improving standup scooter steering trail stability

[aethyr]

So I've custom modified a scooter similar to this:

to go about 50mph. However, at those speeds the steering is extremely sensitive. I feel I need to have an extremely careful and firm grip so I don't twitch in the slightest otherwise I could crash. For stability at high speeds, I need more trail, but that would typically mean I need to make the scooter more like a "chopper", by extending the entire steering out forward. But that's not really feasible and still have a compact scooter.

I've noticed that many stock high speed scooters seem to have this design in their front forks:

This image is of a dualtron thunder, capable of 50mph. I can't quite determine whether this design increases trail (and thus stability). I want to say that it doesn't.

I've also considered putting a motorcycle steering stabilizer on it, but I figured that first if there was a way to increase the trail, that would have a more dramatic effect than the stabilizer.

Any ideas? In reading the reviews of the Dualtron and other high speed scooters, the reviewers all mention how stable they were at high speed, which is what I definitely do NOT feel with my scooter.

 

[AussieRider]

Looking at the pic, you could undo the 2 bolts each side that hold the fork blades to the suspension then flip the blades so they curve forwards instead of backwards as they do now.

AussieRider

 

[aethyr]

So I think I figured it out. I basically need to make the wheel axle move inwards/backwards, with respect to the steering axis. As it stands, the wheel axle is offset forward from the steering axis, and any forward offset from the steering axis decreases trail:

As you can see from this picture, the wheel axle is offset forward from the steering axis. Now imagine moving that wheel axle backwards towards the rear of the bike, which means you're moving the offset back. You can then see that the trail increases as you move it back.

The best way to visualize how offset and trail affects stability, imagine a castor wheel on a shopping cart:

Imagine if you attached a handlebar on the pivot axis so you could steer this wheel. Now imagine if you are going left. That wheel will constantly "fight" your steering because the wheel will naturally want to be behind the pivot axis. That's because in this situation, this setup has negative trail. You always want positive trail, meaning the wheel's axle is behind the steering/pivot axis to some degree. Every bike, motorcycle has positive trail, even though the wheel axle is in front of your handlebars, if you extrapolate the steering axis line down, the wheel axle is always behind.

Note the location of the wheel axle with respect to the steering axis of this weped scooter, also capable of 50+mph speeds:

The wheel axle is definitely behind the steering axis by a good bit, to ensure a high amount of trail and stability.

In the case of my scooter, I've calculated I have exactly 0 trail. Not negative, but no positive trail either. No wonder its so hard to control. I will need to do some welding to move the axle back with respect to the steering axis so I actually have some positive rake. This should help tremendously.

 

[bobwalton]

You might be interested in this:
https://youtu.be/oprWwrEmjmI
https://1drv.ms/u/s!AnrTeoVMhHXktSduwyBxEME-7Qgz?e=j3lRes

The 'negative rake angle' makes it so stable, it even works without handlebars:
https://youtu.be/5MQ7qDzfENo

.... or if you want suspension too:
https://youtu.be/ECzFlrXNry8