yz handling at speed


37 replies to this topic
  • Jim813

Posted August 08, 2009 - 02:51 PM

#1

I am having a hard time with my 2008 yz450f. The bike is very unstable almost everywhere. Through rocks the bike wanders and deflects, in whoops the bars are always twitching, and in fast single track with lots of turns the bike doesn't feel connected. I have tried everything that would seem to help. I have an RTT stabilizer, suspension done by one of the best in the business, and have checked and tightened my steering stem bearings repeatedly. The forks have been slid up in the clamps 8mm and the rear race sag is set around 110mm. I know Yamahas like race sag around 95-100mm but that would put even more weight on the front end, which leads me to think the problem would get even worse. I run 15psi front and rear. The front is a Dunlop 755 and the rear is a Maxxis IT. Any ideas to help fix this unstable, non-confidence inspiring feel?

  • mikedabike

Posted August 08, 2009 - 04:12 PM

#2

How much do you weigh and what type of riding? The newer YZ's are the best suspended stock bikes I have ever ridden. Also if your suspension was done by the best in the business why are you not talking to them. Best in the business means they help get it set up correctly. Also more weight on the front wheel is not necessarily a bad thing.

  • e30M3

Posted August 08, 2009 - 05:33 PM

#3

You may want to consider moving the forks down (on my 426 I run them at "0 mill" and run the bars up and forward with a Dunlop MX51 front tire. Moving them up should add some stability but at a loss of corning. Moving the bars up and forward gets me up further and the bike turns better than I do...

Now the my new '09 YZ450, I am running it in stock form at 5mill and it seems to work pretty good... I do get some wondering as you describe bit honestly I think it is either me (riding to stiff and not flowing with the bike) and maybe the cheap front tire the bike came with?

  • Jim813

Posted August 09, 2009 - 01:05 PM

#4

How much do you weigh and what type of riding? The newer YZ's are the best suspended stock bikes I have ever ridden. Also if your suspension was done by the best in the business why are you not talking to them. Best in the business means they help get it set up correctly. Also more weight on the front wheel is not necessarily a bad thing.



I weigh 200lb-205lb in street clothes. I am also working with my suspension tuner right now and he is helping to get it set up correctly. I am wondering if this isn't a suspension issue or if something is not working properly?

  • nickeenoo

Posted August 09, 2009 - 01:50 PM

#5

You may want to consider moving the forks down (on my 426 I run them at "0 mill" and run the bars up and forward with a Dunlop MX51 front tire. Moving them up should add some stability but at a loss of corning. Moving the bars up and forward gets me up further and the bike turns better than I do...

Now the my new '09 YZ450, I am running it in stock form at 5mill and it seems to work pretty good... I do get some wondering as you describe bit honestly I think it is either me (riding to stiff and not flowing with the bike) and maybe the cheap front tire the bike came with?


Moving forks up would do just the opposite of what you said. It will add cornering but lose stability. Next, a 426 and a late model YZ are no where near the same bike. You might as well be talking Honda and Kawasaki when it comes to settings.

To the OP; check first with your suspension guy. YZ's are the most stable stock platform available. Most everyone who complains says the bike won't turn. They never say the bike is unstable.

Also, I am curious why you would not use the sag and fork height settings that all on this forum suggest?

I would try some different sag settings on my own (just for my own curiosity). Also, I would have your suspension guy on the phone for some answers.

Nate

  • e30M3

Posted August 09, 2009 - 02:38 PM

#6

Moving forks up would do just the opposite of what you said. It will add cornering but lose stability. Next, a 426 and a late model YZ are no where near the same bike. You might as well be talking Honda and Kawasaki when it comes to settings.


My error was not clarifying moving "them" up (as in the triple clamps). Yours was in not reading the whole post but you are right on both accounts, although both points go without saying...

Moving the forks up would do the opposite of what I said since I said to move the forks down!. Also, I said my new bike was set up differently than my old bike and it is working well. Your statement that the 426 and the new bikes are no where near the same, again, goes without saying...

My point was to give the op some suggestions of things he might consder trying. The forks on my 426 is set at 0 mill and I would venture to say most people run them at between 5 and 10. I went the other way to get stability (which the op was looking for) and made an adjustment to my bars in order to regain some of the "lost" steering.

