Descending - Cornering - the geometry?

[hiero2]

Bicycles are not motorcycles.

Quite true, and no argument there, I think I said something like this at the beginning of the thread. However, there are very significant similarities. Lean-in while cornering is one. The physics are the same. The two points you make alter the effectiveness of certain techniques - but do not invalidate the similarities.

Hanging off is a good example - as it is practiced in motorcycle racing. I don't see how it could be nearly so helpful in bicycling, since a major part of why it makes cornering faster is that you can continue to apply power while also leaning-in thru a corner.

The thing is tho, is that understanding why hanging-off works may be key to understanding how it is possible for knee-dropping or the Phinney technique to actually be functionally helpful. The physics have thrown me a surprise curve. I would have thot them to be simple - hanging off would apply leverage to counter the centrifugal forces (or more accurately increase the centripetal forces), but it seems rather that hanging-off is decreasing the gravitational segment. Which doesn't make sense to me - I would have thought decreasing the gravitational forces would lead to a quick flipover - so I haven't "got it" yet.

Lastly, if in fact one counter steers on a bicycle, the rear wheel can slip something vaguely like a motor bike and you'll live to tell about it. It alters your line slightly, but that's about it. 'cross riders who corner on the rivet can back me up on this. I've done it on the road too. Dropped knees not required.

The technique you are talking about - slipping the rear wheel in the direction of travel - is called drift (or drifting). I certainly believe you on this one - no need to check with 'cross riders. On a motorcycle this technique is greatly assisted by the use of power at the rear wheel. Which I'm sure you already know.

 

[hiero2]

I have the highest regard for Jobst, but he is a curmudgeon.

LOL, I've been validated! By no less than bikesnobNYC!

http://bikesnobnyc.blogspot.com/

See his WEDNESDAY, SEPTEMBER 29, 2010 "Organic Panic: Weaver of Dreams, Chamferer of Nightmares" post. I had to laugh.

 

[Hangdog98]

Validation?

Was it his reference to "not bathing"? or do I have to read the whole thing

 

[hiero2]

He refers to Jobst as the uber-curmudgeon. Search the page for Jobst, you'll see it.

 

[NashbarShorts]

Response to the OP:

omg, just go ride and trust yourself.

First time you got laid, did you insist on reading a manual first??

 

[Hangdog98]

First time you got laid, did you insist on reading a manual first??

No, but I did a fair bit of practice with visual aids

 

[hiero2]

Cornering - the apex

Ran across this

When should you use an early, middle, or late apex? For increasing radius, constant radius, and decreasing radius/limited visibility curves-in that order. When a curve's radius increases, the early apex works because the road straightens out as the radius increases. The constant radius curve is increased the most (remember changing the radius of the curve) by selecting a middle apex. When you have a decreasing radius or a curve with limited sight distance, stay wide as long as possible. This way you have the most visibility around the turn as well as a better path of travel for when the road gets tighter. Remember, if you encounter several constant radius curves together (a mix of left and rights), don't choose the middle apex for the first or any of a curve set. Selecting the middle apex puts you in a bad position to enter the next curve. Selection of a middle apex puts you in a position to run wide in the next curve. For multiple curve sets, choose the late apex. It will put you in the best position for the next turn.

From here: http://www.mgnoc.com/article_much_ado_about_cornering.html

It fills out what Tony Foales' says in his book, and does it very clearly. This is for motorcycles, so the condition that will usually apply to a bicycle will be the constant radius, or slightly decreasing, since a bicycle can not maintain power through the corner.

I'm still working on the leaning in.

 

[hiero2]

Response to the OP:

omg, just go ride and trust yourself.

First time you got laid, did you insist on reading a manual first??

Did I do something wrong then? Oh, sheesh. I am SOOOO embarrassed. My manual had nice pictures. Didn't have to read that much.

The point is that sometimes it is nice to know, and not just do. Some folks like to just do, some folks like to just know, some folks fall in the middle. I'm in the middle. BTW, some folks like to just do nothing, too, but I've left them out of my survey.

I didn't like the answers I got on this question 30 years ago, and I don't like most of the answers I'm getting today. We KNOW enough to provide a reasonable answer to this question that will have the highest probability of being correct. I want to know what that answer is.

There. Are you happy now? We don't have a roflmao smiley, or I'd put it here! All said in good spirits.

 

[Hangdog98]

I'll take those "good spirits" and drink to robust conversation. To continue the motorcycle theme, the Superbikes I worked with in the 90's had far fewer chassis adjustment options than today's motoGP bikes yet they still had over thirty six million different set up combinations. Each bike was different and each rider rode differently and each track was different and each day on that track, indeed each hour on each track was different.

It is for this reason I would respectfully submit to you that succeeding to map out the ideal line for cornering on a bicycle is not possible. There are guidelines, like those you have mentioned, but even small changes in variables will alter that line outside the guidelines considerably.

