Tech Tech Tech, or...So you want to build a trike?

DeathBySnuSnu

DeathBySnuSnu

Old Redneck Motorhead
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So here we go.
In cooperation with Stinger (and any other tech head that wishes to contribute) the beginning of a place to put tech info.

As this is in the VW thread it will have a heavy VW tilt to it. But many aspects of of building is universal.
 
Geometry.....

Whether you put a kit on a wing or hand build a big ole v8 you must have certain things right.

Rake and trail.

Just like a motocycle but in trike form typically a lot less trail.

Rake....not no big deal. Make it what you want it to look like. You may effect turning radius but drivability will be ok.

Trail....the big deal. No matter what rake angle you choose the trail must be right. Typically around 2 inches or even less.

8152290896_75e1300982_o_zps7iq9xgov.jpg
 
Alert...Alert...Alert

If you are looking at a used custom build
CHECK THE TRAIL
lots of home builders dont do the math, just want it to look cool with the front all angled out there.
It is a very rare thing for a front end off a bike that has been welded on with increased rake to have correct trail.
Luckily too much trail is not deadly. Makes for hard steering and head shake on decelerating.
 
I bet our friend Zook can tell us a first hand story about trail. I think he has a kitted bike.
Wings and glides are factory made with lots of trail. Their intended purpose is highway cruising with high speed stability, slow steering, no twitchyness at all.
So those bikes have around 4 inches of trail.
You can buy the trike kitted bike and the "ez steer kit" is an option (and an expensive one).
Lots of folks skip the option.
Guess what....too much trail for a trike.
Heavy gorilla arm steering and decell head shake.
So what then? Ez steer kit.
What it is is carefully designed raked trees.
Reduces trail to around one inch.
Instant "power steering" feel and no decell head shake.
So when you buy a kit or a kitted bike go ahead and get the ez steer kit (or whatever the vender calls it today). The venders like to hide the theory from you (change in trail).
So there......you can hop over the the wing section and learn about the same design concerns as we have with our custom builds. Geometry is geometry. Watch your numbers.
 
Great info snu, I've been dealing with trail for a couple months now, reading and expirementing with different rockers. Also at the same time trying to get the "flop" out. I have an old rusty DNA springer 10" over at 53 degree rake. Trail is at 9" at this time and It acually drives ok. I never really cared for the cheap dna anyway so yesterday I finally bit the bullet and sent deposit for a Sugar Bear springer. I told him what I had been dealing with and of course he said no problem, he could make my troubles go away,lol. Very cool fellow btw. Looks like they'll be 26-30" over with the #4 rockers. Expensive and 3-4 month wait but excided as hell. We'll be talking again in a few days so i'll be sure to mention it's a trike so thanks for that info.

choptrk
 
Well that is a killer way to fix it!!

Be sure to give sugar bear absolutely correct numbers. All his math will be based of what you tell him. His drop pivot rockers are ZERO trail.
And they work.

Styles of front ends is probably the next discussion.

On the lucky side for us is that the rear engined vw trike is so light weight in the front. It does not take gorilla arms to steer big trail. Backing up is a pain and some low speed decell shake.
 
So a recap.

Now we know that there is no "ideal" rake.
Differences in rake will give a bike different characteristics.
Take a crotch rocket..... very steep forks, not much rake and also not much trail. Very very quick handling, twitchy, the sports car of the bike world. Exciting to drive and you have to pay attention and drive it all the time.
Then the long front chopper. Assuming it is built correct, not too heavy on the bars, slower to change direction, takes more input to make a change, lazy, forgiving, does not take constant attention to keep it in a straight line.
In general all the same traits when applied to a trike. Except a trike will not forgive large trail like a bike that leans.

Ok so now you have read the tech link and have a grasp on the general theory.
Put the rake on it however you like or want.
I dont like long rake and the long front ends that go with them. My personal choice based on how I want mine to perform. I am more of a middle of the road, I want the looks of rake but I want to keep it bit more quick handling but not a crotch rocket personal choice, make your personal choice based on what matters to you.
Then.....
Make the trail fit.
You have the angle you just have chosen.
As the diagram above shows, get the relationship of the neck angle to the front axle.
Now you know where the front axle must be.
Next is picking a front end that fits those dimensions.
 
This is already an awesome start to this "tech" thread.

What I think I will end up doing, if it's okay with you Rex, is start adding these links that you've provided, to the original post.

At least that way they won't get lost in the shuffle of posts.

If this builds up to being the type of thread I believe it will be, then we will most likely "sticky" the thread to ensure it is easy to follow and find.



So, with all that said, let's all pay close attention to what Deathbysnusnu has to say. As most know, he is an awesome trike builder!!!!!!!!
 
I am not a professional trike/bike builder at all.

I am an old motorhead.
I am a mechanical engineer by trade.
I do build custom machinery for factories.
I do something different every day.

And Stinger. It is up to you how things are organized. I am offering up tech links and trying to direct thoughts on how to understand it all.

Feel free to add and/or organize as necessary.
 
You guys probably know this but, you can tell alot about how a sidecar or trike is going to steer just by turning the handle bars lock to lock. Watch how far the bike moves side ways. If it only moves a small amount say 2" then it doesn't have much trail and steering should be relatively easy. If it moves say 4" it has more trail and will uaually be harder to steer.
 
Word to the wise, boys and girls, pay very close attention to what these guys are saying about trail. Mine wasn't right on the first build (bought the frame that way and learned the hard way), which resulted in a wicked understeer. I crashed hard when the front end washed out, and I'll never be the same again.

Just wanted to make the point that this goes way beyond handling. It's definitely a valid safety concern as well.

Sorry if this is out of place, but I felt it needed to be said...

PEACE and ride safe!
 
Hey Snu, I'll let you in on a little secrete. You, Dano and the whole VW gang are some of the most admired, appreciated and followed guys on this site. Forum admins have the ability to see who has read a thread via a cumulative list generated and displayed at the bottom of every thread page and I will tell you that you'd be surprised how many people religiously follow the VW posts. You guys rock man!
 
Working today. Got the men at lunch right now.

Thanks for the input fellow members.

I will be off the next couple day. I will try to put in another installment.
 
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