Suspension SETUP, a 'how to' guide...

PB Forum :: Mechanics' Lounge
Suspension SETUP, a 'how to' guide...
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Posted: Aug 5, 2020 at 13:31 Quote
commental wrote:
I've got a 2018 Fox Factory 36 Float that I want to reduce to 140mm. I've got the new air shaft and I'm happy swapping it out. The fork has a top out knock, does anyone have any advice? Is it something that's easy to resolve when I've got the fork apart?

There are so many things that could be.

If your rebound is set way too fast.
If your damper is low on oil.
These two problems will be unaffected by changing the spring. The issue will continue.

If your damper is not as long as your air spring (very unlikely unless someone has been messing about with your forks internals) shortening the air spring will probably fix the issue.

Most likely however, your air spring is simply not swapping air properly, in which case changing the spring shaft *may* fix your issue. Check there isn't way too much grease around the piston, or excessive float fluid in the -ve chamber.

If this doesn't sort it, you prob need to let someone look inside your fork.

Posted: Aug 5, 2020 at 20:22 Quote
Anyone want to help me out a bit. Not finding a "perfect" setup yet on a Calling I just built up.

Shock is the OEM RS Super D RC3. I weigh 165lbs

Today I did some test track runs to get it bracketed a little better.

Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow.

Rebound is 5 clicks from closed with 8 total available

Compression is 3 position so not really adjustable.

I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression?

I am finding the bike to not have much pop to it, which is the whole point of why I built the bike.


If it matters the fork its paired to is a 2020 Lyrik Ultimate.

80 psi, 0 HSC, 8 clicks from closed LSC, 13 clicks from closed rebound. Feels pretty good. Not worried as much about the fork as the shock.

Thanks

Posted: Aug 5, 2020 at 22:37 Quote
yourrealdad wrote:
Anyone want to help me out a bit. Not finding a "perfect" setup yet on a Calling I just built up.

Shock is the OEM RS Super D RC3. I weigh 165lbs

Today I did some test track runs to get it bracketed a little better.

Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow.

Rebound is 5 clicks from closed with 8 total available

Compression is 3 position so not really adjustable.

I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression?

I am finding the bike to not have much pop to it, which is the whole point of why I built the bike.


If it matters the fork its paired to is a 2020 Lyrik Ultimate.

80 psi, 0 HSC, 8 clicks from closed LSC, 13 clicks from closed rebound. Feels pretty good. Not worried as much about the fork as the shock.

Thanks

Might need to add a band to the shock if your at sag and still bottoming out mate.

Posted: Aug 6, 2020 at 0:38 Quote
gabriel-mission9 wrote:
commental wrote:
I've got a 2018 Fox Factory 36 Float that I want to reduce to 140mm. I've got the new air shaft and I'm happy swapping it out. The fork has a top out knock, does anyone have any advice? Is it something that's easy to resolve when I've got the fork apart?

There are so many things that could be.

If your rebound is set way too fast.
If your damper is low on oil.
These two problems will be unaffected by changing the spring. The issue will continue.

If your damper is not as long as your air spring (very unlikely unless someone has been messing about with your forks internals) shortening the air spring will probably fix the issue.

Most likely however, your air spring is simply not swapping air properly, in which case changing the spring shaft *may* fix your issue. Check there isn't way too much grease around the piston, or excessive float fluid in the -ve chamber.

If this doesn't sort it, you prob need to let someone look inside your fork.

Thanks, fingers crossed changing the air shaft will sort it.

Posted: Aug 6, 2020 at 8:11 Quote
yourrealdad wrote:
Anyone want to help me out a bit. Not finding a "perfect" setup yet on a Calling I just built up.

Shock is the OEM RS Super D RC3. I weigh 165lbs

Today I did some test track runs to get it bracketed a little better.

Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow.

Rebound is 5 clicks from closed with 8 total available

Compression is 3 position so not really adjustable.

I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression?

