If there's no accident, the guy's a genius.
If there is an accident, this guy's dumb.

All contextual.

At least wear a helmet...

That's really fast...that's in KPH right?

Why is this tagged with "accident"? I've been deceived!

>> ^TheJehosephat:

Why is this tagged with "accident"? I've been deceived!


Although we didn't see it, I can't really imagine it ending any other way... Maybe, if the dude was lucky and didn't try to keep that up for very long.

Actually, I wonder how the hell he got started with that. He must have followed the truck from the on ramp.

Seems likely to me that he'd be able to brake faster than the truck could break, and if the truck started pulling too far away leaving him exposed, he could coast on the shoulder till he can safely stop.

I'm not saying I would do this, but it doesn't seem all that dangerous. I guess the one thing to worry about would be road debris, since he can't see it coming.

Tags for this video have been changed from 'bicycle, highway, stupid, truck, accident' to 'bicycle, highway, stupid, truck' - edited by jonny

I think I know where he got the idea from...

http://www.youtube.com/watch?v=J1jzs6dk4bs#t=136s

>> ^maestro156:

Seems likely to me that he'd be able to brake faster than the truck could break, and if the truck started pulling too far away leaving him exposed, he could coast on the shoulder till he can safely stop.
I'm not saying I would do this, but it doesn't seem all that dangerous. I guess the one thing to worry about would be road debris, since he can't see it coming.

I dont think its about who can stop the fastest, its about how fast you can start stopping.

He's about half a metre away from the back of that truck. He's doing 90kph. Human reaction time is about .2 of a second. Lets do the maths.

90,000m/3600s = 25m/s
25m/s*0.2s = 5m

He's going to travel 5 metres before he even starts slowing down. If that truck has to brake hard he will go into the back of it. Granted, his speed relative to the truck won't be very high but it would prolly be enough to send him arse over tit. at close to 90kph. and he aint exactly in leathers.

I'm not even sure he could stop faster than the truck. Sure, the truck is heavier, but it has 4 wheels, big thick tyres and a lower centre of gravity. Lets do the maths.

The coefficient of friction between road bike tyres and average russian tarmac is...no I kid.

So maths ...

according to this website: http://www.csgnetwork.com/stopdistinfo.html, a vehicle slows at roughly 15 feet per second per second, which means in the 0.2 seconds that it takes the bike rider to discover that the truck is braking, the speed of the 90km/h truck would have reduced to about 86-87km/h

which means while the bike will travel 5m in those 0.2 seconds, the truck will travel about 4.8m, putting him 20cm closer to the truck.

Once again, too close for my comfort, but I don't think I'd call it stupid. Just risky, like base jumping and wingsuits.

God, thank you. Jinx's crappy math was really peeving me. you are an asset to the sift

>> ^maestro156:

So maths ...
according to this website: http://www.csgnetwork.com/stopdistinfo.html, a vehicle slows at roughly 15 feet per second per second, which means in the 0.2 seconds that it takes the bike rider to discover that the truck is braking, the speed of the 90km/h truck would have reduced to about 86-87km/h
which means while the bike will travel 5m in those 0.2 seconds, the truck will travel about 4.8m, putting him 20cm closer to the truck.
Once again, too close for my comfort, but I don't think I'd call it stupid. Just risky, like base jumping and wingsuits.

as maestro has astutely pointed out, you've errantly assumed this truck can full stop in zero time. Hurp de durp de durpidy pthhhhhhhhhhh

>> ^Jinx:

>> ^maestro156:
Seems likely to me that he'd be able to brake faster than the truck could break, and if the truck started pulling too far away leaving him exposed, he could coast on the shoulder till he can safely stop.
I'm not saying I would do this, but it doesn't seem all that dangerous. I guess the one thing to worry about would be road debris, since he can't see it coming.

I dont think its about who can stop the fastest, its about how fast you can start stopping.
He's about half a metre away from the back of that truck. He's doing 90kph. Human reaction time is about .2 of a second. Lets do the maths.
90,000m/3600s = 25m/s
25m/s 0.2s = 5m
He's going to travel 5 metres before he even starts slowing down. If that truck has to brake hard he will go into the back of it. Granted, his speed relative to the truck won't be very high but it would prolly be enough to send him arse over tit. at close to 90kph. and he aint exactly in leathers.
I'm not even sure he could stop faster than the truck. Sure, the truck is heavier, but it has 4 wheels, big thick tyres and a lower centre of gravity. Lets do the maths.
The coefficient of friction between road bike tyres and average russian tarmac is...no I kid.

