Re: New Bridgestone BT023, now poor handling.
 

Interesting theory you have..
Except all of the above is simply not true.

a. "Pulling on the bars at the wrong time" would only cause the bike to turn where you didn't want it to and is not a possible cause of a tankslapper.

b. Bikes can only be turned by countersteering.

c. The bike can only hinge at the steering head.

d. I'd like to see any evidence anywhere of anyone other than yourself citing over input to the bars as a possible cause of a tankslapper.

Buy a copy of "Twist of the Wrist" by Keith Code and enjoy a good read by someone who really knows the mechanics of motorcycle riding.

Re: New Bridgestone BT023, now poor handling.
 

Really? :)

Ok, that was a simplistic explanation. I'll expand. "Pulling on the bars at the wrong time". If you are applying any pressure to the bars and the front wheel hits a bump or rise or hole, the pressure on the front tyre reduces and your leverage on the bars, turns the front wheel for the fraction of a second it is unloaded. When it lands it is then no longer straight and the bike will try and straighten up. Landing a crossed up wheely is the extreme version. When the wheel hits the ground it reacts to being "Not straight" and flicks the other way. This can set up an occilation that then counters itself and the tankslapper begins. A steerng damper does its best to counter this occilation. (See tankslapper thread where we go through this)

Crossed up wheelie tankslapper
http://www.youtube.com/watch?v=ZzNh0...eature=related

Losing the rear tanks slapper
http://www.youtube.com/watch?v=hNlW7...eature=related

So lets say you've just left a corner on a bumpy B road and you're actively countersterring. If you happen to hit a bump that causes the front wheel to lose contact with the ground then the active counter steering (you) moves the wheel too much and when it lands again the bars are crossed up. You can pretty much expect a very decent tankslapper to begin.

That is what I meant by turning the bars at the wrong time. Maybe I should have said at an "unfortunate time" or "unlucky time" or even "bad time"? inexperienced bikers tend to use the bars to pull themselves up after a corner and this is a very good way of causing a tankslapper. Experienced bikers tend to use weight transter and pressure on the foot pegs so they don't have to use as much direct input with their arms on the bars. Or in other words, don't use the bars to pull yourself around the bike.

Above a certain speed! At low speed you steer directly. As I mentioned above you can counter steer by shifting weight and also applying pressure to the foot pegs. Counter steering is hinging the headstock. Anything that hinges the headstock is countersterring. Ask any kid that has ridden a push bike with no hands on the bars. He or she can still go round corners. maybe they do it by throwing their weight to one side. maybe they do it by hitting their knee off the cross bar. Maybe they twist the seat using their thights (my preferred option)

When using weight transfer it isn't the actual weight transfer that steers the bike it is the *change* in weight transfer. (delta). Any force in the centre of the bike that is to the side or up or down will hinge the headstock. You can hit your knee off the tank, stomp on the footpeg, slowly move your body and then stop it. All will steer the bike. If these are used in conjunction with direct input on the bars then its obvious that you'll need less input on the bars.

Want a very quick way of testing this? Go out on your bike, choose a straight road and take your hands off the bars and wiggle your hips. Job Jobbed.

And please don't bring up the link from the Californian superbike school where the claim you cant use footpeg weight then weld the headstock solid. Its ********. If they'd used a bike with a standard headstock it would work. I use it every time I ride. So do all of the blokes I race with.

Remember you are not trying to completely turn the bike with this, you're using it to reduce the amount of direct bar input. You still need your hands on the bars because once the bike is over ( along way) you have to maintain light pressure on the inner bar to hold the turn. If you don't the bike has a natural tendency to straighten up. You can hold a light turn just by hanging off to the side as the kids showed you on their pushbikes.

Of course. I haven't suggested anything different.

Lots of reading for you

Erm, Thats common knowledge. I've known that for 25 years. My mates have known it for as long as they have been biking. They knew it fropm the first time they had a tank slapper and I joined the biking fraternity when every bike used a 16" front wheel and everyone had tanklslappers every day :)

I've got both. 1st edition and second. I under stand them fully. Great books.

If anyone hasn't got them and wants them they can be Downloaded here free

C

Re: New Bridgestone BT023, now poor handling.
 

Ok tankslappers...

By the way, my playground IS a bumpy B road taken flat oot. Lots of countersteering and wibbles from the wheel leaving the ground.

You only get a tankslapper if you happen to have excited it at the wrong frequency and there is something in the chassis to create a feedback function with same phase. Thus causing a tankslapper rather than the steering simply whacking back to the middle and the oscillation settling very quickly.
Steering dampers add damping to the system which is similar to a pendulum.


