Help! Yz250f twitchy front end

Ichnusa
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Hello, I'm 140lb and I have respring my bike with 0.44 springs in the fork and a 5.2 kg/mm in the shock, like RT calculator recommend.
I have 105 mm of sag and 1.5 turs out in the HSC but the rear of the bike feels low, harsh and bottoms in g-outs so I turn in 1/4 of turn the HSC and the bike feels better in g-outs but the rear feels more high and the front end it's become twitchy! Can I compesate the HSC increments dropping a little bit the SAG? What can I do for set the bike at the better? I hope you guys can give me some advises!
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kb228
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2/17/2022 9:45am
Adjust fork height
Ichnusa
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2/17/2022 10:04am
kb228 wrote:
Adjust fork height
Less than 3mm over the clamps?
murph783
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2/17/2022 10:10am
You could definitely drop the forks a touch. Maybe flush with the cap. But if the front feels twitchy I’d think you want the rear lower. Try fork height, then maybe try 100mm sag and 110mm, see which direction you like more.
Ichnusa
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2/17/2022 10:39am
murph783 wrote:
You could definitely drop the forks a touch. Maybe flush with the cap. But if the front feels twitchy I’d think you want the rear lower...
You could definitely drop the forks a touch. Maybe flush with the cap. But if the front feels twitchy I’d think you want the rear lower. Try fork height, then maybe try 100mm sag and 110mm, see which direction you like more.
I went from 103 to 105mm of SAG and the bike was way better so I think I will try to drop a little bit more the SAG like 1/4 or 1/2 turn and see if it compensate well and without side effects the HSC increment I did last sunday. I think that I need even a little more conpression damping in the shock but I didn't add it for fear of accentuate the twitchy reaction at the front.

The Shop

Ichnusa
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2/17/2022 10:57am
What's the difference in how the bike feels between raise or drop the fork in the clamps and raise or drop the SAG? It's raise/lower front or rear but maybe it feels different in bike handling.
Falcon
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2/17/2022 11:54am
Remember that raising or lowering the forks does not change the damping factors on the forks, while changing the shock sag does change them for the shock.
For handling purposes, you would be better off adjusting the fork height, assuming you like the feel of your shock.
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wrc777
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2/17/2022 12:21pm
Twitchy entering corners I would look for fork adjustments. 0.44 front springs are probably way too soft unless you are running off-road. At the minimum you probably need to increase the spring preload since the bike was designed to have the correct attitude with 140-160 lb rider with the stock springs.

The RT spring calculator assumes you are using their valving specs...You probably want to use stock fork springs or maybe 1 rate softer. You are about at the target weight for a 250f.
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Ichnusa
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2/17/2022 12:29pm
wrc777 wrote:
Twitchy entering corners I would look for fork adjustments. 0.44 front springs are probably way too soft unless you are running off-road. At the minimum you...
Twitchy entering corners I would look for fork adjustments. 0.44 front springs are probably way too soft unless you are running off-road. At the minimum you probably need to increase the spring preload since the bike was designed to have the correct attitude with 140-160 lb rider with the stock springs.

The RT spring calculator assumes you are using their valving specs...You probably want to use stock fork springs or maybe 1 rate softer. You are about at the target weight for a 250f.
Do you think i should change to stock only the fork springs? I did install a 5.1nm in the rear
Ichnusa
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2/17/2022 12:34pm
I did search in q-springs calculator and it reccommended 4.4nm fork springs
wrc777
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2/17/2022 2:30pm
wrc777 wrote:
Twitchy entering corners I would look for fork adjustments. 0.44 front springs are probably way too soft unless you are running off-road. At the minimum you...
Twitchy entering corners I would look for fork adjustments. 0.44 front springs are probably way too soft unless you are running off-road. At the minimum you probably need to increase the spring preload since the bike was designed to have the correct attitude with 140-160 lb rider with the stock springs.

