5Th Gen Suspension Modifcations

[Terry]

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.vfrdiscussion.com/forum/index.php/files/file/219-fork-gold-valve-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.

[KevCarver]

Next thing to try is to shim the rear mount point a bit. I too have the DMr 929 built to 5th Gen height. I shimmed it 5mm between the top of the shock and the frame. Any more and there wouldn't be enough threads to fully engage the nut. If you know you want more rear height, the easier way is to have it built taller to start out. But I didn't do that.

Net result is that it feels more biased on the front end, and turns in quicker.

[Terry]

The CBR929 shock I bought from Jamie was already longer than stock (by 5mm or so IIRC); the rear tyre is only just off the floor when the bike is on the centrestand. I also have the forks slid down by about 6mm, and the preload cranked out which makes for a nice turn in and line holding. The standard suspension also gave me that, because the front springs are pretty soft so the front is already riding low.

[KevCarver]

That's about where I am with my set up. I have the front end converted to SP1 though, and my handle bar controls have limited my front lowering. On the C stand, I can't spin the rear unless it's worn nearly to the cords, front too. I have to find a high spot to park my bike in order to spray the chain on trips.

[JamieDaugherty]

I think I might have found something that will help you: in the third picture of your original post I can see the rebound valve piston is installed backwards! That will definitely screw things up for sure. I would suggest getting that fixed and go back with the stacks I originally sent and I think you will be just fine.

Give that a shot and let me know what you find out.

[Terry]

Well-spotted Jamie, I did realise the valve bodies were backwards in the photo, but they were installed the right way up, with the larger ports/recess against the check valve shim and the small ports against the shim stack.

Yesterday I succumbed to temptation and visited a local wrecker, and picked up a set of slightly bent VTR1000 forks. I cannabalised these last night and after checking the parts were straight, installed the fork caps and rods into the VFR cartridge tubes, so I now have the ability to adjust the rebound damping externally. This is a really easy switch, the only change I had to make was to shorten the fork spring spacer by 21mm to match the longer fork cap.

There looks to be plenty of adjustment available over a couple of turns of the screw, from not much damping to "wow that is slow to extend"! Before the eagle-eyed Mr Daugherty points it out, yes the locking nuts are off in the photo, and the preload adjusters are not set the same. The 21mm difference was measured with both adjusters fully screwed in.

I now also have the lower fork legs from the VTR in good shape, so if I get tempted I could now ditch the linked brakes and slap on some 4-piston VTR brakes. I'm not sure whether I will do that as I really like the LBS, I've never ridden a bike that felt so stable under brakes, and with EBC HH pads up front there is plenty of power.

[Rush2112]

CBR600 F3 fork caps & rods also fit the 5th gen forks and allow for rebound adjustment... I'm pretty sure the last year of the F2 also has these parts that will fit the 5th gen.

[zupatun]

I went the route of cBR F4i forks, lowers and internals...0.95 Online springs and new comp and rebound shim stacks...lots o fun! Also de-linked the brakes and I like the feel of that better than linked systems...

Matt

[Rush2112]

I went the route of cBR F4i forks, lowers and internals...0.95 Online springs and new comp and rebound shim stacks...lots o fun! Also de-linked the brakes and I like the feel of that better than linked systems...

Matt

Did I get my CBR F? 'ing numbers mixed up? Sorry, it has been a while.. is it the F4 that fit the 5th gen and the last year of the F3?

[Terry]

F4/F4i has 43mm forks and I assume are a straight swap on a 6th gen. F3 and the VTR use 41mm so can be used on the 5th gen.

Sent from my iPhone using Tapatalk

[rangemaster]

Terry, Not to put to fine a point on it, but what do you weigh? I'm going to do my forks some time this winter and I'm trying to figure out a set up for me (135#) Thanks.

[Terry]

Depends who you ask!

"About" 80kg or 176 lb.

0.9 kg/mm springs are recommended by RaceTech and were what JD supplied.

I took the first ride yesterday with the modded forks and I'm really happy at last. Having the VTR rebound adjusters is the icing on the cake.

