I had the same problem on my Gen1, always bottoming out. Racetech's calculator said the stock springs were bang on for my weight. They tested my springs when I had some work done on the forks and found them to be way lighter than advertised. New set of Racetechs springs and gold valves cleared that right up.
Gen 1: Fork travel, oil height, tuning...
n00bie to the forum, just bought myself a gen 1 and very impressed so far!
However, my forks had a blown seal so while changing that i'm trying a few things to make the standard forks a bit more compliant and work as well as they should.
Does anyone know the mechanical fork travel on the gen 1 forks? Will it bottom out on the axle casting or is it before then?
I've rebuilt them with a motul 5wt oil and set the oil height slightly lower than the stock 91mm at 100mm. So far they seem very smooth and controlled, but under really hard braking i'm pushing the zip tie down to about 10-13mm from the bottom - does anyone know if this is bottoming out or if i'm pushing it down onto the oil lock part of the travel?
I'm just wondering if i've got the oil height a little low and could up it a bit to provide more support at the bottom, or if i've fluked it at about right?! haha
I think the stock springs are spot on for me - not too soft. I'm getting a good 35mm sag (20mm free and further 15 laden) with only 3 lines of preload.
So my only concern is that the oil height is a bit low meaning they're maybe bottoming out? But if the mechanical bottom out is right to the casting then the 10-13mm i'm getting to might be about perfect.
Anyone with any experience tuning the stock gen 1 forks at all?
thanks
However, my forks had a blown seal so while changing that i'm trying a few things to make the standard forks a bit more compliant and work as well as they should.
Does anyone know the mechanical fork travel on the gen 1 forks? Will it bottom out on the axle casting or is it before then?
I've rebuilt them with a motul 5wt oil and set the oil height slightly lower than the stock 91mm at 100mm. So far they seem very smooth and controlled, but under really hard braking i'm pushing the zip tie down to about 10-13mm from the bottom - does anyone know if this is bottoming out or if i'm pushing it down onto the oil lock part of the travel?
I'm just wondering if i've got the oil height a little low and could up it a bit to provide more support at the bottom, or if i've fluked it at about right?! haha
I think the stock springs are spot on for me - not too soft. I'm getting a good 35mm sag (20mm free and further 15 laden) with only 3 lines of preload.
So my only concern is that the oil height is a bit low meaning they're maybe bottoming out? But if the mechanical bottom out is right to the casting then the 10-13mm i'm getting to might be about perfect.
Anyone with any experience tuning the stock gen 1 forks at all?
thanks
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Thanks for that - yeah it makes sense from what i've seen too.
I only weigh 175 with gear and am easily getting good sag numbers - so there's no chance the springs in mine are the 10s i've seen mentioned as stock. They must be more like 9s or just above to give me good sag figures, and even then i think i could go up to 9.5s for hard track use/heavy braking.
When yours were bottoming were you getting metal/metal contact at the bottom of the axle casting?
I only weigh 175 with gear and am easily getting good sag numbers - so there's no chance the springs in mine are the 10s i've seen mentioned as stock. They must be more like 9s or just above to give me good sag figures, and even then i think i could go up to 9.5s for hard track use/heavy braking.
When yours were bottoming were you getting metal/metal contact at the bottom of the axle casting?
I changed out to race tech springs and gold valves. Made a huge difference. Its very difficult to to tune the harshness out of the stock forks. I go 235 in gear and they were to harsh for my weight. You could start by running zero compression and see if that helps. Were you able to get static sag set properly. The problem is the variable rate springs the Race Tech straight rate springs just work better.
Thanks for the info mate - that's what i'd read so much about the harshness of them.
What's strange is that even at my 175lbs i've got a good 35mm sag with preload in the middle of adjustment. 20mm free sag and an extra 15mm when i get on.
They don't look like aftermarket springs, there's no markings on them. Makes me wonder if there's quite a range of stock springs out there from the kawasaki shelf - anything from 9s to 10s.
I think putting the lighter weight oil and lower oil level in has really made them less harsh in terms of damping too - if anything i'm worried i've gone a bit far and they may be bottoming. I just don't know where the mechanical bottom is on these forks?
in future thought i'll definitely be lookin at springs and a piston kit.
