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a tight kick sound
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Discussion Starter · #1 ·
Hey all, thought I would post here too. Maybe will get more info here.
I will admit right up front that I do not know that much about the technical aspects of my suspension and it's design characteristics. So, I hope this post will help me out a little.

Here is my question:
What does a leverage ratio tell me about my suspension and what does it tell me about how my bike will ride over varying terrain?

Currently I ride a nicolai helius FR (horst link).
It has travel from 6, 5.5, 5, and 4.5 The shock is 7.875 X 2.25 for these travel measurements(06 dhx air).
Thus I think the leverage ratio is as follows :
6/2.25= 2.67:1
5.5/2.25= 2.4:1
5/2.25= 2.2: 1
4.5/2.25= 1.78:1

So what does this tell me?

The reason for all of this:
I would like to move the shock mount forward to decrease the BB height a little as well as slacken the HA a little bit. However, I cannot do this with the same shock. I need one with the same eye-eye but shorter stroke so the wheel does not hit the seat tube!

Therefore, I will use a 7.875 X 2 shock (04 fox vanilla rc coil).
The leverage ratio is as follows for this set up (I think with this shorter stroke I will lose
0.5-1" of travel:
5/2= 2.5:1
4.5/2= 2.25:1
4/2= 2:1
3.5/2= 1.75:1

Hopefully this will keep the tire from hitting the seat tube and allow me to get the new geo that I want! However, I am not sure what this will do to the ride quality.

What I really want to know is, does the shock make more of a difference in ride quality than leverage ratio or is it a combination of both? I presume it would be both, but in that case how do you go about setting up the best combination?

Any thoughts on this subject would be a warm welcome

Thanks
Jason
 

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noMAD man
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That 2" stroke shock will probably achieve what your looking for, but you can't be sure unless you do some measurements on your bike to insure that the wheel won't hit the frame. Now this is easy on a simple single pivot because there is only one pivot with no axle related pivots like yours, so I'm not sure how your bike will react if you just mimic that 7.875 X 2.0 shock in the shock mount holes that you want to use. Right off the top of my head, I'd say if the tire is hitting the seatpost only minimally with the 2.25" shock, then knocking off that .25" will give you the clearance you need. Since you're not changing the shock length...usually a more critical change...giving up a .25" should not present other problems.

As to what's the biggest impact on ride performance, there are so many variables that it's an almost impossible question to answer. They are intertwined to a degree that it's hard to distinguish. There's a general rule that suggests that a lower leverage ratio produces a better ride overall and is easier to tune, but with the advent of higher tech suspension components...maybe not as big a factor.
 

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boone said:
What I really want to know is, does the shock make more of a difference in ride quality than leverage ratio or is it a combination of both? I presume it would be both, but in that case how do you go about setting up the best combination?

Any thoughts on this subject would be a warm welcome

Thanks
Jason
I probably know as little as you do (or less) on this subject, but since I have a full suspension frame now I'll respond anyway :p . Couple of things...
  • The shocks gotta fit on the bike (iow, not hit the ST or whatever). Why does the shock you have on there not fit?
  • The leverage ratio I believe is the average leverage ratio, meaning that the ratio changes somewhat throughout the suspensions cycle
  • I would guess the frame (or maybe shock) manufacturer should be able to recommend the ideal shock length for the bike (and the travel setting) and spring rate for your bodyweight.
  • Suspension characteristics come in many flavors, with falling and rising rates, and sometimes with different charecteristics at different points in the suspensions travel.
  • Sometimes frame manufacturers get "custom-tuned" shocks that are suited well to their frames suspension.
  • If the suspension design is good (iow, doesn't rely on shock technology to make it perform well) then probably almost any quality, adjustable shock will work OK.

I realize that I didn't really answer any questions. And I don't know what I'm talking about anyway, so hopefully someone who has a clue will correct the stupid things I said. :D

Patrick
 

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a tight kick sound
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Discussion Starter · #4 ·
Sorry, the shock I have now does work just fine in the one position!
More below with pics.

Thank TNC!
The frame has 3 slots, I am in the most aft position now.
There are actually two slots forward of where I am now.
The one all the way forward puts the tire into mad contact with the seat tube!
The one just aft of that puts the tire just up against the seat tube. So I think it should work.

As for the shock, I will be using an 04 fox vanilla rc in place of the dhx air for the shorter stroke. It is not pushed at all. I would like to see how the bike feels without adding any bells and bling :) That way I can get it set to what I think feels best, then discuss with push to ee if we can make the "feel" any better. I wont go into that one :)

So, with a shock that has minimal to no pro-pedal, an appripriate spring rate for my weight and appropriate leverage ratio (let us say 2.5:1) will this be an easier question to answer about ride performance?

booner
 

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a tight kick sound
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Discussion Starter · #5 ·
Here is a pic of what is going on.
Hope you can see it ok?

