KTM Forums banner
  • Hey everyone! Enter your ride HERE to be a part of December's KTM of the Month Challenge!
1 - 16 of 16 Posts

·
Registered
Joined
·
513 Posts
Discussion Starter · #1 ·
Any of the Gen 3 owners here regularly use this screw? So I was talking with the local dealer mechanic today and he mentioned they regularly use them on the dirt bikes and road bikes that have them when in for a service to release built up pressure, got me thinking so when I got home I undid them (about 12 to 13 turns) with a rag at the ready (didn't need it) and it sounded like letting air out of the tyre for a few seconds, be interesting to see if the suspension is any plusher on my next ride, he recommended doing it after any long ride.
Just wondering if anyone else out there does it regular and notice the suspension difference
 

Attachments

·
Dirt tracker
Joined
·
3,366 Posts
Air pressure builds up in forks. Normal occurrence due to temperature and pressure changes inside sealed fork. Slight increase in pressure inside has same effect as increasing spring rate. This can cause harshness. The Air bleeder releases this pressure buildup. Off road guys have been using this method for decades with good results. Aftermarket bleeder is much easier than removing screw when bleeding air from forks. You simply push plunger to release air pressure
 
  • Like
Reactions: kbkato

·
Registered
Joined
·
618 Posts
KTM has long had these bleeders, I remember first seeing them on the RC8R in 2012. Funny how not other sports bike etc has them…

Dirt bikes I know have long had them. I’ve never bled mine yet and the bikes nearly a year old.

PS. are you not meant to raise th front wheel off the ground before bleeding them? 🤷🏻‍♂️
 

·
Registered
Joined
·
513 Posts
Discussion Starter · #4 ·
KTM has long had these bleeders, I remember first seeing them on the RC8R in 2012. Funny how not other sports bike etc has them…

Dirt bikes I know have long had them. I’ve never bled mine yet and the bikes nearly a year old.

PS. are you not meant to raise th front wheel off the ground before bleeding them? 🤷🏻‍♂️
@Trebor27 Gen2 didn't have it so new to me (uneducated aye ) mechanic said just undo it after long rides to release pressure, didn't mention raising forks off ground and I didn't, seemed to work with a decent amount of air releasing
 

·
Registered
Joined
·
618 Posts
@kbkato You may be right, the first time I read this, I read it as, raise the front with a workstand. But I think it's just a run-of-the-mill, "make sure the bike won't fall on you when working on it, so put it on a rear paddock stand", line instead?

 

·
Registered
Joined
·
513 Posts
Discussion Starter · #6 ·
@Trebor27 I can definitely see your way of thinking but its probably just KTM arse covering.
 

·
Registered
Joined
·
618 Posts
Yeah I have to agree. I tried backing the bleeders out on mine, nothing, not a peep.... When you did it, was it straight after a ride when the suspension is hot?
 

·
Registered
Joined
·
513 Posts
Discussion Starter · #8 ·
Yeah I have to agree. I tried backing the bleeders out on mine, nothing, not a peep.... When you did it, was it straight after a ride when the suspension is hot?
Couple of hours after a 300 km ride mate, took about 12 to 13 turns
 

·
Registered
Joined
·
513 Posts
Discussion Starter · #10 ·
Interesting. I kept turning until I took the bleeder screw out! 😂

Bike has been standing though, I’ll maybe try again at a later date.
Definitely @Trebor27 after a longish ride do it as soon as you get home
 

·
Registered
Joined
·
513 Posts
Discussion Starter · #12 ·
Tried my bleed screws the day after a track day, and no pressure inside, nothing. it must just dissipate.
That's interesting, must only be for use during rides or right after
 

·
Registered
Joined
·
618 Posts
Honestly, I suspect it’s completely pointless. If you bleed it immediately, your suspension is “hot” so it will let some out. But when it cools it’ll just draw a bit of a vacuum…

But I dunno… Ohlins, doesn’t have bleeder screws, so unless there is something “sub-par” about the WP suspension where you maybe need to equalize occasionally, then I suspect it’s more gimmick than anything. Or may it’s good for track hero/racers… I dunno….
 

·
Registered
Joined
·
513 Posts
Discussion Starter · #15 ·
So it seems it may be more important in the motocross world than road bike depending on type of roads you are riding on, took this explanation from a motocross site:
WHAT IS IT? As you ride your bike across rough ground, the movement of the fork creates friction. The byproduct of the friction is heat. If you don’t believe us, reach down and grab your fork leg with your bare hand after a moto. The fork tubes will be hot—although on an air fork, the oil leg of the fork will be hotter than the air side. All this heat makes the air inside your fork tubes expand. And when air pressure rises inside a closed container, such as a fork leg, it resists being compressed. The hotter your forks get, the stiffer they become.

Now, you may think that since your bike has coil-spring forks, your bike is not affected by the expansion of hot air. Wrong! All forks, whether they are air forks or coil-spring forks, are air forks. There has to be an air chamber in all fork designs to compensate for the collapsing movement of the forks. And that air chamber, when it gets hot, will make your forks stiffer. How much stiffer? It depends on the ambient air temperature, the roughness of the track, the rider’s weight and his speed, but 4 to 5 psi on a WP air fork is a ballpark number.
After a long, tough moto, your forks will be considerably stiffer than they were when the moto started. If you don’t bleed the expanded air out of the forks before your next moto, they are going to get a lot stiffer. Every manufacturer puts a bleed screw on the top of the fork caps to allow the rider to release the trapped air with a screwdriver or a #20 Torx driver. Bleeding your forks should be high on your must-do list between motos.
 

·
Registered
Joined
·
618 Posts
Thanks for sharing that, it makes a lot of sense! It’s to release excess pressure caused by the air inside expanding under increased temps. I assume road bikes tend the specify the air gap based on hot temps then. As bleeders are not common, but even I can feel the difference between cold and hot forks on track. That’s most likely down to oil viscosity than anything else though.
 
1 - 16 of 16 Posts
Top