DR650 Shock Rebuild

[P-nut]

I put the shock back in tonight. Rick and I are going to try and ride tomorrow if it doesn't snow. I am anxious to try this configuration out. I rode Rick's bike a few weeks ago and we made a slight adjustment from his to mine.

[P-nut]

We just finished the first test ride. It was a little snowy, but we still managed to find some clear roads to test at speed. I love my setup. It seems to be working fine for me. Rick was pretty close with his guess as to what I would need. The only adjustment was to add a little bit of rebound. There was a huge difference on the washboards. Before my bike would slow down to a crawl when I opened the throttle on the WBs. Now it slows down only a fraction of what it did and holds. Rick's bike was setup with a much stiffer valving (Rick correct me if I'm wrong). I rode his to compare. For me it was way to stiff. It wasn't unrideable, it just was a little jarring. A few more rides and I think Rick will have all the kinks worked out.

[NC Rick]

I am super happy with he shocks setup as it stands. Based on the riding we did this past Saturday, we were able to test two entirely different damping arrangements with Eric's shock being a small modification over the last generation as well as being calibrated for his weight. Eric had spent time riding my bike before this and that gave he and I both a feel for what changes I needed to make.

Eric, if you don't mind, please let me know what could make the shock feel better to you at this point. I also would like clarification on what you describe as "slowing down" on washboard. With me on the bike, I notice that the rear end takes a site "set" or squats just a very small amount but accelerates smoothly and controlled at full throttle while cornering on a gravel washboard road, even up or down hill. (this tends to be an easy to find "test" condition around here!)

The rebound adjustments we made to Eric's shock involved turning the new adjustment knob that is located at the bottom of the shock by 4 clicks. This adjustment was mad with a riding gloved hand while the bike was on the side stand and running at the side of the trail. At that point the shock felt so good, I choose to not make any additional adjustments. The stock compression adjuster screw that is located on the right side of the bike and was left at the mid point. These adjusters have some control over the way the shock responds to sharp bumps or the "high-speed" movement of the shock.

We also spent time checking wheel rate as well as spring rate and have developed the opinion that the stock 6.5 KG spring is good for riders up to 200 lbs or so and that a larger rider will be better served by a spring closer to 7.5 KG (200-250 lb rider). The spring rate recommendation can change for riders of 20 lbs or so either side, dependent on their preference and riding style. (rider wights WO gear).

There is no problem fitting the Eibach Jessie spring to the shock and we have two customer DR shocks in this initial build who will be having those installed.

[neepuk]

Originally Posted by NC Rick

We also spent time checking wheel rate as well as spring rate and have developed the opinion that the stock 6.5 KG spring is good for riders up to 200 lbs or so and that a larger rider will be better served by a spring closer to 7.5 KG (200-250 lb rider). The spring rate recommendation can change for riders of 20 lbs or so either side, dependent on their preference and riding style. (rider wights WO gear).

There is no problem fitting the Eibach Jessie spring to the shock and we have two customer DR shocks in this initial build who will be having those installed.

Ok I must be just totally stupid or something.... I don't get it at all! My very limited experience with suspension and suspension set-up has led me to believe two things about suspension. Please correct me if I'm wrong.

1. Springs provide the ride height and are what need to be adjusted or changed to provide correct amount of sag.

2. The valving and other internals of a fork or shock are the parts that do all the dampening.

If these two statements are true.... How is the stock rear spring anywhere near strong enough to keep a 200 pound rider up high enough in the spring? What is the sag of your rear shock with a 200 LB rider on it?

If you've got time please explain this theory to a suspension dummy that's trying to learn. Just seems to me that the spring would need to be stiffer so that a rider can use all of their suspension travel and the only way to do that is to start out with the correct ride height which is to be determined by the spring.
I do understand that just throwing a stiffer spring on without revalving can be a bad idea since the spring will overpower the valving and you'll end up with a pogo stick... Your valving should help that though, right?

