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[Videos] MTB Rear suspension series

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hello guys! My name is Andre, I'm from Portugal, and I'm an recreative and passionate mountain biker (at the moment I only do Downhill, but I used to do Enduro, XC and also road cycling 15 years ago). I always enjoyed to see/learn/know/discuss about rear suspension of mountain bikes.

Therefore I created this thread to share some of my knowledge and opinions about rear suspensions of bikes. I have some youtube videos, that I will share here.

MTB REAR SUSPENSION SERIES

Episode 1: Basics (Topics: Leverage Ratio and Progressivity).


Episode 2: Forces and SAG (Topics: LR ratio, Force curves at rear wheel, SAG and progressivity)


Episode 3: Shock preload vs Sensitivity (Topics: How does preload negatively affects suspension sensitivity. Force curves).


Episode 4: Suspension systems (Topics: Why it does not make sense to compare suspension systems)

Episode 5: How-to CORRECTLY adjust the rebound (Very important video!...)

Episode 6: [DIY] FREE Suspension Data Acquisition

Episode 7: Tuning Tips: Compression and Rebound damping

Episode 8: Breakaway force

Episode 9: IFP forces


LINKAGE ANALYSIS:


More bikes analyzed here:
https://www.youtube.com/playlist?list=PL4tH8eqoJoZ9N-v5D6bW3iHK6hXB2m38Q

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Hope you liked it. Sorry for the video "overload" :D Don't see them in a row or you might cause a short circuit on your brain synapses :)

I will upload more videos in the next days :)

We can discuss any question, suggestion, etc.
Thank, have fun :)
 
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andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hello guys! Just want to share a new episode. Probably the most important one.

I found that many riders out there have a completely "wrong" rebound setting on the rear shocks. In this video I will explain how to correctly tune your rebound damping for achieve a great stability & traction balance. To the best of my knowledge this is the most reproducible and easier method to tune the rebound of a shock. It is also a great starting point for fine-tuning.


Hope you like, any question feel free to ask :)
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hi guys! For those who saw the last video of rebound, just wanted to share some REAL DATA from my shock with different rebound settings in the curb test... You can see the oscillations now
The green line was in slowest rebound setting. So slow that the shock stayed "packed down" after the curb impact... It did not recover to the equilibrium position (SAG).




In the next days I will upload a video to show you a FREE method to do these suspension real data acquisition. This is really awesome! :)
Stay tuned! Bye.


PS: BTW, it seems that Buggy's have a rebound at the critical damping or even slightly overdamped...no oscillations at all! Nice :)

 
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andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hi Guys!

My most innovative video ever! A FREE method for Suspension Data Acquisition without fancy equipment. Check it out! :)


Hope you like it.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hello!

After many requests, here it is the video with some tips and my personal advice to adjust the Low and High-speed compression and rebound (HSC, LSC, HSR, LSR).


I hope you find it useful!

Bye :)
 

lobsterCT

Monkey
Jun 23, 2015
278
414
2016 xl Jedi with Fox RC4 fat shaft and 500 pound spring:

My scale is sketchy, but I seem to be getting about 40 pounds pushing the seat down about 3/16 of an inch.

2015 xl Nomad with Rockshox air type rear shock, monarch debonair:

Showing about 60 pounds. Just cleaned the bike for next season and reset all frame bearings before measuring. I have a coil shock arriving for this bike on monday, and I'm curious to see if it brings this measurement lower.

Edit. Just put a 2016 fox van with 550 lb spring in the Nomad. Showing 42 pounds on my scale.
 
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Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Hi guys! New EPISODE, easy test !
Learn how to check your suspension sensitivity and how to measure its breakaway force.

Thanks for sharing, this is very cool.

Can you share some data from your simple DAQ experiments showing the percentage of time over a run (on a rough track, ideally with not too many jumps) that both F/R suspension is in the 0-15% travel range (or negative travel range as you call it)?

@kidwoo @djjohnr @buckoW
I think this is useful and it puts some actual numbers on what I was talking about.
The part from 9:00 - 11:00 goes into depth about the practical importance and the ideal scenario.
 