Sent from my iPhone using Tapatalk

[Terry]

I gave the bike a really good work-out yesterday on my favourite (and challenging!) local roads. The front end is now pretty much faultless, it doesn't bottom, jolt, wobble or bounce, no matter what I throw at it. The bike on the whole has a great sure-footed feel under acceleration, brakes and cornering, and I can really concentrate on where I want to go rather than what I am riding over, which makes for a more relaxing ride at a greater speed. The footpeg feelers took a bit of a pasting at times as well, in spite of the longer shock and stiffer springs front and rear.

I do like the ability to "tune" the rebound damping using the VTR adjusters, but I have stayed with 1 1/2 turns out, which "felt" right when I was bouncing the forks before re-installing them, and turns out to be really good in use as well.

So my recipe for 5th gen front suspension happiness:

Compression: DMr or Gold Valve body, C32 valve stack (2 x 0.15 x 17mm shims plus the supporting shims)

Rebound: Stock HMAS 4-port piston, 6 x 0.15 x 17mm shims plus clamping shim

5-weight oil, 120mm height from fork top, fully compressed, springs out

VTR rebound adjuster 1 1/2 turns out from full in

0.90kg/mm forks, 59mm spacer, minimum preload.

I hope this info is useful to some of the other folks here.

[VFRMAN]

Great job on getting the suspension set up right for you Terry, without starting another thread what's the consensus on just replacing the rear shock, hagon,showa,wilbers? I might just change the fork oil, I'm happy enough if the bike is freshened up,not going to go to deep into suspension tuning for basic street riding,thanks for any advice.

[KevCarver]

Original Poster and I have OE 929 shocks made by Showa. They are cheap on the interwebs. They are replacing OE VFR Showa shocks. They key is that they are revalved and resprung to the rider's spec's. The reason to go with CBR over VFR is that they have additional adjustments.

You could get a great deal on an Ohlins that is way oversprung for you and it would do you no good.

You'd have to find a suspension builder in the UK to rebuild something for you. Shop around, maybe Jamie Daugherty with international shipping is still the best price for you?

[rangemaster]

Thank you for the final specs that you are riding with, its a big help.

[Terry]

Thank you for the final specs that you are riding with, its a big help.

You are most welcome. With amount of trial and error I went through I feel I have a bit of ownership in the final outcome.

[Terry]

Great job on getting the suspension set up right for you Terry, without starting another thread what's the consensus on just replacing the rear shock, hagon,showa,wilbers? I might just change the fork oil, I'm happy enough if the bike is freshened up,not going to go to deep into suspension tuning for basic street riding,thanks for any advice.

Hi Saoirse

Just like Kev says above, I bought a CBR929 shock from Jamie Daugherty who runs Daugherty Motorsports http://daughertymotorsports.com/vfr800.html in the US and is a bit a of a VFR modification guru. Jamie buys up used CBR929 shocks, modifies the shock with the correct spring weight for the rider, and rebuilds with new shims and seals. More importantly he also machines the shock top and fabricates an extension that bolts on, because the CBR shock is too short for a 5th gen otherwise. There are other ways to do this using a modified top shock mount but Jamie's system is very elegant and well finished, and plug and play. The cost for this is US$420, which seems pretty good value when something like an Ohlins would be three times that. The CBR shock gives me rebound, compression and preload adjustment; you'll get the same degree of adjustability from a high end Ohlins or Wilbers I think. You can also rebuild a CBR shock easily, unlike the VFR which is a sealed unit. I had an Ohlins shock on another bike, and honestly for road riding I doubt there's any real benefit to be had (but they are awfully pretty!).

The modified CBR shock is also 5mm or so longer than stock, which lifts the back of the bike and gives a bit more ground clearance and improves the front end geometry making the bike turn in a little quicker.

As you can probably tell from my enthusiastic posting, I am really pleased with the transformation of my VFR; I have ridden the 8th gen and while it felt "newer" in the gearbox and clutch, I much prefer the way my 5th gen works now. If you start down the suspension mod path, be prepared to go the whole way. Mechanically there's nothing complicated about the procedures, you can immediately feel the improvement, and I hope you'll get the same sense of satisfaction as me.

[Cogswell]

Thanks Terry. This has been a very informative and helpful series of posts. I'm looking forward to doing the same over "parking season" here in the north.

By the way - it occurs to me that while we up in the north are settling in with the big chill, summer's coming in New Zealand. When I was there I thought all those twisty roads would be great riding. (Just curious - do you ever get to the South Island to ride?) If you happen to post up a ride report pr two those of us bound by the chill would surely love to see them! Cheers.

