I thought I would share my findings on tinkering with my 5th gen suspension. I bought the bike in well-maintained but totally stock form back in April this year. I fitted a DMr-modified CBR929 shock in May, and then in September I installed new fork springs and compression valve from DMr, plus modified the rebound shims. I'll admit to being a total do-it-yourselfer with this, as I have been messing around with bike suspension since 1983 when I used a number of 20 cent coins to pre-load the fork springs in my CB400N, thus making it the only time in recorded history when one of those bikes increased in value...
I had the shock in my VF750F rebuilt by a former racer, and when I got my second VFR700 I really went to town, with a Fox Twin-Clicker, PS springs and newly-invented Catridge Emulators for the forks. I blame Motorcyclist magazine for that, they ran an article on transforming the VF750 that way, so how could I resist?
I kept my Suzuki RF900 bone stock for a while but the modification bug was nibbling, and I ended up swapping my stock shock plus cash for a second-hand Ohlins shock from another forum member in Singapore, and then adding 0.95kg/mm springs and Gold Valves. I was ridiculously trusting, mailing my perfectly good shock to a far distant land in the hope that a stranger would send something back, but it worked out well. I had a local suspension expert rebuild the Ohlins (it had been very well used) and it was wonderful. The RF was always a pretty decent handler, but properly set up it was a demon on back roads, always a bit heavy steering but super-stable.
So the VFR was a bit of a blank canvas, but there was plenty I liked about it, with great fit and finish, comfy for me in the way the Suzuki wasn't, and in spite of leaping around on tired, stock suspension, a certain "rightness" about the way it handled.
The CBR shock has been a good improvement, to the point where when riding the back end works just fades from your awareness. I gave the bearings a good check over and as a credit to PO's they were like new, apart from that I have left the spring set where it came from Jamie on the 3rd position, and have the compression damping set at 1.5 turns out and rebound likewise at 1.5 turns out.
The forks have been a different story. The 0.9kg/mm springs are dead-on, I get just the right amount of sag and no bottoming, but I have not been entirely happy with the shim stack as supplied, and hence I have been fiddling (or wasting more time on that bloody bike as my wife might see it...). I've been looking for suspension nirvana where the bike soaks up every bump (even the big beastly ones) without getting kicked up, while maintaining steady composure, and so far I have rebuilt the forks seven times. The good news is that I have the process down to 80 minutes, including cleaning up!
For anyone who is interested in these things, here is what I have learned.
Firstly, the 5th gen fork uses very similar but not identical damper parts to earlier VFR's, and also to the 6th gen. Although the 6th gen fork is 43mm, it uses the same 20mm damping cartridge size as the 5th gen. Thus the combinations of shims and valve bodies that works well in one model will work just the same in another. This has become apparent as I have worked through changes to the VFR, because the same combination did the same job in my Suzuki RF900 (had I known this I would have swapped them over directly). Similar sized parts are also used in USD forks like the CBR954, so your humble 5th gen forks can damp just as well as fancy upside down forks, albeit without some of their other benefits of stiffness and external adjustability.
Secondly, there is a nearly infinite combination of compression and rebound shims that you could use, but in practice if you veer too far away from a "middle-of-the-road" set-up, they don't work nearly as well. The shim selection chart that RaceTech provide (available in the downloads section http://www.vfrdiscus...e-installation/) is pretty much spot-on when using a high-flow compression valve body such as a Gold Valve. I doubt that you could get similar results from the stock valve body as it is very restrictive to flow, so buying a new part is good value.
Thirdly, the compression, rebound and spring rate need to work together. If you use less compression damping, then rebound control becomes more critical, and dive and bottoming are more likely, so you can't really make these changes in isolation. And if you fit stiffer springs, you might need less compression damping and more rebound.
As well as the shim stack, there is a fixed orifice in each valve body that provides low-speed damping control and bypasses the shim stack. The 5th and 6th gen rebound pistons flow oil from a small port drilled through the damper rod just above the valve that drains out through the hollow of the shaft. When an adjuster from a VTR or similar is added, the end of the needle is acting on this circuit and allowing fine tuning of the low-speed rebound damping force. The 6th gen looks to have the same setup in the through the hollow shaft of the compression body, but the 5th gen does not, so any aftermarket part needs to have a single small hole (1.3mm) drilled through the wall of the valve body.
What the shim selection chart doesn't really convey is how the changes feel to the rider, and what the trade-offs are when you change shims, especially in the compression stack.If you add compression shims, you increase the high speed damping force. This means the fork does not travel as far on a bump, so more of the bump energy is passed through to the chassis. Less work is done by the rebound circuit as it has less spring energy to control. This does provide better feedback and stability, and provides a feeling of "control", but the trade-off is a loss of plushness as there are more jolts felt by the rider.
Be careful what you wish for though, because if you use less compression shims you lose high speed compression damping force, which means the wheel travels further through its stroke, and the rebound has more work to do. At an extreme, this is felt as a vagueness or looseness, and a sense of less control, and goes along with more fork dive and reduced stability under brakes.
For me the happy medium is to use 2 x 0.15 x 17mm shims in the compression stack, one shim was too loose, and three was too harsh. For the rebound circuit, I ultimately followed the RaceTech set-up as I found the DMr stack as supplied was too light when lighter compression valving was used. So my rebound shim stack on the standard piston now uses 6 x 0.15 x 17 mm shims.
I have tried both 5W and 10W oil, and found that the 10W was a bit too firm but provides the best feeling of feedback; on a track I think this would be great, less so on the street. I have also stuck with an oil level of 120mm from the top of the legs, fully compressed with springs out, on the grounds that you don't want to make too many changes at once!
So have I found suspension nirvana? Not quite, but having experimented a lot I think I have a better understanding of the gains and losses for each set-up, and I have found what I consider to be the optimum for the VFR. Looking ahead the only other change I could see being useful to a road rider would be to move to a low-friction oil seal, and If the parts could be had cheaply, adding an external rebound adjuster off a CBR or VTR. If I was focussed on track riding (and the VFR might not be the best bike for that) then a switch to a stiffer USD fork and brakes would make sense.
Sorry about the lack of photos; I always seem to have a liberal coating of fork oil on my hands when I do these changes.
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