I am finding the bike to not have much pop to it, which is the whole point of why I built the bike.


If it matters the fork its paired to is a 2020 Lyrik Ultimate.

80 psi, 0 HSC, 8 clicks from closed LSC, 13 clicks from closed rebound. Feels pretty good. Not worried as much about the fork as the shock.

Thanks

There are kind of 2 statements here that are in opposition to each other
1) "Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow."
2) "I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression"
but I suspect the second statement's "harsh[ness]" is from bottoming out so you either did not have enough base spring or you need to increase the progressivity.

You've already stated that you've upped the PSI which is what I would start with before adjusting the spring curve shape to increase progressivity.

"I am finding the bike to not have much pop to it, which is the whole point of why I built the bike." Usually when i hear someone say the bike lacks "pop" that means the bike doesn't have enough midstroke support, and increasing progressivity can make the midstroke support worse. If this is the stock shock for the bike, it may have come with some volume reducers already installed as the mfg default. If after your ride today with the increased pressure you find the you are still experiencing the " harsh[ness] at the end of its [stroke]" but not actually bottoming the shock out, then slide the air can sleeve off and remove any volume reducers in there and then try again.

Also note that because the front and rear work together as a system to suspend you and the bike, changing the settings on the shock may require changing some settings on the fork. For example, if your increased air pressure in your rear shock makes the bike ride higher in the back than in the front, then you may feel like the bike is pitching you forward, so you might need to increase the PSI on the fork a little to get the bike to feel balanced. That then may have some other side effect like increasing harshness on from the fork which you might be able to address by reducing LSC. Tuning is kind of a recursive process IME, so this might be a bit of a "journey" of addressing one problem and then creating (hopefully) a more minor problem that you can then address in the next round of tuning until you find a good compromise across all your suspension goals.

Good Luck

PS don't get caught up in the trap of thinking that if your bike isn't using 100% of its travel that your sus isn't set up correctly. If the bike feels supportive and predictable but you still have 10-20% of travel left after your average ride, that is better than having a bike that is not supportive and predicable but does use all its travel.

Posted: Aug 6, 2020 at 8:25 Quote
freestyIAM wrote:
yourrealdad wrote:
Anyone want to help me out a bit. Not finding a "perfect" setup yet on a Calling I just built up.

Shock is the OEM RS Super D RC3. I weigh 165lbs

Today I did some test track runs to get it bracketed a little better.

Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow.

Rebound is 5 clicks from closed with 8 total available

Compression is 3 position so not really adjustable.

I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression?

I am finding the bike to not have much pop to it, which is the whole point of why I built the bike.


If it matters the fork its paired to is a 2020 Lyrik Ultimate.

80 psi, 0 HSC, 8 clicks from closed LSC, 13 clicks from closed rebound. Feels pretty good. Not worried as much about the fork as the shock.

Thanks

There are kind of 2 statements here that are in opposition to each other
1) "Shock is at 210psi. I bottomed it and it shouldn't on this trail. I have pumped it up to 220psi for tomorrow."
2) "I would say that it feels ok except for big hits I think it is spiking a little and is kinda harsh at the end of its progression"
but I suspect the second statement's "harsh[ness]" is from bottoming out so you either did not have enough base spring or you need to increase the progressivity.

You've already stated that you've upped the PSI which is what I would start with before adjusting the spring curve shape to increase progressivity.

"I am finding the bike to not have much pop to it, which is the whole point of why I built the bike." Usually when i hear someone say the bike lacks "pop" that means the bike doesn't have enough midstroke support, and increasing progressivity can make the midstroke support worse. If this is the stock shock for the bike, it may have come with some volume reducers already installed as the mfg default. If after your ride today with the increased pressure you find the you are still experiencing the " harsh[ness] at the end of its [stroke]" but not actually bottoming the shock out, then slide the air can sleeve off and remove any volume reducers in there and then try again.

