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[Videos] MTB Rear suspension series

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Vrock are you Antonio Osuna?

Thanks for sharing your knowledge :)

As a curiosity, do you know any example here the CC is not within the IC-axle line? I know this is very "nerdy", and I don't want to go super tech with this, but it's just a curiosity.
 

Vrock

Linkage Design Blog
Aug 13, 2005
276
59
Spain
Yes it's me.

CC it's always in the same line, but people only use this term when they want to argue that one system works almost the same as another and that's just bullshit. It's 2016 and we have to be precise.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Yes, I agree. Many people think the CC is the virtual pivot, and there are even some brands that contribute to that confusion.... Like the usual G brand...






To be fully clear to everyone, the point 2 of the image is not the IC. It's the center of curvature (CC), and you can basically ignore that point for simplicity (and the G marketing claims also... :D )
 
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Mo(n)arch

Turbo Monkey
Dec 27, 2010
4,444
1,431
Italy/south Tyrol
But it's moar efficient?!:think:;)
BTW, do you already have a video about the Giant Glory 27,5" posted?
Really interested in that frame for the future. Because efficient.
 

hmcleay

i-track suspension
Apr 28, 2008
117
116
Adelaide, Australia
I think I figured it out (with some days of riding).

In a static world, those bikes that have 130-100% of AS would be just fine pedaling uphill, this means that you have a completely smooth surface with no grade changes and the suspension never activates.

The issue is many of those bikes have a falling AS curve/rate that drops off rapidly, as you go through say half the travel, the amount of AS goes way way down, 30% or less (just throwing that out, but common with many linkage bikes).

As you ride over bumps, roots, etc, your suspension compresses, if you try to keep pedaling, all of a sudden it's a wet-mattress effect as your pedaling input keeps the shock compressed. Probably not much of an affect downhill, but uphill pretty huge. In reality, the suspension is working all the time, maybe a soft 2" bump, or a 4" root, the suspension activates to a large extent, maybe going through 60-75% of travel on rocky uphills, but even on more moderate ones it probably still uses at least half the travel frequently. Possibly a little bit of weight-transfer "bob" will even start to affect this, depending on the bike of course. That's where it's not really telling the full story, because our rides are not static and this is where I notice that I can just "keep pedaling" and accelerating over the bumps on a bike with a 100-130% flat AS line.

From the video and website, the reign isn't a great example, because it has a significantly falling AS curve as well, so both the reign and the Enduro would suffer from the same basic issue, with the enduro being a little less through the travel according to the figures. Look at Yeti or modern DWs to see the difference.

The linkage website seems to only be qualifying the "pedaling" or "efficiency" at the sag point.
What you're describing there is something I've been going on about for a few years now.
The slope of the AS curve (not just the value) has a significant impact on the pedalling performance.
If the AS curve increases with suspension travel, then it has the effect of increasing the wheel rate when pedalling.
If the AS curve decreases with suspension travel, then it has the effect of decreasing the wheel rate when pedalling.
In contrast, the AS value (not slope) determines how much additional wheel force (not rate) there is when pedalling.
You can think of it like this: AS value increases your spring preload, and AS curve increases your spring rate.

Many bikes have an AS curve that decreases with suspension travel, which significantly reduces your wheel rate when pedalling.
This is hardly ideal, at a time when your rear wheel is carrying a significant % of your mass (due to weight transfer), and results in your "wet-matress" effect.
 

hmcleay

i-track suspension
Apr 28, 2008
117
116
Adelaide, Australia
I'd also like to reinforce what andrextr and Vrock have already pointed out.

The 'Centre of Curvature' (CC) metric in Linkage is meaningless.
By definition, the true centre of curvature is the Instant Centre (IC).

Linkage calculates the CC by selecting two consecutive positions of travel, and intersects the the two lines from axle to IC for each position. Therefore, the CC is always on the same line as a line drawn between the axle and IC.
The position of the CC is entirely dependent on the distance between these two 'consecutive' axle positions. In this case, I believe Linkage uses 1mm. But you would get a different CC position if you chose a different distance.
If you were to choose two positions that are infinitely close together (say 0.00001mm), then the CC would approach the position of the IC.

