measuring trail?

[Privateer]

I decided to make sure my bike's geometry is all accurate after I'd swapped out the forks and rear shock.  The manual for 04 620 says Trail should be 96mm.

So I had the bike upright and measured straight down with a level from the axle nut, marked that on the ground.  Then I measured along the forks with a straight edge, bisecting the axle nut again, and marked again on the ground.

My understanding is the distance between those two marks would be the trail.  I measured ~135mm.  So either I did something wrong or my bike is effed up.

I measured the fork legs and they appear to be the same length, and when I installed them, I matched the distance between the axle nut and the bottom of the lower triple plate.

I feel like I did something wrong either in the measuring or installing the forks.  Any ideas?

[64duc]

  
 Picture and description.


http://www.customtripletrees.com/MAIN%20PAGES/tech.html

[Privateer]

 
 Picture and description.


http://www.customtripletrees.com/MAIN%20PAGES/tech.html

thanks

so I measure through the angle of the headstock, not the forks? 

[stopintime]

To me, it looks like it should be measured at/through the center line of the head tube. No?

[Case S2R]

From the bicycle world...
"Trail is the distance from the contact point of the front wheel with the riding surface to the intersection of the steering axis (head tube) with the surface. The trail is a function of the head angle, the fork rake, and the tire diameter. Trail has a major effect on the handling of a bicycle. More trail increases the bicycle's tendency to steer straight ahead. A bicycle with a largish trail dimension will be very stable, and easy to ride "no hands". A bicycle with a smaller trail dimension will be more maneuverable and responsive."

Fortunately the moto world uses the same laws of physics.

Hope this helps

[Case S2R]

Another thought,

If you subtract the offset of your triples from your findings you should have your number.  135mm (your measurment) - 96mm (factory measurment) = 39mm

So either you have 39mm offset triples, your frame is out of spec or... you could be 3mm off using a ruler and marks on the concrete to measure a distance that typically requires specialized tooling to be 100% accurate.  (assuming you have 35mm offset triples).

Knowing nothing about the bike, I vote #3

[Speeddog]

Trail is a hard thing to measure, as you've found out.

And yes, even in the moto world, it's the distance between the intersection of the steering head axis with the ground and the center of the contact patch of the tire.