Harsh fork full extension

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3/4/2019 11:21 AM

Hoping more knowledgeable suspension guys than myself can answer this for me.

2016 KX450 SFF TAC with PC Spring Conversation.

I have noticed that when I come off a smaller high suspension speed hit such as small sharp double or table that doesn’t have a large enough ramp for the entire motorcycle I can feel the fork top out sharply enough to not feel normal. I am going to disassemble this afternoon to inspect but wondering if anyone else has ever noticed this sensation, I don’t notice this with my 06 KX250 with standard KYB AOS forks.


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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

3/5/2019 2:02 PM

Sounds like maybe the oil level is too low.

Paw Paw

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3/5/2019 6:55 PM
Edited Date/Time: 3/5/2019 6:55 PM

I had this with a spring conversion that I tried making myself out of KX250F SFF parts. The damping leg does not have a top-out spring, since the balance chamber in the TAC typically handles that function. I never solved it and ended up buying some KYB forks for it, but damn was that u settling when the fork would top out in the air!

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3/5/2019 7:42 PM

Paw Paw 271 wrote:

Sounds like maybe the oil level is too low.

Paw Paw

Thanks Paw Paw!

I disassembled and everything looked normal I had 450ml in the spring side. I’m in a little bit of a weird spot because I have FC valving and they won’t make a recommendation on oil volume because it’s a PC conversion. I called PC and they said they couldn’t recommend a volume because of the FC valving!!!

I went on RT and they recommended 525 with their conversation kit so I thought the 450 was a good starting point and I have only bottomed a couple times on some large hits.

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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

3/5/2019 7:48 PM

Jbulz wrote:

I had this with a spring conversion that I tried making myself out of KX250F SFF parts. The damping leg does not have a top-out spring, since the balance chamber in the TAC typically handles that function. I never solved it and ended up buying some KYB forks for it, but damn was that u settling when the fork would top out in the air!

That’s what I was actually thinking it might be. As long as it’s sorta normal I can live with it, overall it is such a positive change getting rid of the air spring. I’ll probably get a 19 soon and not have to worry about it!

Thanks for the response I appreciate it!

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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

3/5/2019 8:01 PM
Edited Date/Time: 3/5/2019 8:03 PM

Funny thing I haven't ever felt KX250F SFF's top out like you explain, I have first gen (2012) SFF's on my KX250. I just put the Race Tech spring conversion in my 18 KX450F but haven't had a chance to ride it yet so I will be curious to see how it tops out. I wonder if Racetech or Pro Circuit offer different top out springs for the conversions or could explain how to make it less noticeable (IE more oil or a different top out spring stiffness).

Now I'm even more anxious to try out the spring conversion.

Maybe Slipdog or DaveJ will chime in.

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2018 KX450F
2005 KX250
2003 KDX 220
1984 KX 80
1982 RM 80
1980 RM 80
1977 XR 75
1969 Honda Mini 50

3/5/2019 11:33 PM

dkurtd wrote:

Funny thing I haven't ever felt KX250F SFF's top out like you explain, I have first gen (2012) SFF's on my KX250. I just put the Race Tech spring conversion in my 18 KX450F but haven't had a chance to ride it yet so I will be curious to see how it tops out. I wonder if Racetech or Pro Circuit offer different top out springs for the conversions or could explain how to make it less noticeable (IE more oil or a different top out spring stiffness).

Now I'm even more anxious to try out the spring conversion.

Maybe Slipdog or DaveJ will chime in.

Yeah it's weird, on a normal low suspension speed jump it does not do it at all. When hitting whoops, rollers, or small doubles that send you more up than out it's a distinct feeling when it hits full extension. I would be interested to hear back when you have a chance to ride your 18 450 with the RT conversion. Everywhere else it has been very positive to the overall feel and handling of the bike, no more front wheel wandering/ hunting at turn in, center out is more precise and I can actually get it to settle in a rut!

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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

3/7/2019 7:25 AM

bvm111 wrote:

Hoping more knowledgeable suspension guys than myself can answer this for me.

2016 KX450 SFF TAC with PC Spring Conversation.

I have noticed that when I come off a smaller high suspension speed hit such as small sharp double or table that doesn’t have a large enough ramp for the entire motorcycle I can feel the fork top out sharply enough to not feel normal. I am going to disassemble this afternoon to inspect but wondering if anyone else has ever noticed this sensation, I don’t notice this with my 06 KX250 with standard KYB AOS forks.


I’m running a similar setup to you. FC revalve and a JGR spring conversion. The PC and JGR spring kit are almost identical. JGR recommended 350ml oil in my setup where I’ve seen guys running closer to 500ml in the FC setups. I may be incorrect in thinking this way but the PC & JGR kits may require less oil because of the air cartridge volume. Mine tops out hard as well but overall I’m very happy with it.

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3/7/2019 11:11 AM

bdavis435 wrote:

I’m running a similar setup to you. FC revalve and a JGR spring conversion. The PC and JGR spring kit are almost identical. JGR recommended 350ml oil in my setup where I’ve seen guys running closer to 500ml in the FC setups. I may be incorrect in thinking this way but the PC & JGR kits may require less oil because of the air cartridge volume. Mine tops out hard as well but overall I’m very happy with it.

Thanks for the info... did 450 in the spring side and I’ll do 350 in the cartridge side tonight. I am also very happy with the conversion, the damn thing actually turns now!wink

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Don’t piss off the old people - the older they get the less “life in prison” is a deterrent for them!

2020.5 KTM 450 SXF FE
2006 KX250

3/19/2019 5:42 PM

BVM111, finally had a chance to ride my 450 with the RT spring conversion. I was pleasantly surprised at how well it rode and cornered. I didn't do anything with valving, just fresh oil and SKF seals in both legs. I went with 550ml of oil in the spring side. I weigh 160 and started my clickers at 8 comp and 10 reb, at the end of the day I ended up at 10 comp and 12 reb. I will probably play around some more on a different track.

I didn't notice any of the topping out noise you have dealt with, I tried hard to listen for it and never heard any of it. I believe with my weight the top-out spring in the RT conversion is ideal and still think there is correlation to spring stiffness and top-out spring stiffness. Also preload could play a factor, I set my preload at 5mm, RT recommends 3 to 5. I actually went one stiffer on the spring then the RT site recommended, it recommended a .88 and I went with a .92.

If the weather holds I plan to take it too another track and play with it some more this weekend.

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2018 KX450F
2005 KX250
2003 KDX 220
1984 KX 80
1982 RM 80
1980 RM 80
1977 XR 75
1969 Honda Mini 50