A good old fashioned math battle. Feels good to be back.

Where do math battles rank in comparison to Goodwin's Law?

>> ^dystopianfuturetoday:

A good old fashioned math battle. Feels good to be back.

>> ^CaptainPlanet:

as maestro has astutely pointed out, you've errantly assumed this truck can full stop in zero time. Hurp de durp de durpidy pthhhhhhhhhhh
>> ^Jinx:
>> ^maestro156:
Seems likely to me that he'd be able to brake faster than the truck could break, and if the truck started pulling too far away leaving him exposed, he could coast on the shoulder till he can safely stop.
I'm not saying I would do this, but it doesn't seem all that dangerous. I guess the one thing to worry about would be road debris, since he can't see it coming.

I dont think its about who can stop the fastest, its about how fast you can start stopping.
He's about half a metre away from the back of that truck. He's doing 90kph. Human reaction time is about .2 of a second. Lets do the maths.
90,000m/3600s = 25m/s
25m/s 0.2s = 5m
He's going to travel 5 metres before he even starts slowing down. If that truck has to brake hard he will go into the back of it. Granted, his speed relative to the truck won't be very high but it would prolly be enough to send him arse over tit. at close to 90kph. and he aint exactly in leathers.
I'm not even sure he could stop faster than the truck. Sure, the truck is heavier, but it has 4 wheels, big thick tyres and a lower centre of gravity. Lets do the maths.
The coefficient of friction between road bike tyres and average russian tarmac is...no I kid.


No I didn't? I just assumed the truck would slow enough that he could go into the back of it. So ok, the truck travels 4.8ms, the bike travels 5m. He's now 30cms from the back of the truck, and only now is he gonna start braking. Assuming they decelerate about the same, and I'm not even sure you can stop faster than a truck on a bike, there is still a 3m/s difference in speed with 30cms of room between them. Like I said before, he won't be going very vast relative to the truck when he collides, but his wheels are still going to be spinning prty quickly and I'd guess that would be enough to put him on the pavement...or you know, the risk is large enough that I wouldn't want to try it.


And this is ignoring all the myriad other risks from travelling at 90kph blind. Maybe his attention is on somebody in a car with a video camera in the lane next to him, and suddenly his reaction to the truck braking is delayed...maybe a pothole appears under the truck. Or a puddle. I'd rather base jump than do that.

I used do this all the time. Not at 90kph (my gears don't go high enough), but I've done 70+. Trucks slow down way, way slower than bikes. If you wanna math battle about it, a cyclist's ratio of braking power-to-mass is much higher than any vehicle that's worth drafting. Even if the cyclist bumps the truck (which I have done too at high speed when my brakes failed), it just scares you and slows you down. He'd have to hit with a very high speed difference (not just a high ground speed) for anything bad to happen.

The biggest real risk is debris or pot holes that the cyclist can't see. That's why I've mostly stopped doing this. That truck is a drafter's wet dream though with such a low profile in the back, and I would not be able to pass it up.

There is no way that bike could out-brake that truck. There's no way if the truck slammed on the anchors like he meant it that the guy could stop without hitting it. He has one finger on the brake levers. The first 0.2 seconds would be until he started moving. The next 0.2 seconds (the 0.2 seconds that would put him into the back of the truck) would be for him to get his fingers properly onto the levers.

All this is if he's extremely alert and fully focused as the truck started to brake. You can play around with the maths all day long, if that truck has to stop in a hurry he's gonna lose a huge amount of skin.

I trust the guy who's actually done it over the guy who uses fuzzy math.

Then you also trust the guy who crashes over the guy who uses fuzzy math.>> ^DarkenRahl:

I trust the guy who's actually done it over the guy who uses fuzzy math.

Think I'd prefer back to the future style, and let the damn thing pull me instead of trying to pedal to keep up with it.

That trucker won't know what hit him. Literally!

Fuzzy fucking maths? Its only the laws of physics honey. I don't wish to disrespect others personal experience, but I knew a guy who had lots of personal experience of not having accidents, despite his speed and somewhat reckless driving...until he had an accident. The good news is he won't be having anymore accidents. The bad news is he won't be having anymore anything.