I have the dhx air 7.875 X 2.25 in position "A." Just like the shock on the bike pictured.
It works just fine this way, no contact with the seat tube! This gives me a 14.2" BB and about 68-68.5 HA with 6" travel.

What I would like to do is use position "B" with the same eye-eye but a shorter stroke shock so that when I move the whole system forward, the decrease in shock stroke will compensate for this forward motion and thus keep the tire from hitting!

Make sense?
Anyway, I am just experimenting with something I don't know very much about in hopes I learn a little before the shock gets here :)

B
 

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noMAD man
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2nd position

boone said:
Sorry, the shock I have now does work just fine in the one position!
More below with pics.

Thank TNC!
The frame has 3 slots, I am in the most aft position now.
There are actually two slots forward of where I am now.
The one all the way forward puts the tire into mad contact with the seat tube!
The one just aft of that puts the tire just up against the seat tube. So I think it should work.

As for the shock, I will be using an 04 fox vanilla rc in place of the dhx air for the shorter stroke. It is not pushed at all. I would like to see how the bike feels without adding any bells and bling :) That way I can get it set to what I think feels best, then discuss with push to ee if we can make the "feel" any better. I wont go into that one :)

So, with a shock that has minimal to no pro-pedal, an appripriate spring rate for my weight and appropriate leverage ratio (let us say 2.5:1) will this be an easier question to answer about ride performance?

booner
Yeah, the second position sounds like a guaranteed fit. I think you'll notice a significant performance decrease with the stock RC. PUSH does a heck of a job with the RC if you're intending to keep it. It would rival or exceed the performance of your DHX-Air IMO. It would be designed to your bike, your weight, and your riding preferences. If you can't afford to PUSH it, I'd say wait until you have the money for another more modern shock.
 

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Looking at the photo, seems like the shock will be parallel to the top tube at the end of the stroke. Hence shortening the stroke with different shock will give you same room on the moving from eye forward. So let's say distance between position A and B is 0.5", so you need to get shock with same eye2eye but 0.5" smaller stroke.

Or other way around, if you planning to use 2.0" stroke instead of 2.25" then you can move shock mount forward by 0.25"

Or ... you can just try to run bigger sag and old shock at the beginning to get feel of the new geometry.
 

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Couple of things;

* using a different stroke shock will change ride quality alone simply due to the different internal volume of the shock. This is absolute, not hypothetical info - it's physics.

* the leverage ratio's you are using are only an average. There may/not be a "spike" or "dip" in the curve along the way which may/not change things. When riding along in the shocks mid-stroke is where you'll feel this difference the most. Changing the fore/aft position of the shock's mount on the frame will change this even with the same shock.

* you're missing part of the picture - your picture - that you posted. There are 4 mounting positions for the shock's mount to the swingarm. These will have a greater affect on the LR then the mount to the frame. Check it on a linkage simulator and you'll see if for yourself. Dependant on the geometry, it can be small or big. This will also change how much clearance you have with shock travel. Have you looked into this option yet? Results?

As for your ultimate Q - i'm with TNC mostly. It'll at least be "easier" to tune with a lower LR.
 

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Hi - Jack.

PCinSC said:
I probably know as little as you do (or less) on this subject, but since I have a full suspension frame now I'll respond anyway :p . Couple of things...
  • The shocks gotta fit on the bike (iow, not hit the ST or whatever). Why does the shock you have on there not fit?
  • The leverage ratio I believe is the average leverage ratio, meaning that the ratio changes somewhat throughout the suspensions cycle
  • I would guess the frame (or maybe shock) manufacturer should be able to recommend the ideal shock length for the bike (and the travel setting) and spring rate for your bodyweight.
  • Suspension characteristics come in many flavors, with falling and rising rates, and sometimes with different charecteristics at different points in the suspensions travel.
  • Sometimes frame manufacturers get "custom-tuned" shocks that are suited well to their frames suspension.
  • If the suspension design is good (iow, doesn't rely on shock technology to make it perform well) then probably almost any quality, adjustable shock will work OK.

I realize that I didn't really answer any questions. And I don't know what I'm talking about anyway, so hopefully someone who has a clue will correct the stupid things I said. :D

Patrick
What frame did you get?????????????/
 

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boone said:
Hey all, thought I would post here too. Maybe will get more info here.
I will admit right up front that I do not know that much about the technical aspects of my suspension and it's design characteristics. So, I hope this post will help me out a little.

Here is my question:
What does a leverage ratio tell me about my suspension and what does it tell me about how my bike will ride over varying terrain?

Currently I ride a nicolai helius FR (horst link).
It has travel from 6, 5.5, 5, and 4.5 The shock is 7.875 X 2.25 for these travel measurements(06 dhx air).
Thus I think the leverage ratio is as follows :
6/2.25= 2.67:1
5.5/2.25= 2.4:1
5/2.25= 2.2: 1
4.5/2.25= 1.78:1

So what does this tell me?