I am probably heavier than you and I probably brake much harder and later than you do. I'd bet that you could not follow my line at the same speed. Your line however, may be faster for you. I tend to apex late, I tend to carry quite high corner speeds, I don't mind pushing the front tire a bit, I use the back brake to un-hook the rear tire if I want it to come around a little. I have broken every limb at least once. There are probably at least a million riders who are faster than I am. Their style or set-up or desire or processor speed... or all or some of these things, are better than mine.

Tony Foale had some very interesting front-end designs that were going to change the world. Notice that you don't see them on any production motorbikes. "However beautiful the strategy, you should occasionally look at the results". (Winston Churchill) Tony may not be the best guy to ask.

Here's an ROFLMAO Smiley for you

 

[hiero2]

I quit riding the powered bikes after a run-in with a car. Left me with my leg in two pieces, but they put it together pretty well - it all works. I didn't start racing bicycles until 15 years later.

I'd take your bet on the weight - I might stand a chance there, the rest I'll let you have. And, I understand what you are saying about the many gazillions of setups - but we are talking about theoretical optimum guidelines, not holy rules. I think what I've put here is good info for that purpose, although my target audience is cyclists, not motorcyclists. Although, I will say, even on a bicycle, if this is a turn I don't intimately know, a slightly late apex will leave a larger safety margin for reserve lean. Not much point, on a bicycle, in a really late apex, unless you're in a pack and have no choice.

More to come.

 

[hiero2]

We have an answer!

Ok, folks, if you're following this, we have an answer.

Not some "expert" opinion , however well educated, oh no. We have a scientific body of experimentally validated results. Woooohooooo!

Drum roll, please.

Yes, dropping a knee, hanging off, leaning inboard ARE effective! So is the earlier mentioned "Phinney" technique of pushing the bike down and keeping the body more upright. Changing the relative position of the center of mass relative to the plane of the bicycle does change the lean angle and steering dynamics of the bike.

The paper I got this from is so new the ink is still wet. However, it pulls from more than a dozen other works done in the last decade or two - each a building block to this one.

Not being a physicist myself, nor an engineer - just a smart computer type guy who happens to be good with words and calculations - I can't say that we now know if a rider at the limit in lean angle can increase that limit by using body lean - or, in other words, get through the corner faster - but I would say that all the evidence and work to date strongly indicates that this is the case.

Oh, and by the way, this study picks up on some very significant response differences between leaning in and leaning out - both have an impact, but (apparently) for different reasons, and with different dynamics for each.

For those who want the reference, it was presented at the very recent symposium in Delft on bicycle and motorcycle dynamics, organized by Ruina etc. The paper is: "Comparison of a Bicycle Steady-State Turning Model to Experimental Data", authors S.M. Cain and N.C. Perkins, from the Univ. of Michigan, Ann Arbor.

So, now I can quote Cain, and Sharp, and Cossalter, and Foale, and . . .

I'd better preen quick, before somebody slams me down!

 

[Boeing]

Response to the OP:

omg, just go ride and trust yourself.

First time you got laid, did you insist on reading a manual first??

...trust yourself even if the other party isn't consulting.

 

[NashbarShorts]

I think cyclists can be broadly split into two camps: people who 'just ride', and techies.

This is definitely a techie thread!
Next up, a thread on the biomechanics of descending a flight of stairs.

 

[hiero2]

This is definitely a techie thread!
Next up, a thread on the biomechanics of descending a flight of stairs.

As my teenage son would say:

"And this is an issue why?"

I'll let you handle that bit about the biomechanics of descending the stairs. I'll sit back and watch the freestyler vids on that.

 

[Boeing]

a better thread would be how to teach a Brit to cook a steak

 

[hiero2]

Funny thing - I don't recall twisting your arm to read this thread.

 

[Apolitical]

Not to disagree that with others that just have to get out there and do it, and the best descenders probably couldn't tell you everything they do and why it works. I know I use both the lean in and lean out techniques depending on the situation.

One thing to keep in my with the phinney method is you are not really leaning out so that you flop over (and slide out tangentially to the radius you were following - back to you're concern on centrigual forces). Remember you are pushing on the outside pedal and on the inside bar, thus you are leaned over with the bike and balancing out the forces.

I still disagree about the requirement to countersteer to turn. In practice you need probably need to do this to get around a rea life turn. However, here's a simple thought experiment. Roll a balanced wheel down a ramp. It will go straight. Counterwieght it to on one side and it wil vere in that direction in a large radius. Put a saddle bag on one side of the bike and if you don't do anything the bike will keep wanting to vere in that direction. Maybe there's some symantics here...

 

[flicker]

Not to disagree that with others that just have to get out there and do it, and the best descenders probably couldn't tell you everything they do and why it works. I know I use both the lean in and lean out techniques depending on the situation.

One thing to keep in my with the phinney method is you are not really leaning out so that you flop over (and slide out tangentially to the radius you were following - back to you're concern on centrigual forces). Remember you are pushing on the outside pedal and on the inside bar, thus you are leaned over with the bike and balancing out the forces.

