To bleed or not to bleed, that is the question ?

[hobiee 28]

Just trying to start up a convo on something I've pondered in the past.  Ok so you roll your bike of choice up the ramp and cinch those tie downs tight for the ride home.  Do you bleed the forks??   If yes, why ?  If no, why not ?  You have just unloaded your bike after driving up to the mountains to ride.  It's been strapped down tight for a few hours, do you hit the bleeders to "acclimate" your forks to the new environment?  Why or why not ?   Been doing a bunch of hard laps on the track and you roll into the pits and throw it up on the stand for a rest,  hit those bleeders ?     What exactly are we doing when we do this ?   How does air get in there in the first place ?   Why does it build pressure ?  Are we saving our fork seals by doing this ?   What happens if we never even take those pesky little screws out and put the fancy bleeders in and never ever touch anything but th ie clickers ?   I have way to much time on my hands.........

 

PS  I have learned a ton on suspension in the last few years and I seriously think it is probably the most important part of what we do in order to feel comfortable on our ride of choice.  It truly can make or break a ride or a great ride in my opinion.

[SoCalMule 106]

https://www.suspension101.com  ask for George. 

[Goofy Footer 548]

 

I'm a luddite in terms of suspension. I was riding hard in the dez last year and my forks started to audibly grunt upon compression impact. While stopped on the trail I decided to let air out the forks (bike Not on a stand) and air hissed out. It definitely changed the fork feeling but I'm too dumb to tell exactly what. I've also never touched my clickers...

 

I've read equalizing pressure in the fork with bike suspended is healthy. Air takes up space, just like oil level height

 

 

Show me the way!

[tntmo 927]

I don’t know, do new bikes come with the bleeders from the factory?  My thought is it helps minimally but it’s not necessary.

[Pokey151 267]

on the race track I feel the difference.  As the oil heats up, air pressure builds and creates basically a preload to my understanding.  I am not a suspension guy but I spent many many many thousands on suspension on my race bike(s) and when I get them re-tuned from Enzo, they always ask if I bled, I ask why, and that's what was mentioned to me.

[hobiee 28]

On 9/22/2021 at 1:01 AM, Goofy Footer said:

 

I'm a luddite in terms of suspension. I was riding hard in the dez last year and my forks started to audibly grunt upon compression impact. While stopped on the trail I decided to let air out the forks (bike Not on a stand) and air hissed out. It definitely changed the fork feeling but I'm too dumb to tell exactly what. I've also never touched my clickers...

 

I've read equalizing pressure in the fork with bike suspended is healthy. Air takes up space, just like oil level height

 

 

Show me the way!

In a perfect world our suspension would always be in a  vacuum  so to speak.  Operating under perfect conditions always. Good suspension set up can make the day.  I wonder how many people write a certain bike off cause they never get the boingers set up correctly.   People will spend thousands on exhaust or programers or oil or tires or a new seat or whatever.    Get the suspension set up period. Biggest improvement period !   Learn about whatever bike you have.  How rebound effects how comfortable you are how compression slows you down, how the two work together.    I can tell when a clicker is turned on click now and I'll bet I could tell when my forks have been bled or not.  Theres a ton that goes into suspension and it's sooooooo over looked in my opinion in the big picture.

[cj54x 57]

I bleed my forks once a year weather they need it or not, it sounds like letting the air out of a tire when I do.  The seals in my KTM only lasted 13 years though.

Don't forget to clean the dust seals regularly and try these...

 

 

[DSM8 390]

While George is the go to person for all thing suspension this is my understanding.
The Air Gap acts like a spring, if you were at sea level and went up to 9K feet that along would increase the pressure the air gap has in the forks.
Same with heating them up.

I tend to do it when I am riding on trips as I go from sea level to 8K or above and will be staying there for a few day (riding in CO for example).

It puts less strain on the seals if you release pressure but how much or is it really significant i don't know. And I am not a good enough rider to notice much of a difference unless the altitude change is very large, then the forks are just a little more harsh due to the higher pressure but that could also be my imagination.

Call and talk to George, he will take care of you esp if you need any work done, to say his work transforms the suspension on these bikes is an understatement, and that has been repeated by a number of people I have sent his way as well.

 

[hobiee 28]

7 hours ago, DSM8 said:

While George is the go to person for all thing suspension this is my understanding.
The Air Gap acts like a spring, if you were at sea level and went up to 9K feet that along would increase the pressure the air gap has in the forks.
Same with heating them up.

I tend to do it when I am riding on trips as I go from sea level to 8K or above and will be staying there for a few day (riding in CO for example).

It puts less strain on the seals if you release pressure but how much or is it really significant i don't know. And I am not a good enough rider to notice much of a difference unless the altitude change is very large, then the forks are just a little more harsh due to the higher pressure but that could also be my imagination.

Call and talk to George, he will take care of you esp if you need any work done, to say his work transforms the suspension on these bikes is an understatement, and that has been repeated by a number of people I have sent his way as well.

