Roller stability?

But in each position the contact patch is at a different horizontal distance to the fork steerer axis.

alienator said:

But in each position the contact patch is at a different horizontal distance to the fork steerer axis.

No, I don't think so. The contact patch moves as does the intersection.

9606 said:

No, I don't think so. The contact patch moves as does the intersection.

Look at that picture and imagine a roller placed in front of that wheel so that the contact patch is directly at the end of the dotted-line extension of the steering axis (zero trail). How would that be the same amount of trail as a roller placed directly under the hub of the wheel where the contact patch is positioned as currently depicted in the sketch?

9606 said:

No, I don't think so. The contact patch moves as does the intersection.

Note that the contact patch is where the tire is contacting the roller. If the contact patch were to stay in the same position relative to the steering axis, as you suggest, it's center would lie on one unique line parallel to the steering axis, always. That's not the case here.

alienator said:

Note that the contact patch is where the tire is contacting the roller. If the contact patch were to stay in the same position relative to the steering axis, as you suggest, it's center would lie on one unique line parallel to the steering axis, always. That's not the case here.

You are correct. My mental (visual) block. Thaks for explaining it so nicely.

9606 said:

You are correct. My mental (visual) block. Thaks for explaining it so nicely.

Here's a visual, I think part of the confusion is that the steering axis is always virtual. IOW, that point of the tire doesn't touch the (flat road) pavement. Putting the bike on rollers changes the contact patch and its distance to that virtual axis, but the steering axis itself isn't changed.

-Dave

daveryanwyoming said:

Here's a visual, I think part of the confusion is that the steering axis is always virtual. IOW, that point of the tire doesn't touch the (flat road) pavement. Putting the bike on rollers changes the contact patch and its distance to that virtual axis, but the steering axis itself isn't changed.

-Dave

Nice drawing. That's why you got the free bike goodies! 😎

alienator said:

Nice drawing. That's why you got the free bike goodies! 😎

Glad ya like it, just Photoshop fun, 'cept it looks like I messed up the alignment on the normal trail illustration, that's supposed to be contact patch top dead center on the roller...

-Dave

Is there a real world situation when one experiences negative trail?
Say when one is mountain biking, or doing trials, or trick bmx?

9606 said:

Is there a real world situation when one experiences negative trail?
Say when one is mountain biking, or doing trials, or trick bmx?

When the motorcycle riders on youtube are doing front wheel stands, just before the steering gets all wobbly and they end up on their face.... that's very close to negative trail. 😄