Front fork dive?

[CycleRob]

Yes, I read all the complaints about the excessive front fork dive under braking, heavy or otherwise. I knew the easy/inexpensive solution to that problem would be to add more fork oil to each fork tube, raising the oil level. When that occurs, the compression ratio of the top air space increases, emulating a stiffer spring. Then I got my `09 F800ST and was surprised at how almost normal it behaved on a heavy front brake squeeze at speed. Yes, it dives about 2.5" of it's 5.5" of full travel under very heavy front braking. That does not seem excessive. How can that be? Check the fork oil level! It's very easy if you have a CenterStand and a small thin screwdriver to pry out the circlip. I was really surprised at how little spring preload there was on each fork cap. Two thumbs can compress the fork cap and one can hold it down for circlip removal. As the picture below shows, there was no danger of rocking off the CenterStand with the forks fully collapsed.

http://i142.photobucket.com/albums/r87/ ... apRemv.jpg
http://i142.photobucket.com/albums/r87/ ... pParts.jpg
http://i142.photobucket.com/albums/r87/ ... ilLevl.jpg
http://i142.photobucket.com/albums/r87/ ... MG9963.jpg

The industry standard method to set or check the fork oil level is with the spacers and springs removed with the fork tube at full compression. I found the oil level at 120mm. Wanting to make a change, I set it to 110mmm. With the spring inserted for the reassembly, that brought it up to the bottom surface of the upper tree, virtually a hydraulic lock condition. That means the fork cannot compress enough to bottom out on the hydraulic stop, effectively reducing full suspension travel . . . . not good. I reset it back to 120mm.

The 120mm oil level setting is very high for a stock bike with 5.5" travel and I suspect BMW raised it recently to squash any and all fork dive complaints. It works for me. Now I'm curious about what the oil level is set to on those older F800 bikes.

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[Buckster]

cyclerob,
Could you have swapped out the spacers for some longer ones to help out brake dive. I put some longer ones in on a Yamaha I had and it helped a lot. It also helped out in cornering as well.

[CycleRob]

Adding more spring spacer preload raises the front ride height. That will make the bike want to go straight like a chopper and reluctant to corner unless the rear ride height is also raised. The stock .830kg/mm springs are OK for my rider weight, so no change is needed there. I've planned the suspension setup and will have to train Ann on taking the measurements -after- I install a set of front fork Gold Valves . Handling is fine as is, so that's why I know it isn't far off. The Gold Valve addition takes away the stock suspension's small fixed orifice compression damping and adds an internally adjustable high speed blow-off progressive rate poppet valve. That allows the front wheel to track over the bumps that otherwise would cause wheel hop in a corner or huge bumps that knock you off the seat on a straight-a-way. After participating in the installation of at least a dozen of these GV's on SV-650 track bikes and getting glowing owner feedback, I can say with certainty the change in suspension performance is absolutely worth the investment, when set up properly - - - which unfortunately for the average rider, is a rarity.

If you live near Washington NJ (USA), you can have this work performed in just such an experienced sportbike street/race service & suspension setup shop by Pappa John (WCW website in profile). Being retired and gone, I do not profit in any way from this referral, but my brother PJ and nephew Ron do. In a lasting way, so does the customer, when the bike is rider specific dialed in.

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[bobw]

Many folks use the spacer to adjust sag when there are not adjusters present. Too much adjustment in this way can have a negative impact on travel/harshness and it is then better to look at proper weight springs, oil and/or valving. Both front and rear sag should be properly adjusted together. It does raise the height, but only as it pertains to sag. YRMV

Cheers

[sweatmark]

First impression during my F800S test ride: weak fork springs, lost of fork dive.

Second impression via long ride back home after F800S purchase: not badly sprung, a good balance of spring rate and damping for normal roads, maybe too wimpy for trackday use, but really not bad. I was making the comparison beween the F800S and my Rockster, our former Roadster, and my current Buell XB with custom suspension tuning (e.g 0.95 springs and rock-hard damping) for forks and rear shock.

