Are footpegs superior if you don't pedal?

[Chalo]

[You still seem to be operating under the impression that the rider is swinging around. He's not. The bicycle is swinging around the rider.

Assuming you have sufficient pavement, that is. What happens riding down a log lengthwise, or a very narrow changing single track?

You don't get to lean in that case, unless it's to fall down. Anyway, you have to countersteer the bike out from under you to change direction, and the only thing you can interact with to do that is the surface.

 

[BalorNG]

[You still seem to be operating under the impression that the rider is swinging around. He's not. The bicycle is swinging around the rider.

Assuming you have sufficient pavement, that is. What happens riding down a log lengthwise, or a very narrow changing single track?

You don't get to lean in that case, unless it's to fall down. Anyway, you have to countersteer the bike out from under you to change direction, and the only thing you can interact with to do that is the surface.

In highly technical terrain (think close to bike trials) and low traction situations, 'body english' IS a major factor. Again, woefully apparent on a highly reclined recumbent. But otherwise the bike is balanced by steering using already mentioned 'inverted pendulum' mechanics.

 

[speedmd]

Balancing - Steering can also be done by hopping either end or both. Don't have to be moving much at all. Been doing that for decades. Obviously easier on the pedal bike.

Looking like we are rounding the basses. On the inverted pendulum side, we can certainly mostly agree. The more static side (bike) is classic case outside the fuel rolling around and the relatively minor lateral and vertical movements the steering induces. The wide tire effect is well documented on how to handle it. Interesting on degrees of freedom the test apparatuses were noted to have. On most that were mentioned, were only a few degrees before the control apparatus limits were exceeded. This may be significant with human control limits even with their ability to change a bit and help balance this all out.

On the dynamic side (rider), they can flex in multiple directions at the foot- ankle, knees, hips, waist, as well as flex the torso in addition to two arms and two legs that can expand- contract. Robot folks are still working this all out and come a long way. We have two pivot points to help balance, one under each leg that also can be torqued and articulated at the foot and joints above. Two legs possibly more like a very wide tire or more like two separate ones. Not sure how to simplify and model this all. Good exercise for certain. This all changes the combined COG as noted earlier.

It is looking much clearer to me at least why the bicycle trials guys all say No Way to clip in shoe cleats. Not using them allows much more foot placement latitude in addition to the easy foot off capabilities. Also helps explain the trend to wider foot pegs in the moto trials circles also. More like a shorter running board. either will allow some significant pivot point changes for them just for starters.

 

[Hummina Shadeeba]

The topic is broad and I think people have been talking about different aspects. Im wondering about traction and hoping someone can confirm: a lower center of gravity requires a greater lean angle but that’s not a detriment in itself as long as the tire is rounder and more so shaped for that lean angle?

 

[donn]

Im wondering about traction and hoping someone can confirm: a lower center of gravity requires a greater lean angle but that’s not a detriment in itself as long as the tire is rounder and more so shaped for that lean angle?

The diagram Chalo posted on page 7 illustrates the relation between center of mass and lean angle. For the simplest case of "lower", there isn't any relationship - lean angle won't be any different than for "higher."

As bicycle and rider are not a fixed, rigid unit, it's possible to assume various conformations, where (as shown) the bicycle may lean less than the rider, for the sake of tire contact. As you go about making the center of mass lower, whatever you do there could also, hypothetically, reduce the extent to which you can displace the center of mass from the bicycle angle, and if so, the bicycle will have to lean more.

 

[Hummina Shadeeba]

“ Bikes with fat tires and low center of mass must lean more than bikes with skinnier tires or higher centers of mass to negotiate the same turn at the same speed.”

https://www.fxsolver.com/blog/2015/06/03/motorcycle-leaning-angle/

I assume with all other things being equal a lower center of gravity will require more angle, but is a bigger angle inherently less grippy?

the bike lean angle is effected by the rider center of gravity too but assuming the same rider center of gravity and a lowered bike center of gravity and same tires...is the greater lean angle more likely to slide out?

 

[Chalo]

“ Bikes with fat tires and low center of mass must lean more than bikes with skinnier tires or higher centers of mass to negotiate the same turn at the same speed.”

https://www.fxsolver.com/blog/2015/06/03/motorcycle-leaning-angle/

I assume with all other things being equal a lower center of gravity will require more angle, but is a bigger angle inherently less grippy?

It's not about having adequate grip, which is assumed in this analysis. The thing about a fat tire is as you lean, it places the contact patch farther off the centerline of the bike, which makes the effective lean angle less than the bike's apparent lean angle.

I think tires are something of a wild card, because changes in their cross-sectional shape seem to change the interaction between lean angle and turn radius. I say "seem to" because I can't tell if the shape actually changes the radius resulting from a given lean angle, or only the tendency of the bike to "fall in" or "stand up" when at that angle. The math that would govern a squishy rubber shape rolling on the ground is way beyond my ability to grasp, so I'm limited to observation.

