Do Laws of Physics control absolute top speed of riding a MX/SX track?

Of course physics limits absolute top speed around a track, but we are nowhere near that yet. The rider is still the limiting factor and always will be. That's why our sport is so much different than most.

Yes, 299,792,458 m/s (6.706e+8 mph) is the limit.

Well played sir.

Maybe it's the engineering element of the laws of physics that limits, and the human engineering inability to suss out and control all variables that go into a motorcycle with forces across three axes, a power plant confounding that, and erratic terrain.

But we have made some great incremental gains over the years!!

KTM's pds system in Supercross and Stew on the initial reverse engine Yamaha are extreme examples, as is Marquez's struggles the last few years on Honda in MotoGP.  But I think a lot of top rider crashes simply are the rider's talent or  courage exceeding the limits of the engineering team.  And when than team makes some thing better, that improvement may chase or reveal another flaw or imbalance.  

I think that is one of the reasons you cannot say riders from a prior era are not as good as riders going faster now.  The demands are different, but the talent and courage that make top riders as good as they are does not really change.  

I think we are closer to that limit of top speed possible than ever before and have gotten closer every year. All the bikes are good all the riders are VERY fit it pretty much has come down to technique both riding wise and line picking and processing speed/eye speed. The last variable is how much guys are willing to risk it so "sending it" more or less. 

The laws of physics determine EVERYTHING.

That said, the squishy part hanging onto the motorcycle is the limiting factor in this case. Someone could probably go faster around a track if he could withstand greater g-outs, more braking forces, etc. 

Of course they do at some point, but in Mx/Sx I think it still comes down to mostly the rider. Its why we have kenny on a bike thats way behind in RND than the others who is still arguably one of fastest in the world. If it was mostly physics holding everyone back the team with the best engineering would be dominant consistently. Like in F1 for example 

After watching some of the freestyle stuff they do - Pastrana for example I think those guys defy the laws of physics daily!

Laws of physics absolutely are the limit, but the difficult thing is that those limits are variable. I think it comes down to at least these three factors that limit rider's ability to ride on the absolute limit of physics.

1. Variability in terrain: Take for example a rut through a corner. The absolute limit of how much force the rider can exert on that rut is never consistent from lap to lap. So even if a rider 

2. Lag in the feedback loop: When a physical limit is exceeded (like the front tire starts losing traction and washing out), the reaction is the tire will decompress then the suspension will start to rebound and finally the handlebar will start to move away from the rider, but this whole reaction is dampened so for a few fractions of a second it will feel just like a normal bump to the rider. The rider cannot know immediately that he has lost traction. By the time the rider feels the front tire start to wash out it might be too late to react. Even then, if the rider does react in time, there's a lag in his input back to the bike and the ground. Let's say the rider gets the signal that his front tire is starting to wash out and the way to save it is to get off the front brake. Even if that rider is able to react immediately, there's a lag in the reaction between releasing the brake lever, the pressure in the brake line releasing pressure, the return spring pushing the pads back apart, etc. Same thing if the reaction is to apply more throttle. There's always a lag in the signal input and in the rider's reaction.  

3. Human Reaction Time: things on a motocross track happen in milliseconds. The riders are so used to their bikes and the environment that they are reacting to inputs subconsciously, which allows them to react in about half the time of conscious reactions. Even so, the human body has limits to how quickly it can move. Some reactions can be quick, like releasing the brake, because they only require the finger to move. But other reactions like shifting your weight around to stay balance require legs, core and arms all to fire and move exactly the right amount. 

Would love to see a Kawasaki Science of Moto dive deeper into this and put some measurement behind it. 

Someone get in here and start a reply with "as an engineer" already!

The laws of physics determine everything. They're the reason riders don't "fly" the bike from the pits to the start gate because, well, gravity. They have to ride it there. That's a bit of a ridiculous example, but the same holds true everywhere. The force a rider/bike experiences around a corner limits their speed. Or it could be the available traction that limits their speed (related to the force). Both are related to the laws of physics. But there's more to it all:

The rider's skill is in "competition" with the laws of physics. Imagine an 80 foot supercross triple, but with a REALLY steep landing. Skill comes into play as that's an easily jumped obstacle, but a difficult one to time and land correctly. Land perfect and all is smooth. Over jump or case it a little and the laws of physics bite hard. Similar analogies can be made for cornering.

Engineering is applying the best compromise in making the bike hold up to the laws of physics and allowing the rider's skill to do it's work. For example, you could engineer a bike to take the hits of that triple mentioned above when the rider's skill falls short, but it would be heavy and terrible performing in the corners. So instead, the design is compromised to do both well. The engineer's job is to manage that compromise and optimize the design to be the best it can be and get the rider around the track as fast as possible. Sometimes the rider's skill exceeds (of falls short of, e.g. a crash) the design limits or sometimes the engineer screws up, and parts break. If the engineer makes the wrong compromise or the mechanics tune the bike with the wrong compromise, then the bike is slower around the track than it could be. This is often the case in mud races as they're always trying to find the best compromise. If the weather shifts, then the compromise chosen may not be the best and another rider/team with a better compromise will do better. 

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Have a one-on-one discussion with Jet and his synopsis on the LAWrence of physics at absolute top speed.    

I can't let it slide. What part of the suzuki is behind on R/D? Is it the frame material, maybe the round wheels, or the water cooled engine?

