Why the Master's suspension is terrible, and how to fix it.

[Phi1osopher]

https://youtu.be/tgWxYBd9IAg

My thoughts on what is wrong with the Begode Master's suspension. The video has low production quality, but hopefully unpacks some good information. I want to preference all this by saying my measurements and numbers are approximate. I made quick and reasonably accurate measurements and calculations that should be good enough to initiate an informed conversation. If your numbers are similar but a little different, please let me know.

Basically, the Master's linkage geometry is really really bad and the shock is not good enough for the bad linkage design. Actually no shock is good enough to compensate for the bade linkage design.

Let's talk about the Master's suspension. The Master has 70mm of actual wheel travel (as measured from 5mm top bump stop to 5mm bottom bump stop) and 21mm of shock travel (normally you'd want about 50mm of shock travel). This 70mm to 21mm yields a 3.33:1 wheel-to-shock-travel-ratio, which is incredibly bad -- the worst I've ever seen. A typically decent MTB (mountain bike) will have an approximate 2.5:1 ratio, +/- 0.4. When this ratio is higher a stronger spring is required for any given weight; suspension geometry with lower ratios will require less spring for the same load. This means a heavy MTB rider might seek out a bike whose rear suspension geometry has a lower ratio. Remember EUCs are HEAVY.

The Master's absurd 3.33:1 ratio means it needs a strong spring. How strong? Most calculators I used suggested the Master would require an absurd >2400lb/in rated spring for an approx 220 lb rider. A typical MTB might use a spring closer to 400lb/in. This HUGE spring is a real problem.

This explains why everyone with a Master has to buy a special aftermarket shock pump to over inflate their air shock to >400 psi, even though the shock is only rated up to about 250 psi. Yes, 400-500psi technically will create enough spring pressure to hold up a 220lb rider and mostly reduce bottoming out, but it will also grossly overpower the shock until it has lost all it's value: for instance, the high psi will overwhelm it's compression dampening, and slam back to fully extended, causing constant top outs. these high pressures will physically destroy the shock while utterly ruining any advantageous ride characteristics supposedly provide by having suspension in the first place. Additionally, a mere 21mm of shock travel simply is not enough to make all the magical suspension things happen: good shocks have a lot going on, and all the cool suspension things take time to happen, as measured in millimeters of travel. So, basically, the Master's stock suspension completely sucks.

What can be done about this? One suggestion has been to upgrade the shock. There are a few options out there - basically anything is better than the crappy "190-35" stock shock - but even the best shock in the world can't escape the linkage geometry's 3.33:1 ratio and it's miniscule 21mm of travel. (Remember, changing the shock will do nothing to change the 21mm of travel. The shock travel is determined by the linkage's geometry and the wheel's travel, both of which are effectively unadjustable.) The "190-50 RockShox Monarch" is a pretty good shock at a fair price point, and it definitely should make the Master ride a little better. There is also another inexpensive sub-$100 coil shock out there that is fairly nice and can really help change how the Master rides. But in the end I see these as only band-aids to the more serious problem of the geometry. They can't fix the 3.33 ratio and the horrible 21mm of travel. They just work with it a little better than the stock shock.

So the geometry. Right now the only marketed solution that I know of happens to be an incredibly good one: the Kuba Link/ Torque Pads linkage kit. (Yes, Kuba and Torque Pads formed a partnership. As far as I know their linkage can only be bought through the Torque Pads website.)
Why is this linkage kit so so good? It completely replaces the stock suspension linkage to yield a whopping 50mm of travel, and it does this without compromising space, retaining a mostly standard 190mm eyelet to eyelet shock spacing. 50mm of travel changes the ratio from 3.33 to 1.4! Remember, the lower the number, the more weight it can handle. Several different MTB rear shock spring rate calculators indicate that increasing the shock travel from 21mm to 50mm reduces the amount of spring required for a 220lb rider on a heavy EUC (heavy compared to a bicycle) from 2400lb/in down to about 400lb/in.

This is exciting. A 400 spring is a very normal spring. That puts us exactly in the middle of the weight rated range of basically every decent air & coil shock out there. Or in other words 50mm of shock travel means that the shocks can finally work like actual shocks, managing the wheel & rider's weight, providing real bottom-out protection, and allow for real fast & slow compression rebound adjustments. Note the stock shock is a 190-35 air shock with basic adjustable compression dampening - it's maximum compression is 35mm, so when you replace the linkage you will want a shock with at least 50mm of travel.

