Mountain Bike Reviews Forum banner

1 - 18 of 18 Posts

·
The Riddler
Joined
·
1,036 Posts
Discussion Starter #1
I guess this is a volume spacer question. I have 2016 Fox 32 @ 120mm and it came factory installed with a volume spacer. I've had a hard time getting the fork dialed (some of which is a result of also riding a sweet, plush 140 Pike).

It's been a little harsh and I've had a hard time using all of the travel. I've experimented with taking out air pressure, but it eventually starts to not sit very high in its travel, even if it doesn't bottom out. Will adding another volume spacer allow me to run less air pressure but still keep the fork sitting high?

On the other end, I removed the air token and ran it without, but found I had to run a lot of air pressure to keep it from bottoming.

Is the moral of the story that volume spacers allow for a little less air to be used and keep the fork a little more cushy, but won't miraculously transform an XC fork into a trail fork? And/or is the moral that I should get a 120 Pike?
 

·
Fat-tired Roadie
Joined
·
18,453 Posts
I don't think adding a spacer will help the fork sit much higher in the travel but it should help some. Try it.

My guess is you're going to find you have to compromise between plushness and ride height.

Sent from my E5803 using Tapatalk
 

·
Registered
Joined
·
1,177 Posts
1 spacer shouldn't make a huge difference. I view them as fine tuning elements. I wouldn't expect adding 1 token to make an very noticeable difference in ride height...more in bottom out or end stroke behavior. I'd look into adding compression damping to settle the front end of your bike.

Sent from my HTC6525LVW using Tapatalk
 

·
Registered
Joined
·
552 Posts
Theoretically, if you take out a volume spacer and run the same pressure, you should still get the same (or very similar) initial sag. It will bottom out easier with less force, as you experienced. It sounds to me like you need 1/2 of a volume spacer (total) instead of 1 full volume spacer to make it plusher without bottoming out harshly, while also making it sit up at initial sag. Other people have their own methods, but I like to target a specific initial sag (20% for the fork in my case), and then play with the number/size of the volume spacers until I can just barely bottom it on the biggest hits.

If you add another spacer (2 total) and run a little less pressure, you will sag a little more than before, and probably still not be able to bottom the fork.
 

·
Registered
Joined
·
1,432 Posts
I had a bunch of stuff written but what it comes down to is have you tried adding more high speed compression?
 

·
Fat-tired Roadie
Joined
·
18,453 Posts
I dunno. 120 mm isn't a ton of travel. Volume spacers can give better bottom-out resistance without messing up small-bump compliance. Certainly it's turned out well for me in my Reba 100. So unless Fox uses a much smaller air chamber, I think that's relevant.

Sent from my E5803 using Tapatalk
 

·
Registered
Joined
·
9,741 Posts
I suggest forgetting about pressure and use sag instead. For example, if you set sag to 25% you can note the pressure. Put in a spacer and set sag again to 25% and you'll see that you need a little less pressure. This is the pressure when you're not sitting on the bike with it sagged. When you are sitting on it, the pressure will be the same in both cases. However, with the spacer there is now less volume so the spring rate will be higher and it will ramp up quicker, which is good if you're heavy or taking big hits and bottoming. If it's harsh and you're using less travel than you'd like, you need more volume, not less.
 

·
Registered
Joined
·
636 Posts
air-shock-coil-spring-rate.jpg

Here are a couple different approaches normalized to a 30% sag point.

The problem is more likely that rebound or compression damping is set wrong, though.

Rebound damping controls how fast the spring extends after it's compressed. Too much damping on rough terrain and the spring can't recover fast enough, so you blow through your travel. Too little damping results in your wheel bouncing and following every hole.

Compression damping controls how fast the spring can compress. It's resistance that adds to your spring rate if you hit something that would cause a fast compression. To little means, again, you can blow through your travel quickly. Too much prevents the spring from absorbing the shock of the bump, so the tires and you absorb it instead.

All four make the bike feel harsh.
 

·
Registered
Joined
·
9,409 Posts
I dunno. 120 mm isn't a ton of travel. Volume spacers can give better bottom-out resistance without messing up small-bump compliance. Certainly it's turned out well for me in my Reba 100. So unless Fox uses a much smaller air chamber, I think that's relevant.

Sent from my E5803 using Tapatalk
When you add volume spacers, the bottom of the travel gets harder to reach and deep stroke rebound becomes less controlled. If you drop air pressure to maintain full stroke then the fork sags too far and they start to wallow.

The mid stroke gets really short and soft between too much sag and too much progression. Basically it starts to suck all round.

Too much progression is a really bad thing. Virtually all riders need a linear spring.
 

·
Fat-tired Roadie
Joined
·
18,453 Posts
When you add volume spacers, the bottom of the travel gets harder to reach and deep stroke rebound becomes less controlled. If you drop air pressure to maintain full stroke then the fork sags too far and they start to wallow.

The mid stroke gets really short and soft between too much sag and too much progression. Basically it starts to suck all round.

Too much progression is a really bad thing. Virtually all riders need a linear spring.
So I had my fork tuned really nicely in its stock air spring volume, which had no spacers that year. And for a while, I was happy.

One of the things that had occasioned getting the new bike was that I moved and was closer to trails, on a steeper, rockier mountain.

