Why does a bike turn

[Donal]

Sadly, I have a predilection for cogitating. It has afflicted me most of my life.
Counter steering is counter intuitive but it's what I endeavor to do all the time but I really use it when going fast on twisty roads. Riding 2 up most of the time means that I have a lot of mass to get moving to change directions and counter steering gives good leverage on the handle bars. While vacantly cogitating while tour riding I probably share the steering load between both hands but when going fast I tend to counter steer using one hand to initiate the turns.

^^squared

 

[Fred W]

I'll bet that you use both hands any time that you are not consciously thinking about it.

Of course that would be impossible to know since once you think about it, you are no longer not thinking about it.

It is the natural thing to do, and using both hands would give more precise control.

 

[wheatonFJR]

I use the inside hand on hard turns so my hands don't work against each other in the turn.

 

[N4HHE]

The reason we think so little about the physics of steering is because it has no importance whatsoever in the outcome. Most of us physically learned how to ride a 2 wheeler before we even learned to add and subtract, so clearly an understanding of "how" it happens is not very important. Once you have learned through muscle memory what inputs are required, and what the outcome will be, there is no good reason to waste neurons deliberating over the physics that occur in between, unless of course you just enjoy cogitating.

No, not that at all. The reason it is important to know what is happening is that many riders get hurt or killed in emergency avoidance situations when they yank the handlebars as if it was a steering wheel. That serves to throw the rider from the bike directly into that which one desired to avoid.

 

[Fred W]

Huh? You guys are scaring me. Didn't you ride bikes as a kid?

Not sure how one hand is fighting the other one when you push the inside bar and at the same time pull the outside one, obviously with some degree of control. I don't think yanking the steering wheel of a car works all that well either.

 

[NTXFJR]

Some of us know enough about physics and formulas to be dangerous, and some of us know little at all, I'm in that category me thinks. It seems to me that Lee is using an analogy incorrectly to arrive at a desired conclusion. For instance, a motorcycle tire has a round left to right profile, if properly inflated, it is only slightly flattened under weight onto the road surface. The contact patch location on the front tire moves to the side the bike is leaning toward, which induces more rearward force on the inside fork and less on the outside fork. I think that's how a bike can be steered simply by leaning it with no hands on the bars. \

If what you say is true then a slight imbalance in fork spring rates left/right will cause a motorcycle to "pull" to one side when upright like an automobile with poor wheel alignment. However, we know that is not what happens. Dirtbikers commonly mix spring rates they have on hand to get a rate they do not. Some motorcycles have only one spring in one fork leg. Many do compression damping in one leg, rebound in the other.

The typical fork assy is rigid enough to overcome those imbalances which forces both forks to move at the same rate with each other. With a rigid enough assembly, one heavy enough spring and damper assy. on one side or the other would work just as well. In a balanced fork assy there is less induced drag on the bushings which act to keep the fork sliders lined up.

 

[bigjohnsd]

NEPRT Bound I think

 

[MajBach]

Personally, I don't try to delve into how a bike works, I really don't care. I try to relax, feel wut the bike wants, feel wut the bike does, 'n let it do it's thing.

I agree. And even in my never-ending but always dwindling thirst for knowledge, I do find it intriguing to understand how bees fly and why the toilet flushes clockwise. But in this instance, I'm more interested in establishing credibility to someone that has authored a highly recommended read within the biking community. If he has this one wrong, maybe some of the other other stuff that goes beyond letting the bike do its own thing is also wrong.

 

[MajBach]

I'm happy to read all these opinions. Surprisingly none have really shared my initial train of thought of why I felt this explanation is inaccurate. I envisioned the forces involved on a unicycle, or a motorcycle with solid steel rims or a quater rolled across the table the inevitable leans over and spirals inward. Certainly in the latter two examples, there aren't dissimilar radii that cause a differential turn but there is still lean.

 

[MajBach]

Interesting article here it focusses on hanging off but does a good job of explaining steering/ counter steering IMO

That article somewhat validates what I was implying. The author states that 40 years ago, bike tires were round (meaning cross-sectionally symmetrical) which would have the result of the contact patch not changing in shape regardless of how much lean there is.

