Cutting springs
- Thread starter Papakeith
- Start date
Pete Payne
MX-Tech Suspension Agent
- Nov 3, 2000
- 933
- 38
When done right - its works well ! when done wrong - its a mess!
order the lenght and rate you need from cannon racecraft.
order the lenght and rate you need from cannon racecraft.
I wrote an article couple months ago, unfortunately the pictures are anywhere on my computer :-(
but keep in mind, first measure the spring for spring travel. if the spring travel is shorter than the fork travel you will reduce fork travel and maybe damage the cartridge!!!
Instruction - How to make fork springs stiffer
Basically the spring rate depends on material, diameter, wire thickness and number of coils of the spring.
The more coils, the softer it is.
1. chapter what you need
2. chapter how stiff can you make the springs
3. chapter how to cut your springs
1. what you need
you need an oxyacetylene torch, a grinder or angle grinder and you need to know how to get spacers (I have access to a lathe so I make them myself)
2. how stiff can you make the springs
every manufacturer has different springs (coils and wire thickness) so you have to find out the spring travel. The more spring travel you have compared to the fork travel, the stiffer you can make the springs.
- Measure the distance D1 between two coils at any point of the spring but not at the end of it.
- Count the coils of the spring. In my example it has 30 coils.
- take the number of coils minus the two outer coils (in my example 30 - 2 =28) and
multiply it with D1 (for example D1 = 11,8mm, then it's 28 x 11,8mm = 330,4mm)
- measure the distances D2 and D3 of the outer coils and add them to the result above (if D2 =11,5mm and D3 = 11,2mm then we have 330,4mm + 11,5mm + 11,2mm = 353,1mm in this example) - that's your spring travel.
Ok, you have a 0.47kg/mm spring for example and want to make it a 0.50kg/mm spring.
If 30 coils are 0.47 then 1 coil is 0.47 x 30 = 14.1kg/mm. Take the rate of 1 coil and divide it over the spring rate you want (14.1 / 0.50 = 28,2) that's the coils your spring must have. I prefer to calculate in 0.5 winding steps, so lets make 28 coils instead of 28.2 w.(then you will get 14.1 / 28 = 0.504kg/mm )
30 coils it has now and 28 coils you need, that means you have to cut 2 coils off of the spring (shown as a green mark in the picture)
Caution: The spring travel must be at least 5mm + spring preload more than the fork travel
Otherwise you will damage your cardridge!
What does that mean? Before you cut off your springs you have to calculate the new spring travel.
Take your original spring travel minus cw x D1. (cw means coils to cut). In our example it's 353,1mm - 2 x 11,8mm = 329,5mm
In this case it's no need to measure the fork travel. If we suppose a max. travel of 310mm of the fork and a spring preload of 5mm we need to have a spring travel of at least 320mm.
If the calculated spring travel is less than 320mm you have to find out your actual fork travel, maybe it's only 300mm then you can cut your springs down to 310mm spring travel
If you wonder if you can make a 0.47 CRF450 spring into a 0.50 spring - I did it a few weeks ago, the stock springs had enough spring travel.
Even a 0.52 spring rate is possible with these (2005 CRF450) springs.
3. how to cut your springs
It’s a good idea to write down your original spring length, then cut the springs with a grinder or angle grinder. The spring end now looks like pic a
Heat the spring up at the point shown in pic b and bend it carefully with a gripper. Repeat this ¼ turn further towards the end of the spring and repeat it once again, then your spring should look like shown in pic c.
Now grind the end of the spring until it stays almost 90° on the floor (pic d)
Heating the spring and bending it is a kind of art to get a perfect looking spring end – but it is not that important, the spring starts to move not until after the first coil.
Now put the spring into the fork leg, reassemble it and look how much free play you have. Add 5mm (or what you want to preload) and cut the spacer to this length.
If you use aluminium or plastic spacers, they will displace more oil than the cut off piece of the spring. Take care if you want to fill in the max. oil quantity. (for example max. oil for the CRF was 420cc, now that I cut off the springs it is 410cc).
Note: if you have the right tools it's an easy procedure - to create an article like that is much more complicated :whoa:
but keep in mind, first measure the spring for spring travel. if the spring travel is shorter than the fork travel you will reduce fork travel and maybe damage the cartridge!!!
Instruction - How to make fork springs stiffer
Basically the spring rate depends on material, diameter, wire thickness and number of coils of the spring.
The more coils, the softer it is.
1. chapter what you need
2. chapter how stiff can you make the springs
3. chapter how to cut your springs
1. what you need
you need an oxyacetylene torch, a grinder or angle grinder and you need to know how to get spacers (I have access to a lathe so I make them myself)
2. how stiff can you make the springs
every manufacturer has different springs (coils and wire thickness) so you have to find out the spring travel. The more spring travel you have compared to the fork travel, the stiffer you can make the springs.
- Measure the distance D1 between two coils at any point of the spring but not at the end of it.
- Count the coils of the spring. In my example it has 30 coils.
