Weight transfer under braking

[fjman]

I'm reading through TotW2 for about the zillionth time, each time taking more concepts and trying to apply them into my habitual riding style (which is why it's taking so long, teaching an old dog new tricks...)

Anyhow, I ran across this, and can't think of why/how it should be interpreted:

After braking, some riders stay stiff-armed on the bars; the upper body is driven forward by a deceleration force of about 0.2 to 0.3 G, leaving extra weight on the front-end of the bike. Potentially, up to 100 pounds of weight is transferred to the front end when that weight could be on the seat or tank, 24 to 36 inches further back. Forgetting to relax is all this really is.

Okay, here's my questions about this:

1: Under braking, don't you want weight transferring forwards? Not so much to life the rear wheel, but as much as you can get away with otherwise? The more load the front wheel has, the more traction it has, the more braking force you can apply without sliding, right?

2: You shouldn't be stiff-armed at any point, though it would help transfer weight to the bars... you lose a bit of control if you're too tight. Right?

3: After braking, you're not decelarating anymore, I'd think? Not really noticably, anyhow... and weight is transferring backwards as your suspension is unleashing stored energy from braking forces being lifted.

4: Don't agree with #3? Well... If you're braking for a corner, and you're not on the gas yet, then you're at the turn-in point. Don't you want the front end loaded a bit as to steepen your geometry and reduce the amount of time you spend wrestling the bike over into the turn?

5: Any physics majors? If you have a given deceleration force on a bike, does it matter where the weight is being applied (bars, seat, or tank) if the center of gravity hasn't changed? E.g., holding on with your legs or arms makes no actual difference to the amount of downward force applied to the front tire under braking? (This I don't know about, but have to ask just to better understand things...)

Any clarification is appreciated.

[R6Andrei]

Originally Posted by fjman

I'm reading through TotW2 for about the zillionth time, each time taking more concepts and trying to apply them into my habitual riding style (which is why it's taking so long, teaching an old dog new tricks...)

Anyhow, I ran across this, and can't think of why/how it should be interpreted:



Okay, here's my questions about this:

1: Under braking, don't you want weight transferring forwards? Not so much to life the rear wheel, but as much as you can get away with otherwise? The more load the front wheel has, the more traction it has, the more braking force you can apply without sliding, right?

2: You shouldn't be stiff-armed at any point, though it would help transfer weight to the bars... you lose a bit of control if you're too tight. Right?

3: After braking, you're not decelarating anymore, I'd think? Not really noticably, anyhow... and weight is transferring backwards as your suspension is unleashing stored energy from braking forces being lifted.

4: Don't agree with #3? Well... If you're braking for a corner, and you're not on the gas yet, then you're at the turn-in point. Don't you want the front end loaded a bit as to steepen your geometry and reduce the amount of time you spend wrestling the bike over into the turn?

5: Any physics majors? If you have a given deceleration force on a bike, does it matter where the weight is being applied (bars, seat, or tank) if the center of gravity hasn't changed? E.g., holding on with your legs or arms makes no actual difference to the amount of downward force applied to the front tire under braking? (This I don't know about, but have to ask just to better understand things...)

Any clarification is appreciated.

#1 and 2: Any extra weight to the front would only lead to extra strain on the forks. Stiffening up on the bars prevents the suspension from doing it's job of tracking the pavement properly. Putting extra weight and stiffening up the bars can only lead to bottoming out the forks faster and wheel lock up. Both of which is not part of the bike's design. Chime in if I'm wrong...I love that book BTW.

R6-Andrei

[fjman]

#1 and 2: Any extra weight to the front would only lead to extra strain on the forks. Stiffening up on the bars prevents the suspension from doing it's job of tracking the pavement properly. Putting extra weight and stiffening up the bars can only lead to bottoming out the forks faster and wheel lock up. Both of which is not part of the bike's design.

Extra weight to the forks in a smooth fashion (i.e., not grabbing a shitload of brake in a hurry), should allow the forks to compress and still track over bumps. If your fork bottoms, you don't have the right spring, is the conventional thinking! (Though, let's face it... I've been able to put the tripleclamps tight against the dust seals on everything I've ever ridden. Admittedly I've never ridden anything with a few grand worth of Ohlins up front....)