Basically, I believe the only real solution to redeem the Master as one of the Best wheels available is to first replace the suspension linkage geometry, and then put literally any upgraded coil spring or air shock on it. And if you were to install a really good shock it ought to be able to truly shine, providing true high quality, possible real professional racer-quality suspension.

[Planemo]

Interesting stuff, and good to see someone pull up some decent data.

21mm shock travel is indeed 'shocking' for 70mm wheel travel. I had no idea about the Master's suspension as I've never been interested in the wheel but as I say your post is enlightening.

My MTB runs 65mm shock travel for 160mm wheel travel (2.46-1), so your quote is about bang on.

It's interesting that the Sherman S (and V11 etc) decided to opt out of rising rate linkages. I can see the point - after all RR was primarily intended to deal with the increasingly long travel of the MX bikes - not exactly what we need on EUC's, and especially not with the Masters meagre 70mm.

[Tryptych]

7 hours ago, Phi1osopher said:

the only marketed solution that I know of happens to be an incredibly good one: the Kuba Link/ Torque Pads linkage kit

Last I checked Kuba links are impossible to get. Has the situation changed? Google isn't helping - where exactly can we get this mythical Kuba stuff?

 

 

 

Edited November 22, 2022 by Tryptych

[Whalesmash]

3 minutes ago, Tryptych said:

Last I checked Kuba links are impossible to get. Has the situation changed? Google isn't helping - where exactly can we get this mythical Kuba stuff?

 

 

 

Aren't they ordered through torquepads now?

[Tryptych]

1 minute ago, Whalesmash said:

Aren't they ordered through torquepads now?

Yeah I found it here eventually

Very expensive... Pisses me off that we have to do this... I think I'd rather put that money towards a better wheel...

 

[mrelwood]

@Phi1osopher, good post, you have dug into the issue in decent detail. However, I was surprised that you completely left out volume spacers. In addition to the shock travel being very short, it isn’t positioned to the end of the shock’s travel. Hence, the original shock benefits from a large volume spacer in a significant way, as was found out by a Master owner who printed himself one. I’m sorry I don’t remember which thread they talked about it. Actually, I’ve heard that the Kuba links anda quality shock don’t completely remove the usefulness of a volume spacer either.

A correctly sized volume spacer will give the shock the progressive behavior that air shocks are designed to utilize. You can therefore lower the pressure to regular levels even on the stock linkage and shock.

 Most importantly, a single volume spacer costs maybe $0.1 to print, while the Kuba + Monarch combo will set you back several hundreds of dollars.

 If you want the best possible ride, go with Kuba and a good shock. Then again, considering that buying a Master one has chosen to compromise anyway, I think a volume spacer is what should be the immediate step #1 to take when receiving a Master. If that’s not enough, only then consider the more expensive options.

[EMA]

@Phi1osopher good informative post with some numbers for those who doesn't have the master in their hands

13 hours ago, Phi1osopher said:

Note the stock shock is a 190-35 air shock with basic adjustable compression dampening - it's maximum compression is 35mm, so when you replace the linkage you will want a shock with at least 50mm of travel.

i've the 1st batch stock shock on my table and it's a 195 with a 45mm travel , maybe yours is different than mine ?

i'm personally done some tests with modified linkage, final version will come soon, something similar to kuba design but with a better curve imho.

 

other numbers for those interested:

on stock geometry (25mm)i use the DNM with 1250lbs spring and something like 260 psi on stock shock

to get a similar feeling with a 35mm design i run the 750lbs and around 160 psi

final design use full 50mm travel with a nice straight curve 

 

[organicparadox]

I've gone ahead and tried it with the kuba links and a foxfloat rear DPS and the feeling between that and the default config is night and day.  No more weird rebound and pogo feeling from needing to over-inflate the default shock.  There is finally a sweet spot in dialing it in to my weight and I have modes for different street conditions.

 

There is plenty of travel now when rolling over large potholes at speed and the adaptive pre-load makes for a stable recovery when you hit something you didn't plan on. 

 

Coming from v11 suspension experience on wheels

[Planemo]

14 hours ago, mrelwood said:

Hence, the original shock benefits from a large volume spacer in a significant way

In this application I still can't help feeling it's a crutch though. Spacers should only ever be used to help prevent bottom-out, nothing else.

I accept it may help in this situation though, but only because the stock setup is so wildly out of kilter that wacky solutions not even intended for the purpose may actually be beneficial.

[mrelwood]

Well, bottoming out is the resulting issue of the bad design. So the use of volume spacers is a completely rational solution to the issue. And it has already been tested and proven to be a huge improvement to the stock setup, so crutch or not, it’s a well working solution.

