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THIS IS AN OLD POST I DID ON THE OLD QRHQ SITE
I am working on putting a set of YFZ450 front shocks on my zilla and in order to get the E2E I need so they don't bind the ball joints I need to move the upper mount .75 inches up. Problem occurs when I do this and remain at the same angle as the original shocks as the upper shock eye hits the frame in the new mount point.
If I move the upper mount towards the outside more will it increase or decrease the leverage as the shock cycles?
I was working with Carl on something called Motion ratio but have not heard back from him in a couple of days so I need a hand if anybody knows about PROPERLY setting up a front suspension PM me or post it up before I F it up too bad
At this point I am going to need to fab new shock mounts, most likely working off the modified OEM ones.
Thanks
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fasttrackfab
fasttrackfab is offline Semi-Pro
Join Date
Jul 2009
Location
port huron, michigan
Posts
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To calculate motion ratio it is a simple formula:
mr=(d1/d2)^2
mr= motion ratio
d1= distance from lower a arm pivot point on frame to centerline of ball joint
d2= distance from lower a arm pivot point on frame to cneterline of lower shock mount
a brief explanation of motion ratio:
(K)
A-----B-----P
P is the pivot point, B is the spring mount, and A is the wheel. Here the motion ration (MR) is 0.5... imagine a spring K that is rated at 10 lb/in placed at B. If you want to move A 1 in vertically upward, B would only move 1in*MR = 0.5 in. Since K is 10 lb/in, and B has only moved 0.5 in, there's a force at B of 5 lb. If you balance the moments about P, you get 5(B)=X(A), and we know B = 0.5A, so you get 5(0.5A) = X(A). A's cancel and you get X=5(0.5)=2.5. Which is 10*MR*MR or 10*(MR)^2.
now the problem you run into when moving the upper shock mount is changing the angle of the shock, ie.. the angle of the shock to the ground, moving the upper mount more outboard will stand take the shock angle closer to 90 versus moving the upper mount inboard lays the shock down and decreases the angle. What this does is the effects the spring rate needed for the same ride.
To calculate the spring rate needed go to this site and use their calculator. It also explains where to take measurements from. Much easier than me typing it in here.
http://www.f-o-a.com/calculator.html
I am being very brief here. if you have more specific questions please ask.
Last edited by fasttrackfab; 09-11-2010 at 06:39 AM. -
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Ok FF got the info you are looking for:
The stock 08 YFZ 450 stock spring rates are:
It's a dual rate spring
112 lbs/ in
224 lbs/in
Here are the 500 measurements:
D1 =14 (to BJ center)
D2 = 6.5 (to lower shock mount center)
(Now if I go to the center line of the wheel D1 = 16.875 on my sand tires)
So
MR=(16.875/6.5)^2
MR = 1.26
Let me know what else you need or I need to do.
Thanks for your help -
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wheel travel measurement
1. put quad on jack stands
2. take front wheel off
3. take shock off
4. remove spring from shock
5. put shock back on without spring
6. measure from the ground to a point on the spindle at full droop
7. cycle the suspension to the max upward postion in the travel
8. measure from the ground to the same point on the spindle
9. reassemble shock and spring, and reinstall
This will give you the max travel out of the suspension. The reason for removing the spring is just for ease of doing this measurement. If you can compress it with it still on the quad than leave it. I find it easier to remove though.
Measure the angle of the shock and full droop, I tend to always use this measurement for calculating spring rates.
Guys just be careful when you cut bump stops and such. Bump stops are actually an integral part of the shock if properly used. They have their own spring rate and can be had in either a liner rate or a progressive rate. You actually design the suspension to utilize the bump stops, they are not just there to stop the shock from bottoming out.
I will try and get the location of the upper mount done tomorrow but cannot promise anything. -
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Okay based on earlier description of the motion ratio formula:
Zilla:
mr=(14/6.5)^2
mr=(2.15)^2
mr=4.6
YFZ:
mr=(14.5/9)^2
mr=(1.61)^2
mr=2.595
Okay best way to fit the yfz shock on the zilla:
Move upper Shock mount hole: .5" upward
Move lower shock mount on a arm: 2" outboard (closer to ball joint) (or 8.5" from pivot point on lower a arm)
This gives us a new motion ratio of:
mr=(14/8.5)^2
mr= 2.71
This will provide a tad softer ride than the yfz but should not be noticeable or require a change of springs. If you keep the lower a arm mount at its current location the leverage against the shock is too great for the yfz shock to be effective and provide the kind of performance it is capable of. This requires a little more work to make right but this is not a hard modification to make on either the a arms or the upper mount. Let me know if you have any other questions. -
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Thanks for the pics Shorty, does the spring hit the upper A-Arm when the suspension is at full drop?
Also from the looks of this full drop is less than stock as the shocks are mounted so much higher? Looks like they are a good 3 inches above the stock mounts? Also is this a YFZ450 shock or what is the E2E on this?
More info on leverage ratio:
Called Wayne at PEP yesterday about some other stuff and ended up talking about this as he also runs a LT500 for his duner bike.
Stock LT500 is 2.4/1 with the OEM rims (2/3 rims)
LT500 with 3/3 rims (from FSS) Leverage ratio is 2.5/1
Stock YFZ450 is 1.95/1 with the OEM rims (1/4 rims)
YFZ 450 with 3/3 rims (from FSS) Leverage ratio is 2.25/1
Wayne said running the stock YFZ450 shock will work on the zilla I just need to be mindful of the compressed length of the shock when re-locating the upper perches so it does not bottom out on the frame rails.
Having to make new upper perches will post up when completed.
thanks for all the help -
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Ok here is the update:
Fabed up new upper mounts tonight after making mock ups yesterday and learning a few things needed to be corrected.
Made these out of 1.5X2 square tubing 180 wall mild steel.
Did all the measuring etc and got them tacked up pretty good tonight, ran them through the cycles and everything works great, good clearance no bind just need to get the shocks adjusted as they are a little soft but I have not messed with them at all so we will see what I can do to get them tuned in perfect for my fat arse.
Here are some pics:
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Ok got them welded up and cleaned up, shocks mounted and adjusted, should be painting tomorrow and then finally done and ready to ride.
Here are some shots of the work start to finish & how they look finished on the bike unadjusted.
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Could the shock mounts on the a arms be relocated to achieve the same result? Then the frame wouldn't have to be modified.
Nice work by the way! -
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I'm working on putting LTR-450 shocks on the front of mine. I have to re-do both the frame mounts & the A-arm mounts.
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Could the shock mounts on the a arms be relocated to achieve the same result? Then the frame wouldn't have to be modified.
Nope that is as far as they could go before they hit the upper arms with the stock A-Arms. Right now there is under .25" clearance on the upper arms through the cycle.I'm working on putting LTR-450 shocks on the front of mine. I have to re-do both the frame mounts & the A-arm mounts.
Brian you do not have to redo them but if you want the ball joints to be correct with these shocks on the OEM a-arms you will need to move the upper mounts like I did. I know you have some special Baja arms and the YFZ 450 shocks might work good with your set up if done right.
In fact I might know someone what a set for sale if interested get in touch. -
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Looks good man planning on doing this on my build but I'm not a metal fabricator at all so I have to see if m buddy that does metal fab will help me with it. You might know someone with a set of 450 shocks for sale? Let me know what they might want.
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did moving the mounts up hit the plastic when you put it on?
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did moving the mounts up hit the plastic when you put it on?
I made an aluminum support bar and used some energy suspension shock tower mounts to make a 1.25" spacer across the front fender mount, this raised the fenders enough to clear the new shock tower mounts.
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