Dougal do you have data logging equipment to confirm the velocities?

 

Nope. It's on the list though.

 

I think it's probably important to know what you're equipment is going to do in that event just to know that they're won't be any nasty surprises. Before I got back into bikes heavily I was really interested in automotive motorsport dampers since I autocross. In that context the shock tuners will typically only dyno out to around 10 in/sec because "that's where all the interesting stuff happens". On these kind of dampers they will typically have the digressive knee way down around 3 in/sec. Everything below that is considered shock movement just from weight transfer and is intended to control body roll, pitch, and heave. Everything beyond that knee is considered bump (wheel input) suspension velocity. Penske even sells a piston that can be setup to be digressive for most typical speeds but blows off and becomes regressive at extreme speeds.

I've wondered before what it would be like to setup a mountain bike this way. I feel like a strongly digressive setup would be a nice supportive platform for pedalling and pumping through stuff while still being able to absorb bumps. In the case of a mountain bike I do think the "rider induced weight transfer" would be capable of generating much higher velocities than what you'd find in a car though. I'd be really interested in knowing just how fast a strong rider could pump and excite an mtb suspension.

Dougal, I feel like you would be interested in reading the thoughts and theories of this guy: Autocross to Win (DGs Autocross Secrets) - Shocks You can just read the articles on shocks. He was a very successful shock tuner in the autocross world. It's all in an automotive context but I think a lot of the theory could still apply.

 

That's exactly where the twin-tube dampers with poppets came from. The Ohlins TTX25 damper was designed for excellent control of car chassis through those low speed body movements. But once blown open they are digressive.

The Cane Creek Double Barrel and Ohlins TTX22 rear shocks are evolutions of those. The Fox X2 brothers are also from there. The big difference between those two groups are the X2's have very soft compression poppets so they are very digressive.

Big riders who need more damping to take out big hits on the X2 shocks wind in the adjusters and find they get firmer and harsher but still just blow through on the big hits.

There's so much stuff I'd like to read but so few hours in the day.

As a fellow automotive enthusiast and autoxer...

Take everything you know about automotive suspension and throw it out the window for mountain bikes. A good set of videos to watch on bike suspension is "Tuesday Tune" from Vorsprung on YouTube. He talks a bit about the difference between automotive and bikes too.

Dougal, it's an interesting theory you have and it makes sense on paper. High speed = high energy, which seems like it would be the most likely type of event to cause harshness. Without data though, we are guessing.

Far from guessing, because you can model pretty much anything you want to put the time and physics into.

The issue with data is many believe it to be the holy grail but don't understand the limitations. If you rode the same trail at the same speed with two different compression settings, the firmer setting would give far lower compression speeds. So which data set do you choose?

Throw a data logger on a pro level rider and you might find a whole lot fewer impacts as they literally launch over rough sections that mere mortal riders have to punch through.

Data logging (and dyno testing) can only measure the outside of the box. It gives no understanding of what is happening inside.

Here's an example of solely data driven approach giving the opposite conclusion on brake rotor sizes:

 

As a fellow automotive enthusiast and autoxer...

Take everything you know about automotive suspension and throw it out the window for mountain bikes. A good set of videos to watch on bike suspension is "Tuesday Tune" from Vorsprung on YouTube. He talks a bit about the difference between automotive and bikes too.

Dougal, it's an interesting theory you have and it makes sense on paper. High speed = high energy, which seems like it would be the most likely type of event to cause harshness. Without data though, we are guessing.

 

As a fellow automotive enthusiast and autoxer...

Take everything you know about automotive suspension and throw it out the window for mountain bikes. A good set of videos to watch on bike suspension is "Tuesday Tune" from Vorsprung on YouTube. He talks a bit about the difference between automotive and bikes too.

I just watched the whole series again this weekend and like to bring a few relevant ones here.

Ep6 is about the shaft speed vs. travel of a single large impact. In the graph, 0-0.5m/s is labelled as low speed, and 0.5m/s to 8m/s as high speed.

Ep16 is on a single square edge hit and harness. He uses the horizontal and vertical movement to approximate the shaft movement and time to explain how excess shaft speed causes force on bar, or harshness. This model certainly is only accurate for 90deg head tube angle but it is very insightful anyway. He went on to discuss there is a "pain threshold" for each individual. He almost suggested a digressive system, that the initial portion needs to be stiff enough to support the rider, and the force at the highest shaft speed has be below the pain threshold. He also explains why less pressure in tire could help reducing the shaft speed.

