Learning MTB-Speak. Today's lesson, mid stroke support

[RebornRider]

Let's suppose I am a product design engineer who recently joined a bike company to work on a new mountain bike design. Let's also suppose I got interested in enduro style riding recently (as opposed to fire roads), so I'm not sure what people mean when they use terms such as "mid stroke support", which appears in just about every review of mtbs and mtb suspension products.

If I want to design a rear suspension that provides good mid-stroke support, what design choices should I make? Does "good mid-stroke support" mean a relatively high spring rate in the middle of the travel? Does it mean high (hard, stiff) compression damping in the middle of the stroke? How does rebound damping affect mid-stroke support?

In general, how would you guys describe mid-stroke support in terms of suspension design?

(BTW, I'm not designing a bike. I just want to learn.)

 

[Mikerb]

Mid stroke in general is the majority of the shock or fork travel............referred to as mid only to differentiate from the "top" of the stroke mostly absorbed by SAG and the final part of the stroke reserved for the hardest/highest hits you are likely to come across in line wwith how you set up your suspension. So people want the top of the stroke to be plush, the mid stroke ( ie most of the rest of the stroke) to absord the terrain and not burst through the travel, then the last part of the travel reserved for big hits and to a void the suspension bottoming out.
Since all air suspension is progressive it should of course be possible to use whatever user controls are provided to achieve all of that, although invariably it is only only the higher end models it becomes more achievable.
Having set air pressure ( or spring) for SAG, the control over the progress of the stroke is then achieved using low speed compression, high speed compression, and high speed/low speed rebound controls ( if provided). On lower end models high speed compression is pre set by the manufacturer but some low speed compression together with low speed rebound is usually made available for the end user.

How does rebound effect the stroke?? Well firstly is depends what damper unit is being used. Some ( higher end models) are more sophisticated and will include separate controls for high and low speed rebound. To see what effect rebound has on your suspension ( and the best way to set up your suspension:-
1. Keep all rebound and compression settings open/fast and set SAG
2. Still with compression settings wide open start setting rebound by doing several runs with different settings until it feels right.
3. Set compression.

( note rebound can mimmick compression even though it relates to the return stroke......mores so in some dampers than others......hence set rebound before compression)

 

[RebornRider]

Mikerb, I appreciate the time you spent responding to my post, but my current interest is trying to understand what mtb'ers mean by the word support. Does good support translate to a relatively higher spring rate? Or does it translate to relatively stiffer damping?

According to Steve at Vorsprung Suspension, air springs are stiff at the beginning of the stroke (high spring rate), relatively softer in the middle of the travel (lower spring rate), and quite stiff as they reach full compression.

Link to Tuesday Tune video snippet

This makes me suspect that "more support" (or "good support") really means a higher spring rate. But that's just my guess, and I'm only beginning to climb the learning curve.

 

[Gary]

"Support" simply refers to the suspension's ability supporting the rider (and bike obvs).
"Good" support would simply mean a combination of supportive enough damping and spring rate to not blow through travel too easily or "trapdoor" on harder hits/compressions but still being able to remain supple enough to aid good traction.
Remember midstroke support doesn't just come from the shock. It comes from a combination of the shocks spring rate, the shocks damping circuit/setting AND the bike's suspension leverage curve (leverage ratio throughout the stroke)

Just watch more of Steve's videos and you'll end up with a far better understanding than most of the replies you're likely to find here. He pretty much answered your question in the following few minutes after the clip you posted a link to

 

[RebornRider]

I agree that Steve provided an answer, and he seems to be a genuine Subject Matter Expert, but I'm always looking for additional input.

So far I haven't seen anything that suggests the following statement is wrong: A coil spring is said to have "better" mid stroke support than an air spring because, in the middle of the travel, it has a higher spring rate than the "equivalent" air spring. This is assuming they are tested on the same bike and with properly adjusted damping.

I'm listening!

 

[Gary]

and now I'm no longer listening

He already explained the questions you're asking. Watch the video again

 

[RebornRider]

G'bye princess! And congratulations on missing one of the points. (Hint: what do the people on this forum think "mid-stroke support" means?)

Finally found the curve of spring rate versus travel I remembered from one of Steve's videos.

 

[Gary]

any well designed FS frame should have it's spring curve optimised for either a coil or air shock (and in the case of air it should have been designed with a specific air shock in mind)
Many frames designed to be used with an air shock will perform worse with a coil shock.
midstroke of the frames leverage curve will be way out paired with the more linear (coil) spring. [edit] - as you've just found a graph to illustrate [/edit]

There have been plenty threads on here where folk are adamant they need to have an expensive coil shock fitted to their Eeb to improve it's performance. When in actual fact fititng a coil shock to many of their bikes will have been detrimentral to the performance of their suspension. and this is also why you'll find these same people struggling to find the correct spring weight. (because there really isn't an ideal weight spring once you've messed up leverage that badly)
But oddly enough you'll still find these people proclaiming the "percieved" improvements of their purchase.
so I honestly wouldn't put too much value in

what most people on this forum think

 

[Gary]

suppose I am a product design engineer who recently joined a bike company to work on a new mountain bike design.

I'm not sure what people mean when they use terms such as "mid stroke support"

My question would be. How the hell did you get the job?

 

[Mikerb]

Mikerb, I appreciate the time you spent responding to my post, but my current interest is trying to understand what mtb'ers mean by the word support

.........same as a jock strap....it means kept things under control when subjected to miscellaneous forces.
Stop overthinking it mate. You are not a design engineer, you are a rider. Set the thing up right and go hit some trails. If it sucks, change it. If it does the job, ride more trails.