[VFROZ]

Just curious, how much was the VTR innards in Australias most eastern state?

And, do you know what spring rate JD used on the rear?

[Terry]

I paid NZ$200 ( probably equivalent to about AUD40!) for a pair of VTR forks; one stanchion was bent and fit for the bin and the other I'm selling on our Ebay equivalent, but I the lower legs are in good nick, and likewise I now have a full set of bushes and seals that look pretty unworn. How does that compare to the West Island?

The spring that JD supplied was 1100lb-in (I must be a fat bastard, looks like 19.64kg/mm), 6" long, 2.25" ID. Theres also a spacer fitted to the spring to fit the shock nicely.

[Terry]

Thanks Terry. This has been a very informative and helpful series of posts. I'm looking forward to doing the same over "parking season" here in the north.

By the way - it occurs to me that while we up in the north are settling in with the big chill, summer's coming in New Zealand. When I was there I thought all those twisty roads would be great riding. (Just curious - do you ever get to the South Island to ride?) If you happen to post up a ride report pr two those of us bound by the chill would surely love to see them! Cheers.

Yep we are blessed with some cracking roads. You are right that the South Island has more than its fair share and I have driven them for work quite extensively, but sadly have never managed to get there on two wheels. I live in the North Island, and getting to the SI involves about 8 hours riding plus a 3 hour ferry ride, so my riding consists of basically tearing around within a 200km radius of home. I'm lucky enough to live right at the edge of the city so the twisty country roads are only 5 minutes away. My ride reports would be a bit dull...rode for a bit...stopped for a bit...rode a bit more...got home.

We're passing through unsettled spring weather right now so it is generally a bit gusty and wet, but come Feb through May or so our conditions are just about perfect. I've found adding an action cam to my rides has been good fun as I can edit down to just the really good twisty bits and relive those happy moments over again. Could be a good fix for the Winter Blues that you all seem to suffer from. I ride right through winter here but it never gets particularly cold, 45-50F would be a bad day for us. Old age is creeping on for me though and the circulation in my hands just sucks, so one accessory I added (which I never thought I would need) is a set of heated grips.

[Mac Morgan]

Good piece on suspension. Been riding a 98 since new and now have 2. Installed RaceTech valves in my VTR a few years back but found the combination of .95 springs and over-aggressive valving too stiff for our back country roads but now I have a complete VTR fork set with the RaceTech valving to play with.

Mac Morgan

Hockessin, DE.

[VFROZ]

A bit of an old thread, but I thought I would add my two bobs worth on my own findings.

Thanks for the post Terry, it was the inspiration to work on my 01.

I more or less ended up some where near your own conclusions, with some small changes.

I weigh 75kg, but I do a lot of two up and long trips, so I went for 0.95 springs as a bit of a compromise.

I already had the DMR rear shock, and after a lot of adjusting, I think I have it as good as its going to get, which is well above what the original could ever achieve.

I now have 1.1mm bleed hole in my compression high flow pistons, and 1 x 0.15-17 + 2 x 0.1-17 shims, plus supporting shims as Racetech guide.

My stock rebound piston has 5 x 0.15-17 shims.

I use 7w oil as I didn't like the 5w action, I think there is too much leak through the top bush in the cartridge, and found 10w too heavy.

I've also raised my oil height to 110mm, but will drop to 115mm on my next experiment.

I've dropped the forks back to standard height, as the bike handles so much better now and its so predictable and composed.

By far the biggest change has been to pitch control, and the ability to soak up bumps and ripples mid corner without affecting your line.

The near complete absence of diving under brakes is a major plus.

I agree on the statement that you can now concentrate on the corner, and not the surface.

The best part is that it handles just as good loaded up and with a pillion.

And this is the best part of the VFR, I can take it out with the boys on a Sunday morning and keep up with their latest toys.

I can load it up and put the wife on the back, and head off for a long weekend at a great pace over any surface.

Or I can take my daughter to the shops for a coffee all on the same bike.

How good is that?

Last fork rebuild took me 2 hours, a bit messy but worth it.

What are you all waiting for? Get to it.

You will never look back.

PS: I will also buy new high speed rebound pistons and add them to the mix.