Suspension modifications, F800ST and others . . .

Inspired by CycleRob, this section is devoted to all flavors of the F800.

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CycleRob
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Suspension modifications, F800ST and others . . .

Post by CycleRob »

Well, I finally installed the Z-8 rear tire, while keeping the not-yet-worn-out Z-6 on the front. As expected, the racebike handling went away, requiring a suspension adjustment like front and/or rear preload settings. Being that it now was reluctant to corner as eagerly as before, I raised the rear preload to near maximum, an additional 2 turns to see how much of a change it would make. That's making the easy shots first. Adding more rear spring preload very very slightly steepens the front fork rake angle and reduces the steering axis trail, both of which make cornering easier - - with near zero effort. Riding the bike showed only a small improvement . . . so . . . the front fork tube height had to be readjusted, after returning the rear preload to it's optimal static sag setting, 3.0 turns away from the maximum preload stop. Front fork tube height IS the only remaining proper readjustment for my bike as modified because the front fork static rider sag is already near it's maximum 35mm, eliminating the reduction of internal preload spacers (increases static sag) as an option to change the suspension geometry as needed. Most of the time, some suspension shops will just use the font fork's preload adjusters (not available on the non-adjustable F800ST) to lower the ride height of the front end. There are negative consequences to doing that if the rider sag becomes excessive (like 45mm). In that case, riding fast thru a curve that crests over a hill that drops off elevation quickly will have the suspension going to full extension, the geometry temporarily transforming your bike into raked out chopper, and in the process scaring the CRAP out of you as your bike suddenly wants to go wide . . . off the road . . . into the woods. Definitely a safety hazard nobody wants to be responsible for. THAT's why the good shops* insist on taking all the time needed to optimize the settings of the F/R preloads, rider sag height, compression/rebound damping and finally the front fork tube height and even the rear shock's overall length adjustment (if provided). Bikes with bodywork and non adjustable suspensions make it more difficult and time consuming, especially since those preload adjusters can be quickly used to temporarily indicate with a test ride the magnitude of the tube height change needed. Fine tuning these +/- settings by trial-n-error is a virtual impossibility, especially if nothing is known about how EACH adjustable parameter changes the handling and stability under different road conditions and riding style (street/race/cruiser). There are even special suspension settings for the shop's racebike for racing in the rain, that actually make the bike easier to ride fast and better able to recover when a 1 or 2 wheel slide occurs (it will). Some of you guys know what fun it is to ride dirt bikes in 1 or 2 wheel controlled slides, especially so if your dirtbike was properly set up.

These are the adjustment compromises most suspension shops know, specifically, what NOT to change when "adjusting things", so new and different undesirables are not added on. This is why it is nearly impossible to do an optimal suspension adjustment remotely, using the internet. It has to be hands-on, with the tools, fluids, parts, helper(s) and time to do so. Once you understand the simple basic rules, it becomes easier to:
1-Ride the bike thru sharp curves, bumpy corners and squeeze hard on the front brakes, or letting go of the bars and staying on course while cornering.
2-Note responses/anomalies and make assessments. :-k
3-Make the many suspension changes (or front-rear wheel alignment) needed from the "as received" setup
-and-
4-End up with the correct settings on the 1st or 2nd adjustment session.

There are also consequences to raising the fork tubes TOO high:
1--front fender or fork seals may hit the lower fork tree before the forks bottom out. #-o
2--the side stand will hold the bike too far upright (not enough lean-over). [-(
3--putting the bike on the centerstand will be much harder. :oops:

After installing the RaceTech Gold Valves in my 2009 F800ST, the stock 12mm tube height (the part sticking above the upper fork tree) needed to be increased to 15mm (obtained by the educated guess change-n-ride method) to alter the bike's willingness to corner with little or no handlebar counter-steer effort. I removed the left & right lower body panels to gain easier wrenching access to the lower tree pinch bolts with the hand ratchet and torque wrenches. The additional 2mm forktube raise is essentially the normal minimum/maximum tube height increase for reluctant handling that is just a little bit "off" from it's ideal setting. This varies from different make bikes, as we found out trying to get a Suzuki 1200 Bandit to corner easier (without being forced to). In that case we raised the tubes about 20mm with no apparent improvement at all, whereas half that distance usually results in a dramatic, even an excessive "improvement". The solution was in extending the rear shock's overall length with a mounting point spacer washer. That too will cause problems with the drive chain occasionally rubbing the top of the swingarm, a larger variation in chain tension as the suspension works AND the bike leaning over farther on the sidestand. Despite those negatives the owner decided he liked the improved handling much better.

