Of Compression and rebound and things...

[Andymann]

I had an interesting (read heated!) discussion with my LBS recently about the rebound performance of my Fox 32 Float RL100. What I had noticed when it came back from a fork service, is that the rebound settings (there are about 14 clicks depending if you count from 0 or 1) only work from fully screwed in (where the rebound is super slow) and then the following two clicks directly after that. After then, progressively clicking the rebound adjuster out offers no rebound speed change whatsover. They then proceeded to tell me that I can't be expected to feel the rebound difference through the whole range, and also that my fork pressure (set to give a sag of 22mm - for my weight) was way to low - thats why I couldn't feel any rebound change(!). They then pumped the fork to max pressure (a sag of around 5mm!) and sent me on my way. Now I am no bicycle fork expert, but I have done my fair share of MX and I know on a MX fork the rebound clicker is very responsive thoughout the whole range of clicks, so why should it be any different on a high-end bicycle fork? I also suspect that the air chamber is completely separate to the oil chamber, so surely the pressure settings used to set sag should have no influence whatsoever on rebound speed? Am I completely off the mark here, and is the LBS correct in saying I shouldn't be able to feel a difference, or is there something else wrong, like an incorrect oil grade used during the service, incorrect oil amount, or a sticky shim of damaged needle on the rebound adjuster?

[Mike Bike]

from my limited experience a sag of 5mm is waaaay to hard, you will rattle yourself to pieces. on my revelation the rebound also only feels different to me on the last few clicks.

[droo]

Smells to me like your mechanic is speaking through an orifice that's not his mouth.

 

Two options - one, the damper oil is too light; or two, the damper cartridge needs a rebuild.

 

As far as the pressure goes, you should be aiming for 20 - 30% sag depending on riding style and fork travel, so 5mm is way too hard. May as well ride a rigid fork.

 

Your assumption that spring and damper are separate is correct - the spring's in one leg, damper's in the other. However, spring rate and rebound are related - the stiffer the spring (or the higher the pressure), the more you'll need to slow the rebound down. Which makes sense. What your bloke says is rubbish.

 

If you're in CT I'd be happy to have a look at it for you.

[Andymann]

Unfortunately not in Cape Town, but I suspected that there might be more to this story. I'm lucky that I was once in the Technical department at Yamaha SA, so was able to have a chat this morning to Hylton Hayward, he of Hayward Suspension - the bloke who designed suspension for KTM Austria a while back. While he's also not a bicycle fork expert, he mirrored exactly what you have just said - sounds like too light an oil, or a sticking shim in the rebound system...

[travisza]

Unfortunately not in Cape Town, but I suspected that there might be more to this story. I'm lucky that I was once in the Technical department at Yamaha SA, so was able to have a chat this morning to Hylton Hayward, he of Hayward Suspension - the bloke who designed suspension for KTM Austria a while back. While he's also not a bicycle fork expert, he mirrored exactly what you have just said - sounds like too light an oil, or a sticking shim in the rebound system...

 

Sounds like your LBS is telling tall stories.

 

I would expect the rebound adjustment to make a difference throughout the range.

 

You won't find better advice on suspension performance than Hilton so I'd definitely go with what he says

[droo]

Unfortunately not in Cape Town, but I suspected that there might be more to this story. I'm lucky that I was once in the Technical department at Yamaha SA, so was able to have a chat this morning to Hylton Hayward, he of Hayward Suspension - the bloke who designed suspension for KTM Austria a while back. While he's also not a bicycle fork expert, he mirrored exactly what you have just said - sounds like too light an oil, or a sticking shim in the rebound system...

 

A fork is a fork, aside from a few inertia valves and a substantial weight difference...

 

If you're in the JHB area then get hold of Johan at yellow saddle. Avoid the Fox agents like the plague.

[Johan Bornman]

I doubt you'll see a click-by-click difference in rebound speed.

 

The only time I can see it working for definite, is if I remove the damper cartridge (like in a FIT model's) and move it up and down in the bench. Then I can feel it but not see it. Witht he cartridge fitted and air int he spring, there's too much other "noise" to see a difference. I consider the setting as a small/medium/large affair and anything other than that is too subtle for observation when stationary.

 

Some forks emit a nice schlurrping noise and then at least you can hear it but my eye isn't trained well enought o distinguish between click number two and click number 6, for instance.

 

Futher, Fox dampers are so incredibly robust that I doubt there's anything wrong with it.

[droo]

I doubt you'll see a click-by-click difference in rebound speed.

 

The only time I can see it working for definite, is if I remove the damper cartridge (like in a FIT model's) and move it up and down in the bench. Then I can feel it but not see it. Witht he cartridge fitted and air int he spring, there's too much other "noise" to see a difference. I consider the setting as a small/medium/large affair and anything other than that is too subtle for observation when stationary.

 

Some forks emit a nice schlurrping noise and then at least you can hear it but my eye isn't trained well enought o distinguish between click number two and click number 6, for instance.

 

Futher, Fox dampers are so incredibly robust that I doubt there's anything wrong with it.

 

Click-by-click no, but there should certainly be a marked difference between click 2 and click 14. If, as the OP says, there's no change over the majority of the range, then there's something definitely wrong. I'd bet on too light a grade of oil being used over damper trouble, but without seeing the fork it's hard to say.

 

Incidentally, (@Andymann) does the lockout still work or has it also gone a bit softer than usual? Light oil usually decreases lockout performance too.