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I rcently changed the #10 fork oil in my '12 Bird 1600. The old oil was sludgy and I was hoping for a less abrupt response on road ridges (bumps that protrude out of the road) with new oil. Since that didn't happen I was wondering whether a lighter oil - #5 - instead of the recommended #10 would help. I know this is a simple question and I realize forks are a complex device. If anyone has tried this and thinks it would help please share your thoughts.
Thanks.
 

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I rcently changed the #10 fork oil in my '12 Bird 1600. The old oil was sludgy and I was hoping for a less abrupt response on road ridges (bumps that protrude out of the road) with new oil. Since that didn't happen I was wondering whether a lighter oil - #5 - instead of the recommended #10 would help. I know this is a simple question and I realize forks are a complex device. If anyone has tried this and thinks it would help please share your thoughts.
Thanks.
I have been using #5 for years. I went to #5 when I changed my fork seals and I just noticed one leg starting to leak so I'm planning on going that way again. My rear shocks are on softest setting and I weigh about 170. Works good for me.
 

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At the same labeled oil "weight", viscosity is all over the place between brands; there are multiple viscosity parameters for fork oils so 10W from Motul isn't even close to 10W from JP1, for example. Look here: Fork Oil Weights . Yeah, I don't get it either. After my usual excessive research, I found the closest combination of viscosities to the Triumph spec (Showa AHSS8 10W) is Bel Ray "High Performance" 10W. Just a reference to start from and going purely by the numbers,

If you want to change your front-end behavior, start with the springs. A high-quality linear-weight spring with spacers cut to give you 30-35mm of rider sag is essential if you want to make predictable adjustments. Takes some patience and perseverence but you only have to do it once. I've been happy with Sonic Springs (TBird Springs). Looks like they've pulled their online spring rate calculator so contact them to determine the best spring rate for your weight; they only have two for the TBird. After you've got a properly set up front end and if you're still unhappy, then start playing with oil viscosities but don't count on the "weight" label to too much.
 

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Discussion Starter #6
At the same labeled oil "weight", viscosity is all over the place between brands; there are multiple viscosity parameters for fork oils so 10W from Motul isn't even close to 10W from JP1, for example. Look here: Fork Oil Weights . Yeah, I don't get it either. After my usual excessive research, I found the closest combination of viscosities to the Triumph spec (Showa AHSS8 10W) is Bel Ray "High Performance" 10W. Just a reference to start from and going purely by the numbers,

If you want to change your front-end behavior, start with the springs. A high-quality linear-weight spring with spacers cut to give you 30-35mm of rider sag is essential if you want to make predictable adjustments. Takes some patience and perseverence but you only have to do it once. I've been happy with Sonic Springs (TBird Springs). Looks like they've pulled their online spring rate calculator so contact them to determine the best spring rate for your weight; they only have two for the TBird. After you've got a properly set up front end and if you're still unhappy, then start playing with oil viscosities but don't count on the "weight" label to too much.
Hey Papasmurf, thanks for the excellent information.
I am looking to soften up the front end to reduce the “impact” nature of the stock springs when hitting a “break” in the road every 100 feet or so which is a characteristic of some of our roads here due to the “freeze/thaw” seasonal cycles here in Ontario.
Also, doesn’t the oil flow inside the fork also effect the “rate of compression” nature of the fork when an abrupt bump is hit? In other words doesn’t the oil flow also contribute to fork stiffness?
Were you looking to soften up the front with the new springs as I am?
 

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Discussion Starter #7
Just got off the Racetech.com suspension website which states stock spring rate is .83 kg/mm. Sonic offers 1.0 and 1.1 kg/mm which are both stiffer. So that does not appear to be what I am looking for.
 

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Discussion Starter #8
Has anyone installed "progresive rate" fork springs such as the Hagon brand?
 

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.....Also, doesn’t the oil flow inside the fork also effect the “rate of compression” nature of the fork when an abrupt bump is hit? I n other words doesn’t the oil flow also contribute to fork stiffness?
The oil flow contributes to the compression and rebound rate and to some extent, so does the amount of air in the tube. The air is compressible, the oil is not. If you want to soften the onset of bumps you can first try dropping the oil level a little.

