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Unstable steering, tank slapping or whatever I have...!


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I wasn't going to write this but I had 2 times feeling of crash! btwn 130~140 kmh, hardly controlled it. And many times "unsecure feeling" around +120 kmh and had to slow down. I have very little courage to go over 130 kmh anymore

 

For I got the bike (07-SM) six month ago, I am the 2nd owner, the front feels shaky around +115 kmh and more. 

 

First I was thinking it is bec. of forks and setups. We made full rebuild of forks (bushings,oil,seals) but nothing changed. I checked the forks alignment, no bend/curves/scratches... They seems work pretty normal.

 

Then I checked the reb/comp. values, they were very close to manual values. I made them same as what manual says, no change on steering again.

 

I was finding I am leaning(not sliding) too much to behind when open throttle. May be rear is too much soft or low. Or front is too high. I stiffed the rear shock a bit but couldn't see noticeable difference.

 

Then after first ride of my friend's DRZ,,, :crazy:  I become certain about there is definitely smthng wrong with my front end. The other DRZ was too straight at high speeds against mine. I even tried a couple of time to put it in thank slapping (tried to shake handlebar) and bike did not respond and keep on straight. Rear shock was stiffed till its end on that bike, I noted it down. It was "scary fast falling" when leaning and moving much in corners. But I fixed it with fork reb setup. The bike got a perfect handling on both straight and corners. And I turned to my bike  :angry:  ....No, to pre owner!

 

I talked with pre owner, confirmed that no "head crash" and just a fall while trying wheelie. He also said didn't make wheel rod/balance setup when he changed the tyres long ago.  :thinking:

 

I was waiting to change tyres. I made it a month ago. The service man made it very well, and a computer-machine balance setup. They added a "big" weight dot(what ever it is) to wheel and I said  :banana: . I thought it was the problem but of course I was wrong. When I ride it...it is still same.

 

Between the front tyre, I put rear a 140/80 tyre and it make rear ~1.4 cm higher than before and I made shock more stiffer like other drz. No change again...

 

Only one thing left behind, in my mind, is the 120/70 MT60-RS front tyres... It was on the bike when I got it and I put new. But I don't think they are the reason.

Edited by Syanur
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I'd check out the sag setup. What's your rear race sag, and where do the forks sit in the clamps? How much do you weigh in gear?

 

Probably the rear sits too high, and maybe the front a little low. This changes the front fork angle (rake) and thus the trail - you'd have too little trail, making the bike unstable. You could compare with your friend's bike.

 

It's that or some mechanical thing that needs fixing. Might be both.

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My DRZ (Owned by a guy who was a VERY different build / weight to me beforehand) was VERY unstable at high speed and quick-steering when i got it.

 

this!

 

I bought my S off a much more heavily built guy than me. I think I remember you saying that you were roughly my weight Syanur, I'm between 70-75kg? If so then we're probably both lighter than most and it wouldn't be unusual to have to change the preload on a used bike.

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Guys you great, thanks first.

 

I really get depressed from can't solving this. I am keen on speed (don't like actually) but being able to ride btwn 115-145 kmh easily was the real reason for me moving up from my precious 250-SM bike to DRZ.

 

We put the bike side by side one day and realized blue DRZ rear is ~2cm higher than mine(black). Everything started with this. I was like chopper riding on my bike. From then to now rear height is raised in 3 step. Nothing changed, thats why I am not suspicious from sag/shock setup. But I will check the sag anyway. And yes I am ~75 kg 🙂

 

But @seven your picture is different than mine!! My forks are standing out of clamp ~2cm or more... I was thinking mine is the Factory setup. This photo make sense to me. I realized that the handlebar tend to shake even at lower speed. So this is may be bec. of fork height.

 

Handguards.... Nope, I didn't laugh at it. I heard some like this about wind before. Actually handlebar tries to shake me more at windy rides. But my speed had never passed 140kmh yet. For example 120 kmh is a low speed for handguard resistance for me.. But who knows, I will try/test  👍

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OK! That fork position is going to have that effect! At least that's the first thing I'd change. As you have a reference bike to compare against, then set the rear sag about similar and the forks about similar.

 

Ideally you'd want to measure and set your rear sag according to a rule (and then adjust to your preference) - the rule of thumb is that rear race sag should be 1/3rd of suspension travel.

 

However, use the rules-of-thumb to set your bike to a "zero" configuration and then adjust to your preference! There is no right or wrong, just chassis dynamics according to the laws of physics - and then each rider is different and likes different things.

 

For example on my S I have my rear race sag set a bit more than is usually recommended or discussed - iirc 110mm - and I have my fork tubes flush with the yoke. So it's noticeably more straight-line stable than the stock setup. It's actually a tiny bit too stable right now for technical dirt stuff but it's very enjoyable on the street. However, an unexpected bonus of having the steering "overly stable" in the default riding position is that it encourages getting up over the front wheel to weigh it more. It's subtle and interesting.

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Head shake comes in many issues and the main one is Head angle/trail, if it is to steep it will slap steer stop to steer stop and 60 and above. My race had a different issue which was chatter in high speed corners (50 and above), tried everything, went through clickers and 14mm to 20 mm offsets and could not get it dialed. Turns out my rear spring was to light, was for someone who never eats (140lbs), changed spring and BAM. Now I can rail that 450 :D If you start messing with clickers, PLEASE keep a pen and paper handy. Make a adjustment and write it down, go ride, if not right try another setting but write that down. So helps when you find the correct settings for you. 

 

 For me I have different settings for different tracks I race at so this way I am a bit ahead of the game when I get there. 

 

 Hope you get this sorted.

Edited by Debi
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the front fender gets blamed a lot. and handguards. and '120 series' front tire. and stiff arms. and 'luggage'. and 'tire pressure too high/low/hot/cold'. 

 

then, you put the bike up on  a stand and see the stem bearings have 1/16" play at the top, or that the tire has a 1/4" deviation from true, or the wheel bearings are so loose you can push paper through them, or the frame is cracked at the steering tube...

 

scary stuff those tank slappers. usually the same things fix it easily though. 

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Guys you helped me a lot, really. I mean the idea of fork height turned me to life again! Thanks to all of you.

 

Tonight I will go my garage bec it is snow(ice/froze etc) out there now. Can't ride. So good time to maintenance 👍 

 

I mostly wonder about fork height change. I don't know when I will be able to test. I will try to check the sag if I can tonight.

 

By the way, I don't hold the bar too tight, I know what you mean  😉  I mostly check the tire pressures too. And I hope there is no crack at anywhere 🙂

 

Syanur, have you checked your steering stem bearings and that the steering stem is properly torqued and without any play? 

 

Swing arm bearings?

 

Wheel bearings?

 

First, no. Swingarm bearings and wheel bearings are checked before. But I will double check them again

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Shoot .. Dang .. Debi ..

It looks like your about to be turned into a Chicken Wishbone 😢

 LMAO 

 

 I just really wanted to give the ground a big BEAR HUG! lmao. Just knocked out for about a minute, cracked a rib and bent the plates in my pelvis a tad hehe. But the good thing out of it is I saved the bike bwaaaaaaaahahahahahaaaaaa.

 

 See, that turn don't SCARE ME hehe (btw, I am riding with a blown out knee, fractured tib/fib and torn tendon all in the right leg hehe)

 

 Oh and "note" the head shake when I come out of 8/9 and stay on the gas 😉

Edited by Debi
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