Cornering - hmph and yay

[Jacomus-rides-Gen]

Ever since my big crash a few months ago I've been rubbish in corners. Cr@p. Captian slow. All other aspects of my riding have got better - I've been training loads, and can even say with confidence that I am the best climber out of any of my cycling friends. But DAMNIT my total loss of cornering ability means that while I wait at the top of hills, even newbies beat me down descents.

I met a cycling coach after my crash, as I was just starting to get back out on the roads, and he helped me a lot with my climbing, and some bike fit issues I had... but he is responsible for destroying my cornering prowess. He was riding behind me and watching my knees for lateral movement, when we stoped he told me that the saddle tweaking we had done sorted the knee thing, but that he was very concerned about my cornering.

I have always cornered my bicycle as I corner my motorbike. Coming into a serious corner (not talking about just a little bit of lean) I shift forward slightly on the saddle, turn my inside knee in a bit and lean over the bike. Keeping the pressure on the outside pedal and outside bar. My body takes a tighter radius than the bike i.e. I'm leaning further into the corner than the bike is, and my sightline is where I want to be on the exit.

He got me to adjust my sightline to be more shallow, and to lean with the bike, so bike and rider are at the same angle, and to stop turning my knee into the corner. I have struggled and struggled with this ever since.

Yesterday I dove into a corner too fast and naturally cornered like on my motorbike - I got through it and was shocked that my line tightened up, and that I could have taken it faster. Since then I have gone back to doing what I know best and I am so so much faster now.

So hmph for him being rubbish at working out how I should corner best, and yay, because I've got my pace back! So I'm happy

 

[Melvil]

Good for you! It's a great feeling taking a corner at a fair clip.

 

[Mr Phoebus]

Yay!!!!! And you never soiled yourself either! Nice one!!!!

 

[Chris James]

Glad you have got your confidence back Gen. And that's what it sounded like you needed - confidence.

Having said that, your coach is right about cornering technique!

 

[Jacomus-rides-Gen]

Really?

Because he was so good at technique I wasn't quite prepared to believe that he was so wrong about cornering. Sir Sheldon also told me that my preferred method was the wrong way to take a fast corner.

Other cycling sites had varying views.

The only thing i know is that before I started leaning with the bike instead of off it, I was one of the fastest descenders in my club. When I changed I was the absolute slowest, and now I can tell I am very fast again.

Naturally I need to take it easy as I get used to cornering this way again, but I'm happy with it. Maybe it has more to do with what I am comfortable with as a rider, than the actual technique.

Do you lean with the bike then?

 

[Tim Bennet.]

There is a fundamental difference in the physics between a motorbike and a bicycles when cornering and that is the relative masses of the machine and rider.

Although any method of leaning will provide the required grip, the better 'technique' is the one that allows you the greatest freedom to act and correct any problems should the need arise after you become committed to the corner.

With the motorbike having the greater inertia, you can pull yourself back up onto it if needs be, but the same action on a bike would result in the bike being pulled down to the rider, who in this case has the greater inertia.

That's why the techniques are different and it can be difficult to switch from one to the other. So weight on the outside peddle, no pressure on the saddle, and firm pressure on the inside handle bar with a straight-ish arm will ensure the bike is weighted correctly and is leaning more than the rider, who will still have the option of altering the angle of bike lean if needs be.

Knee in or out is more debatable. I still stick it out, but Lance Armstrong says in his coaching book the inside knee should be planted against the top tube so as to dampen any twitchiness from the bike.

 

[Canrider]

I remember reading an article on cornering in Bicycling magazine (before it became nothing but advertising). It had three different cornering techniques for use in different situations, including shifting the rider's weight (bike stays largely upright), leaning the bike, and countersteering.

Hm, stop the press, they've put an abbreviated version on their site:
http://www.bicycling.com/article/0,6610,s1-4-41-244-1,00.html

Not sure if that'll do more harm than good, but there you go.

 

[Jacomus-rides-Gen]

What you say makes a lot of sense Tim, apart from the bit about pulling oneself back onto the motorbike - its a thrust of the hips that does it, not pulling against the bike.

