FRONT FORK Tuning

[Rick G]

My experience has been positive, with air assisted forks. My valves were salvaged from old motorcycle inner tubes . If you cant find these where you live , I will send you a pair!

[VisionMeister]

Humber,
there is much useful information here about fork tuning and chassis stiffening, but I think your main problem is mismatched and maybe old tires.
When I look at F17 Dunlops I think cruiser tire, not for 170 kph sweepers. Also with that type of tread it is much more vulnerable to uneven wear on the small tread blocks.
I couldn't find K51 tire reference... I did find K510 reference for Kawasaki ZRX400 sport bike for European market. A sport tire rear with a cruiser front is bound to have problems when pushed.

I have tried many tire combinations and found that generally if you have a matched set of 90/90-18 and 110/90-18 or 100/90-19 and 120/90-18 you will have good handling... given that bearings are good, fork oil is correct level rear preload is set correctly.
I recently tried 80 series tires front and rear and thought they were ok to start with, but they cupped quickly and did not have as much cushioning from bumps and tar gaps etc. due to the lower profile. I won't be trying them again, I think they are wrong for our narrow rims.

Your bike is more stable with your girlfriend on the back because the extra weight lowers the rear which in turn kicks out the steering rake giving more trail. This same effect, of varied steering rake, can be made with adjustments to rear preload and front fork height in the clamps as well as front spring weight (or preload) and can be effected by tire profile/ aspect ratio. The Vision's steering geometry is very sensitive to minor adjustments here.

My bike sits low in the rear due to an aftermarket shock. It steered very slow (and stable) until I figured it out and lowered the front to compensate for the low rear height. I had run progressive fork springs for years, and just recently put the stockers back in because many of the backroads I ride are rough and I wanted more suspension compliance.

[Rick G]

VM  Humbers post is dated in 2002. He sold his XZ550 in 2005  or 2006.  He bought an Opel  , which had more problems than the XZ!!  He married his girl friend on 2010 or 2011.  He stops by here about once a year.

[VisionMeister]

Oh, well better late than never. I hadn't paid any attention to the dates other than this string had come to the top with recent comments.
Now it is definitely old tires.

[supervision]

  Oh kay Riku Im just going to start with one leg at a time.   Hey meister kind of early isn't it?

[supervision]

  Rick, I did the same thing on the caps of our IT125H just drilled the thru the jam nutted a tube stem now I see on the fork tube ref page that it is the same size tube as our vision so now i can try it out. easypeesy

[motoracer8]

 In my opinion, the worst thing about the front forks, other than them being 35mm damper rod forks, IS the crummy rear shock.

[The Prophet of Doom]

In my opinion, the worst thing about the front forks, other than them being 35mm damper rod forks, IS the crummy rear shock.

You can stop it from being a damper rod fork by adding racetech cartridge emulators, and rear shocks are available from every major
shock manufacturer.  Others have made used R1, Triumph and other shocks fit with some modifications.

[Rick G]

There 37 mm forks not 35..Not that it matters.

[The Prophet of Doom]

There 37 mm forks not 35..Not that it matters.

35mm !! :police:.  It matters if buying racetech emulators, fork braces, seals, headlight brackets, gaiters, clip-ons etc. 

[motoracer8]

 Get those calipers out Rick, or maybe you need a new pair of cheaters, the forks on my 83 Vision measure 34.95mm.

I upgraded the suspension on my Vision years ago, I started with a Hagon rear shock that made a big difference.  I installed the racetech imulaters shortly after, I messed around with spacers and springs and what I ended up with was the OE springs and 60mm spacer plus an additional 1/2" spacer plus the gold valve body is about 19mm. That's 92mm, or 3&5/8" total preload, that gave me about a inch and a quarter of sag and no bottoming. 10w oil works for the rebound, two turns of preload on the compression valves works for me.

As with all damper rod forks the imulater valves are a great improvement, I've installed several over the years with no complaints.