What's strange is that even at my 175lbs i've got a good 35mm sag with preload in the middle of adjustment. 20mm free sag and an extra 15mm when i get on.
They don't look like aftermarket springs, there's no markings on them. Makes me wonder if there's quite a range of stock springs out there from the kawasaki shelf - anything from 9s to 10s.
I think putting the lighter weight oil and lower oil level in has really made them less harsh in terms of damping too - if anything i'm worried i've gone a bit far and they may be bottoming. I just don't know where the mechanical bottom is on these forks?
in future thought i'll definitely be lookin at springs and a piston kit.
The Gen 1 bottoms at about 5 mm from the bottom, so you'll never go all the way down. As to oil level thats not too low and won't be an issue with bottoming. To give you an idea on stock I ran 190mm, Ohlins 30 mm I ran 200mm, and my Bitubo gas I run around 220mm air gap. If you're concerned about bottoming add a turn or two of preload in the front to keep you off the bottom.
That's great info, thanks!
I did think i'd been quite conservative with only going to a 100mm gap so that makes sense. Having said that even with my compression damping wound right up/in i can push a zip tie right down with some prolonged, heavy braking. Maybe the springs are a bit soft. Or maybe it's the lighter oil i've gone with.
I have a feeling i'm not close to mechanical bottom, but there seems to be a 10mm or so 'oil lock' bottom where the damping goes incredibly hard to stop mechanical bottom occurring - and i think i'm getting down to that.
Thanks for the info though, i'll have a play with preload and springs.
Is it also the case that the stock valving tends to give too much rebound damping? I have my rebound wound right out and still it's not bouncing right back up to me, certainly no pogo or settling into a 2nd stroke. Not that i want that, but am surprised how much rebound damping there seems to be. Or maybe again though, a heavier spring would push back a bit more
I did think i'd been quite conservative with only going to a 100mm gap so that makes sense. Having said that even with my compression damping wound right up/in i can push a zip tie right down with some prolonged, heavy braking. Maybe the springs are a bit soft. Or maybe it's the lighter oil i've gone with.
I have a feeling i'm not close to mechanical bottom, but there seems to be a 10mm or so 'oil lock' bottom where the damping goes incredibly hard to stop mechanical bottom occurring - and i think i'm getting down to that.
Thanks for the info though, i'll have a play with preload and springs.
Is it also the case that the stock valving tends to give too much rebound damping? I have my rebound wound right out and still it's not bouncing right back up to me, certainly no pogo or settling into a 2nd stroke. Not that i want that, but am surprised how much rebound damping there seems to be. Or maybe again though, a heavier spring would push back a bit more
Couple things for ya. Bottoming resistance and damping are two separate things. The "oil lock" is not damping, but the air gap compressing all the way and keeping you from moving in the stroke. If you were to change nothing else but the oil level you would be able to push the forks further in the stroke. This is why we run very low oil levels, to help eliminate the air gap and then control stroke/bottoming with spring rate and preload.That's great info, thanks!
I did think i'd been quite conservative with only going to a 100mm gap so that makes sense. Having said that even with my compression damping wound right up/in i can push a zip tie right down with some prolonged, heavy braking. Maybe the springs are a bit soft. Or maybe it's the lighter oil i've gone with.
I have a feeling i'm not close to mechanical bottom, but there seems to be a 10mm or so 'oil lock' bottom where the damping goes incredibly hard to stop mechanical bottom occurring - and i think i'm getting down to that.
Thanks for the info though, i'll have a play with preload and springs.
Is it also the case that the stock valving tends to give too much rebound damping? I have my rebound wound right out and still it's not bouncing right back up to me, certainly no pogo or settling into a 2nd stroke. Not that i want that, but am surprised how much rebound damping there seems to be. Or maybe again though, a heavier spring would push back a bit more
If those springs are stock they should be plenty to get what you need to do. I would highly suggest adding a couple turns of preload and see how that feels. This will help with your prolong braking and keeping it off the bottom of the stroke.
And as to rebound, I suspect you're feeling the bleed and not the stack itself. With such a high oil level in there you may not be able to generate enough force to really feel what the front end is doing. Also be careful when "tuning in the pits". You can never generate forces like on the road/track, so I would go more off what the bike feels like while riding vs what the bike does in your garage. Good luck!
