Suspension help

[Windjammer]

Recently installed Wilbers rear shock and progressive springs up front. Overall suspension performance is MUCH improved all the way around. The bike is easier to ride and well balanced.

However, I still experience what I perceive as too much dive under braking. I used 10 wt fork oil in the amount specified in my Wilbers instructions, which was 90mm airspace. In the past (on other bikes) I never used anything less than 15 wt fork oil, but I thought this might be too heavy for the cartridge style fork in the FJR. As far as the settings on the top of the fork, I've got two lines showing and 14 clicks out (just centered the click adjustment)

Is there any way to decrease fork dive under braking without upsetting the applecart too much? I like the suspension now, except for the dive, so I don't want to make it harsh in the process of fixing the dive.

Suggestions? :huh:

 

[twowheelnut]

Adjust your compression, too. I also use the rear brake most of the time, too. Helps a lot with the dive. Crank in another round of preload, too - you can always back off.

 

[jestal]

This is partly why I ditched the Wilburs progressive fork springs and went with straight rate RaceTech springs for the fork. With the progressive springs I found it impossible to get the compression damping where I wanted it. If it was firm enough for the light part of the spring (intial dive under braking) then it was too firm on a big bump where the spring went into the stiffer coils. If it was soft enough for the big bumps then it was too soft for the initial travel and allowed too much brake dive. That has been the case everytime I tried variable rate springs like that.

The straight rate springs match the compression damping required in a more linear fashion and don't allow nearly the brake dive I saw with the variable rate springs. Plus, since the spring is distributing the load in a more linear fashion over the entire amount of travel you can run the fork oil much lower and have less air space effect on the spring rate and actually soften the ride over the larger bumps since the suspension "catches" it sooner. It is a liittle more stiff or taut feeling over the smaller bumps but not objectionable and much more controlled overall.

 

[mindtrip]

This is partly why I ditched the Wilburs progressive fork springs and went with straight rate RaceTech springs for the fork.

What spring rate did you get?

 

[worldbound4now]

I was just nosing around on the RaceTech site and they have a pretty easy calculator for the spring rate. Give it a try. I just might try these springs when I do my fork rebuild this summer.

 

[jestal]

Mine were listed at 1.0Kg/mm. I weight around 200 with gear and all and have added some mass to the front with the HID ballasts and such.

One thing to remember about the RaceTech springs is that they are longer than the stock length so you need to cut the tubular spacer on the spring mount to get the correct mounting length. Simple hacksaw or tubing cutter job but you do have to cut it or find another piece of steel tubing and make a similar spacer to length. Also, some people have complained about the RaceTech springs banging inside the fork tubes due to the RaceTech springs being smaller on the OD so they bow a bit during compression and can make some noise. I added a 5 inch piece of 1/2 PVC pipe inside the spring as a spacer/guide and it takes the noise out completely.

I put the RaceTech gold valves in both the compression and rebound damping positions and have tried a number of combinations of springs and valving changes and ended up exactly at their recommended settings. I'm pretty happy with the fork performance. Very compliant and tolerant of small bumps. Doesn't "hop" over bumps anymore. Good damping characteristics and the damping control is well within the range of the external adjustment screws.

 

[Windjammer]

Thanks for the info guys, it's definitely appreciated!

One thing that surprised me when I took the forks apart on my '05 was that the stock springs appeared to have a progressive winding already. In fact, they had the same number of coils as the Wilbers springs but the Wilbers were a bit longer, about as long as you could go without cutting down the internal spacer like Jestal did.

When I put Progressive brand progressive springs in the forks of other bikes I had, it made a huge difference and got rid of the major brake dive thing. But then those were not cartridge style forks and had no adjustments on them at all, other than changing fork oil weight. Seems to me the Progressive springs for those bikes had much tighter winding of the coils and as a result were much stiffer. Not a very scientific analysis there, but that's what I remember.

Is it common for cartridge style forks to dive so much under braking? Is this part of the "new school" suspension thinking - that better handling and control are derived from softer spring rates? Is it normal to replace most of the fork internals to get front forks that "work right" and don't use over half their travel up on brake dive? I'm asking because this is my first bike with this style of forks.

Meanwhile, I'll go through the motions of doing the simple things first, trying some different settings to see if there's any help there. Might even try heavier fork oil, maybe 20 wt like the old Norton. I'm not thrilled about spending the time and money Jestal had to spend, but if it turns out that's the only path to the grail, then so be it.

Wierd, seems like modern suspension should be better and easier to set up. Oh, well, at least the forks come off without too much hassle.

 

[jestal]

I assume you have cranked down the compression damping adjustment to see what happens?? It is simple and easy and you can back it off in seconds if you don't like the additional firmness. I went round and round with the adjustments before I changed springs again.

Going to heavier fork oil is really pointless unless you have run out of adjustment with the stock adjusters. I actually run the absolute thinnest oil I can find (a local suspension shop's 2.5 weight) and make the adjustments to compression and rebound with the external adjusters. If you get the compression adjuster completely closed then consider heavier oil but it is a LOT easier to change the adjuster screw than change fork oils constantly. Besides, the thinner you can go and stay within the range of the external adjusters the better for temperature consistency, also.

With those springs you can also try adding more fork oil and decreasing the air volume slightly. That adds more and more air space rate increase with dive and could help the problem you are trying to fix. No harm in trying.

I have had my forks out about 20 times at least making changes so the only way to really get them where you want is to keep trying stuff until they are right for you. Pretty impossible to just wing it with the changes and get it perfect. And it ain't gonna heal itself and start working right unless you try stuff....LOL. Crank down on the adjusters and see if it is too firm.