 

[Hummina Shadeeba]

If two identical bikes have the same geometry, same round tires, same fixed position rider, and same combined weight, but one bike has its center of mass much higher than the other, which is more likely to slide out in a sharp turn? Does the angle effect traction? I’m seems it doesn’t..as long as ur not leaning so far as to hit the ground.

 

[speedmd]

We are solving for angle with the over simplified angle equation that scrubs out length of the inverted pendulum part of the dynamic. Not the whole story here. We also need to solve the kinetic energy side of the dynamic. My Math is a bit rusty on the complex dif.eq's for me to get through it with any confidence. There is a second formula that I so far have not followed through all the way but so far leave in the length. Would be great if someone in the group looked at the lagronge formulas a bit more in depth if they understand it well.

 

[Chalo]

We are solving for angle with the over simplified angle equation that scrubs out length of the inverted pendulum part of the dynamic.

It does not make a difference in turn radius vs lean angle. What is so hard about that for you?

Yes, it has implications (good or bad) for getting to that lean angle. It makes a difference in roll rate. It makes a difference in pavement width needed to maneuver. But inverted pendulum length makes no difference at all in correlating a lean angle to a turn radius.

 

[Hummina Shadeeba]

. But inverted pendulum length makes no difference at all in correlating a lean angle to a turn radius.

Are u saying center of mass location doesn’t effect bike lean angle in a turn?
I’m just trying to find out if it’s true that a lower center of mass is going to result in a greater lean angle and if that results in less traction

 

[donn]

Are u saying center of mass location doesn’t effect bike lean angle in a turn?

Correct! The formula I believe speedmd pointed us to -- θ = arctan ( v-squared / g r ) -- applies regardless of height.

 

[donn]

If you want to do the actual calculation ... If your computer has a Python interpreter for example, put this in a file. Answer for this speed and turn should be 18°.

#!/usr/bin/python
import math
g = 32.2  # gravity: 32.2 feet per second per second

r = 80.0  # 80 foot turn radius
fm = 5280.0/3600.0  # factor mph -> fps
v = 20.0 * fm  # 20 mph

print math.degrees(math.atan(v**2 /(g*r)))

 

[Hummina Shadeeba]

Are u saying center of mass location doesn’t effect bike lean angle in a turn?

Correct! The formula I believe speedmd pointed us to -- θ = arctan ( v-squared / g r ) -- applies regardless of height.

So it’s widely misunderstood?

“ Bikes with fat tires and low center of mass must lean more than bikes with skinnier tires or higher centers of mass to negotiate the same turn at the same speed.”

https://www.fxsolver.com/blog/2015/06/03/motorcycle-leaning-angle/

Not that I know what I’m talking about but they seem to.

 

[donn]

Did you read Chalo's reply to that?

 

[Hummina Shadeeba]

I haven’t read anyone say what I posted is wrong. Is it? I’m reading conflicting understandings.

 

[speedmd]

Great topic looking at what drives mans maximization of influence over the machine.

Lower center of gravity helps stability in most all moving and stationary objects. The lop sided objects (mass concentrated at one end) are a interesting case when looking at how they act stationary or some what anchored to the ground on tires vs in a free trajectory. Take a long handle sledge hammer or axe for instance and (overhead) throw it toward a target. You would see the handle rotate in a much larger circle than the head (assuming a light wood type handle). It rotates around the center of gravity. How quickly it accelerates or stops its rotation gets a bit complicated but well established in Newtonian Mechanics. The further the mass is spread out from this center, the more energy it takes to spin it up or slow it down.

In the larger moto case, the rider is a much smaller percentage of the overall mass and thus somewhat less potentially influential. Being able to move his mass closer or further from the COG is certainly a factor and possibly the single largest one.

Don't get hung up on angle. Just understand that the taller it gets the further the top end moves off center for that same given angle. Both horizontal and vertically. This added distance takes more time or speed to cover. If mass is concentrated at the top or even bottom ends, it will also take more energy to rotate around its COG. When dealing with smaller angle changes near vertical, many folks working out the math will ignore the vertical components as they change very very little. Just understand that they do exist and are real and can not be simplified out when nearing the extremes. It becomes very apparent in the case of the MotoGP class when they go through the S bends or going from counter steer to turn lean how these vertical movement components effect tire contact - traction. Rider or suspension must minimize this hop off center and deal with the potential loss of traction -contact with the ground. A well timed rider move from one side to the other side can help minimize this and also reduce this swing angle. Concentrating the mass closer to COG will lighten and quicken this swing also.

 

[BalorNG]

Balancing - Steering can also be done by hopping either end or both. Don't have to be moving much at all. Been doing that for decades. Obviously easier on the pedal bike.

