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Discussion Starter #1
Howdy, just replaced the stock front fork springs with Progressive springs on my 2009 KLR - BUT, bike is still diving when I touch the brakes when going very slow. This what I did:

1. I removed both forks and drained the oil.
2. I used a few hundred mils of oil to flush both forks.
3. I filled with oil to 135mm from top of tube
4. Inserted new spring, washer and 3" spacer.

Maybe I'm expecting too much or did something wrong? When I'm going like 1 m/hr and touch the front break the bike noticeably dives. Just as much as with the stock springs. I have added another 50 mil of fork oil, but no difference.

Should I keep adding oil? Ideas???????
 

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Pete -

When brake dive occurs there are two things going on.

The KLR fork is not very fancy. All it has is some holes in the tubes for the oil to try and go through. The resistance of the oil going through those holes is what controls the speed at which the fork goes up and down, and so it controls how rapidly the brake dive occurs.

The forks' spring rate resists the compression of the fork under a load, so the stiffness of the spring controls how much brake dive occurs.

Now, I figure you used the progressively wound Progressive springs. Progressively wound springs are great in the right application because they are soft over small bumps but harden up with big hits (after the softer-wound portion gets stacked). The softer-wound section allows the forks valving to do it's job of controlling the forks' action over the small bumps.

Except the KLR don't have no steenkin' valving, only those holes for oil to flow through.

What you may have done is put a progressively wound spring in that has a lighter spring rate in the soft section than the stock springs had overall. That will make brake dive worse, of course. If the soft section of the progressive spring is about equal to the stock spring, then, of course, that spring will also do nothing to improve brake dive.

There are only three things I can think of that will help, and two have drawbacks.

Installing a thicker oil will make the spring compress more slowly and help to control the rate at which the dive occurs. The downside is that it will also control the rate at which the fork recovers from compression (rebound) and that may really deteriorate the handling over rough, fast terrain like washboard or stutter bumps. It won't control how much dive there is.

The second option would be install a rather decent valve like the RaceTech Emulator. The downside is that they require tuning and are expensive.

Adding oil makes the 'air spring' stiffer, that will have an effect on the brake dive if the air spring is softer than the progressive. You might play with some extremes on that and see what happens.

You cannot eliminate brake dive, but you can improve how much occurs and how fast it occurs.

Tom
 

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Install Racetech's. I haven't yet in this bike, but they are good in my other.
 

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Have Progressive front springs in my KLR250; don't think they appreciably affected braking dive, because . . . the initial spring rate is not unlike that of the stock springs.

After the initial compression, however, the spring rate changes dramatically, improving handling markedly over the gnarly stuff, in my experience; YMMV.
 

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not sure about your installation so I will point you to the video I used as guidance . I did use an heavier oil and the bike is now stiffer than the stock, but not too much to beat off my forearms on the trails. Yes the bike still dives but not as much. I used the cheaper option of just the spring and cut the original spacer to arrive at the same length as the original + spacer.

Ride Safe....
 

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Discussion Starter #6
Thanks everyone for their responses.

I'm starting to think that maybe the problem is my understanding (lack there of) of how the front springs work! I just made the assumption that by putting the Progressive springs in that the annoying dive that I get when stopping my bike, when going slow, would be gone. I haven't had the bike up to speed since the upgrade, so I guess I'll to that tomorrow and see how things feel.
 

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Valving is the only way to effectively affect brake dive while retaining the ability to handle harsh bumps (like wash board etc.)

Drop in cartridges work great. They use a weight that opens the valve stack slightly when the axle moves quickly allowing the suspension to respond faster. When slower bumps are encountered (or brake dive where the upper fork tube/bike load the suspension), the valves are tighter allowing the oil to move slower thus reducing suspension action (and brake dive).

I use Ricor Intiminators which work this way as do the other drop cartridges.

Ricors are calibrated to use a very light oil which allows drop in without consideration of the OEM rod dampers (oil just runs on through them with limited action).
 

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Thanks everyone for their responses.

I'm starting to think that maybe the problem is my understanding (lack there of) of how the front springs work! I just made the assumption that by putting the Progressive springs in that the annoying dive that I get when stopping my bike, when going slow, would be gone. I haven't had the bike up to speed since the upgrade, so I guess I'll to that tomorrow and see how things feel.
The oil height in the forks (actually think remaining air volume) affects the progressive action of even straight rate springs. The higher the oil (less air to compress) makes the effective spring rate stiffer as the forks compress.

So you have 1)spring rate/pre-load setting, 2) air volume, and 3)dampening rate and viscosity - all working together and tuned to happiness (for any given type of terrain/riding, weight/loading, of course).
 
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