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Discussion Starter · #1 ·
OK, I feel a little idiot with this question but heck, maybe I'll go to bed a little less idiot tonight! haha

Last night I was riding quite fast on a relatively buff singletrack when I got myself into quite a spill. At high speed, I hit a root followed by a rock, both maybe 2-3 inches so nothing to give me any kind of problems normally except maybe the fact that I was coming quite fast.

So I kind of went flying while the bike basically stayed there. After picking myself up, nothing major some scratches on the elbow, I tried to figure out what the heck happened there. I'm looking at this root and rock and can't believe what happened. The only symptom I can think of is that I kind of felt a "bang" on my handlebar before I went flying. Kind of like if I had bottomed the fork but the bumps were not very big and basically I've never bottomed it before.

Then I had a flash. I read a few times that Fox forks had some kind of compression spikes. I have a Fox Talas. So could it be that kind of thing that happened to me last night? Does a spike feel a bit like bottoming? Does it happen only after several repeated hits or can it happen on 1-2 hits only? Does it happen when going fast?

Thanks.
 

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Yes, it feels like bottomming and it only happens when going fast. Basically, when you hit a root or a rock, or even a rut, at very high speeds, the wheel needs to go up and over in a big fat hurry. For the suspension, this creates very high shaft speeds. As the damper piston moves through the oil, the ports and valves needs to be able to flow a lot of oil. If the ports or the valves are not sufficient to flow that much oil, the damping force becomes extremely high, and basically the shock sort of hydraulics, becomes effectively rigid. Now I'm not saying that's what happened to you or not, my Fox worked pretty good. It was a little harsh over fast stutter type bumps, but then again, I don't think I've ever hit anything like you are describing.
 

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BanzaiRider said:
So could it be that kind of thing that happened to me last night? Does a spike feel a bit like bottoming? Does it happen only after several repeated hits or can it happen on 1-2 hits only? Does it happen when going fast?

Thanks.
Yes, Yes, No and Yes, and Yes. To my knowledge a compression spike is when the oil in your fork gets stuck, kinda like the fork can't keep up. I've also heard Fox's fork dampening is kind of lacking. I'm sure Jm_ or someone will explain it alot better.

-TS
 

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the fox forx should not spike because they have shimmed dampers that flex and open oil ports as they absorb impacts. Forks that spike do not have shims that flex and they try to force the oil through a fixed-size oil port, that is why they spike. Your "problem" must be something else, jammed internals or something else.
 

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Supposition and speculation...

High speed/low speed damping: You have been deep in travel from the root and the fork may have not yet rebounded when you hit the rock (packed up). The rock bottomed the fork and your weight was too far forward and OTB you went.

and/or

Low compression damping: TALAS is a very linear fork without any ramp up at the end to prevent bottoming. You may just blown through the travel (fork dive) and OTB you went.

Any of the above could have been exacerbated by hitting the brakes and/or descending where more of your weight was distributed forward. Also, I remember reading you are a lightweight and switched to lightweight oil. This may have helped contribute to the problem.

These are all just guesses and by no means definitive though.
 

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Hi Mario,

It sounds a little bit like spiking, but I was not aware that Fox had this issue.

I once rode a friends bike that had a JrT on it. This fork is well known for its spiking. I had a superT at the time, and where I really noticed the spiking was on the stutter bumps in Whistler. My superT would just hammer through them all nice and happy. The JrT felt like it was packing down and not able to recover, eventually feeling like it bottomed out. It definately occured at high speeds as I never felt that on his JrT when doing technical shore rides.

Can it occur over 1 or 2 hits? Well one hit I can not see it as that would be classified as blowing through the travel. 2 hits and I suppose you could start to feel it.

Hope you find the answers you are looking for!

TJ
 

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Compression Spiking

Hey guys/gals,

Compression spiking, or "hydraulic lock", is a characteristic that can be caused by many things inside a damper whether shimmed or orifice style. The RL and RLC Fox Forx are very good and have a very complex series of events that take place each time the fork compresses and rebounds. They do however, suffer from spiking under square-edge bump situations at speed. Due to the recirculation design that they have, the fluid traveling through the cartridge rod to the top cap, can sometimes get choked up depending on the position of your damping dials.

Also, due to the fairly linear rebound damping rate, the fork can pack at higher speeds.

Understand that these aren't problems with the design but more of an issue of Fox having to supply a product that suits a very, very broad rider base. As you all know, we're big fans of the Fox product.

Later,

Darren Murphy
Push Industries
 

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Discussion Starter · #8 ·
Thanks a lot Darren...

Very nice of you to take the time to clarify stuff for us, specially for people with very limited knowledge like me! haha

By the way, I hope nobody jumps to the conclusion that I took a spill because of my Fox fork. Yes I flew in the air a little, haha, but most of it is probably caused by poor rider skill and going too fast for my ability... And I like my fork quite a bit since I changed the oil for lighter weight.

Thanks to all for providing some info.

Cheers.

PUSHIND said:
Hey guys/gals,

Compression spiking, or "hydraulic lock", is a characteristic that can be caused by many things inside a damper whether shimmed or orifice style. The RL and RLC Fox Forx are very good and have a very complex series of events that take place each time the fork compresses and rebounds. They do however, suffer from spiking under square-edge bump situations at speed. Due to the recirculation design that they have, the fluid traveling through the cartridge rod to the top cap, can sometimes get choked up depending on the position of your damping dials.

Also, due to the fairly linear rebound damping rate, the fork can pack at higher speeds.

Understand that these aren't problems with the design but more of an issue of Fox having to supply a product that suits a very, very broad rider base. As you all know, we're big fans of the Fox product.

Later,

Darren Murphy
Push Industries
 
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