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Old 12-19-2012, 08:40 AM   #106
larryboy
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Just a thought, build the top mount with three mounting holes for the shock. Try like hell to get it right with the center hole, then there is some adjustment on either side.

This is why I like the CR500 stuff I used on my Bandit, I can change out the links on the lower linkage to adjust for design errors.
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Old 12-19-2012, 03:29 PM   #107
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Quote:
Originally Posted by larryboy View Post
Just a thought, build the top mount with three mounting holes for the shock. Try like hell to get it right with the center hole, then there is some adjustment on either side.

This is why I like the CR500 stuff I used on my Bandit, I can change out the links on the lower linkage to adjust for design errors.
Planning something very similar, but it will be scrap to get the holes located. Everytime you drop the bike down on it's weight it changes so I want to make a mockup and get the hole located. Then I will design a nice one and have it waterjet cut for me and weld it up.
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Old 12-20-2012, 02:36 PM   #108
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Screwed around in the shop all day today working on the bike. I can't say it was super productive but I did manage to get some numbers down on paper regarding the suspension.

I build a jig that uses the stock Ninja shock bolt and drilled a few holes to try and see if I could find a workable location. I was confined by a few dimensions that I think will ultimately not allow ideal sag/rake bottoming protection.

On one setting I got 60mm static sag, 114mm race sag, others varied but I never could seem to get close to the 115 race sag number that I read was a good one to shoot for. The KTM PDS shock is apparently supposed to have 35-40mm static sag.



My brain is hurting trying to think about this. I have a 12.5 spring which Slavens spec'd for me for the CBR project based on a weight similar to the KTM 690.

If I have too much static sag, this means the spring is too light correct?

Also of concern is trying to keep the swingarm angle reasonable so the chain doesn't saw through the guard every revolution. And the anti of this being to keep the wheel out of the bottom of the subframe at full compression.

I think with so many practical limitations (hitting subframe, swingarm angle) that I might have to compromise the ideal suspension settings. I will fully admit on the FZ1 I basically eyeballed the location after getting the rake set. And it works great.

Here's a shot of the bike at full compression with no spring. Tire has about an inch of clearance to the plastic tray in the subframe



My jig for trying to locate the top shock mount. The shock, if unbolted up top, will only rotate so far forward due to interference down at the swingarm. So that limits how far forward it can be.



I spent a lot of time today, trying new locations, spring on, spring off, up down, up, down, measure, change etc. I don't feel like I really made any progress other than to confuse myself even more. I have half a mind to just burn in the top mount using another KTM as a guide and living with it.

On the plus side, I mounted my new spacer which fits the swingarm and gets me almost perfect alignment with the chain.
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Old 12-20-2012, 06:29 PM   #109
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Well I'm an idiot. I was measuring race sag as the difference between bike on ground no rider and bike with rider. It's supposed to be difference between bike with wheel off the ground and bike with rider. Which would account for my weird numbers. If I crank 4-8 mm preload into the spring I should get much better numbers. Will redo the suspension calculations and report back tomorrow.

So really the numbers I was getting were 60ish mm static sag and 175-200 race sag. If I crank the preload and rejigger the numbers I should be able to get the race sag back to 115mm and static sag into the 35-40mm range hopefully. Should also make the swingarm angle much easier.

But if I have this wrong please let me know
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Old 12-20-2012, 06:58 PM   #110
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Quote:
Originally Posted by sailah View Post

If I have too much static sag, this means the spring is too light correct?
Probably not :) After you've adjusted the preload to get the loaded sag correct, then if there's too much static sag your spring is too hard.

It's a lot more intuitive if you set the preload for the correct static sag. Then measure the loaded sag. Too much loaded sag = too light a spring, too little sag = too hard a spring.

Of course to tune the bike with the spring you've got, set the loaded sag and live with whatever static sag you get.


I have a spreadsheet that you can plug the weights and geometry into and it will tell you the shock travel, progression, spring rate, and preload. If you'd like to mess with that I can send it to you.


Quote:
Originally Posted by sailah View Post

I have half a mind to just burn in the top mount using another KTM as a guide and living with it.
Always an option.



If you'd consider changing shocks I have a non-pds WP shocks from the LC4 kicking around that you're welcome to. The reservoir sticks out sideways rather than at 45*, and I think it's shorter for the same travel. 416mm eye-to-eye extended, 110 mm stroke. It just might fit better. I can measure more stuff on it if you might want it.
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Old 12-20-2012, 07:06 PM   #111
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Quote:
Originally Posted by sailah View Post
Well I'm an idiot. I was measuring race sag as the difference between bike on ground no rider and bike with rider. It's supposed to be difference between bike with wheel off the ground and bike with rider. Which would account for my weird numbers. If I crank 4-8 mm preload into the spring I should get much better numbers. Will redo the suspension calculations and report back tomorrow.

So really the numbers I was getting were 60ish mm static sag and 175-200 race sag. If I crank the preload and rejigger the numbers I should be able to get the race sag back to 115mm and static sag into the 35-40mm range hopefully. Should also make the swingarm angle much easier.

