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fork oil wt & qty

Old 06-07-2005, 09:30 PM
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Re: fork oil wt & qty

Yeah, you want to go to racetech's site and enter your info on their calculator. They use a height figure instead of volume. I bent a coat hanger wire to the length for me (155mm) and filled to that height. They specify a lighter weight oil but that's if you're using their gold valves.
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Old 06-08-2005, 06:45 PM
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When rebuilding forks, I always use 5wt oil - typically motul if I can source it.

As for setting the fork oil, you'll only need a single bottle as that does both forks with just a tiny bit left. To set the height, find a syringe and stick a piece of silcone tubing on the end of it. Trim to the desired height using the base of the syringe to the end of the tube. Then fill the fork, stick the syringe down the fork with the base of the syringe sitting on the end of the open fork tube and keep sucking the oil out until you're just pulling air. Bingo, fork oil height perfectly set.

For VTRs, I find that 110mm is the best setting or go to 120mm if you want a fraction more plush ride.

FWIW, I've written up a huge tutorial on how to do your own fork rebuilds (which I've also submitted to the KB here earlier today). The direct link is:

http://www.vlc.com.au/~justin/about/...valve_kit.html
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Old 06-08-2005, 07:46 PM
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Re: fork oil wt & qty

Whoa! Excellent page mithaldanator or whatever your name is! Consider it bookmarked for future reference. Too bad I didn't have it the first time I did goldvalves. It's waaaay better than racetech's instructions/video.

I hope this will encourage those on the fence due to labor costs to rethink it and do it themselves.
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Old 06-09-2005, 10:44 AM
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Gah, I just looked at the end of that tutorial page and it seems like it has reverted to an earlier version of the document. It's missing a few of the photos and the final bit about the pattern to do up the bolts on the forks. I'll try to get that fixed over the weekend.

One more thing to note - a given oil weight number varies between manufacturers. Some are lighter than others even though they're labelled "5W", "10W" etc. Motul is on the thicker end of the scale. Silkolene is the other brand I'll use if I can't find motul and is quite similar. The local brands like Barhdahl here in the PNW is like using water and effects the damping quite a bit. I've tended to steer clear of the local brands and just use those two above simply because I know their properties very well. (FWIW, I've modified probably 40-50 sets of forks over the years, so I'm relatively competent in that area if you have any specific detail questions).
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Old 06-09-2005, 11:47 AM
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Originally Posted by Mithrandir";p=&quot View Post

FWIW, I've written up a huge tutorial on how to do your own fork rebuilds (which I've also submitted to the KB here earlier today). The direct link is:

http://www.vlc.com.au/~justin/about/...valve_kit.html
HaHa that's too funny. I just did mine last weekend and that's one of the pages that I printed. I even looked to send you a thanks this a.m. Was lots of help. There were a few small differences, but overall it helped to get the job done.

People think doing forks is difficult, but really it's about as hard as changing the oil in my car.
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Old 06-10-2005, 06:25 AM
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Why would you "always" use 5w fork oil?
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Old 06-10-2005, 07:33 AM
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Re: fork oil wt & qty

I was told by Roger to use 5wt w/ GV and 10wt with stock. He also had me set the level to 145mm.
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Old 06-10-2005, 08:10 AM
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Dan, if all you are doing is replacing the springs, you don't even need to go that far - the forks can stay in the bike. Just make sure the front end is off the ground and pop the caps off and undo the damping rod from the bottom of it. Pull the spacer, washers and springs out the top. Then measure and cut the new spacers and drop them straight back in. You don't even need to change the fork oil if you don't want to - but you will need to top the oil up a little as you'll have removed a reasonable amount on the spring itself.

I always use 5wt for three reasons:

Firstly, it means I have a common base to work from when setting up shim stacks. Stacks are set up based on the oil weight, so given the same rider/bike combo, the stack will be different based on the oil. It's one less variable I have to play with when doing someone's forks.

Second reason is that the weight effects the damping characteristics (well, duh ). The heavier weight you go, the more the oil influences the characteristics and the less the valving and shimstack do. That makes it harder to control the precise responses. This issue, is very closely linked to the next reason....

Thirdly, the heavier the oil, the quicker it gets effected by riding. Heating the oil as you're riding around the characteristics dramatically. The heavier the oil, the more that changes. Conversely, the lighter the oil, the less that heat effects it. As heat effects the oil, it reduces the amount of damping. So, the idea is to go with as light a weight oil as possible so that this is not an issue (and it is, even in simple street riding).
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Old 06-10-2005, 09:33 AM
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None of that makes sense to me.
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Old 06-10-2005, 09:38 AM
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As in you don't understand the technical parts of what I was saying, or you don't agree with it?
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Old 06-10-2005, 11:19 AM
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As in, I can't fathom the technical logic of your choices.

The one thing I understand is that you are trying to limit your options. So you decide to limit yourself to a single fluidic velocity, in this case a light one.

However I can't understand how this would lead to a better ultimate outcome, just a quicker one with potentially fewer wrong turns. Experience might provide the same benefit though.