Also note that because the front and rear work together as a system to suspend you and the bike, changing the settings on the shock may require changing some settings on the fork. For example, if your increased air pressure in your rear shock makes the bike ride higher in the back than in the front, then you may feel like the bike is pitching you forward, so you might need to increase the PSI on the fork a little to get the bike to feel balanced. That then may have some other side effect like increasing harshness on from the fork which you might be able to address by reducing LSC. Tuning is kind of a recursive process IME, so this might be a bit of a "journey" of addressing one problem and then creating (hopefully) a more minor problem that you can then address in the next round of tuning until you find a good compromise across all your suspension goals.

Good Luck

PS don't get caught up in the trap of thinking that if your bike isn't using 100% of its travel that your sus isn't set up correctly. If the bike feels supportive and predictable but you still have 10-20% of travel left after your average ride, that is better than having a bike that is not supportive and predicable but does use all its travel.

This is one of the best things I’ve seen written here for a while.
Just because you have 200mm of travel doesn’t mean your riding style or trail means that it all needs to be used.
To get my bike feeling balanced I very rarely get anywhere close to the 170mm on the front

Posted: Aug 6, 2020 at 9:41 Quote
It is a bit misleading to say increasing progressivity makes midstroke support worse.
Adding volume tokens , but then reducing starting pressure makes mid stroke support worse while bottom out resistance stays similar to what it used to be. However in my experience people very rarely do this.

Keeping your starting pressure constant, while adding volume tokens, will improve mid stroke support and "pop", while making it significantly harder to bottom out.

I'd be interested to know what sag you are getting with 210/220 psi in the shock.

Posted: Aug 6, 2020 at 9:49 Quote
It's also misleading to say increasing progressivity doesn't make midstroke support worse.

• For constant sag, increasing progressivity makes a small increase in midstroke support.
• For approximately constant bottom-out properties, increasing progressivity decreases midstroke support.

Posted: Aug 6, 2020 at 9:58 Quote
Im really not up for another huge debate on this, so I tried to be as clear as possible in my post.

Increasing progressivity doesn't make midstroke worse. Lowering your base pressure makes midstroke worse.

It is true that lowering your base pressure then requires more progressivity to avoid bottoming out much more easily, but it is not this increase in progression that is actually reducing your midstroke support. It is the reduced base pressure.

Posted: Aug 6, 2020 at 10:40 Quote
I agree with all those points, I just want to illustrate two things:

1. There are more effective ways to increase mid-stroke support when that is the objective, i.e. pressure.

2. Volume reducers do not universally improve mid-stroke support. When bottom-out properties are already fine, reducing positive volume (and, presumably, reducing pressure) reduces mid-stroke support.

Mid-stroke properties and the applicability of spares are among the most misunderstood properties in suspension tuning, so I feel it's important to be very clear about such things.

Posted: Aug 6, 2020 at 10:50 Quote
Guys don't fight you two are the solid knowledge in this forum.

Posted: Aug 6, 2020 at 10:59 Quote
You don't get good by sitting back and letting the details slide!

I'll be the first to say gabriel-mission9 does a great job with the advice here and is almost universally spot-on. It's just this one issue on which I want to provide some additional information.

Since we last discussed it, he's framed it differently and I don't disagree with the statements, I just want to ensure they don't lead to sub-optimal actions by anyone less familiar with the subject.

Posted: Aug 6, 2020 at 11:15 Quote
commental wrote:
gabriel-mission9 wrote:
commental wrote:
I've got a 2018 Fox Factory 36 Float that I want to reduce to 140mm. I've got the new air shaft and I'm happy swapping it out. The fork has a top out knock, does anyone have any advice? Is it something that's easy to resolve when I've got the fork apart?

There are so many things that could be.

If your rebound is set way too fast.
If your damper is low on oil.
These two problems will be unaffected by changing the spring. The issue will continue.

If your damper is not as long as your air spring (very unlikely unless someone has been messing about with your forks internals) shortening the air spring will probably fix the issue.

