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Post by the light works on Nov 3, 2013 14:27:24 GMT
I learned something yesterday. and this is more a science project than a myth, but I thought it might be worth sharing, and it might be suitably telegenic.
ever since traffic collision analysis was invented, analysts have used skid marks as evidence in investigating the crashes; but that all changed when the proliferation of ABS systems made skid marks all but disappear. However, I went to a minor accident yesterday, and was completely surprised to see a set of skid marks on the wet pavement. on closer investigation, I saw that the skid marks were visible, because they were where the pavement was left dry. (US meaning of pavement, not the UK interpretation as pedestrian walkway)
now, since we cleared the lane to get traffic moving, the dry marks went away pretty promptly; but it left me wondering if the marks were caused by the braking stresses heating up the tires and the asphalt; which evaporated the water; rather than just scrubbing the water off the surface. if that was the case, then it should be possible to take a picture of an accident scene with a thermal imaging camera, and have images showing when and how hard people were braking.
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Post by User Unavailable on Nov 4, 2013 5:18:45 GMT
I've seen traffic pass by on wet roads and leave a dry strip where the tire passes. I reckon this is simply where the tire tread moves the water out of its way, the way the tread is supposed to.
Heck, you can see it as you follow a car down the road in the rain. A nice set of tracks to folllow, from the traffic in front of you, depending on how hard it is raining.
So a tire track on damp pavement, should be drier than surrounding pavement, because the tire tread shed that wTer out if it track.
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Googling skidmark analysis of ABS breaks, yielded several discussions on the topic, especially on ABS equipped vehicles.
ABS present skids differently than locked breaks for sure.
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Post by the light works on Nov 4, 2013 14:35:02 GMT
I've seen traffic pass by on wet roads and leave a dry strip where the tire passes. I reckon this is simply where the tire tread moves the water out of its way, the way the tread is supposed to. Heck, you can see it as you follow a car down the road in the rain. A nice set of tracks to folllow, from the traffic in front of you, depending on how hard it is raining. So a tire track on damp pavement, should be drier than surrounding pavement, because the tire tread shed that wTer out if it track. --------------- Googling skidmark analysis of ABS breaks, yielded several discussions on the topic, especially on ABS equipped vehicles. ABS present skids differently than locked breaks for sure. I've seen traffic leave a strip without standing water; which fills back in rather quickly. but this was a set of marks that was dry for at least 5 minutes before I got to the scene. definitely different from the marks from regular traffic considering we ran our heavy rescue across them without leaving matching marks.
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Post by User Unavailable on Nov 4, 2013 15:49:07 GMT
I've seen traffic pass by on wet roads and leave a dry strip where the tire passes. I reckon this is simply where the tire tread moves the water out of its way, the way the tread is supposed to. Heck, you can see it as you follow a car down the road in the rain. A nice set of tracks to folllow, from the traffic in front of you, depending on how hard it is raining. So a tire track on damp pavement, should be drier than surrounding pavement, because the tire tread shed that wTer out if it track. --------------- Googling skidmark analysis of ABS breaks, yielded several discussions on the topic, especially on ABS equipped vehicles. ABS present skids differently than locked breaks for sure. I've seen traffic leave a strip without standing water; which fills back in rather quickly. but this was a set of marks that was dry for at least 5 minutes before I got to the scene. definitely different from the marks from regular traffic considering we ran our heavy rescue across them without leaving matching marks. Could be as simple as the difference in the style of tread between the wrecked vehicle and your rescue rig, combined with the car being under heavy breaking, nose down, more weight distributed to the front tires, increasing contact friction.
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Post by the light works on Nov 4, 2013 15:56:51 GMT
I've seen traffic leave a strip without standing water; which fills back in rather quickly. but this was a set of marks that was dry for at least 5 minutes before I got to the scene. definitely different from the marks from regular traffic considering we ran our heavy rescue across them without leaving matching marks. Could be as simple as the difference in the style of tread between the wrecked vehicle and your rescue rig, combined with the car being under heavy breaking, nose down, more weight distributed to the front tires, increasing contact friction. mmm... somehow I think if it was just pressure loading, there's no way the car could exert more pressure than the heavy rescue. - but if that were the case, you'd think we would see similar marks from the Bronto; which has such a high weight per tire that it is not legal in some states. no, this was definitely something different from just the tires pressing the water off the road in passing. it was definitely a result of the hard braking. the question in my mind is WHAT made the difference.