The RT spring calculator assumes you are using their valving specs...You probably want to use stock fork springs or maybe 1 rate softer. You are about at the target weight for a 250f.
Ichnusa wrote:
Do you think i should change to stock only the fork springs? I did install a 5.1nm in the rear
I would start with the front. You could just change one side and see if that moves you in the right direction. Dropping forks in the clamps should also help as will turning in the compression clickers on the forks but that may make it harsh in other places.
mx724
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2/18/2022 5:27am Edited Date/Time 2/18/2022 5:29am
Some pointers that might help.

If your bottoming in G outs Id try increasing the rear shock compression. HSC is more for fast hard reactions, think bucking and chop on strait a ways, that's the way I tend to think about it.

I had to do quite a bit to get this same chassis to settle.

I run a lowering link from Devol on their recommended setting. Im about 5mm up in the clamps on the forks. However; the biggest difference was when I removed 10cc of oil from the forks and added the SDI pro perches. The Pro Perch isnt necessary at all but allows you to run lower oil while maintaining bottoming resistance off big hits.

I run my HSC about a 1 1/4 turn out. HSC will effect the ride height of the rear to some extent. You should set sag first and proceed to set ur HSC at stock. Find where you like your compression and then come back and fine tune ur HSC. Also may want to verify you rebound settings. Its possible your rebound is slow and creating a packing effect. Its all about even weight bias and getting the bike level and working equally front and back. Watch video if you have too.

Having your bars in the front position is best. If you have them in the closest to rider position it will really mess with things.
Ichnusa
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2/18/2022 9:13am
mx724 wrote:
Some pointers that might help. If your bottoming in G outs Id try increasing the rear shock compression. HSC is more for fast hard reactions, think...
Some pointers that might help.

If your bottoming in G outs Id try increasing the rear shock compression. HSC is more for fast hard reactions, think bucking and chop on strait a ways, that's the way I tend to think about it.

I had to do quite a bit to get this same chassis to settle.

I run a lowering link from Devol on their recommended setting. Im about 5mm up in the clamps on the forks. However; the biggest difference was when I removed 10cc of oil from the forks and added the SDI pro perches. The Pro Perch isnt necessary at all but allows you to run lower oil while maintaining bottoming resistance off big hits.

I run my HSC about a 1 1/4 turn out. HSC will effect the ride height of the rear to some extent. You should set sag first and proceed to set ur HSC at stock. Find where you like your compression and then come back and fine tune ur HSC. Also may want to verify you rebound settings. Its possible your rebound is slow and creating a packing effect. Its all about even weight bias and getting the bike level and working equally front and back. Watch video if you have too.

Having your bars in the front position is best. If you have them in the closest to rider position it will really mess with things.
"Having your bars in the front position is best. If you have them in the closest to rider position it will really mess with things"
Really? Why? I have it in the closest rider position
mx724
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2/18/2022 9:57am
Talking from experience. You want your bars centered over the forks not in front of or behind. Even if you go front mount holes and rotate the clamps back, that is what I opted for.
Ichnusa
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2/18/2022 10:02am
I mount it back because I'm not so tall I'm 168cm but I will try it a little more in front
murph783
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2/21/2022 6:19am
Ichnusa wrote:
I mount it back because I'm not so tall I'm 168cm but I will try it a little more in front
I run mine in the rear position when I’m using a stock clamp. It’s all rider preference
mx724
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2/22/2022 7:23am Edited Date/Time 2/22/2022 7:37am
It is rider preference to some degree.

But frame ergos matter. Spring rate, sag, how far back you rear wheel is, how high are your forks in the clamps etc all have significant impact on how the bike reacts at speed. If you have a twitchy front end I often read that as to much weight on the front. You can alter that in a variety of methods. Start with one change at a time. Go back to stock recommendations and start working thru it. Either your rear is to stiff putting load on the front, or your front is to soft, maybe both. The yz of this generation is known for the stinkbug stance out of the box. Record your current settings before you go back to stock so you have a pt of reference.