So the predictable thing happened. I got more comfortable riding off bigger things. And, I started bottoming out. D'oh! So I added a couple psi and the ride got harsh. Lame. At least I wasn't bottoming out.

Adding a volume spacer and keeping otherwise the same tune as what I liked stopped that harsh bottom-out.

I think we may be coming from different directions in our attitudes, though. Because I didn't want to change my air pressure and I was essentially going through more than 100% of my fork stroke. So I didn't want to maintain it - I wanted to use only 100%. Less, really, because of sag.

I don't keep records of my sag. It's not very repeatable, while I can read air pressure off the gauge on my shock pump. So I'm not sure if I ended up with significantly less sag. I'm sure I ended up with a little less just because that's how the math works. But since the difference in spring curve is so much greater near full compression, I see volume spacers more as a way to give a fork more bottom-out resistance without changing the rest of the tune.

Sent from my E5803 using Tapatalk
 

·
Registered
Joined
·
9,467 Posts
Dougals got it %100 right in my opinion.

I messed around with this a lot last year and learned a ton. I think there's 2 schools:
Set by sag, not pressure vs, Set by pressure, not by sag. I prefer set by sag, and a more linear shock will give you more mid-stroke support.

Either way, like photography, you can't change one variable without affecting the others.

Will adding another volume spacer allow me to run less air pressure but still keep the fork sitting high?
No, adding a spacer and running less air, will make the fork more plush off the top, you still probably won't get full travel often, and the fork will ride lower in it's travel. The fork will ramp up faster, farther into it's stroke.

I'd ditch the spacer and expect to add a bit more PSI to keep the same sag point.
 

·
Registered
Joined
·
9,409 Posts
So I had my fork tuned really nicely in its stock air spring volume, which had no spacers that year. And for a while, I was happy.

One of the things that had occasioned getting the new bike was that I moved and was closer to trails, on a steeper, rockier mountain.

So the predictable thing happened. I got more comfortable riding off bigger things. And, I started bottoming out. D'oh! So I added a couple psi and the ride got harsh. Lame. At least I wasn't bottoming out.

Adding a volume spacer and keeping otherwise the same tune as what I liked stopped that harsh bottom-out.

I think we may be coming from different directions in our attitudes, though. Because I didn't want to change my air pressure and I was essentially going through more than 100% of my fork stroke. So I didn't want to maintain it - I wanted to use only 100%. Less, really, because of sag.

I don't keep records of my sag. It's not very repeatable, while I can read air pressure off the gauge on my shock pump. So I'm not sure if I ended up with significantly less sag. I'm sure I ended up with a little less just because that's how the math works. But since the difference in spring curve is so much greater near full compression, I see volume spacers more as a way to give a fork more bottom-out resistance without changing the rest of the tune.

Sent from my E5803 using Tapatalk
Does your fork not have adjustable compression damping?
 

·
Registered
Joined
·
529 Posts
Hi Dougal! I've been on the Mattoc thread for a long time, you always offer great advice. Would the same advice apply to the IRT in a Mattoc? Or is it fundamentally different from volume spacers as to not affect it as much. I fell into the habit of adjusting the IRT psi upward as a way to keep from bottoming hard, then saw your advice to use compression for that and the IRT more for mid support. I imagine it makes the fork more progressive, it sure seems to running it at recommended pressure. Wondering now if I am better off taking it out for a more linear spring would be better at the cost of a bit of mid support.

Also have a DB inline with a large volume spacer in, the idea was to add more pop to it, but been thinking of taking it out for a while now. My bikes a pretty linear/regressive design, and I put it in almost right away thinking it would need it. I have always been a set and forget type of person, so having this much tuneability now has me wondering if I should just go back to the stock set up and work from there. I can't say either front or rear is bad at all, much better than I had in the past. But I don't want to lose performance by getting too fancy either.
 

·
Registered
Joined
·
9,409 Posts
Hi Dougal! I've been on the Mattoc thread for a long time, you always offer great advice. Would the same advice apply to the IRT in a Mattoc? Or is it fundamentally different from volume spacers as to not affect it as much. I fell into the habit of adjusting the IRT psi upward as a way to keep from bottoming hard, then saw your advice to use compression for that and the IRT more for mid support. I imagine it makes the fork more progressive, it sure seems to running it at recommended pressure. Wondering now if I am better off taking it out for a more linear spring would be better at the cost of a bit of mid support.

Also have a DB inline with a large volume spacer in, the idea was to add more pop to it, but been thinking of taking it out for a while now. My bikes a pretty linear/regressive design, and I put it in almost right away thinking it would need it. I have always been a set and forget type of person, so having this much tuneability now has me wondering if I should just go back to the stock set up and work from there. I can't say either front or rear is bad at all, much better than I had in the past. But I don't want to lose performance by getting too fancy either.
The IRT is different again, it's not there to provide more progression at end-stroke. It's instead there to provide a completely tunable mid-stroke. Yes it will make the fork more progressive at higher pressures, but that's secondary and due to the volume the IRT parts take up in the air chamber.

The biggest problem with air springs is a weak mid-stroke. This is a big problem riding steep trails as the forks hang too low, geometry gets even steeper, not enough travel remains and it's all bad.

The IRT lets you adjust in a firmer mid-stroke to keep the fork riding higher in these situations and providing more support.

Start with all spacers out.
 
1 - 18 of 18 Posts
Top