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Living the Dream
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1,798 Posts
Discussion Starter · #1 ·
I am thinking of putting 10-15 Wt oil in my AM1 to help with brake dive and the fork unloading harshly when I wheelie or pick up the front end. Does the oil weight affect both rebound & compression rate? What are the pros & cons of using a heavier oil weight?
THanks
 

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Elitest thrill junkie
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38,852 Posts
Does heavier oil help with brake diving?

Yes, and so does turning the TST adjuster to the AM setting. The problem is that using heavier oil to reduce the brake dive will make the fork much harsher on impacts. Brake dive is impossible to get around on a telescopic fork, and a plusher fork will have less compression damping and more diving, while heavier compression damping (by heavier oil or adjuster) will be much harsher on impacts.

Does heavier oil affect rebound and compression rate?

No, if you are referring to the "rate" of progressiveness, it has no effect. It will "slow" the fork though, so if you run the rebound adjuster in the full "open" position, you may not get the fork to be as "fast" as you want it with heavier oil, because the oil will slow down the compression and rebound strokes. So depending on where you run the rebound adjuster, this may or may not be a good idea and you may or may not be able to get what you want out of it.

I'm no lightweight, but I almost never put heavier oil into forks. At higher speed, heavier oil tends to make the fork "spike" on compression more and pack up during rebound (fork can not rebound fast enough to react to the next bump). I actually go and put light weight in a lot of forks that I own. This makes them feel "bouncy" at slow speed, but makes them feel much better to me at high speed. My forks "dive" when I brake, but that's just inherent to the telescopic fork. The closest anyone has gotten to "removing" that from the equation is the fox interia valve, and the fact that it won't allow any upward comression forces. It works, but there are still quirks with the system. A plush/sensitive/good-feeling fork that does not dive on braking is something that I've yet to find.

Lastly, if your fork is "topping out", which is a harsh feeling of the fork extending when you lift the front wheel, then the fork is broken and not operating correctly. It needs to go to marzocchi to be fixed if that is a problem (seems to be indicated by your post).
 

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Living the Dream
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1,798 Posts
Discussion Starter · #3 ·
Thanks Jayem

You always give great info. I guess I'm goona send it in to Marzocchi--I can't get the ETA to stay down, and yes I have the right oil volume & have even tried adding a little more. I appreciate the info. I will stay with the 7.5 wt and deal with the brake dive. My Firefly SPV+ was awesome at not brake diving, however, I felt like I was developing arthritis after long downhills due the piss-poor sensitivity/small bump compliance & high speed dampening.
Do the different TST settings act like compression dampening? DS would be full open & AM would be midrange dampening?

Are you still doing the flying thing?
 

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Elitest thrill junkie
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38,852 Posts
Alpenglow said:
You always give great info. I guess I'm goona send it in to Marzocchi--I can't get the ETA to stay down, and yes I have the right oil volume & have even tried adding a little more. I appreciate the info. I will stay with the 7.5 wt and deal with the brake dive. My Firefly SPV+ was awesome at not brake diving, however, I felt like I was developing arthritis after long downhills due the piss-poor sensitivity/small bump compliance & high speed dampening.
Do the different TST settings act like compression dampening? DS would be full open & AM would be midrange dampening?

Are you still doing the flying thing?
The negative spring that keeps the fork from topping out is in the ETA cartridge, so if the ETA cartridge is not operating correctly, it adds more weight to the possiblity that the two are interconnected.

The different TST settings increase the compression damping in different amounts, and on the AM setting the fork basically has more low-speed compression damping (the kind that fights brake diving). There is a "blowoff" that allows the fork to react when it hits something really hard, this will also function on the higher settings of the TST, all the way to the lockout one. The problem is that this "blowoff" is set at a really high threshold, so you're going to feel quite a jolt before it actually gives way. On the AM setting, this is not really noticable, but on the higher settings the fork is almost unusable except for riding on the road. The blowoff will work, but not after it's given you quite a jolt.

AM is kind of the "midrange" setting, more low speed compression damping. DS is "fully open" and the setting that I used it in pretty much exclusively. I put 5wt oil in my AM1 and I liked that better for bump sensitivity and suspension performance, but if you did that it would be going in the opposite direction and give you even more brake dive.

The rate of the spring will also affect the brake dive, a linear fork will not dive as much as a progressive fork that is set to the same end-spring-resistance. This is another factor that is sometimes left out, although going to a higher spring rate will make the fork more harsh. Again, this is something that some people can live with, and some people can not. To make marzocchi forks linear, you have to take the oil heights down to the minumum level, and then adjust(switch) the coil spring or air pressure untill you don't bottom out. The fork will feel much harsher with the higher spring rate required to keep it from bottoming out, but it won't dive as much.

If someone ever does come up with a fork that doesn't dive but remains as plush as what I am used to, I may look at it a little closer. I have trouble with the geometry though, if the front of the bike remains at the same height in a turn, then the rear of the bike is going to sag even more through the turn, and the resulting head angle will be much slacker than I want. Both ends of the bike would have to remain level in the turn to keep the geometry the same, except that the BB height would be higher and the bike wouldn't be as stable. I don't think SPV is an end-all suspension damping system. It solves some problems, but introduces others like the front end not moving during corners and harsh suspension action. I've yet to see anything in the field in this respect that has my attention. At this point, I'm pretty anti-platform-anything.

Yeah, I still do the flying thing. I'm a flight instructor for ERAU. Fun stuff and a constant challenge.
 
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