I still disagree about the requirement to countersteer to turn. In practice you need probably need to do this to get around a rea life turn. However, here's a simple thought experiment. Roll a balanced wheel down a ramp. It will go straight. Counterwieght it to on one side and it wil vere in that direction in a large radius. Put a saddle bag on one side of the bike and if you don't do anything the bike will keep wanting to vere in that direction. Maybe there's some symantics here...

I just tweeted Lance and he has a 1.5 kilogram counterweight on all his Treks as compensation.

 

[hiero2]

I just tweeted Lance and he has a 1.5 kilogram counterweight on all his Treks as compensation.

Man, now that's funny!

One of the very interesting things about this study is that it seems that BOTH methods work to improve the ability to get through a corner faster. Also, each seems to benefit from a DIFFERENT steering torque (remember your comment disagreeing with the "countersteer requirement").

When you lean to keep you body upright, and to push the bike down, it seems that "countersteering" is the way to go. It is more accurate to say that the rider benefits from keeping the steering torque negative - the rider is pushing the steering slightly out of the turn, closer to a straight line. The advantage in this case may be because the rider has moved the center of gravity closer to the point of traction - where the rubber meets the road.

When you lean into the turn, (somebody else might say down, or hanging off) you are keeping the bike's lean angle (aka roll angle) smaller. In this case, this study indicates the best steering torque is positive - pushing the steering slightly more into the direction of the turn. In hanging off, the advantage may be because the rider is increasing the effective lean angle, without increasing the actual lean angle. One thing to note, is that when hanging off, you are moving the CoG DOWNWARDS towards the horizontal (just as you said), and not OUTWARDS. Foale says the rider is reducing the gravitational component, which doesn't make sense to me. It seems to me that this action must be increasing the centripetal force, but I'm having trouble getting the physicists to address this question clearly. However, what is apparent is that it legitimately works as a cornering technique.

It is all way more complicated than the aerodynamics that transferred from skiing to cycling (and look at how long that took), and, overall, has less impact, but I find it interesting.

Since most of us are very very rarely taking a corner at or near limits, we can do any of this stuff, and never know if it helped or not - we aren't close enough to the limit to find out.

If you search on youtube for Cancellara, you may find some wonderful vids of him descending this year. He clearly uses both methods.

This may all be too much talk for some folk, but it's been fun to me.

 

[Apolitical]

Man, now that's funny!

Since most of us are very very rarely taking a corner at or near limits, we can do any of this stuff, and never know if it helped or not - we aren't close enough to the limit to find out.

If you search on youtube for Cancellara, you may find some wonderful vids of him descending this year. He clearly uses both methods.

This may all be too much talk for some folk, but it's been fun to me.

That was funny, and this is interesting. Just come see the gear on local rides, it's clear people like the techy side...

I think both methods are valid at the right time. I tend to use the body-in on sweepers (and anywhere I need to pedal). I do believe it's harder to make quick adjustments with this method because - as the article said - you need to move your whole body, but you can keep (or maintain) speed. Moto GP does this technique for clearance.

I use the body-out gets used on tighter, off camber, bumpy, etc. curves/turns. It allows quicker adjustments. Motox/dirt guys tend to do this.

Of course this is a generalization. There was an MTB article I read once about what they called something like turning vs. steering and when to use which technique. I'll try and google it.

 

[NashbarShorts]

It was really vivid --

Hiero, I had a dream last nite we were in a race and bombing down a descent. And then you crashed.

 

[hiero2]

LMAO - oo, ouch, that hurts,

aa, groan, oh man, that hurts . . .

 

[Hangdog98]

One thing to remember (or learn) is that counter-steering or leaning, hanging off, dropping the knee etc etc does not make the bike turn. These actions make the bike lean over one way or the other.

The steering, or more correctly 'change in direction' is caused by the tires being off the center strip and the difference in the circumference of the outer edge Vs the inner edge in the same way an ice cream cone rolls in an arc. However you choose to get the bike to lean over is up to you. By and large, counter-steering is more effective at initiating the change in direction. The physics of body position (amongst many other factors) affects the rate at which the bike turns and the exhaustion of available grip during the turn.

Centrifugal force, centripetal force, 'gyroscopic' effects or magic do not stop the bike from falling over. Counter-steering does, period. If you're riding a bicycle then you are counter-steering, even if you don't know it.

 

[hiero2]

Concur. Concisely said.

 

[escheator]

I just wanted to ask for few advices that could improve my descending.

How to descend when the tarmac has many longitudinal patches and the holes here-and-there? The edges of the patch could "catch" the wheel which could result in loss of control (did happen to me few times) which in during fast cornering pretty much means the fall. Catching optimal entry to the corner by switching sides between exit of previous corner and the entry to the next one by using all the lateral space would mean crossing over those problematic areas. How to do this in the best way, trade-off the trajectory or ...?
How to identify problematic patch edges without previous reconnaissance, that is during the descend itself?