  • Jim813

Posted August 09, 2009 - 05:29 PM

#7

Moving forks up would do just the opposite of what you said. It will add cornering but lose stability. Next, a 426 and a late model YZ are no where near the same bike. You might as well be talking Honda and Kawasaki when it comes to settings.

To the OP; check first with your suspension guy. YZ's are the most stable stock platform available. Most everyone who complains says the bike won't turn. They never say the bike is unstable.

Also, I am curious why you would not use the sag and fork height settings that all on this forum suggest?

I would try some different sag settings on my own (just for my own curiosity). Also, I would have your suspension guy on the phone for some answers.

Nate


I am not using the sag and fork heights on the forum for a couple reasons. The main reason is that I am testing the ranges of a stiffer rate rear steel spring, which reacts much differently than my stock lighter rate titanium spring. I have simply been thoroughly evaluating the way the new spring reacts and have not reached the 95-100mm suggested race sag setting. The other reason is the spring may be too soft and I do not feel comfortable pre-loading the spring beyond where I feel comfortable. Also, I am adjusting the fork height in small steps to dial in the way I like my bike to corner.

  • Jim813

Posted September 09, 2009 - 08:42 PM

#8

Sag set at 101.5mm, experimented with different tires, tire pressures, sag settings, and thoroughly went through almost every compression and rebound clicker adjustment and still experiencing this issue. Any thoughts?

  • Sider_steve

Posted September 09, 2009 - 10:26 PM

#9

I am having a hard time with my 2008 yz450f. The bike is very unstable almost everywhere. Through rocks the bike wanders and deflects, in whoops the bars are always twitching, and in fast single track with lots of turns the bike doesn't feel connected. I have tried everything that would seem to help. I have an RTT stabilizer, suspension done by one of the best in the business, and have checked and tightened my steering stem bearings repeatedly. The forks have been slid up in the clamps 8mm and the rear race sag is set around 110mm. I know Yamahas like race sag around 95-100mm but that would put even more weight on the front end, which leads me to think the problem would get even worse. I run 15psi front and rear. The front is a Dunlop 755 and the rear is a Maxxis IT. Any ideas to help fix this unstable, non-confidence inspiring feel?


There are sveral things that could cause this.
So I will start with the external ones.

You say you have your front forks slid up in the clamps 8 mm anytime you raise the top of the fork tube out of the triple clamp further than recomended cornering is improved with a loss of high speed stability. If the fork heights vary from one side to the other (I.E. 1 side is 8 mm the other is 7mm) this will make the high speed head shake show up at lower speeds.

Rebound settings are not the same on each fork leg. This will also cause the handlebars to twitch. Follow your manuals instructions and turn them all the way in and count the clicks. then return them to the correct setting.

Compression settings are not set the same. Follow the same procedure as the rebound settings.

Have you ever ridden a harley chopper?
Yes they look cool, but man they dont turn well and are not the most stable at speed.
Settin your sag past the window that is recomended is almost like putting ape hangers on it for handlebrs.

Hope your suspension guy gets you dialed in.

Because if none of the things I brought up are out of spec,odds are it is an internal problem.

  • Clicked

Posted September 10, 2009 - 03:32 AM

#10

I run uneven clicker settings and have never had that create a headshake problem. In adequate damping yes, uneven clicker settings no.

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  • YamaLink

Posted September 10, 2009 - 06:02 AM

#11

Adding to the great input already in this thread, the only thing I can think of - and it's a remote one - is your lower triple clamp bolts too tight? You've been moving the forks up and down: if the lower clamp bolts are too tight it will bind the forks which might possibly be the culprit for questionable front-end handling.

Long shot, but just throwing it out there.

  • Sider_steve

Posted September 10, 2009 - 07:32 AM

#12

I run uneven clicker settings and have never had that create a headshake problem. In adequate damping yes, uneven clicker settings no.


You run different settings for each fork leg?

  • Wiz636

Posted September 10, 2009 - 09:30 AM

#13

I run the sag on my '08 at 98mm, forks in stock position in the clamps, weigh 205 in street clothes, and my YZ is completely stable at any speed.

I use a Scotts damper and have the suspension dialed in with Smart Performance (stock springs though), however, I had no problem running at speed with the suspension completely stock.