StiHacka

Compensating for something
Jan 4, 2013
21,560
12,506
In hell. Welcome!
Not sure if related but can the IFP pressure in the piggyback play a role here, too? It's how I test if still charged with N2 - without spring, I push the shock against a weight scale. ~40lbs is desired for my Avy shock, according to Craig.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Not sure if related but can the IFP pressure in the piggyback play a role here, too?
Definitely, you can calculate it really easily too, worked examples at bottom of this post.
It's a useful consideration on shocks with adjustable IFP pressure, with lower pressures being better unless you explicitly need it higher for some reason.
 

djjohnr

Turbo Monkey
Apr 21, 2002
3,054
1,768
Northern California
@kidwoo @djjohnr @buckoW
I think this is useful and it puts some actual numbers on what I was talking about.
The part from 9:00 - 11:00 goes into depth about the practical importance and the ideal scenario.
Udi - yes, in order to get as close as possible to achieving zero breakaway force with an air shock you'd want a linkage rate that offsets that force as much as possible.

Pragmatically speaking - I don't think the forces we're talking about with the latest air shocks are a detriment to the riding experience.

Some data - I performed the scale workflow andrextr laid out and here are my results:

Shock - Fox Float X2 on a Knolly Delirium
Fork - '15 Fox 36 w/ '16 cart

Weight of rear uncompressed: 17.4 lbs
Rear slightly compressed: 42.8 lbs

Weight of front uncompressed: 16.0 lbs
Front slightly compressed: 42.6 lbs

So the breakaway force between the front and rear of the bike to be basically even; the bike feels balanced. Now you could argue that the breakaway force of the latest air forks is still too high, although I would disagree. The ride experience is more then good enough for me, YMMV.
 
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andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hi guys! I will take note of the values and share the results in a future video.

Yes IFP pressure and shaft diameter affects the IFP-derived breakaway force. I will talk about that in another episode. But just multiply the IFP pressure (in PSI) by the shaft sectional area (in square inches) to get the breakaway force result in pounds. I already did the math (considering that my bike has an initial leverate ratio of 3.5) and the theoretical values matches very well with the real value. (actually propedal also increases the breakaway force by 10 kg but it's a different effect and I will talk about that in another episode... lol)

Udi, do you mean telemetry data from that data acquisition video?

Sorry I have to leave now, I will reply better later. :)
 
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Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Udi, do you mean telemetry data from that data acquisition video?
Yes, particularly in the scenario and region of travel that I mentioned, if you have some raw output in a spreadsheet or something from your program - time vs. position in travel.

Now you could argue that the breakaway force of the latest air forks is still too high, although I would disagree. The ride experience is more then good enough for me, YMMV.
You're still missing the point that good enough /= the best. Why purposely strive for mediocrity?

I'm not saying your bike sucks (at all), but I'd rather shoot for the stars. Of course I'd argue that breakway force on air forks is too high (ridden virtually all), and unfortunately disagreeing doesn't make you correct. The video explains why in sufficient detail.

Food for thought:
The moment everyone settles for mediocrity, is the moment that progression stops. Many would have said air spring technology was "good enough for them" 8 years ago, but if everyone said that, you wouldn't have your new Pike/36/etc with a substantial improvement in linearity. I say let's keep going, we're not there yet.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
@MmmBones

Actually I don't know that system, so probably I understood it wrong, but looking for the schematic diagram it seems a interesting concept, but I'm afraid that it offers some problems... Namely the rebound and compression damping amount are equal in that system... In fact, you need much more amount of rebound damping than compression damping... Typically the amount of rebound damping is 2-3 times higher than compression damping. By the simple fact that during the compression motion most of the energy of the bump goes to the spring (while a fraction of that energy is dissipated by the compression damping), while during the rebound motion, all energy stored in the spring needs to be dissipated by the damper. So, rebound damping coefficients are higher than compression ones, thus, ~70% of all heat produced by the damper occurs during the rebound phase. PS: Ok, I checked on wikipedia and it seems that this design can use alternative tricks such as check valves to solve this problem of compression vs rebound: https://en.wikipedia.org/wiki/Oleo_strut

So, without dyno data I don't know exactly what to think about it... It's the first time that I see that, I don't have an opinion for now :)

@Udi
I don't have many "telemetry" data yet, because I don't own a GoPro (I have to borrow from my friends)... But I have some shock histogram data from a trail here in Portugal, it's not a very bumpy trail, and the data is not the most accurate (filmed with 60fps, instead of 120fps, with a bit of distortion angle). But, I guess we can have a good ideia.... This data was obtained from a friend's movie. It's interesting to note that there is an asymmetry between LSR and LSC. Indeed, my friend filmed this before watching my Ep.5 of rebound tuning, so we had a crazy fast rebound speed on his bike (low LSR damping), this is why there is an asymmetry. Now we already tuned his rebound properly.