Most likely however, your air spring is simply not swapping air properly, in which case changing the spring shaft *may* fix your issue. Check there isn't way too much grease around the piston, or excessive float fluid in the -ve chamber.

If this doesn't sort it, you prob need to let someone look inside your fork.

Thanks, fingers crossed changing the air shaft will sort it.

I know it doesn't take much, but there was no oil in the air chamber above the piston when I broke the fork down. Installed the new air shaft, put in the required oil and top out knock seems to be a thing of the past. Thanks for your help. tup

Posted: Aug 6, 2020 at 12:55 Quote
R-M-R wrote:
You don't get good by sitting back and letting the details slide!

I'll be the first to say gabriel-mission9 does a great job with the advice here and is almost universally spot-on. It's just this one issue on which I want to provide some additional information.

Since we last discussed it, he's framed it differently and I don't disagree with the statements, I just want to ensure they don't lead to sub-optimal actions by anyone less familiar with the subject.

I'll second the motion that gabriel-mission9 is a great source of sus info on this forum and on a higher level than me. No hate here, just apparently some minor quibble about where to start with addressing midstroke support and what the best practices is when adjusting pos spring volume.

FYI, using AndreXTR's AIR SPRING SIMULATOR.xlsm, I took 9mm out of the length of the positive chamber (like if you crammed a bunch of volume reducer bands) of a Monarch Plus simulated with my rider weight and preferred pressure. Note that i keeping the air pressure the same. See the pre and post curves in the image below and


Note also that the resultant sag with less volume and same pressure was ~3% lower (33% pre v 30% post), i.e. a pretty small amount and i think within a lot of peoples acceptable range for static sag.

So at least one free off the internet air spring simulator (i.e. take this all with a grain of salt), supports Gab's claims that keeping PSI the same while reducing pos chamber air vol *does* increase midstroke support.

So what about leaving the volume of the pos air chamber alone and addressing this from the pressure side instead as RMR advocates? See below for a 15PSI increase in pressure which again takes the sag from 33% to 30%


To my eye, it looks like A) the gap between the pre and post line starts to separate earlier (i.e. starts providing more midstroke support sooner) and B) the gap is taller throughout and C) the actual rise over run in the increased Pressure scenario seems steeper (which i translate as more supportive) than when compared to the reduce volume graph.

Hopefully this is a good analysis but i welcome constructive criticisms and if this isn't way off the mark, hopefully this helps bridge the gap a little between the suggested tuning paradigms.

Cheers

Posted: Aug 6, 2020 at 12:57 Quote
I appreciate the responses.

I don't think I ever claimed that I was searching or wanting full travel, actually quite the opposite. I was stating that I was bottoming on a trail that the bike shouldn't use full travel on. I never take using full travel as a sign of proper set up. I always have some "oh sh%$" travel left.

Rode 220psi today and was left with 5mm or 10% of stroke left. So thats good. Also less spiking on the hits, but still pretty progressive, so maybe it was just the bottoming out.

Biggest issue is I am just not getting the pop I expect.

I understand that in general volume spacers reduce the linear action (and often the mid stroke support), hence why when people say they want a coil like feel, but then add spacers they are doing the opposite and making it more progressive.

I am finding it interesting that I assume the volume band in the shock is actually set up for someone like me. Don't most setups come set up for the average rider and weight?

I would prefer not to have to put in a larger spacer, because I don't want a more progressive feel and I want more mid stroke support.

What I am not getting is that I seem to be entering the end use of the effective rebound adjustment.

What else am I not getting?

P.S.

Gabriel, I didn't see you ask my sag. I checked my sag 5 times at 220psi and it was 30% 4/5 and ~27% the other. This was about the same sag I got when I started adjusting pressure at 185psi. Hence why I usually start working on the air spring at a recommendation and then keep messing with it until I rarely and appropriately bottom out.


 
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