2010 YZ450 - OEM fork spring quality, rate change after time

Didn't want to put this post in the general suspension topic, since I would like feedback from other 10/11 YZ owners -

I am curious about the quality of the OEM fork springs, more specific the accuracy of the 0.47kg stock spring rate and the tendency to lose some of the spring force after time. Seems my YZ worked great when new, and now it tends to feel like the front end is softer compared to when it was new. Not so much of a damping difference, but maybe more sag. Has anybone measured the stock spring rate after say 50+ hours?

How about recommendations for aftermarket springs, any difference between quality of springs from Factory Connection, Race Tech, etc?

Thanks for any input.

Yamaha suspension, particularly the forks, always feel stiff when new, then "loosen up" in a few hours. Most brand new springs will yield a little after being worked hard for a while, too.

Dave Johnson of SMART Performance, who is a KYB dealer and has access to any spring he wants to use, is of the opinion that the KYB springs are the highest overall quality spring available for the fork, period. They're more expensive, and less profitable per unit, but that's typically what he goes with first.

My '06 has the OEM springs at both ends, and the sag has been quite stable for a long time.

Yamaha suspension, particularly the forks, always feel stiff when new, then "loosen up" in a few hours. Most brand new springs will yield a little after being worked hard for a while, too.

Dave Johnson of SMART Performance, who is a KYB dealer and has access to any spring he wants to use, is of the opinion that the KYB springs are the highest overall quality spring available for the fork, period. They're more expensive, and less profitable per unit, but that's typically what he goes with first.

My '06 has the OEM springs at both ends, and the sag has been quite stable for a long time.

I agree with you on the KYB springs and SMART Performance.

Maybe you just need to replace your oil in the forks. If you do the inner cartridge, by the manual, then you would be bleeding them wrong. I had to get some parts for a 09 Yamaha 450, and he sent detailed instructions on how to do this correctly. I myself always use the KYB fork oil from Yamaha (expensive), but I hear great things about SMART oil. Just have a few cases of KYB, so I continue to use that in my KYB forks.

After I had 22 hours on my 2010 YZ 450, I thought the forks bottomed to much. I changed the fluid in the forks, bleed the cartridges as specked by Smart, and they didn't bottom anymore. Had that firm ride like when they were just broke in. Same thing with the rear shock. The oil just wears out, I guess.

The manual isn't really wrong, it's just difficult to understand what's being said because of the translation, and it's a little over simplified.

Here's what I do, based on info from SMART:

http://www.thumpertalk.com/forum/showthread.php?p=8762814#post8762814

If you get in there, the part in the manual about having a particular gap at the rod lock nut may confuse you. Notice how it's assembled as you take it apart, and read this:

http://www.thumpertalk.com/forum/showthread.php?p=8002008#post8002008

Something that works well with the KYB fork is to use a heavier oil in the outer chamber. This increases the bottoming resistance once the fork hits the oil locks near the bottom, and allows you to run the oil level a little lower for a nicer overall feel. It will require you to change oil a little more often, though, because bottoming the fork will have a tendency to drive the heavier OC oil into the cartridges past the seal on the rods.

It will require you to change oil a little more often, though, because bottoming the fork will have a tendency to drive the heavier OC oil into the cartridges past the seal on the rods.

That's interesting, I'd be up for trying that out. I run 5wt now, how much heavier do you go in the outer chamber 7wt/10wt ? I'm not a big fan of changing cartrige seals, not that I can't do it myself.. I'm just not crazy about causing an issue. I'm making the assumption that the oil in the OC pushing past the seal will damage it ? Wouldn't the oil that get's pushed past the cartridge seal end up making it's way out the bleed holes ? How often do you change the oil in your forks ? Do you suggest changing the oil in the forks more often because of cross contamination between the two oil weights in the inner chamber ?

That's it.. I'm all out of questions...

The seal isn't damaged by oil being forced past it "backwards". Unless a seal is built with bi-directional lips, like having two seals back to back, it will seal against high pressures in one direction only, and pressure from the opposite direction will blow the lip down and bypass it. This happens all the time in the KYB fork, and it may even be a designed in function, as it sort of ensures the cartridge stays full and bled free of gas that might develop. And yes, the excess simply works its way out the bleed holes, almost at the same time it comes in.

The concern is really only that your cartridge oil becomes thicker as it gets contaminated with the heavier stuff from outside. It could be necessary to change it as much as twice as often, but that entirely depends on how often you use the very bottom inch of travel. In the last inch or so, the cone shaped oil lock collar at the bottom of the cartridge is force into a cylinder at the bottom of the lower tube. The closer fit of theses two parts makes it more difficult for the oil trapped under the cartridge to escape past the end of it, and serves as a "brake" to prevent bottoming. Obviously, the pressure in that volume of trapped oil can be quite high, and the rod seals are exposed to it. So you see the problem.

Dave at SMART is working on a solution to this at the moment, and it might be available before too long.

If you run 5wt, try either a 7wt or a 10wt from the same manufacturer. Since some mixing is unavoidable, you need to be certain that the oils are compatible. Most of them are.

The manual isn't really wrong, it's just difficult to understand what's being said because of the translation, and it's a little over simplified.

Here's what I do, based on info from SMART:

http://www.thumpertalk.com/forum/showthread.php?p=8762814#post8762814

If you get in there, the part in the manual about having a particular gap at the rod lock nut may confuse you. Notice how it's assembled as you take it apart, and read this:

http://www.thumpertalk.com/forum/showthread.php?p=8002008#post8002008

Something that works well with the KYB fork is to use a heavier oil in the outer chamber. This increases the bottoming resistance once the fork hits the oil locks near the bottom, and allows you to run the oil level a little lower for a nicer overall feel. It will require you to change oil a little more often, though, because bottoming the fork will have a tendency to drive the heavier OC oil into the cartridges past the seal on the rods.

Good stuff. Good info.

what is the weight of KYB fork oil? Since you can't get different weights, I figure you can't mix this oil. Just asking for reference.

Nobody seems to have any really solid info regarding KYB S1, the recommended oil for the twin chamber YZ forks. Its weight is roughly 4wt, but it's awfully expensive, and not very durable.

My da*n issue is I drink to much beer...so my springs are always getting soft

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