yeti-sb150-explained.jpg
VIDEO

Suspension Analysis - Yeti SB150

Words Cam McRae
Video Trail POV
Date Feb 28, 2020
Reading time

This local guy is following in the footsteps of Andrextr on youtube by trying to demystify some of the more complex elements of mountain bike suspension. I'm no engineer, but my consultation with Uncle Dave, one of our resident engineers (we have 3 contributors who match that description) suggests this guy has the broad strokes "mostly right."

I can confirm his analysis of the Yeti SB150 match my on trail observations, so either we're both wrong or we've both nailed it. He's also got videos on the Santa Cruz Megatower, Scott Ransom, and Ibis Ripley. You can find them all here. While I put a decent amount of time on the Megatower I really need some time on my local trails to give a more comprehensive verdict.

Armchair enginerds, please give us your verdict on this gentleman's conclusions.

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Comments

fartymarty
0
fartymarty  - Feb. 28, 2020, 7:24 a.m.

It would be interesting to see how different this is from a single pivot - say something like a Starling.

Reply

shoreboy
-2 BkrAdam Dan V
Shoreboy  - Feb. 28, 2020, 9:02 a.m.

I think I remember reading that the Starling has a very linear (even somewhat regressive) leverage ratio.  This means you will need a shock with plenty of progressivity to stop it from blowing through its travel. Being a pure single pivot, it is going to have high levels of pedal feedback, and the rear end is going to noticeably firm up under braking.

Reply

xy9ine
+2 Pete Roggeman Andrew Major
Perry Schebel  - Feb. 28, 2020, 12:01 p.m.

i've ridden a yeti 5.5 & starling (both reviews on NSMB) - though not back to back. the starling did have a bit less end stroke ramp for sure, but not something that couldn't be tuned around. pedal feedback / braking were non issues for both bikes. both fun bikes, though i preferred the handling of the starling a bit more (esp. in corners), which trumped any difference in suspension performance. one man's opinion, of course.

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shoreboy
-1 Ron Chang
Shoreboy  - Feb. 28, 2020, 12:18 p.m.

Riding is always the best proof. If you have ridden both, then you are in a strong position to know how they both ride. I was only stating what the graphs and numbers say about the Starling and it’s suspension design.   How it feels when you ride it is a different question.

Reply

fartymarty
+1 Pete Roggeman
fartymarty  - Feb. 29, 2020, 4:57 a.m.

Perry, it was a slightly loaded question as I ride a Murmur.  Steve Jones review confirmed my I initial thoughts and your review sealed the deal for buying it.

I know the answer but am always curious to know if all these fancy linkages and sliders (read very marketable) most bikes have are worth the added maintenance time and cost (and also initial cost) compared to a simple single pivot.  Or is it simply marketing and marginal differences at best.

I'm a firm believer you are best to spend the extra money on a Storia V3 (or similar v. high end shock) which I will do one day when funds permit.  Keep the frame simple and let the shock do the magic.

Reply

Varaxis
+1 Jerry Willows
Dan V  - Feb. 28, 2020, 12:45 p.m.

I have a single pivot like the Starling.

Very linear is accurate. Can get it to be somewhat progressive if the forward shock mount was lower, such as if you ran a shorter length shock to fit better, but it's so slight that it don't matter. If it were mounted to the top tube, it'd be somewhat regressive, but it'd be more accurate to call it linear still.

You don't need progressivity to stop it from blowing through its travel. You want progressivity if you want it to blow through travel, such as wanting it to be plush running a lot of sag. I see no problem running coil, but going to need a firmer/racier spring rate, which gets chassis stability (geo retention) and efficiency over cushiness.

It has an imperceptibly similar level of pedal feedback compared to a majority of other susp like this Yeti. The Yeti, and some VPP, have a slightly difference in that it drops off harsh pedal feedback for the last 30% of travel. I suppose this little bit matters when you're after fractions of a second to win races.

It preserves geometry under braking, meaning it better balances out the forward rotation that causes the fork to dive, just like the Yeti. In other words, it more completely cancels out brake jack, which is the tendency for the rear end to extend under braking (hence why it's called anti-rise, or brake squat).

