USD Forks

Simple solution is to fit some offset risers.
 

Yes, that would be the most basic way to fix the issue. But I'm really trying not to change anything more than I absolutely have to. I want the general look and feel to remain the same, and that includes the handlebar position. 

Perhaps you should look at getting a quote to replicate the stock yolks the width you need and with the correct sized fork openings and using the stock stem (and with a "step down" if required for the fork adjusters) ? this way the ignition switch, instrument mounts, bearings etc will all be as stock

Stereordinary wrote:

Yes, that would be the most basic way to fix the issue. But I'm really trying not to change anything more than I absolutely have to. I want the general look and feel to remain the same, and that includes the handlebar position. 

In that case you have not much choice except for the stepped yoke option.
You could always have fork extensions that replace the top caps but have the preload adjusters etc recessed so that they don't protrude above the top yoke.
I had a set like that which came with the ZX7R forks i'm using but it was tricky getting to the adjusters so it was one of the reasons i machined most of them off .
The extensions were actually welded to the original caps so not a lot of machining to make them..

Before.
   
During.
 
And after.
 

Wookie58 wrote:

Perhaps you should look at getting a quote to replicate the stock yolks the width you need and with the correct sized fork openings and using the stock stem (and with a "step down" if required for the fork adjusters) ? this way the ignition switch, instrument mounts, bearings etc will all be as stock

For all intents and purposes, that’s what I’m trying to design myself, figuring that if I do the CAD work myself, I’d save money over paying someone else to do it.

Easier said than done though, obviously. I suppose a real professional at this could maybe 3D scan the original yoke to save time, or have some other means of reverse engineering that I’m not able to do.

Back to the axle spacers, I think I can actually make the ones I already had made up work, but there's a weird problem. It turns out the counterbore on the left ZX6R fork is shallower than the right fork. Photo below.

It's basically a full millimeter deeper on the right side. In a way I'm relieved, because that means almost all of my other calculations and measurements were correct. Hooray! But I didn't think to measure both sides independently when I originally started, I measured the right side and then just mirrored it to the left. 

So ideally my solution would be boring the left side that one millimeter more to match the right. I can't find a tool to do the job though, and finding a reliable, quality machine shop in my area has so far proven impossible. Anybody got any ideas?
 

The depth of the counter bore doesn't matter and neither does the length of the sleeve nuts ( as long as they don't bottom out on the wheel spacers ) they will still tighten and do their job and it's the wheel spacers that keep the wheel central.
You could either leave that side protruding 1mm or reduce the head height to match the other side.
Have you measured the depth from the bottom of the counterbore to the inside face of the leg.
It's likely that they measure the same but the casting is 1mm wider on the left .
 

Quick update. While I contemplated zed1015’s comment thoroughly, I checked and rechecked measurements and ultimately found that that 1mm difference was important and if not taken care of would bend the forks in toward each other. Rather than change my spacers, I liked the idea of having symmetry in the forks themselves. I searched for a long time and couldn’t find a tool to bore a 37mm hole, until I checked AliExpress. Less than $9 and two weeks later I had a hole cutting tool designed to cut a 37mm hole. It was difficult to get it to stay centered and I had to modify it slightly plus add a bolt and washer to help drive it, but I got there. So now I have spacers that fit the ZX6R forks and hold my original Zephyr axle and front wheel. Long ways to go, but feels good to make some progress. 

I feel like I'm still not getting all of this stuff about the rake angle, fork offset, and trail. I do get that an increase in trail means slower steering, and a decrease in trail means twitchier steering. But some of how you measure those things in the first place and how each one effects each other is still perplexing. At this point it looks like while I'm using forks that are about 30mm shorter, but compensating for 10mm of that by dropping the top fork, I'm actually increasing the trail by about 6mm. So how do shorter forks increase the trail? I would assume that would drop the front end down and make the trail less. 

 

What trees are you using ?

I’m designing my own. 

 

Are you using the downloadable calculator I posted a link to earlier in the thread ? Shortening the forks can't increase the "trail" as lowering the front steepens the rake and reduces trail (not by much though unless you have cartoon levels of rake - play with the calculator) If you use Zed's method to extend the forks 20mm along with the 10mm drop in your tree's you will be back to stock (with the original wheel) for rake. If you replicate the stock "offset" in your new trees along with the fork extensions then the geometry will be exactly the same as stock (you could increase the offset if you want to quicken the steering but probably best left stock if you are happy with how it steers)