Thats the same move on a bicycle (well, to be specific I've only done it once, so its not really a fair example I suppose). I went into a corner, and spotted gravel on my line. I was really going too fast for the corner, and knew I couldn't pull the bike further into the corner to avoid it that way, so I sat the bike upright sharply with the hip thrust thing, braked for dear life and dropped into the corner a second time to try and avoid the verge.

Small adjustments to direction in the corner are made simly by moving the riders sightline. To pull in tighter, look further into the corner, and to drift wider, look shallower.

All the above said though, I do accept that this may not be the best method of cornering a bicycle but it seems to be the best for me.

p.s. I still hit the verge, but remained on the bike, unlike the rider a couple of bikes back who ploughed into the verge with quite some force. Luckily he was fine though, just a couple of bruises and scrapes and a dinged front wheel. Apparently the marshalls only started warning people that the corner was dangerous after the 5th or so actual crash. Most people I spoke to had gone a little agricultural on the exit.

 

[Tim Bennet.]

its a thrust of the hips that does it, not pulling against the bike.

You can 'thrust' with any part of the body you like, but whatever you do will impart an equal and opposite reaction on what ever you are thrusting against. All this 'thrusting' will have an effect in proportion to their relative inertias.

If you want to debate this further, I'm afraid you will have to go on to www.newtonwasatosspot.com

 

[Chris James]

I agree with Sheldon Brown:

Leaning in Turns
To turn a bicycle, you must lean inward toward the direction of the turn. The faster you are going, and the sharper the turn, the more you must lean. You have no choice about this, for a given speed and turn radius, the center of gravity of the bike/rider must be moved sideways a particular amount or the bicycle will not balance.
What you do have control over is whether you lean the bicycle more than, less than, or the same amount that you lean your body, to get the overall center of gravity to the place that it has to go.


Leaning the bicycle sharply while keeping your upper body more upright
This approach is popular with beginners who are scared to lean over sideways, and who feel less disoriented by keeping their bodies more upright.

This technique is recommended by some racers and coaches as offering the possibility of recovering from a skid, but I don't believe it.


Leaning the upper body sharply while keeping the bicycle more upright
This approach is popular with riders who are afraid of striking a pedal on the road. This is a particular concern for riders of fixed-gear bicycles, since they cannot coast through corners.

This technique is also recommended by some racers and coaches as offering the possibility of recovering from a skid, but I don't believe it.


Leaning the upper body and the bicycle together, keeping them in line as when riding straight.
This technique has the advantage of keeping the steering axis, tire contact patches and center of gravity all in the same plane. This preserves the proper handling characteristics of the bicycle, and makes a skid less likely. You can verify this yourself by performing an experiment suggested by Jobst Brandt:

"Some riders believe that sticking out their knee or leaning their body away from the bike, improves cornering. Sticking out a knee is the same thing that riders without cleats do when they stick out a foot in dirt track motorcycle fashion. It is a useless but reassuring gesture that, on uneven roads, actually works against you. Any body weight that is not centered over the bicycle (leaning the bike or sticking out a knee) puts a side load on the bicycle, and side loads cause steering motions if the road is not smooth. Getting weight off the saddle is also made more difficult by such maneuvers.
"To verify this, ride down a straight but rough road standing on one pedal with the bike slanted, and note how the bike follows an erratic line. In contrast, if you ride centered on the bike you can ride no-hands perfectly straight over rough road. When you lean off the bike you cannot ride a smooth line over road irregularities, especially in curves. For best control, stay centered over your bike."

 

[Tim Bennet.]

To turn a bicycle, you must lean inward toward the direction of the turn. The faster you are going, and the sharper the turn, the more you must lean. You have no choice about this, for a given speed and turn radius, the centre of gravity of the bike/rider must be moved sideways a particular amount or the bicycle will not balance.
What you do have control over is whether you lean the bicycle more than, less than, or the same amount that you lean your body, to get the overall centre of gravity to the place that it has to go.