Ep24 is also on harshness but with transmissibility in the picture, with a more precise decomposition of force into the parallel and perpendicular direction of the fork movement. He also talked about how "critical damping" and "reducing hysteresis" are irrelevant for MTB, and touched on that "high frequency" is different from "high shaft speed". Steve defines "harshness" as the total acceleration/force on bar, and the force could be from deep stroke build up from spring, or excessive high speed compression damping.

Overall, a truly excellent series but not very popular. Most of the videos have about 5k view only...

 

Penske Piston = Treks Reactiv damper.

To add to mike156, Chris Porter also has some interesting thoughts on progressive damping for mtbs instead of digressive: https://nsmb.com/articles/chris-porter-geometronnicolai-g1-story/

Dougal measure that.

 

To add to mike156, Chris Porter also has some interesting thoughts on progressive damping for mtbs instead of digressive: https://nsmb.com/articles/chris-porter-geometronnicolai-g1-story/

It sounds to me like he's talking about progressive damping with regard to position not velocity.

 

Suspension velocity has long been an interest of mine. Many people are only interested in compression speeds that are quite slow (0.2-1.0 metres per second or 8-40 inches per second or 0.7-3.6 km/h).

I believe that higher velocities are far more important and dampers need to be designed to handle compression speeds of at least 5 m/s to provide acceptable ride quality over rough terrain at speed. This view is controversial.

Opposing arguments are based around those compressions being such a small percentage of time and riding that they do not matter. It is only important that the hardware survive such impacts.

I'm not sure what your beliefs are based on, or why you chose 5m/sec as an important suspension velocity, but the actual velocity information does exist.

Here's a clip of some pretty high velocity impacts on a 160mm front fork along with the actual suspension velocity data from the bike using an on-board data logger. The left(Red) data is the front fork, and the Right(Yellow) data is the rear shock. As you can see average peak suspension velocity is 1m/sec with the absolute peak being approximately 1.4m/sec on compression. No where near 5m/sec.

Darren

 

I'm not sure what your beliefs are based on, or why you chose 5m/sec as an important suspension velocity, but the actual velocity information does exist.

Here's a clip of some pretty high velocity impacts on a 160mm front fork along with the actual suspension velocity data from the bike using an on-board data logger. The left(Red) data is the front fork, and the Right(Yellow) data is the rear shock. As you can see average peak suspension velocity is 1m/sec with the absolute peak being approximately 1.4m/sec on compression. No where near 5m/sec.

View attachment 1322315

Darren

And that above is the data driven approach which says that higher velocities don't matter and you should instead focus on averages.

I applaud this approach and would like everyone else in the industry to keep doing that. They shouldn't waste their time on higher velocities or fleeting impacts.

Surely they're taking the piss? Bigger rotor on the back, rear brake pads wearing twice as front pads?
I go through front pads twice as fast as rears, and went to a smaller rear rotor because it was too easy to lock up.

But that's the result of a scientific data driven approach with expensive data loggers!

It's a fantastic example of selection bias. When you test beginners and pros of course they use the back brake more. Beginners are scared of the front brake and pros don't need to actually stop, they just need to keep pointing the bike at the finish line.

But even using one brake more is zero reason to invert rotor sizes.

 

Darren, you guys did record 6-8m/s impacts though... its not impossible velocity. Its just a pretty nasty hit.

For me personally, I want to reconcile my personal experience riding over rocks at an average pace. I've gotten beat up by forks to the point where my arms hurt the next day. I've also halfass reshimmed my own stuff going off of what seemed like good ideas and entirely eliminated that pain riding even faster over the same trails. What I do know for certain is that almost all suspension is pretty rough, when the trail gets rough.

I'm having trouble pairing what exactly 1m/s is, honestly. At 15mph on a 29er, how big of a square rock can you hit to cause a 1m/s shaft speed?

Please correct me if im missing something at all. Using a 29er, hitting a 6 inch square rock, you need to travel 12 inches to clear it (I just measured with a ruler).

15mph = 264 inch per second. So at 15mph, it would take 0.045 seconds to clear a square 6 inch rock on a 29er.

6in/0.045sec = 133 in/sec, or 3.38 m/s.

Theres a small correction because 3.38m/s is directly vertical instead of at the 60whatever degrees your fork hits it. I guess just round to 3.4m/s.

This is all undamped, unsprung free movement... I guess cut it in half and call it 1.7m/s.

Smashing 6 inch rocks at 15mph sound like it could potentially damage a wheel, so thats a practical limit too. How fast can you get a wheel moving before damage is likely?

 

Darren, you guys did record 6-8m/s impacts though... its not impossible velocity. Its just a pretty nasty hit.

