Suspension Data Acquisition

Subscribed! (I don't have a set-up but love geeking out)

I've got a few sets of the Motion instruments kit, been running it since pre-production and in the beta testing group. Also own an Aim EVO4S (motorsports) logger which isn't as easy to use but is super powerful and lots of room for expansion and custom sensors.

I would say that you don't really aim for certain damper speeds, as they very much depend on the exact bike, terrain and set up. So while there will be a range of speeds you expect to be see, they have to be viewed in conjunction with everything else (average position, maximum travel, travel distribution etc). You are best to bracket some different adjustments (eg spring to begin with) and watch how each metric changes, but also don't forget how the bike feels to you as well! And over time you will start to build up a picture of the kinds of values you can expect to see. 

Love this thread and I'm really curious about it. Have never used data acquistion, but I've done a ton of product testing and bracketed back to back suspension testing and I'm curious: What different parameters are measured and which ones are useful? I heard the OP mention dynamic sag, shaft speeds, and total travel, but are there others?

I'm really curious what the graphs look like and how they become useful in suspension setup. My guess is they're super helpful early on when one setting is way out of whack, but after that they only become helpful when a rider has done so much testing with the data acquisition that they know what values they like to see.

I mostly look at dynamic sag and the travel distribution plot to begin with as they will help guide spring rate/pressure/tokens, but can also give some good insights to the damping too. The actual values I expect have a fairly wide range to begin with, and I'll compare them to the other metrics to decide if they are in the ballpark or not (eg 20% dynamic sag at the shock and 28% on the fork could be quite acceptable, but if they are on the same bike then something is out of whack....)

Typical values can be -

Dynamic sag -

Shock 20-35% (note that the rear wheel will have a different number, whether its higher or lower depends on the frames leverage ratio so keep that in mind!) 

Fork 10-30% 

Maximum travel fork - 75-90%

Max Travel rear - 80-90%

Peak compression speed - 2000-8000mm/s (2000 would be your typical weekend warrior, 8000 is a world cup downhiller, I usually see 3-5m/s from most people)

Peak rebound speed front - 1500-2500mm/s

Peak rebound speed rear - 1000-1800mm/s

Longer travel bikes will have higher damper speeds

Softer springs encourage high compression speeds and low rebound speeds

I look at the shape of the travel histogram a lot too - it should be quite sharp and tight around the dynamic sag

Don't get to drawn in to the peak damper speeds as they are extremely situation and terrain dependant. You will often find changing the spring rate/pressure has a bigger effect on the shaft speeds than adjusting the damper. Your damping histograms are a better gauge for fine tuning the damper settings. The biggest trap I see people get in to is chasing peak speeds, so something like the rebound speeds are "too low" so they wind the dial all the way out and it doesn't change so they think it needs a revalve, when really they either needed a stiffer spring or it was actually perfectly fine.

I do a lot of analysis in Python by exporting the files but I'll use a screenshot here from MIQ- 

Left is the original tune, right is after changes

Yup, a "tighter" histogram is a good indication of a more stable chassis as the bike isn't bouncing up and down past sag all the time. If its spread out a lot that can suggest a bunch of things - offset towards the end of the travel (relative to the dynamic sag number) can mean too little compression damping, too much rebound damping or not enough progression. And vice versa, if its higher than sag it could have too much compression or not enough rebound damping. Although a track with lots of jumps will skew the values heavily towards zero!

MIQ lets you export a bunch of different options - like a zip file with .csv's of the suspension data and gps data, or a single JSON file with everything including metadata as different key's

(I don't know how to add other quotes)

"I agree with you that these tools are amazing when first setting up a bike. But I still use them everyday to confirm things I feel. Sometimes I’m wrong and want to make changes then or I want to make changes in the wrong direction.

The craziest thing is how much your balance can change depending on how tacky the dirt is and how steep the trail is. Like on my fork it could be (5-6psi) difference."

Yeah different trails will give wildly different values so early on its worth not making too many changes and get a feel for the variability, then also conversely make some big changes, note how it feels to you and then go see how different it looks in the data!

I'll definitely always bang on about not using the numbers as your sole guide - its more of a tool that helps you narrow down your adjustment options. ie if you're bottoming out often, you already know its going to be something like add more pressure or more compression damping so you can go straight to those values and one will likely jump out. Focus on improving 1 thing at a time your bike can do better and hone in on that

Oh data logging....there's a lot to unwrap with that subject!

Stoked on this thread - I've been messing around with the MI kit for a few years with mostly good results, though I think they could provide a bit more guidance as the learning curve is a bit steep.  

Anyone try the BrakeAce kit yet?  I have a set but haven't had time to play with it yet, need to track down an Android phone because they don't have an iOS app yet.

Yeah its come along way in what feels like just a few years! That Commencal looks like its has the Aim EVO4 which is the previous version of my logger....they are a super powerful tool but weren't designed with push bikes in mind! I didn't have much of a computers/electronics background at that stage so even just the basics like getting power to it....and turning it on.....took some work They kind of expect them to be attached to something with a power source already. I'm pretty sure looping the cables around this much is not great for signal noise/interference in an analog sensor too. Just mounting the sensors was the hardest part! Again, no off-the shelf mounts existed and every frame/fork is very different and potentiometers need to be mounted very rigidly to get an accurate signal, as any shaking will mess up the readings big time. Theres way more solutions out there now but it can still be a challenge!

Oh and speaking of brakeAce....spot the prototype sensors on the bike here! I know Matt really well and he is another Rotorua Local

I was always pretty interested in set up from when I got proper in to mtb 20 years ago, and slowly learned more and more about the physics of mountain bikes, especially as I started to specialise in suspension more around 2009. But it was only about 6 years ago I came to realise that if I actually wanted to measure bikes and learn what was really going on I would need to buy my own dyno & data acquisition gear to do it.There was no one using a dyno or DAQ gear in NZ at that stage (a few people have bought dynos since then, but AFAIK no one else with data loggers which is crazy) which is why I decided to start my own business so I could finally learn this stuff for real. So I finally got to order my own dyno & data acquisition gear 5 years ago and been playing with it nearly every day since then! Its definitely one of those things were you pretty quickly end up with more questions than answers, and every year or so learn something that makes you realise there was some massive errors in your previous tests........And thats not supposed to put you off, its kind of how its should go or else you're not actually learning anything. Pretty much every smart person I talk to will acknowledge they made some terrible mistakes and oversights in the past, since the ones that aren't that clever just prove they couldn't see their mistakes in the first place. 

So my main advice is probably pretty boring, but for the most part I would remove all assumptions and always keep in mind that you might be wrong about your interpretation of the data or feedback. Even if you are pretty sure the bike needs a softer spring, still try a stiffer spring just to see. And don't assume that a stiffer spring needs the rebound to be slowed down or the compression made softer. Sometimes thats true, sometimes the exact opposite is needed and sometimes the damping is actually fine once paired with the correct spring. You never 100% know for sure until you try it, and with time you will be able to get away with a few assumptions as long as you still hold on to that possibility you could be wrong and are prepared to backtrack on it. 

On the topic of "preferred" speeds - be careful to correlate rebound feel with rebound speeds, since a large part of that feel is tied to the spring and compression damping. I often work on set ups that "feel" very fast but the peak rebound speed might only be 800-1000mm/s and after working through it, the main problem is too little compression damping. In the end it would get firmer compression, more air pressure and a slightly softer rebound tune which would "feel" slower (ie more composed) but the peak rebound speeds got slightly higher, around 1100mm/s despite that slower feeling. The point is the bike "feeling" fast is a legitimate thing to work on, but don't automatically jump to thinking that means the rebound is too fast and needs to be brought down.

That video with Henry Quinney actually has a few red flags to me - the software apparently is telling him to go faster on rebound but the damper is maxed out, while also he doesn't feel as supported in the front end pushing in to corners. So really he just needs to make it a touch firmer on air pressure but has been drawn too much on what the rebound speeds say, as well as thinking he MUST have 20% sag up front or whatever it was. 

Lastly as for learning python - I've taught myself that from websites and youtube where you can do it all for free as there are are ton of resources for it. I might share a few basic examples in the future but I'd highly recommend taking it with a grain of salt since I probably have some terrible coding habits  But since its free and easy to acquire it's definitely worth diving in and playing around with understanding the basics at any stage

30% fork sag 

Agreed 30% is gross 

But what about 30% Dynamic sag? I’ve heard some pretty hardcore bike nerds who ride pretty hard, as well as WC guys mention running 30% dynamic f/r. Does that still sound outrageous? Does the amount of travel a bike has dictate how much dyn sag it should be run with for optimum performance? 

My bad - I rewatched that section and he said 20% dynamic sag, although not sure if that was his actual numbers or just talking general terms. I had also heard other people talking about 30% fork sag and must mixed them up. Still, 20% is very middle of the road for fork sag and certain riders/conditions/forks will require less than that. It is also possible their static sag is about 25% and combined with wild fast rebound is why the dynamic sag is lower. 

I've heard people talk 30% sag recently too.....but I don't think it was specified if that was static or dynamic, and if its static then how they measure that too. There could be more context to it that explains things better, but in general I don't have hard and fast rules for how things "should" be set like that.