Single pivots have a more rearward axle path. They can be more precise, suffering from less torsion and tail wag (fewer pivots, less play, between pivot and rear axle). They're more hardcore than horst links. GG argued there was no benefit with Horst Link, and that they could simply mimic their single pivot kinematics with it. There's a world of difference between a Knolly 4x4 (or Liteville horst link) and a GG horst link. Not so much difference between GG's horst link, Switch Infinity, and Starling single pivot.

Tantrum Missing Link is one of the few innovative linkage designs. It happens to be regressive and needs a progressive shock (DVO Topaz is a good choice), but it's the only one that stands out from the crowd. In contrast, the vast majority behave similarly. Not much difference among single pivots like Trek, Evil, Marin, Cotic, etc. and 4 bars like CBF, VPP, etc.

The draw to the Starling design is its chassis stiffnesss characteristics. It has a forgiving springiness. It's carries its weight really well--the steel frame does a lot to negate pedal feedback.

Reply

andy-eunson
0
Andy Eunson  - Feb. 28, 2020, 8:47 a.m.

Did he say seal friction increases with pressure increases? Really?

Reply

cam@nsmb.com
+1 AJ Barlas
Cam McRae  - Feb. 28, 2020, 12:36 p.m.

It would make sense to say that it is more difficult to overcome seal friction as pressure increases, but seal friction at a given point should be related to velocity shouldn't it? Which will be impacted by pressure. But the friction of the seal itself should be independent of pressure within the system. I think. Maybe. Sort of. #lettheenginerdsspeak

Reply

davetolnai
+3 Andrew Major AJ Barlas Cam McRae
Dave Tolnai  - Feb. 28, 2020, 5:35 p.m.

Ya, I don't know about this one.  I'm sure there is somebody at either Fox or Rock Shox that could speak about this endlessly.

As trailpovguide points out, there probably is a good argument that higher spring pressures cause higher absolute friction on a shock shaft.  However, if we're talking about a higher leverage bike, which by definition has higher forces acting upon the shock, this becomes less clear.  It seems to me the relative friction (i.e. how much friction is the seal exerting on the shaft relative to the force handled by the shock) would be the most important thing.  Does this relative friction force go up higher relative to the increased forces on the suspension, or are these friction forces actually dwarfed by everything else going on as the pressures go up?  Does the relationship remain linear?  What about the differences in shaft speed in a high/low leverage system?

My guess is there's no simple answer for this, and if there were, we'd have all the shock companies working to figure out ways to lower their pressures as much as possible.

Reply

trailpovguide
+1 Jerry Willows
trailpovguide  - Feb. 28, 2020, 6:33 p.m.

Hi Dave, all good points. I definitely don't claim to be a shock internals expert (Fox and Rockshox engineers have many more years of experience in this area). My claim about friction came from my personal experience with seals in a pressure regulator I was designing as well as a few articles I had read specifically about this subject.

It should be noted that high leverage ratios also lead to the shock moving slower that with a low leverage ratio and thus having less damping forces. This requires different shims to account for the low damping forces to ensure the system isn't a pogo stick. But this get's way too deep for an 8min video :)

Reply

trailpovguide
+1 Andy Eunson
trailpovguide  - Feb. 28, 2020, 2:26 p.m.

Hi Andy, two things are at play with seal friction:

1. In order to keep in higher pressures the seal often needs to be tighter to ensure that air can't deform and squeeze past the seal.

2. The high pressure air also pushes against the wall of the seal causing it to flatten and exert more pressure on the shaft of the shock.

Reply

robnow
0
robnow  - Feb. 28, 2020, 7:05 p.m.

I think we all get that but the question comes up when you have the HIGH leverage of the kinematics working against the shock to overcome the higher pressures. Norco even markets this with the new Sight/Optic and their short strokes/high leverages as having great small bump compliance. Seems to me though the trend for most Enduro and DH is going to longer stroke lengths (mainly for higher oil and less suspension fade?).