There is a reason you are advised to keep a good distance between you and the vehicle in front, its not just some random theorycrafting. If you rly don't trust the numbers then I suggest you hop on your bike, find a truck to coast behind and wait. Remember to video it and link me to the result. Oh, and try not to die, I don't think videosift will let me post snuff.

I guess it's relative. If you're worried about damaging your bike/car, keep your distance for sure. If you're worried about your life, get as close as you can. If that truck slams on its brakes and you're right next to it, you'll hit the back with a non-lethal force and stick there for as long as the brakes are slammed on.
If I had to choose between this braking scenario on a bike, or some accident while base jumping, I'd choose the bike for sure. Although the chances of a trucker needing to slam on the brakes are probably more remote than having an accident in base jumping.

Of course, as messenger said, I'd be much more worried about debris and potholes...

The Bicycle can without a doubt stop faster than the truck.

However it would be impossible for the bicyclist to stay on the bicycle while its doing a full break.

So lets say this.

Bicycle stops faster than truck
trucker stops faster than bicyclist

The stopping issue is rather secondary to what happens when the truck runs over a piece of 4x2 or a brick on the road.

@CaptainPlanet @Jinx

Sorry to interrupt you both, but why don't you just assume that they're both stationary and then work out how fast and how far they each start travelling backwards at different times using their difference in velocity; you're ignoring friction anyway so they're both inertial reference frames and may be treated as such. It'll make it a lot easier, conceptually, to find out how far apart they will be IF he reacts that quickly. I'm not gonna do it because it's already turned into a pile of shit pseudo intellectual argument, but i'm just saying.

Also, try to have discussions about maths/science in a nice and friendly way, because otherwise you just look like a youtube idiot who knows nothing about the subject. The last thing i want to see on the sift over crap like that is "hurr durr" comments.

Anyway, this is a bit of a stupid idea. To be fair they're only going between 55-60 mph which i suppose isn't motorway speeds, it's more like dual carrageway speeds. If he was on the motorway i'd say he had a death wish. As it is i'd say he's pretty desperate to be paralysed and have half of his skin grated away by the road surface.

And just why isn't this in * eia?

I think it's reasonably clear that with some combination of hard braking and slow reaction you'd definitely touch the truck when following that close. You get bumps with cars following too close reasonably regularly, and I don't think the physics (and certainly not the biology) are going to be all that different. I think the question is consequences of a touch:

Even if the cyclist bumps the truck (which I have done too at high speed when my brakes failed), it just scares you and slows you down.


I think that's what happens 9 times out of 10, but that last time I think you go down - and going down at that speed is going to often be a reasonably serious injury (especially without a helmet). Even at more moderate speeds, sometimes little bumps take you down - especially if you have any angle on your wheels or are pumping hard.

Multiplying that all out, I think the probability of serious injury in this situation is low; significant enough that I wouldn't try without a good reason and extra attention, certainly not something I'd do regularly.

Drafting like a boss. Dying like a dumbshit.

>> ^maestro156:

So maths ...
according to this website: http://www.csgnetwork.com/stopdistinfo.html, a vehicle slows at roughly 15 feet per second per second, which means in the 0.2 seconds that it takes the bike rider to discover that the truck is braking, the speed of the 90km/h truck would have reduced to about 86-87km/h
which means while the bike will travel 5m in those 0.2 seconds, the truck will travel about 4.8m, putting him 20cm closer to the truck.
Once again, too close for my comfort, but I don't think I'd call it stupid. Just risky, like base jumping and wingsuits.


Adding to the maths frivolities there are some factors that need to be considered....

1) It is a 5 axle truck (they usually have 18 wheels)
2) We don't know if the truck is loaded or not
3) The friction coefficient of bicycle tyres is about 0.75
4) The friction coefficient of truck tyres is about 0.8

If the truck is fully loaded the stopping distance is going to be very far - probably well farther than the bicycle.
If the truck is empty the stopping distance will be a lot less than the bicycle (18 wheels at a higher friction coefficient = stopping on a figurative dime).
So unless we know more information, the calculations are guess work with a very wide margin of error.

Sadly *dead as the video is now private
Was it this one? Looks like the thumbnail.


I’ve drafted up to 90kph, it’s not hard if you have the gearing.

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