The main reason I disagree on soft forks for elite riders because the natural frequency of the suspension is what determines how quickly the wheel returns to full extension and that is mostly a function of your mass and spring rate. Even with no damping at all there is a hard limit to how fast that wheel returns (because physics) once the compression force is released and the spring is allowed to return on its own. Therefore the main driver of how the bike follows the ground is the spring, then the damping is used to reduce excessive oscillations beyond that. 

Another way to think of it is the spring controls the time between each cycle (period, or the inverse of frequency) once the system is set in motion and the damper controls the number of cycles(or part cycles) the system makes before it stops. Regardless of how damped the suspension is, each cycle will still take a similar amount of  time (until you get very close to critically damped, then the period does noticeably increase) but will do fewer cycles. 

I mean you surely can make a bike with 30% fork sag functional, especially if its matched with the shock and an overall well put together bike but I would be surprised if it the actual optimum set up

In regards to amount of travel specifically - you will usually settle on less sag for shorter travel forks one way or another 

Oh one thing I feel important to point out - most of us mtb suspension guys are predominantly or entirely self taught so we are always still learning. While I disagree with some peoples opinions, a lot of them are very clever and overall do an excellent job. There are also likely a lot of gaps in the things I've learned, so I will always be open to learning new things too! 

I'm interested in getting one of these kits in the future... Does anyone have experience with both kits? MI vs BYB. It seems like the byb might be easier to transfer over to a moto kit later on if I wanted too. 

MI - seems cheaper to start but then you have to pay for their app, easier to setup

BYB - more expensive but not subscription based, harder to setup. Better deal if you buy the moto/mtb kit together but its a lot.

Anyone have any pro's and con's on these systems? Which app works better?

Thanks

So I own and have used the MI kit, and it's great. The only issue I have is that I've had some rear sensor issues more recently and have tried to get in contact with the folks at MI (who used to be very great and responsive) and it's unfortunately been crickets (Update: Rob's reach out in the forum, so this no longer applies. Massive props for this). 

As far as sag percentages go, I do feel like its very much spring dependent. I tend to feel like I need less sag overall (or care less about it in general) with coil rears as opposed to air springs, which tend to be very position sensitive due to the nature of how the shock likes to be balanced against its positive and negative air chambers. 

Extending that to the fork, I usually attempt to run as "soft" as I can before the mid stroke really starts to suffer. This usually means 15-18% sag unless I'm running something like a Vorsprung Luftkappe or even a secus where I can get some more midstroke support and run a slightly higher sag. What's even cooler is being able to see their impact in the data if you are using something like a MI setup. 

As far as rebounds go, and how they interplay with the spring, I do find that the faster the rebounds the more it holds the suspension higher in its travel, so you can kinda claw back some of the geo benefits of running less sag by speeding up the rebound in higher sag setups.

For anyone who wants to nerd out even more on the topic, I highly suggest the Race Tech Motorcycle Suspension Bible. 

For all I know, I could be completely wrong about everything, so take what I say with a grain of salt. 

 

What kind of sensor issues have you been having? I've spent plenty of time fixing sensors so might have some things to try. Weird that MI haven't responded though - they've still been pretty active, I had emails with them a month or 2 ago and I see they just pushed an app update yesterday. Maybe try again or through something like instagram as Rob used to be on there a lot too

As for comparing the systems, I haven't used the BYB but it appears to fix a lot of the problems I have with my Aim system, like better software and much more mtb-specific support on the app side and hardware. So I'll compare the things they have in common though

BYB/Aim

Pros-

More sensors like  wheelspeed, braking and IMU (accel/gyro) 

Options for custom sensors

Generally more precise data and the ability to look at the whole bike rather than just suspension

Can compare runs, overlay speed and isolate sections easier

Cons-

Lots of wires to run, adds complexity

More things to mount sturdily and out of the way

generally more time consuming to use

MIQ

Pros-

Relatively simple to bolt on and go

Wireless - only need to mount the sensors & cable tie the transceivers

While the app is more simple it gives you quick access to the important info

Good support & database of frames built in

Cons-

Less scope to expand on sensors and analysis

No desktop software (but you can export the files to excel, python or matlab)

If you just want something to help set your bike up I would recommend the Motion Instruments, as it is easier to get going and you will be more likely to use it. It does 99% of what you need really well. If you want to dive deeper in to the science of bikes, race analysis and other things then something like the BYB has more to offer.

On the software front - I am usually torn on subscription based things, but software costs a lot to develop so one way or another there will be a cost involved (after trialling other software I can see why AIM's is free.....) which is either a large up front expense or a smaller continual one which is easier to get in to and helps to fund further development. It does mean having faith that the company will continue to update it and so far MI has been very good at improving the software since they started. I haven't used the BYB software, it looks quite good but I don't know how often it gets updates or bug fixes which is important for these things and hopefully they are on top of that too