Reply

RoboDuck
0
RoboDuck  - Feb. 29, 2020, 1:31 p.m.

It does. As someone else said the air pressure forces the seal onto the shaft hard. However to go and make a claim for any sort of leverage ratio from this wildy mistates the situation. 

The seal forces will be completely overdriven by damper/spring effects from the leverage curve. Higher leverage allows the suspension to push through any seal friction at a much higher proportion than the seal friction is increased by running higher pressures. 

Notably Rockshox justified the use of larger pistons in the Deluxe/SD lineup in order to allow lower pressures to be run for the same shock force in order to reduce seal friction. This is more of a shock design parameter than a bike design one. Shaft diameter (and therefor seal contact area) also has an influence on seal friction and will offset some of the benefits of larger pistons.

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tehllama42
0
Tehllama42  - March 4, 2020, 8:21 a.m.

Technically yes, perceptibly the answer should be no.  At higher pressures a bit more of the compliance stack related to tire/wheel/frame give will soak up a bit more of the energy before overcoming the stiction contributions from seals, but again those are the kind of difference that will happily hide under the inevitability that most of us aren't rebuilding our suspension on a monthly basis (or yearly, if I'm honest).

There are relevant figures of merit such as the damper hysteresis which sound terribly impressive, but are at best a way of squeezing out the last 5% of possible performance on a system where most of the time the dials, pressures, and volumes are much further off because of the vagaries of click spacing, gauge accuracy, temperature, and mostly users who are rarely savvy enough (myself included) and often partial to the feel of a suboptimal setup because it's just more consistent.   

As a big heavy oaf, I always appreciate systems with leverage that doesn't have me straining my hand with a suspension pump to get myself up towards the 30% sag mark (245lb riding weight here), and have me worrying about exploding seals (Santa Cruz bikes with X2 shocks jump to mind here), and those tend to come on more overbuilt bikes are a rule which helps for my riding style (all the speed low talent and high commitment can support)

Reply

davetolnai
+3 Jerry Willows Andrew Major twk
Dave Tolnai  - Feb. 28, 2020, 5:52 p.m.

I see the Cam threw me under the bus with my tepid endorsement that I provided late last night after skimming through this video.  I believe my words were “nice graphics and it seems mostly right.  He got some stuff wrong about single pivots though.”

First, the good.  I don’t watch many/any videos like this on the Internet, so I’m not sure if anybody else is doing things like this, but I really liked his animations that demonstrate the graphical method for anti-squat/anti-rise.  I’ve never seen it shown like that and I really appreciate watching how those things change as the bike moves through travel.  It tends to be a lot of lines pointing at shit, but it’s kind of cool.

I haven’t done an in depth analysis of this bike, but his conclusions that he draws on anti-rise, anti-squat and leverage ratio seem to be mostly right.  There are a couple of really big howevers, though:

First, I tend to be really suspicious of anybody making really binary claims from these analyses.  There’s no perfect anti-squat number.  We all ride differently.  We all have different preferences.  Shit, even if you take these numbers as gospel, we all have a different center of gravity.  I have a real problem any time anybody makes claims about having the perfect anti-squat numbers.  Same goes for anti-rise.

Next, there were a couple of incorrect conclusions drawn about single pivot bikes.  The big one for me was stating that a single pivot bike has a flat leverage curve.  This is not necessarily true, and I think this is a mis-interpretation.  Yes, single pivot bikes tend to have fairly straight leverage curves, but not necessarily flat.  What's the difference?  Straight means that your leverage ratio has a steady rate of change.  Flat means that it remains constant.

Have a look at the curves for these 3 single pivot Oranges, for some examples:

Orange 5 - Straight but falling - http://linkagedesign.blogspot.com/2016/08/orange-five-275-207.html

Orange Alpine - Straight and flat -  http://linkagedesign.blogspot.com/2016/08/orange-alpine-6-275-2017.html

Orange 324 - Straight and rising - http://linkagedesign.blogspot.com/2018/04/orange-324-rs-275-2018.html

Straight =/= flat

Beyond that, there are some differences in the analysis done here compared to the Spanish Linkage Blog.

http://linkagedesign.blogspot.com/2019/09/yeti-sb-150-29-2019.html

This video is much prettier, but who is right?  This is the second time I've cut and pasted this in to something today:

¯\(ツ)

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trailpovguide
0
trailpovguide  - Feb. 28, 2020, 6:37 p.m.

