What actually makes a bike turn?

[Nibblet99]

so that's where bLaZe went to...

[Posthumane]

While I don't want to step into the discussion about what forces exist and which don't, I will say a word about communication.

Some people seem to be jumping on sv-wolf for the fact that he attempted to answer the question in an academic manner using vocabulary that was found to be confusing. I will point out that this is a non-trivial physics question being asked, and while trying to explain the answer to it over an internet forum (without the use of diagrams and other aides), you have to be very precise about your choice of vocabulary to avoid confusion. This is why in my attempts at an explanation of why a bike turns, I tried to explain every statement which may have been ambiguous.

I would like to challenge Zoo's statement 'If someone says, "The centrifigal forces created by the spinning wheels..." we all know what that means...' The problem is, everybody doesn't know what that means. That statement, due to its ambiguity, can be interpreted in several different ways, and judging by some of the posts in this thread, that is quite likely. The result of these differences in interpretation can be quite confusing, and can cause major problems when used in, say, and engineering project or science problem, rather than just an internet forum. While to some it may sound like an argument of semantics (centripetal vs centrifugal force), these differences can be quite severe in some situations, which is why the use of precise and accurate vocabulary is so important.

Anyway, I'm done my rant. In case you guys are wondering, I'm currently doing an engineering intership with the department of national defense, so while I do have a fair bit of academic experience, I also do live and work in the real world.

[ZooTech]

I'm concerned if sev has a crypt under his abode

I'm more worried about the fact that he keeps his car down there!

I would like to challenge Zoo's statement 'If someone says, "The centrifigal forces created by the spinning wheels..." we all know what that means...' The problem is, everybody doesn't know what that means. That statement, due to its ambiguity, can be interpreted in several different ways, and judging by some of the posts in this thread, that is quite likely. The result of these differences in interpretation can be quite confusing, and can cause major problems when used in, say, and engineering project or science problem, rather than just an internet forum.

Clearly the use of proper vocabulary has its place and can even mean the difference between a successful moon landing and a catastrophe. However, it should not become the focus of the thread. I think it's safe to assume everyone who rides motorcycles is familiar with the forces exerted by their spinning wheels at speed, so when a reference is made to those forces (real or not) I believe we're all playing from the same deck at that point. You also have to remember that not everyone is an engineering or physics major and quite a few probably don't even care about such sub-issues as "centrifigal" versus "centripetal" forces. When trying to convey a theory explaining how a bike turns, while including several factors at once (gyroscopic forces, tire shape and width, slippage, forward momentum) I think it's best to keep things in simple terms since it's already difficult enough to explain what it is you believe is happening. For instance, I have my own theory about how a bike turns which involves several things already mentioned plus one that hasn't been, but I have refrained from throwing in my two-cents since I'm not sure how to put what I envision into words that won't open their own can of worms.

[Sev]

so that's where bLaZe went to...

Someone had to deal with the runt...

And who needs a car when you have a bike??

[sv-wolf]

Not "Going over the other way." Going in a straight line! It is the bikes natural desire brought on by it's forward momentum to carry on in that straight line. When you alter the handlebars creating lean you work against its forward momentum and cause it to turn.

While I many have been wrong to call it centrifical force simply because that is the way I view it the statement remains true.

There has to be something pushing against the force of gravity, or the up down force that is native to the planet.

cen·trif·u·gal Audio pronunciation of "centrifugal" ( P ) Pronunciation Key (sn-trfy-gl, -trf-)
adj.

1. Moving or directed away from a center or axis.

Meaning that the bike is pushed outwards from the center of the lean as a result of it's forward acceleration or velocity. The parts closest to the center of the circle experience the strongest push, the parts furthest experience the least (I believe).

Regardless, if the rider were to push the lean to far the bike would low-side, which is to say the tires lose contact with the road at which point gravity is no longer being balanced by anything and takes over the bike goes down.

Like I've said before, while I may be incorrect to call it a Force in the truest sense of the word, that is the simplest way to describe it. I will however apologize for trying to explain it in simple terms rather then hauling out my thesaurus as Zootech so aptly pointed out. I think I have one in the basement somewhere....

Sev, believe me, I really am sorry to be so negative about many of your posts but the fact is, some of the things you have been trying to describe simply don't hold up to physical reality. Yes, you have quite admirably been using simple language in much of what you have said, and I applaud you for that. but actually you have also been using a technical vocabulary: 'forces', 'inertia' centripetal force' and so on - and these things have very precise definitions and relate to each other in mathematically precise ways.

If you had stuck to simple language and used terms which were not so highly defined, then I would have had no issue with your posts. Plenty of people just want to be able to get some rough idea of what is going on in their bike, and far be it from me to object to that. There are plenty of areas beyond my knowledge of mechanics where I do the same. But if you start using the technical language of mathematics then I feel that I have the right to point out where you are misusing it and where you are drawing illogical conclusions.

And, of course, you are not wrong in everything. You are close, but not close enough. In the broad terms in which you write, for example, your first paragraph above is pretty much correct (except that "going over the other way" is a direct quote from your first post - your language, mate.)
On the other hand your attempt, further down to explain how a bike turns is way off beam.

I'm trying to put together a post using some diagrams. I'm doing it on Word so I hope it will paste in here. I will try to explain, as clearly as I can how the basic forces on rotating objects are understood in mechanics. And believe me, I am very willing to be proven wrong, if it is done in a logical and informed way. I am intrigued with this stuff and am open to learning anything I can.

In the meantime. Have fun and stay safe.

Best wishes

Richard

[ronboskz650sr]

I think my garbage truck has one or more square wheels (feels like it sometimes)...and it leans more when fully loaded. It this okay?

[niterider]

It is okay if the truck leans, the centrifugal force will keep it from falling over.