Now, if I could have springs custom wound that were quite stiff at nearly full compression, why wouldn't this be the norm, if it improved handling dramatically enough? The only reasons that I can think of are cost, and that it wouldn't improve handling enough to justify the effort. So I'm rather unsure of why a bike isn't designed for more complete transfer of weight to the front without bottoming the forks... (unless it's what I guess, and cost is the overriding issue there.)

[R6Andrei]

Originally Posted by fjman

Extra weight to the forks in a smooth fashion (i.e., not grabbing a shitload of brake in a hurry), should allow the forks to compress and still track over bumps. If your fork bottoms, you don't have the right spring, is the conventional thinking! (Though, let's face it... I've been able to put the tripleclamps tight against the dust seals on everything I've ever ridden. Admittedly I've never ridden anything with a few grand worth of Ohlins up front....)

Now, if I could have springs custom wound that were quite stiff at nearly full compression, why wouldn't this be the norm, if it improved handling dramatically enough? The only reasons that I can think of are cost, and that it wouldn't improve handling enough to justify the effort. So I'm rather unsure of why a bike isn't designed for more complete transfer of weight to the front without bottoming the forks... (unless it's what I guess, and cost is the overriding issue there.)

I guess I was exxagerating a bit. Bottoming out the forks would be hard to do unless you exceed your current suspension settings. I should have said that you would reach your suspension's travel limit faster. I also should have said that weighting the front bars would lend to that extra load going downwards. If you brace your weight at the tank, then the load transfer wouldn't be as drastic. You would carry your weight forward first (with the bike). (Wouldn't your weight load in the end be the same anyway?) So basically all I'm trying to speculate on would be the initial load in the front. Correct me if I'm wrong...

R6-Andrei

[Poudre10]

If you have a given deceleration force on a bike, does it matter where the weight is being applied (bars, seat, or tank) if the center of gravity hasn't changed? E.g., holding on with your legs or arms makes no actual difference to the amount of downward force applied to the front tire under braking?

You are correct. Hold on to the bars as tight as you can or relax -- makes no difference to this force. Deceleration of the entire bike/rider mass is still present and loads the front in the same fashion. The quote you provide above from TOTW2 is nonsense.

My suggestion to the multitudes of TOTW readers on this site: Realize there are many good riding tips in the books, such as relaxing your arms during cornering. However, the physical reasons given are often wrong. Relaxing on the bars prevents unwanted control inputs, no doubt, but does not change the weight transfer as mentioned. Much of Code's technical writing is wrong or misleading -- if you really want to learn the physics of riding, go elsewhere. I've said it before on this site: He needs to edit and update his books. Until he does, I won't be a TOTW fan. An unpopular and minority viewpoint to be sure, especially on this messagenet.


(Edited to remove incorrect comment.)

[incognito]

Originally Posted by fjman

I'm reading through TotW2 for about the zillionth time, each time taking more concepts and trying to apply them into my habitual riding style (which is why it's taking so long, teaching an old dog new tricks...)

Anyhow, I ran across this, and can't think of why/how it should be interpreted:



Okay, here's my questions about this:

1: Under braking, don't you want weight transferring forwards? Not so much to life the rear wheel, but as much as you can get away with otherwise? The more load the front wheel has, the more traction it has, the more braking force you can apply without sliding, right?

Yes you want weight forward. Watch GP races. Your body also helps to slow the bike down when you're sitting up. It creates drag and slows the bike. Last part, yes

2: You shouldn't be stiff-armed at any point, though it would help transfer weight to the bars... you lose a bit of control if you're too tight. Right?

Correct

3: After braking, you're not decelarating anymore, I'd think? Not really noticably, anyhow... and weight is transferring backwards as your suspension is unleashing stored energy from braking forces being lifted.

True you're not really decellerating anymore. You are more idle-throttle and leaning as you hit your apex. As you get more skilled at riding on the track you will start to hold the front brake very lightly all the way until the apex to keep the front suspension planted down. As you come out of the apex you get on the gas and the weight transfers to the rear

4: Don't agree with #3? Well... If you're braking for a corner, and you're not on the gas yet, then you're at the turn-in point. Don't you want the front end loaded a bit as to steepen your geometry and reduce the amount of time you spend wrestling the bike over into the turn?

