Tracking a bicycle...

[Firelite]

Er...Hello?....Does anyone come in here any more?

Since you are reading this you obviously have. I miss this section, it used to be so much fun, so I thought I would ask a question (I know the answer, but had great fun getting to it...)

One Sherlock Holmes story involves the question of the direction taken by a bicycle, the tracks of which the intrepid detective arrived at part way along. The question is, is it possible to determine the direction taken by a bicycle if you arrive at its track at some midway point. it is too far to follow both ways, so you have to say which direction it was headed in.

Have a think about it, don't look it up straight away. By the way, most contemporary commentators consider Holmes's interpretation to be at least a bit flawed, and possibly wrong. For the sake of this particular argument, you aren't allowed to interpret any splashing of mud or water. Nonetheles, if you have observations about the splashing arguments, do post them, I would be interested.

Finally, what other information about the 'quarry' bike be determined?

Have fun with it!

Regards,

Firelite

 

[boatman]

No knowledge of nineteenth century tyre tracks but if forward pointing Vs that is one obvious way. More weight on rear wheel except when braking then weight is thrown forward, possibly.

Bit too tyred to work it out.

 

[bearbait]

If terrain is hilly it would be going more slowly uphill and the front and rear tracks would likely wobble around a central line more than downhill.

Skid marks due to excessive breaking would likely show direction. Also if the bike stopped, e.g. for the view, mapreading, a footprint may help.

Sign on the underlying substrate may indicate direction, according to type of substrate and time since passing. Transfer of substrate from one to another medium e.g. sand to rock.

Excessive torque on the pedals can damage the ground due to wheel slippage and indicate direction.

Width of the tyre track and pattern can indicate road bike or MTB.

 

[stone monkey]

The rear wheel will always track in a straight line wheras the front wheel will weave so if you check which wheel track is crossing over the other you can determine the direction of travel. If it was me riding the bike the direction of travel would be towards the nearest pub !!

 

[ol smokey]

My understanding of this is that when the cycle wobbles, the end of the loop where the wheels part and then join up again
are more pointed in the direction of travel, and any stones dislodged will be propelled backwards from the spot where
they had originally lain. If I remember correctly I got this from a very old book by Baden Powell, when I was a lad.
Now just turned 80. Hope I have not been wrong all these years. Cheers Stuart.

 

[Tomteifi]

As long as the bicycle(and in this scenario, a Victorian one and not any of the modern ones around today)is being propelled forwards i.e. front wheel first, then the rear wheel track will always be imprinted over the top of the front, therefore, deciding the direction of travel would be very simple. Even if the tyres on it were not 'treaded' ones, each would differ in their wear patterns and marks picked up from use and that, added to the fact that the front wheel marks would be in less of a steady line than the rear, would be a clear indication of direction. Once the rear wheel mark is established, the front is easy to identify in that manner. Any splash marks would bolster the already made decision of direction thereby totally confirming it my dear Watson. I should add that each time the rear wheel passes over the mark made by the front wheel, the mark it makes in the mark left by the front will 'point' the direction.

 

[Quixoticgeek]

A lot of modern bike tyres have an intended direction of rotation, so assuming the tyres have been put on the bike properly, you can usually tell from the orientation of the tyre tread.

Obviously for slicks like on road bikes, that won't work...

J

 

[John Fenna]

If it is a mountain bike check the ground for blood spatter... most mountain bike trips involve the rider crashing (Youtube shows great examples) and the blood spoor will show the direction of travel by the splash pattern.

 

[woof]

And if they are "roadies" they shave their legs, so look for leg shavings......

Rob

 

[21st century pict]

If the cyclist is anything like me, you'll easily find some footprints pushing the bike uphill
I'm just off out so ill have a closer look today ,
I would like to read the Sherlock Holmes reference, and the Baden Powell Reference Ol Smokey.
Cheers for the challenge Firelite ...

 

[General Strike]

This explanation will identify which of the two tracks is formed by the front wheel, and which by the rear. However it will not identify the direction of travel, since rear will always 'over-ride' the front, whether the bike is going East or West, for example. I think that you would need to observe the asymmetry of the front wheel track to establish the direction of travel - most of the time there will be a steeper part of the loop away from the rear wheel track and a long smooth correction back towards the rear wheel track, and this long 'return points in the direction of travel. This will be more distinct with slower riders, more challenging terrain and less experienced cyclists.

 

[Bishop]

Where a 'bunny-hop' manoeuvre has left an impression in soft ground or mud then the diameter of the wheels and frame size of the bicycle could be determined. May also be able to work that out from a wobble or change of direction.

 

[John Fenna]

Shaved leg hair blow in the wind too much and rarely stay on the route ... a poor indicator of all but wind direction....

 

[Robson Valley]

I'd look in the tire tracks for very small stones displaced from their original locations.

 

[Klenchblaize]

Er...Hello?....Does anyone come in here any more? I miss this section, it used to be so much fun.

It's got more life in it than "Fair Game"!!

K

 

[pieinthesky]

In the UK we ride on the left side of the road, so it should be pretty obvious which way the cycle was going


On exiting any damp, oily or muddy patch the resulting tyre marks will fade in the direction of travel and will not exist before.

To initiate a left turn you first have to push the handlebars to the right, I suspect this will show up in the tyre tracks but I don't know exactly how.

 

[bearbait]

In the UK we ride on the left side of the road, so it should be pretty obvious which way the cycle was going

And on the pavement. And the wrong way down one-way streets. And through red traffic lights.

 

[Klenchblaize]

And on the pavement. And the wrong way down one-way streets. And through red traffic lights.

And all with an unhelpfully aggressive 'attitude' born of an equally ill-advised mission statement:

To ensure all other road users are regarded with the no less disdain than is normally reserved for advocates of animal testing.

K

 

[Chaard]

I know the theoretical answer to this one but I did do an MSc in forensic investigation so ill just sit here and get a tan

 

[Firelite]

There are some really surprising responses there, thank you all - I particularly liked the one involving looking for where the cyclist stopped and put a foot down. I suspect (more than a little) the one about leg shavings is tongue in cheek? General Strike correctly points out an error one or two have made - That is that the overlapping of tracks alone doesn't assist in determining the direction. Holmes' own solution has been criticised heavily by contemporary mathematicians - his answer involved the deeper tracks caused by there being more weight over the rear wheel. Several have included the greater "wobbliness" of the front wheel, caused by the fact that on slower sections at least, it can be seen to deviate more from the position of the centre of the line of travel. That is central to the 'maths' answer.

An interesting point I will raise for anyone interested enough either to work it out, or look up: Did you realise it is (theoretically) possible to even determine the distance between the wheels of the bike that made the tracks as well as the direction of travel? That could theoretically allow differentiation between two suspect bicycles. I have looked at a lot of bicycle tracks in the park, and I have some doubts about its application in the real world, but the maths is sound. perhaps you know otherwise, in which case, please share.

Here is a link to one of the articles that prompted the post:

http://www.math.ucsd.edu/~ebender/87/bicycle.pdf

Thanks for taking part!

All the best,

Firelite.