I also think your point about thinner fluids is incorrect. Denser materials absorb heat less quickly. Thicker fluid would tend to remain cooler, but cool to ambient more slowly. Thinner fluid, it seems, would have a higher velocity and pick up more frictional heat. In essence, it would be more stable. But maybe I don't understand what you mean?
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Old 06-10-2005, 01:46 PM
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More viscous fluids do take longer to absorb heat. The issue is that in a bike fork, they come up to heat very quickly due to low volume and heavy usage. Even something as small as 2 miles is enough to bring the fork oil up to a temp that is enough to effect damping characteristics. There's lots of heat from different friction sources - fork sliders, axle, movement of the oil in the fork etc. Forks have a small volume and large surface area exposed directly to the elements such as wind, water etc. As a result fork oil temps can change dramatically over short periods of time.

The heavier the oil, the more it's viscosity changes from baseline. That's the issue that is the reason for going to lighter weight oils. A lighter oil doesn't change viscosity nearly so much as a heavier one, which means less deviation from the base, and therefore the damping doesn't go all over the place. Even if the oil heats up and cools down far more rapidly in the oil, the damping is not going to change a noticable amount, compared to the heavier one.

If the goal of finding the "right" damping characteristics, then you want to make sure that it's consistent over all operating conditions. For this reason, you want to eliminate the oil from the damping characteristics as much as possible. A lighter oil is going to flow through the valves and shimstacks much easier than a heavier one. If the oil doesn't change properties much, then that means we only need to concentrate on the right valving. That's all I'm aiming for in the choice of oil weights.
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Old 06-10-2005, 07:45 PM
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You make a number of assumptions I could take issue with. And your recommendations are pretty unique. I suppose we should just agree to disagree.
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Old 06-11-2005, 10:37 AM
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Yes, anyone that does suspension work, either professional or amateur have their own quirks. Have a dig around the net for Dan Kyles opinions on stock honda valving, and what everyone else thinks of that

As far as my personal recommendations, they're far from unique. I don't make assumptions and do a lot of research, including modifying my own bikes first to test things out. I'm basically middle of the road for suspension setup recommendations. 5wt oil is de rigeur for professional shops, at least in Oz and the racing scene there, and I'm basing that on former GP suspension tuners like Frank Pons (ex Mladin days in the world GP times) down to the backyard racers I used to race against. So, yes, we disagree, but that's not unusual in the suspension world. All I know is that all the people I've modified their suspension for are more than happy with the results.
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Old 06-11-2005, 11:59 AM
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Sorry, I don't know, or have I ever heard of anyone (myself included) who recommends one-size-fits-all for fork oil and I wouldn't recommend it to folks here.

In the case of the RaceTech stuff (which works pretty well) their recommendations are always great starting points.

I don't doubt you, and I'm happy you've pleased your customers, but I don't agree with you either.
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Old 06-14-2005, 09:49 AM
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Sorry, it should be with the forks compressed. That's an error on my old version of the website. Just as a bit of back story, I've had my server eat 3 hard drives in the last 3 months and the backups have gotten rather screwy as a result. That webpage is one that is about a year old, and not the most recent one (I had a heap more pictures added). I spent a couple of hours over the weekend trying to find the most recent version of the page from the backups, but with no luck. Combined with selling my aprilia (disappeared last night), and servicing the forks in my XX, I didn't get a chance to update back to the correct info.

As for height, that's really dependent on the ride quality you want. The springs in/out will make a small difference to the oil height as the springs take up some of the volume too. So, 13cm without springs is probably about 11cm with them in. It would be close enough to no matter as most riders can't feel the difference that small amounts like that make. Oil height really only effects the damping characteristics right at the limits of fork travel. Unless you are really hard on the brakes all the time and/or you do track riding (basically the same thing ), then you should be right in the ballpark.

The front of the bike will definitely sit much higher if you've just fitted new springs. Remember the springs are what take the weight of the bike, so a stiffer spring will hold the same amount of weight with less compressing. To regain the old handling, I would first recommend spacers under the rear shock before dropping the forks. Lifting the rear will gain you more ground clearance during cornering. If you have already raised the rear, then by all means drop the forks through at the front. From memory, my old VTR was running 8mm of spacers on the shock and dropped 12mm through the clamps up front - fairly aggressive setup for street riding.
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Old 05-20-2006, 09:44 PM
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Mith,

Sounds like you know your **** regarding suspension. We should get along well. Just wondering if you do this as a hobby or are you starting a small business (or play money on the side). There's much more to learn. Start by checking out the Independent Bike Suspension Forum (IBSF) at http://www.activeboard.com/forum.spa...ForumID=105037 . My screen name there is gRReg.
Just buying valving kits and replacing with recommended shim stacks is easy. Expand deeper into the black art of suspension and you'll find that there are ways to get the HMAS valves to work quite well just by shimming. Albeit there are many tricks of this trade, and several ways to achieve the same result, with some very minute differences in suspension feel that most of us can't feel.

Good job on the webpage. I might recommend a few things such as maintaining ultimate cleanliness in the workbench area, as well as using plenty of brake fluid to clean the fork internals. Compressed air works well to dry parts.

If you ever have any questions, I'll do my best to answer them. Or if you want to shoot the **** over suspension you can email me, and I'm also on MSN Messenger.

Cheers,

GN

PS Which kit did you end up getting from Suspension Tech? Their BPC Street kit valves look a lot the newer HMAS 3-ports. Did they give you a mid-compression stack or just straight comp and reb?
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