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Discussion Starter · #1 · (Edited)
so yesterday i replaced my fork springs with Progressive brand springs, initially used 15w fork oil. rode around all day, and then this evening just for a comparison switched over to 10w fork oil.

the 15w performed amazingly in the corners and turns better than the 10w. the bike felt incredibly planted, firm and stable, no wobble from the front, no looseness, etc. very confidence inspiring, but riding on the highway was another story. tiny bumps were easily taken care of, but once the bumps got larger the ride became harsh, especially on washboard-type stuff or lumpy roads. got to be fairly unplesant after a while, but man, i loved the way the turns felt, and brake dive was totally non-existant.

the 10w fork oil offerred a more 'plush' ride, handled a better variety of bumps better, more cushy, more 'cloud-like'. this allowed a much more comfortable and enjoyable ride on the highway, but the down side is that even though the performance in the corners was better than the stock springs, it was definately not as planted and confident as the 15w. and if i braked really hard, i got just the smallest touch of dive in the front end, but eventhough the dive was noticable, it was smooth, and not a 'shock to the system' like what you experience with the stock springs.

currently i am torn on what i am going to go with. there is such a difference in the corners between the 15w and 10w, and i felt a lot more confident hitting corners with the 15w, but given that i live in southern california, you have to hop on the freeway to get anywhere, and the 15w was a bit harsh when crusing on the freeway.

i considered blending equal parts of 10w and 15w to make 12.5w, but i asked threee different people if this was possible, and all three said not to do it, stating that it wouldnt 'blend' the way you would think it would, and that you would basically have two differnt weight floating around in there, not one combined weight.

since the 10w is in there now i will stick with that for a while and see how it feels for a week or so, and if i just dont like it in the twisties i will go back to the 15w and just suck it up on the highway (for me it may almost be worth it to deal with the harshness on the highway since it really made that much of a difference in the corners to go with 15w).

if anyone is curious, i weigh 180lbs, used a 2.75" pvc spacer (the instructions recommended a 2.5 inch spacer, but then also recommended that once everything is installed that it is flush with the fork tube or slightly over, so the 2.75" spacer brought it pretty much flush with the fork tube, and set the oil leverl at 140mm from the top of the tube when it was fully compressed and empty before adding the spring and spacer.
 

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I played around with different fork oil weights and ended up with 15 w to achieve the stability I was after in corners. I am 95 kg
 

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and if i braked really hard, i got just the smallest touch of dive in the front end, but eventhough the dive was noticable, it was smooth, and not a 'shock to the system' like what you experience with the stock springs.
you want and need some dive. Slight and smooth is good.
and yes fork oil is weight mixable.Use the same brand.
 

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Discussion Starter · #5 ·
sweet, i think i am going to mix some fork oil for round 3! will either mix the 10w and 15w 50/50 or mix it 60/40 (60% 15w, 40% 10w).
 

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Factory is 10w. I started with 15w when I changed springs and switched to 10w because the ride was too harsh. Haven't really noticed any difference in handling but I only weigh 155lbs.
 

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Good info sbpark - I have been thinking about this. In fact suspension is somewhat of a current topic isn't it? Makes a refreshing change.

Anyway, having done static sag measurements my bike is not set up right yet, although it feels wonderful compared to stock. I think I am going to ride for a couple of weeks, but then I'm going to adjust the spring preloads for the sag, and almost certainly put 15W oil in the front.

Good stuff - posts like yours help me decide a course of action.
 

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Discussion Starter · #10 ·
heading off to the store now to get more fork oil, think i am going to do a 70/30 mixture between the 15w and 10w, the 70% being the 15w.
 

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Discussion Starter · #11 ·
screw it. i just put the 15w back in. didnt want to lose the stability in the turns!
 

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sbpark, I weigh about 30# more than you and totally agree, the 15W makes the curves spectacularly stable; but it also seems too harsh on uneven road surfaces so I'm thinking of doing a 50/50 mix. You don't find the ride too harsh on normal to rough roads?
 

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Will a Mighty Vac pump draw out all the oil in the fork legs? This sounds like an easier alternative to removing each leg and pouring the oil out. I'll be due for a fork oil change at the next service interval (24,000 miles).----James.
 

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By the time you're done messing with a pump and the clean up associated you can have both fork legs off, drained, refilled and back on. They really are the easiest forks to remove I have ever worked on.

That is not to say that using a vac pump or whatever are not valid methods - they certainly are - for me I just bite the bullet and pull the legs. I should think that mighty vac pump would work OK.

I use the opprtunity to clean and check everything while the legs are draining too.
 

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Discussion Starter · #15 ·
By the time you're done messing with a pump and the clean up associated you can have both fork legs off, drained, refilled and back on. They really are the easiest forks to remove I have ever worked on.

That is not to say that using a vac pump or whatever are not valid methods - they certainly are - for me I just bite the bullet and pull the legs. I should think that mighty vac pump would work OK.

I use the opprtunity to clean and check everything while the legs are draining too.
i agree with prop. its really is very easy to remove the fork legs. i am not the fastest person, and can do the job start to finish in about a hour, granted i've done it three times in the last week since i keep switching the oil!

and to respond to a previous post, yeah it is a bit harsh on rough or uneven roads, but for now i am willing to make the sacrifice, but would be interested in your feedback on the 50/50 mix. when i was considering the mixing i was thinking more along the lines of 60/40.
 
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