Anti dive geometry - cat among the pigeons?

[Minority]

Just before we lost some of the posts on the change over, there was a thread about antidive brakes.
It included some discussion about where to position the link to the fork and the theory behind it, which included some fancy diagrams of parrallelograms.
My theory is much simpler and goes along these lines:
As the caliper mounting bracket is now free to rotate around the axle, when you apply the brake, the forces generated on the caliper mounting bracket are rotational about the axle.
Therefore the tie rod should be mounted so that the opposite force to resist the rotational force, is at 90 degrees to the tie rod caliper mounting point/axle axis.
This would provide maximum anti dive effect with no tendancy to either "dive" or "rise" under braking loads.
Suspension movement would have a slight effect of course and you could adjust the effect you want - angle greater than 90 degrees = tendency to rise under brakes, angle less than 90 degrees = tendency to dive under brakes.
This is just my personal theory and please feel free to shoot me down in flames.

[warts]

The whole point of anti dive is to avoid braking forces adding to the suspension compression, so leaving some movement available to deal with the inevitable surface discontinuities.
When various weird and wonderful systems - both mechanical and hydraulic - were tried on bikes, it was eventually found some dive was good, it helps with feel and gave that reassuring dip as you applied the brakes. It was also found that some set-ups produced such strong anti dive effect, the suspension effectively locked, which was the opposite of what was wanted, this would be a reason to use a parallelogram type geometry as this would not be able to become locked as the various links fought each other.
Racers also found that by having some dive rather than none, the rake and trail was decreased, and the turn in was quicker and they seemed to prefer that.
I suppose it comes down to individual riders to adjust the amount of dive to give the feel they are comfortable with. It's quite likely you could even get to pro-lift
While your scenario is true when the bike is static, any articulation of the suspension will alter the geometry, so the amount of anti dive will inevitably vary.
Spring sag and damper settings will also combine to alter the feel, modern USD bike forks achieve control of dive through more sophisticated valving.
Tony Foale has written a book and accompanying software to enable plots of various suspension systems to be made and to evaluate the effects of changes.
How do you find it feels when using your set-up? Because that is the criteria, isn't it

[Minority]

Great reply! That's the sort of discussion I was hoping for, to increase my knowledge from others experience.
I must admit it was very strange to feel absolutly no apparent dip when I fitted the anti dive kit, maybe I'll have to lower the link and see what happens.
Even at this setting however it is far preferable to the very sharp dip experienced before fitting, I just had to touch the break lever and the front end dived.

[warts]

Sounds like you are well on the way to getting it right for you,
Many years ago, I had a horrid thing which would rise up as you braked, as you say weird.

[coaster]

Interesting post, I will soon be installing an anti-dive setup on my Jet and was wondering about the placement of the lug I was going to weld onto the forks. Because of the likely need to experiment to get the right 'feel' I'm now wondering if a clamp on arrangement like Minority's would be better. Alternatively I guess I could make the weld on lug a bit longer with 3 or 4 holes?

Are the clamp on brackets available seperately?

colin

[warts]

only this?
http://scootrs.com/moreinfo.cfm?Product_ID=2018

[corrado]

Are the clamp on brackets available separately?

The scootrs kit comes with the clamp on bracket plus the weld on lug. The idea being to get it set in the correct position [for you] with the clamp and then welding on the lug when you're happy. So you may be lucky and get a bracket from someone who's done just that. In reality it looks like people just leave the clamp in place.

[corrado]

only this?
http://scootrs.com/moreinfo.cfm?Product_ID=2018

Just spotted this too .....

http://www.lambretta-teile.de/Clamp-for ... -Lambretta

[coaster]

Cheers guys, I will try a wanted add for a ScootRs one and see what happens otherwise it'll be the LTH version. It's not for a ScootRs stylee brake, I'm doing a home brewed one using a Zip front wheel and I have an adjustable rose jointed link to use.

[Angry Bloke]

Cheers guys, I will try a wanted add for a ScootRs one and see what happens otherwise it'll be the LTH version. It's not for a ScootRs stylee brake, I'm doing a home brewed one using a Zip front wheel and I have an adjustable rose jointed link to use.

Hi Colin -I've got a bolt on ScootRS one you can try if you like