Shortening Forks

Seems to me that you could take the fork tubes to a machinist and have two inches cut off the top and the tubes rethreaded, but I have never tried it.

77KZ650 wrote:

caffcruiser wrote:

Effects handling significantly though...

in what way though?

Well, it's a matter of sprung and unsprung tension.

The springs are made to be at a specific "load" when the weight of the bike and the rider or an average weight are on there. If you add in spacers you are basically putting them at a greater load at all times.

Think of it this way. If I take a spring, and I push down on it till it is 2/3 its height and let go, it will bounce up so far.... but if I push it down and hold it till its half its height and do the same, it will bounce up higher. The reason? It has a greater potential when more tension is put on it.

That's what you're doing with a spring in a fork tube. Add a spacer in, and it looses some of that for travel when you are riding.

This is a problem to consider in the car world too when all these kits are lowering down their cars. Handling is usually negatively effected.

As steell pointed out, the optimum idea would be to go to a machinist and see about cutting off a portion and having it rethreaded. I wouldn't see any reason why they couldn't do that.

Of course, to make it handle well, you'll need a shorter spring with a slightly higher spring rate. You can't cut a spring and expect that to work well, since springs are usually progressive, which means that are purposefulle made to compress in one area before another.

***It's also a matter of purpose. Is it a cruiser? Is it a vintage race bike? Lots of long stretches? Mountain pass corners? If it doesn't need to corner at its greatest potential, like a chopper, then who cares? If you want it to corner *better* than it did, then it's a concearn.

I hope the O.P. posts some more pics though.

Post edited by: caffcruiser, at: 2006/10/01 10:18

caffcruiser wrote:

Well, it's a matter of sprung and unsprung tension.

The springs are made to be at a specific "load" when the weight of the bike and the rider or an average weight are on there. If you add in spacers you are basically putting them at a greater load at all times.

Think of it this way. If I take a spring, and I push down on it till it is 2/3 its height and let go, it will bounce up so far.... but if I push it down and hold it till its half its height and do the same, it will bounce up higher. The reason? It has a greater potential when more tension is put on it.

That's what you're doing with a spring in a fork tube. Add a spacer in, and it looses some of that for travel when you are riding.

This is a problem to consider in the car world too when all these kits are lowering down their cars. Handling is usually negatively effected.

As steell pointed out, the optimum idea would be to go to a machinist and see about cutting off a portion and having it rethreaded. I wouldn't see any reason why they couldn't do that.

Of course, to make it handle well, you'll need a shorter spring with a slightly higher spring rate. You can't cut a spring and expect that to work well, since springs are usually progressive, which means that are purposefulle made to compress in one area before another.


I hope the O.P. posts some more pics though.

That makes a lot of sense, its just like how the new sport bikes are "strapping" the front end. makes it lower with less travel, and it puts more tension on the spring at the same time. would make for a stiffer ride, and a new spring would be wanted like you pointed out, if they wanted the feel of stock springs. if they wanted stiffer springs, the mod would kill 2 birds with one stone

Post edited by: 77KZ650, at: 2006/10/01 11:55

77KZ650 wrote:
if they wanted stiffer springs, the mod would kill 2 birds with one stone<br><br>Post edited by: 77KZ650, at: 2006/10/01 11:55

Actually, therein lies the problem.

It won't make them "stiffer". The rate of the spring is predetermined by the manufacture of the spring.

It just increases unsprung tension. Which isn't a good thing per se.

The proper way to do the job would to be to either get clip ons and lower the clamps as aformentioned by another poster, or to shorten the tubes as steell said, and get shorter progressive rate springs made for it.

Or, as I said before, just look into some modern sportbike front ends that are standard telescopic setups which are usually a little shorter. Maybe SV front ends, since they have bar clamps on them from the factory?

Post edited by: caffcruiser, at: 2006/10/01 12:32

I lowered the front end on my KZ900 by 3 inches by using lowering blocks I bought from Schnitz Racing. The ride is a little firmer but i'm use to it now. I would try these lowering blocks first before I do any cutting on that front end. If you don't like the ride of the lowering blocks you can always take them out and they are easy to install.

tw

why do you need to drop the front end that much? on my bobber i didnt have to? what do you have for ground clearance? what height is you rear axle at? did you build in any rear stretch? if you need any help let me know. i have done the one you saw an alot of other models also. (i used to build frames as a bussiness)

Well, the frame is in the process of being modified as we speak. I am having 4 inches of stretch put in with about 5 inches of ground clearance. The guy that is doing the mod suggested that we do about a 5 degree rake to level the frame. I am not too excited about raking the frame as I wanted to keep it closer to a bobber, but after going over the design and numbers, without shortening the forks significantly, I need to have a small rake.

that 5 degrees is gonna put it in weeds by itself without cutting forks.all of that rake is gonna make corners a major pain for ya though!

I don't know, I think I am gonna have to beg to differ. I don't think 5 degrees is significant enough to significantly effect the handling or style. Look at the diagram below and you can get an idea for just how small a 5 degree rake is.



Post edited by: Kellen79_650, at: 2006/10/03 17:12

Kellen79_650 wrote:

I don't know, I think I am gonna have to beg to differ. I don't think 5 degrees is significant enough to significantly effect the handling or style. Look at the diagram below and you can get an idea for just how small a 5 degree rake is.

<br><br>Post edited by: Kellen79_650, at: 2006/10/03 17:12

the diagram shows that after the rake was done, LONGER forks are used...

Post edited by: caffcruiser, at: 2006/10/03 21:18

Obviously the diagram shows longer forks, but that is not what the issue is here. The issue being discussed is what a 5 degree rake actually looks like.
Post edited by: Kellen79_650, at: 2006/10/03 18:13

Post edited by: Kellen79_650, at: 2006/10/04 12:04