After all, that’s what the upgraded linkage does as well, uses the shock deeper into it’s travel. The linkage changes the travel, a volume spacer changes the end point.

[btl]

Thanks for that in-depth explanation, Phi1osopher! Now i understand the problem of my Masters Suspension. I also ride it with an aftermarket shock, the Fox Float and pumped to a pretty high 350psi (its rated for 375 max). Its for sure a lot better than with the stock air can, but i do see the reason why the Kuba Linkage system  should provide so much better results.

I do however not like that the kuba linkage does stick out so damn long. The lever it provides could possibly wreck the Masters frame on the first impact. 

Perhaps EMA's solution is more compact? What ompression ratio does your idea have?

 

Greets,

Beetle

[EMA]

1 minute ago, btl said:

Perhaps EMA's solution is more compact? What compression ratio does your idea have?

the shape is similar and stick out the same (mine more on top), that's the only way you can get a proper leverage, the difference is the resulting curve.

my curve is almost straight from the beginning to the end, in terms of riding i have more support at the beginning and in the mid stroke

kuba is more exponential

to give you some numbers kuba it's 1:1 in the last 15mm.

mine is 1:1 in the first 10mm
 

[Funky]

I have given up on perfect wheel. Just shows again and again how idiotic are those EUC makers.. They don't know what the duck they are doing.

 

They should let EUC riders make a wheel. Community produced project. I bet we all could build WAY.. WAY... Better wheel together. And because the project is available to all. We could see problems right from the beginning. And fix them before wheel sees the daylight.

Let that won't happen, because we live in greedy world.

Edited November 22, 2022 by Funky

[Planemo]

1 hour ago, mrelwood said:

And it has already been tested and proven to be a huge improvement to the stock setup, so crutch or not, it’s a well working solution.

I accepted that it had been tested and was better than stock.

The progressivity must be mental to achieve 70mm wheel movement to 21mm shock movement without bottoming out. That was my point of a spacer being a crutch as spacers increase progressivity which is OK to a point but the graph in this case must be reaching for the stars. In any event the air pressure at full compression must be well over what the can is designed for as obviously it will be even more than a shock without spacers that is bottoming out (which IIRC is around 400psi no load?).

Out of interest do we know what % sag and at what pressure people running with the stock shock and a volume spacer?

 

 

Edited November 22, 2022 by Planemo

[mrelwood]

46 minutes ago, Planemo said:

The progressivity must be mental to achieve 70mm wheel movement to 21mm shock movement without bottoming out.

Doesn’t that depend on which part of the shock’s travel the 21mm is located at?

46 minutes ago, Planemo said:

spacers increase progressivity which is OK to a point but the graph in this case must be reaching for the stars.

Maybe the spacers that were used didn’t reach for the stars, but indeed only did it up “to a point”?

46 minutes ago, Planemo said:

In any event the air pressure at full compression must be well over what the can is designed for as obviously it will be even more than a shock without spacers that is bottoming out (which IIRC is around 400psi no load?).

Obviously the spacers do not fill all the space that’s left in the shock at full compression, so the pressures can’t get too astronomical. Based on the modeling I did on my V11 shocks, it isn’t even possible to fit a spacer that would do that, since there is a good amount of volume left in the valve opening, the cutout for installing, etc.

 Also, the pressure at full compression is irrelevant if the rider can’t compress the shock that far anyway. The pressure won’t get notably higher than it would with a shock perfectly designed for the same linkage, since the pressure carries what the pressure carries, no matter the volume.

46 minutes ago, Planemo said:

Out of interest do we know what % sag and at what pressure people running with the stock shock and a volume spacer?

This guy runs his at 180 psi, but I didn’t see him mention measuring the sag:

 

[Whalesmash]

I can't speak to the volume spacer, but I did something similar in just filling the shock with more oil. Not very scientific with the amount that I used but I was able to run a much more manageable 300ish PSI for a comfortable ride (I was using 400 before for trails). Didn't get any bottom outs in general riding, but if you dropped it from a distance it would still bottom out. My complaint with this method is that it still lacks compression dampening, and the rebound adjustment still didn't work as well as I would like. To date, I have tried:

1. Stock Shock
2. Stock shock with extra oil ($5)
3. Fox shock with volume reducer (New $350+ or maybe $100-150 used if you want to gamble)
4. EXA 291R with 1250lb spring ($75)

My favorite was the fox shock (big surprise, it's a $350 shock, it better be good). It had everything that I wanted, very granular rebound adjustment, enough compression dampening settings for different situations. Problem is that I blew out the rebound after 600 or so miles. I presume that this was partially due to me running higher than specified pressure (350-375 psi), as well as the sort of trails that I ride. Just can't get around the fact that you need higher pressure to compensate for only using a fraction of the shock travel even with the volume reducer. Either that or it's just not meant for EUCs. I'm not the only person to blow out this shock either. RogerEUC also nuked his doing presumably similar trails.

