Fork spring shortening

[rollingthunderx2]

Im about to modify my spare forks, as the standard spring is too soft, how much should I cut off to stiffen it.
I have a workshor and do realise I need to rebend the cut to level it again.

[popkat]

I reckon it would be trial and error but for £75-80 you can get k tech springs of with the spring rate you want. Also fork springs have a designed length and storm springs are not long ones to start with.



.

[rollingthunderx2]

Most replacement springs are not the same length as the originals.
I may check the spring weight with a clamp and scales as I cut them.
Im not looking to spend any more money on my spare bike.

[Cadbury64]

The cut and test method does sound best, the standard sping is progressive so I'm not sure that it would be a simple matter to calculate a rate. If it helps, I run 0.85kg/mm straight rate springs in my VTR and weigh 85kg (+/- christmas "conditioning"). The standard springs are listed at 0.585kg/mm. Spring rates depend on the total length of the wire in the spring and it's diameter plus number of turns, which is then twisted torsionally when the spring compresses. If the stock 0.585 kg/mm spring was straight rate then you would get to 0.85kg/mm by reducing the length by roughly 1/3, but that will be too much for a progressive spring.

[popkat]

Most replacement springs are not the same length as the originals.
I may check the spring weight with a clamp and scales as I cut them.
Im not looking to spend any more money on my spare bike.

I've fitted quite a few sets of springs to firestorm forks and all have been the same length as standard, you might have to alter the length of the spacer if the spring rate is heavy but other than that they are pop in.



.

[Roger Ditchfield]

The total length of the spring + spacer ONLY (without the washers) should be 410mm.
Cutting down springs is a dangerous practice. You can have a serious accident as a consequence.
Front suspension is not something that should be subject to "trial and error" with the dramatic changes you propose.
Suspension is governed by the Laws of Physics and you cannot go outside these parameters.
If your spare bike is not worth buying aftermarket springs then sell it and invest the money in the no1 bike.

[rollingthunderx2]

Oh dear, next people will be told not to modify forks as suggested in the workshop knowledge base.
Drilling holes in forks may cause sudden death..etc etc.

[rollingthunderx2]

Wire diameter =W

Center to center coil diameter =C

Number of active coils =N

W⁴x80400/(8xC³xN)

Answer given in N/mm. Convert to Kg/mm by dividing by 9.81

[AMCQ46]

Oh dear, next people will be told not to modify forks as suggested in the workshop knowledge base.
Drilling holes in forks may cause sudden death..etc etc.

Given that Roger D does this for a living, and is the person many of us have sent our forks to to get them fixed, his opinion holds a bit more weight than most of the rest of us! [and the fork mods page in the knowledge base is a copy of some of the changes Roger does, but not all]

and I have to add, that it is a lot of work to save £100 on new springs that will work out of the box...... also you have to factor in that you will need to add extra spacers to get back to the 410mm length,.... then you need to be sure that they won't go coil bound on full compression.

its your bike and your time, so only you can work out the value for money for your time and risk.

[sirch345]

Oh dear, next people will be told not to modify forks as suggested in the workshop knowledge base.
Drilling holes in forks may cause sudden death..etc etc.

Knowing what Roger is like, he's only looking out for you,

Chris.

[Roger Ditchfield]

There are a number of improvement modifications that are perfectly safe to install that affect compression and rebound which do not compromise safety. Shortening progressive OEM springs will make them become coil bound before the full travel of the for is reached. This will cause the front wheel to skip under heavy breaking often resulting of loss of control. It is a free world and riders can do what they want but I strongly recommend not to go down the road of spring shortening to avoid the possibility of going down the road!

[rollingthunderx2]

I think you missed out the word may........

[rollingthunderx2]

I am more than aware of the effects of modifications and will be as usullal, informedly cautious..im not dome idiot butcher...and dont presume any effect..it may work or not but the fork travel will be checked..maybe others would not...but I will.
Spring shortening is actually quite common among professional suspension tweakers..Im more than a bit surprised that just because some people havent heard about it that it is supposedlydangerous....any modification can be dangerous if not done PROPERLY.......
"I never heard of that"
So it must be wrong.....
That ranks with "Honda spent thousands of hours designing it do it must be perfect."
I am not about to produce a deathtrap.

[rollingthunderx2]

Oh..and there are lots of replacement springs shorter than a bikes original length.