Are footpegs superior if you don't pedal?

[speedmd]

Is a higher or lower mass on a bike more likely to slide out or what? I don’t believe the ladder analogy is appropriate. U could have all the mass of the bike on the top and I think it will stick to the road just as well in a turn. It’s the same downward force and if anything the higher com will allow a lesser lean angle. Or is the angle the same!! I read different things all over the web and here. And then again the angle in itself doesn’t seem to decide if the bike will stick.

Let’s assume rider and bike are fixed together and no rider movement possible to keep it simple.
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Your getting back to "angle" vs mass or mass distribution again. You will need to prove that to yourself most likely. The faster you go, the more angle and higher centrifugal force for a given turn radius.

The ladder shows a uniform weight distribution at the maximum angle for the available traction to maintain stability. adding weight or even redistributing it to the lower section would make it more stable as he put it. From what I can gather, The dynamic of how a bike slips out (And how well one can maintain-control the slide), gets into moments of inertia and angular velocities and the math gets much more difficult to follow. In my experience, Some bike setups are just way better at sliding. If you have had some time practicing this (flat track or skid pad practice) on various dirt bikes you may have some feel for what control some have more of than others at it. Just so happens, that all the examples of ones that have been developed to be great at it that I can find, are not top heavy. So far all the Math I find justifies it also.

 

[Hummina Shadeeba]

The faster you go, the more angle and higher centrifugal force for a given turn radius.

That’s simple enough but how does a higher center of mass effect grip if at all? The ladder vid doesn’t seem analogous and I think the center of mass doesn’t have an effect on grip (unless mass is so low as to require some lean angle that’s too much for the tire shape). That’s what I’m believing but hoping someone can tell all

 

[Chalo]

The faster you go, the more angle and higher centrifugal force for a given turn radius.

That’s simple enough but how does a higher center of mass effect grip if at all?

By itself? It doesn't.

By weighting the outside peg or pedal in a turn, you can add a kind of suspension action that improves grip, though. The wider and lower your pegs or pedals are, the more you can use this effect.

 

[Hummina Shadeeba]

So how does the ladder analogy relate if at all?

 

[Chalo]

So how does the ladder analogy relate if at all?

I think the ladder analogy is bad, because it implies a static force from the wall that you can only resolve as a centripetal force on a bike. Confusing and not helpful.

 

[speedmd]

So how does the ladder analogy relate if at all?

I think the ladder analogy is bad, because it implies a static force from the wall that you can only resolve as a centripetal force on a bike. Confusing and not helpful.

Honestly, I am glad that it is somewhat confusing. That means your paying attention. He talks about how difficult the topics in this section of 801 are for most to gain a true understanding of. Does not help that we missed the previous half dozen or so lectures and the math gets a bit overwhelming for most of us. Don't let the simplistic experiments he brings to his brilliant lectures have you miss the much deeper understanding he is attempting to teach with them. He does this often from the little bit of them I have tried to stay with and fully understand.

He starts the lecture with the two equations needed for equilibrium. What is at work here, I believe is the second one, the torque equation side is the one he is attempting to get ones head around.

 

[Hummina Shadeeba]

why dont they use bigger wheels in moto gp for traction?

 

[speedmd]

The faster you go, the more angle and higher centrifugal force for a given turn radius.

That’s simple enough but how does a higher center of mass effect grip if at all?

By itself? It doesn't.

Examples? Proof? I keep looking for them and can not find any. On a bike, it is clearly of interest how it handles skids and slick surfaces in a more reliable -manageable manner. For me, its A key measure in assessing "stability" (as in), "not crashing" to the deck.

By weighting the outside peg or pedal in a turn, you can add a kind of suspension action that improves grip, though. The wider and lower your pegs or pedals are, the more you can use this effect.

Good point on the softer loading of the added flex. Much like softer sway bars will allow cars from breaking traction as suddenly. That and the lower loading point is a big improvement to skid control IMO.

Don't believe your lying eyes?
Take a yard stick, and tape you pocket knife near one end and stand it against the wall as in the ladder example. Buff out each end to match. On a smooth well rubbed off (wax if need be) floor, Slowly move the bottom out away from the wall. Do this with the weighted side up and the weighted side down, and compare the points of slip - angles.

 

[Chalo]

The faster you go, the more angle and higher centrifugal force for a given turn radius.

That’s simple enough but how does a higher center of mass effect grip if at all?

By itself? It doesn't.

Examples? Proof? I keep looking for them and can not find any.

For grip, you have a contact patch (with its coefficient of friction) and a force vector to that contact patch. Explain to me what could possibly change the tire's adhesion if the magnitude and direction of the force are both the same, and only the distance to center of mass changes.

Now, swinging through a range of lean angles and turn radii gets very different depending on the distance between CoM and contact patch, because both rotational moment and contact patch traverse across the ground increase in proportion to CoM height. But there's an optimal range for whatever application (speed, lane width, turn radius, etc.) Both too short and too tall create problems. For low CoM it's instability (tipping over faster than steering reaction time), and for high CoM it's slow roll rate, increased use of lane width, and running out of control authority due to one or another of these factors.