Stock shock is still alive, but I don't fancy it. After riding the fox, it just doesn't have the rebound adjustment that I am looking for, and it doesn't have any compression dampening at all. Perhaps if I really fill it with a lot more oil I can run something like 200psi. Perhaps under lower pressure, the rebound will work a little bit better and I can loose the pogo effect. Not particularly high on the list of things to try unless the coil doesn't work out.

I am currently running the EXA291R with a 1250lb spring. Only roughly 50 miles in. It does most things okay, but for the trails I ride, I have to crank the preload a lot. I'm light (155lb geared roughly), and the 1250 is still too soft. It's very comfortable under low preload if someone out there is only looking for light street riding, but I trail ride a lot and i need a heavier spring despite being so light. I'm also relying on the bottom out foam to prevent me from clonking on big drops despite the preload. Also no adjustable compression dampening here, but it's more supportive than the stock suspension. 1500 and 1800lb springs are on the way (these are meant for a 160mm shock, so they are shorter springs, but since the master uses so little shock travel, these will still work. It will also fit the linkage better). The 1250lb spring required me to space the suspension arms in order to have the clearance to fit, hence why I am going for springs designed for a shorter shock. The rebound on this thing isn't nearly as good as the fox, but it actually does something unlike the stock shock, none of that top-out clonking that the stock one constantly does. 

I'm not going to draw any conclusions yet in terms of what I would recommend, but at the time of writing, the Fox was definitely my favorite. It's a shame that it died, but the reality is using the shock to compensate for bad linkage ratios is the wrong way to go about it. For the time being, I'm reluctant to go get the kuba linkage since that plus another aftermarket shock is going to set me back $500, but I could see myself trying it in the future. We'll see if I'm content enough with the 291R for now.

Edited November 23, 2022 by Whalesmash

[btl]

I also run the Fox Float (Performance, not the very much more expensive Factory edition), but i got it in 210x55mm and i guess its too long for the Kuba Linkage.

I love the Fox' 3-way setting, i ride in medium for a cushy ride, and put it to "locked", wich is not a total lock but more firm than medium. When lighter riders try my wheel i set it to soft. It would be great to have the Kuba linkage AND the comfy Fox shock, but i'm hesitant to sink another 500 Euro into the Master.

I do have a 190x51 DNM AOY.38, but will that be better with the Kuba system than my Fox with the large volume reducer? 

[Planemo]

1 hour ago, mrelwood said:

Doesn’t that depend on which part of the shock’s travel the 21mm is located at?

I'm not sure what you mean.

1 hour ago, mrelwood said:

Also, the pressure at full compression is irrelevant if the rider can’t compress the shock that far anyway. The pressure won’t get notably higher than it would with a shock perfectly designed for the same linkage, since the pressure carries what the pressure carries, no matter the volume.

I don't know what you mean by irrelevant. Lets assume that a given rider has a stock setup running 400psi and is bottoming out. So he adds a token and now he gets the ideal travel whereby he's using all of it (all 21mm ) and is say 0.5mm from bottom out. The air pressure at full compression therefore has to be higher with the token than it was without. After all, he's not bottoming out anymore.

As an aside, the rider may well be lulled into thinking they are running less pressure throughout the travel because the token will allow a lower no load pressure to achieve the same sag as before. But the token is certainly ramping up that progressivity with menace which means that at full compression it's higher than without the token.

 

1 hour ago, Whalesmash said:

My favorite was the fox shock (big surprise, it's a $350 shock, it better be good). It had everything that I wanted, very granular rebound adjustment, enough compression dampening settings for different situations. Problem is that I blew out the rebound after 600 or so miles. I presume that this was partially due to me running higher than specified pressure (350-375 psi), as well as the sort of trails that I ride. Just can't get around the fact that you need higher pressure to compensate for only using a fraction of the shock travel even with the volume reducer. Either that or it's just not meant for EUCs. I'm not the only person to blow out this shock either. RogerEUC also nuked his doing presumably similar trails.

