Progressive Front Springs and Oil Height ?

[ripper980]

Got done ripping the forks off  my 97 Tourer.
Good news, the previous owner had progressive springs installed at some point.

I bought this bike late last summer and always found the front end real firm with some hard jarring on the bumps.

I drained out the fork oil ( dirty ) and really have no idea what viscosity was in there, or how much oil came out of each fork.

For the rebuild..

I am tossing in new seals and bushings in both legs.
Going with Amsoil 10w Fork Oil on the rebuild.

Is there any difference in fork oil height that is recommended by progressive vs. the OEM specs ?
I do not have the install instructions for these springs..

Thxs. 

[hubcapsc]

Is there any difference in fork oil height that is recommended by progressive vs. the OEM specs ?
I do not have the install instructions for these springs..

I put progressives in my bike when I got it. There were no instructions about oil level that
came with mine that I remember. I used the amount specified in the manual. I didn't use
the "by volume" measurement, I used the "inches from the top, springs out" measurement.

I love my forks, I think of them as somewhat stiff and aggressive, definitely not soft
and mushy... Stanley Steamer put 15 weight in his to make them stiffer and more
aggressive, but he pushes it harder than me sometimes...

Some people put less than the manual specifies, I don't know how they
decide, it seems like a crap shoot to me, but they like it so it is right
for them...

-Mike

[big poppa pump]

I have progressive springs on both my bikes. I tore down the front forks on both the bikes for a complete rebuild and I went with the volume method. I like to ride both my bikes aggressively especially with the twisties and as such went with 15W oil. I did remove 1 Oz from both the sides, works just perfectly.

[ripper980]

thxs for the replies folks..

I don't ride aggressive enough anymore to warrant stiff front suspension that much, with 15w oil.

Going with the 10W Amsoil and stock oil height as per manual..
Won't be able to road test it til the snow clears outta here in a couple months though 
Guess I can bounce up and down on the bike once I get it back together .. 

thxs Dan

[Gryphon Rider]

Really, the OEM oil volumes and measurements are to get an effective spring rate as determined by Honda.  There are two considerations:
1.  Is there enough oil to lubricate the fork and ensure the damping mechanism is never sucking air, i.e., it is always submerged in oil throughout its travel.
2.  Because the remaining air above the oil level gets compressed as the fork is compressed, it is providing resistance to compression at a progressive rate, which is added to the coil spring's spring rate.  If you have a higher oil level than stock, there is less air to compress, thus it takes more force to compress the fork the same linear amount.  Honda specifies how much oil should be in there, which determines the volume of air, which has an effect on how effectively stiff the forks are, not considering damping.

What adds complexity to this is that by changing springs, you are changing the volume of the springs, i.e. how much oil they displace and thus how much air is filling the remaining space.  Neither the measure down method or the measured oil volume method compensates for this.  If there was a way to measure down with the springs in place, you could do this with the old springs and the new springs to ensure the level is the same, but I don't think this is possible.  The best you can do if the spring manufacturer doesn't give you corrected measurements, is either rely on the experience of others, or decide by experimentation how much oil to add to, or remove from, each fork.  I would suggest (and assume that you would be) changing each side by the same amount.

[ripper980]

Makes sense to me ..
I willl try the stock oil height and see how it works for me.
Can adjust if needed after a few rides..

Thxs for the info !

Dan

[Patrick]

As mentioned there was no mention of oil with the Progressives at the time [ about 15 years ago]. I used 10wgt and the amount Honda species for each side. [ each side is different]. I thought it rode too harsh so I took out 2 ounces out of each fork and its been like that ever since.

[Gryphon]

when I put Progressives in my last Valk, I went with 10 wt and the stock height on the oil.  It gave me improved handling without beeing overly harsh.  I think it felt a bit stiffer, but not enough to be an issue.  Your results may vary, but it worked for my 5'11" and 212# self.