 

[speedmd]

For grip, you have a contact patch (with its coefficient of friction) and a force vector to that contact patch. Explain to me what could possibly change the tire's adhesion if the magnitude and direction of the force are both the same, and only the distance to center of mass changes

Yet the angle vs hi center of mass of the ladder or stick examples yield reasonably proof in significant static balance- slip difference. You can also put sections of scrap inner tube over the stick ends to better represent tires and let us know what you get. That certainly should allow more lean before slip.

Certainly not proof of what is driving the dynamic side of the analysis as to why one setup can drive the tires into controlled slide and others tend to go out from under you. MI are very different in the one side weighted stick example. That example would eliminate the adding of weight as another variable.

The torque vector locations also very different. May need to crack down and attempt to put some numbers to it. Professors example shows that d (distance of the added loading from the bottom end) is less than or equal to L/2 to improve grip. That is with a uniform mass distribution of the ladder. Easy to calc the MI. Back to school. Not so simple.

M/2 x cot of angle is given as frictional force(in his terms, force toward slipping out). This would be consistent with more lean making more force. Moving the mass center further up from the center (M/2 as simplified in his math) would increase the force as the mass center is no longer at mid point but further up the ladder. Moving mass center closer to the contact patch would reduce it. So far, that is how I am seeing it.

https://youtu.be/0NegJkO_ZM4?t=1109

 

[speedmd]

It is looking more clear to me that pedals would add a significant advantage in range of rider motion -loading even if you do not use them to power the bike much if at all. It would require that you put the correct one in place and mostly load one leg, but still of some significant advantage. Pedals rotating on their axles also a significant motion improvement over a somewhat more flat footed limitations of a static peg. Pegs will certainly be easier to find blindly and either foot can load one independently and will not wiggle around as does a crank set with only one foot on board and off saddle a bit.

 

[speedmd]

Anyone catching the DAKAR. Interesting watching these guys fly along standing tall on the pegs intermittently while flying along in some extremely varied terrain. Higher and further back is where I see them reaching for when things get a bit squirrely. The 450-500 class is smoking it.

 

[calab]

I watch a little of it and its interesting to watch the expensive rigs fly over the bumps with the suspension bouncing and the vehicle body moving very little but thats what they paid for now go watch the bums in their cheap vws and jeeps doing the race if there is such a class for dakar like there is in the baja.

Anyone catching the DAKAR. Interesting watching these guys fly along standing tall on the pegs intermittently while flying along in some extremely varied terrain. Higher and further back is where I see them reaching for when things get a bit squirrely. The 450-500 class is smoking it.

 

[speedmd]

I watch a little of it and its interesting to watch the expensive rigs fly over the bumps with the suspension bouncing and the vehicle body moving very little but thats what they paid for now go watch the bums in their cheap vws and jeeps doing the race if there is such a class for dakar like there is in the baja.

Anyone catching the DAKAR. Interesting watching these guys fly along standing tall on the pegs intermittently while flying along in some extremely varied terrain. Higher and further back is where I see them reaching for when things get a bit squirrely. The 450-500 class is smoking it.

The factory 4 wheel teams are insane! Audi ETRON! WOW Even the classic classes would require a huge budget to finish this, and a whole lot of luck. Lots of privateers' in the moto classes that get very little coverage. Some of the pro's are showing some incredible air skills at speed when miss judging the bigger whoops.

 

[calab]

The highlights from all the classes will be fun to watch from the big semis to the quads and brave motorcyclists crushing the bumps to the blooper reel. The lowly peasant class of racers is still a pretty penny to enter and show up but then its crossed off the bucket list.

The factory 4 wheel teams are insane! Audi ETRON! WOW Even the classic classes would require a huge budget to finish this, and a whole lot of luck. Lots of privateers' in the moto classes that get very little coverage. Some of the pro's are showing some incredible air skills at speed when miss judging the bigger whoops.

 

[speedmd]

Interesting development in fuel tanks. Many have been extended to lower and more centralize bike mass. Pictured is one that looks like what many are using now.

 

[ebike4healthandfitness]

Excellent low center of mass handling qualities:

[youtube]5UBWTshFEIg[/youtube]

This one drives much much better:

https://youtu.be/W_RVHDaA3X0

(Sweet Launch from a stop at 1:07 into the video)

 

[Hummina Shadeeba]

I don’t see how this recumbent is going to handle much better. They could move the weight higher but I still see it analogous to balancing a pencil on ur palm vs balancing a longer stick on ur palm.

How does center of mass height effect racetrack speed?

 

[speedmd]

As far as pegs and pedal placement for control goes, this is a great example of positioning them in the worst possible location. Rider is also in a "inverted turtle" position. :lol:

This whole setup should be relegated to three wheels minimum. Reminds me of riding a tandem with a out of sync larger rider in the rear cockpit.

 

[Hummina Shadeeba]

9:30 he says less lean angle needed for higher center of gravity. he has a video showing what seems to show it. is it true?