Fork Upgrade on a Budget (Custom Shim Stacks)

I was disappointed in my 1991 VFR’s forks. As with all VFR’s, it had a lot of dive to the front end and rather unresponsive in the twisties. I wanted to re-spring and make my own shim stacks. So, here is what I did.

1. Installed straight rate springs from SonicSprings. For my weight this turned out to be 1.0 kg/mm. The guys at Sonic are great! They have software like Racetech to pick the appropriate spring rate and they have great customer service. They were $20 cheaper than Racetech and they will even swap you springs (free of charge with prepaid return shipping if you want to change spring rates). The resuts on changing spring rate was dramatic. No more front end dive and no major change in harshness. This upgrade alone is nice and worth every penny of the $90 I spent.

2. Tore the forks down and rebuilt my shim stacks as illustrated below. I listed the stock shims and the new shims. I made a rather light compression stack that sucks up the bumpy stuff but still has enough firmness for the slow speed damping events. I also stiffened up the rebound with 17 x 0.15 shims. The results were impressive. The fork is very plush on the freeway and feels like it is nailed to the pavement in the twisties. Recetech claims that they get superior results with high flow custom valves. The Showa valves really are not that restrictive. I think my set up is probably very close with zero dollars out of my pocket. Also, this was surprisingly easy to do. I had a friend help me with the shim design and he also cut new shims for me. There are a lot of shim set ups on the web and you can buy assorted shim kits for less than $50. Your local dealer/shop may even be able to hook you up with a few shims.

I have a few good reference on how to disassemble and reassemble the fork and shims. I can email these if anyone is interested.

One note is that Ohlins and Traxxion like to use a preloaded compression shim stack for superior feel. This will be my next experiment, if I can get my hands on the needed ring shims. My friend has ordered a punch set to cut these.

Stock (compression)

(5) 17 x 0.10 mm
8 x 0.23 mm clamp

New (compression)

17 x 0.10 mm
(2) 11 x 0.13 mm
8 x 0.20 mm clamp
(2) 11 x 0.13 mm base


Stock (rebound)

(10) 17 x 0.10 mm
8 x 0.20 clamp

New (rebound)

17 x 0.15 mm
17 x 0.10 mm
17 x 0.15 mm
17 x 0.10 mm
17 x 0.15 mm
17 x 0.10 mm
17 x 0.10 mm
8 x 0.20 mm clamp
11 x 0.41 mm base



Example of an Ohlins or Traxxion preloaded compression stack.

(preloaded compression)

17 x 0.15 mm
17 x 0.20 mm outer ring (14 mm ID) with a 14 x 0.15 mm inner ring
(2) 17 x 0.15 mm
10 x 0.2 mm clamp

 

Dude, I would not suggest using a punch to make valving shims. The shims need to VERY flat with no raised bumps or edges. I doubt you would even be able to get close with something at home. Shims are not really that expensive and are readily available through RaceTech, Traxxion, etc, etc. Don't skimp here or your results will suffer.

 

Jamie,
Your absolutely right! You need a perfect surface and edge on the shims as well as the correct material. My friend did not cut these at home. He is a senior engineer in my engineering department. These were professionally made and are perfect!!

Tim