Topic: Need some help with trail on kawasaki kz1000 ltd front end

[Dime]

Did a little mock up today using our cb750 triple trees as a starting point. They would have to be bored out slightly to be made work with the kz1000 ltd forks. I would also have to slightly adjust the brake mounts but nothing serious.

When I plugged in the numbers for the 750 @ 27 degree frame rake, 2.45" triple offset, 33 3/4" fork length and 0 degrees rake in the trees, 19" wheel. I came up with 4.38" trail.

The problem is that doesn't allow for the leading forks. I am not sure how to allow for this.

I know that the cb750 stock is in the 3.3" range for trail. The leading forks should bring the trail number down but I need to figure out by how much.

Would appreciate your help. Thank you.

[Dime]

Use the calculator at the bottom to help-
https://www.rbracing-rsr.com/advchoppercalc.html

I plugged in all the numbers into that calculator and got 4.16" for trail. But it also doesn't allow for the leading axle

[Dime]

Trail is calculated by axle centerline to ground, intersecting to top of trees. Leading, trailing, or inline to the fork is immaterial (to my understanding) to the overall rake/trail calculation.

“Trail: Distance defined by vertical line from axle to ground and intersect of centerline of steering neck and ground.”

Everything I was reading about these Kawi leading axle forks is that Kawasaki used them.because their bikes had more rake and by using these forks reduced trail.

It would make sense what you are saying though because I can't find one reference on how to specifically calculate it with leading axle

[pekingduck]

Kawasaki, like other Japanese makers, used leading axle forks to give the illusion of a longer, more stretched out front end on their cruiser models. That also meant the tanks were narrower at the front or were mounted more rearward so they wouldn't get hit when the forks were turned.

Dirt bikes use them because they have long travel, and the fork tubes engage the slider over a longer distance.  The offset of the triple clamps, the distance between the stem center and a line drawn between the fork tube centers, is reduced to compensate. 

There is no difference between leading axle and straight axle forks when measuring trail, as others have said. I would recommend using the Kawasaki triple clamps with the leading axle forks,as they probably have at least an inch less offset.

[Dime]

Kawasaki, like other Japanese makers, used leading axle forks to give the illusion of a longer, more stretched out front end on their cruiser models. That also meant the tanks were narrower at the front or were mounted more rearward so they wouldn't get hit when the forks were turned.

Dirt bikes use them because they have long travel, and the fork tubes engage the slider over a longer distance.  The offset of the triple clamps, the distance between the stem center and a line drawn between the fork tube centers, is reduced to compensate. 

There is no difference between leading axle and straight axle forks when measuring trail, as others have said. I would recommend using the Kawasaki triple clamps with the leading axle forks,as they probably have at least an inch less offset.

I found the specs for a 1981 kz1000 ltd and plugged them into the calculator. With the known 105mm trail this would give a 2.70" offset as opposed to our 2.45" offset.

That being said using all of the cb750 numbers with the kz1000 forks I end up with 105mm trail.

So I see no differnce using the cb750 trees with the kz1000 forks.

The cb750 is 28 degree rake as opposed to the kz1000 of 29. The cb750 wheelbase is 58 as opposed to the kz1000 of 59.3. The slight differences make it a wash trail wise.

[Dime]

Boring the stock cb750 trees is not going to work. It would take out too much material.

Trying to come up with a kawasaki triple tree now

[Dime]

What are the Kawi forks in OD? The GL used 39mm.

38mm

[bryanj]

Boring out the top tree sounds risky to me as they crack on standard honda forks

[Dime]

Boring out the top tree sounds risky to me as they crack on standard honda forks

Appreciate it. I already decided against it. Now just to come up with a triple tree

[Dime]

So I have the kz1000 ltd triple trees. Measured the offset to be 31mm or 1.22".

With this new information the 19" front and 16" rear this puts my trail now at 5.28".

Obviously more than stock but midway between the 4-6" accepted trail numbers.

I am not looking for a road race bike just a nice cruiser. So I believe this will be acceptable.

[Medyo Bastos]

What is your concern? You will be fine as long as you don’t run negative trail this causes you uncontrollable wobble. Your front end will feel heavier at slower speeds with larger trail numbers. 4-6 is ideal, but is a matter of preference, you can compensate for more trail by learning to countershift your body weight.


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[Dime]

What is your concern? You will be fine as long as you don’t run negative trail this causes you uncontrollable wobble. Your front end will feel heavier at slower speeds with larger trail numbers. 4-6 is ideal, but is a matter of preference, you can compensate for more trail by learning to countershift your body weight.


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My old Harley had similar trail numbers as with the kz1000 ltd setup. I didn't find it bad at all just not as nimble compared to my old 1980 cb750c.

[Dime]

Slower speed steering is best effected by more aggressive counter-steering. Body weight shifts have essentially zero effect on steering. Weight shift for steering is a much propogated myth of motorcycle riding. Unless the handlebars turn, the bike won't either. Simple as that.

To be transparent I never got a handle on counter steering until I got my Harley then I had to learn quick the benefits

[Don R]

  The leading axle is hard for me to wrap my brain around. At a glance I'd think it would add a caster-like property to steering, like it would add a self-centering feel.
  That said, my 81 GS1100E has a leading axle, that bike for sure feels bigger than my gl1000 in a tight turn. I considered swapping it for a different fork to get dual piston brakes but after some stopping tests, I talked myself out of it.

[Dime]

  The leading axle is hard for me to wrap my brain around. At a glance I'd think it would add a caster-like property to steering, like it would add a self-centering feel.
  That said, my 81 GS1100E has a leading axle, that bike for sure feels bigger than my gl1000 in a tight turn. I considered swapping it for a different fork to get dual piston brakes but after some stopping tests, I talked myself out of it.

You are probably right about the leading axle. As for the braking I think it will be a definite upgrade to the single disc brake I had stock, plus the addition of the disc brake rear. Just trying to figure out the rear master cylinder and spindle for the rear brake now.