Hi again Dave, again all good points. I'm trying to make these videos to provide good info for the masses without going into ever single detail, because viewers often don't care about the nuances. Certainly the Orange has a flat + linear leverage ratio because the shock is almost inline with the movement of the pivot it's attached to. If the shock were to be placed at a 45 degree angle to the pivot mount (like some bikes from the 90s) then the leverage curve would indeed be linear but sloping either regressive or progressive. Additionally, if one moves toward a linkage driven single pivot such as the Delta system by Evil Bikes, then you end up with a leverage ratio that is super bizarre and not even linear, even though it's still technically a single-pivot.

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davetolnai
0
Dave Tolnai  - Feb. 28, 2020, 9:18 p.m.

Ya, I can totally appreciate the challenge of breaking down technical stuff for a mass audience.  Like I said, I think your animations are some of the clearest explanations I've seen.  Cool stuff.

Reply

dan_l
0
dan_l  - Feb. 29, 2020, 10:02 a.m.

I think the information was technically correct and presented in a clear manner. I really like kinematic reviews like this because it gives me ideas on what to try should I want my bike to operate differently. I've been interested in the lower link VPP kinematics but haven't seen anything for the V3 Bronson. The Mega Tower is probably close to the Bronson so I watched that video first.

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tehllama42
0
Tehllama42  - March 4, 2020, 8:24 a.m.

The engineer in me would insist that it wasn't entirely technically correct, but for the intended audience was broadly correct and far more useful than the more precise pedantry that my ilk tends towards.

I would actually like to see a longer in-depth breakdown with more precise detail and nuance (kinda like a 40-minute SME breakdown talk), but to keep seeing a lot of the wider audience friendly analysis all of which can keep pointing back to that longer video for connoisseurs and others that want to know more in depth.
I also think we got quite a bit spoiled with the Vorsprung Tuesday Suspension talk series... which might be a handy supplement.

Reply

cam@nsmb.com
+1 dan_l
Cam McRae  - Feb. 28, 2020, 11:02 p.m.

TBF you live under a bus. And TB even more fair, it's not accurate to say I threw you under the bus by quoting you verbatim but not ad nauseum or exhaustively.

Next time I will use more of your words though.

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davetolnai
+1 Cam McRae
Dave Tolnai  - March 2, 2020, 9:18 a.m.

It was a friendly bus.  A soft one.

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LoamtoHome
+1 twk
Jerry Willows  - March 2, 2020, 10:09 a.m.

is it a short one?

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tehllama42
+1 Cam McRae
Tehllama42  - March 4, 2020, 8:25 a.m.

I wasn't on it for a change, so I'm not sure.

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cam@nsmb.com
0
Cam McRae  - Feb. 28, 2020, 11:02 p.m.

This comment has been removed.

tehllama42
0
Tehllama42  - March 4, 2020, 8:34 a.m.

I really enjoy being able to see relevant wheel rate charts and compare those side to side - especially since I can pull up some of the various volume spacer trends/tendencies from separate charts and see just how much overlap is realistically possible.
Pivot locations, and linkage-driven variants can all modify the leverage curves for linkage driven, but that mirrors my opinions on those that it's a linear leverage ratio curve, but flat is actually somewhat difficult to achieve (and never desirable anyway).  In a lot of regards, this simplicity can actually provide a fair bit of value with appropriately matched damper setups, especially for linkage driven variants where more can be done for the initial wheel rate, and realistically the deeper travel segments are going to be close enough to become dominanted by suspension tune anyway.  I do think that the multi-link driven single pivots (of which DELTA is a great example) might as well be handled as a completely separate animal.

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