Urgent appeal for advice!

[Locutus]

Please help, fellow Zombies!

(Side note: I posted this same question in my build thread, but I want to be sure this is read today so I started a thread here also. My apologies for the redundancy.)

Before I can continue with the build, I need to figure out a detail....

Look at the two photos below. In the first, I have the boom at 9 inches off the ground where it's welded to the BB, and tilting upward such that the cross beam is at the correct position on the steering head tubes. In the second photo, the boom is level with the cross beam at the same positioning with the steering head tubes. However, that puts the whole boom at 11 1/4 inches above the pavement.

Also, notice the angle of the chain stay of the suspension triangle. In the first photo, it angles upward back from the BB, so that there is an obtuse angle with the boom. In the second photo, the chainstay is more in line with the boom. I feel this is an important consideration because the latter may better resist the springing action during hard pedalling that sometimes plague suspension bikes.

Keep in mind that I'm planning a mid drive for this trike. The power chain will be on the left side and hopefully will not require a tensioner. The triple chain ring and front deraileur will actually be on the BB shown, behind the seat. Another detail not to be overlooked is the fact that the pivot is just above the BB, not the BB itself. This will change the angle of pull to slightly above the chainstay.

So my question is, which configuration would be a better design choice, and why?

P.S.: Using one or the other configuration will also vary the caster angle of the steering head tubes by approximately 5 degrees.

http://i59.photobucket.com/albums/g292/Locutus59/Workshop/Bikes217.jpg?t=1240269204

http://i59.photobucket.com/albums/g292/Locutus59/Workshop/Bikes216.jpg?t=1240269266

[GregLWB]

[QUOTE=Locutus;22999]Please help, fellow Zombies!

I think the second photo is the way to go. I don't have a lot of technical reasons but, I think the angle looks better. I think you would have less chance of the rear end hitting your seat tube on a pot-hole.

Also for me and this is just personal preference I like to sit a little higher (there are a lot of log trucks around here and I don't like my head at the same level as their axle.:jester:

I don't know if I have helped but I hope so.:)

Greg

[25hz]

When you say "boom", I assume you'ere talking about the "frame" because the "boom" is out the front of the trike. Yes?

Anyway, a couple considerations for suspension when you are concerned about pogo effects.

1) run the chain UNDER the swingarm pivot because the chain tension trying to pull the swingarm down can help to counteract the pedalling pogo.
2) if you want no pogo, you need to be able to draw a straight line that connects the rear tire contact patch, the pivot and the rough location of the CoG. If the line goes above or below the CoG, it will either cause the rear end to raise or lower under pedalling torque - I forget which, but you can find the answer by looking up some info on 4 link rear suspension on rock crawler rigs.

[Locutus]

Thanks for the feedback guys. I went with photo 2 as suggested.