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My Rear Suspension Mods


blackout

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A close up of the link installed.  It is 3/16" shorter than stock and that raised the rear 5/8" measured from the rear axle bolt.  I drove to work today and really noticed very little difference, but that is expected, I suppose, for street riding.  I won't be tracking the bike till next spring, but from everything that I have read, the smart guys say raising the rear is only going to help.
 
 
0828161649_zpsopdrjsbx.jpg

Craig Mapstone
Upstate New York

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I won't be tracking the bike till next spring, but from everything that I have read, the smart guys say raising the rear is only going to help. 

 
I am definitely not one of the "smart guys", but I just had a big test with the rear suspension link made by one of the guys who is...Andy of AP MotoArts.
 
The link WORKS. At least it did for me anyway. The bike turns better, which is weird because I thought it was telepathic before. It also holds a line better and I'm able to finish the corner better as well. The extra ground clearance is a really big help too. I'm able to eek out more lean angle without fear of scraping hard parts.
 
Turn in, and just about everything else (handling-wise) happens a little bit faster now. I didn't realize it until I got stuffed into a corner and had to stand up the bike to avoid rubbing elbows with some guy. When I did make that mid corner "adjustment", it happened way faster than I'm used to. But it was still perfectly controllable without any nervousness.
 
I think you'll like the change...
 
:)
 
- Paulie
 
 
 
 
 
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Paulie, thanks for the info!
 
twf, yes, there is an aluminum spacer on both sides. The aluminum rod-end has a 1/2" bore with a 5/8" shank. The frame pivot bolt is 12mm, so I used a piece of .014" wall brass tubing to shim the 1/2" down to 12mm. Worked perfectly. I could have gone with metric rod-ends, but QA1 does not sell metric aluminum rod-ends. I wanted the weight savings for shizzles and the aluminum is plenty strong for pure tension and compression loads. Plus, that's what the shock end is anyways. My link assembly weighs 4 ounces less than stock. Not much, but something.
 
0828160958_zpssl3gkqpr.jpg?1472490595804&1472490599009&1472490607488
 

Craig Mapstone
Upstate New York

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Looking at the link ( beautiful machine work BTW. sooo jealous), I agree it should be strong enough but worry a bit about the bottom bolt being loaded in the middle of a long run. The spacers won't add much stiffness. What about a pair of conical Al spacers either side with the widest ends towards the link. make them a tightish tolerence and that should help the bolt stay straight. Still a lot of load over a fair unsupported run though.
I agree that raising the rear makes it handle better. I am running a 25mm raised rear ( Extreme Creations link) and it improved markedly ( with a similiar Nitron). The spring supplied was a bit too stiff like yours but I only use the bike on the road so not too worried.
Pattonme , points out that conventional wisdom is that the bike is short on trail std and shortening it should be a no no. But I have found that it is not at all unstable and the vague feeling is lessened since the raise.
I suspect there may be two things contributing. One is that the std front is so soft that it shortens the trail more than it would be. Stiffer springs have made the static stance higher and so the trail is increased. The second suspicion is because the bike has a strong rear weight bias, it makes the effect of any trail greater .
Now that I have my suspension software working again I have managed to recreate the bike geometry and the short linkage does indeed make the effective spring curve a bit straighter.

Go forth and modify my son...go forth and modify...