I have pointed this out to the developer of Linkage, and he agrees, and actually removed that feature from the software briefly, before it was soon brought back due to 'popular demand'.

The only potential benefit to the CC metric, is in cases where the IC moves very rapidly through suspension travel.
For example, with Lawwill suspension systems, the IC is behind the rear axle, and moves upwards faster (and further) than the axle moves.
Normally, if you saw an IC behind the rear axle, you'd think that the wheel must have a rearward arc, but this observation doesn't consider that the IC moves faster than the axle. For this situation, the CC calculated between consecutive suspension positions would be positioned in front of the rear axle, allowing you to visualise the axle path curvature more intuitively.
In any case, CC shouldn't be needed to visualise the axle path, because Linkage already draws the axle path for you!
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Thank you hmcleay for sharing your knowledge :) Nice to see here so many deep content :)

As you point out, CC can also be helpful to visualize the IC movement in more exotic cases, such as the Rocky mountain maiden, here the IC also starts behind the wheel, then it goes back to the infinite and then it shifts to the "front" infinite after the links being parallel ... :D

 

Jm_

sled dog's bollocks
Jan 14, 2002
19,449
10,081
AK
What you're describing there is something I've been going on about for a few years now.
The slope of the AS curve (not just the value) has a significant impact on the pedalling performance.
If the AS curve increases with suspension travel, then it has the effect of increasing the wheel rate when pedalling.
If the AS curve decreases with suspension travel, then it has the effect of decreasing the wheel rate when pedalling.
In contrast, the AS value (not slope) determines how much additional wheel force (not rate) there is when pedalling.
You can think of it like this: AS value increases your spring preload, and AS curve increases your spring rate.

Many bikes have an AS curve that decreases with suspension travel, which significantly reduces your wheel rate when pedalling.
This is hardly ideal, at a time when your rear wheel is carrying a significant % of your mass (due to weight transfer), and results in your "wet-matress" effect.
Yes, to put it in operational terms, you are pedaling along uphill and a root comes up, you keep pedaling and the suspension compresses maybe through half of it's travel, because it's a low speed event. At that point, all of a sudden, you need a lot more pedaling-force to keep the bike moving the same speed, and due to the significantly reduced AS, less of your pedaling energy goes to moving you forward, since a percentage is going towards keeping the shock compressed (squat) even more. Now do the same with multiple roots and rocks and all of a sudden you are having to power through that tech section with much more power as the rear end dives with each impact under power, unweighting the front end significantly. In other words, with a significantly decreasing AS curve, it's going to make the bike use more travel than it should while pedaling through such terrain and possibly cause you to stall out as it slows due to more energy going towards keeping the shock compressed or the front end wandering. Of course, you can have a relatively "flat" AS curve through the travel, which is what I'm experiencing now, but it's definitely a huge departure from the ones that drop off. Then you have to think about when you get tired and your pedal strokes get more jerky, contributing to more chassis movement that could active the rear suspension or sprinting, which will do the same. Again it will have an impact and make a noticeable difference between the falling AS-curve bikes.

But the linkage site seems to keep describing the ones that have 90-130% AS at the sag point as "excellent pedaling", no matter what happens after the sag point.
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
I'm not sure if I understand the previous comment, but.... I will bring my view to the table:

A lower anti-squat doesn't mean that the pedaling force compress the suspension. That only happens with negative anti-squat values (in this case, chain tension compresses the suspension. eg; Specialized Demo on lower rear cogs). For anti-squats higher than 0%, the chain tension is trying to extend the suspension. With a 50% AS for instance, it means that chain tension is not able to extend the suspension enough to fully counteract the squat caused by the acceleration. However, a 50% AS will bob less than a 0% AS. With a 50% AS the chain is still trying to extend the suspension and counteract the squat. With a 0% AS, the suspension is fully neutral to pedaling forces. With a 300% AS for instance, the chain tension extends so much the suspension that you get pedal bob caused by extension and not squat (for each pedal stroke the suspension extends and lifts your weight up).

