Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Physics of Staying Alive and Healthy

Discussion in 'General Motorcycling Discussion' at netrider.net.au started by Bravus, Feb 25, 2016.

  1. I guess I was just thinking about the extent to which some intuitive understanding of the physics of motion is helpful in riding.

    Obviously just understanding velocity, distance and time is helpful in leaving space: you don't tailgate a metre off the back of a car at 100 km/h if you understand that that gives you 0.036 s to react and even MotoGP riders take something like 3 times that...



    But things like relative speed: if it's a choice between a head-on and getting off the road even if it means hitting roadside furniture, there are no great outcomes, but the one with the lower relative velocity is the better one.

    I'm sure there are plenty of other examples people can think of. It's not rocket surgery, but the way many people ride suggests to me they're not thinking this way.

    (potentially interesting side discussion of physics over law-abiding, but if that takes off this should be shifted to the relevant forum)
     
     Top
  2. It would be nice if somebody would publish average stopping distances ( with Standard deviations and bike ranges - cruiser, tourer, supersport) ) from 40,60,80,100, 110 ( plus 120, 140, 160 for those in the NT). Also what would be the minimum turning radius at these speeds assuming a 45 degree lean and photo examples of such corners. I have been on a few rides where people have sat up in a corner and thought they can stop within perhaps 6 to 8 metres of roadway before the edge/trees. I often wonder whether the decision to sit up and brake has been made without considering whether they could in fact make the corner with more lean. Other than experience there is no published info (the physics) to consider before making what could be a fateful decision.
     
     Top
  3. Hey Bravus. Get bored inside the helmet today.
     
     Top
  4. As a guess I would say that there would be a lot of variables. My Guzzi weighs a bucket load more than my old bike but pulls up so much more shorter and more stable.
     
     Top
  5. Go out the back blocks or find a quiet street and practice quick braking.
    Every bike is different.
    My cruiser(m109r) is very different to my sports tourer bike (cbr1100xx) to my dirt bike.
    You have to go out and establish especially if you have just purchased a new bike, to get the feel of what it can do.
    Especially if it slides under braking, I find I can slide my cruiser in braking quite nicely but when it comes the cbr I am not all satisfied with it's stopping power so I tend give myself alot of breathing room.
     
     Top
  6. ...and driving.

    Many years ago, when my wife and I were fairly new in Oz, I was driving a car across the Sydney Harbour Bridge.

    I was headed North, and in the furthest right lane.

    Another car, same direction, one lane to the left of me, suddenly wanted to be in the bit of road I occupied.

    It veered towards me, and it's driver, and my wife, were VERY surprised when I swerved hard towards the other car.

    The logic was, if I continued, and got hit going straight on, chances were high, I'd be the one facing the oncoming traffic, but, if I built up enough force going to the left, I'd have a chance of staying in my lane after any impact.

    As it turns out the other car that wanted my bit of road, lost interest and went away.
     
     Top
    • Like Like x 2
  7. Sshhh - don't tell, but I'm a physics educator shilling for business. ;)
     
     Top
  8. To be perfectly honest, any published info is more likely to be ignored, forgotten or mis-understood. :(

    As a sweeping generalisation,..... never give up on a corner.

    If you throw your bike into a corner and suddenly think:-"Oh Shit, I am going too fast." do you really thing..."Ah, yes, but I have 15 degrees more lean available." ?

    If you keep on trying for the corner, and get it wrong, odds are you'll have a lesser accident than if you sit the thing up and try to stop in about 10 inches.
     
     Top
    • Like Like x 2
    • Agree Agree x 2
  9. Yep: this is one of those instances in which our instincts tell us exactly the wrong thing. Just repeating "trust the bike, the tyres and yourself and lean harder" is itself helpful advice in these situations.

    Of course, remembering "slow in, fast out" a few seconds earlier is even better advice. ;)
     
     Top
    • Agree Agree x 1
  10. And as has been said before, KNOWING it doesn't mean you'll DO it when the time comes.

    There's a lot to be said for playing out scenarios in your head as you ride along. I think that - just like practicing cornering and braking builds 'muscle memory' -practicing critical decision-making helps make it easier to make a good split second decision when you really need to.
     
     Top
    • Agree Agree x 3
  11. BTW, I dunno if that came from physics at school, or a mis-spent youth playing snooker.
     
     Top
  12. Certainly does help. While re-learning ( after a long break from riding) just knowing I had more lean left ( size of chicken strips) has saved me more than once by giving me the confidence to override the typical "learner" SR to brake and instead dig deeper into a corner way more than what felt comfortable at the time.