For me personally, I want to reconcile my personal experience riding over rocks at an average pace. I've gotten beat up by forks to the point where my arms hurt the next day. I've also halfass reshimmed my own stuff going off of what seemed like good ideas and entirely eliminated that pain riding even faster over the same trails. What I do know for certain is that almost all suspension is pretty rough, when the trail gets rough.

I'm having trouble pairing what exactly 1m/s is, honestly. At 15mph on a 29er, how big of a square rock can you hit to cause a 1m/s shaft speed?

Please correct me if im missing something at all. Using a 29er, hitting a 6 inch square rock, you need to travel 12 inches to clear it (I just measured with a ruler).

15mph = 264 inch per second. So at 15mph, it would take 0.045 seconds to clear a square 6 inch rock on a 29er.

6in/0.045sec = 133 in/sec, or 3.38 m/s.

Theres a small correction because 3.38m/s is directly vertical instead of at the 60whatever degrees your fork hits it. I guess just round to 3.4m/s.

So for a slow descender on nasty trails, my theoretical 3.4m/s seems pretty easy to actually hit a few times, no?

Take that 3.4 m/s, throw in a soft 2.6" tyre with a foam insert and an overdamped fork that actively fights moving at higher speed.

Bingo. 1 m/s and a big kick to the bars.

Which is where the entire industry is driving riders.

 

I edited while you posted. I think I have an error for spring and damping.

 

Surely datalogged suspension travel speeds don't really tell enough of the story because if you have a damper that gets to 1m/s and cannot flow any more oil past that your logger is going to show that you never get more than 1m/s so why bother looking there but your rider is going to complain that some sections were rough AF.


Do you just assume that as long as most of your numbers are lower than your highest recorded values that it's ok?

 

Surely datalogged suspension travel speeds don't really tell enough of the story because if you have a damper that gets to 1m/s and cannot flow any more oil past that your logger is going to show that you never get more than 1m/s so why bother looking there but your rider is going to complain that some sections were rough AF.

Do you just assume that as long as most of your numbers are lower than your highest recorded values that it's ok?

Asking the important questions!

*You must spread some Reputation around before giving it to PhillipJ again.*

 

No value in doing something like logging and comparing acceleration of lowers vs crown? I guess you could just get something you knew was very softly damped an use that to establish a maximum expected value.

 

Yes I use an accelerometer on the crown so you can see how fast the fork is travelling during any sharp impacts the come through to the bars

 

The trails are busy around here. Doesn't matter how good you are as a rider, sometimes (often) you're just jamming on brake to slow down for hikers or slower riders. The rear brake does nothing for this. Nevermind the pros, casual riders on busy trails need to ride the front brake pretty hard, or you're crashing into the group of hikers with headphones in.

I think normal riders who need to actually slow down use the front brake more.

 

Double Post

 

Mc2 gets a surprising amount of lsc while keeping hsc workable. My understanding is that avalanche and push pull this off too.

Not full firm, but still.

I think most riders haven't been on anything capable of actually having lsc without crazy spiking. We still get reviews praising Moco, which grinds to a halt with any lsc.

 

Mc2 gets a surprising amount of lsc while keeping hsc workable. My understanding is that avalanche and push pull this off too.

Not full firm, but still.

I think most riders haven't been on anything capable of actually having lsc without crazy spiking. We still get reviews praising Moco, which grinds to a halt with any lsc.

True, I haven't worked on mc2 or an act cart but the push damper increases damping in the areas that provide the best support with going overboard so it works out. Most dampers suffer from an lsc adjuster that increases hsc at the same time which makes it tough to get anything useful

 

Here's the companion to Motion Instruments for suspension analysis - BrakeAce with a focus on brake telemetry and performance analysis:

https://www.brakeace.com/

 

Matt (BrakeAce) and I spent a day with one of our top enduro racers late last year, this is a POV from the day with data overlay-
Red=Front Brake Blue=Rear

There wasn't room for a velocity trace so here is the front and rear damper speeds-

 

Off-road moto translates most closely. Baja buggy/truck design is probably a close second. The problem with automotive theory being translated to bikes is tires on trucks are huge and have the advantage of linkage at all corners.

As others said, it's crazy how complicated MTB dampers are. Even some of the most advanced MotoX damper are far more simple than our bladder dampers.

At some point we're just throwing more parts at the problem instead of doing what the motocross guys do - custom tunes. It's pretty cool that Formula has that "drop in" CTS tune option. Manitou makes stuff easier for the end user to tune their own stuff. This is probably why so many pros get on just fine with the same dampers as most people are riding - they got their stuff custom tuned (and in some cases on a per-track basis.)

I'm no expert, but aren't motocross bikes are using something more akin to the GRIP and Charger RC dampers?

What I do find interesting is that air suspension on dirt motos does occasionally make a comeback usually as a "high end" option, but as a whole coils are preferred and better understood. You can't help but feel that MTB went air for the ease of logistical flexibility (easier to install shock at factory without worry about end user weight differences). Meanwhile it's pretty common for dirt bikes to be sold with a single spring rate that riders of all different sizes have to deal with (unless they want to upgrade).

 

Off-road moto translates most closely. Baja buggy/truck design is probably a close second. The problem with automotive theory being translated to bikes is tires on trucks are huge and have the advantage of linkage at all corners.

As others said, it's crazy how complicated MTB dampers are. Even some of the most advanced MotoX damper are far more simple than our bladder dampers.

At some point we're just throwing more parts at the problem instead of doing what the motocross guys do - custom tunes. It's pretty cool that Formula has that "drop in" CTS tune option. Manitou makes stuff easier for the end user to tune their own stuff. This is probably why so many pros get on just fine with the same dampers as most people are riding - they got their stuff custom tuned (and in some cases on a per-track basis.)

I'm no expert, but aren't motocross bikes are using something more akin to the GRIP and Charger RC dampers?

What I do find interesting is that air suspension on dirt motos does occasionally make a comeback usually as a "high end" option, but as a whole coils are preferred and better understood. You can't help but feel that MTB went air for the ease of logistical flexibility (easier to install shock at factory without worry about end user weight differences). Meanwhile it's pretty common for dirt bikes to be sold with a single spring rate that riders of all different sizes have to deal with (unless they want to upgrade).

Agreed on the custom tune route. I've seen complaints about customer service from some of the suspension tuning shops in the MTB world but I don't think I've ever heard anyone say "I wish I'd stuck with the stock damping".

I blow through rear pads at least twice as fast/often relative to front. I actually kinda agree with that IG post. You can't get away with much (if any) front brake while standing, descending and trying to turn....but you can still drag that rear brake to modulate speed.

The rear brake gets all the dust, water, and mud kicked up by the front tyre. That doesn't help pad life either.

 

Something isnt adding up. If push found the charger 2.1 plots to be well damped, HC97 wouldnt exist. So there was some problem identified in those graphs that were addressed by push. It looks like LSC is a bit soft but HSC is kept under control. Theres no crazy damping ramp, so thats good... but HC97 is still addressing a deficiency in RS's damper tune.

It sounds like charger went from tunable in version one, to a closed off unit later, so theres really no tuning to be done. You gotta just replace the top damper assembly, right? All things considered, I think the charger guys got excluded from any real tuning.

 

I gotta ask

in general

if no one likes the stock damping, then who are the fork/shock makers building these for ??? I have a 1000 dollar fork, on day one, it's full of potatoes then ?

 

I gotta ask

in general

if no one likes the stock damping, then who are the fork/shock makers building these for ??? I have a 1000 dollar fork, on day one, it's full of potatoes then ?

The people who just buy the bike they think want without really riding it and just assume that sram/rockshox make an acceptable product? Like they still keep making forks with motion control, people have hated that for a decade, but it probably only costs them $6 all in for the compression part of the damper unit and people keep buying them so they dont have a reason to change. Hopefully the Z2 forks pretty much immediate success will at least force them to **** can the moco revelation as more and more bike manufacturers seem to be replacing revelations with Z2s in their lineups.

 

Couple more comparisons just to show I'm not on crack

First pic- charger2 RC and charger 2.1 RC2

2 pic, charger 2.1 rc2 side by side will Douglas pic yo show it's the same as mine, plus a photo of the 2.1 needle sliding inside it's bolt, ie no hard stop

 

Here is a marked up version to make it even clearer:

 

Darren,

On a tangential note. If one of your customers had access to something like Motion Instruments would you be interested in that data when doing a build/tune for them?

Sent from my SM-N975U1 using Tapatalk

 

delete

 

For what its worth, on Pinkbike a few days back the Rockshox guys were doing a Q&A session in the comments section I asked:

"Do you guys factory modify forks for your enduro riders or are they riding fully OEM forks than any of us can buy?"