By placing the bars in front of the forks or behind the forks you alter the turn in geometry significantly. I'm only 5'10" and I initially moved the bars back bc it felt awkward in the front position. First thing I did to try and improve things was move the bars back to the front and found a bend that was more suitable, this helped a bit. The bike became far more predictable after that. Then I added the lowering link and raised the forks to the 5.5mm This got the overall bike squatting more level and performed much better thru corners and ruts.

If you want to find good settings you have to try different things. Its pretty well known that the best place to start with your bars is centered over the forks, I'm speaking to my experience with this particular chassis.
murph783
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2/22/2022 12:20pm
That actually brings up a good point, I’ve found running my rear wheel farther back works well on the yamahas
Ichnusa
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2/23/2022 4:36am
I've tryed to drop the sag but it made not much effect so I've set back the hsc to 1.5 and it had calm down the front but the bike but, under acceleration, it's back to squat too easily, in exit of corners the rear end goes up and down, moves side to side and in big bumps blows thru the sroke. The front pushes. I'm thinking It's maybe the rebound too open that allows the suspension to move too easily and makes too easy load transfers back/front-front/back. it's possible?
My rebound it's set to -14 front/rear pretty far from stock that's -7 front -9 rear. Suspension makes me confused 😅
wrc777
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2/23/2022 7:05am
Yes too fast rebound (not enough damping) can cause pitching. Not only that but the rebound adjusters affect mid-valve compression and rebound. So if you change rebound you generally need to compensate with the compression clicker the opposite direction to maintain the compression dampening you had before the rebound adjustment. So reduce rebound 1 click, increase compression 2 clicks to compensate and maintain the compression.
mx724
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2/23/2022 7:16am
add 1-2 clicks to your regular rear compression not your high speed if you feel like it dips under hard acceleration in the rear. This is all assuming you have the right spring rate and sag set.

If that doesn't give you the results you want go back to the prior compression setting and try turning the HSC in 1/4 turn or less. Most ppl don't realize how sensitive HSC can be.

Moving the rear when back does a few things.
1.) It puts more leverage back into the shock shaft altering how the shock works under the same settings.
2.) Gives you a wider wheel base which can stabilize the bike on fast straights.

-If you move the rear wheel in closer to the pegs its going to decrease the wheel base and leverage, consequently makes the bike more front bais and can help turn in in some instances.

Keeping all this in mind.... these are small incremental movements we are talking about. Its all about balance and working in sync front and back. I tend to run my wheel middle to back of bike. Mark any current setting prior to changing. Otherwise you will just be chasing your tail.
Ichnusa
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2/23/2022 7:55am
I've already tried to turn in 1/4 the hsc and it solve the shock diving but gives a sinkbug feel, front end heavy and twichness so I'm back to 1.5 HSC and close 4 clicks in compression but it don't do the trick... so I'm whatching for the rebound that like wrc777 said affects even the compression and it's the only thing thad I aven't tried yet
soggy
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2/23/2022 8:45am
Ichnusa wrote:
I've already tried to turn in 1/4 the hsc and it solve the shock diving but gives a sinkbug feel, front end heavy and twichness so...
I've already tried to turn in 1/4 the hsc and it solve the shock diving but gives a sinkbug feel, front end heavy and twichness so I'm back to 1.5 HSC and close 4 clicks in compression but it don't do the trick... so I'm whatching for the rebound that like wrc777 said affects even the compression and it's the only thing thad I aven't tried yet
In my experience rebound is the cause of more setup issues then compression dampening. A lack of rebound dampening can cause pitching or give you a harsh feeling in the stroke. Sounds like your rebound is set up super fast.
wrc777
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2/23/2022 8:54am
Set all clickers and sag back to stock and start over. You are so far out in the weeds you are not going to be able to figure it out from your current settings.

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