Ok, I'm done... Can anyone clear this up in my head?

[P-nut]

Originally Posted by NC Rick

I also would like clarification on what you describe as "slowing down" on washboard.

When I would hit the washboards with the stock shock the bike literally felt like it was slowing down even though I was opening the throttle.

[Frank Warner]

Originally Posted by neepuk

1. Springs provide the ride height and are what need to be adjusted or changed to provide correct amount of sag.

Over simplified ...


You only have one perameter - ride hieght

That can be set with any spring - change the preload and you can set the ride heigh where ever you like!

To set the spring constand kg/cm or lbs/inch needs two hights ... and two weights.

Ride height is one of them .. say 20-30% of travel on a dirt bike
The other could be sag with the bike alone .. say 10% of travel .. you set that with the preload and then check the ride height is ok .. if not change the spring rating.

Another way is to look at the amount of travel you are using when riding normal/hard. if You use less than 80% of the availble travel you need softer springs .. no point in having travel if you are not using it! If using more then harder springs.


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If the bike squats on wash board - too much rebound damping.
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Both the adjustors should adjust high speed, mid speed and low speed. (Speed here refers to the shock travel speed .. not the bike speed!)

[NC Rick]

Excellent post Kneepuk! I'm just a dummy trying to sort all this out. Your correct the spring is what supports the weight of the bike and rider. As far as absorbing bumps and irregularity's, the spring mostly stores energy and the damping converts the energy to heat. If the spring absorbs and stores all of the energy of a given bump then the shocks rebound has a big job to control the springs release and converting that energy on the rebound stroke. That is the way the old bikes worked. With more sophisticated damping, we can "help" the spring by absorbing and dissipating some of that initial bump energy using compression damping. This allows us to control the absorption rate based on speed as well as by stroke as the spring will. Doing this also allows us to design a shock that is more balanced and actually will generate less total heat within the damper. How do we determine the right spring rate? A rule of thumb would be to set the sag to where we want (dirt bike general number 100mm or 4 inches?) and then check the unladen sag looking for a number (25mm or 1 inch for a typical dirt bike?).

My DR right now has 1.5 inches or 38mm of unladen (only the weight of the bike) sag and with a rider of 224 lbs with gear sitting on the bike sags 3.9" or 99mm.

Using this data, and comparing it to the "rule of thumb" I sited, this indicates that the stock spring is too stiff for the 224 lb rider because the unladed sag is not enough for the "rule".

It would be great to see what some of the rest of you are seeing for your sag settings.

More later. Fire away, I always learn from these kind of discussions and really enjoy the process.

[NC Rick]

Sorry Frank, I type slow as can be and I missed your post. I concur! I still think this "rule" stuff is just a way to check that you in the ball park.

Interesting data but a bit flawed:

[Frank Warner]

Originally Posted by NC Rick

With more sophisticated damping, we can "help" the spring by absorbing and dissipating some of that initial bump energy using compression damping.

One way of looking at it .. but not absolutely correct!

What is wanted is the bike to stay stable while the wheels follow the track ...

The compression damping stops the wheel leaving the ground at the end of an upwards movment - and that is primarily the effect of the unsprung mass moving upwards .. not the spring ..

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One of the really old damping systems was friction damping - same damping effect for both compression and rebound.

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Rick .. Rule = guide for wise people.

I'd rather see suspension travel expressed as a percentage of total travel .. that way it works for all on similar bikes ... with similar terrain.?

[ncTRAILBOSS]

Just thinking here but if you are running the comp. adj valve all the way in[DR650],and feel that the comp dampening is ok[for me],but rebound is lacking,could you not put a heavier shock oil in,then,back out the comp valve a few clicks.rebound dampening would increase and by backing out the comp. valve,have pretty much the same comp. dampening as before changing the oil.Just a poor boy dreaming or not?I do have aliittle shock tuning experience working with 1/8 scale R/C racing.By the way,I have a set of shocks for a R/C race truck that were made by Progressive Suspension Co.,pretty cool stuff.

