front fork spring mounted upside down ?

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Jul 31, 2014
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Kirkenes, Norge
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ST 1300
Hi
I have started to overhaul the front fork. When I disassembled it, was springs mounted with the closes wound coils up. According workshop manual should these be down. Is it someone out there who can tell me what is right?
Best regards
Tore T
PS: It looks like that the fork has been overhauled earlier
 

dduelin

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I follow the service manual recommendation but the truth is it probably doesn't matter. Tapered side down is a tiny amount less unsprung weight when the softer end is compressed enough to become coil bound.
 
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usually the tighter wound coils are at the bottom.

For the spring itself, it doesn't matter, it compresses from both ends regardless of which way its installed.

Where the difference occurs is how much fork oil the spring displaces in the tube. If the tight coils are down it will displace more oil, and the oil level will be higher. The factory setup is usually to fill the oil to the prescribed level without the spring in the fork, then put it in with the tight coils down, and the desired oil level should be achieved. If you put it in the other way the oil level will be lower than desired, but fork tuning doesn't have one right setting, its all variable depending on your weight and riding style.
 
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I believe it does matter to have the tight end downward, due to the fact the large end may force itself over the dampening rod platform and lock the front end up.
On most of the aftermarket springs (sonic) etc. the springs are the same dia. at each end and it does not seem to matter.
.02
 
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I believe it does matter to have the tight end downward, due to the fact the large end may force itself over the dampening rod platform and lock the front end up.
On most of the aftermarket springs (sonic) etc. the springs are the same dia. at each end and it does not seem to matter.
.02
I believe the stock springs are the same diameter at each end as well, the only difference is how close the windings are at each end. I've never actually measured them, but they appear to be the same diameter throughout.
 
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I believe the stock springs are the same diameter at each end as well, the only difference is how close the windings are at each end. I've never actually measured them, but they appear to be the same diameter throughout.
On the 1300's the springs are larger dia. On one end, measure it for yourself.
 
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On the 1300's the springs are larger dia. On one end, measure it for yourself.
I totally missed the fact that this was in the 1300 suspension category, I was thinking 1100, sorry. that is surprising though, I've never seen springs that were tapered, wonder why they did that?
 
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usually the tighter wound coils are at the bottom.

For the spring itself, it doesn't matter, it compresses from both ends regardless of which way its installed.
The soft end compresses more quickly than the rest of the spring. The unsprung weight is affected if the entire spring must travel upward to compress the top coils first.

Where the difference occurs is how much fork oil the spring displaces in the tube. If the tight coils are down it will displace more oil, and the oil level will be higher.
The amount of air in the fork will be unaffected because the looser coils at the top will allow for more air. It is actually the amount of air that is being set by oil level.
 
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The amount of air in the fork will be unaffected because the looser coils at the top will allow for more air. It is actually the amount of air that is being set by oil level.
yeah, I knew the trapped air was part of the suspension response equation, but I never thought about its volume that way, thanks for pointing that out. You're right, the volume of air is the volume of the tube, minus the volume of oil, minus the volume of spring steel, so direction wouldn't affect that calculation at all.


The soft end compresses more quickly than the rest of the spring. The unsprung weight is affected if the entire spring must travel upward to compress the top coils first.
So you're saying that if the soft coils are on the bottom, the fork compression works directly upon them and the rest of the spring length doesn't really move during compression. But if they're on the top, the stiffer coil section has to move upward to compress the softer end, so the weight of that part of the spring would be considered additional unsprung weight. That makes sense, but I suspect for street riding the practical difference is pretty small given the total unsprung weight vs. the weight of that part of the spring.

Thanks for bringing this up, these are both things that I'd just never taken the time to think through, but seem pretty simple now that I have.
 

mlheck

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I hate to bust anybodies bubbles, but on a 740# bike the little bit of difference in unsprung weight from having the spring in upside down is not going to be noticed. The same with what little bit of air that is displaced. On a 300# sportbike maybe.
 
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