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Post by silverdragon on Nov 6, 2013 9:36:17 GMT
Yes and no. Mostly under hard braking you have water displaced which 'dries' the surface. How much drier it gets depends on the construction of that surface, tarmac, concrete, whatever.... And how much rain. You would have some heat transfer from tyre to ground, if you watch police video of helicopter chasing moving vehicle with a thermal camera, you can see the tracks left by the car, and they CAN tell by the intensity of the heat if the car is braking hard or not.... But it doesnt last long. Those heat trails even out pretty quickly.... I would estimate mere seconds before much of the heat has gone, whats left may not be enough to be used as evidence.... Water, dependant on if it is actually raining "now", how much rain has fallen, the tyre tracks will either stay, get filled with fresh rain, get filled with standing water flowing over the road (Hopefully in the direction of nearest drain) or dry up. To many variables to say it could be used in any other way than to show a vehicle has passed that way "Recently".... Weight. During hard braking, much of the weight of the vehicle is pressed through the front tyres. This "Squashes" them down on the road, more tread footprint, more grip, which is handy at that time, as your trying to stop?.... The tyres deform more during braking giving a greater amount of tread on the road which will displace more water. You may find therefore that it was the FRONT tyres of that vehicle that created the greater difference here.
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Post by the light works on Nov 6, 2013 15:56:14 GMT
Yes and no. Mostly under hard braking you have water displaced which 'dries' the surface. How much drier it gets depends on the construction of that surface, tarmac, concrete, whatever.... And how much rain. You would have some heat transfer from tyre to ground, if you watch police video of helicopter chasing moving vehicle with a thermal camera, you can see the tracks left by the car, and they CAN tell by the intensity of the heat if the car is braking hard or not.... But it doesnt last long. Those heat trails even out pretty quickly.... I would estimate mere seconds before much of the heat has gone, whats left may not be enough to be used as evidence.... Water, dependant on if it is actually raining "now", how much rain has fallen, the tyre tracks will either stay, get filled with fresh rain, get filled with standing water flowing over the road (Hopefully in the direction of nearest drain) or dry up. To many variables to say it could be used in any other way than to show a vehicle has passed that way "Recently".... Weight. During hard braking, much of the weight of the vehicle is pressed through the front tyres. This "Squashes" them down on the road, more tread footprint, more grip, which is handy at that time, as your trying to stop?.... The tyres deform more during braking giving a greater amount of tread on the road which will displace more water. You may find therefore that it was the FRONT tyres of that vehicle that created the greater difference here. but once again, it can't be ONLY weight as the car simply didn't have THAT much weight to transfer. (we used 2 men to push it off the road with a man sitting in it to steer) and there had to be something that caused the tracks to remain dry for as long as they did. (I didn't think to look if they were obscured where we ran the heavy rescue over them)any by dry, I mean dry, not just less wet.
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Post by Cybermortis on Nov 6, 2013 21:31:31 GMT
Could it be oils or something similar being pushed out of the threads under the pressure, or being pulled out of the road surface, when the car brakes hard? Oils would push the water to the sides, which might allow the tread patten to remain visible for longer.
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Post by the light works on Nov 6, 2013 21:39:53 GMT
Could it be oils or something similar being pushed out of the threads under the pressure, or being pulled out of the road surface, when the car brakes hard? Oils would push the water to the sides, which might allow the tread patten to remain visible for longer. I considered the transfer of rubber, but most tires are not naturally water repellent. of course, the transfer of rubber would also involve heat from the friction involved - which takes us back to the heating question.
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Post by Cybermortis on Nov 6, 2013 22:51:01 GMT
No, I mean oils in the rubber, oil/diesel which has been collected between the treads as the car has been driving and which is forced out as the car comes to a sudden stop or oils that are pulled out of the road surface due to suction.
It wouldn't take much to cause an area where water didn't collect as quickly, revealing the tread pattern. The oils would eventually wash away or sink into the road.
*Edit*
Oils forced out of the tire or treads during heavy braking might get pushed into the roads surface, preventing them from being washed away instantly.
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Post by the light works on Nov 7, 2013 3:39:19 GMT
No, I mean oils in the rubber, oil/diesel which has been collected between the treads as the car has been driving and which is forced out as the car comes to a sudden stop or oils that are pulled out of the road surface due to suction. It wouldn't take much to cause an area where water didn't collect as quickly, revealing the tread pattern. The oils would eventually wash away or sink into the road. *Edit* Oils forced out of the tire or treads during heavy braking might get pushed into the roads surface, preventing them from being washed away instantly. It is an interesting theory. I wonder how we would test for it. addendum: it would have to be just enough to resist the water without being so much as to create a visible oil pattern
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Post by silverdragon on Nov 7, 2013 7:47:01 GMT
But all the weight it DID have was transferred to where it was needed most... over the wheels doing all the braking....