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Looking at the link ( beautiful machine work BTW. sooo jealous), I agree it should be strong enough but worry a bit about the bottom bolt being loaded in the middle of a long run. The spacers won't add much stiffness. What about a pair of conical Al spacers either side with the widest ends towards the link. make them a tightish tolerence and that should help the bolt stay straight. Still a lot of load over a fair unsupported run though. I agree that raising the rear makes it handle better. I am running a 25mm raised rear ( Extreme Creations link) and it improved markedly ( with a similiar Nitron). The spring supplied was a bit too stiff like yours but I only use the bike on the road so not too worried.
Pattonme , points out that conventional wisdom is that the bike is short on trail std and shortening it should be a no no. But I have found that it is not at all unstable and the vague feeling is lessened since the raise.
I suspect there may be two things contributing. One is that the std front is so soft that it shortens the trail more than it would be. Stiffer springs have made the static stance higher and so the trail is increased. The second suspicion is because the bike has a strong rear weight bias, it makes the effect of any trail greater .
Now that I have my suspension software working again I have managed to recreate the bike geometry and the short linkage does indeed make the effective spring curve a bit straighter.
I hear you on the lower bolt, but after much thought, and no math, lol, I doubt there is any flex there.  It surely would not break, a small amount of flex would be the only concern, but with the bolt at double shear, and my experience with cars, I see no problems.  I have seen shocks mounted single shear with 1/2" bolts using 3/4" spacers on 3,000 pound cars!  Remember, a shock only sees loads equal to the weight of the rider and bike, there are no extra loads created by g-forces, race tires, and sticky pavement that would need to be predicted during cornering.  Something that needs to be thought about during frame and control arm design.  I have seen upper control arms destroyed during unusually hard breaking on a CP Mustang running sticky autocross slicks.  Now if the shock bottomed out at the Isle of Man TT, that would be a different story. 

Craig Mapstone
Upstate New York

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I won't be tracking the bike till next spring, but from everything that I have read, the smart guys say raising the rear is only going to help. 

I am definitely not one of the "smart guys", but I just had a big test with the rear suspension link made by one of the guys who is...Andy of AP MotoArts. 
The link WORKS. At least it did for me anyway. The bike turns better, which is weird because I thought it was telepathic before. It also holds a line better and I'm able to finish the corner better as well. The extra ground clearance is a really big help too. I'm able to eek out more lean angle without fear of scraping hard parts.
 
Turn in, and just about everything else (handling-wise) happens a little bit faster now. I didn't realize it until I got stuffed into a corner and had to stand up the bike to avoid rubbing elbows with some guy. When I did make that mid corner "adjustment", it happened way faster than I'm used to. But it was still perfectly controllable without any nervousness.
 
I think you'll like the change...
 
:)
 
- Paulie
 
 
 
 

@pgeldz I need your help getting parts from Andy! I need that link and rearset plates. PM me if you can help.
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I wasn't thinking flex nor break as much as bending. I came through both the motorcycle suspension ( from the early 70's) and the MTB suspension revolution( early 90's to naughties) and have a ( based on some experience but certainly not infallible) a fear of long run bolts unsupported. Was very common in early rocker suspensions when everybody was experimenting.
Even on a mountain bike ( comparatively much lower loads) I have had long run spaced bolts ( hi ten) bend.
I think the math would give a multiple of the rider/bike weight because of the lever ratio of the suspension ( more than 2:1 I think) but without , as you say, doing the math and checking the vectors involved it's hard to say. One thing that gives me a pause for thought is the fact they used 2 needle bearings in the OEM one, instead of a narrower single one . That could have been for reliability of course.
Both ends of the shock get from what I can remember 8 or 9 thousand Nm. loads at full compression ( that may have been KG I did the spring graphs quite a while ago).
I wait to see how it goes. If you are right and it stays straight, it will just prove what most of my friends say about me over-engineering everything...

Go forth and modify my son...go forth and modify...

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I wasn't thinking flex nor break as much as bending. I came through both the motorcycle suspension ( from the early 70's) and the MTB suspension revolution( early 90's to naughties) and have a ( based on some experience but certainly not infallible) a fear of long run bolts unsupported. Was very common in early rocker suspensions when everybody was experimenting. Even on a mountain bike ( comparatively much lower loads) I have had long run spaced bolts ( hi ten) bend.
I think the math would give a multiple of the rider/bike weight because of the lever ratio of the suspension ( more than 2:1 I think) but without , as you say, doing the math and checking the vectors involved it's hard to say. One thing that gives me a pause for thought is the fact they used 2 needle bearings in the OEM one, instead of a narrower single one . That could have been for reliability of course.
Both ends of the shock get from what I can remember 8 or 9 thousand Nm. loads at full compression ( that may have been KG I did the spring graphs quite a while ago).
I wait to see how it goes. If you are right and it stays straight, it will just prove what most of my friends say about me over-engineering everything...
The two needle bearings would indeed spread the forces out closer to the frame.  I'll give you that.   
You got me thinking on this one.