 

[Fred W]

The turning has nothing to do with the cross-sectional profile of the tire or the contact patch shape. That's a total fabrication.

On a racing bicycle the tires are as narrow as possible and have essentially no cross section, and they are inflated to extremely high pressures so that they offer the least possible rolling resistance, and so thee is very little squish, yet they turn just the same as a motorcycle.

Now... the real question is: Would a stationary motorcycle on a conveyor belt turn with no forward momentum?

 

[rushes]

The turning has nothing to do with the cross-sectional profile of the tire or the contact patch shape. That's a total fabrication.
On a racing bicycle the tires are as narrow as possible and have essentially no cross section, and they are inflated to extremely high pressures so that they offer the least possible rolling resistance, and so thee is very little squish, yet they turn just the same as a motorcycle.

I wonder how a bicycle would turn with a car tire on the back...

 

[NTXFJR]

The turning has nothing to do with the cross-sectional profile of the tire or the contact patch shape. That's a total fabrication.
On a racing bicycle the tires are as narrow as possible and have essentially no cross section, and they are inflated to extremely high pressures so that they offer the least possible rolling resistance, and so thee is very little squish, yet they turn just the same as a motorcycle.

Now... the real question is: Would a stationary motorcycle on a conveyor belt turn with no forward momentum?

How could it not be stationary if it has no forward momentum?

 

[ionbeam]

...Now... the real question is: Would a stationary motorcycle on a conveyor belt turn with no forward momentum?

How could it not be stationary if it has no forward momentum?

Search this term: +airplane +conveyor one of the threads this turns up should have about a 1,000 pages and is often referenced when there is no consensus on very simple things. Call it a Forum custom.

 

[NTXFJR]

Ah! I should have know Mr, Fred had some interlaced humor in there somewhere!

 

[MajBach]

The turning has nothing to do with the cross-sectional profile of the tire or the contact patch shape. That's a total fabrication.
On a racing bicycle the tires are as narrow as possible and have essentially no cross section, and they are inflated to extremely high pressures so that they offer the least possible rolling resistance, and so thee is very little squish, yet they turn just the same as a motorcycle.

Now... the real question is: Would a stationary motorcycle on a conveyor belt turn with no forward momentum?

On reconsideration, that does make sense. A steel ingot in the shape of a styrofoam cup would essentially have no contact patch yet it would still roll a circular path.

I think your hypothetical is genius! The answer to it would surely result in an answer to my post title. Im inclined to believe the bike would flop on its side.

 

[wil780]

Search this term: +airplane +conveyor one of the threads this turns up should have about a 1,000 pages and is often referenced when there is no consensus on very simple things. Call it a Forum custom.

I'm not sure if you regard the topic of this thread as a simple thing, or if you're referring only to the +airplane +conveyor thread.

If it's the former, then it's simple only in a very restricted way. Of course, the front tire can generate a sideways force only if it is slipping sideways, although even that is too difficult for many journalists to understand. That's why there's so much nonsense on the subject in the motorcycle press and in books about riding.

If you broaden the question slightly, to "what forces cause the tire to reach and maintain the right slip angle for the corner", then it becomes an immensely complicated subject. The standard reference text, "Motorcycle Dynamics" by Vittore Cossalter, goes on for well over 300 pages. More recently a couple research groups in engineering departments at reputable universities have been constructing and testing models based on that text, and finding it incomplete. Their papers have been published in very prestigious journals, and the topic was recently selected by the British science newsmagazine "New Scientist" as one of the hottest areas of science. Other universities are establishing research programs on the topic and trying to recruit staff. It is not a simple subject.

 

[Fred W]

forehead slap

How does anything have NO forward momentum if it is NOT stationary?

 

[ionbeam]

MajBacH can't solve the conundrum of how a motorcycle goes around corners.

Form a hypothesis.

Devise a test.

Run the test while making observations or if relevant, taking measurements.

Think about the action and reaction from the test. Observe and repeat as necessary.

Mentally put it together.

Achieve enlightenment.

 

[NTXFJR]

Dammit Fred, I'm out of likes todayl! Can you take a rain check until tomorrow??