Odd that you are having a stability problem...that is very unlike a YZ. Bound up forks maybe?

  • grayracer513

Posted September 10, 2009 - 09:55 AM

#14

You run different settings for each fork leg?

It would really be splitting hairs to do that, but it wouldn't cause much of a problem. Nor would it be of much benefit unless each fork were valved differently.

Dave Johnson's original approach to his groundbreaking Phase 4 modification to the KYB single chamber fork was to build one fork for all of the compression damping, and the other for the rebound in order to bypass the lack of separate adjusters for the rebound and mid valves. Worked extremely well. A lot of builders mix spring rates to get exactly what they want, like using a .44 and a .46 to get a .45 average rate. As long as the axle stays tight, it's all good.

Instability in the whoops and over really rough ground can result from pulling the forks up too far, or having something out of line, but most of the time it gets down to suspension. I know mine is vastly more stable since it was redone.

  • Jim813

Posted September 10, 2009 - 10:24 AM

#15

I am having a hard time with my 2008 yz450f. The bike is very unstable almost everywhere. Through rocks the bike wanders and deflects, in whoops the bars are always twitching, and in fast single track with lots of turns the bike doesn't feel connected. I have tried everything that would seem to help. I have an RTT stabilizer, suspension done by one of the best in the business, and have checked and tightened my steering stem bearings repeatedly. The forks have been slid up in the clamps 8mm and the rear race sag is set around 110mm. I know Yamahas like race sag around 95-100mm but that would put even more weight on the front end, which leads me to think the problem would get even worse. I run 15psi front and rear. The front is a Dunlop 755 and the rear is a Maxxis IT. Any ideas to help fix this unstable, non-confidence inspiring feel?


A couple things have changed. I switched to a Dunlop MX31 (80/100-21) front tire and a new Maxxis IT on the back (110/90-19). As I've done more testing, I've come to realize that twitching is not the correct way to describe the way the bike is reacting. It's more of a loose unstable feeling at the bar that leaves me guessing if the bike will track straight through a rough section or if the front end will kick one way or the other. The sensation is not so evident in the bigger whoops, but the smaller more square-edge acceleration and braking bumps that can be littered with rocks.

  • Sider_steve

Posted September 10, 2009 - 12:35 PM

#16

like a speed wobble?
The lower clamp being to tight could cause the feel to be harsh in the end of the fork travel,but to me it sounds like some type of bind being caused by 1 fork working different than the other and it doesn't take much.
I rode a friends bike and it just felt strange like it wanted to shake you lose.
Turned out one rebound clicker was at 5 clicks out the other at 2 clicks out.
which meant 1 side was rebounding faster than the other,trying to twist the axle. Even the slightest twist will cause the gyro effect of the from wheel to be noticeable.
Oil levels being uneven would cause the same type off effect.
A small chunk of debris blocking an oil passage will also do the same.
I would recheck everything right down to the front axle on the front end of the bike.
If it were me I would reset everything to stock setting or setting I knew worked before and take baby steps from there.

  • grayracer513

Posted September 10, 2009 - 01:06 PM

#17

... to me it sounds like some type of bind being caused by 1 fork working different than the other and it doesn't take much.

You either didn't read, or didn't believe my earlier post, eh?

  • Sider_steve

Posted September 10, 2009 - 01:34 PM

#18

You either didn't read, or didn't believe my earlier post, eh?


:busted: :thumbsup: :banana: :banana: :banana: :banana: :banana:

Best wishes on finding your problem Jim.
Might try the suspension forum in the tech section.

  • BaileyAZ

Posted September 10, 2009 - 02:56 PM

#19

I have an 2008 as well and am running stock suspension and OE tires and don't have any issues as you describe. I also ride here in AZ thru terrain as you describe. Have you thought about ditching the Maxxis? I have ran several on my CRF450X and loved the wear factor, but I hated how stiff the side walls were. You can really feel a difference compared to other brands. I also had issues running and SI front in the desert terrain. Just a thought, and worst case you are out $100 and have a second set of tires.

  • twenty34

Posted September 10, 2009 - 06:55 PM

#20

The YZ is one of the more stable bikes out there. Go back to stock settings fork position and start over in small increments.





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