we hit a slight rise and my brother decided to get out of the saddle. His bike slowed so rapidly that we instantly had half a wheels overlap, I can see why pro cyclist have so many accidents

and I now always slipstream a little further back and to the side.

On a more amusing note I was once chased by two super strong racers on an social ride (my boss and his boss) who eventually caught me only to the scream "there's no tow". Ah the fun of riding a recumbent.

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