Steering angle

[Clive Taylor]

Here's something to ponder during lockdown. How did Greeves achieve the steeper steering angle on the trials bikes when compared with the road bikes. I have compared my 20DC with my 24TE and the difference in the fork angle is quite noticeable, not surprisingly. I can't see however how it is arrived at. The front beam appears the same as though it is the same casting and the angle of the top tube looks about the same. Maybe the top crown plate and the bottom fork plate are different.
Come on, someone must know.
Regards
Clive

[modelman]

I would imagine the two alloy beams to be the same, therefor the forks to beam angle will be the same, but if the rear of the bike is raised, then the fork angle to ground will be steeper.
Rear jack up kits or lowering the front forks on some bikes achieves similar results. ( sharper steering )
Why not try & 'align; the two machines & have a 'sight; across the two just to be sure!
I did the same on one of my 1400s, but it made it a bit scary, soon reverted it back to factory!

[IanCordes]

The top crown plate is straight on the roadster, with a pronounced 'V' shape on the trials models. The bottom yoke of the roadster is central to the fork legs, whilst that of the trials models is offset backwards in the legs. In combination, this steepens the fork angle on the trials models. Simples...

Ian C.

[Clive Taylor]

Thanks for that chaps. All good ideas. Modelman's suggestion has merit but remember that the front wheel is 21" on the trials bike so I guess that would jack up the front even more than the back.

Indeed Ian, you are correct, the crown plate on my TE is a vee shape and swept forward compared with the road bike but the bottom plate seems to be welded to the legs in a more rearward position thereby maintaining a degree of parallelism with the steering tube.
I ponder however, that your idea would mean that the expander plugs would be at a different angle to the fork legs or if, on assembly the plugs were inserted into the top of the legs then the taper roller bearing would not align correctly.
I wonder, is it possible the the top tube was welded to the steering head bearing housing at a more acute angle and the shell moulding box modified (or another one made with modifications) to allow for the change in angle. That would ensure that the new angle is achieved and everything else would remain in line.

I think I have too much time on my hands !!! Its too cold in the garage this morning to do anything constructive !!
Regards
Clive

[Ftwelder]

Some things to consider. Changing the fork crown angle mostly changes your trail dimension. If I was to take my Anglian frame apart and make a road model, I would take 15 degrees out of the bend in the main tube, cut some 6" off below the bend , put shorter suspension units on and make trail changes with fork crowns or possibly shorten front swinging arm.

Regards, Frank

[IanCordes]

Sounds drastic! I would first of all fit a set of roadster forks & crown plate, or even those off a scrambler, to gauge the effect, the crown plate of which is V'd forward, not back, like the trials models. The experimentation has already been done! Why try to reinvent the wheel?

Ian C.

[Clive Taylor]

I'm not doing anything. Just making idle chat really and wondering how Greeves solved the problem of achieving a steeper fork angle on their trials bikes with minimum changes to components and tooling. I'm leaving my bikes perfectly standard.
Regards
Clive

[Ftwelder]

A more direct answer is that it would be very easy. to use the same beam for several purposes by changing bends and lengths of the tubes and how you drill the engine cradle.

I am very curious myself regarding the geometry of banana fork to see what the actual offset is and how the head angle and trail changes under compression. Regards, Frank