Ok, I have done several searches and keep coming up with different numbers. Also, some of the links that were in the old threads are gone. So, I need to know how much fork oil to put in each tube. I am just using the stock springs. I found the 380ml's amount but that seems like a lot.

Is 380ml for each side correct?

Also, I want just a little stiffer than stock feel on the front. A friends dad, who is a very reputable bike mechanic/builder, suggested using 10w-30 motor oil, as he says it give just a little better performance feel than regular 5w or 10w fork oil.

So what would be a good weight of oil for me to run?

I am not track racing or anything, but want a sportier feel than stock.

Any help is appreciated. Thanks!

David

service manual says 382 ml.  Yes, that's for each side, or per fork.   You can also get the old oil out somehow and add fluid until it is 3.9 inches from the top of the fork.  It's important that the fork is compressed all the way when you measure.  That way you don't have to worry that you didn't get all the oil out and overfilled it.  

Never heard of using car oil.    Stock oil is 10wt.  

Alot of people (including me) use 15wt and it slows down the compression and rebound a noticable amount.  (less bottoming, less like a pogo stick)

Depending on the year, though, your springs might be way too soft and the weight of the oil won't matter at all.  My stock 1990 springs were .45kg/mm.  I needed .85kg/mm.   I could bottom out the stock springs in my driveway!

I just did a heavier weight fork oil swap because i could bottom them out simply by bouncing on them in the driveway. i emptied as much of the old fluid as i could using some tubing and a vacuum pump. then i put in about 375ml of  20 weight fork oil in each one, sealed them back up and blam. No bottoming out, way stiffer, and so much better in every way. I only weigh 160lbs so you might want a little stiffer, but i'm really happy with the way it rides now.

Great guys! I really appreciate it.

My bike is a 92, and I can't really afford to buy different springs right now, so I will up the oil to maybe a 15w and see where that gets me.

Glad I found this thread!  I just bought new seals & covers! I'm going to do the spacer mod off the mod page & change the oil to 15w & see how that works
Thanks again

Quote from: bandit79 on June 06, 2009, 11:19:16 AM
Great guys! I really appreciate it.

My bike is a 92, and I can't really afford to buy different springs right now, so I will up the oil to maybe a 15w and see where that gets me.

$80 from sonic springs.

The manual does *not* say 382ml per fork. The manual says to start with 382ml, and use a fork oil level tool to set the oil level to 99mm (with no spring, and the fork fully compressed.) If you simply pour in 382ml of oil, the level will not be correct, and given that the GS runs a very high oil level to begin with, you're very likely to end up blowing out a fork seal.

Keep in mind that the 99ml level is for the stock spring. If you have an aftermarket spring, that oil level may cause you to enter hydraulic lock, which will blow out a fork seal or two. If you have aftermarket springs, 120mm would be a better starting point.

I believe 15 weight oil is stock. I run 20 weight, but that's with emulators, for race use.

I'm running racetech springs with the oil at 100mm. Seals still holding up fine *crosses fingers*. FWIW these springs are similar in size to the originals with slightly thicker coils. You could get all fancy and measure the volume of both the original and replacement springs. Subtract the difference in volume from the amount of oil you pour in. Not too many people keep graduated cylinders and stuff like that in their garages though

Thanks Deros514. Have you measured your suspension travel? If so, how much are you using?

I have racetech springs and emulators, and just raised my fork oil level from 120mm to 100mm because I was bottoming out.

I had progressive springs put in last year and I was still bottoming out on gutters.  I am having the seals replaced and changing to 20w oil. I will get her back tomorrow and let you know how she rides. Its a 94.

Haven't measured. I don't feel like I've ever bottomed out since the change but I'll grab some zip ties and some measuring tape next time I go riding.

Mine did bottom out, but I didn't feel it happen.

Just got mine back. Progressive springs and 20w oil. It rides freaking awesome. I had already had the progressives, the 20w oild must be what is making the difference. I have only gone about 6 miles so far but I'm lovin it.

The oil makes a huge difference, especially if the old stuff had been in there for a while. Fork oil brakes down and thins out over time.

My 94 was bottoming pretty easily so when one of the seals began to leak I took the forks in for new seals and 15w oil.  Stock oil is 10w for my year at least.  It's better but I still need more.  Shouldn't have left the stock springs in.  They're too soft.  I weigh 195 lbs.  It seems to me that progressive springs (or stiffer single-rate) with 15 or 20w oil is the answer for this bike depending on how much you weigh.

Well I guess I am bottoming out. After several hard stops I came with a consistent dive of 3.25 inches. I can't imagine going any stiffer unless I got some emulators too. IMO at that point, I'd be trying too hard to make the bike something its not. While its still bottoming, its still a vast improvement above stock and I am content with its performance.

I went racing this weekend with 100mm oil level and Racetech springs and emulators. I didn't blow a seal, so I guess that oil level works okay.

I talked to my suspension guy. He said that 30 weight oil would have been better for this hot weekend, but that I should stick with 20 weight since things will be cooler at the next two races.

Deros514: Your springs might be a little soft. I run .85 at the track, which are on the soft side of things, and I weigh ~175lbs.

I used racetech's calculator for street. It recommended like a .857 so I went with the .85kg springs. I'd say its a fair balance of comfort and performance. Not looking at hitting the twisties with a racetrack pace anyway.

15 weight did wonders! Might even try 20 wt. I weigh 180 lbs. Tried to put some 1/2 spacers in but couldn't get the caps back on myself. so no go. I wonder what that would have been like

In any case go 15- 20wt. for sure.

Stock, the GS runs 25mm of preload - which is already a lot. Not sure I'd want to add much more than that.

I find that the easiest way to get the caps on is with the fork tubes out of the triples. Push down on the cap, and spin the fork tube.

Also, I think 15 weight oil is stock. The improvement probably came from replacing your used oil with fresh stuff.