Telelever - Where's the Flex

[Deleted account 210609001]

Here's a question that I'm sure someone can answer easily.

The telelever wishbone pivots at the back, so the front bit (where it connects to the fork brace affair) doesn't travel in a straight line, but in an arc. This must mean that EITHER the angle of the forks changes as the suspension compresses and extends, OR there is some displacement in the junction between wishbone and fork brace.

Can anyone tell me which it is and, if the former, how is the change in fork angle achieved in what appears to be a rigid set up?

It's been keeping me awake....

Thanks,

Robin.

 

[jnrobert]

Its a ball joint not a fixed pivot like the back of the arm.

 

[gavin]

That's right, a ball joint in the top yoke.

 

[Jinx]

Excellent article on the Telelever here.

Look down the page under "suspension" and click on the English version. Must be English, your flag is on it.

An excellent site overall. Highly recomended.

 

[gavin]

That's a most excellent site!, interesting bit about the twin cylinder engine too.

 

[Den]

They pivot at the top of the fork legs where they enter the top yoke . There is a rubber bush in there which flexes. Non GS models have a different arrangement, a sort of pivot in the yoke.

 

[Deleted account 210609001]

THANKS!

Thanks for the replies. Great website, Jinx - hours of reading pleasure on a long winter's night!

Robin.

 

[The Mechanic]

What bush will flex that far eh!

They pivot at the top of the fork legs where they enter the top yoke . There is a rubber bush in there which flexes. Non GS models have a different arrangement, a sort of pivot in the yoke.

Nope sorry theres no bush to 'flex', besides it would be to unlike Mr.Bnwubbleu to adopt such a device.

Look at the excellent diagram further back on this thread and you can work it out for yourself.

See.......as the front fork compresses and unloads (rebound) the fork gets shorter and longer (depending on suspension movement) therefore the front wheel spindle will move in a gradual arc in relation to the (or any fixed point on the main frame) steering head and the lever mounting.

In other words the lever projects an arc that corresponds to a similar arc produced by the front wheel spindle.

Good in'it!

 

[Den]

Sorry Mr Mechanic... you are wrong.... The non GS models have a upper ball joint below the top yoke. The GS not having this has to flex at the fork top where it enters the yoke

 

[Dutchman]

Sorry Mr Mechanic... you are wrong.... The non GS models have a upper ball joint below the top yoke. The GS not having this has to flex at the fork top where it enters the yoke

Not quite correct.....the RT, GS & R models all have the same arrangement. The exception is the RS model.

The lower wishbone is located to the fork brace by means of a ball joint.

The upper yoke is located above the cast alloy forward frame component by means of a straightforward ball race.

The top end of each fork stanchion is located into the upper yoke, not merely by a rubber bush (although that's what it looks like from above & below), but what BMW call a 'pot joint'....item 3 in the picture below. The steel component which is ball shaped with a threaded hole through it, is screwed onto a bolt which protudes from the top of the fork stanchion and the hard rubber element bonded to it is cylindrical in shape and a special tool fit to the upper yoke, retained by a circlip on top.

Effectively it's a metalastic (rubber & steel) bush which allows the limited & pre-determined degree of 'rotational' movement necessary for the suspension to work in the manner so well illustrated in Jinx's post....

 

[Den]

C,mon Duchy, Im not wrong, I just wasnt precise enough with my models. I originally said that the flex was in rubber bushes in top yoke which is correct. The rs has a ball joint.

 

[Dutchman]

C,mon Duchy, Im not wrong, I just wasnt precise enough with my models. I originally said that the flex was in rubber bushes in top yoke which is correct. The rs has a ball joint.

Easy, Den....wasn't being critical......I've got this really annoying habit (so my wife tells me) of researching tecnical stuff down to the last particle, especially if I'm responding to a question.....

I know it seems hard to believe that BMW would use such a low-tech device (the pot bushes) on such a relatively high-tech suspension system......but it's rotation at the yoke is less than two degrees, so I guess a 'proper' ball joint would be over-engineering that even BMW resisted.......!

 

[BarcodeMan]

Phew...

Like watching a couple of heavyweight boxers slug it out in the ring.

Has Den (with the assistance of Dutchman) dealt the killer blow or is there time for one last flurry from Mr M?


Anyway, whatever the outcome, I've certainly learnt a bit more about the mechanics of my faithful steed. Thanks!

 

[(RIP) Kaister]

You're all wrong - its done with mirrors

Phil

 

[The Mechanic]

To Den...

Hey Den ... I'm with you, quite correct. I hadn't realised that BNwubbleu had stooped so low, by the time I'd gone off at a tangent about angles (little pun there) I had completley missed your point.

As an aside these bushes seem like something out of the dark ages of Girder fork development.