Rocker re-design for long chop

[Nanny Frank]

Krymis (and others), firstly, thank you very much for placing your wealth of knowledge on the web. I feel that I have only scratched the surface of my learning with these suspensions, and feel myself being dragged deeper and deeper.

I have a long chop that has been raked to 45*. There is no offset in my trees. Currently the trail is over 12" and the wheel flop is quite pronounced. Here's a crappy pic:


Following your build rules and diagrams I used DraftSight to re-design the rockers. My current front wheel is a 3.00/18 Pirelli MT66. For the CAD, I set the rim diameter at 18" and set the tire sidewall at 90mm.

I set my trail at 0.125" and applied the 90* rule. I set the spring leg hole at half the angle of rake from a horizontal zero...i.e. my rake is 45* so i moved off horizontal 22.5*.

The points are merely hole centers and are not yet scaled for true axle or leg diameters. I would appreciate the board's review, critique, suggestions, etc. Thanks!





Thanks

[krymis]

looks good. move your trail to 2" and your 90* angle to 105* and post your drawing. I want to see what you got.

[curt]

nice ride

[Nanny Frank]

@curt: thanks!

@krymis, here's the numbers moving the 90* rule to 105* and trail to 2"

[Customize IT]

Killer Chop!

Want more pics?

[Nanny Frank]

Krymis, can you further explain to me the rationale for setting up with 0.125" of trail?

[krymis]

I already drew it out. Use a 105* angle between the axle and steering Centerline. Basically you need to flip your angle to the top instead of underneathand use 2" of trial. you should handle great

[gww25]

That last diagram won't work as shown since the geometry between the rocker pivot points won't allow for full spring compression unless I'm reading the drawing wrong.

[Nanny Frank]

Currently the biggest problem is that the springer doesn't function as a springer at it's current geometry. Currently the only suspension comes from the rear leg flexing.

I thought that by re-designing the rockers I could improve the trail, reduce neck flop, and correct the geometry so that the springer actually, springs, rather than simply flex/bounce on the rear leg tubes.

Today a mechanic buddy and I took more detailed measurements and pulled out the laser. Turns out the rake is 55 degrees, not 45, so this makes all the drawings I did previously not apply.

We are going to jig it up and get the geometry right, it's just going to take some figurin'.

Stay tuned, and thanks for all the replies so far.

[railroad bob]

nice ride

What he said...

Is that an Invader front wheel?

[Nanny Frank]

Here are a couple of more pictures to better show the current set up, and to hopefully help guide me in the best direction.

[Maxthegardener]

Are those rockers on upside down?.or is that a stupid question?

[gww25]

I looked at this all over again and the first diagram you posted would have been close to perfect even with the additional 10-degree rake thrown into the mix.

[gww25]

Just as a side note. On long springers it's pretty typical that about 80% of the perceived suspension comes from the legs flexing which is just to bad but almost unavoidable unless you're using 2-inch diameter legs. When the legs flex then the rockers and springs don't get a chance to work. You can improve this somewhat by changing the angles between the front and rear pivot pin hole locations but you really nee to do this by trial and error so it can get expensive.

[Nanny Frank]

Krymis and gww25, thanks for your insight. Curt, I haven't forgotten about you, I haven't disassembled the front end yet!

So I have gone back to the drawing board, corrected the rake to 55 degrees. Krymis, as you asked, I went to a 2 inch trail at a 105 degree rule.

Do my results look appropriate? Thanks all!