This is entirely true. All bikes in a corner automatically have to have these things in balance. The centrifugal and gravitational forces will always appear to act through a single point and will be exactly opposed by the frictional (and other) forces acting on the same point. That's why you are stable. It can not be any other way.

But how you arrange your masses to produce this required centre of gravity is immaterial. Gravity doesn't care. They will always be 'in line' if you are stable. Later he talks about 'side loads' but these can only exist if the combined centre of gravity is producing a bending moment, but to do this the combined centre of gravity would have to move, which is can't do if things remain in stable and in balance. Therefore all that is tosh.

I have never heard 'preventing skidding' as being the reason to adopt different cornering techniques. The argument I have heard is that it enables you to react easier to changes in the severity of the corner as you go round. Which is not addressed by either of the above excerpt

 

[Chris James]

Tim,

I don't think you are really disagreeing with the excerpt I quoted.

You say: 'But how you arrange your masses to produce this required centre of gravity is immaterial'

Sheldon Brown says: 'What you do have control over is whether you lean the bicycle more than, less than, or the same amount that you lean your body, to get the overall center of gravity to the place that it has to go'

i.e. the same thing.

As far as the bending moment comment, you are only considering the bike and rider as a single article, with a comnbined C of G. This is not actually the case but is convenient for simplification. By sticking out a leg you are actually applying a bending moment about your interface with the bike, but as you pointed out, for the bike to be in control this is actually counteracted by the fact that the rest of your body has to adopt a different position on the bike - appplying another bending moment equal and opposite.

However, by doing this you are making the bike intrinsically less stable in that a small bump in the road surface can cause your C of G to change it's position above the bike (suddenly the requirement that the forces must be in balance because the bike is in control is no longer the case because the bike is no longer in control).

When you have large levers sticking out out the plane of the bike / road interface then small bumps can make a sudden and huge change in the balance. Consider how stable a bag of potaoes balanced on a bike would be and a 60 foot ladder suspended at it's mid point on the bike would be in comparison. Hence the comment 'side loads cause steering motions if the road is not smooth' by Jobst Brandt (A Stanford gradutae in Mechanical Engineering).

I can't see how adopting any body position whereby a small movement will make the system totally unstable would help one to react more easily to chnages in the road severity. I would have thought the exact opposite for the reasons given above.

 

[Tim Bennet.]

Consider how stable a bag of potaoes balanced on a bike would be and a 60 foot ladder suspended at it's mid point on the bike would be in comparison.

I guess this is why tight rope walkers carry a bag of potatoes and not a long pole. Oh, hang on....

 

[Chris James]

I guess this is why tight rope walkers carry a bag of potatoes and not a long pole. Oh, hang on....

So why one would you rather have on your commute?

Tightrope walkers carry a large heavy pole - often with weights at the end of it - because this means that any minor changes in their (i.e. the walker's ) C of G will be dwarfed in comparison to the C of G of the system.

They also carry it in the centre of the pole to allow them to adjust to small motions more easily. They don't - for example - decide to stick one leg out as much as possible and hold the pole off centre to allow them to 'adjust for the severity' of the tightrope.

In fact they go to great lengths to get their body's C of G and the pole's C of G in line above the wire. They don't lean their body over and say it is fine because as long as all the forces balance themselves out then they will be just as stable.

Sheldon Brown, Jobst Brandt and I were all suggesting, for the same reason. that it is advantageous to have all the C of Gs in the same plane.

So, ignoring the sarcastic comment, what is wrong with Jobst Brandt's account? Obviously anyone can have an off day but the Stanford qualified Mechanical Engineer and author of mnay books on bicycle physics would appear to have a fair grasp of the subject to me (B Eng (Hons) Mech Eng Sheffiled University albeit a few years go) and just dismissing his theory as tosh seesm a bit off hand.

I'll be genuinely interested to see what you come up with as I am open to persuasion on the subject. By the way, how do you corner?

 

[nickwill]

I tend to corner by pushing on the inside of the bars (thus countersteering, putting my weight on the outside pedal and, yes, sticking my inside knee out.. This may go against the physics as stated above but it seems to work. Most of the pros seem to stick their knee out as well!