Great post. And you highlighted the problem with running higher than optimal air pressures, especially those over the manufacturers limits. Up the air pressure and rebound damping has to be upped by default. The problem comes when damping circuits can only give so much before their guts get ripped out by trying to work against a massive air pressure that they were never designed for.

Edited November 23, 2022 by Planemo

[mrelwood]

1 hour ago, Planemo said:

I'm not sure what you mean.

The stock linkage allows 21mm of movement in the shock? The stock doesn’t reach fully compressed state, but I’m not aware that that it would reach the fully opened state either. So the shock only moves somewhere in between, but I haven’t seen anyone mention where exactly.

Although, thinking about it more, I can’t see how the progressivity would be any more mental than it is with a Kuba+Rockshox of the remaining minimum air volume is kept the same (in relation to the max air volume).

 

1 hour ago, Planemo said:

I don't know what you mean by irrelevant. Lets assume that a given rider has a stock setup running 400psi and is bottoming out. So he adds a token and now he gets the ideal travel whereby he's using all of it (all 21mm ) and is say 0.5mm from bottom out. The air pressure at full compression therefore has to be higher with the token than it was without. After all, he's not bottoming out anymore.

Of course. Since it doesn’t bottom out, the shock has more lift at maximum compression, hence it has a higher pressure. But not more than a high quality shock would. Or the original shock pumped up so high that it doesn’t bottom out.

Do you have a reason to believe that the original shock wouldn’t handle a regular rider’s weight under compression with the original linkage? So that the only reason it doesn’t break under normal usage is because the system bottoms out?

 If so, pumping it so high that it won’t bottom out is practically as harmful as using volume spacers, of any size.

1 hour ago, Planemo said:

But the token is certainly ramping up that progressivity with menace which means that at full compression it's higher than without the token.

If you’re comparing bottoming out vs not bottoming out, of course. But again, if the goal is not to bottom out, the different methods to do so arrive in approximately the same maximum momentary pressure anyway. Tokens or not.

[Planemo]

11 minutes ago, mrelwood said:

The stock doesn’t reach fully compressed state

That does seem to be the case, if it's actual intended stroke is around 35mm.

11 minutes ago, mrelwood said:

, but I’m not aware that that it would reach the fully opened state either.

It should do! At least when unloaded.

11 minutes ago, mrelwood said:

Although, thinking about it more, I can’t see how the progressivity would be any more mental than it is with a Kuba+Rockshox of the remaining minimum air volume is kept the same (in relation to the max air volume).

I would assume that the Kuba/Rockshox setup is designed to use more of the shocks stroke? ie more than 21mm. Is this not the case? Can't see much point in changing the linkage otherwise...unless it's just changing the shape of the leverage curve and not the start/end point ratio which is a bit futile really when what we need to get away from is running 70mm of wheel travel for just 21mm of stroke.

11 minutes ago, mrelwood said:

Do you have a reason to believe that the original shock wouldn’t handle a regular rider’s weight under compression with the original linkage? So that the only reason it doesn’t break under normal usage is because the system bottoms out?

Possibly yes if it bottoms out before it reaches it's max operating pressure. It's a shit way of staying within pressure limits though, no shock should be bottoming out, ever. 

11 minutes ago, mrelwood said:

But again, if the goal is not to bottom out, the different methods to do so arrive in approximately the same maximum momentary pressure anyway. Tokens or not.

Agreed, the same momentary pressure at full compression could be achieved with tokens or without but one will be better for sag than the other, which as always is the 1st thing to get right, everything else follows. If the shock is bottoming out at the right sag (around 25%) then adding tokens is the only viable option as simply upping the pressure without tokens will likely see the shock topping out everywhere (as the OP states) and generally riding like crap. The problem is trying to get the right sag, an acceptable curve and no bottoming out with only 21mm to play with which will always be a right pain in the ass whichever way we cut it.

[Chiway Black]

[Cerbera]

1 hour ago, Chi-Way Black said:

 

Oh interesting. You got a link for that ? - I'm not typing in that URL from a bitmap !

Edited November 25, 2022 by Cerbera

[Tawpie]

https://drive.google.com/drive/u/0/mobile/folders/1-7Fv4bge8eDnlygpQ6PHLKdKVuh7EnC5

 

[Cerbera]

Excellent, thank you, @Tawpie. They remesh nicely as well, not that 3D printers give a shit what the topology is doing... 

So what, I wonder is different about these, and presumably we have to print them in metal ?

Edited November 25, 2022 by Cerbera

[EMA]

not perfect but better than stock, i've put them on cad for you :

30mm travel from 180 to 150mm is better than 25mm from 190 to 165