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Video Analysis of Suspension

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I got a high speed camera to film my suspension in a test environment.   Since 95% of my riding is 2nd gear tight trails, with 4-6" obstacles, I
figured a video of me riding over a 4" soft bump (log) in 2nd gear would be a good, repeatable test for suspension setup.

 

This is a KTM Freeride 350 4 stroke. The suspension springs have been properly installed for my weight.  The front and rear sag has also been properly set up.  Maxima 5W - 120mm oil height. 

 

Here are some interesting points:
(1) the front wheel sucks up 3 or so inches, then starts to lift the bike.
(2) the compression is quick, rebound is also quick, but because the bike is up in the air, the front wheel is still off the ground by 2" or so. It takes a bit for the front wheel to come down.

I did a series of tests, with large adjustments of fork compression and rebound.  In all cases the results were similar.

Is it possible that the midvalve compression damping is too stiff?

 

thanks for looking.

 

Edited by ClakTap

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Looks like the front is too stiff/too progressive.  The rear seems like it could be a tad softer too.  The tire bottoms out against the rim before the suspension starts to move.  What tire pressures are you running?

 

The front wheel touches back down twice as far out as the rear wheel.

 

Got a video of it at normal speed?

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How does it feel?

 

I've read that compression and rebound damping adjusters on the fork control low velocity damping. I assume that is a higher velocity event?

 

I would be interested in seeing an overlay of the vertical difference between the two nodes you have for both the front and rear wheels. You could see what your suspension travel is doing independently of bike displacement. You might find out more about the front and rears relative stiffness's.

Edited by Blowin_Trannys

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Thanks for looking.

 

This is second gear speed with a big gear on the back, so not too fast.  About 10mph. See below for a full speed video. 

 

Running 10psi front and rear.  Its wet and slimy around here so we run a lot of low pressures.  Rear is tubliss system, front tube is greased like a pig.  Although it may not look like it, I rarely (if ever) pinch flat.  I dont bend rims either.  

 

I agree, the first few inches of fork travel are quick and responsive, then it hits a wall.  A friend said to take a hard look at the midvalve compression valves

 

How does it feel?  Unlike the top line, I can feel the bump somewhat hard in my wrists, I would like to have it smoother. After I revalve the midvalve, we'll see how it goes.

 

Once I get this adjusted and working right, I will take on high speed damping by using a square edge bump.  I will also put a series of bumps together, to look out for rebound packing.

 

My lofty and unlikely goal is the top line stays horizontal, the wheels stay on the ground and the wheels do not bounce.  May as well shoot for the stars!

 

 

 

 

 

 

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I have never seen an analysis like this before. While I am no suspension engineer, suspension is always a give/take relationship. Is this typical of the type of obstacle or terrain that you are struggling with on the trails ?? As it would seem a single bump of that size on a trail you would simply just wheelie over. If you had consecutive bumps that size then the suspension would react differently. Slow-mo footage is cool but wouldn't it need to be more specific ??

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Our trails are technical and slow.  Full of logs, roots and glacier/river rock.   The above test reduces these typical trails to a simple test that can easily be repeated, analyzed and then adjusted.  This is not to take place of "seat of the pants" suspension tuning, but helps to isolate specific problems.  

 

 

Here are a couple of examples:

 

 

 

 

Edited by ClakTap

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It's s high speed shim stack problem on the base valves

 

You have my interest.  I dont have a solid understanding of the interaction between the compression circuits in the base and mid valves, e.g. when one is in play versus the other. In my case - where the compression stroke hits a wall after 3 or so inches - why would it one versus the other?  Any thoughts on what the specific problem is?

 

thanks for the help.

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You have my interest. I dont have a solid understanding of the interaction between the compression circuits in the base and mid valves, e.g. when one is in play versus the other. In my case - where the compression stroke hits a wall after 3 or so inches - why would it one versus the other? Any thoughts on what the specific problem is?

thanks for the help.

The log you show while small (ish) and low speed, because of the shape of the hit is a mid to high speed suspension problem

When I talk about low or high speed problem it's fit bike speed but shaft speed and because of the shape of the log it's activating the high speed part of the compression shim stack then the wheel is coming off the ground as the rebound is too slow to get it back on the ground

Suspension tuners change add or subtract shims in the stack to work for you over a broad area but can also be made to be very specific (think supercross) and that's possibly what your after here a very specific stack (compression and rebound) to handle the sharp hits

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