I would venture to say that the laws of physics pertaining to the difference in R&D between manufacturers is fairly small. It's not like Ken is riding am RM85 against 450s. It's entirely possible that a machine could be the best, even if it was developed in 2018. (I'm not making this argument, but it's possible.)
Just because something is newer, doesn't necessarily mean it's better. 

Yes, but I think you're asking a much more nuanced question. If absolute top speed means a bike's maxed out straight line speed held wide open around an entire track (turns and all) then yes, the laws of physics would dictate that a bowl turn would be impossible for the rider and the machine to endure. If you factor in jumps (think supercross-tripple) at top speed, that rider would likely over jump the course entirely, after all physics will tell you that your breaks don't work well while soaring over the track markers into the bleachers. 

IF by absolute speed of riding what you really mean is fastest way of navigating a track (making turns, breaking where needed, limiting jump distance to the intended downside, going as fast as you can on straights) then no. Physics do not control absolute speed (at least layman's physics). That is controlled by 1/ mechanics and 2/ human capabilities. The biggest factor is the engine and the tires, engines (even electric engines) do not have zero second 0 to max speed ability, even if they did, to make it matter, your tires would need to have perfect traction, your chain would need to have zero flex, and the rider would need to be strapped to the bike and able to withstand extraordinary g-forces. You would need the same for breaking, perfect traction, zero delay between lever and pad, tires that aren't made of rubber ... the simple fact that we ride on lose dirt, makes maxing out physics nearly impossible. 

With how good and fast the bikes are now a riders balls are the only limiting factor for speed, and I believe their focus and reaction time at that speed determines whether they crash or not for the most part. 

When do we get to quantum uncertainty . . . 

The physics governing the function of my brain matter cause me to absolutely hate the slang: 'suss out'

Physics creates an absolute limit, but the riders can't reach that.  So the limit is riders capabilities.  But a riders ability to get closer to the physical limit is what makes them faster than others. 

Oh, I'm a big Who fan, so suss it, lol. 

I mean since Suzukis are heavy they don’t slide as easy…  Try something lighter.  

Surprised no ones mentioned tires. All the physics including power, suspension and riders ability ultimately boil down to the bike has to stay on the track, and that task is all about the tires gripping the track. You can only go as fast as the tires allow. That seems like the ultimate limiting factor physics wise. At least in my poolman peabrain lol.  Prove me wrong 

Well, as an engineer.

I am a dimensional engineer, but watching a proper guy calculate suspension geometry is an eye opener. 

Setting cars up on a flat patch to get all the corner weights perfect on solid tubes insread of springs , and seeing the difference it makes is something most folk dont grasp.

As for MX, you can only go so fast and scrub so hard, you cant accelerate while you are in the air , so you get to a point where Vmax is determined by how long you can be on the ground for. 

Thats kind of my point, if it was physics holding riders back more than the riders themselves, then a near on 10 year old machine would be way behind. The fact it isn’t with a good rider proves we’ve pretty much got to a point where with the technology available today, the bikes are as good as they can be and its the skill and ultimately the balls of the riders that determine how fast they can go. 

"The last variable is how much guys are willing to risk it so "sending it" more or less"

This is the only variable. If a rider can do it one time, it can be done again. But, we are up against the laws of "talent". The talent that allows the rider to repeat that one successful pass of that obstacle at an extreme speed every time. Presently we call it "sending it", but as the rider's talent gets better it becomes the normal and expected. Yes, the mechanics of how everything the bike does affects the riders ability to go faster, but we are still at a point where the bike can go faster than the rider can control the bike, at a bikes limiting speed.

TM

In fact sometimes "newer" is not as good. A change is made to make one thing better but the unintended consequences are, there is a decrease in performance in another area. Only to be found after all the money has been invested in the change and we have to wait for the next change.

TM

I'm 180 the opposite on this.   The bikes hold them back, and when they send it they now crash harder because the set ups allow them to go faster.  But understanding the variables and calculating all of the forces to make a set up "perfect," especially track to track and with a track changing during the day, is a lot harder to attain than getting a guy to twist it harder.  

The riders are far more talented (or mindless crazy) than the bikes are perfected, and the perfection of bikes is the engineering application of physics.   An important skill for someone as good as a champ contender is to know when to go slower because the bike cannot handle it.

Racing is a chasing game. You're always looking for that something extra. IF it weighs too much, you need to drop weight. But when the weight changes, you need to redo the suspension because the weight behaves differently.... Every time you change one thing, there is another that you can change. Sometimes the change is incremental, sometimes it's monumental. Sometimes many incremental things turn monumental. When you stop making changes, you don't know what could be. So, you just decide "it's good enough".

You don't agree that if an obstacle can be done at what we consider in insane speed a single time, that isn't proof it can be done? I believe we are at a risk/reward point in that the reward is not worth the risk. But in many venues, there's always the "first rider" to attempt an obstacle, showing it can be done and then the other riders decide they have to do it too or they'll lose too much time.

No, what I am saying is that if an obstacle has been done once that doesn't mean that you've identified, controlled, and mastered all of the forces such that you can do it safely time and again.   You might have been lucky when you wrote a check the bike could not cash 8 times out of 10.  

The easiest input to control is how hard you twist the throttle, i.e., the rider.  

Tomac hit that wicked downhill rut section at Thunder Valley multiple times before he crashed in 2015.  The problem wasn't Tomac's willingness to go fast.  Guys at that level stretch frames, break wheels, etc, trying to go faster, and the inability of those parts to stand up is a physics issue embedded in the engineering.