Again thanks man, very helpful!Couple things for ya. Bottoming resistance and damping are two separate things. The "oil lock" is not damping, but the air gap compressing all the way and keeping you from moving in the stroke. If you were to change nothing else but the oil level you would be able to push the forks further in the stroke. This is why we run very low oil levels, to help eliminate the air gap and then control stroke/bottoming with spring rate and preload.
If those springs are stock they should be plenty to get what you need to do. I would highly suggest adding a couple turns of preload and see how that feels. This will help with your prolong braking and keeping it off the bottom of the stroke.
And as to rebound, I suspect you're feeling the bleed and not the stack itself. With such a high oil level in there you may not be able to generate enough force to really feel what the front end is doing. Also be careful when "tuning in the pits". You can never generate forces like on the road/track, so I would go more off what the bike feels like while riding vs what the bike does in your garage. Good luck!
As for rebound i see what you mean entirely. The old Dave Moss 'bounce' on the bike treatment is one thing but as you say no way you can replicate the forces of some bumps and heavy braking at speed.
I'm sure the springs must be fine too. In fact i've been surprised that at my 175 i've even been able to get good sag numbers after reading so much about them being pretty hard springs. But my sag seems pretty good within the middle of their preload range.
Interesting with the oil lock stuff and about the small air gap i've used. I'd been reading some stuff like this - Peter Verdone Designs - Oil Locks
I was under the impression most stock forks have this mechanical oil lock piece to support undersprung stock forks from bottoming under any extreme circumstance. I can see for guys like yourself doing a lot of track/race use it's best to get rid of this altogether, but maybe a good little extra insurance on my crappy, bumpy UK roads.
But nevertheless interesting to know i'm not using a low oil level by any means - far from it.
Just fitted some 16/40 sprockets (which in part help just cancel out the bigger 55 tyre) and a 112 chain to get the axle a little closer to the back, so need to get out and just do some serious miles.
Thanks for the help.
Thanks again, big help!Couple things for ya. Bottoming resistance and damping are two separate things. The "oil lock" is not damping, but the air gap compressing all the way and keeping you from moving in the stroke. If you were to change nothing else but the oil level you would be able to push the forks further in the stroke. This is why we run very low oil levels, to help eliminate the air gap and then control stroke/bottoming with spring rate and preload.
If those springs are stock they should be plenty to get what you need to do. I would highly suggest adding a couple turns of preload and see how that feels. This will help with your prolong braking and keeping it off the bottom of the stroke.
And as to rebound, I suspect you're feeling the bleed and not the stack itself. With such a high oil level in there you may not be able to generate enough force to really feel what the front end is doing. Also be careful when "tuning in the pits". You can never generate forces like on the road/track, so I would go more off what the bike feels like while riding vs what the bike does in your garage. Good luck!
Definitely right about the rebound and using the old Dave Moss bounce on the bike, nothing like the forces of bumps and hard braking.
Also been very surprised, given the reputation of stock springs being pretty firm, that i could even get good sag numbers at my 175 weight. But they seem good so i'll stick with them.
As for the oil i see what you mean with air spring etc. But i'd been reading some stuff like this.. Peter Verdone Designs - Oil Locks
It was that i was thinking i was getting down towards. I noticed when bleeding the forks with the damper rod after filling with oil that it's a nice smooth action until the last 10mm or so. I assumed that was this oil lock piece mentioned above. Seems like a good extra insurance on bumpy UK roads, but probably not something you more track/race oriented guys would use at all.
Good to know my oil level is by no means low though - far from it.
As said i just need to get out and ride it more now to go by feel. Just fitted 16-40 sprockets and a 112 chain to get the axle back a bit and a 55 rear tyre, so best get out riding!
thanks again
Repped for helping a member with your professional knowledge. :thumbsup:Couple things for ya. Bottoming resistance and damping are two separate things. The "oil lock" is not damping, but the air gap compressing all the way and keeping you from moving in the stroke. If you were to change nothing else but the oil level you would be able to push the forks further in the stroke. This is why we run very low oil levels, to help eliminate the air gap and then control stroke/bottoming with spring rate and preload.
If those springs are stock they should be plenty to get what you need to do. I would highly suggest adding a couple turns of preload and see how that feels. This will help with your prolong braking and keeping it off the bottom of the stroke.