So, if you have a falling AS rate after SAG, it means that chain tension decreases a bit it's ability to extend the suspension. But it still extends... Unless it goes to negative AS values... So, although a stable AS 100% around the SAG zone is the ideal scenario (constant pedaling efficiency), I still don't think that a falling AS is a very problematic scenario (the efficiency might change a bit, but you still have plenty of it)... Unless you have a extreme falling rate around SAG... but that's not very comum.
That's my view as an enthusiastic (not an expert...).

Bye
 
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Vrock

Linkage Design Blog
Aug 13, 2005
276
59
Spain
Hugh is a bit biased because he is always riding and designing bikes with a lot of AS and very little PK... :D
For the rest of the world PK is a problem and bikes with lowish AS numbers and steep AS curves work pretty good when the trail gets very complicated...
 

andrextr

Chimp
Aug 6, 2007
63
67
Portugal
Hello people :)

Just want to share a quick video about the brake-squat effect principle, I know that these type of videos were already done, but it's always nice to see it. It would even nicer to do this with a bike with a IC below the ground to see the jack effect (extension of the suspension). If anyone has a SC Nomad and wants to try these things, then doing this test at bottom-out it might result in jack effect... (please film that) :)


I also know that some experts have the opinion that these videos don't make sense because of not considering the ground, and I understand their point, but actually, this is valid and it shows the basic principle of the brake-induced squat. For the anti-rise percentage value calculation then you need to consider the ground, wheelbase and center of mass height (this basically accounts for the Rise effect caused mainly by rider weight transfer, which you need to know in order to determine the anti-rise value as a percentage, being the anti-rise forces those shown on the video)...

Bye :)
 
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Jm_

sled dog's bollocks
Jan 14, 2002
19,449
10,081
AK
With a 50% AS for instance, it means that chain tension is not able to extend the suspension enough to fully counteract the squat caused by the acceleration
And key for me is that every pedal stroke is an acceleration, more so when your cadence slows down or you really try to jam on the pedals, but even when you are trying to "spin". I don't buy that 0% AS is fully neutral to pedaling because that assumes no acceleration, which is impossible IMO. That's only when you are coasting IMO.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
As Vrock cheekily points out - attempting to have the perfect AS curve on an idler-less bike starts having detrimental PK effects, which for most people (at least in this forum hopefully) is going to be a problem on the more important/enjoyable part of the ride - going downhill.

I'm all for stressing the importance of getting things exactly right - but let's not forget that perfecting one aspect of a bike can have detrimental effects on another (for example idler equipped bikes have historically always been heavier than ones without - I'll be the first person on board when that changes) and often it's important to consider these detriments simultaneously.

However in the same breath - a thing that no one talks about is PK and its relation to forward velocity and hub engagement points. This is a changing relation, and I believe the way kickback is currently discussed (as a very static behaviour) is grossly incorrect. It essentially assumes the bike isn't moving forward at all. Has anyone mapped it out? Perhaps Vrock's dynamic program considers this?
 

Vrock

Linkage Design Blog
Aug 13, 2005
276
59
Spain
I have done a lot of dinamic simulations about this topic, and you don't even need the program to understand how this works... If you are rolling over something while coasting, the wheel need to rotate to go over it, that angle of rotation (+ Hub engagement angle...) is always bigger than the kickback that you get as you compress the suspension, so you don't notice anything (Link). The only way to get some pedal feddback is if you are pedalling through a rock garden, in a very slow drop to flat, casing a double, or landing a jump in the middle of a rock garden and getting the wheel stuck in a hole...
 
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Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,982
1,342
SWE
What you're describing there is something I've been going on about for a few years now.
The slope of the AS curve (not just the value) has a significant impact on the pedalling performance.
If the AS curve increases with suspension travel, then it has the effect of increasing the wheel rate when pedalling.
If the AS curve decreases with suspension travel, then it has the effect of decreasing the wheel rate when pedalling.
In contrast, the AS value (not slope) determines how much additional wheel force (not rate) there is when pedalling.
You can think of it like this: AS value increases your spring preload, and AS curve increases your spring rate.