    May be forgotten but if you have not read or considered options you have NO options just SR which tend to be wrong. M

    Seems like you reactions were based on something that you had read, been taught or experienced in the past and NOT forgotten.
     
     Top
  13. Hi there, Returned.

    Have you just done a CSS course, or read Keith Code's stuff?

    Now that's a better measure of available lean than reading some table published by some unnamed person on unknown road surface on unknown tyres, on a bike that may, or may not, be set up like the one you are riding......

    I ask about the CSS, 'cos that is the best way that I can think of for someone to establish their, and their bike's, tyres', setup, etc. cornering ability in a reasonably safe environment.

    But, I repeat, as a cheap short-cut.... "Never give up on a corner."

    The basic idea is that, if you really have over cooked your speed, but you continue trying to turn, the bike will probably, once past its limit.... low side.

    So it, and you, are now sliding...... but, the bike will (hopefully) hit whatever solid thing there is to hit, before you get there......

    This is much better than you hitting solid object, then bike hitting you.

    Most of the time, for most riders, the bike will actually turn better than they think it can.
     
     Top
    • Agree Agree x 4
  14. Yep, before I got back into riding I read a lot which included Keith's stuff and the physics of motorcycling ( heavy reading ). I also practice what I read. My original post was aimed trying to help others ( mainly learners) realise the folly of trying to stop a bike from 60kph+ in 6 to 8 metres. If you know you are not going to stop then your SR should be the only other logical action.
     
     Top
  15. I guess you have never used the freeway in Perth then?
     
     Top
    • Agree Agree x 2
  16. See plenty of people doing it here on the M1 between the Gold Coast and Brisbane.

    I mean, let those who ride decide, it's their choice: I just know enough physics to know they're living more dangerously than necessary. You're still doing the same speed of you're doing it a couple of car-lengths back and defending your space.

    It's like investment: risk v reward. But there's no real reward that compensates for that risk.
     
     Top
  17. Hi Bravus,

    Here's a question for you. When I first did my compulsory rider training, back in the early 90s, one of the instructors told us an anecdote about riding fast on a country road on a cold morning. Since it was a pretty chilly, he put track suit pants on under his leathers. Long story short he dropped the bike crossing a bridge at speed, (bridges stay frosty longer, so there is more than one lesson in his cautionary tale), and the resulting slide built up enough heat to melt the synthetic fabric into his leg resulting in skin grafts. His message was; "If you wear synthetics next to your skin when you ride, make sure you like the colour as it could be with you for a longer than you expect!" He had the scars to support his point too.

    I have never heard anybody propose this as an issue since. It did make perfect sense, low melting point fabric and so on and I have seen images of thermal burns through leathers after offs on track at very high speed. However, since there is now a huge array of synthetic riding gear around now, I kind of suspect that it's either a somewhat specialised problem relating to very high speed, (as in race track speeds) or it's just plain wrong. Any thoughts?
     
     Top
  18. There are two main kinds of polymers, thermosetting and thermoplastic. The former set hard, like an egg, when heated. The latter are more like chocolate - they can be repeatedly melted. My guess is that trackie dacks are thermoplastic and decent quality synthetic life gear is thermosetting.
     
     Top
  19. I like where you are going with that :) but Cordura is Nylon which will melt, as will Polyester based fabrics..
    but they'll melt at >200deg.. so that's pretty hot

    polypropylene should melt at much lower temp than those two(?).. so that means cheap thermals are not ideal next to skin..

    some info on different textiles used in MC wear Materials Guide Fabrics
     
     Top
    • Like Like x 1
    • Informative Informative x 1
  20. Thanks Bravus,

    no the synthetic fabrics with the exception of things like kevlar and it's cousins are pretty much all thermoplastics. I think thermoset underwear might be a bit uncomfortable. As oldcorollas mentioned, the melting points do differ markedly. They do use polypropylene for thermals quite a lot and that does have a low melting point. I used to see polypropylene climbing ropes used for canyoning because they float, but if you're abseiling with them then you want the damn things wet or you go very slowly to keep the heat down because it melts at 80ÂșC.

    I was wondering whether there might be a clever formula for calculating the heat generated in a slide, where it would be possible to work out how far and how fast you would have to slide to start melting your undies but I'd be just as happy to settle for some anecdotal evidence if there are folk on here who might have some direct experience, either of sliding with thermals on and not having it melt or vice versa. My suspicion is that the guy was telling it as it happened, but that he may have been going a hell of a lot faster than I ever will on a public road.
     
     Top
    • Like Like x 1
    • Informative Informative x 1