And as to rebound, I suspect you're feeling the bleed and not the stack itself. With such a high oil level in there you may not be able to generate enough force to really feel what the front end is doing. Also be careful when "tuning in the pits". You can never generate forces like on the road/track, so I would go more off what the bike feels like while riding vs what the bike does in your garage. Good luck!
hmm,
well i've just been for a good couple of hours in the twisties and i'm definitely bottoming at times and getting way too far through the stroke too easily. It's really limiting my confidence in the front while braking and into corners. Even with increased preload and/or compression damping it seems to move through the stroke too easily.
I wonder now whether the 5wt Motul oil i've used is too light for stock valving and is flowing too fast? Or maybe just heavier springs would help. My instinct is that heavier springs are the 'proper' way to do it, as surely heavier oil just slows down the fork too much.
it's not like with the 5wt oil it's pogo-ing and chattering all over the place, it's just too much dive too easily.
well i've just been for a good couple of hours in the twisties and i'm definitely bottoming at times and getting way too far through the stroke too easily. It's really limiting my confidence in the front while braking and into corners. Even with increased preload and/or compression damping it seems to move through the stroke too easily.
I wonder now whether the 5wt Motul oil i've used is too light for stock valving and is flowing too fast? Or maybe just heavier springs would help. My instinct is that heavier springs are the 'proper' way to do it, as surely heavier oil just slows down the fork too much.
it's not like with the 5wt oil it's pogo-ing and chattering all over the place, it's just too much dive too easily.
5wt is too light, that's for mx bikes. and like others said, get the racetech springs and valving. For someone like you, its worth it.
That's kind of subjective. 90% of the street stock forks we service use 5wt oil. Hell, Ohlins oil used in pretty much everything is the same CST as Motul 5wt.5wt is too light, that's for mx bikes. and like others said, get the racetech springs and valving. For someone like you, its worth it.
I was just looking through your post again and you mention you have 20mm of free sag? Just so Im clear, you consider free sag the distance from the suspension full extended to the where the bike sits under it's own weight? And then laden is the distance from the weight of the bike to where it sits with you on it?hmm,
well i've just been for a good couple of hours in the twisties and i'm definitely bottoming at times and getting way too far through the stroke too easily. It's really limiting my confidence in the front while braking and into corners. Even with increased preload and/or compression damping it seems to move through the stroke too easily.
I wonder now whether the 5wt Motul oil i've used is too light for stock valving and is flowing too fast? Or maybe just heavier springs would help. My instinct is that heavier springs are the 'proper' way to do it, as surely heavier oil just slows down the fork too much.
it's not like with the 5wt oil it's pogo-ing and chattering all over the place, it's just too much dive too easily.
If that's the case it sounds like you might be backwards. Free sag should be around 10 to 15mm and rider sag is about 20. That would explain the dive, not enough support at the topend of the stroke.
As to the oil, Motul 5wt is closer to a 7.5wt for most other fork oils. Is this hurting you? Maybe, maybe not. If this was my bike or one of my riders I would be looking at spring preload before oil viscosity.
Thanks! I'm always here to help when I can.Repped for helping a member with your professional knowledge. :thumbsup:
Again, massive help man. Thanks!I was just looking through your post again and you mention you have 20mm of free sag? Just so Im clear, you consider free sag the distance from the suspension full extended to the where the bike sits under it's own weight? And then laden is the distance from the weight of the bike to where it sits with you on it?
If that's the case it sounds like you might be backwards. Free sag should be around 10 to 15mm and rider sag is about 20. That would explain the dive, not enough support at the topend of the stroke.
As to the oil, Motul 5wt is closer to a 7.5wt for most other fork oils. Is this hurting you? Maybe, maybe not. If this was my bike or one of my riders I would be looking at spring preload before oil viscosity.
You're right that's how i'd got my sag figures - from what you've said i would think that means the springs are too firm with too little preload? But weirdly i can wind my preload all the way down to max and still bottom the forks too easily.
Also, just measured even on nearly max preload i'm getting a comfortable 20mm or just over of sag purely under the bikes weight alone.
Based on that and the fact i have some k-tech 9.5 springs sat here recommended to me buy a k-tech tuner i'll put those in and see what happens.
Can springs get old/tired/soft? Maybe they're beyond their usable range and simply need replacing due to age.
