Front end wobbles on decel

[RhythmRider]

[UPDATE: SOLVED] Front end wobbles on decel

UPDATE:
So, after more than a year without knowing what was causing the crazy tank slapping on this bike during deceleration, I finally found the answer. It was the TIRES. I just put new ones on, and it is stable now.

The old tires were slightly deformed, at least the front tire was... I believe "cupping" is the term that is typically used, but for lack of a better word, the best description I can give is that it was an "alternating ridge pattern". The deformity was subtle, not enough to produce a bumping feeling in the handlebars, but if you let go of them, they would begin to wobble, and it would continue to get worse until you put your hands back on. I wonder if this is a common thing with the EX250? I'm just glad it wasn't a bent part or something.

Original post:
Bike is an '07 Ninja 250. Previous owner was a n00b... dropped and/or crashed the thing. Doesn't look like anything serious has happened to it, but when I decelerate from a high RPM and take my hands off the bars, the front end quickly begins to oscillate with high frequency. I can stop it by simply putting my hands back on the bars, but I wonder where it is coming from? I'm planning to have a look at the front end this weekend, but do you people have any ideas about what could be causing it??

 

[CAmudgeon]

How's the rear spring preload set? Is it appropriate for your weight?

How are the tires and pressures?

If the front end is getting light (decelerating from high rpms = a lot of engine braking) which lightens the front end just like applying rear brake only). This is is being compounded by taking your weight off the front end by letting go of the bars.

Having too little preload on the back or incorrect tire pressures might compound the situation further. Some tires, or badly worn tires will also make headshake more likely.

 

[CAmudgeon]

^^^ Once you've checked the basics, the steering head bearings, front wheel spacers, rear wheel alignment, and straight forks are all worth checking out IMHO.

 

[stangmx13]

If the front end is getting light (decelerating from high rpms = a lot of engine braking) which lightens the front end just like applying rear brake only). This is is being compounded by taking your weight off the front end by letting go of the bars.

. weight transfer forwards due to decel does not lighten the front end. yes the rear also squats a bit, but its not going to take weight off the front as well.

 

[TheRiddler]

^^^ Once you've checked the basics, the steering head bearings, front wheel spacers, rear wheel alignment, and straight forks are all worth checking out IMHO.

Yeah, this.

The Ninja 500 is well known for having headshake caused from improper rear wheel alignment. The marks on the swingarm are off (mine are actually off by 2 dashes, so a pretty big difference). I expect the 250 suffers from a similar problem.

 

[CAmudgeon]

. weight transfer forwards due to decel does not lighten the front end. yes the rear also squats a bit, but its not going to take weight off the front as well.

Dammit I kmew someone would call me out on this . Yeah if the rear spring preload is set to noting and op is bigger, the swingarm will deflect up on throttle snap shut, but I guess the main effect of that will be a change in fork rake as the rear squats down rather than lightening the front. In any case, shutting the throttle abruptly can impart a force into the steering.

 

[RhythmRider]

I weigh 150lbs, so it's not like I'm too big for the bike, but I'll check the pre-load and make sure it's set correctly. I'd be curious to see what the rear wheel alignment looks like... I haven't checked it out yet. That sounds like a probable cause for the wobble since it's related to the engine braking. Tire pressures are at the recommended levels on front and back. Thanks for the pointers, guys.

 

[JimE]

After you check all the basic stuff the others have listed......

This happens to me when I hit the wear marks on my front tires fairly often.

 

[toothpickdude]

[youtube]c0dkpQJREno[/youtube]

Also try loosening up the lower and upper triple bolts, then re-tighten to make sure everything is straight since the previous owner crashed it.

Have fun with the two fiddy aaron. Let me know if you need some parts.

 

[tonedeaf]

my 250 had the same exact issue, i discovered it the night i bought it and scared the crap outta myself. i just didn't do that from then on, and it steered well even going as fast as i could at laguna. i just figured the no-hands shake didn't translate into a problem handling well while riding normally

 

[Maddevill]

Some bikes just do that with hands off the bars. I don't know if the 250 is one or not. As long as your tires, wheel bearings, suspension and frame are all good I wouldn't worry too much about it.

 

[kelsodeez]

with my 2000 ninja 250, head shakes with your hands off the bars is always the rear wheel being misaligned. its scary as hell, esp when the bike starts doing the pendulum thing on you at speeds over 30mph

 

[RhythmRider]

[youtube]c0dkpQJREno[/youtube]

Also try loosening up the lower and upper triple bolts, then re-tighten to make sure everything is straight since the previous owner crashed it.

Have fun with the two fiddy aaron. Let me know if you need some parts.

Interesting video, Amos! I'll hit you up about the parts.

 

[423yjl]

On mine it would do it if the front tire was worn, also the front/top engine mount bolts vibrated loose which would allow the frame to bend more and cause all sorts of weirdness.

 

[Ironbutt]

Bike is an '07 Ninja 250. Previous owner was a n00b... dropped and/or crashed the thing. Doesn't look like anything serious has happened to it, but when I decelerate from a high RPM and take my hands off the bars, the front end quickly begins to oscillate with high frequency. I can stop it by simply putting my hands back on the bars, but I wonder where it is coming from? I'm planning to have a look at the front end this weekend, but do you people have any ideas about what could be causing it??

I'm gonna call it; lack of compression damping in the forks.

And the remedy is catrtige emulators. <if your rear shock isn't sacked too>

 

[TT03gsxr]

On mine it would do it if the front tire was worn, also the front/top engine mount bolts vibrated loose which would allow the frame to bend more and cause all sorts of weirdness.

+1 check front engine bolt, mine vibrated loose recently and if it were not for the fairing holding it in, would have fallen out and dumped the engine on the floor. Tightening the bolt reduced my head shake on decel considerably. Still some there though, sadly.

 

[RhythmRider]

So, after more than a year without knowing what was causing the crazy tank slapping on this bike during deceleration, I finally found the answer. It was the TIRES. I just put new ones on, and it is stable now.

The old tires were slightly deformed, at least the front tire was... I believe "cupping" is the term that is typically used, but for lack of a better word, the best description I can give is that it was an "alternating ridge pattern". The deformity was subtle, not enough to produce a bumping feeling in the handlebars, but if you let go of them, they would begin to wobble, and it would continue to get worse until you put your hands back on. I wonder if this is a common thing with the EX250? I'm just glad it wasn't a bent part or something.

 

[RickM]

I believe it is common with the stock tires on the ex250.

I don't notice it with pirelli MT75 or dunlop gt501.

I have one with new sport demons right now. I will try if that one exhibits the wobble tomorrow and report back.

 

[RhythmRider]

right on

 

[Diezel]

Kinda odd to see all the guesses on here, Not point to front tire cupping. That would have been where I would have looked first.

Then again, I've experienced this on multiple bikes.