Many bikes have an AS curve that decreases with suspension travel, which significantly reduces your wheel rate when pedalling.
This is hardly ideal, at a time when your rear wheel is carrying a significant % of your mass (due to weight transfer), and results in your "wet-matress" effect.
I noticed that the I-tracks bikes have mainly an increasing AS curve in the pedalling zone.
What are the advantages of that vs a flat AS curve if both show the same level of AS at SAG, let say 100%?
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,368
6,422
borcester rhymes
I've always thought about that when people discuss pedal kickback. I've almost never felt it on the trail. Most of my bikes stick with high antisquat values and therefore should have some higher degree of pedal kickback, but it's almost only on very steep climbs at very low speeds and happens very rarely, if ever. Maybe I'm unique, but the practical aspect of pedal kickback has almost never materialized in the real world for the same reasons mentioned above. Even with my Evil, which is a relatively high pivot, and my onyx zero-engagement hub, pedal kickback is unnoticeable on the trail. Being able to climb almost anything thanks to aggressive anti-squat values is, however....
 

StiHacka

Compensating for something
Jan 4, 2013
21,560
12,507
In hell. Welcome!
I've always thought about that when people discuss pedal kickback. I've almost never felt it on the trail. Most of my bikes stick with high antisquat values and therefore should have some higher degree of pedal kickback, but it's almost only on very steep climbs at very low speeds and happens very rarely, if ever. Maybe I'm unique, but the practical aspect of pedal kickback has almost never materialized in the real world for the same reasons mentioned above. Even with my Evil, which is a relatively high pivot, and my onyx zero-engagement hub, pedal kickback is unnoticeable on the trail. Being able to climb almost anything thanks to aggressive anti-squat values is, however....
Not even when climbing up ledges / big square edges? I could feel difference between two chainrings on a high single pivot bike, or between frames with high/low AS.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,368
6,422
borcester rhymes
No, because if you're climbing and encounter a big ledge, how often are you simply JRA in the saddle? Most of the time I have to get out of the saddle, even a little bit, to get the wheel over the ledge. That unweights the wheel, unloads the suspension, and mutes kickback. Maybe it's just the technique that I use, or maybe it's all the meat on the pedals, but most of the time there is some balancing force to the force of the pedals coming back, like speed, unweighting, or extra power on the pedals (like from standing up).
 

kidwoo

Artisanal Tweet Curator
Or your bike just bounces or tire skips instead of giving you pedal feedback.

Just because it's not a tangible sensation directly through the cranks, doesn't mean it isn't manifesting itself somewhere. It just takes a lot to overcome the force of a downward pedal stroke. Between moving you and moving the bike, I know which one is lighter. That's not even a fat joke. :D
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,449
10,081
AK
I'm not going to lie and say my DW doesn't feel more firm riding up (under power) over tech stuff, but by the same token I seem to be making that tech stuff relatively easily because the suspension doesn't seem to be bogging down in/at all of the bumps either. It's as if the bikes with significantly lower AS later on in the travel use "moar" travel uphill under power than they should/would, compared to if you were just coasting in the opposite direction. Then when the suspension bogs in those bumps it seems like the bike requires a ton more pedaling force to keep going and although you feel like you have "ultimate traction", you are taking a big hit in other areas.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,368
6,422
borcester rhymes
Or your bike just bounces or tire skips instead of giving you pedal feedback.

Just because it's not a tangible sensation directly through the cranks, doesn't mean it isn't manifesting itself somewhere. It just takes a lot to overcome the force of a downward pedal stroke. Between moving you and moving the bike, I know which one is lighter. That's not even a fat joke. :D
You aren't wrong. Those things absolutely happen, and I'm fat too. I just think that, for a long time, the industry was concerned with pedal kickback as a buzzword, and the reality of PK out on the trail is minimal. I don't really experience the bike bouncing, as that seems to coincide with other motion or speed which mutes it.