But answering you question, it depends on the "bumpiness" of the trail, but I would say that our suspension spends around 30% of the time in the "negative travel" (below SAG). Note that the 15mm position was the SAG zone. The vertical scale is the frequency in % ! So, it represent the relative percentage of time spent on that travel (or velocity) region, during the full trail.

Sem Título.jpg



Off-topic: You can watch my video on this "Burros" trail, where I crashed into a XC rider.... lol :D


Bye :)
 
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Flo33

Turbo Monkey
Mar 3, 2015
2,092
1,319
Styria
Assuming a sag point around 15 - 16 mm he spent 25 % of the riding below sag, 25 % at sag. To state that sensitivity below sag is of no importance is, ahm, interesting. Like Steve M told and tells everybody.

I have to get hold of a gopro. This is to my nerdy liking.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
This data was on a "flowly" trail. In a fast & bumpy/rocky trail the histogram will shift more towards a 50/50% scenario. So the initial sensitivity is very important, and all manufacturers are working in the direction of decreasing the breakaway force (indeed, to reduce IFP-derived breakaway the EXT ARMA uses very low IFP pressure; the Ohlins TTX and DVO Jade uses a bladder, and the Vivid uses a negative coil spring behind the main piston of the damper). All of that in order to reduce breakaway.

With zero breakaway force, the wheel stays better planted to the ground because the shock absorbs the tiny impacts. Indeed, the drop-test is great to simulate and test how the bike reacts to a fast and small impact. I will talk in more detail about this in another video. But I can tell you that the drop-test creates a impact force of 20-40 kg (45 - 90 pounds of force) on the rear wheel, depending on the height that you release the bike (so it compresses 15-25% of the travel). And produces a max compression velocity in the shock of 30 IPS (which is a very high-speed comp velocity, similar to a fast hit on a square edge bump).

Bye
 
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Flo33

Turbo Monkey
Mar 3, 2015
2,092
1,319
Styria
You ever ride an old original fox float before they had any kind of appreciable negative spring?
No, not really. I remember riding a 2001 or so Stumpy on tarmac. Doesn't count at all and can't remember anymore. My first real air shock experience was an 05 Enduro with 5th Element air shock. I bought my first air shock equipped bike around Oct 2008 and it had an X-Fusion O2. Prior to that I always rode steel springs or hardtails.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
@Udi
I don't have many "telemetry" data yet, because I don't own a GoPro (I have to borrow from my friends)... But I have some shock histogram data from a trail here in Portugal
View attachment 121714
So the initial sensitivity is very important, and all manufacturers are working in the direction of decreasing the breakaway force. With zero breakaway force, the wheel stays better planted to the ground because the shock absorbs the tiny impacts.
Excellent, thanks for sharing that, it's exactly what I was looking for and confirms my thoughts.

To state that sensitivity below sag is of no importance is, ahm, interesting.
Agreed. Luckily for us, and as I said before, stating something doesn't make it true. :)
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
So the breakaway force between the front and rear of the bike to be basically even; the bike feels balanced. Now you could argue that the breakaway force of the latest air forks is still too high, although I would disagree. The ride experience is more then good enough for me, YMMV.
Hi Djjohnr, actually for the front fork, you have to do a trick in the weight scale method :) Indeed, the breakaway force is the result of Preload (static force) + Stiction. Since the fork has a angle of ~65º, by using the weigth scale test you are applying vertical force, thus you create extra stiction on the fork bushings. For the rear suspension you don't have this problem.

So to measure breakaway force in the front fork the scale needs to be perpendicular to the fork. So, just put the rear wheel on top of a box :) I believe that you might get a lower value with this method :) Bye
 

djjohnr

Turbo Monkey
Apr 21, 2002
3,054
1,768
Northern California
Hi Djjohnr, actually for the front fork, you have to do a trick in the weight scale method :) Indeed, the breakaway force is the result of Preload (static force) + Stiction. Since the fork has a angle of ~65º, by using the weigth scale test you are applying vertical force, thus you create extra stiction on the fork bushings. For the rear suspension you don't have this problem.

