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Sag OK, bottom out easy on drop to flat.

Dh builder

Chimp
Sep 30, 2013
54
2
I have a Fox dhx rc4 shock.

My sag looks OK, if anything it is below 25%.

I notice that if I do a drop to flat, say only about 2 to 2.5 feet I will bottom out my rear shock.

What should I adjust to help fix this? I have all my adjustments at the lowest settings.

Adjustments I have are.

Low speed compression
High speed compression
Bottom out control
rebound

Thanks
 

metalMTB

Monkey
Sep 14, 2005
699
3
Richmond, VA
no need to worry about rebound for this. how does your bike handle fast, repeated hits at high speed? does it run through it's travel quickly? what about dips and just bouncing on the bike? if it's blowing through its travel too much on fast, repeated hits, then turn up the high speed compression. if it blows through its travel on dips and low-speed impacts then turn up the low-speed compression.

turning in the bottom-out control will help the shock ramp up towards the end of the travel making it feel more progressive. this would definitely solve your issue but you still want to consider your and high and low speed compression.
 

Dh builder

Chimp
Sep 30, 2013
54
2
I'm going to turn up that bottom out control.

Would a 3 foot drop to flat effect the high speed compression or the low speed compression?
 

Jm_

sled dog's bollocks
Jan 14, 2002
18,855
9,560
AK
Less than 25% sag and bottoming on a 2.5" drop? Something isn't adding up here (but yes, turn in the bottom-out control).

The other thing that would help is low-speed compression. Drops are low-speed events (relatively), so this would likely help. Shock shaft has has to move a lot faster when you hit a 5" bump at 25mph.
 

Dh builder

Chimp
Sep 30, 2013
54
2
I agree something wasn't adding up. The odd thing is I could have sworn my shock didn't bottom out so easily.

I decided to put my shock air pump to check the pressure in the bottom out control and it seemed to not have any air pressure at all. I then pumped it up and noticed the air pressure drop. I did hear a small hiss.

I wasn't sure if my pump was leaking, so I tried it on an air shock I had and while turning the pump I broke the rubber hose on the pump.

I'm not sure if I let the air out with the bad pump or if it had no air in it at all.

I think the fox DHX rc4 had no air pressure in the bottom out control as I was watching the gauge while screwing it in and never saw any pressure.
 

metalMTB

Monkey
Sep 14, 2005
699
3
Richmond, VA
shock pumps are notoriously inaccurate. try to get one of the standing floor pumps where can unscrew part of the valve so you don't lose pressure when disconnecting pump.

with this kind of valve:



i use that at work and its spot on. i hate those stupid hand shock pumps. They lose pressure when you disconnect them and you end up putting so much pressure on the hose it eventually leaks.

we use the specialized air tool uhp at work. looks like lezyne also makes a digital one.
 
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Dh builder

Chimp
Sep 30, 2013
54
2
metalMTB thanks for the tip, I just ordered one earlier today. A rockshox 300 PSI pump from Amazon. It had decent reviews and they say little air escapes.

Well, I went and pushed the sharder valve at the bottom of my DHX Rc4 shock and heard a hiss. So maybe its not completely blown? I thought it was at 0 PSI when I left it.
 

Gallain

Monkey
Dec 28, 2001
183
43
Sweden
[QUOTE="i hate those stupid hand shock pumps. They lose pressure when you disconnect them and you end up putting so much pressure on the hose it eventually leaks.

we use the specialized air tool uhp at work. looks like lezyne also makes a digital one.[/QUOTE]

In 998 times of 1000 that air rushing out you hear is from the hose, unless you got a really bad puump or valve. Been using Rockshox and Fox handpumps since 2000-2001 as a mechanic and never had any issues...
 

Jm_

sled dog's bollocks
Jan 14, 2002
18,855
9,560
AK
Yeah, the only air pump I've had that just didn't work was a Stratos, of course I made the mistake of trying to fill my 5th element with it, I'm not sure how much pressure I had or didn't have in the shock, but I am sure I blew it based on the puddle that was below it the day after the first ride at N*. Since then no problems with various fox and other pumps. Modern RS pumps are nice and sturdy. Been using the same one for years.
 

kickstand

Turbo Monkey
Sep 18, 2009
3,441
392
Fenton, MI
You need a minimum of 125psi in your bottom out canister (or whatever the technical term is for it) according to Fox. You can turn that in or out to make the resistance better, or you can also add more air, and a few clicks of compression shouldn't hurt either. I like to start with 4 clicks of high speed and 2 clicks of low speed and work from there based on feel.
 

Dh builder

Chimp
Sep 30, 2013
54
2
Well, I got my new air pump and the pressure was around 60PSI, but that may because I let a lot of air out by pressing the valve and the problem with my old pump.

I filled it up to 170PSI, and cranked the bottom out a little higher, and the bike doesn't bottom out on those jumps anymore.

I checked my PSI when I got home after a long ride and it was still holding 170PSI.

I'm not sure if I lost any PSI in shock, it is a coil shock, or I just didn't crank the bottom out control enough when I was bottoming out.

Maybe I could have a slow leak also, I'll have to keep my eye on the pressure every so often.