So, I bought a '24 FC450 and need a stiffer shock spring. I have an older 48n/mm spring from my 2017 KTM that is 260mm in length, but the new Husky has a 240mm long spring. The FC suspension is lowered from the factory and not sure if the 260mm will be a proper replacement. Any help is appreciated.
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I used a 260 mm length spring on my '24 KTM 450. Works fine and puts the locking screw in a better position.
The common consensus is that the 260mm spring will coil bind at full travel, and this could be a dangerous situation. I have not measured this for myself, but among tuners, this is what is agreed on.
I have a 2024 KTM 250 SX , it came with a 45-240 spring and I had a new 51-260 spring that came with my last bike and it works fine.
Thanks for the info guys. I knew the 260mm would fit, but didn't even consider coil binding. After a little research I'm going to purchase a 240mm spring since that is what the suspension is designed for.
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Shock travel on each style of shock is 5-1/2” or so. There’s way more space between coils on the shorter and longer springs than that. Not sure how coil bind would be possible.
Which tuners state this is a problem?
Looks to be more space between the 240 spring between coils, right? That should to a larger extent prevent coil bind.
But at same time if travel is equal on both shock types, it shouldn't matter.
Conflicting conclusions I feel is possible here 🤔😄
Interesting. I wonder why the KTM group went to a shorter spring? Maybe weight, but I’m not sure there is much measurable difference.
Like you said, the husqy has lowered suspension right (less travel)? It would make sense they compensate with a shorter spring to keep the preload the same.
It doesn't matter. 8mm preload is 8mm no matter length of shock or linkage ratio.
But I am curious to if the less coil space can cause binding on 260 springs when used on new chassi.
Of course it matters, you want your spring to start somewhere in the middle of the adjustment range. If you just throw in a longer spring you will max out the adjuster at the top, or at least loose the adjustment there. That is not to say it can't work, but stands to reason they shorten the spring for husqy to compensate and lose the weight too
You will not max it out. It doesn't matter. You have 60mm range, worst case you get 5-7mm preload which you anyway need. You should not go under that.
If the spring is 258, better, 263 worse. Most WP is +-1mm and Ktech normally 258-260.
Ok fair enough, didn't know that. I thought the difference would be bigger
Coil bind happens before the physical contact of the coils. Manufacterers determine the coil bind clearance specification depending on wire metallurgy specs and diameters. I'm not in direct contact with WP, so i can't speak to what that clearance is for their shock springs, I was just passing along what I have been told about why they spec the shorter spring for the new shock.
IMO, saving $150 on a spring isn't worth any risk for me personally or someone that I'm doing work for.
Ah so it's kind of a state in the coils itself that is coil bind, and not the physical touching?
Chatgpt was wrong again when I asked it 😄
I think these nameless suspension tuners are trying to sell more shock springs, personally.
Potentially. But "thinking" doesn't make me qualified or certified to make a call that could affect the safety of another rider.
Correct. There is an engineered "spec" +safety margin. Shock springs of course don't cycle at high frequency like valve springs or something like that, but there are still mechanical limits that apply.
The Husky and the KTM bikes have the exact same shock. The Husky shock is not shorter. They use the same springs, when comparing same generation chassis. The shortness of the Husky suspension is all in the linkage. The shock has a thicker bump stop cap to prevent tire to fender contact from the lowered linkage.
Next, the overall, eye-to-eye length of the shock has no determination at all on whether or not a shorter or longer spring is more likely to coil bind. What matters is the stroke length of the shock. So, you'd have to compare the stroke length of the older gen shocks vs. the new gen shocks to determine if a 260mm spring has potential to coil bind on the new shock. I have a sense they went to a 240mm spring just to save weight and make nicer packaging on the newer chassis. So long as the 260mm spring is not past the threads for the preload adjuster and you are able to obtain correct preload and sag numbers, it is likely just fine. Based on the fact that there's numerous guys saying they've already done this, seems like a closed case. Also worth pointing out that even on the older gen bikes, not all the springs were 260mm length. Some of the lower rate springs were 250 or 240 already.
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