So to measure breakaway force in the front fork the scale needs to be perpendicular to the fork. So, just put the rear wheel on top of a box :) I believe that you might get a lower value with this method :) Bye
Andrextr, while that would be a more accurate measure of breakaway in a perfect scenario, that's not what happens on the trail. What you'd really want is a measurement that takes into account average trail conditions.
 
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andrextr

Chimp
Aug 6, 2007
63
67
Portugal
@djjohnr Actually in the trail the impact angles are rarely vertical (maybe on flat drop's they are close to 90º).



Higher the bump the more horizontal the force direction will be. If you crash into a wall it will be fully horizontal :D

Indeed headangle affects how the fork reacts to bumps. So, a 65º headangle works with a maximum sensitivity on a 25º bump angle (somewhere between the 2nd and 3rd example on the pic). Bye :)
 
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djjohnr

Turbo Monkey
Apr 21, 2002
3,054
1,768
Northern California
Yes, that amounts to what I just said - measuring breakaway at a perfect 90 degree angle isn't an accurate representation of a trail impact. In the real world you will have resistance from the bushings as you pointed out earlier.
 

Flo33

Turbo Monkey
Mar 3, 2015
2,092
1,319
Styria
What's the point of measuring the breakaway force at trail conditions? No trail is similar to any other one.

I think it's about getting comparable results for different forks and fork models. And Andre's method seems to do pretty OK at this task. It eliminates the difference in force vectors influenced by fork lenght and steering angle. As a result you can tell which fork is basically smoother at a comparable basis. Of course you can't eliminate the neg effects of bushings play and stiffness flaws causing misaligned bushings, but I think that's not the point. There is another variable on the trail, you and position of your CM in relation to your handlebars.

So let's stick to Andre's bodyscaled bike on blocks/boxes and see which fork has the lowest.

A friend of mine is fiddling with acceleration sensors connected to a Bluetooth radio to collect data from the handlebars. All in early alpha atm.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Did the front fork test with the box thing, it gave me a slightly lower value (24 vs 20 lbs, on a RS Domain dual crown), but the experiment is not so easy and reproducible. I prefer the rear suspension one :)

Regarding the Rear Shock breakaway, already have 8 values from people, all of them from traditional IFP-shocks, and the breakaway forces are very similar between them (around 35 pounds). Which strongly indicates that the major player here is the IFP-derived breakaway forces..... If any of you have a ROCKSHOX VIVID, a DVO JADE or an OHLINS TTX, please send me the data to compare with traditional shocks! :) Bye
 
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djjohnr

Turbo Monkey
Apr 21, 2002
3,054
1,768
Northern California
What's the point of measuring the breakaway force at trail conditions? No trail is similar to any other one.

I think it's about getting comparable results for different forks and fork models. And Andre's method seems to do pretty OK at this task.
It depends on what your goal is. For what you described (comparing shocks/forks) the method works well. If however you are trying to measure/compare front/rear breakaway force while also accounting for bushing friction you'd want to know how much friction you'd need to account for. I'm not advocating doing this, just pointing it out.
 

djjohnr

Turbo Monkey
Apr 21, 2002
3,054
1,768
Northern California
Assuming a sag point around 15 - 16 mm he spent 25 % of the riding below sag, 25 % at sag. To state that sensitivity below sag is of no importance is, ahm, interesting. Like Steve M told and tells everybody.

I have to get hold of a gopro. This is to my nerdy liking.
Did someone state that sensitivity below sag is of no importance?
 

Flo33

Turbo Monkey
Mar 3, 2015
2,092
1,319
Styria
It depends on what your goal is. For what you described (comparing shocks/forks) the method works well. If however you are trying to measure/compare front/rear breakaway force while also accounting for bushing friction you'd want to know how much friction you'd need to account for. I'm not advocating doing this, just pointing it out.
True that. I was thinking about a method to compensate by adding another measurement with a scale perpendicular to the floor, in riding direction. You would get two force vectors. I'm having a cold and just too tired to think about it properly...

Did someone state that sensitivity below sag is of no importance?
Maybe :D
 
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andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Since there is some confusion about negative air springs volume/pressure vs breakaway vs sensitivity, I just want to upload this picture to explain the differences... I will talk about this on a future episode. Bye :)
Neg Chamber (Large).jpg
 
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