Telix fork brace how too?

[Steve in Golden]

Me likee the way my R1150R handles, and it has no fork brace. Not that I push it all that hard in corners or anything.

You are mistaken, sir.

What do you think the end of the A-arm is resting on? The "Fork Bridge" (part #31427654089). Your fork brace just isn't at the top of the sliders (like a telefix), it's 1/2 way up, behind your fender.

Plus, you have much larger diameter tubes and (I believe) a larger diameter axle held in stronger clamps (than an airhead), all of which helps combat those forces.

Well, one learns something every day, it seems. Thanks for straightening me out, Major.

[Chuey]

Also, Steve's bike doesn't have independent fork stanchions and sliders. It would be very hard for one to move up without the other one going the same distance.

The thing those forks do is make braking fun.

Chuey

[Major Softie]

No sorry, I'm still not getting this...

If you resolve the forces acting on a bike in a curve using - say - a vector diagram there will be a number of differing forces. These will include gravity, precession from the rotation of the wheels, inertia from the movement through the bend and others. These can all be resolved into one overall 'force' known as the resultant. With emphasis on the assumption that we are talking about a balanced bike in a constant bend on a smooth surface, the point where that resultant intersects the ground must be within the contact patch of the tyre (if it isn't, the bike will fall into or out of the bend which means that our initial assumption is no longer true). It follows that, in these somewhat idealised circumstances, the resultant must be parallel to the vertical axis of the bike... or at least within a degree or two of that. This being the case, the pressure applied to each stanchion will be (more or less) the same and there is no reason for one stanchion to be compressed more than the other.

Rob

Regardless of how you describe the forces in the bike itself, the pressure of the contact patch on the tire/wheel does point up the "resultant" you have described, and does not push evenly on the wheel and thus the axle. It is pushing sideways on the wheel (unless the contact patch is in the center of the wheel). That's where the torquing of the forks comes from.

I believe that your description of the forces at work is dependent on a theoretical lower fork and wheel assembly that transfers all forces without flexing. In such a fork, angled forces on the contact patch would be transfered straight up the fork without any creating any flex in the fork, but such a fork does not exist (in the motorcycle world).

[Steve in Golden]

Also, Steve's bike doesn't have independent fork stanchions and sliders. It would be very hard for one to move up without the other one going the same distance.

The thing those forks do is make braking fun.

Chuey

Yes, the front end hardly dives at all when I brake. I love the telelever front end!

[Major Softie]

Also, Steve's bike doesn't have independent fork stanchions and sliders. It would be very hard for one to move up without the other one going the same distance.

The thing those forks do is make braking fun.

Chuey

Yes, the front end hardly dives at all when I brake. I love the telelever front end!

They actually originally designed that front end to have zero dive, but test riders found it disconcerting, and they decided riders would not like it, so it was re-engineered to put a little dive back in.

[vanzen]

Also, Steve's bike doesn't have independent fork stanchions and sliders. It would be very hard for one to move up without the other one going the same distance.

The thing those forks do is make braking fun.

Chuey

Yes, the front end hardly dives at all when I brake. I love the telelever front end!

Yup. And ... the Telever is designed such that the "sliders", axle, and fork-brace/A-frame pivot
work together as a structure. A "seat of the pants" felt advantage vs. any Telescopic.

The R12S Telever has certainly raised the bar in terms of my expectations of front suspension performance !

[Rob Frankham]

Regardless of how you describe the forces in the bike itself, the pressure of the contact patch on the tire/wheel does point up the "resultant" you have described, and does not push evenly on the wheel and thus the axle. It is pushing sideways on the wheel (unless the contact patch is in the center of the wheel). That's where the torquing of the forks comes from.

Don't agree,

The resultant is the synthesis of all of the forces acting on the bike. Forces don't act in isolation. In a balanced bike, whether in a curve or not, that resultant will be parallel to the vertical axis of the bike. The 'force' from the ground will always be equal and exactly opposite to the cumulative forces acting through the contact patch and there are are no lateral forces (relative to the vertical axis of the bike) so there will be no lateral force from the ground against the wheel. I accept that this may seem counter-intuitive... until you look at it through a vector diagram, then it is quite clear.

Rob

[Ken in Oklahoma]

Don't agree,

The resultant is the synthesis of all of the forces acting on the bike. Forces don't act in isolation. In a balanced bike, whether in a curve or not, that resultant will be parallel to the vertical axis of the bike. The 'force' from the ground will always be equal and exactly opposite to the cumulative forces acting through the contact patch and there are are no lateral forces (relative to the vertical axis of the bike) so there will be no lateral force from the ground against the wheel. I accept that this may seem counter-intuitive... until you look at it through a vector diagram, then it is quite clear.

Rob, I"ve been staying out of this discussion because I believe there are others who can explain the question with greater clarity. To be sure, the summation of forces on a bike going through a curve will be zero, as long as no accelerations are going on. But it will do little good to focus on the whole bike. What we're discussing is forces on the fork legs during a turn and whether that can cause a distortion in the fork geometry such that the fork action is impaired compared to a straight ahead condition (i.e. no corner "generated" loads).

Since you're talking vectors I suggest we look at a free body diagram of the wheel with axle just by itself.

http://en.wikipedia.org/wiki/Free_body_diagram (For anybody who may not know what a 'free body diagram' is about)

Since we're talking about a steady state cornering condition, we don't have to worry about the fore and aft forces of acceleration and deceleration. I'm picturing a left hand turn in my mind as I talk. It could just as easily be a right hand turn. The forces I'm talking about we will represent as forces parallel to the fork tubes (ignoring the axle offset on the sliders for talking purposes).

With this in mind we can see a single force acting from the tire patch from the ground and in the direction as the fork legs. Countering that force there are two forces acting in the opposite direction, one force on each side of the axle. The summation of the two forces on the axle are equal and opposite to the single force through the tire contact patch. However the two forces are not equal to each other. The left hand force (from the L/H slider) is greater than the right hand force.

The unequal forces on each side of the axle result in a twisting force which, if you imagine spaghetti fork tubes, you can see the fork tubes bending in response to the twisting force. This is what I and others are talking about.

Now imagine a fork brace, Telefix or San Jose, and you can see that the fork brace serves to keep the two fork sliders being held more rigidly in alignment with each other and thus less of a bind is being put on the fork tubes.



Ken

[Major Softie]

Thank you, Ken. Perhaps yours is the explanation that's going to get Rob over the hump.

But I still have my doubts....

[Duane Ausherman]

Ken describes very well what I see as the forces in action. The /5 has the simple inverted U and it does a fair job. The /6 has far more resistance to those forces, but is a pain to install without something getting tweaked. The aftermarket Telefix can serve to do a better job, but may actually cause more trouble than it fixes. It must be installed on a perfectly aligned fork and not alter that alignment. In the early days we saw the San Jose brace alter the alignment and the result was quite a bit of stiction. We only worked on a few bikes so equiped, so maybe the data base was too small.

The fork brace that is properly designed and installed will do more to resist twisting than a special top clamp.

OK, is somebody going to step up and argue that alignment isn't important?