The reason for all of this:
I would like to move the shock mount forward to decrease the BB height a little as well as slacken the HA a little bit. However, I cannot do this with the same shock. I need one with the same eye-eye but shorter stroke so the wheel does not hit the seat tube!

Therefore, I will use a 7.875 X 2 shock (04 fox vanilla rc coil).
The leverage ratio is as follows for this set up (I think with this shorter stroke I will lose
0.5-1" of travel:
5/2= 2.5:1
4.5/2= 2.25:1
4/2= 2:1
3.5/2= 1.75:1

Hopefully this will keep the tire from hitting the seat tube and allow me to get the new geo that I want! However, I am not sure what this will do to the ride quality.

What I really want to know is, does the shock make more of a difference in ride quality than leverage ratio or is it a combination of both? I presume it would be both, but in that case how do you go about setting up the best combination?

Any thoughts on this subject would be a warm welcome

Thanks
Jason
It's not going to work quite like you think. Your leverage ratio calculations are wrong for the reduced travel shock. Firstly, reducing the stroke of your shock does NOT change the leverage ratio at all, it just reduces the maximum travel available. Moving the whole shock forward on the frame mounts will have some effect on the leverage ratio (probably quite small) due to the change in angle of the pivot. You would be best consulting Nicolai about this effect. You will most likely end up with a lower BB, reduced travel, but with a very similar leverage ratio. Which means you'll have to run a stiffer spring and therefore less sag to prevent bottoming the shock. This will then raise your effective BB again and you'll just be going round in circles! So I don't think it will work out. Personally, I would just increase the sag on your current setup (softer spring or less preload if you already have any) and increase the bottoming resistance on the shock to compensate.
 

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AndrewTO said:
Couple of things;

* using a different stroke shock will change ride quality alone simply due to the different internal volume of the shock. This is absolute, not hypothetical info - it's physics.
That relates more to air shocks, where the rising rate of the air spring varies with air chamber volume. There's no particular reason why a coil sprung shock should have different spring or damping characteristics just because the stroke changes.
 

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conjoinicorned
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sorry uktrailmonster, but i think you guys are mixing terminology. the leverage ratio he is talking about is defined as the travel / stroke length, so changing the stroke will certainly change the leverage ratio. however it isn't possible to really know how it will affect the amount and quality of travel, i agree with you on that one!

many people perform this mod on different bikes, whether or not it works i don't know. search the forums, i believe the azonic saber is commonly done to prevent the tire from hitting the seatpost.

to change a head angle/BB height, i would do other things like taller AC fork, 24" rear wheel etc. before i did this, but hey let us know how it goes.
 

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ferday said:
sorry uktrailmonster, but i think you guys are mixing terminology. the leverage ratio he is talking about is defined as the travel / stroke length, so changing the stroke will certainly change the leverage ratio. however it isn't possible to really know how it will affect the amount and quality of travel, i agree with you on that one!

many people perform this mod on different bikes, whether or not it works i don't know. search the forums, i believe the azonic saber is commonly done to prevent the tire from hitting the seatpost.

to change a head angle/BB height, i would do other things like taller AC fork, 24" rear wheel etc. before i did this, but hey let us know how it goes.
No, I'm not mixing terminology. I think he's made some incorrect assumptions about how reducing the shock travel is going to affect the resultant wheel travel. For example if he fitted a 2" stroke shock with the same eye-to-eye length as his 2.25" shock in the same mounting positions on the frame, the leverage ratio would NOT change from 6/2.25 to 6/2. It would remain at 6/2.25, but max travel would be reduced from 6" to 5.3" at the wheel. The ride would be identical until the shock bottomed out at 5.3"!! Now moving the whole shock forward is going to change the starting point for the pivot, which may have some effect on the leverage ratio (since the pivot will be operating on a different segment of its arc) but probably not much.

You are right in saying that many people perform mods like this to their bikes. How many of them do you think understand the maths?
 

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AndrewTO said:
* the leverage ratio's you are using are only an average. There may/not be a "spike" or "dip" in the curve along the way which may/not change things. When riding along in the shocks mid-stroke is where you'll feel this difference the most. Changing the fore/aft position of the shock's mount on the frame will change this even with the same shock.
With a typical four (or faux)-bar, the leverage ratio should be pretty linear, especially through the middle of the stroke. VPPs and other wacky designs can have some odd curves, but the well-designed ones should at least have smooth curves through the middle.

* you're missing part of the picture - your picture - that you posted. There are 4 mounting positions for the shock's mount to the swingarm. These will have a greater affect on the LR then the mount to the frame. Check it on a linkage simulator and you'll see if for yourself. Dependant on the geometry, it can be small or big. This will also change how much clearance you have with shock travel. Have you looked into this option yet? Results?
I don't think the OP missed it. Those are the four travel positions he referred to (and he calculated the leverage ratios).

