Is cycling behind a truck a bad practice?

Question

Sometimes on a highway outside my city, Nairobi, I have been passed by fellow cyclist cycling behind trucks. As much as it is similar to holding onto the back of the track this is different since you are basically pedaling either faster or slower to keep up with the speed of the truck while watching its brake lights and indicators just in case it brakes so that you can brake too.

One time I tried this when I was on a fairly steep climb with a relatively fast truck. It was fun trying to maintain my speed up the hill and towards the end the truck was accelerating. I was so obsessed with keeping the pace on my road bike till I passed the place I was to branch off the highway by like 3 kilometres. When I narrated this to a friend a fellow cyclists he laughed at how I had managed to cycle at 40 kph for over 30 kms. Though I didn't feel the strain immediately but there was an effect later and I had to keep practicing daily to remain fit though these days I just do 25 kph.

But my friend warned me that if I was going far and the truck accelerated faster and left me behind or it branched off too soon than my destination I would be exhausted drastically battling with the wind. Anyway personally I feel like I can cycle behind a truck as a way to train. I don't know what others here on this platform would advice me on this.

Answer 1

It is really dangerous to follow a large vehicle closely. It is possible behind a directeur sportif in a passenger car which is smaller: you can see through it, and the driver is a cyclist who knows you and knows about you.

You cannot see what is coming in front of the truck. If they choose to brake hard, watching the brake lights will be of no use; you have simply no chance to brake so fast as many cars can (the truck can be unloaded or transporting light goods). You do not see what kind of obstacles or potholes are coming, how the truck will avoid them, and so on.

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Note that I was assuming a road bike without any front suspension fork.

Ride On says "Cars will generally stop faster than bikes due to their more efficient brakes and lower centre of gravity," and they indicate a bicycle stopping distance of 31.5 m from 40 km/h. However, take into account that this is from a prepared rider who knew he had to slam the brakes, not just noticing a brake light. A passenger car will stop at something like 26 m.

Even for motorbikes it is dangerous, and the stopping distance can vary with the experience of the rider by a factor of 2. [1, 2]

And of course, even a car tailgating another car will often crash into the preceding one. The two-second distance is often required by law. That is 22 m at 40 km/h and 28 m at 50 km/h. That is not compatible with drafting behind the vehicle in many, if not most, traffic rules.

Answer 2

This is called "Draughting" or "Drafting" depending on your locale, when done as described. If done on a track it can be motor-pacing or similar. There are even world speed records for bikes that are shielded behind a vehicle.

Like anything in cycling, safety is relative.

You can choose to ride behind a large solid vehicle, knowing that:

• This may be illegal in your location, by your local road laws as "following too close" or "tailgating"
• your vision is obscured and your line of sight is shortened
• Your reaction time is minimised
• your visibility to other road users is almost zero from some angles
• you're breathing really hard right right behind a vehicle's exhaust
• if you fall for any reason, any following vehicle may not be able to avoid you
• at significant speed, the vehicle can flick up road debris faster than you can react.

On the positive side:

• the "assist" is significant - you can often go much faster for the same effort.
• the shape of the vehicle can provide shelter from wind and rain. Busses and square trucks tend to be best. Vans are middling, and cars are mostly useless.
• There's a motivation to "hold the wheel" which can feed the desire to stay in the wind shadow. If there's an undulating road, the tow vehicle will slow for climbs and corners, and possibly get away from you on straights and downhills. So you push extra hard to stay in place.

It's up to you if this is cheating - in pro sport its absolutely cheating, unless the tow vehicle is another cyclist in which case its "tactics" or "racecraft".

If you get a Strava PR or KOM with this technique - you're still riding the bike and making a big effort, so it's not really any different from a powerful tailwind.

Here's someone clearly draughting on Strava. Is it fair?

As for training - it's not a free ride. You have to be super-attentive and you're riding really hard to stay with the tow car. So yes that's sprint training. It's not interval training or similar. So there's no more training here than a normal hard ride. However it is practice for riding at speed - good luck taking a drink at these speeds!

Answer 3

I once tried to cycle behind a truck out of sheer exhaustion and curiousness to see what it feels like doing that. It was easy at first since all you had to do was wait downhill for a truck to come by. I had seen other cyclist do it and others even hold onto the back of the truck and get pulled by the truck uphill.

So for my case I just wanted the truck to be my pace setter so I could climb the hill with motivation. Towards the end of the climb the truck was gaining speed and I was sort of lagging behind. Another truck was behind me too and it was catching up with me and I realized I had to give way. Before I could do so a car was overtaking the truck behind me when a bus appeared from the other side. I would say it was my lucky day because all I remember was waking up in a hospital bed with shocked faces of my parents. Me and my bike survived but the lesson of not risking cycling behind a truck was big. I can't think of a better answer than that.