Only one way to test this. On a wet road, one pass, no brakes, one pass HEAVY brakes.
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Post by Cybermortis on Nov 7, 2013 12:59:02 GMT
No, I mean oils in the rubber, oil/diesel which has been collected between the treads as the car has been driving and which is forced out as the car comes to a sudden stop or oils that are pulled out of the road surface due to suction. It wouldn't take much to cause an area where water didn't collect as quickly, revealing the tread pattern. The oils would eventually wash away or sink into the road. *Edit* Oils forced out of the tire or treads during heavy braking might get pushed into the roads surface, preventing them from being washed away instantly. It is an interesting theory. I wonder how we would test for it. addendum: it would have to be just enough to resist the water without being so much as to create a visible oil pattern *Scratches head* Slam a rubber stamp down on a small section of wetted road surface?
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Post by the light works on Nov 7, 2013 15:13:09 GMT
But all the weight it DID have was transferred to where it was needed most... over the wheels doing all the braking.... Only one way to test this. On a wet road, one pass, no brakes, one pass HEAVY brakes. I've already SEEN that. the question is HOW and WHY.
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Post by Cybermortis on Nov 7, 2013 15:17:47 GMT
Might be a daft question, or one that you can't answer, but how new were the tires?
Don't new tires have some sort of coating to protect them during transport and storage? And if so is it possible that it is this coating that is rubbing off on the road rather than the rubber under it?
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Post by the light works on Nov 7, 2013 15:25:01 GMT
It is an interesting theory. I wonder how we would test for it. addendum: it would have to be just enough to resist the water without being so much as to create a visible oil pattern *Scratches head* Slam a rubber stamp down on a small section of wetted road surface? make a rig. the great advantage is that in California, tires get a LOT more chance to absorb oils from the roadway. you have a strip of asphalt, and a tire. the rig applies pressure, motion, and braking force. that way you can isolate variables. also, do chemical analysis of brand new tires VS used tires. if you can get the mark; then you can spray water on it under magnification to see how the water reacts.
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Post by the light works on Nov 7, 2013 15:25:59 GMT
Might be a daft question, or one that you can't answer, but how new were the tires? Don't new tires have some sort of coating to protect them during transport and storage? And if so is it possible that it is this coating that is rubbing off on the road rather than the rubber under it? not that new. as in most likely still factory tires on a car that was not brand new.
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Post by silverdragon on Nov 8, 2013 8:55:15 GMT
Absolutely not..... Ok, here is the way it was explained to me, you can not put ANY coating at all on tyres just in case someone "Forgets" and doesnt remove that said coating when fitting it. The tyre MUST be ready to use immediately. ...I think there may actually be laws on how they are manufactured and fitted that cover that?....
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Post by the light works on Nov 8, 2013 15:26:09 GMT
Absolutely not..... Ok, here is the way it was explained to me, you can not put ANY coating at all on tyres just in case someone "Forgets" and doesnt remove that said coating when fitting it. The tyre MUST be ready to use immediately. ...I think there may actually be laws on how they are manufactured and fitted that cover that?.... tires with colored sidewalls often have a protective coating over the sidewall to protect it from discoloration. it appears to be some sort of water soluble paint; because it washes off with a quick scrub - or the next time the person drives in the wet, if the installer doesn't bother with it (like if they are installed with the whitewall to the inside)
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Post by silverdragon on Nov 11, 2013 9:37:49 GMT
Tyres in the UK should come with 'chalk marks', as in a coloured band of something that gets scrubbed off quite quickly, (Couple of miles)on the tread. This is kind of hard to replicate, its almost a sort of "Watermark", and its proof that the tyre has not been on any other vehicle. I think its made with some form of "rubber paint" when the tyre is formed in the mould?...
Anyway, thats the only thing allowed on the tyre bit that goes on the ground.
Now some tyres are "Shrink-wrapped", as in delivered in Plastic, to protect them from damage whilst in transport.... Thems the expensive "Showroom" ones.
But no tyre is allowed to have any coating that may be left on if the tyre hits the road.... There are strict guidelines even to using "Tyre black", that shoe-polish type stuff they use in showrooms to make the tyres shiny?... You are not allowed to put that on the working surface of the tyre.
Even price and information stickers that may be put on the tyre, the first thing you read should be "REMOVE BEFORE USE".
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