I do wonder about tire skipping though. I feel like I've experienced it with both too much anti-squat, but moreso with too little. All of the lower pivot bikes I've owned spun the tires going up dusty climbs when I tried to lay down the power. The worst was an older specialized FSR. That thing couldn't climb at all.
 

kidwoo

Artisanal Tweet Curator
Go try pedaling out of a g-out on an orange frame or some of dw's bikes running too much sag. It's not minimal, it will straight up throw you off the bike. It's especially fun on some of those high forward pivot bikes because it's so easy to be at the end of the travel all the time with their screwed up leverage ratios. It's not that the effect is minimal, it's that you mostly ride bikes that don't completely ignore it in the design so the end result is just that it's not extreme. It depends on the bike, and some of them do suck royally in that respect.

For pedal kickback to happen there has to be tension in the system. The tire gripping and holding is one end of that system, which is why I mentioned it. If your tire slips, that's the relief of that tension, not your knees buckling. That's also why you really notice bikes with a lot of kickback in compression scenarios.....the tire has traction.
 

slimshady

¡Mira, una ardilla!
The discussion in the last posts got me thinking about something I experienced in my last trip to the mountains, a couple of weeks ago. At one point, there were simply too many of us to be shuttled to the top in the back of my friend's Hilux, so we opted to have three of us towed with some ropes tied to the top of the cargo door (one at each side), and one rope tied to the hitch rack mount. When starting to pedal uphill to avoid the slingshot effect from the pickup's start, I felt as if either my rear tire was punctured and very low on air, or as if the rear brake was locked.

This behavior got exacerbated when being towed with the external ropes, which were tied higher, leading to the front end feeling lighter, and my weight being displaced to the rear of the bike. When I looked at the shock of my Rallón, I was well north of the 50% of the stroke, maybe around 60% (with the shock's lightest compression setting). when towed with the center rope, tied significantly lower, the effect was somewhat mitigated.

So I was thinking maybe the PK in that zone led to moar powah being required to move the bike forward, as described in the previous posts.
 

StiHacka

Compensating for something
Jan 4, 2013
21,560
12,507
In hell. Welcome!
This behavior got exacerbated when being towed with the external ropes, which were tied higher, leading to the front end feeling lighter, and my weight being displaced to the rear of the bike. When I looked at the shock of my Rallón, I was well north of the 50% of the stroke, maybe around 60% (with the shock's lightest compression setting). when towed with the center rope, tied significantly lower, the effect was somewhat mitigated.
 

fluider

Monkey
Jun 25, 2008
440
9
Bratislava, Slovakia
You aren't wrong. Those things absolutely happen, and I'm fat too. I just think that, for a long time, the industry was concerned with pedal kickback as a buzzword, and the reality of PK out on the trail is minimal. I don't really experience the bike bouncing, as that seems to coincide with other motion or speed which mutes it.

I do wonder about tire skipping though. I feel like I've experienced it with both too much anti-squat, but moreso with too little. All of the lower pivot bikes I've owned spun the tires going up dusty climbs when I tried to lay down the power. The worst was an older specialized FSR. That thing couldn't climb at all.
For PK, just try to pedal up the rooted trail (with roots tall almost as steps) on a 2x9 drivetrain (but don't tell anyone that you weren't on 1x zilion drivetrain) of a better pedaller like Banshee Rune. Gear in to the granny with one of the biggest sprockets and you'll feel the pedalkickback even while seated. Once you start pedalling hard and roll over the tall root you'll feel strong force pulling your chain back, against your feet. Designs like Banshee Rune require good pedalling technique even on clippless pedals while in granny.

I'd say the older FSR was really low anti-squat design. With low anti-squat, even though you put your power via chain into the rear wheel, but there is weak force keeping the rear wheel against the ground, that's why it starts to spin over.
 

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,982
1,342
SWE
Thanks for the video!
Does it means that there is no such thing as a too big negative spring? beside practical and physical limitations off course
 

Vrock

Linkage Design Blog
Aug 13, 2005
276
59
Spain
Yep, but at some point you are going to need a separate valve to adjust the negative pressure, bypass ports are not the best option.