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Discussion Starter · #1 ·
Well I am building a new midsize bike and seeking advise on the shock setup. I modified a spare frame I had and changed the steering rake and swingarm pivot point. The bike is coming together but I have been putting off setting the rear end up. The time has come, I have a M1-A6 i-shock arriving this week. Here is a pic of the rear setup, yes it just looks like all the rest, but I know you guys like piccys.....

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This particular swingarm has a higher than usual lower shock mount and also is positioned further back than usual toward the wheel. This has always given it a fairly laid down attitude (dissimilar to a laid back attitude!)...sorry...As i have dropped and shifted the swingarm rearward, the top shock mount now needs to be moved to accommodate standard shock lengths, and gives me the opportunity to set the laid down angle anywhere I want. Keeping in mind that I have jigged this frame and swingarm, fitted twin bearings to each side of the swinger and everything is running dead true. The i-shock has pivot bearings as well so all unwanted stresses should be minimised.



So where do I want it?
 

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The first thing that I would suggest is NOT to use that I-shock since the M1-A series is designed for an A style swinger.

Next if I also understand correctly, you need to move the top shock mount to make the frame ride evenly and sit the way you want it. That being the case, first determine your leverage ratio. You do this by measuring the distance from the pivot to the rear axle (center to center). You then measure the distance from the pivot to the lower shock mount (again center to center) divide those numbers and you will get your leverage ratio. Ex. 15.5" swingarm, 4.25" pivot to shock mount =3.65 to 1 leverage ratio. Once you have your leverage figured out then you will know how much travel you will have for a given shock. Say for example the above numbers were accurate for your bike and your shock is a 2" stroke shock then ideally you would have a total rear travel of 7.3"

As far as angle of the rear shock, this is where it gets tricky. You have to decide how you want your travel delivered, how progressive or linear do you want it. If you want a linear feel then you will lean more towards a verticle mounting possition. You must be careful here, if you go too far then it will go into a falling rate which is bad!! To avoid this, make sure that you never at any point have your accuator (in this case your swingarm) and shock pass 90 degrees. Having a progessive set up is also tricky, laying the shock down too much will cause it to ramp up too hard too soon, making the rear suspension feel too stiff at the wrong time. A good place to start is not to go beyond 45 degrees. The fortunate part is that with pitbikes the travel is usually not enough that a few degrees +or - will really be that noticable. A good bike to copy angles from is a KTM 65 or a Pitster Pro X2. Good luck.
 

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Discussion Starter · #3 ·
Thanks for the great help here trailpimp! Ok, well i have a leverage ratio of 4.1 with the wheel set right to the back of the swingarm which is where I want to run it for the extra wheelbase. Is this ratio going to be too hard on shocks? I notice that your x2 has a much greater laid down position than the x4. You obviously think that the x2 is running a better config than the x4 by recommending to copy it? What sort of ratio are these bikes running?
 

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Macka said:
Thanks for the great help here trailpimp! Ok, well i have a leverage ratio of 4.1 with the wheel set right to the back of the swingarm which is where I want to run it for the extra wheelbase. Is this ratio going to be too hard on shocks? I notice that your x2 has a much greater laid down position than the x4. You obviously think that the x2 is running a better config than the x4 by recommending to copy it? What sort of ratio are these bikes running?


4 to 1 is high but still lower than the Reeg and BBR chassis. With that ratio you will need a 1000lb spring or higher. The laydown of the shock on the x2 vs. the x4 is somewhat deceiving and dependant on the leverage block on the x4. The x4 also uses a longer shock so that changes the varible a bit. You have consider the entire stroke, so with a shorter stroke shock you can lay a bit flatter. But if you were to copy the x2 it would perform very well.

The x2 has a 3.1 to 1 leverage ratio and the x4 with the red block is 3 to 1.
 

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Discussion Starter · #6 ·
Ah ok. So yeah, if you fit a long travel shock and lay it down too far you could end up sitting on your rear tyre!

Are pitster using a 290mm long DNM shock?
 

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Discussion Starter · #8 ·
I have a swingarm that would run a 3.1 to 1 ratio. And 290mm would be the exact height needed to balance the bike without further modification. The DNM would certainly be a cheaper option and I would have the benefit of shock development for the x4 at this length in the future. So the question now would be...provided the shock is durable enough in time, do you think, or have you already been able to get it performing as you would like it to. Also the 292 high and low adjustable version is available too.
 

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Macka,

I think that would be a great option, esp. going with the H/L adj. version. The DNM shocks are good and each batch is better than the last. I know that you will hear "Elka, Elka!!" on here alot, but for the money the DNM is a really good shock and you can upgrade the valving just as easy.
 

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Discussion Starter · #10 ·
That settles it then. Thanks for the very helpful advise trailpimp.



Now I don't have to cut my frame again... the wife won't be mad at me for as long... and the DNM shocks use a great neutral colour range so the bike will be happy too.
 
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