[neepuk]

Rick N Frank,
Thanks to both of you for helping me to understand the concepts... I'm out of here for about 5 days, riding in Death Valley. Looking forward to checking out the progress when I return.
Good luck with the project Rick. I've got a feeling I'll be sending you a shock sometime soon...

[DRinda505]

Been watchin this thread for the last week or so. It has me excited. I believe you can count me in for an upgrade, should complement my DRZ front forks nicely. However, I'm contemplating shortening my dogbones a touch to increase my ride height an inch or two in the rear to get my steering geometry back closer to stock. Would the shorter dogbones change the swingarm leverage on the shock and hence require a different rear shock spring or damping setup???

Keep up the good work.

[NC Rick]

Neepuk, you lucky... That sounds so cool! I wana come and ride!

Frank, I am overly simple sometimes no doubt that the primary function of the damper is to provide critical damping to the spring and the controlled mass to prevent over or under shoot of the reaction. The damping does more providing feel and "helping the spring" Sometimes the damper and spring are controlling the wheel movement over the ground and other times they are controlling the bike and rider with the wheels staying closer to stationary (with respect to the dampers). Not at all simple and I really think the art of getting a good setup transcends the pure theory (this is a nice way to say that I don't understand it all ) On the DR, the shock may be providing something like 600 lbs of force at the rear wheel when it is being compressed by 5 inches / second.

BigMaggot, the oil viscosity has a limited effect on the damper forces because the shim deflection should be the primary control. It will effect bleed and cause a firming of the low speed performance of the shock. The heavy oil has other undesirable effects including more temperature caused viscosity change and potentially causing a big spike in damping force at high damper speeds. The compression damping adjuster on the DR is a controlled "blow-off" and effects the shock primarily on "hits". You can do what you want by just modifying thee rebound shim stack and that is a perfectly viable thing to do. That is something you can do if you have a few tools and a source of dry nitrogen to refill the shock. People who send shocks to us for that would typically pay about $100 or so to have that done. Very importantly, doing that kind of work would include the critical service of the shock. I recomend that everyone service their shock at about 12 to 15K miles or even much sooner if the bike gets used real hard.

DRinda, the dogbone change will change both wheel travel and lever ratio, with our shock modification, you could just use the ride height adjuster to dial in the additional height. What I would want to do is to look at the additional travel in the front and think about extending the shock in a way that give a little more travel. Lets say we add 1" of hight to the rear, we could then add 1" of wheel travel. Another possible way to address the same issue would be to add an internal spacer to the new fork to correct the ride height and travel at the front. I am 6'1" and have problems with my toe finding mother earth on some of the sidehill conditions in the woods. More hight isn't always what we want. For jumps, it would be great! I have an extra set of DRZ forks here and was thinking about a swap like that one day. I know from owning a DRZ that I would want to do a revalve of the fork at the same time.

[Frank Warner]

Originally Posted by BigMaggot

Just thinking here but if you are running the comp. adj valve all the way in[DR650],and feel that the comp dampening is ok[for me],but rebound is lacking,could you not put a heavier shock oil in

If you are changing the oil .. then you are stripping the shock .. in that case you may as well have the alter the rebound it self (shims) rather than change the type of oil! And it the adjuster is not near half way then have those shims changed too.. the point about having an adjustor is being able to adjust in either direction .. not about having it set to max or min for 'normal' operation.

Originally Posted by NC Rick

no doubt that the primary function of the damper is to provide critical damping to the spring and the controlled mass

In theory the primary function of

The Damping is to reduce the oscillation of the unspring mass.

The spring to support the vehicle while providing vertical movement.

Now that is simple?

Yes the secondary effects come into play (and third and forth etc) .. but some people consider those to be the primary things .. and need to be informed. Why? So they have a good understanding when they come to adjust the things.

[eakins]

been following more as this progresses.
i'm still very interested as long as the cost is worth it VRS doing a spring only upgrade.