Tie-Downs ??

[rairden]

I'm new to the sport.

Does it hurt the front fork springs, or any other part in the forks, to have them tied down in the back of a truck for extented periods of time or any amount of time. I don't think it affects it at all, but I would like to know for sure.
why I asked . . .
I was riding with some friends and one told me while I was loading my dirtbike up to not tie it down that much. I really tied it down as far as I could because I didnt want it going anywhere.

 

[atc3434`]

Fork seals can let go under constant pressure. Just had it happen to my buddy taking him home two weeks ago. I usually watch the fork as I'm pulling it tight, and go to just less than half the travel, if that. Its not really needed to be any tighter, your not doing the Baja with your bike on the back! :)

 

[Malcolm M]

I didn't realize that the springs put pressure on the seals. After the initial compression of the fork, once the fluid has been displaced through the shim stack, I thought the hydraulic pressure inside the fork whether extended or compressed is about zero. Guess I learn something everyday...

 

[RM_guy]

It won't hurt anything. Think about how much the forks compress in one lap around the track. The seals are designed to seal tighter as the internal pressure builds up. I have always tightened the tiedowns to about 3/4 fork compression with no problems. I'd rather have it secure in the truck, especially on some of the roads that you have to drive on to get to the track!

If your forks leak then there is some other problem going on. Check for dirt under the seals or a nick in the inner fork tubes.

If you are really paranoid you can always bleed the air out of the forks after you cinch it down. Just don't forget to re-bleed them after you unload it.

 

[atc3434`]

Perhaps I stand corrected... definatly wouldn't be the first time! ;)

 

[Green Horn]

Originally posted by atc3434`
Fork seals can let go under constant pressure.

I'll agree with atc. Sure, they don't go when riding a track but there is no constant pressure for a LONG period of time. And no it's not the springs putting pressure on the seals. It's the fluid being compressed into a smaller area. When landing a big jump your forks are fully compressed for maybe a few seconds at most. Hauling your bike for an hour or longer means the forks are more than likely fully compressed the entire time. I have not actually blown seals because of this happening but I'd rather be safe than sorry. I bought a front fork brace that goes between the tire and under the fender. This way I can crank down on the tie downs w/o compressing the suspension. You can also cut down a 2x4 to wedge in between the tire and fender too. I've seen people do that too.

 

[RM_guy]

I think this whole issue is more personal preference than anything. It's been beaten to death and technically speaking there is no reason not to compress the forks and leave them there. There are a lot of aftermarket products that rely on unfounded fears for sales and I'm sure that will always be the case.

 

[jmics19067]

I believe in RMguy,

the spike in air pressure< created while bottoming out the forks on the track would most likely be greater on the seal than the constant air pressure of the forks being locked down at 3/4 travel. If your forks are squeezed tight the only pressure that the seal should see is the dead air space getting smaller.

about the only detriment snugging your tie downs tight that I could think of is maybe ......MAYBE your fork springs sacking out earlier than if the only force they have seen was a track.

My opinion is snug them down tight and smile that you are not going to be buying a radiator when the bike falls over in the back of your truck .

ps double lipped seals do seal tighter the more pressure behind them

 

[Green Horn]

Originally posted by RM_guy
I think this whole issue is more personal preference than anything.

most definately...

and technically speaking there is no reason not to compress the forks and leave them there.

Not trying to be a smart ass but I'd like to read more on the "technical" reasons why it won't hurt the forks/ seals. Is there any other good threads or reads on this topic? Maybe my common sense is way off but it makes sense to me that any un-needed pressure on anything will promote problems.

 

[jmics19067]

http://dirtrider.net/forums3/showthread.php?threadid=48596&highlight=fork+seal+leaking


well this is a fork seal care tip but not much tech into it but it is a start.

 

[RM_guy]

Originally posted by Green Horn


Not trying to be a smart ass but I'd like to read more on the "technical" reasons why it won't hurt the forks/ seals. Is there any other good threads or reads on this topic? Maybe my common sense is way off but it makes sense to me that any un-needed pressure on anything will promote problems.

jimics's link to Jer's fork seal care guide is a good one.

Any hydraulic seal system is designed to withstand the pressures that the application creates. Any design worth it's salt uses a design margin (formally called a safety factor) to accommodate for manufacturing tolerances so it will continue to function as advertised. The concept in it's most basic form is a clearance hole for a bolt. If the hole was the exact size of the nominal bolt but the bolt was slightly over-sized, it wouldn't fit. If the hole was made to accommodate the upper limit of the bolt size, it would always fit.

In the case of fork seals, they are designed to withstand much more force than could ever be generated in normal use. This alone would insure that the pressure generated by leaving the bike tied down would not "blow" the seals. And as jmics pointed out, an instantaneous high load on the forks (a huge G-out for example) would be worse than staticly compressing the forks 3/4 of the stroke.

The design of the lip on the seal is what makes all of this happen as it should. You will notice when you examine a fork seal that there is a spring around the seal lip that holds the seal tight against the inner tube. This is necessary because there is no pressure inside the fork. You need the spring to maintain the seal until the pressure builds up enough to do it. Since the pressure inside the forks acts equally on all surfaces, and the oil is behind the sela lip, it conveniently forces the lip tighter against the inner tube as the pressure increases. Again, cinching down the bike actually makes the seals seal better.