Craig Mapstone
Upstate New York

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I punched some numbers. Assuming a maximum force of 1,500 pounds. This is the amount of force needed to bottom out a 625 lb/in spring on the FZ-07 shock (61mm stroke length). Deflection in the middle of the 12mm bolt with no spacers would be .0280". This is substantial in my opinion, BUT with the .75" diameter spacers installed the deflection drops down to .0066". This amount is small and would not be enough to permanently deform the bolt. If I used 1" diameter aluminum spacers max deflection would drop to .0026".

Craig Mapstone
Upstate New York

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To add, I calculated any bending assuming the ends of the bolt were free to pivot, like shown below. But the ends are not free to pivot, so any actual bending is less than the numbers I computed above.
 
 
beam%20bending_zpsvl7dly7h.png

Craig Mapstone
Upstate New York

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  • 8 months later...

So I installed the higdonion skid plate and bars on my bike and now when I take corners a little to fast I scrape the skid plate... I was wondering if this which lift would be better? And if there is any other companies making a rear lift link for our bikes... the 2 I'm looking at is apmotors and extreme creations from Australia.. can you guys please give some in sight....

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So I installed the higdonion skid plate and bars on my bike and now when I take corners a little to fast I scrape the skid plate... I was wondering if this which lift would be better? And if there is any other companies making a rear lift link for our bikes... the 2 I'm looking at is apmotors and extreme creations from Australia.. can you guys please give some in sight....
 
 
Those are the two suppliers that I know of.
 
I have yet to hear any negatives with raising the rear suspension.
 
You can also raise the rear with a taller tire. Some have done this with good results.

Craig Mapstone
Upstate New York

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I have 2 caveats on the raising the rear.
I am a believer in doing it for most things BUT:
As pattonme pointed out the stock trail is very short. With the rear raised it gets shorter and ,in theory, shorter than usually wise. I would be testing for instability on tracks with very high speed long straights. The braking at the end of the straigh could be...er...interesting. That is where it WILL become a problem.
My opinion is because the weight is so rearward biased that it mitigates the effect of the short trail. If however you mod the bike in such a way as the weight bias moves forward sufficiently that mitigating effect is lessened it will need a rethink. Changes to fairings ( including extra downforce at the front) or any other weight movements could move the CoG far enough forward for instability to become a problem. Needs testing. One of the reasons I have been a bit hesitant in looking for a bigger fuel tank. Certainly changing the exhaust to an akro carbon moved the weight forward ( 4kg lighter and all of it behind the CoG), but I can't get anywhere fast enough to test it ( not doing it on these roads).

Go forth and modify my son...go forth and modify...

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Thanks for the input, I decide to go to a local shop to get them to make me a custom dog link I told them 2inch is preferred but also said with please keep in mind my stability so if you need to go less do it...

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Forgot to mention. A taller tyre eg 180/60 will weight more. All of that weight will be extreme outer edge rotational ie it will affect the ability to lean/turn greater than the lower/lighter one. Especially if you go to a 60 profile in front. The front gyro will have more to overcome in the bigger gyro of the rear ( both the diameter component AND the mass component). It will show up as a desire to run straight in high speed corners rather than turning. It will help stand the bike up better when accellerating OUT of corners.
It's a snmall part of why I believe a 160 or 170 /60 is a better tyre for this bike.
 

Go forth and modify my son...go forth and modify...

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