2019 Stumpjumper Evo

PB Forum :: Specialized
2019 Stumpjumper Evo
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Posted: Nov 10, 2019 at 23:35 Quote
R-M-R wrote:
Arierep wrote:
In this case I blame it on the very high AM9 anti squat.

I'm not doubting your experience of the two bikes having different bump compliance, but I think you've incorrectly attributed it.

For a given sprocket combination, bikes with high anti-squat have a high virtual pivot point ("instant centre"). There's a little more to it than that, but that's the general idea. It's widely believed a high instant centre improves compliance: this is one of the reasons for the recent appearance of some high pivot designs with idler sprockets to manage kickback. Therefore, high anti-squat usually results in better impact management, all else being equal.

The ways in which high anti-squat can harm compliance:

1. Pedal kickback interfering with suspension function.
2. Derailleur clutch force interfering with suspension.

Pedal kickback while coasting is a myth and this can be calculated:

• Take the circumference of the wheel.
• Calculate the maximum pedal kickback in any given sprocket combination, in degrees.
• Multiply (kickback / 360°) × circumference. This is how much the wheel would have to rotate to negate all kickback.

• Take the speed you usually travel while using the sprocket combination from the previous calculation.
• Calculate how long it would take you to travel the distance from the previous calculation. This is the maximum allowable time in which to fully - from top-out to bottom-out - compress your shock for any pedal kickback to occur, let alone enough kickback to be a problem.

• Divide you shock's stroke by this time you just calculated. That's the shaft velocity of the slowest possible impact that will produce any kickback. You will find this shaft velocity is unrealistic. If your shock goes from top-out to bottom-out in 0.03 seconds, for example, you have bigger problems than a little kickback.

But wait, there's more!

This calculation didn't even account for any delay in the engagement of your hub's driver. If the average engagement is, say, 10°, then the average amount of engagement is 5°. This takes 5° off the average possible amount of kickback in a full travel impact, making the situation even less likely to produce any kickback, let alone problematic kickback.

Similarly, it's essentially a myth that the derailleur clutch can interfere with suspension. I'll be more brief this time:

1. The clutch doesn't move immediately and often doesn't move at all.
2. If the clutch does move, the clutch breakaway occurs after the suspension starts to move, so it doesn't contribute to "breakaway" force.
3. If the clutch does move, the static friction does hamper suspension performance, but the force is so small, relative to everything else happening in an impact event.
4. Once the clutch is in motion, the dynamic friction and spring force simply add to the spring and damper forces of the suspension.
5. The motion of the clutch is so small. Work = force × distance. The force is small: you can easily move it with one finger; think of how small that is, compared to the impact. The distance is small: the clutch rotates only a few degrees. Thus, the work to overcome is it virtually nothing.

So, why did Gwin and Mulally have great results without chains? It certainly wasn't because of the "improved" suspension performance from not having kickback and/or clutch interference. My guess is they knew they had to be super smooth, since they couldn't recover from a mistake with some pedaling, so they rode with fewer errors and perfectly executed the "slow in, fast out" philosophy of corners.



P. S. Regarding the discussion of EXT shocks in this thread: I ride an EXT Arma. It's really nice. Difficult to say whether it's worth the price, but it really is nice. Did I mention it's nice?

EXT is cheaper than a Push and not much more than a Fox.... out performs both.

Posted: Nov 12, 2019 at 8:32 Quote
severniy wrote:
vasilly wrote:
After a month on alloy S3 29" I would say - go for 29"! I've been on a 27,5" for 4 years prior and after a first day I was impressed by the way the 29" smooths the trails. No lost for joy of jumping at all. Grip in cornering better also.

What's your height?

5'11. S3 suits me perfect.

Posted: Nov 13, 2019 at 13:55 Quote
R-M-R...I brought the following over from another thread:

"It's not surprising the Cane Creek shock wasn't super plush: unless a Cane Creek shock as their LinEAir can, the negative spring is small, so the off-the-top feeling isn't great"

What are your thoughts on a RS Super Deluxe with MegNeg for the Evo 29? I believe you mentioned it has a large(r) negative air spring. Thanks.

Posted: Nov 13, 2019 at 14:08 Quote
kwapik wrote:
R-M-R...I brought the following over from another thread:

"It's not surprising the Cane Creek shock wasn't super plush: unless a Cane Creek shock as their LinEAir can, the negative spring is small, so the off-the-top feeling isn't great"

What are your thoughts on a RS Super Deluxe with MegNeg for the Evo 29? I believe you mentioned it has a large(r) negative air spring. Thanks.

