Cycling UK Forum

CREPELLO wrote:So it seems that there are two different ways of bike control in a corner. Who's a body leaner and who's a bike leaner then?

I'm a body leaner.
My trike does not normally lean ........

.......... unless I'm taking a corner at a silly speed and I get it on two wheels, then it get "FUN" ........

There are no "bike leaners" and "body leaners". We all start a turn by leaning the bike and body combination into the corner. The misunderstanding arises over how we do this. If perfectly balanced, we and our bikes would continue in a straight line with our centre of gravity directly over the line joing the two points of contact with the road. We cannot move our centre of gravity to one side because we have nothing to push on to do this. If we were to lean our upper body to the left, then our lower body and the bike would lean to the right and our combined centre of gravity would remain central. The only way we have of creating the desired lean is to move the bike away from being directly under us by turning the bars slightly in the wrong direction and using the friction between tyre and road to provide the necessary force. Of course, in practice we are constantly turning the bars slightly one way and then the other to correct for slight imbalances. All we have to do to create our lean for a gentle turn therefore is to fail to correct for the beginning of a fall in the right direction. A sharp turn requires a more specific effort to create the lean by moving the bike away from under us.

Sticking our knee out when turning as is most noticeably practised by racing motor cyclists is for a different reaon. They in fact move their whole body inwards in the turn. This is not done to move the centre of gravity, it is done first to allow the bike to remain more upright while turning to keep nearer the centre of the tyre tread, and second to lower the combined centre of gravity. We pedal cyclists do the same thing, but to a much less marked degree.

All cycling (two wheels) is an exercise in continuing to correct the natural tendency for such a configuration to fall. When cycling a (more-or-less) straight line, this invoves turning the bars to keep the point of road contact directly - on average - beneath our centre of gravity. When turning, the points of road contact have to be kept to one side of our centre of gravity so that this tendency to fall inwards is exactly - again on average - balanced by the centrifugal force provided by turning the bars and riding round a curve. We keep our balance not by moving our centre of gravity but by moving the points of road contact from one side to the other under a more-or-less static centre of gravity. Neither tricyclists nor motorists are able to do this. They therefore rely entirely on the steering mechanism to force the vehicle to turn. The outside wheel simply takes a bigger proportion of the weight and maintains the vehicle upright.

Remember there is no such thing as centrifugal force.

Interesting analysis there BigG.
Of course I'm not all bike lean and no body lean, so perhaps it's rather pointless to ask for one or the other. I'll just say that to have the quick reflex reaction of a MTBer, or a savvy urban commuter, you are going to lean the bike first. If the manoeuvre is sustained at sufficient speed, the body will follow. It may be that with normal road cycling that the two elements occur almost simultaneously that one might conclude that it is simply the cyclist leaning the bike into the curve.

We keep our balance not by moving our centre of gravity but by moving the points of road contact from one side to the other under a more-or-less static centre of gravity.

This is new to me. Isn't it the case that you move your body/bike combination when cornering because you need to overcome centrifugal force, which would otherwise overcome your COG. You relocate your COG in the opposite direction in order to maintain a balance against the centrifugal force.

rualexander wrote:Remember there is no such thing as centrifugal force.

This is fun! What is occurring to throw you off the bike on a corner if it's not CF???

CREPELLO wrote:

rualexander wrote:Remember there is no such thing as centrifugal force.

This is fun! What is occurring to throw you off the bike on a corner if it's not CF???

You're havin a laugh reeet?

As someone already pointed out on this thread, there is only inertia which tries to make a body move at a tangent to the curve. But this feels like a force trying to throw us off, and is often referred to as "centrigugal force", even though it doesn't exist, because it's a useful concept.

snibgo wrote:As someone already pointed out on this thread, there is only inertia which tries to make a body move at a tangent to the curve. But this feels like a force trying to throw us off, and is often referred to as "centrigugal force", even though it doesn't exist, because it's a useful concept.

Ok, perhaps I am a dullard and I do not comprehend. Thanks for the insight, So is centrefugal force always simply inertia?

Editted: for comprehension.....(of physics)

Yup. See http://en.wikipedia.org/wiki/Centrifugal_force

and here

Yes, that's a neat explanation.

Above, I managed to type "centrigugal force" when I meant "centrifugal force".

Re the body vs bike leaner question. Had similar debate before, but it wasn't so much whether to lean the bike or body (as leaning the bike does move the body to the side of the centre, so in effect, leans it), but rather, whether one stays in line with the bike frame in corners.

What I mean is: imagine going round a corner, look at the bike and rider from directly behind, draw a line from the centre of the BB, up through the centre of the saddle and continue it up through the rider. Does it go, more or less, up the rider's spine and through their head, or is it going off at an angle to the rider's spine on the inside of the turn?

If sat down through a sweeping curve then the former seems to work fine, but if jinking through tight hair pins then the latter is (IMHO) better - throwing the bike around under you (DH MTB style) is a much quicker way of changing the direction that it is heading.

I lean and tilt my bike, the Thorn Raven MK1 then grounds a pedal and I get into trouble.
Spinning my legs and leaning into corners is something I try and avoid nowadays.

Si wrote:Re the body vs bike leaner question. Had similar debate before, but it wasn't so much whether to lean the bike or body (as leaning the bike does move the body to the side of the centre, so in effect, leans it), but rather, whether one stays in line with the bike frame in corners.

What I mean is: imagine going round a corner, look at the bike and rider from directly behind, draw a line from the centre of the BB, up through the centre of the saddle and continue it up through the rider. Does it go, more or less, up the rider's spine and through their head, or is it going off at an angle to the rider's spine on the inside of the turn?

If sat down through a sweeping curve then the former seems to work fine, but if jinking through tight hair pins then the latter is (IMHO) better - throwing the bike around under you (DH MTB style) is a much quicker way of changing the direction that it is heading.

That's exactly what I'm suggesting.

Does the gyroscopic effect of rotating wheels make a difference? If a wheel is rotating on its axle, like the front wheel on your bike, and you turn it left by using the handlebars, then it will also try to lean - I'm not sure which way, but I think a bicycle wheel will want to lean against the turn. This ought to exert a twisting effect on the frame, but it may not be strong enough to notice.