Of course there are things that can happen that can muck you up. Dirt under the seals is the major culprit. Even a small piece can prevent the lip from sealing and cause a leak. Just plain out worn seal will leak too. Once the lip wears past a certain point it will leak.

Speaking of wear. All objects that slide along each other needs lubrication and fork seals are no exception. It is difficult to see with the naked eye but there are very fine "scratches" on the inner fork tubes. This surface roughness is designed to trap a small amount of oil that the seal can ride against. It is the same concept as cross hatching on the cylinder wall. If the inner tubes were perfectly smooth the seals would stick and soon be destroyed. You may say that the seals are designed to leak and you would be correct but it is nothing that you would notice or have to worry about.

How's that?

 

[atc3434`]

:worship: :worship: :thumb:

 

[jmics19067]

Pretty darn good :thumb:


two mistakes I want to clarify in my previous post


one after reading the link I posted I learned that the springs wear by cycles not by static load

two it doesn't matter if it a doublelipped seal a singlelipped seal will seal tighter when the pressure increases around the lip.

 

[Green Horn]

Ok, I see what you're saying now. And I totally agree with your "G-out" theory. It's definately not as harsh on the suspension to cinch it down w/ tie downs vs. landing a 90 ft triple.

it conveniently forces the lip tighter against the inner tube as the pressure increases. Again, cinching down the bike actually makes the seals seal better.

This is the part that I'm not totally convinced on. I won't go as far as telling you you're wrong since I would most definately be in over my head. I have always believed in the X factor. This meaing that everything in existance has a breakdown point of X. How much time before you get to X is purely based on how much wear and tear it receives. Granted seals can also go bad from a high lack of use as well. My thinking though is that the more you force the seals to do their job the more "mileage" (for lack of better terms) you're putting on them the shorter the time till X happens. Sure I now understand that they can handle the force when a bike is strapped down but why put the extra stress on them??

In closing, I do appreciate the well thought out and informative reponses RM_Guy. I guess I am just not easily convinced (stubborn). :thumb: Please feel free to make more corrections to my reasoning as I do enjoy learning new things about these motorbikes. :)

 

[RM_guy]

You are right about the "X" factor and it is accelerated by wear which is a function of relative motion. But when you cinch down the forks for transport, there is no movement between the inner tube and the seal. It just sits there so there is no wear taking place, just pressure.

You can have some wear when the pressure cycles but you need some major deflection for that to happen and the seal doesn't deflect, it compresses. Any wear due to that would be very insignificant.

I'm glad you are willing to learn. Some people get stuck in a rut and just won't budge, no matter what. MXA tech articles come to mind...;)

Knowledge never hurt anyone:)

 

[Green Horn]

Originally posted by RM_guy
You can have some wear when the pressure cycles but you need some major deflection for that to happen and the seal doesn't deflect, it compresses. Any wear due to that would be very insignificant.

Is what you're trying to say is that the actual seal "shrinks" in a sense when pressure is applied? I was under the uneducated ASSumption that it expands as the pressure increases. I am not familiar with "deflection" vs. "compression" when using these terms in discussing fork seals.

I'm glad you are willing to learn. Some people get stuck in a rut and just won't budge, no matter what. MXA tech articles come to mind...;)

Knowledge never hurt anyone:)

I can be very hard headed when it comes to topics I KNOW about. Anything else I don't waste time arguing since that's when ignorance sets in. :thumb:

Thanks again for taking the time to explain these things...I'd give ya a Karma point or two but we're all out of them on this site. :)

 

[RM_guy]

The seal compresses like when you take your pencil and push the eraser down onto a desk. The force you are applying to the eraser is synonymous with the oil pressure inside the fork and the desk would be the surface of the inner tube. The eraser tries to flatten out, or compress. Tension is the opposite and is when something is stretched apart. Deflection is what happens when to take a long object, like a ruler, and hold one end while you bend the other end down. The amount you bend it down is the deflection.

If you really want to get confused, when you bend the ruler, there is actually compression and tension along the length of the ruler. If you can imagine a neutral horizontal plane at the center of the ruler there is compression at the bottom (in the direction of deflection) and tension at the top.

Sorry for all the lessons but I read my July issue of MXA today and their "tech" articles were so full od crap I thought I'd scream :confused:

 

[Green Horn]

Originally posted by RM_guy
If you really want to get confused, when you bend the ruler, there is actually compression and tension along the length of the ruler. If you can imagine a neutral horizontal plane at the center of the ruler there is compression at the bottom (in the direction of deflection) and tension at the top.

Oh my, believe it or not but I actually do undertand the above. :scream: Kind of like bending a garden hose. It squishes together on the inner part of the curve while it stretches along the outer part.

None the less, I think I'll still use my fork brace. But now I atleast am a little more "in the know". :thumb: Thanks so much for all the free edumocation. :confused: I'm not worthy!! :worship:

 

[MrLuckey]

Hehehe - the last time I saw someone using one of those fork brace thingys they were bragging about how great it had been for so long, the next day after the trip to the riding area the brace thingy was gone and the bike was very loosy goosy. Sorry BigLou if anyone figures out it was you :laugh:

 

[biglou]

Yeah, I got two of them things for sale if anyone wants'em. I hate those things... :p

 

[Green Horn]

Originally posted by BigLou
I hate those things... :p

Aw c'mon. Be lover and not a hater. :laugh:

Hey Lou, ya got an orange one to match my bike? :confused: