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Dougal

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Discussion starter · #1 ·
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 started this new thread due to a post by One Pivot:
One Pivot said:
I did just see that push recorded pro data at 8.5ms and 7ms. If we suck really bad, couldn't we still hit 2ms? Why is there such a focus on <1ms and no one cares about totally non theoretical higher speeds, when double or even triple, or 8x the posted 1ms speeds are doable?

High speed choking is real. If pros can hit a value, isn't that the absolute upper limit we should be looking at?
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#4 ·
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.
 
#5 ·
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.
 
Discussion starter · #6 ·
freetors1 said:
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.
Click to expand...
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.

mike156 said:
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.
Click to expand...
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:
 
#8 ·
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.
Click to expand...
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
 
Discussion starter · #10 ·
PUSHIND said:
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
Click to expand...
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.

Mudguard said:
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.
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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.
 
#11 ·
Dougal said:
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.
Click to expand...
The data doesn't say that 5m/sec doesn't matter, it shows that on this section of trail it doesn't exist....not even one impact! This data is also very consistent with what we see in the real world from both amateur and professional riders.

I was just trying to provide some real world information to show you that your "belief" that 5m/sec as a velocity range to focus on isn't really something you shouldn't put any time or effort into.

Darren
 
Discussion starter · #12 ·
PUSHIND said:
The data doesn't say that 5m/sec doesn't matter, it shows that on this section of trail it doesn't exist....not even one impact! This data is also very consistent with what we see in the real world from both amateur and professional riders.

I was just trying to provide some real world information to show you that your "belief" that 5m/sec as a velocity range to focus on isn't really something you shouldn't put any time or effort into.

Darren
Click to expand...
That's perfectly fine. You keep focusing on the averages and I'll deal with the outliers.
 
#14 ·
mike156 said:
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.
Click to expand...
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...
 
Discussion starter · #15 ·
upsha said:
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...
Click to expand...
Steve's ideas on the subject match mine pretty well. He's got more data on it and his guys are going bigger than most. So his setup is more geared towards controlling big springs and big hits where mine are more about rough ground at speed.

The low view numbers are probably because the average persons head starts spinning in the first video.
 
#17 ·
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?
 
Discussion starter · #18 ·
One Pivot said:
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?
Click to expand...
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.
 
#20 ·
mike156 said:
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.
Click to expand...
I used to dork around with E-Stock MR2's for autox. Thats a whole different animal, but its fun thinking back to those days. We were all grossly undersprung (ES rules) and just cranked rebound damping up to keep the corners from rolling all over in turns. It worked better than it sounds, but most of ES setup was about trying to corner more flatly. Wheels in the air were bad for traction.

Most of my MTB tuning has been trying to keep the bike from beating me to death. My autox car definitely beat me to death on the street.
 
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