I'm not sure what you are saying here....do they drill out the high speed or low speed orifices? In the FJR's case there is nothing to drill out in the high speed circuit, they replace a spring loaded one way valve with a shim stack that has variable (and higher) oil flow. There isn't any technical reason to use a heavier viscosity oil after drilling out an orifice since that partially cancels what you are trying to achieve.....except to lower the cost of the oil. For some reason the manufactures offer the heavier weight oil (at a big discount) in 55 galleon drums and the suspension shops go through a lot of oil.Once you modify anything to change the damping in the stock forks, everything changes. Most suspension shops recognize that the stock forks have high speed orifices that are too small, giving excessive high speed damping when the low speed is properly dialed in. So... the drill them out. A lot. And then they use a heavier viscosity oil in their setup.
I think you would be guessing wrong. Oil height is a backdoor way of achieving the correct air space inside the fork after the springs and spacers are added. Heavier springs usually occupy more space than the springs they replace and some manufactures also include spring guides and different spacers....anything new that occupies space inside the fork is going to lower the recommended oil volume, the oil viscosity has nothing to do with the oil volume requirements.And I would guess the fork oil weight has very much to do with volume recommended for the components. I know I am at way less then stock oil height in the shock. So much I called to be sure. So less oil, heavier weight in my case. It would depend on the fork manufacturers parameters for weight and oil height to work with their set up.
I would guess others would argue with you. My springs in no way shape or forum took up more space then the factory springs. Oil weight and volume make a huge differance even on original fork springs. Sorry not buying it but I will not argue with you I would say you need to talk to some companies like Hyper Pro, Traxxion, and Race Tech to see why they recomend less head space and in my case heavier oil. As you can see the Omni on top is smaller then factory.I think you would be guessing wrong. Oil height is a backdoor way of achieving the correct air space inside the fork after the springs and spacers are added. Heavier springs usually occupy more space than the springs they replace and some manufactures also include spring guides and different spacers....anything new that occupies space inside the fork is going to lower the recommended oil volume, the oil viscosity has nothing to do with the oil volume requirements.And I would guess the fork oil weight has very much to do with volume recommended for the components. I know I am at way less then stock oil height in the shock. So much I called to be sure. So less oil, heavier weight in my case. It would depend on the fork manufacturers parameters for weight and oil height to work with their set up.
I'm not seeing any spacer with your OEM spring....probably because it is very narrow and barely fits over the damper rod taking almost no space at all inside the fork....in contrast your aftermarket system has both a thick plastic spacer and a spring guide. The air space is used to to give a progressive resistance at the end of the stroke to prevent bottoming and is very sensitive to volume changes. Too little air can result in excessive air compression and can blow out fork seals. Suspension companies recommend heavier oil because that is what they are able to buy in bulk sizes and use to develop their damping pistons and curves...the calculation of the correct air space is totally independent of oil viscosity because it doesn't matter what the oil weight is, it is not going to compress inside the fork and offer a progressive resistance. Its either going to move out of the way or create a hydraulic lock.I would guess others would argue with you. My springs in no way shape or forum took up more space then the factory springs. Oil weight and volume make a huge differance even on original fork springs. Sorry not buying it but I will not argue with you I would say you need to talk to some companies like Hyper Pro, Traxxion, and Race Tech to see why they recomend less head space and in my case heavier oil. As you can see the Omni on top is smaller then factory.I think you would be guessing wrong. Oil height is a backdoor way of achieving the correct air space inside the fork after the springs and spacers are added. Heavier springs usually occupy more space than the springs they replace and some manufactures also include spring guides and different spacers....anything new that occupies space inside the fork is going to lower the recommended oil volume, the oil viscosity has nothing to do with the oil volume requirements.And I would guess the fork oil weight has very much to do with volume recommended for the components. I know I am at way less then stock oil height in the shock. So much I called to be sure. So less oil, heavier weight in my case. It would depend on the fork manufacturers parameters for weight and oil height to work with their set up.
Fred, you don't have to answer my question unless you want to clarify your comments....I just thought it wasn't clear what you were actually conveying.It isn't about the spacer or the spring displacing more oil. It's about how much headspace you want over the oil. That space (air) over the oil surface acts like a logarithmically progressive air spring that boosts the physical coil spring in the suspension. If you put a stiffer spring in, and want a less progressive action, you would drop the oil level in the fork. That's all it amounts to.
PS - MCRIDER007 I haven't blown you off in regard to your question about what I meant with aftermarket fork damping mods and oil viscosities. I just haven't had the time to properly reply yet over the busy weekend. I will try to do that early this week. (this answer was a quicker one)
Fred, you don't have to answer my question unless you want to clarify your comments....I just thought it wasn't clear what you were actually conveying.It isn't about the spacer or the spring displacing more oil. It's about how much headspace you want over the oil. That space (air) over the oil surface acts like a logarithmically progressive air spring that boosts the physical coil spring in the suspension. If you put a stiffer spring in, and want a less progressive action, you would drop the oil level in the fork. That's all it amounts to.
PS - MCRIDER007 I haven't blown you off in regard to your question about what I meant with aftermarket fork damping mods and oil viscosities. I just haven't had the time to properly reply yet over the busy weekend. I will try to do that early this week. (this answer was a quicker one)
I agree its about how much headspace you want over the oil, but that headspace is going to be impacted both by the oil level and the suspension parts (such as a thicker spring/spacer or a spring quide) that are sharing the space above the oil level. You bring up a good point about using a stiffer spring, an air spring can add about 25 percent resistance to the spring's resistance.....if the new spring is 25 percent stiffer than the old spring than the air spring probably is not desired at its previous level and one could lower the oil level to reduce the air springs effect and save a little money on oil at the same time.
I agree with this aspect but not size of spring and blah blah. The spacer takes no room and the oil fill was with or without the spring buffer. You can make your stock springs respond differently with the head space and oil weight. Also I was not shipped a 55 gallon barrel of oil as my list above provesFred, you don't have to answer my question unless you want to clarify your comments....I just thought it wasn't clear what you were actually conveying.It isn't about the spacer or the spring displacing more oil. It's about how much headspace you want over the oil. That space (air) over the oil surface acts like a logarithmically progressive air spring that boosts the physical coil spring in the suspension. If you put a stiffer spring in, and want a less progressive action, you would drop the oil level in the fork. That's all it amounts to.
PS - MCRIDER007 I haven't blown you off in regard to your question about what I meant with aftermarket fork damping mods and oil viscosities. I just haven't had the time to properly reply yet over the busy weekend. I will try to do that early this week. (this answer was a quicker one)
I agree its about how much headspace you want over the oil, but that headspace is going to be impacted both by the oil level and the suspension parts (such as a thicker spring/spacer or a spring quide) that are sharing the space above the oil level. You bring up a good point about using a stiffer spring, an air spring can add about 25 percent resistance to the spring's resistance.....if the new spring is 25 percent stiffer than the old spring than the air spring probably is not desired at its previous level and one could lower the oil level to reduce the air springs effect and save a little money on oil at the same time.
No, the buffer doesn't displace any oil. What it does is take up some of the volume in the air space above the oil (buffers are not compressible).I agree with this aspect but not size of spring and blah blah. The spacer takes no room and the oil fill was with or without the spring buffer.
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