But if I have this wrong please let me know

That sounds better.

How much suspension travel do you want? The same as the KTM?
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Old 12-20-2012, 08:59 PM   #112
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As a manufacturer of Air spring shocks in the 1970's "Motorsport Air Shocks", I thought I understood my shocks at the time. I still use spare parts to build my own shocks today.
Charlie Curnutt started the rule of 25% sag. Meaning when you sit on the bike you have 25% sag. Charlie was the first American made shock manufacturer.

Works Performance Shocks started out modifying Curnutt Shocks. I started a little later and a year later there were a dozen people making aftermarket shocks. Then the bottom fell out because the manufacturers used progressive geometry and a linear shock to get progression instead of a progressive shock and simple geometry.

Back to the problem at hand.
Sag is controlled by a combination of two things -- Spring rate AND preload. For offroad use, I think you want as soft a spring as you can get away with (with some help from compression). In that case 25% sag is appropriate. If you chose a stiffer spring with less compression damping, 15-20 % sag is a better choice. The function of the sag is to let the wheel go down into the whoop.

I think the primary thing you should be looking at first is the progression of the geometry. I don't have any numbers as to how much progression to put in a shock. What do the current bikes have?
In my shocks, I used 7:1 compression ratio of the nitrogen in the shock. Each time the volume was cut in half, the pressure doubled. That provided extreme progression. It had a very soft rate going over small bumps and a lot of spring rate in the last inch to keep from bottoming. You used a lot of the travel.
The easy way to figure the progression is to measure the ratio of wheel to shock travel at each end of the travel. Twin lay down shocks could achieve up to 1.5:1 progression (If my feeble memory serves me correctly). My WAG (wild a$$ guess) estimate for a linkage shock might be over 2:1.

Once you get the travel and progression set, the springs should fallout easily.

I hope I have not overextended my so called knowledge. PM me if you have any further interest.

Don
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Old 12-21-2012, 05:31 AM   #113
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Quote:
Originally Posted by Luke View Post
Probably not :) After you've adjusted the preload to get the loaded sag correct, then if there's too much static sag your spring is too hard.

It's a lot more intuitive if you set the preload for the correct static sag. Then measure the loaded sag. Too much loaded sag = too light a spring, too little sag = too hard a spring.

Yeah, I was trying to accomplish too much yesterday and didn't stop to RTFM. I quickly searched online and found some sag settings to see if I was even close but neglected to read HOW to measure race sag.


I have a spreadsheet that you can plug the weights and geometry into and it will tell you the shock travel, progression, spring rate, and preload. If you'd like to mess with that I can send it to you.

Sure send along, love to look at it. disappearinggoose@(googlesfamousemailserviceDOTcom )


Always an option.

I've taken that option more times than I care to admit



If you'd consider changing shocks I have a non-pds WP shocks from the LC4 kicking around that you're welcome to. The reservoir sticks out sideways rather than at 45*, and I think it's shorter for the same travel. 416mm eye-to-eye extended, 110 mm stroke. It just might fit better. I can measure more stuff on it if you might want it.

Thanks for that I think I am going to stick with what I have and know. With my new knowledge I will head back to the garage today and hopefully can quickly hone in on an ideal location for this shock mount and perform some cycles to ensure all things are go.
Quote:
Originally Posted by Luke View Post
That sounds better.

How much suspension travel do you want? The same as the KTM?

That was the plan. I have full travel up front from the dirt forks, looking to match the rear. I might change this by raising the forks in the triples to get seat height lower, but I probably won't. I like tall bikes, my first ADV bike was a 2004 KTM 950S
Quote:
Originally Posted by Salsa View Post
As a manufacturer of Air spring shocks in the 1970's "Motorsport Air Shocks", I thought I understood my shocks at the time. I still use spare parts to build my own shocks today.
Charlie Curnutt started the rule of 25% sag. Meaning when you sit on the bike you have 25% sag. Charlie was the first American made shock manufacturer.

Works Performance Shocks started out modifying Curnutt Shocks. I started a little later and a year later there were a dozen people making aftermarket shocks. Then the bottom fell out because the manufacturers used progressive geometry and a linear shock to get progression instead of a progressive shock and simple geometry.

Back to the problem at hand.
Sag is controlled by a combination of two things -- Spring rate AND preload. For offroad use, I think you want as soft a spring as you can get away with (with some help from compression). In that case 25% sag is appropriate. If you chose a stiffer spring with less compression damping, 15-20 % sag is a better choice. The function of the sag is to let the wheel go down into the whoop.

I think the primary thing you should be looking at first is the progression of the geometry. I don't have any numbers as to how much progression to put in a shock. What do the current bikes have?
In my shocks, I used 7:1 compression ratio of the nitrogen in the shock. Each time the volume was cut in half, the pressure doubled. That provided extreme progression. It had a very soft rate going over small bumps and a lot of spring rate in the last inch to keep from bottoming. You used a lot of the travel.
The easy way to figure the progression is to measure the ratio of wheel to shock travel at each end of the travel. Twin lay down shocks could achieve up to 1.5:1 progression (If my feeble memory serves me correctly). My WAG (wild a$$ guess) estimate for a linkage shock might be over 2:1.

