T140V Progressive Fork Springs

[Lordmac]

Just bought a pair of progressive fork springs and was wondering if anyone knows or has an opinion about the direction the closer-wound coils should be . . . up or down? There surely is a performance differential. The literature which comes with the springs states: "For minimum unsprung weight when progressive rate springs are fitted we recommend fitting the spring so that the closer wound coils are at the top." Well, I must say, I don't fully understand exactly what that means; "minimum unsprung weight"? That really doesn't clue me, and it seems they can go either way, so, what's the deal? Anyone? Bueller?

 

[Rudie]

anyone knows
about the direction the closer-wound coils should be
The literature which comes with the springs states: "For minimum unsprung weight when progressive rate springs are fitted we recommend fitting the spring so that the closer wound coils are at the top."
don't fully understand exactly what that means; "minimum unsprung weight"?

Over a given length, the end of a progressive spring with closer wound coils at one end is heavier than the end with wider wound coils.

The slider and damper are unsprung weight. Therefore the end of the suspension spring on top of the damper is unsprung weight. Therefore, if you put the lighter end of a progressive spring on top of the damper, there is less unsprung weight than if you put the heavier end of a progressive spring on top of the damper.

up or down? There surely is a performance differential.

None. If a progressive spring has closer wound coils at one end and wider wound coils at the other end, the "progressive" is by the closer wound coils becoming coil bound first; this will happen irrespective of which way up the spring is.

Just bought a pair of progressive fork springs

Have you also bought the damper head O ring replacement from L.P. Williams? Ime, the standard O rings contribute significantly to stiction, reduces the effectiveness of good progressive springs.

 

[solomon]

That was as a brain teaser!
But now it's been pointed out, it's obvious! The tighter coiled end is heavier. At the top it doesn't move up and down. At the bottom it would follow every bump.

 

[Lordmac]

Over a given length, the end of a progressive spring with closer wound coils at one end is heavier than the end with wider wound coils.

The slider and damper are unsprung weight. Therefore the end of the suspension spring on top of the damper is unsprung weight. Therefore, if you put the lighter end of a progressive spring on top of the damper, there is less unsprung weight than if you put the heavier end of a progressive spring on top of the damper.


None. If a progressive spring has closer wound coils at one end and wider wound coils at the other end, the "progressive" is by the closer wound coils becoming coil bound first; this will happen irrespective of which way up the spring is.


Have you also bought the damper head O ring replacement from L.P. Williams? Ime, the standard O rings contribute significantly to stiction, reduces the effectiveness of good progressive springs.

Thanks Rudie. I learned more than I thought about springs. I now know what "minimum unsprung weight" means! It makes perfect sense once one gets all the particulars. I'm pretty sure I bought a set of those square, super "o" rings a while back but have not yet got back into the whole fork removal thing yet. I will at least see how these new springs act and go from there. I appreciate your input.

Now, if only I can find that can of fork oil I used to see what viscosity it is . . .

 

[Rudie]

find that can of fork oil I used to see what viscosity it is . . .

If you have bought the Progressive Suspension springs, the fitting instructions advise setting the damping oil to the same level in each leg, not the same volume as Triumph recommended. Setting the oil level the same in both legs ensures the volume of air in each leg is the same when springs and stanchion top caps are fitted. The trapped air in each leg contributes to the suspension performance.

I start by pouring the recommended fork oil volume into each leg without the springs then I lower the front of the bike slowly until the stanchions are as far into the sliders as they will go. Then I measure the distance from the top of each stanchion to the top of the oil in the leg. I have never found the same oil depth in both legs on the same Triumph ... I raise the 'low' level with extra oil until it is at the same level as the 'high' level; if I inadvertently add too much oil to the leg that had the 'low' level, I use a drinking straw to remove small quantities of oil until the oil in both legs is at the same level measured from the tops of the stanchions.

have not yet got back into the whole fork removal thing

When the forks are dismantled, also compare both damper rods side by side, ensure the slots into the inside of the rods are the same length, are in the same position relative to the undersides of the damper heads and neither rod has any extra slots, holes, etc. the other does not have.