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Rear spring advice - DRZ400S

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It was recommended that I ask this in the DRZ sub forum instead of the suspension if I wanted faster answers.

Thank you bmwpowere36m3 for your reply in the other thread. If I knew how to contact a moderator to have the thread moved I would have.

Normally it wouldn't be a big deal but I need to get this figured out and new parts in my hands if necessary before Friday.

My issue is that I'm bottoming out the rear shock on rough terrain.

6'1 weighing 221lbs with normal gear.

Racetech calc says I want a spring around 5.88kg.

I ride atv, single track woods trails, logging/fire trails and minimum maintenance roads as aggressively as I can.

Measurements.

Un-sprung - 25 1/2"

Static - 23 1/4"

Race - 20 1/8"

It shows I currently have 5" (127mm) of race sag and 2"(50mm) of static sag.

My reading shows I want 95-100mm race sag and ~30mm static sag.

Looks like I should be able to crank the collar down to decrease the sag.

But from what I'm reading it sounds like the better option is to get a new spring that's meant for my weight.

Looking for your thoughts on this. Should I go with the Eibach 5.7 or the Eibach 5.9?

Will the 5.9 be to stiff? Would the shock need to be re-valved with that much of a spring rate change?

If the spring rate is to high for the rider weight does it cause the bike to pogo instead of the suspension taking the bumps?

Just not sure how much I trust online calculators and want to verify with your guys experiences.

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+1 with the previous poster, I just went through this with my other bike.

Valving is so important, Depending on how in depth you want , pick up a copy of this:

Written by Paul Thede / started RaceTech

suspension bible.jpg

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I have been fighting with this one for a while now. The DRZ400SM is my girlfriends and she weighs 86kg. She is also only 5'3" ( no comments please) so I have lowered the bike 40mm as well. The sag with stock springs was ridiculous taking more than 50% of the travel. The bike is used on the road exclusively for the time being until she gets her new KTM ( 690 or 390), so I have tried an Eibach 6.3 and now a Factory connections 6.7. The 6.7 still takes 40% of the available travel. Bumping up the compression damping just makes it harsher. Still looking for a 7.3 or 7.5 which is the calculated correct rate for her weight AND the shorter travel. If anybody knows where I can get one to fit , I would very greatful.

I did the calcs ( Foale's suspension software) and for your weight and height you are going to have trouble getting near the correct spring rate. You may have to go aftermarket shock if you want optimum rear suspension.

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I installed the Factory Connection 5.8kg spring today. There is a firm difference in ride quality.

I was only able to take it down a gravel road to test but the front seems more responsive to steering now. Going to take some getting use to.

Also put on a 47T sprocket, man is it fun to drive now. Woods riding is going to be a blast. 2nd gear now acts like first gear did for wheelies.

Bring on the fun.

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How does one go about getting rid of head shake after a spring change?

Seems its picked up a somewhat moderate one at 40mph.

I need to recheck my sag tomorrow, maybe that's whats causing it?

Do I need to possibly adjust the fork height?

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I am about the same size as you and racetech recommended at 6.0kg spring, the current 5.7 is way too soft.

I'll be installing new fork springs, cartridge fork emulators and a rear spring tomorrow. I'll check back and let you know how the 6.0 feels.

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Holy crap what a difference. I set the race sag to 3.5" (89mm) should back it off a little and see what 95mm feels like. But WOW, the bike wheelied much better, took the bumps like it should also.

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Looks like the forks are set at 7.8mm from the factory.

Raise the forks a couple mm and see what happens?

I would say “headshake” could be partially attributed to the fact that before the spring change you probably had a lot of sag (rear). Thus the head angle would be greater and provide more high-speed straight-line stability. Now that you reduced the rear sag the head angle is smaller and provides for quicker steering.

I would raise the forks so that the ring (machined just below the fork cap) is level with the top of the upper triple clamp. That way the forks stick out about 5 mm above the surface of the triple.

If you plan on mostly riding the bike on trails, then increase your rear sag to 100 mm. See how it feels. Then see if you can measure your front sag. If you haven’t changed the fork springs, you’ll need to…

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I would say “headshake” could be partially attributed to the fact that before the spring change you probably had a lot of sag (rear). Thus the head angle would be greater and provide more high-speed straight-line stability. Now that you reduced the rear sag the head angle is smaller and provides for quicker steering.

I would raise the forks so that the ring (machined just below the fork cap) is level with the top of the upper triple clamp. That way the forks stick out about 5 mm above the surface of the triple.

If you plan on mostly riding the bike on trails, then increase your rear sag to 100 mm. See how it feels. Then see if you can measure your front sag. If you haven’t changed the fork springs, you’ll need to…

What you said makes sense. I will make the adjustments and see how it feels and acts.

Thank you!

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