If you don't mind me asking you yet more questions, what's your opinion on the stock valves and valving?
Thanks a lot
I know you are and I want to make sure you know its sincerely appreciated. This is what makes this forum special above others.Thanks! I'm always here to help when I can.
:thumbsup:
Again, massive help man. Thanks!
You're right that's how i'd got my sag figures - from what you've said i would think that means the springs are too firm with too little preload? But weirdly i can wind my preload all the way down to max and still bottom the forks too easily.
Also, just measured even on nearly max preload i'm getting a comfortable 20mm or just over of sag purely under the bikes weight alone.
Based on that and the fact i have some k-tech 9.5 springs sat here recommended to me buy a k-tech tuner i'll put those in and see what happens.
Can springs get old/tired/soft? Maybe they're beyond their usable range and simply need replacing due to age.
If you don't mind me asking you yet more questions, what's your opinion on the stock valves and valving?
Thanks a lot
No worries! I can tell you the K-Tech springs are gonna be no bueno. Stock springs are 1.0 kg (about 9.8nm) where the ones from K-Tech are 9.5nm which are lighter. I would also say 9.5nm springs would be a good rate to go with. But the fact that your bottoming leads me to believe there are other issues.
Couple question for you.
Are you actually feeling the forks bottom, or are you going of a zip tie?
Does the rear end lift off the ground during hard braking?
Do you charge the corners? As in do you come in really fast into a corner and then jam the brakes and then throw the bike in?
When you're coming up to a corner, do you feel like you're carrying too much speed to make the corner and grab brake to slow down? Almost like you know the bike wont make the corner at the speed you're at and you slow down to a speed you KNOW you'll make it at?
Stock valving is ok, not bad, not good. I have a suspicion I know what your issue is but I need to confirm a few things (hence the questions).
No worries! I can tell you the K-Tech springs are gonna be no bueno. Stock springs are 1.0 kg (about 9.8nm) where the ones from K-Tech are 9.5nm which are lighter. I would also say 9.5nm springs would be a good rate to go with. But the fact that your bottoming leads me to believe there are other issues.
Couple question for you.
Are you actually feeling the forks bottom, or are you going of a zip tie?
Does the rear end lift off the ground during hard braking?
Do you charge the corners? As in do you come in really fast into a corner and then jam the brakes and then throw the bike in?
When you're coming up to a corner, do you feel like you're carrying too much speed to make the corner and grab brake to slow down? Almost like you know the bike wont make the corner at the speed you're at and you slow down to a speed you KNOW you'll make it at?
Stock valving is ok, not bad, not good. I have a suspicion I know what your issue is but I need to confirm a few things (hence the questions).
Well i had heard that stock springs were 1.0kg but with being able to get reasonable sag numbers even with a good amount of preload i thought these must seem softer at my weight.
I wouldn't say i ride like that no. To be honest i've been giving the bike some harder braking than you might ordinarily just to see what the forks are doing. When doing this i have felt the back wheel starting to go light and sway about a bit yeah.
Ordinarily my riding isn't like that though - i'm a fast group rider on track here in the UK, i do brake pretty hard and trail it in quite deep, coming off gradually. I wouldn't say i'm a jabby, panic braker! lol
My old 5jj R1 had k-tech 20mm piston kit in too and i just felt so much support and feedback from them. With the zx10 forks it just seems to dive too quickly and then i feel it reach that point where all feeling goes and it gets nervous. I assumed that was where i was pushing that oil lock/bottom. Also a zip tie is showing within 5-10mm of the bottom with what feels to me too little effort.
It feels like it needs more rebound to keep control of the fork more, but i've been hesitant to have much rebound at all cos it seemed that would hold it down and make the bottoming even more likely/worse.
Could it be geometry? The forks were pulled a few mm through the yokes but i've dropped them back to stock now just to see.
I'm not sure i've really answered your questions well! But yes i do brake fairly late and hard i'd say. On track i've been pretty comfortable trail braking and feel i'm quite a 'front end' kind of guy. It just feels uncontrolled and too fast the way it dives and dives so far?
Are you gonna tell me it's technique and my rushed, panicky aggressive braking?! lol... quite possibly!
I think i've been spoiled by the support and feedback of a 20mm kit before and now stock forks seem a little less confidence inspiring maybe!
thanks
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