# Thread: building a full suspension frame question

1. ## building a full suspension frame question

Hi everyone,
I'm in the process of designing my first full suspension frame. I currently have made a few dirt jump frames that came out great but I feel like my building prowess will only be satisfied making a full suspension design. The frame is very close in design to a Transition Bottlerocket. My question is as the suspension compresses what's the best way to make sure the shock compresses on a linear plane? I've tried plugging in a combination of numbers in CAD, moving linkage points mm's up down left and right but still can't get a perfectly straight shock compression. I would imagine this is very critical especially in the beginning stroke of the shock because any out of linear movement could effect small bump sensitivity and damping. I've searched for a "magic formula" or some kind of equation that could get me dimensions to achieve a straight line compression of the shock but still to no avail! Thanks in advance

2. I think I understand your question and the answer is that its not possible. The linkage that is driving the shock is rotating around a point, so it is already not moving linearly. Also, linear movement does not matter. The shock has bushing on each end that rotate, those negate the linear movement.

3. Download the Linkage software from bikechecker.com and become very familiar with it. You can watch some videos on how to use the software. Youtube user andrextr has some great videos to help you understand how to use the software and how to analyze your designs.

4. Maybe if you could design some sort of rail or floating shock arrangement the shock rotation could be minimised?

5. Originally Posted by crank1979
Maybe if you could design some sort of rail or floating shock arrangement the shock rotation could be minimised?
But to what end? If you build a complicated system to minimize shock rotation then what have you achieved besides adding complication and weight? The shock wont perform any better or different.

6. Originally Posted by PeopleForScience
But to what end? If you build a complicated system to minimize shock rotation then what have you achieved besides adding complication and weight? The shock wont perform any better or different.
I agree. But it would be an interesting exercise.

7. A fully linear suspension isn't usually desirable... Riders like progression as it makes it harder to bottom out, thus protecting the shock, frame and rider from overly high forces. In frames designed for a coil, the progressive nature is built into the kinematic as springs are linear. You have to drive the shock harder towards the end of the stroke. It's easy to design a system that is effectively a falling spring rate and use an air spring's naturally progressive nature to counteract this, making linear overall. If you really really want a fully linear suspension kinematic in which the levers drive the shock at a constant rate, you'll need a longer bar with a larger radius driving the shock, making the arc negligible, or a system like Trek's in which the shock is fully floating. A careful combination of both ends will allow you to balance the compression to linear. You'll need a coil in this system so an air spring doesn't make it progressive overall.

8. Originally Posted by bluechair84
A fully linear suspension isn't usually desirable... Riders like progression as it makes it harder to bottom out, thus protecting the shock, frame and rider from overly high forces. In frames designed for a coil, the progressive nature is built into the kinematic as springs are linear. You have to drive the shock harder towards the end of the stroke. It's easy to design a system that is effectively a falling spring rate and use an air spring's naturally progressive nature to counteract this, making linear overall. If you really really want a fully linear suspension kinematic in which the levers drive the shock at a constant rate, you'll need a longer bar with a larger radius driving the shock, making the arc negligible, or a system like Trek's in which the shock is fully floating. A careful combination of both ends will allow you to balance the compression to linear. You'll need a coil in this system so an air spring doesn't make it progressive overall.
I've taken his question to be about stopping the actual shock from rotating about it's fixed end during compression, not about the leverage ratio.

9. I see. OP does query that it "could effect small bump sensitivity and damping", but with a proper bushing, or even better a bearing, why would this rotation effect sensitivity?

10. According to Rockshox this is one of the main reasons behind their new Deluxe shock. The bearings at each eye of the shock greatly reduce this affect on small bump sensitivity. The larger Debonair air cans on the newer monarchs are already extremely sensitive off the top. I think that the new shock technology has made this a bit of a moot point.

11. thread bump. Anyone else have good info on the ease of use for bikechecker software? Are there any good discussion elsewhere?

I'd like to use it to design some custom rockers for a Ventana EcDM (tandem). Ventana used to make a longer travel version called the Testigo but discontinued it in 2005... They're super hard to find and Ventana won't build a modern version and no longer offers a "long travel" rocker option on the ECdM.

Why you ask? Because shredding gnar trail with my 10 year old on my old used ECdM is the most fun you can have. And we're at the limits of the current travel range and it's no longer upgradeable with a straight steer tube and 26" wheels. The new ECdM gets me 27.5+, boost, and a tapered headtube. All it needs is more travel in the rear so I can run a 180/160 singlecrown on it. And I have 2 toddlers who also love the back of a tandem. So I can justify the expense/effort of such a boutique bike.

12. Premise is flawed.

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