Were you looking to soften up the front with the new springs as I am?
You must weigh nothing. Most bikes are delivered with overly soft springs up front; they give a much cushier test ride to potential buyers. They also give severe front end dive and pogoing which compromises control in more spirited riding and in emergency maneuvers. If you haven't experienced the front end diving on a hard stop, either you've never had to do one (but you should practice them, anyway) or you're not "of substantial mass" (OK, overweight) like a lot of us (OK, like me).

I've felt the need to stiffen the front end of every bike I've owned. It has always resulted in a much more controllable and predictable suspension. As said previously, I get a linear spring appropriate for my weight (including gear and additional non-stock weight added up front) and set rider sag by cutting spacers to yield around 30-35mm of sag (that's with my fat carcass and all the gear I usually ride with). If not totally happy after that, you can experiment with oil level and/or oil weight. Some people have gone to valve emulators, like Racetech Golld Valve Cartridge Emulators or Ricor Intiminators.

Start simple. You just put fresh oil in; try sucking out 10-15mm.
 

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Been using 15w in mine since soon after i got it in 2009. (preorder bike) My motivation was fork dive under braking was ridiculous. Handles better too. Stiffer springs may have been the better way to go, but in 11 years of ownership this july and 80,000 miles my seals have only leaked once and very little.
 

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Has anyone installed "progresive rate" fork springs such as the Hagon brand?
I’ve used Tec progressive fork springs on a T120 and it greatly reduced brake dive. Also put Progressive progressive fork springs on a 2012 TBird and 2007 RIII Classic. Progressive said to use the weight oil recommended by the manufacturer. I believe my dealer put in heavier oil (15?) on the TBird.
 

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Like PapaSmurfMC mentioned above Oil viscosities are all over the map along with the methodology used. SUS/ Sabolt Universal Seconds was one used buy the oil industry. Be willing to place a wager the 15W fork I used was closer to 12. To me it lessened the "Dive" and added "a smooth slightly firmer" feeling to the front end. Years ago I spent the $$ on progressive springs..requiring a slightly different spacer size. Fork oil age, temperature, springs etc. all contribute to performance along with synthetic vs non. I'm sure the Showa fork engineers would disagree with changing "recommended" oil weights. For me it was what I consider a slight improvement in a "heavy touring bike"
 

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Sounds like personal preference and viscosity are all over the map. Just like opinions on tires and belt tension. Too many decisions, and compromises, but, is their anything better than riding a bike dialed in to your personal preference??? I don't think so. Your results may vary.
I just rebuilt my forks to install new seals, #5 synthetic, and a new Continental Road Attack 3. Waiting on the rain to quit to try it out. Doesn't the light weight oil allow faster reaction time and provide better feel. An extreme example: If you hit something and your tire comes off the ground, it seems like it would react faster and the tire would come back into contact sooner. In normal conditions the tire would follow all the little ups and downs better, like a Corvette. Seems like a heavier oil would dampen the feel of the road, like a Cadillac. The only downer is a little more brake dive in severe examples.
What I learned in the last couple days. The Triumph manual says fill with 677cc and measure 106mm from top with fork collapsed. Measuring as best I could it looks like doing it either way gives the same result. One more way to do it that gives a third and easier option: With tube fully extended and spring and spring seat installed the oil level will just cover the spring seat with 677cc's. I noticed this on my first shock so I filled the second by eyeball without measuring and lo and behold 106mm's when it's collapsed without the spring. No measuring cups or rulers or Triumph tools and less mess. Makes it easier to experiment.
 

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Tool fabricated for measuring fork oil was out of a piece of coat hanger wire with heat shrink tubing measured to length with calipers.
Have a pic some where....have to remember where I put it. Just hangs from top of tube to whatever length required. Pour in oil just till it kisses the L shaped bend.
 

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Tool fabricated for measuring fork oil was out of a piece of coat hanger wire with heat shrink tubing measured to length with calipers.
Have a pic some where....have to remember where I put it. Just hangs from top of tube to whatever length required. Pour in oil just till it kisses the L shaped bend.
Great minds think alike. There's a picture here.
 

