[Video] Rebound Speed vs Suspension Performance

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2/1/2017 3:27 AM

Hello guys,

I would like to share my newest video where it is discussed in deep detail, and using dynamic simulations, the effect of rebound speed and suspension performance.



I hope you find this interesting.

All the best,
André
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2/1/2017 9:24 AM

André, you're right. Perhaps your best yet! Thank you for the detailed explanation and excellent visuals.

Suspension nerds, this is a must watch. Here are some key screenshots for easy reference:















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2/1/2017 10:22 AM

Dialed!

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2/1/2017 10:33 AM

Thank you !!!

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2/1/2017 11:46 AM

As always, excellent videos Andre

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Dan_L

2/1/2017 5:56 PM

Hey Andre-

what about MTB suspension across all design puts the natural frequency at such a tight and specific number?

are all bikes and wheel sizes and riders more similar than we are trained to think?

thanks-


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I am the founder of Memory Pilot I make MTB Fenders and have an awesome sock.

2/1/2017 8:54 PM

In summation: Hi Speed Rebound needs to be fast, and Low Speed Rebound needs to be slow. But, adhere to the curb test, because the shocks have built in hi speed blow off. Yes?

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2/2/2017 12:19 AM
Edited Date/Time: 2/2/2017 12:20 AM

erik saunders wrote:

Hey Andre-

what about MTB suspension across all design puts the natural frequency at such a tight and specific number?

are all bikes and wheel sizes and riders more similar than we are trained to think?

thanks-


I suspect that the natural frequency is a function of unsprung and sprung weight and their respective moments of inertia. That would render the natural frequency independent from linkage systems. But perhaps @Andrextr can clarify?


Great job André, following your vids since the beginning. Curb test is crazy useful.

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2/2/2017 12:31 AM
Edited Date/Time: 2/2/2017 12:34 AM

Erik saunders:

Hi! The natural frequency of a bike (or any vehicle) depends on the stiffness of the spring (which depends on SAG% and amount of travel) and the suspended mass (Kg). For cross country bikes, since they have less travel, and they run lower SAG, they require a much stiffer spring. So, on XC bikes the natural frequencies are a bit higher, around 3 to 3.5 Hz. On DH/Enduro bikes the natural frequencies are around 2 to 3 Hz depending on the cases.I will cover this in a more detailed way in a future video about pedal bob. This is particularly interesting because the natural frequencies of a bike matched exactly with pedal bob frequencies. For a typical pedaling cadence of 75 RPM, for each crank revolution you get 2 pedal strokes, so pedal bob frequencies at this cadence are 150 bobs per minute = 2.5 bobs per second = 2.5 Hz. So, when you see someone on the internet saying that a specific bike bobs a lot and so on, in many cases that's just because he have a fast rebound and the suspension is making resonance with the pedal bob frequency amplifying the bob oscillations (lol)... I will discuss this in a future video. Stay tuned

Sideshow
Hi. Yes, low speed rebound needs to be slower than the high-speed (this does not necessarily corresponds to the number of clicks of the settings!!!). And don't use extreme settings because high and low-speed rebound work together (for instance, in a high-speed rebound event, although the oil flows in the high-speed circuit, some of the oil also flows through the low circuit). If you have a shock with both settings I would recommend to watch this video at minute 9:00 (
). Probably this is not the best way to tune it, but I believe it's a good starting point, at lest it's a balanced way to do it, without going into the extreme settings. If you want to try it tell me if it worked well for you.

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2/3/2017 1:43 AM

Hi Andre,

thanks as well for the very informative videos.

I have one question concerning the difference of high/low speed vs. beginning/ending stroke rebound:
In the video you talk about high/low speed, which makes sense, as you are talking about frequencies. However on the shocks I have owned and own (from the 5th element coil shock to the vivid air r2c) the rebound is differentiated in beginning/ending stroke rebound. I have always interpreted this as different circuits of oil flow, depending on how much the shock is compressed (beginning stroke for first 30%, which is equal to sag, and ending stroke for the rest of the shock's travel).
So is the beginning stroke rebound similar to a low speed adjustment, as it is primarily used to eliminate bob within the range of the sagged bike, while the ending stroke is (similar to the high speed adjustment) used for any impact after sag.

My question would thus be, if - although being different concepts mechanically - low/high speed and beginning/ending stroke rebounds can be used in a similar way?

(A situation, where the analogy might not work, is when talking about jumps, where the frequency is low, but the shock is very compressed.)

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2/3/2017 3:19 AM
Edited Date/Time: 2/3/2017 3:23 AM

Beginning and ending stroke rebound is a nomenclature used by brands to make it easier to understand, but technically is not a correct nomenclature. The correct nomenclature is indeed the low-speed and high-speed rebound (corresponding to the beginning and ending stroke, respectively).

So, why it's not correct? Because you can have (and you do have a lot indeed) high-speed rebound events at the beginning of the travel.

So, when does the high-speed rebound kicks in? Mainly in two scenarios:

1) When recovering from deep in the travel after a big hit. In this point the spring is fully compressed and it's making a "ton" of force to extend. In this case the spring quickly accelerates during the rebound movement, activating the high-speed rebound circuit. --> This is where the term end-stroke rebound comes from.

2) However, you can also have an high-speed rebound event at the beginning stroke. This mostly occurs whenever you hit a square-edge bump at fast speeds. When the wheel hits the square bump, the wheel gets unloaded right after the bump crest, and in many times the tire looses the contact with the ground. In this case, the spring will rebound fast since there is no resistance from the ground. If you see an onboard video of a suspension working on a rocky trail, you will see that the suspension moves up and down very fast (tracking the ground). All of these are high-speed compression and rebound events. You can see my episode 6 (

) in the beginning of the video I quantified the speed of a fork riding over a rocky terrain (the graph is bellow). Almost all rocky bumps induced high-speed movements on the fork despite that the fork didn't use more than 50% of the travel. So, you can have (and you do have a lot) high-speed rebound at the begining stroke.

This graph represents the shaft speeds of a Fox 36 fork over a fast rocky trail (see beginning of episode 6). Note that almost all rocky bumps induced high-speeds on rebound and compression (all of them on the beggining travel):


IPS = Inches per second

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2/3/2017 4:14 AM

Thanks a lot for the carification. I have to say, I find it pretty pointless of RockShox to hold on to the wrong labeling, even explaining things in their product manual, as if it indeed was a beginning/ending stroke setting. When looking for this on the web, you see that there is just a lot of confusion, mainly caused by the information provided by RockShox (I even found a description, stating that beginning stroke rebound is for fast and ending stroke for slow impacts).

So to take away from this is that on the vivid

beginning stroke rebound adjuster = low speed rebound damping
ending stroke rebound adjuster = high speed rebound damping

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