And got the following response:

"The athletes are typically running well serviced and well tuned stock equipment. They spend a lot of time with mechanics tuning air-springs and clickers but typically it's all stock. Maybe a custom shim tune here and there. Occasionally athletes will get prototype equipment to test but it's rarely raced (if it's a true prototype) or it's available to buy within months- ie they get production equipment. -DC"

https://www.pinkbike.com/news/rocksh...tml#cid2547273

For whats it's worth....I don't have any reason to think he's lying but I'm sure some will disagree. I've seen a couple Sam Hill interviews where he says the same, totally stock fork.

That's basically saying they are running custom tunes.

Oh, I'm certain not every pro DHer and enduro rider is, some are not sponsored and some are not sponsored to the extent where it'll buy this kind of equipment, but the higher and more competitive they are in the class, the more I would put money on it, especially from that answer.

 

The pros are fit people in the middle of the weight range for their height, i.e., "average", so it makes sense they would be mostly ok on the stock equipment.

 

That and I don't think anything that people want to change in forks will make you much faster. Like I'd bet almost everyone looking to improve their fork is doing it for comfort, not speed. Hence why coil stuff is getting popular again.

 

Thats the huge huge huge problem with mtb stuff vs dirt bike stuff. On a dirt bike you can open it up and make the changes you need to make.... on a mountain bike, you're massively constrained by the nonsense inside the fork.

You can get the entire brain power and engineering prowess of NASA or something crazy to log data on a motion control fork. You're not getting inside to make changes though, that data doesnt do a lot, no matter how thorough it is.

Keep in mind that PUSH used their testing and equipment to replace a part entirely, like they've done for years now. Very very few companies have the capability to use the data at all.

Some guy telling me to put a shim in my shock is more useful to me than a datalog showing me I need to custom machine a new damping assembly. I can do one, I cant do the other.

 

In defense of Dougal to a certain extent, qualitative tuner vs quantitative tuner.....tuning suspension is def an 'ART'. We have a couple local moto tuners that have great reputations here in Oregon....one is fancy, "Ivan" the other is old school and low key "Rocky", picture rocky IV, stay with me.

Ivan has a $xx,xxx suspension dyno, fancy web page and lots of fancy graphs while Rocky does not have a webpage, is word of mouth and has a 20' x 30' shop is his backyard. Ivan is squarely data based while Rocky is very much testing and experience based. Both get the job done but the general consensus, with several 'elite' level offroad dudes is....Rocky FTW.

I heard somebody say, no suspension guy worth his weight has a good webpage, which I find to be true (in general). Ornery, opinionated and ideas that differ from everybody else tends to define good sus guys in my experience....

You can throw all the fancy electro gizmos at suspension but can't ever lose sight of the 'Art' of it all....no computer (yet) has the ability to really define a good sus setup.

Many old school pro moto guys still reminisce how good some of the bikes back in the 90's were which was 100% old school testing, lots of laps and a DEEP working knowledge of suspension and years and years of suspension acumen.....

 

You can throw all the fancy electro gizmos at suspension but can't ever lose sight of the 'Art' of it all....no computer (yet) has the ability to really define a good sus setup.

Many old school pro moto guys still reminisce how good some of the bikes back in the 90's were which was 100% old school testing, lots of laps and a DEEP working knowledge of suspension and years and years of suspension acumen.....

Yup data tools are no substitute for rebuilding hundreds or thousands of shocks and listening to what riders say. Data gives you a nice quantified number you can reference against that feedback though. If I get a weird result I will check, recheck and then sometimes just decide to throw it out if I can't relate the result with what I'm seeing int the real world

Theres a great story about one of the F1 technical directors (I'm going to say its almost definitely Ross Brawn) arguing with one of his strategists about tyre selection. The strategist is swearing black and blue that the weather forecast is telling him they need dry tyres so Ross grabs him by the ear, drags him outside to point at the rain falling from sky and makes him go change it to wets!

 

Tuckerjt07, why dont you comment something about suspension velocities instead of trying to get dougal to buy some crap he doenst want to buy? It seems pretty clear hes not interested in the product you're pushing.

 

He's successfully moved the goalposts then I suppose. I'm not attempting to get him to buy anything. There are two separate issues.

1. He is tuning somewhat blindly by not being able to empirically track results. Additionally he's talked out of both sides of his mouth with regards to data logging, going as far as insenuating those who use it aren't real tuners.

2. He has continually mistated how a product works and functions. I couldn't care less if he buys it or not but misinformation needs to be corrected.

He's attempted to conflate 1 and 2 to hide the optics presented by 1. Without data logging he truly has no clear picture into what those velocities are doing to rider and bike. He has feel I suppose but that's subjective at best.

Sent from my SM-N975U1 using Tapatalk

 

this thread is why I am never opening up my shock or fork. must be demons inside.

just get new when current one feels wrong.