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Discussion Starter #16
Like PapaSmurfMC mentioned above Oil viscosities are all over the map along with the methodology used. SUS/ Sabolt Universal Seconds was one used buy the oil industry. Be willing to place a wager the 15W fork I used was closer to 12. To me it lessened the "Dive" and added "a smooth slightly firmer" feeling to the front end. Years ago I spent the $$ on progressive springs..requiring a slightly different spacer size. Fork oil age, temperature, springs etc. all contribute to performance along with synthetic vs non. I'm sure the Showa fork engineers would disagree with changing "recommended" oil weights. For me it was what I consider a slight improvement in a "heavy touring bike"
The variation in oil viscosity is an eye-opener for sure. And reading through Racetech's information on damping rod forks and emulators gave me a headache as well. I have concluded to play with the viscosity first and then (if necessary) go to springs, mostly thanks to Fast Eddy Sports, as mentioned below.
Thinking that progressive springs was the answer led me to Fast Eddy as it seems they are the only ones now selling progressive springs for the 'Bird. After almost pressing the "buy now" button on their webside they emailed me asking if there was anything they could assist with and I said I was looking for a way to soften the front end on a sharp bump. He came back with: "The springs will help, but I would first try changing the fork fluid to a lighter weight. This will give it more "mush" for less money". So based on the advice of someone who sells springs I will be replacing my fork oil first with some "genuine" 5Wt. oil (thanks to that chart, PapaSmurf).
The more I read Racetech's info on damper forks the more I believe the fork is a hydraulic "pump" on the compression stroke. I think the spring has very little to do with absorbing the amount of "shock" transferred to the bike upon hitting a bump (compared to the restriction to oil flow through the damper rod orifices) but in fact is used primarily for rebound behaviour (along with the porting controlling return oil flow in the damping rod)". Definitely more to it than first meets the eye. I am grateful for people a lot smarter than me.
Thanks to all who contributed a wealth of knowledge and experience.
Now off to find some oil.
 

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So...you're keeping stock springs and going with 5wt? I hope I understood that correctly...Please post an update on results. The more info the merrier! Still upset with Triumph terminating production on these bikes, but riding out there today just makes me want to keep it. With mask of course....
 

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I rcently changed the #10 fork oil in my '12 Bird 1600. The old oil was sludgy and I was hoping for a less abrupt response on road ridges (bumps that protrude out of the road) with new oil. Since that didn't happen I was wondering whether a lighter oil - #5 - instead of the recommended #10 would help. I know this is a simple question and I realize forks are a complex device. If anyone has tried this and thinks it would help please share your thoughts.
Thanks.
It will help a lot
 

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..... I think the spring has very little to do with absorbing the amount of "shock" transferred to the bike upon hitting a bump (compared to the restriction to oil flow through the damper rod orifices) but in fact is used primarily for rebound behaviour (along with the porting controlling return oil flow in the damping rod)". Definitely more to it than first meets the eye. ....
Not at all. The spring absorbs and releases the energy imparted by impacts on the wheel; it is literally an energy storage device. The oil helps regulate the rate the energy is absorbed (compression) and released (rebound). Ideally, you'd want to tune compression and rebound rates individually, and you can if you have enough money (Ohlins), but without the springs the energy imparted by the "shock" would be injected into the frame and everything in contact with it.
 

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Discussion Starter #20
[/QUOTE]
So...you're keeping stock springs and going with 5wt? I hope I understood that correctly...Please post an update on results. The more info the merrier! Still upset with Triumph terminating production on these bikes, but riding out there today just makes me want to keep it. With mask of course....
Today is supposed to be a rain day so fork oil replacement is on the agenda. I went with the Honda Pro 5W which has a [email protected] deg of 17, which is about half what I have now with the #10. I would have preferred the Torco or some other brand having a high VI but availability was the problem. I will report findings.
Wear the mask if you can't keep 6 feet away from your buddies. The problem is you don't know who has it. No side by side chatting at the stop light! I'm waiting for my FU COVID t-shirt!

Not at all. The spring absorbs and releases the energy imparted by impacts on the wheel; it is literally an energy storage device. The oil helps regulate the rate the energy is absorbed (compression) and released (rebound). Ideally, you'd want to tune compression and rebound rates individually, and you can if you have enough money (Ohlins), but without the springs the energy imparted by the "shock" would be injected into the frame and everything in contact with it.
I agree the spring stores energy and releases on rebound. I suspect though on a high speed bump - bump speed, not bike speed - from a sharp bump in the road - the rate of oil flow has more to do with transmitting shock to the bike than the springs' ability to absorb it. So a lighter oil that will flow faster should make the forks less prone to transmitting that shock to the bike. This is all kinda experimental but hopefully a positive result is the reward.
 
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