Your delta weight transfer simply causes the bike to hinge in the middle about the headstock... inducing countersteer by accelerating a weight across the bike.

Weighting the pegs does nothing... you need to actually move mass to create any force.

Re: New Bridgestone BT023, now poor handling.
 

And "THE" definitive article on it from Mr Code....

http://www.superbikeschool.com/machi...bs-machine.php

See how many times he contradicts himself.

"Another recognizable error, resulting in excess effort used to steer the motorcycle, is the attempt to turn the bike by bulldogging the bars. An interesting combination of pulling up on one and pushing down on the other, rodeo style, like bull wrestling. No, repeat No, steering results from this."

Then in the next paragraph..

"Steering a motorcycle results from the process of pushing the inside bar forward, the same angle and direction the forks rotate in the steering head bearings. You can also pull on the outside bar. You can do both push and pull. That is what turns it;"

Also...

"Before I go any further I want to address off-road motorcycles. An off-road motorcycle will easily steer by pressing down on the inside peg, and in conjunction with shifting the upper body mass, will go over pretty easily . Still not what I would call good control but it can be done fairly efficiently."

"Again, I am not a true tech guy, but it occurs to me that the small contact patch on knobbies or dual sport tires plus dirt bike steering geometry (which is not intended to provide an enormous amount of stability at speed) contribute to the reasons why steering results from weight shifts to the degree it does on a dirt bike."

Which is bollox by the way. Its the inherent steering geometry in an off road bike, combined with the weight and height. if you push down on the peg of a dirt bike you are getting a greater leverage moment. Combined with lighter weight and hence more effect.

So Dirt bikes use and entirely different set of physics to road bikes? More bollox.

So, in effect he's shooting himself in the foot. 9and as his foot is in his mouth, its a headshot :) )

Bikes can and do steer with *change* in weight transfer and *change* in peg pressure. Mr Code's problem is he sees the two as mutually exclusive and not complimentary.

And finally, just to put this to bed. I use clip in pedals on my mountain bike.

I can ride a slalom course with no hands on the bars because I can pull and push up or down on both pedals. I'm counter steering with my feet. Hands no where near the bars. can pull up on one side whilt pushing down on the other and I can steer quite complex and tight paths.

Maybe Mr Code should get a Pushbike with SPD's? ;)

C

Re: New Bridgestone BT023, now poor handling.
 

First contradiction...
pulling UP pushing DOWN.... does not contradict pushing FORWARD and pulling BACK

Second one of yours ;)
Turning moment on pegs... surely is function of the width of the pegs... so a narrow dirtbike will have less moment than a big sportsbike?

http://forums.sv650.org/showpost.php...0&postcount=55

Re: New Bridgestone BT023, now poor handling.
 

I'm surprised Chris. This is Physics 101. Pushing down on the peg has the same effect as pushing the other side of the tank. It is just a different way of applying the force. Ok the tank force has a longer mechanical advantage but the peg still applies a force that tilts the tank and hence "kinks" the bike. Any kink in the bike steers it for as long as the force is applied. A sudden force is hiter than a sustained force (stamp on the peg versus weighting it.) Higher delta force.

C

Re: New Bridgestone BT023, now poor handling.
 

its where the pegs are in relation to the hinge.

I'm doing a picture. back soon.

Re: New Bridgestone BT023, now poor handling.
 

You tell me it is physics 101 and then show me a force that comes from nowhere and creates no acceleration?
Why are you surprised at me? I read same book and came out with a different understanding of it to you which I believe fits my model of system.


That force on pegs does nothing except clamp you in place on the bike UNLESS that force is you moving on the bike. Moving you on the bike will cause the bike to respond by an induced countersteer and a lean.
This is how that off road bike KC is on about is turning, same as you on MTB. Bike leans into corner... you stay upright.

Re: New Bridgestone BT023, now poor handling.
 

Peg singular. We're on the same page then.

Force on one peg tilts the bike over and you stay upright. The force moved the bike. If you are standing up, the bike is indepenent of your weight (balast) and so the effect is greater Remember we're only *initiating* the turn here. Holding the turn comes from the bars or in the case of mountain bike SPD's maintaining the force via the pegs.

Re: New Bridgestone BT023, now poor handling.
 

When sitting on a bike, surely weighting a peg is limited to a fraction of your body mass and little more. You have nothing to lever against so maximum force applicable to a peg is limited to your mass (assuming you are out of the seat, with hands off the bars and the other foot off the peg) x gravity.

I'd be willing to bet that when you are 'loading' the outside peg you are subconsciously applying steering forces to the bars.