5th and 6th Gear High Speed Wobble

[mikej43]

Most of the ridding in our neck of the woods is very tight. Rarely do we see top of 5th and 6th gear. So it was a real suprise when ridding my 1999 KDX220 along a flat railroadbed in 5th and 6th gear. The bike starts to wobble. It wobbles enough that you know you don't want to go any faster. You can make it wobble easily in top of 5th by quickly snapping the throttle open.
So far I have checked the spokes for tightness, they are OK. The bearrings front and back are about 1.5 years old. The bearrings spin freely and there is no slop in them. I have inspected the chain and sprockets as they spin. They do track true. The rear weel is corectly adjusted, chain adj ok and rear weel is square on the axle.
I have always thought that in 5th and high 6th gear the speeed you are at is too high for a two stroke bike the size and weight of a KDX.
Has anyone else had a simular experience/problem. What to fellow KDX'ers think of the performance of their bike when ridding at the higher speeds.

 

[strider80]

My bike feels pretty similar, I attribute it to unbalanced tires and slightly out of round rims. You could balance your wheels with the solder trick. Cut off a piece of solder and wrap it around a spoke opposite of a heavy spot on the tire. Find the heavy spot by spinning each wheel and watching where it comes to rest, this is your heavy spot. You will have to remove the chain and the brake calipers most likely to get the wheels to spin freely.

Or just be like me and slow down!

 

[adam728]

Is this a wooble like headshake, or like an up/down vibration?

When running stock fork springs my bike wasn't very stable at speed in looser soil, the front end would want to shake. Stiffer springs all but eliminated then feeling by making the bike ride level, as it should.

Another thing is the tires. It's easy to mount them up and not have them set evenly around the rim. You can look at where the tire and wheel meet and see if everything is nice and even all the way around. It's easy to get the bead set lower on one half than the other. It will get you quite the bumpy ride at speed, feels like a severly out of balance tire because the radius isn't equal all the way around.

Another is to check the trueness of the wheel as it spins. Easiest way is to hold something (screwdriver, pencil, stick) on the fork or swingarm and note the gap between it and the rim edge as the wheel spins. Same goes for runout on the tire.

I run my KDX at high speed all the time, no problems. Mine is dual sported, so it regularly see's 55-60 mph, and has been over 80 mph. All on unbalanced tires.

Oh, and the easiest way (so I am told) to balance your tires a little better is to get a second rim lock and install it opposite the factory one. I had my tires balanced at one time (not worth the bother) and ended up with a ton of weights exactly opposite the rim lock.

 

[StuckinJersey]

I rarely get into 5th and 6th but they definitely weren't fun gears until I dialed the suspension in. Although I did not encounter anything like what you are experiencing I felt very unstable at high speeds on the bike making me timid to push her. I installed heavier fork springs and adjusted the rear which made all the difference. Hopefully your issue is as easy and cheap to fix as mine was. Good Luck!

 

[razrbakcrzy]

I agree with the other fellows. I think you are experiencing headshake from an ill setup suspension. Check your sag and preload on the front and rear. If you get the rearend alot lower than the frontend (or vise versa) you will get an out of balance situation that causes the bike to want to swap ends hence the headshake. The suspension needs to be balanced for the weight it is carrying. I am a heavy rider and my son is a light rider. He rides ours more than I do so we set it up for him. I just have to fight the urge to rip it! Before we did our setup. My son was riding in a sandy wash, pretty fast about 3rd gear. When he pinned the throttle and shifted to 4th, it shook him hard enough that it flung him off the bike into the weeds beside the trail. It looked like he was riding a bucking bull. Now he rides at what ever speed he wants. There is no accounting for a bad setup.

 

[83MX80]

every time i ride my KDX 175 i gotta get it into 5th and 6th gear at WOT. and im finding that im always looking for another gear. there is tight trails here, like 1st and 2nd gear tops. what i do find is that in 5th and 6th gear it does have an up/down motion, because of the bike sitting and the bottom is a tad bit square. but after a while it goes away.

 

[Rhodester]

On the issue of balancing....Kawasaki put the rim lock on the same side of the wheel as the valve stem for ease of changing the tire. This, however, sets up a problem with balance at higher speeds. My front tire hops in 6th gear without correction. I crimped some split shot (you know, from your fishing tackle box) on the spokes opposite of the rim lock/valve stem to correct the problem (with a dab of silicone to make sure they stay put). It helped considerably. Also, use the lightest valve cap that you can find to keep the weight down on that side of the wheel.

 

[dhoward]

Mmmm....
Steering damper.....
:aj:

 

[KDX CRAZY]

I find with my 2006 kdx that at high speed on slightly looser sand the bike feels unstable at higher speeds , the thicker the sand becomes the worse it feels .
I have not adjusted the suspension from the factory settings .

 

[trevor morgan]

My KDX250 was doing the same at high speed over dirt tracks, my solution came from a previous post, I dropped the forks through the yolks by 10mm to effectively lower the front end. It worked on mine and didn't cost a penny so must be worth ago! Its now stable even at 70mph.

 

[lepper]

Mmmm....
Steering damper.....
:aj:

A steering damper has minimal effect on a stock KDX frontend. To get the full benefit of a damper you must swap the frontend for a KX frontend. A KDX frontend feels like spagetti in comparison. ;)

 

[dirt bike dave]

A steering damper has minimal effect on a stock KDX frontend. To get the full benefit of a damper you must swap the frontend for a KX frontend. A KDX frontend feels like spagetti in comparison. ;)

I've had dampers on my last 2 KDX's ('90 200 w/conventional forks & '91 250 w/inverted forks). The effect was far from minimal. Every offroad bike should have a damper, IMO. One of the best mods ever.

As to Mikej43's problem, a damper would help big time, but I think truing and balancing the wheels would cure the problem. If that did not do it, then suspension tuning should fix it.

 

[lepper]

Agreed on the must have a damper deal... But! If the forks flex badly to begin with (i.e stock KDX forks) then the damper has a minimal effect. Just a fact JACK er..uh.. Dave that is! :laugh:

I've had dampers on my 92 and 95 with stock suspension and the change was noticable but minimal compared to the 03 KX frontend I have on my bike now.

What I'm saying is... to get and feel the full effect of what a damper can do for you... put it on a rigid frontend. I guarantee you will agree with me.

 

[dirt bike dave]

Well, I've probably ridden about 20 different bikes with dampers over the last 12+ years. I'll guess I've ridden at least 10 damper equipped bikes with conventional front ends (KDX, XR, DRZ, DR, RMX, KTM, Gas Gas), and I've owned two (KDX 43mm and my CRE with 46mm Paioli forks).

I've also ridden at least 10 damper equpped bikes with inverted forks (various KX, KLX, KTM, RMX, Gas Gas), and owned one (KDX250).

It has never occurred to me nor have I ever heard anyone mention that the damper helped an inverted fork bike much more than a bike with a less rigid conventional fork.

 

[lepper]

OK... read what you want to read instead of what was written... really makes no difference to me.

It's not that it helps a inverted fork more... it's that it is more effective. Read the text and try to calm down and not think I am trying to offend you in some freakin way.

 

[dirt bike dave]

Dude, all calm here. No need to get your panties in a bunch.

It's not that it helps a inverted fork more... it's that it is more effective. .

So it doesn't help more, but it's more effective? I find dampers to be similarly helfpul and effective on bikes with rigid or flexible front ends, so I guess we will have to disagree.

 

[lepper]

Yup... :cool: