Forks disassembled
05-13-2008, 07:07 PM
#31
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I forgot I even had that account! Don't know what it is. I think I tried to access it a long time ago and couldn't get in.
Give me your new email address and I'll forward it to that one.
Anyway, I was laying in bed last night, thinking about the compression damping thing. I think I figured out what I was missing.
I had to remember the basic role of the spring, which is to define the attitude of the chassis in steady-state. For a track setup, you want to use all off the travel at the highest load. Basically, the suspension is completely compressed under maximum braking load, where the rear wheel starts to lift.
Whether you are on the street or the track, the suspension should be set up to use the full range. If/when your skills start to exceed the bottoming capabilities of the forks then you either need to a) increase slow speed compression, or b) raise oil level (don't forget the air spring).
So the spring defines the suspension position, damping defines how it gets there. By going to a lighter oil, you get faster weight transfer under braking, and a side benefit of more suppleness over small stuff. But the shim stack defines how the suspension reacts over higher speed inputs, providing the level of feedback the rider feels. A stiffer stack gives a more taut feel from the front end.
Yes, the spring rate is selected such that with ~15mm assembled preload (fork cap compresses spring 15mm) then the middle of the preload range will give approx. 25-35mm of rider sag. The VTR forks have 140mm total travel. This gives ample range for the forks to compress and work as they should. You would effectively subtract about 20mm from that travel if you leave the oil locks stock.
The lighter oil, as I described before, allows HSC rates that are higher than with 10wt. It's not so much about weight transfer, since that is mostly a function of LSC. HSC - bumps, LSC - braking. Yes! The HSC is a function mostly from the shim stack. The LSC is mostly a function of the bleed size.
"Taught" can be defined different ways. A small bleed with a stiff stack will give both good anti-dive properties but will beat you up in the rough stuff. A large bleed and a stiff stack will allow more dive and be a little more compliant on bumps. A small bleed with a weak stack gives an effect that is very linear damping because there will be a very small "knee" in the damping curve. A large bleed with a weak stack is just plain mushy and will not control the bike the way it should.
Am I on the right track? I think I might be close to a passing grade for Suspension 101:Fundamentals. I hope I'm getting close to ready for Suspension 201:Tuning.
I'm going to buy some Mojito fixin's and go to Bob's house with a list of questions.
Give me your new email address and I'll forward it to that one.
Anyway, I was laying in bed last night, thinking about the compression damping thing. I think I figured out what I was missing.
I had to remember the basic role of the spring, which is to define the attitude of the chassis in steady-state. For a track setup, you want to use all off the travel at the highest load. Basically, the suspension is completely compressed under maximum braking load, where the rear wheel starts to lift.
Whether you are on the street or the track, the suspension should be set up to use the full range. If/when your skills start to exceed the bottoming capabilities of the forks then you either need to a) increase slow speed compression, or b) raise oil level (don't forget the air spring).
So the spring defines the suspension position, damping defines how it gets there. By going to a lighter oil, you get faster weight transfer under braking, and a side benefit of more suppleness over small stuff. But the shim stack defines how the suspension reacts over higher speed inputs, providing the level of feedback the rider feels. A stiffer stack gives a more taut feel from the front end.
Yes, the spring rate is selected such that with ~15mm assembled preload (fork cap compresses spring 15mm) then the middle of the preload range will give approx. 25-35mm of rider sag. The VTR forks have 140mm total travel. This gives ample range for the forks to compress and work as they should. You would effectively subtract about 20mm from that travel if you leave the oil locks stock.
The lighter oil, as I described before, allows HSC rates that are higher than with 10wt. It's not so much about weight transfer, since that is mostly a function of LSC. HSC - bumps, LSC - braking. Yes! The HSC is a function mostly from the shim stack. The LSC is mostly a function of the bleed size.
"Taught" can be defined different ways. A small bleed with a stiff stack will give both good anti-dive properties but will beat you up in the rough stuff. A large bleed and a stiff stack will allow more dive and be a little more compliant on bumps. A small bleed with a weak stack gives an effect that is very linear damping because there will be a very small "knee" in the damping curve. A large bleed with a weak stack is just plain mushy and will not control the bike the way it should.
Am I on the right track? I think I might be close to a passing grade for Suspension 101:Fundamentals. I hope I'm getting close to ready for Suspension 201:Tuning.
I'm going to buy some Mojito fixin's and go to Bob's house with a list of questions.
One more question:
The low-speed compression orifice has a 12mm shim. Is this just a check valve, to prevent backflow during rebound, or is it a compression flow control.
Since the stock VTR compression valve is not adjustable and has no bleed hole the smaller base shim allows leakage through the valve. It acts as a bleed.
My RC51 valves have adjustable needle-orifice for LSCD. I haven't looked for a LS check valve.
LS check valve? No such animal. The adjuster is the bleed. The check valve(s) prevent flow through the rebound valve on rebound and makes the bleed and shim stack meter the oil flow. Same with the compression (or base) valve.
The low-speed compression orifice has a 12mm shim. Is this just a check valve, to prevent backflow during rebound, or is it a compression flow control.
Since the stock VTR compression valve is not adjustable and has no bleed hole the smaller base shim allows leakage through the valve. It acts as a bleed.
My RC51 valves have adjustable needle-orifice for LSCD. I haven't looked for a LS check valve.
LS check valve? No such animal. The adjuster is the bleed. The check valve(s) prevent flow through the rebound valve on rebound and makes the bleed and shim stack meter the oil flow. Same with the compression (or base) valve.
05-14-2008, 08:12 AM
#32
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Join Date: Dec 2005
Location: South Lake Tahoe, CA, USA
Posts: 1,689
Thanks, Greg.
I knew some of this stuff. But I think I'm starting to piece it all together. At least it seems like my spectrum of understanding is filling in. I now understand the bleed shim.
I sent a PM with my email address.
Much appreciated. You gave me more information than I was hoping for. I look forward to putting it to use.
I knew some of this stuff. But I think I'm starting to piece it all together. At least it seems like my spectrum of understanding is filling in. I now understand the bleed shim.
I sent a PM with my email address.
Much appreciated. You gave me more information than I was hoping for. I look forward to putting it to use.
05-14-2008, 06:31 PM
#33
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It's not too far off from a carburetor. The carb uses an idle jet and mixture screws for low rpm, a needle for mid rpm, and main jet for high rpm.
Forks use a bleed (hole or adjuster) for low speed, and a shim stack for high speed.
You know where you will REALLY learn some good stuff is on this forum:
http://www.activeboard.com/forum.spa...ForumID=105037
It's not very active anymore but the archives are full of really super stuff.
Forks use a bleed (hole or adjuster) for low speed, and a shim stack for high speed.
You know where you will REALLY learn some good stuff is on this forum:
http://www.activeboard.com/forum.spa...ForumID=105037
It's not very active anymore but the archives are full of really super stuff.
05-15-2008, 09:07 AM
#34
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Join Date: Dec 2005
Location: South Lake Tahoe, CA, USA
Posts: 1,689
Just a few more thoughts:
I was talking about what the rider feels, in the way of front-end feedback through the bars. I know this is important for confidence and knowledge about what's going on with the front tire.
But the true function of the suspension, speaking in terms of traction limits, is to keep a nearly constant contact force between the tire and the ground.
So the goal in tuning the damping is to optimize the suspension travel and prevent unweighting the front end, whether on compression or rebound. Excessive compression damping will cause the entire vehicle to accelerate vertically, too little will allow the wheel to overtravel.
The dynamics are complex. I'm still getting my head around it all. I need to get out on the track again and try some things and notice their effects on oversteer/understeer, etc. And that's just talking about the front end!
I'll check that site.
Cheers!
I was talking about what the rider feels, in the way of front-end feedback through the bars. I know this is important for confidence and knowledge about what's going on with the front tire.
But the true function of the suspension, speaking in terms of traction limits, is to keep a nearly constant contact force between the tire and the ground.
So the goal in tuning the damping is to optimize the suspension travel and prevent unweighting the front end, whether on compression or rebound. Excessive compression damping will cause the entire vehicle to accelerate vertically, too little will allow the wheel to overtravel.
The dynamics are complex. I'm still getting my head around it all. I need to get out on the track again and try some things and notice their effects on oversteer/understeer, etc. And that's just talking about the front end!
I'll check that site.
Cheers!
05-15-2008, 11:06 AM
#35
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Join Date: Dec 2005
Location: South Lake Tahoe, CA, USA
Posts: 1,689
The first session of the first trackday with my RC51 forks, my front end was wallowing all over the place. It was unbelievable, the thing just waggled, the bars were turning back and forth - horrible. I couldn't even think about going fast.I thought something was seriously wrong (it was).
I had put Racetech springs in and had valving reworked at BVH. We had set the cold damping rates in the garage.
I hadn't noticed anything unusual on the street. But it was early season, April, I think, and I had only done a few commutes to-from work, to break in the new engine.
I took my bike over to my friend Dana, who is a pretty fast guy and asked him what was up. He added a few clicks of compression damping and a couple clicks of rebound damping. The difference was night and day. Suddenly I was riding rails. I never made more than a click here and a click there after that. Generally I would soften it up a bit for the street.
I had put Racetech springs in and had valving reworked at BVH. We had set the cold damping rates in the garage.
I hadn't noticed anything unusual on the street. But it was early season, April, I think, and I had only done a few commutes to-from work, to break in the new engine.
I took my bike over to my friend Dana, who is a pretty fast guy and asked him what was up. He added a few clicks of compression damping and a couple clicks of rebound damping. The difference was night and day. Suddenly I was riding rails. I never made more than a click here and a click there after that. Generally I would soften it up a bit for the street.
05-15-2008, 11:48 AM
#37
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Join Date: Dec 2005
Location: South Lake Tahoe, CA, USA
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Hey Rick.
I have notes somewhere. I don't recall off the top of my head.
First off, I'm a long way from being an authority, especially when it comes to tuning for better lap times.
Second, I had Honda-Showa 5 wt. oil and Racetech .95 kg/mm springs. I'm not sure how your forks are set up.
But I will say this, and maybe Greg will add some guidance:
My approach to the front end has been to notice the amount of feedack to the bars. Too much compression damping causes everything to be too harsh through the bars. I like to find that place, then back off from it, until I have good feedback, without harshness. Too little compression damping just feels mushy - no fun!
On the rebound side, if the bike is overtraveling on rebound you have way too little. If it starts feeling like a rocking horse, it may be pumping down from too much. Back off on the rebound.
These are all low-speed, needle-orifice adjustments, and based on feedback, not traction limits. Start with your recommended settings, then try going too far in each direction, one adjuster at a time and get to know the suspension, then find what feels best. I did a little of this, and ended up pretty much at the same place each time.
I hope this helps.
I have notes somewhere. I don't recall off the top of my head.
First off, I'm a long way from being an authority, especially when it comes to tuning for better lap times.
Second, I had Honda-Showa 5 wt. oil and Racetech .95 kg/mm springs. I'm not sure how your forks are set up.
But I will say this, and maybe Greg will add some guidance:
My approach to the front end has been to notice the amount of feedack to the bars. Too much compression damping causes everything to be too harsh through the bars. I like to find that place, then back off from it, until I have good feedback, without harshness. Too little compression damping just feels mushy - no fun!
On the rebound side, if the bike is overtraveling on rebound you have way too little. If it starts feeling like a rocking horse, it may be pumping down from too much. Back off on the rebound.
These are all low-speed, needle-orifice adjustments, and based on feedback, not traction limits. Start with your recommended settings, then try going too far in each direction, one adjuster at a time and get to know the suspension, then find what feels best. I did a little of this, and ended up pretty much at the same place each time.
I hope this helps.
05-15-2008, 11:54 AM
#38
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Join Date: Jul 2007
Location: Lithia, FL
Posts: 2,091
Thanks RCVRT that's great advise! I hope to have my swap done by next week and will post up pics and impressions
Rick C.
Rick C.
Hey Rick.
I have notes somewhere. I don't recall off the top of my head.
First off, I'm a long way from being an authority, especially when it comes to tuning for better lap times.
Second, I had Honda-Showa 5 wt. oil and Racetech .95 kg/mm springs. I'm not sure how your forks are set up.
But I will say this, and maybe Greg will add some guidance:
My approach to the front end has been to notice the amount of feedack to the bars. Too much compression damping causes everything to be too harsh through the bars. I like to find that place, then back off from it, until I have good feedback, without harshness. Too little compression damping just feels mushy - no fun!
On the rebound side, if the bike is overtraveling on rebound you have way too little. If it starts feeling like a rocking horse, it may be pumping down from too much. Back off on the rebound.
These are all low-speed, needle-orifice adjustments, and based on feedback, not traction limits. Start with your recommended settings, then try going too far in each direction, one adjuster at a time and get to know the suspension, then find what feels best. I did a little of this, and ended up pretty much at the same place each time.
I hope this helps.
I have notes somewhere. I don't recall off the top of my head.
First off, I'm a long way from being an authority, especially when it comes to tuning for better lap times.
Second, I had Honda-Showa 5 wt. oil and Racetech .95 kg/mm springs. I'm not sure how your forks are set up.
But I will say this, and maybe Greg will add some guidance:
My approach to the front end has been to notice the amount of feedack to the bars. Too much compression damping causes everything to be too harsh through the bars. I like to find that place, then back off from it, until I have good feedback, without harshness. Too little compression damping just feels mushy - no fun!
On the rebound side, if the bike is overtraveling on rebound you have way too little. If it starts feeling like a rocking horse, it may be pumping down from too much. Back off on the rebound.
These are all low-speed, needle-orifice adjustments, and based on feedback, not traction limits. Start with your recommended settings, then try going too far in each direction, one adjuster at a time and get to know the suspension, then find what feels best. I did a little of this, and ended up pretty much at the same place each time.
I hope this helps.
05-15-2008, 06:27 PM
#39
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Join Date: Dec 2004
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Suspension settings are an individual thing. You can start with a recommended setting but what works best for you is likely something else.
With stock suspension it's difficult to "go to far" on an adjuster. The manufacturer makes it this way for liability reasons. Reworked forks is a different story though...
With stock suspension it's difficult to "go to far" on an adjuster. The manufacturer makes it this way for liability reasons. Reworked forks is a different story though...
05-15-2008, 06:39 PM
#40
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Join Date: Jul 2007
Location: Lithia, FL
Posts: 2,091
Suspension settings are an individual thing. You can start with a recommended setting but what works best for you is likely something else.
With stock suspension it's difficult to "go to far" on an adjuster. The manufacturer makes it this way for liability reasons. Reworked forks is a different story though...
With stock suspension it's difficult to "go to far" on an adjuster. The manufacturer makes it this way for liability reasons. Reworked forks is a different story though...
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