Gen 1: Fork travel, oil height, tuning... - Kawasaki ZX-10R.net
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post #1 of 25 Old 05-26-2016, 06:03 AM Thread Starter
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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
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post #2 of 25 Old 05-26-2016, 11:10 PM
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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.
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post #3 of 25 Old 05-27-2016, 05:01 AM Thread Starter
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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?
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post #4 of 25 Old 05-27-2016, 03:13 PM
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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.
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post #5 of 25 Old 05-27-2016, 03:49 PM Thread Starter
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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.
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post #6 of 25 Old 05-27-2016, 04:00 PM
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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.

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post #7 of 25 Old 05-27-2016, 04:20 PM Thread Starter
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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
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post #8 of 25 Old 05-27-2016, 08:09 PM
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Originally Posted by craig_ View Post
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
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!

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post #9 of 25 Old 05-28-2016, 03:03 AM Thread Starter
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Originally Posted by evallarta1 View Post
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!
Again thanks man, very helpful!

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.
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post #10 of 25 Old 05-28-2016, 04:09 AM Thread Starter
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Quote:
Originally Posted by evallarta1 View Post
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!
Thanks again, big help!

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
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