 

Oh Absolutely George is the guy to go to.  I've learned plenty from him.  I was just throwing all this out there for fun conversation is all.  I've gotten pretty darn good at tuning suspension and being able to tell what my suspension needs.  I have a 1090 currently that rides nicer than most folks 300 in the technical stuff.  People get on for a try out and come away in shock.  "That bike is soooooo easy to ride"  I have even had people tell me It's slow because its like riding on a magic carpet.  My 200 is even more amazing but thats just what a 200 does period.

[robertaccio 431]

if you are going up or down in altitude, blow up a balloon and "record it's size, let it ride along with you on the seat or wherever. When you arrive observe the balloon. this is what is going on inside your closed/sealed forks in regard to static air. Add heat it will expand the air more, cool vice versa. The best you can do is neutralize to the current operating area (pressure altitude).

Through experience you can do some self-feel/taught compensation methods on top of that.

On my first AER48 fork set up in the year of riding and racing before my spring install mod. I had a fairly good system for maintaining my preload ("spring Rate"/Air pressure rate) , They were hard to tune for enduros......morning 45-50F by afternoon 75-80, large pressure increases throughout the day = stiffer forks by later in the day when stiff is compounded by physical fatigue.

I found my best pressure ("spring rate") and would set it a little low in the cold morn, knowing they would heat up a bit from operation I found a good start pressure that would have me close or on at operating temp. By afternoon, at rest before tests, I would piss off some pressure and recheck for my happy setting and restart just a little low to compensate for operating heat pressure rise. When I was calculating all this stuff, I found that my spring rate (air pressure=spring rate) could change as much the equivalent of 5 spring rates. So, imagine I usually use a .46 spring (enduro) I was way up in the low to mid .5s (supercross)by the heat of the afternoon. Substantial and very noticeable. 

I know that AER48s are the extreme end of the spectrum when you are dealing with air chamber volume in spring forks, but it was a valuable lesson as to how much, that closed system air pressure can affect your forks feel and operation. I also always maintained that liked the AER48s because I knew how to manage them effectively, most folks don't/didn't.

We (S101) even discussed a regulator valve that could be set to the optimum (your optimum pressure) and when the heat rise came it would (pop off) bleed off the unwanted excess pressure to maintain your best setting.

Note: On site before the ride, especially if moving from one atmosphere to another bleed the air out/in as a habit. Or at the least be aware of the possible changes in feel and stance of your front end.

Edited May 1, 2023 by robertaccio

[Goofy Footer 548]

@robertaccio if we are getting all #SuspensionScientific then What is in that balloon?!

 

[robertaccio 431]

3 hours ago, Goofy Footer said:

@robertaccio if we are getting all #SuspensionScientific then What is in that balloon?!

 

a little more heavy on the CO2 perhaps from your lungs than ambient "air" unless you use a compressed air bottle to fill the balloon........is that kind of where you were going?

[Goofy Footer 548]

@robertaccio I was being a bit facetious with my balloon pic. That said, ambient air should be 21% oxygen and if I recall correctly we exhale 16% oxygen.

Back to our regularly scheduled suspension discussion:

I know our own @SCHWINN (RIP) used to fill his street tires with nitrogen for longevity and less air escape. Makes me wonder if pro teams fill their air forks with nitrogen? What about nitrogen in a standard oil spring fork in addition to the usual shock nitrogen treatment.

Also why Just bleed the forks but not the shock? The shock is smaller and a single unit vs two forks and gets hot to the touch after use.

[robertaccio 431]

shock completely changes when warm/hot. All Pro teams crew chiefs have their set up adjusted accordingly. From my Italian (World Champ guys) very important to have that sag as a neutral place where the shock does not "work", otherwise it is constantly working both directions and heats up more. Remember the shock is separate air and oil by piston or bladder a little different than forks for the most part in that regard 

[Goofy Footer 548]

38 minutes ago, robertaccio said:

shock completely changes when warm/hot. All Pro teams crew chiefs have their set up adjusted accordingly. From my Italian (World Champ guys) very important to have that sag as a neutral place where the shock does not "work", otherwise it is constantly working both directions and heats up more. Remember the shock is separate air and oil by piston or bladder a little different than forks for the most part in that regard 

Sag adjustment aka shock spring preload (adjustable).

Fork sag is more difficult.
 

Old school damper rod forks like the Legendary KLR had a shader valve on the fork cap to allow extra air pressure preload. Oil level was another preload trick - as oil level rises, there is less air but oil is more dense. For dampening ability - oil viscosity changes worked.

Cartridge forks also can work with oil height changes and “15 ml higher” is commonly referenced on forums. Less emphasis is usually placed on oil viscosity changes.

[Goofy Footer 548]

Also @robertaccio while changes in heat and elevation affect fork pressure and can constitute bleeding…

** What about tire pressure!? **

 

I often wonder what my effective tire pressure becomes while bouncing on rocks at 8000ft mid afternoon when I filled up my tires at 3000ft in the morning.

 

Let’s just call it Pinch Flat Insurance

[robertaccio 431]

I have no clue all my offroad bikes have mousses

 

[Goofy Footer 548]

4 minutes ago, robertaccio said:

I have no clue all my offroad bikes have mousses

 

Cheater!