Looking like we are rounding the basses. On the inverted pendulum side, we can certainly mostly agree. The more static side (bike) is classic case outside the fuel rolling around and the relatively minor lateral and vertical movements the steering induces. The wide tire effect is well documented on how to handle it. Interesting on degrees of freedom the test apparatuses were noted to have. On most that were mentioned, were only a few degrees before the control apparatus limits were exceeded. This may be significant with human control limits even with their ability to change a bit and help balance this all out.

On the dynamic side (rider), they can flex in multiple directions at the foot- ankle, knees, hips, waist, as well as flex the torso in addition to two arms and two legs that can expand- contract. Robot folks are still working this all out and come a long way. We have two pivot points to help balance, one under each leg that also can be torqued and articulated at the foot and joints above. Two legs possibly more like a very wide tire or more like two separate ones. Not sure how to simplify and model this all. Good exercise for certain. This all changes the combined COG as noted earlier.

It is looking much clearer to me at least why the bicycle trials guys all say No Way to clip in shoe cleats. Not using them allows much more foot placement latitude in addition to the easy foot off capabilities. Also helps explain the trend to wider foot pegs in the moto trials circles also. More like a shorter running board. either will allow some significant pivot point changes for them just for starters.

Yup. By applying 'differential leaning' on the bars and moving weight from one pedal/peg to an other you can induce balancing correction that are independent from steering corrections - while steering is much faster and 'handier", you cannot always rely on it.
The closer are those 'balancing points' to the 'pivot' (as in - ground in case of a bicycle) and the wider they are - the greater your ability to affect balance indepenent from steering input. (And without actually leaning the body that is extremely awkward and limited by bar reach).
It has nothing with *stability* - but everything with being able to *control* bike in low-speed, low traction situations in particular.

A recumbent with relatively high CG and low (underseat) 'handstandable' wide bars like my Rinzler is MUCH, much better offroad compared to typical recumbents where you are locked into seat, have narrow bars and cannot stand on pedals - hence can ONLY rely on steering. This is fine when riding on asphalt (where traction is not a problem) and moderate/high speeds.

But, again, having high CG is still beneficial for stability - just hard to have in combination with low and wide 'balance points', but a lowracer recumbent with wide underseat bars and upright position can do it... though you'll be plowing the ground in turns if you make it TOO low and too wide

 

[Hummina Shadeeba]

Don't get hung up on angle. Just understand that the taller it gets the further the top end moves off center for that same given angle.

Im hung up on angle for the moment...trying to understand the basics. Assuming the rider isn’t moving out of line from the bike, so not hanging off, ..or forget the rider being there entirely and will a higher center of mass result in a lower angle while turning?
From what you’re saying ..you’re adding another element to counteract the lean angle and seeming to say higher center of mass results in more angle without the rider compensating..I think.

Which is opposite what I read and linked.

 

[speedmd]

But, again, having high CG is still beneficial for stability - just hard to have in combination with low and wide 'balance points',

May have much to do with the development of drop bars and their ability to allow great range of upper body positions. Higher can certainly trip easier. More so with light bike and narrow tires going into soft stuff.

you'll be plowing the ground in turns if you make it TOO low and too wide

There may be some good relationship of rider size to ideal height setup for pegs-pedals for a given specialty - ride type that can be explored a bit for trade offs.

 

[Hummina Shadeeba]

Again I keep reading lower COM resulting in higher lean angle
https://forums.superbikeschool.com/topic/500-center-of-gravity-high-or-low/

 

[speedmd]

Again I keep reading lower COM resulting in higher lean angle
https://forums.superbikeschool.com/topic/500-center-of-gravity-high-or-low/

Careful not to confuse center of mass COM or COG with concentration of mass. Movement "stiffness" about the axis of rotation can be very different. Not stating in steady state that you could calculate a different angle. There are certainly differences the lower center of gravity will have on bike handling at the limits like how it power slides and such, but like I said before, don't get hung up on angle.

 

[Hummina Shadeeba]

Ok, let’s say center of mass. (Although I don’t think it would make a difference here) does the bike lean more when higher or lower? I read lower but some here saying higher or doesn’t matter.

And does lean angle alone effect traction?

 

[speedmd]

Math says no to angle changing. Interested in your testing it. All you need is your cell with a bubble level app and a good speedometer. With and without a weighty back pack should do it if your steady.

IMO angle does effect traction. From my experience, always best to load tires from directly above for max traction.

 

[BalorNG]

Math says no to angle changing. Interested in your testing it. All you need is your cell with a bubble level app and a good speedometer. With and without a weighty back pack should do it if your steady.

IMO angle does effect traction. From my experience, always best to load tires from directly above for max traction.

Aren't bikes have MORE grip in corners exactly because they lean? Has to do with pneumatic tire characteristics and camber stiffness? I admit I've kinda skipped those parts in 'Motorcycle Dynamics' because it complex and nothing I can do about.
And in stead state cornering, you always load the tires 'from above'. Just at higher Gs