- take the number of coils minus the two outer coils (in my example 30 - 2 =28) and
multiply it with D1 (for example D1 = 11,8mm, then it's 28 x 11,8mm = 330,4mm)
- measure the distances D2 and D3 of the outer coils and add them to the result above (if D2 =11,5mm and D3 = 11,2mm then we have 330,4mm + 11,5mm + 11,2mm = 353,1mm in this example) - that's your spring travel.
Ok, you have a 0.47kg/mm spring for example and want to make it a 0.50kg/mm spring.
If 30 coils are 0.47 then 1 coil is 0.47 x 30 = 14.1kg/mm. Take the rate of 1 coil and divide it over the spring rate you want (14.1 / 0.50 = 28,2) that's the coils your spring must have. I prefer to calculate in 0.5 winding steps, so lets make 28 coils instead of 28.2 w.(then you will get 14.1 / 28 = 0.504kg/mm )
30 coils it has now and 28 coils you need, that means you have to cut 2 coils off of the spring (shown as a green mark in the picture)
Caution: The spring travel must be at least 5mm + spring preload more than the fork travel
Otherwise you will damage your cardridge!
What does that mean? Before you cut off your springs you have to calculate the new spring travel.
Take your original spring travel minus cw x D1. (cw means coils to cut). In our example it's 353,1mm - 2 x 11,8mm = 329,5mm
In this case it's no need to measure the fork travel. If we suppose a max. travel of 310mm of the fork and a spring preload of 5mm we need to have a spring travel of at least 320mm.
If the calculated spring travel is less than 320mm you have to find out your actual fork travel, maybe it's only 300mm then you can cut your springs down to 310mm spring travel
If you wonder if you can make a 0.47 CRF450 spring into a 0.50 spring - I did it a few weeks ago, the stock springs had enough spring travel.
Even a 0.52 spring rate is possible with these (2005 CRF450) springs.
3. how to cut your springs
It’s a good idea to write down your original spring length, then cut the springs with a grinder or angle grinder. The spring end now looks like pic a
Heat the spring up at the point shown in pic b and bend it carefully with a gripper. Repeat this ¼ turn further towards the end of the spring and repeat it once again, then your spring should look like shown in pic c.
Now grind the end of the spring until it stays almost 90° on the floor (pic d)
Heating the spring and bending it is a kind of art to get a perfect looking spring end – but it is not that important, the spring starts to move not until after the first coil.
Now put the spring into the fork leg, reassemble it and look how much free play you have. Add 5mm (or what you want to preload) and cut the spacer to this length.
If you use aluminium or plastic spacers, they will displace more oil than the cut off piece of the spring. Take care if you want to fill in the max. oil quantity. (for example max. oil for the CRF was 420cc, now that I cut off the springs it is 410cc).
Note: if you have the right tools it's an easy procedure - to create an article like that is much more complicated :whoa:
Last edited:
helio lucas
~SPONSOR~
- Jun 20, 2007
- 1,020
- 0
pictures would be nice...
very good info... :cool:
thanks
very good info... :cool:
thanks
dirt bike dave
Sponsoring Member
- May 3, 2000
- 5,349
- 3
My friend and I cut fork springs for our KDX200s using the method described by Kawayama (great write up, BTW!).
Stock KDX springs are too soft. We were able to stiffen them up by about 10% without losing any travel. Big improvement, and saved some $.
Never heard of anyone cutting a rear spring, but one of my buddies brazed in some metal wedges between the coils of a DR350 spring to keep that coil from compressing, thereby stiffening the spring. Worked quite well. He repainted the spring, looked stock, worked a lot better.
Stock KDX springs are too soft. We were able to stiffen them up by about 10% without losing any travel. Big improvement, and saved some $.
Never heard of anyone cutting a rear spring, but one of my buddies brazed in some metal wedges between the coils of a DR350 spring to keep that coil from compressing, thereby stiffening the spring. Worked quite well. He repainted the spring, looked stock, worked a lot better.
- Thread starter
- #7
Excellent writeup Kawayama! Thanks. If I plan on going the cutting route I'll post up pics of my progress.
Spring cutting will be a last resort of sorts. I bought a 2004 montesa a few weeks ago and the springs are woefully inadequate for someone of my size. The best "off the shelf" solution gives me 10% stiffer rates. That's still too soft.
I'm currently in contact with MX-Tech trying to find a solution that doesn't include cutting up these springs and making a spacer.
It seems that there is surprisingly little information out there for these trials bike suspensions.
Spring cutting will be a last resort of sorts. I bought a 2004 montesa a few weeks ago and the springs are woefully inadequate for someone of my size. The best "off the shelf" solution gives me 10% stiffer rates. That's still too soft.
I'm currently in contact with MX-Tech trying to find a solution that doesn't include cutting up these springs and making a spacer.
It seems that there is surprisingly little information out there for these trials bike suspensions.
Gerncrf450r
Member
- Mar 1, 2009
- 2
- 0
For $20 I once let someone do that to a set of fork springs. He added a spacer equal to the height of spring removed. Not sure how to calculate it, but it did the trick and saved $$$.
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