When I change the worn out front tire to the new Z-8, I'll likely have to change the tube height setting again to dial it in. Oh well.

Definitions:
static rider sag
= compression amount in mm with the rider in the normal riding position (feet on pegs, hands on the grips, in full riding gear)+ bike at the balance point. Measured by fork compression axial distance of the tube/slider connected to the front wheel -and- the vertical distance the rear axle moves, both from full their "off ground extension" dimension to the compression distance with the rider on board. We take 2 measurements, a push down and let go settling point AND a lift up and let go settling point, then average the 2 readings to eliminate friction induced error.

! important ! - - - Be sure that job 1 is that the F/R tire pressures are where they belong before doing anything.

* Retired permanently and financially from our shop Aug 2005. Click on "suspension" and then "directions" in top menu header for more surprising info.
Last edited by CycleRob on Sat Sep 07, 2019 4:31 pm, edited 1 time in total.
`09 F800ST

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Re: Suspension modifications, F800ST and others . . .

Post by sweatmark »

Rob, what's your long-term review of the emulators?

I wish my local suspension tuner had something for the F800S/ST forks, as he can CNC damping parts.

Tough to find a good setup for my wife's F800 when we both ride it and I weigh 100 lbs more!
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Re: Suspension modifications, F800ST and others . . .

Post by cburgess594 »

How about the "pinging" issue? :-k
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Re: Suspension modifications, F800ST and others . . .

Post by CycleRob »

Pinging? You've got the wrong post.

sweatmark, My long-term review of the emulators is that they work and well worth the time and money. The RaceTech Gold Valves are "catrridge emulators" but they mimic very basic ones. That's OK and an improvement over stock. If you do the 2--4 hour installation yourself the total cost (including fork oil) for me was under $150. For your weight, heavier springs will be needed, but not for your wife. The suspension shop should select the parts and settings for the weight of the rider using the bike the most. It would be unfair to both of you to "mid set" the suspension so both could ride the bike because of the 100 lbs difference (that's a lot).

The Gold Valve's compression and rebound orifices are non adjustable and determined by the RaceTech engineers after testing actual F800ST forks on shock dyno testing machines. All that is needed is for the installer to set 2 bolt turns of blowoff spring preload and tighten it's locknut. Then the stock damper rod has to be drilled, deburred and cleaned (to make the stock metering holes dysfunctional) then reinstalled per instructions. Finally, adding 15W right oil up to 120mm from the top (full compression, GV installed, no spring) then installing the spring, thrust washer, 10mm shorter spacer, end cap and wire retainer completes the job.

The most important thing Gold Valves provide, besides better calibrated compression/rebound performance is uniform high speed compression blow-off. That is, when the front wheel hits a very large bump swell, the Gold Valves can maintain the same soft resistance to oil flow (generated from the bump) even at very high speed (high flow) rates. That's something the stock valving, by design, cannot do. What that means is you will not be launched off the seat when the road gets nasty.

Out on the road the bike just seems better behaved and devoid of drama going thru bumpy, decreasing radius curves - - the one true test of any suspension setup that separates the winners from 2nd place. Other tests are maximum front braking stability and uneventfully negotiating an over-the-rise-fast-dropoff-curve at speed, where the front and rear suspensions will EXTEND EQUALLY, follow the road and then EQUALLY ease the bike back on to the ride height depression without any drama! For that to happen, ALL of your suspension parameters have to be correct!
`09 F800ST

Member since Sept 10, 2001

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