Once you get the travel and progression set, the springs should fallout easily.

I hope I have not overextended my so called knowledge. PM me if you have any further interest.

Don

Don, thanks for the 'splaining. Unfortunately my feeble brain is not capable of comprehending what you just said I'll read it through a few more times though and see if I can glean some nuggets.

In order to avoid trying to refigure KTM suspension, my plan was simply to match what they had originally done. The problem I am finding is that the top location (my only real variable here) is exceedingly difficult to locate precisely and it makes a huge difference moving it just slightly. Add to that the packaging requirements for using a completely different frame and there's a lot of head scratching going on.

Are there any measurements I could give you to tell me if I am on the right track? I assume if I do get it located, have the same ratios as the KTM bikes I am trying to duplicate, have the same sag numbers as I should, and not have the swingarm or wheel hitting anything, AND it feels good, it probably is good enough
Thanks guys for all the comments and suggestions
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Old 12-21-2012, 06:01 AM   #114
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Old 12-21-2012, 07:35 AM   #115
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Quote:
Originally Posted by sailah View Post
Thanks guys for all the comments and suggestions

A couple of things that I keep in mind on my builds, never more than 33 degrees of swingarm angle and 30% race sag on the rear...I like a bike to hook really good for hill climbs, I can ride slower in whoops to make up for too much sag...it's a compromise, but it fits my riding style.

Another thing that I've learned is that a non-linkage rear shock design has more anti-squat(climbs under power) and I should compensate with slightly more rake at rest...keeping 4 inches of trail in mind of course.
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Old 12-21-2012, 08:07 AM   #116
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Finished yet
Are you?

Well thanks to the advice I think I got really close to the numbers I should have.

I tried 5mm of preload and it wasn't enough. Kept adding preload 2 turns at a time and finally got within striking distance. There is probably some slight variations in those numbers especially the unloaded number as it was very difficult to "hold" the mount I made securely so it would actually lift the swingarm/wheel consistently. Once I weld it, obviously it will be much stiffer.

I think I ended up with about 10 turns on the collar. I stopped measuring turns and just measured the actual distance with my calipers.



Sat on the rear end and cranked a cam strap around everything to simulate rider weight. The chain has a good angle and I have about 6" of clearance between the top of the tire and the subframe.







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Old 12-21-2012, 08:11 AM   #117
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A couple of things that I keep in mind on my builds, never more than 33 degrees of swingarm angle and 30% race sag on the rear...I like a bike to hook really good for hill climbs, I can ride slower in whoops to make up for too much sag...it's a compromise, but it fits my riding style.

Another thing that I've learned is that a non-linkage rear shock design has more anti-squat(climbs under power) and I should compensate with slightly more rake at rest...keeping 4 inches of trail in mind of course.
just checked, I'm at 25 degrees swingarm angle under bike weight. Race sag % I'm at 18% I think. 117/660= 18%. Is that how you are figuring?
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Old 12-21-2012, 08:29 AM   #118
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just checked, I'm at 25 degrees swingarm angle under bike weight. Race sag % I'm at 18% I think. 117/660= 18%. Is that how you are figuring?

25 degrees is good, 18% is awfully stiff IMHO. How is the rake and trail at race sag, you have the front strapped down too for your calcs?
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Old 12-21-2012, 10:18 AM   #119
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Originally Posted by sailah View Post
just checked, I'm at 25 degrees swingarm angle under bike weight. Race sag % I'm at 18% I think. 117/660= 18%. Is that how you are figuring?
You are calculating incorrectly, you need to know your total travel to get the % sag.

660mm isnt total travel it's a random measurement between the extended susp and the frame.

Take the difference of the shock bottomed and fully extended then use that number instead of 660

or just use 335mm (rear travel for a KTM RFS) 117/660=34% typically KTMs run about 37/115mm

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Old 12-21-2012, 10:30 AM   #120
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It sounds like you are getting there.

If you set the mount to get the total travel you want, the only other variable is how much progression you could get with that same total travel. You should be close enough where ever you put it.

I looked at the Race Tech KTM - PDS SHOCK SYSTEM Page
http://www.racetech.com/articles/ktm.htm
and used the graphs to estimate the geometry. By checking the spring rate at the top of the travel and the bottom of the travel, the geometry can be estimated. The measurements give a change of rate of 1.45 from the top to the bottom of travel. The spring is effectively 45 % stiffer at the bottom of travel vs the top. With the progressive spring, the combined progressiveness is 2.65 (165 % stiffer).

Sounds good to me.

Try it with the spring you have and if you want a softer ride then get the progressive spring.

Don

Salsa screwed with this post 12-21-2012 at 02:27 PM Reason: I could not figure out what I said!!
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