One thing I imagine a lot of people miss is that you need a different spring rate to match the different leverage ratios (at least at the extreme postions). Air shocks are good if you want to change travel without swapping springs (OP has a DHX Air). I wonder if the stroke of the DHX Air could be reduced by having another bumper added inside the shock body? Might be worth considering.
 

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I'll put it another way, if we assume the leverage ratio is linear (i.e the same over the entire stroke) the calculation should be more like:-

Before (2.25" stroke shock)
6 / 2.25 = 2.67
5.5 / 2.25 = 2.44
5 / 2.25 = 2.22
4.5 / 2.25 = 2 (don't know how he got 1.78??)

After (2" stroke shock)
5.3 / 2 = 2.67
4.9 / 2 = 2.44
4.4 / 2 = 2.22
4 / 2 = 2

i.e. same leverage, just less travel
 

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a tight kick sound
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Discussion Starter · #17 ·
OK,
I'll agree with UKTM, that I was guessing how much travel would be lost by switching to 2.0stroke. I assumed it would be around 5-5.5" of travel final.

The 1.78 was a mistake! I did 4/2.25 in stead of 4.5. My bad.

Also will agree that mods are made without thinking about them or knowing enough.
I have contacted Nicolai and they said "move in as far as you want, just make sure that the tire does not hit the seat tube." No comments were made about how the ride would feel so I thought I would take the opportunity to learn a little bit about what I am doing.

I do not think I will end up going around in circles though :)
There is enough of a change from moving the shock mounts forward to change the geo enough. Just increasing the sag in the most aft poition does not get me to the same point.
I will see though.



So what is this "bike calculator" thing people are refering to and how/where do I get it?

Thanks
 

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uktrailmonster said:
That relates more to air shocks, where the rising rate of the air spring varies with air chamber volume. There's no particular reason why a coil sprung shock should have different spring or damping characteristics just because the stroke changes.
You sure about that? I can see what you're saying with the spring rate - you'd more than likely use the same length spring between to shock's who's stroke's are so similar - but the damping would surely have to change somewhat, yes/no? Or is the amount we're talking about negligible? Agreed with a more pronounced effect with air shocks. Oh, how I know it.

slackdaddy said:
I don't think the OP missed it. Those are the four travel positions he referred to (and he calculated the leverage ratios).[?QUOTE]

You're right - I[/i] missed it. I was looking at the four positions thinking he was referring to the fore/aft shock-to-frame mounts. I was wondering why he was mentioning four when (I thought) there was three. Apologies!
 

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AndrewTO said:
You sure about that? I can see what you're saying with the spring rate - you'd more than likely use the same length spring between to shock's who's stroke's are so similar - but the damping would surely have to change somewhat, yes/no? Or is the amount we're talking about negligible? Agreed with a more pronounced effect with air shocks. Oh, how I know it.
From your previous post, you were referring to internal shock volume. Damping is not dependant on shock volume, damping forces are created from velocity of oil flowing through ports and past shims etc. When people talk about shock volume they are usually referring to air spring volume. Less volume = more rising spring rate. Damping is unaffected. As far as shock settings go, if you reduce travel you will need to increase spring rate to avoid bottoming. Damper settings may need to be increased very slightly to control the stiffer spring, but it's really the unsprung weight (i.e your weight) that has the biggest influence on required settings.
 

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boone said:
OK,
I'll agree with UKTM, that I was guessing how much travel would be lost by switching to 2.0stroke. I assumed it would be around 5-5.5" of travel final.

The 1.78 was a mistake! I did 4/2.25 in stead of 4.5. My bad.

Also will agree that mods are made without thinking about them or knowing enough.
I have contacted Nicolai and they said "move in as far as you want, just make sure that the tire does not hit the seat tube." No comments were made about how the ride would feel so I thought I would take the opportunity to learn a little bit about what I am doing.

I do not think I will end up going around in circles though :)
There is enough of a change from moving the shock mounts forward to change the geo enough. Just increasing the sag in the most aft poition does not get me to the same point.
I will see though.

So what is this "bike calculator" thing people are refering to and how/where do I get it?

Thanks
Yeah, I agree it will lower your static BB height. But you will lose wheel travel as a result, so you will have to run a stiffer spring, which will result in less sag in the new position. So it just depends if you can live with the stiffer sprung ride to get a lower BB?

Whatever you do, don't rely on your shock bottoming out to stop the tyre hitting the seat tube. When the shock bottoms out, the shock mounts are overloaded and you will surely break something (usually damages the shock pivots and shears the bolts off). Besides the damage, it will feel very harsh. You can get away with this once or twice on a ride, but if it happens regularly, you will damage the frame and shock.
 
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