Overtaking vehicles can crush on you when they are confronted by another oncoming vehicle before they can overtake fully the vehicle ahead of you. Drivers are known to sandwitch their vehicles esp cars between trucks when there are many trucks following each other. The driver will see you when it is too late to evade you.

Another important thing is that you may be arrested by highway patrol traffic police over endangering yourself and other road users. I don't know if you have such a thing in your locality.

Answer 4

This is an immensely dangerous practice. The kinetic energy of the smallest car is easily capable of killing a human. A truck would be able to instantly kill a cyclist even at a crawl, let alone at higher speeds. Many cycle deaths in London have been due to cyclists being too close trucks. Truck drivers do not always have the best visibility around the truck or at the back, so this adds to the risk of cycling anywhere near a truck. A bicycle and a truck is an extremely toxic and dangerous combination.

Answer 5

Long ago I used to ride a small relatively underpowered motorcycle (usually 1960's or 1970s 175cc Jawa) about 70 miles between two cities, typically one return journey a week*. Top speed on the level was maybe 50-55 mph. Large trucks would "illegally" exceed the motorcycles speed.

On a number of occasions I tried 'slipstreaming' behind these trucks.
The gains are significant - you can back well off on the throttle, the bike feels much more comfortable and it's warmer (and smellier if a cattle truck). Also - following distance needed to be 1 to 2 metres and the utmost of vigilance was required to stay in the slipstream without hitting the truck. It was hard enough to do that I inevitably lost contact after a few minutes and the truck would pull away, uncatchable.

People here have mentioned relative braking deceleration of bicycles and trucks. Even with superior braking reaction time is an important issue. I tried plugging in various decelerations and reaction times into standard equations of motion and it suggests that at bicycle speeds and typical reaction times and following distances, the risk of rear end impact should be small. However, alexsimmons gives a real world example of a friend being hospitalised, and I was always completely "on edge" and aware that I was dicing with danger, or death.

As well as the rear impact risk when reaction time is adequate, you will often be unlikely to be able to see the truck brake-lights clearly, or at all. If you are out on the edge of the truck where the brake lights are visible you may also be visible to the truck driver. This is a "two edged sword" - some drivers will take extra care if they are aware you are there, while others, sadly, may actively try to trap you. Add to this the other risks of pot holes and unseen objects suddenly "appearing" and it adds up to being a significant;y dangerous activity.

If you like to live dangerously, don't mind dying young and can tolerate being hospitalised with a range of possible damages, then this may be "fun" to try. Most people's risk - reward metrics would suggest that tail-gating trucks is lots of fun but not worth the gains.

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*After some while the young lady who was a significant factor in my making the occasioned weekly visits moved to my city and the visit rate dropped and we usually went by car. I survived the tailgating experiences and we have now been married 45 years.

Answer 6

The energy win is of no discussion.

In a lot of situations, it may be even safer to ride behind a big truck or bus. Where I live, car drivers tend to ignore cyclists, but are pretty much aware of the presence of a large truck or bus. The truck/bus driver stands higher and has better headlights so he can deal with the road situations better than a cyclist. He is usually sober and the cyclist sometimes is not.

The sudden braking is really not an issue - these vehicles tend to brake slower than the cars and they don't run at very high speed in the first place. Even if they stop (and you fail to), you will hit the vehicle at rather small speed difference. Not good for sure, but pretty much better than colliding with a standing object.

The only thing I fear when I tailgate a truck is some object on the road (stone, brick, hole) that the truck can run over with no problem, but I may not see it in time. Busses mostly have low enough clearance so their drivers avoid such problems better.

Exhaust fumes may or may not be a problem. These vehicles have their exhaust pipe either on the left or the left upper back (busses), so the fumes may not reach the cyclist at all. And the cyclist have a choice to follow another, more favourable vehicle. Road dirt and dust in a dry weather, on the other hand, ...

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edit: p.s. as of popular demand, I should add that the practice of closely following a motor vehicle bears risks that are different and can be higher than the risks when cycling alone. The risks are even higher when you use the vehicle drag to cycle faster than you are used to (e.g. faster than you can cycle for an extended period on an empty level road).

Doing so on a lane that is not the rightmost that is used by the motor transport is not acceptable for me.

Use common sense! (Even if this is the narrow meaning of the "common sense" that is compatible with cycling on the public roads in your area.)

Answer 7

No,you can get arrested, hurt and disrespected [that is, increasing the level of overall disdain and disrespect that many drivers have for cyclists.]

Never try or even think about it.

Answer 8

I say its fine as long as the vehicle in front is not carrying any goods and you're keeping a safe distance/speed.

By safe distance & speed I mean the speed you use when going uphill, so that's about < 15km/h and close enough to be able to turn away from it if happens to brake suddenly.

About the goods, i see trucks here in Nairobi carrying pipes & sand/rocks etc. I wouldn't slip stream a truck carrying such goods in case they fall off.