Headshake/understeer on 09 yz450

Hey guys, so i just bought my buddies 09 450 after being away from motocross for about 3 years, and i like the bike alright, but it seems to have pretty bad headshake going through braking bumps, and in corners and ruts, the front end seems to want to turn inwards and not follow the arc of the berm or the rut. the suspension was revalved for my buddy who is the same weight as me, and i haven't touched any of the adjustments because i don't know what i should focus on to get rid of these 2 characteristics. I did not set the sag because like i said, he is the same weight as me, so i figured it would be about right, but if that sounds like a sag related issue, i will look into that. What are some other things i can do? or does this bike just have these traits inherently?

Thanks for any help

If you want it to turn faster, then lower the trible tree's. Start with 10 mm from the top of the legs to the trible tree. But beware, it will make it less stabil at high speed.

The bike naturally tends toward the opposite, frankly. Does it have a set of aftermarket triple clamps?

the triple clamps are stock

How much do you weigh?

180, and the suspension has been revalved for 180, it feels good on jumps, but on braking bumps the back end seems to hop and the front will shake,

Check two things:

The race sag should be about 95-100, favoring 95. The forks may be pulled up in the clamps 5-10mm or so. How far does the front end dive when cornering?

It sounds as if the bike lacks rebound damping at the rear, which would not be uncommon, even with a revalve. See if it improves by cranking the rebound adjuster down several clicks.

so making it rebound slower right?

yes turn up the rebound to slow it down.

so making it rebound slower right?

Correct. Turn the screw clockwise toward "H" to slow the rebound. Test it in the same situations you're having trouble with. If it's improved, then check to see if this has caused any difficulty in other areas. It may be, as is usually the case, that the shock simply needs a stiffer rebound stack, but some can get along with it in stock form if they dial it in tighter.

before you get on here and make yourself look dumb, check your sag..

If your bike is turning too much to the inside of a corner you need to speed up rebound not slow it down, if it's pushing through the corner you need to slow it down,

You could also drop the forks in the clamps or increase sag

In addition to what everyone has said, check the tightness of the stem bearings. My YZF friend complained of the same things and we went over everything.....then I noticed the slop up front when we'd grab front brake and move fore/aft.

But, yes, check your sag. Make sure rebound isn't too slow and packing up or too fast and acting skitterish.

If your bike is turning too much to the inside of a corner you need to speed up rebound not slow it down, if it's pushing through the corner you need to slow it down,
You are talking about fork rebound, I'm talking about the shock.
Make sure rebound isn't too slow and packing up or too fast and acting skitterish.
The complaint is headshake in braking bumps. Slow shock rebound will not lead to this, although slow fork rebound could. If the rear rebound is controlled, the back of the bike will stay lower, keeping the fork angle shallower, and making the front more stable. Every stock YZF shock I've ever seen was way too weak in initial rear rebound. Try it.

OK so i am confused, you think the shock rebound should be slower or faster? I adjusted the sag yesterday, it was at about 105mm so i took it down to between 95-100, was going to see how it felt today in practice before my race, but showed up to late and ended up only doing a few practices laps, and then crashed out in the 3rd corner of the race, so i have yet to really see how it feels

You are talking about fork rebound, I'm talking about the shock.

The complaint is headshake in braking bumps. Slow shock rebound will not lead to this, although slow fork rebound could. If the rear rebound is controlled, the back of the bike will stay lower, keeping the fork angle shallower, and making the front more stable. Every stock YZF shock I've ever seen was way too weak in initial rear rebound. Try it.

Ah, thought it was the forks :smirk:

OK so i am confused, you think the shock rebound should be slower or faster?
Shock rebound should be slower in almost all cases. The trouble is that usually you can't really make it slow enough even by cranking the adjuster all the way closed, and running the shock with no rebound bleed at all often makes it behave oddly in smaller bumps. See if it works better with the shock rebound between 2 and 4 clicks out. That will tell you what's going on, if nothing else.

My 07 had the same issue when I bought it. I set sag at 95mm, forks 5mm up in clamps and the big change was taking 2 clicks out of the rebound in the forks to get them to settle more. All other clickers are stock. I am 180 lbs. No more stability issues and the bike turns just fine.

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