If I was riding the F800S on a trackday, I'd load the forks and shock up as much as possible. There's some rear end chatter in turns during trail braking, but the bike doesn't have the benefit of slipper clutch and DOES have mucho compression braking. For general purpose riding, the OE suspension setup is pretty good... and that's "big ol' me", while my wife (@ 100+ lbs lighter) probably has a perfect F800S suspension setup right out of the box.

We'll see. If needed, our local sportbike suspension expert can be called upon to work his magic.

[CycleRob]

sweatmark,
We spoke on the phone this evening (1st time) about the new-2-her F800S. The suspension magic you're talking about is a set of Race Tech Gold Valves and maybe 15wt fork oil and the correct preload and rebound settings. I doubt heavier springs are required for her weight. I'm also really curious what the 2007 model bike has for the fork oil level, since my bike doesn't exhibit the much complained about radical fork dive when hard on the brakes (with it's 120mm oil level). Since her S model has a centerstand, the fork cap and spring removal is real easy.


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[sweatmark]

Rob, good talking with you about F800 tech.

I'll pop the fork caps when time allows and measure the oil level.

As discussed, the OE F800S suspension setup is probably ideal for Mrs. Sweatmark's use, but I'd need to beef up the forks and shock to better suit my, well, beef. My local suspension guru Dave does great work and machines his own components, including valves. If I was to find myself with another F800, then I'd certainly have him tune the forks and rebuild my Penske shock for the back:

http://www.gpsuspension.com/

In fact, he'd probably be able to use the guts from one of the Buell/Showa fork sets he tuned for me.

Can't wait to get working on some electrical add-ons for my wife's bike. It's a great machine. Wonder if she's ridden it while I've been across the country?

[CycleRob]

About the suspension . . . . I just got around to testing/setting the front & rear rebound settings. The rear shock rebound adjuster is supposed to have clicks, but if there is a click, it's just too subtle. I visually counted the number of quarter turns indicated by the tick mark on one of the 3 knob lugs.

Making the easy shots first, I tested the rebound adjustment by pushing down on the rear rack with the bike at the balance point. One person can do this alone. Start with the triangular rebound adjuster knob at 2 turns out from screwed in lightly to the stop. Tilt it up off the sidestand, holding it at the balance with my right hand, then pushed downward hard and quickly with my left forearm on the rack's rearmost portion. You have to terminate the down push the instant the downward travel bottoms out. Observe what happens when it tops out after you let go. If it bounces, turn the adjustment in a quarter turn tighter and repeat the push down. You want the point where it rises the quickest without bouncing or rising too slowly.

That correct adjustment point on my 2,300 mile stock rear shock was exactly 1.25 turns out.

Too bad adjusting the front fork's way-too-soft rebound damping will require taking them off the bike for a thicker fork oil exchange. Judging from the way it pogos on the top out after a push-down-n-release, I'm guessing I'll be replacing the 10 wt oil with 20 wt oil. It will be combined with the GV installation when they get here. Then it will be dialed in right enough for the track-like roller coaster North Georgia mountain roads, just 25 miles (40.2km) away. I can't wait!

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[sweatmark]

I'm going to inquire next week about the possibility of GP Suspension transferring the internals from a set of Showa Buell forks to the F800S. Might be impossible, but would love to increase the F's fork damping and adjustability. If it's so easy to pull the springs and spacers, then I could swap 'em from OE to some 0.95s for trackday use.

Rob, is the F800 fork an old damping rod type or "cartridge"?

[sweatmark]

Speaking of forks...

Rode our, er, Mrs. Sweatmark's F800S up to Portland today via some curvy side roads. Very impressed by the bike thus far. Upon my return and post-ride inspection, discovered some oil drip on the left side of motor, LHS brake caliper, and then the source: blown left fork seal. Unpleasant finding on the 2nd real day we've owned & ridden the S.

The seal might be a warranty item, or a perfect excuse for some custom suspension tuning. Will start another thread to capture the info.