5: Any physics majors? If you have a given deceleration force on a bike, does it matter where the weight is being applied (bars, seat, or tank) if the center of gravity hasn't changed? E.g., holding on with your legs or arms makes no actual difference to the amount of downward force applied to the front tire under braking? (This I don't know about, but have to ask just to better understand things...)

Any clarification is appreciated.

.

[thwwx]

Originally Posted by Poudre10

You are correct. Hold on to the bars as tight as you can or relax -- makes no difference to this force. Deceleration of the entire bike/rider mass is still present and loads the front in the same fashion. The quote you provide above from TOTW2 is nonsense.

My suggestion to the multitudes of TOTW readers on this site: Realize there are many good riding tips in the books, such as relaxing your arms during cornering. However, the physical reasons given are often wrong. Relaxing on the bars prevents unwanted control inputs, no doubt, but does not change the weight transfer as mentioned. Much of Code's technical writing is wrong or misleading -- if you really want to learn the physics of riding, go elsewhere. I've said it before on this site: He needs to edit and update his books. Until he does, I won't be a TOTW fan. An unpopular and minority viewpoint to be sure, especially on this messagenet.


(Edited to remove incorrect comment.)

You're brave to denounce the guru. But being engineering trained, I do agree with you. I think Keith Code's explainations are not meant to be taken from a strictly technical (as in forces, vectors etc) standpoint, but as an easily accepted concept for the general riders. The top racers don't have enginnering degrees, they won't appreciate theories that will need an engineering degree to understand.

[fjman]

Originally Posted by R6Andrei

I guess I was exxagerating a bit. Bottoming out the forks would be hard to do unless you exceed your current suspension settings. I should have said that you would reach your suspension's travel limit faster. I also should have said that weighting the front bars would lend to that extra load going downwards. If you brace your weight at the tank, then the load transfer wouldn't be as drastic. You would carry your weight forward first (with the bike). (Wouldn't your weight load in the end be the same anyway?) So basically all I'm trying to speculate on would be the initial load in the front. Correct me if I'm wrong...

That's kinda my thinking too, but then I sat and thought about it a bit harder. The actual weight shifting forwards from decelleration is going to cause ALL of the spring compression, not your arms. If you sit on the bike on a (rear) stand, note where your forks are. Now, sit up and lock your elbows. If the forks move, it's a rather smallish amount, and has to do with you shifting your weight back, putting your forks into a more extended position than they were in a normal crouch. If you lean into it, you can compress them very slightly, though. So it's the braking force rather than the body position, making the difference here.

Though, in defense, locking your elbows reduces the force that you have to take with your lower back and legs. Therefore locking elbows will help prevent fatigue to some degree.

Thanks to the engineers, good to have some added insights on this.

True you're not really decellerating anymore. You are more idle-throttle and leaning as you hit your apex. As you get more skilled at riding on the track you will start to hold the front brake very lightly all the way until the apex to keep the front suspension planted down. As you come out of the apex you get on the gas and the weight transfers to the rear

I tend to try to turn the bike while releasing the brakes, oddly enough. If you start turning hard with the fork still compressed, it's far quicker to turn than otherwise, but runs out of ground clearance sooner, so you want to be fully off the brakes by the time you hit full lean. (I run pretty minimal rebound damping on my forks, too.) Old habit from beating the hell out of my prior bike (a `78 yam XS400, turned like a cow). Good habit or not, it's there. It also allows you to hold the brakes longer (important when you've got a single disc with as much stopping power as putting your feet down).

[Poudre10]

Originally Posted by thwwx

I think Keith Code's explainations are not meant to be taken from a strictly technical (as in forces, vectors etc) standpoint, but as an easily accepted concept for the general riders. The top racers don't have enginnering degrees, they won't appreciate theories that will need an engineering degree to understand.

Writing "easily accepted concepts for general riders" is fine, as long as it's not accompanied by erroneous material. In some cases, no harm is done -- riders relax their arms, think weight transfer is affected, and ride better none the wiser. In other cases, wrong info' can lead to confusion and possibly worse riding. The smart rider will then hopefully delve deeper into the problem (like fjman in this thread) and learn and improve in spite of the info', rather than because of it.