First, thank you for correcting my typo. Wink

The MegNeg is a larger negative spring. That's its whole reason for existing. And a good reason it is: too-small negative springs have plagued air shock performance throughout their history.

There are almost no situations in which I wouldn't recommend the MegNeg version of the Super Deluxe. Some bikes don't really beg for it, if they have a highly progressive motion ratio; if the motion ratio is linear or if it has the dreaded mid-stroke "hammock", then the MegNeg will be a revelation.

So yes, the MegNeg would help a SJ EVO more than it would help some other bikes. You could crank up the spring pressure to get the support you need in the middle and end of the travel without the initial travel being overly harsh.

Posted: Nov 13, 2019 at 14:52 Quote
Thank you. I appreciate all the help.

Posted: Nov 13, 2019 at 15:54 Quote
R-M-R wrote:
kwapik wrote:
R-M-R...I brought the following over from another thread:

"It's not surprising the Cane Creek shock wasn't super plush: unless a Cane Creek shock as their LinEAir can, the negative spring is small, so the off-the-top feeling isn't great"

What are your thoughts on a RS Super Deluxe with MegNeg for the Evo 29? I believe you mentioned it has a large(r) negative air spring. Thanks.

First, thank you for correcting my typo. Wink

The MegNeg is a larger negative spring. That's its whole reason for existing. And a good reason it is: too-small negative springs have plagued air shock performance throughout their history.

There are almost no situations in which I wouldn't recommend the MegNeg version of the Super Deluxe. Some bikes don't really beg for it, if they have a highly progressive motion ratio; if the motion ratio is linear or if it has the dreaded mid-stroke "hammock", then the MegNeg will be a revelation.

So yes, the MegNeg would help a SJ EVO more than it would help some other bikes. You could crank up the spring pressure to get the support you need in the middle and end of the travel without the initial travel being overly harsh.

What about the MegNeg on a '17 Patrol? Considering a coil but it seems I could still retain some bottom out resistance.

Posted: Nov 13, 2019 at 21:43 Quote
kwapik wrote:
Thank you. I appreciate all the help.

Salute


dirtnapped wrote:
What about the MegNeg on a '17 Patrol? Considering a coil but it seems I could still retain some bottom out resistance.

As I mentioned, it would take a very unusual situation for a large negative spring to not improve the kinematics of a bike.

Ideally, bottom-out resistance should come from a combination of spring and damper. If you need a lot more support, consider a firmer damper tune.

The Patrol has a fairly flat leverage curve. There's a dip that hits its minimum at around 20% travel, which I assume is to compensate for the rapid increase in spring rate at that point on shocks with small negative springs. For this reason, the Patrol will work fine with the original negative spring or the MegNeg.

What do you find most appealing about a coil spring? Maybe there's a way to get what you're looking for with an air spring.

Posted: Nov 14, 2019 at 10:44 Quote
R-M-R wrote:
kwapik wrote:
Thank you. I appreciate all the help.

Salute


dirtnapped wrote:
What about the MegNeg on a '17 Patrol? Considering a coil but it seems I could still retain some bottom out resistance.

As I mentioned, it would take a very unusual situation for a large negative spring to not improve the kinematics of a bike.

Ideally, bottom-out resistance should come from a combination of spring and damper. If you need a lot more support, consider a firmer damper tune.

The Patrol has a fairly flat leverage curve. There's a dip that hits its minimum at around 20% travel, which I assume is to compensate for the rapid increase in spring rate at that point on shocks with small negative springs. For this reason, the Patrol will work fine with the original negative spring or the MegNeg.

What do you find most appealing about a coil spring? Maybe there's a way to get what you're looking for with an air spring.

Can't say I fault the super deluxe at all, but always looking at trying something else. I've found it tracks really well between 33-35%, but lots of pedal strikes (considering 165 cranks). I'm hoping with coil I can run less sag (25-30% maybe?)and still have it track well, and also keep some pop, and not have it bottom out all the time as well, with it being not super progressive. Currently maxed out on bottomless tokens.

Posted: Nov 14, 2019 at 18:12 Quote
dirtnapped wrote:
Can't say I fault the super deluxe at all, but always looking at trying something else. I've found it tracks really well between 33-35%, but lots of pedal strikes (considering 165 cranks). I'm hoping with coil I can run less sag (25-30% maybe?)and still have it track well, and also keep some pop, and not have it bottom out all the time as well, with it being not super progressive. Currently maxed out on bottomless tokens.

There's a lot to unpack here.

First, remove some tokens, raise the spring pressure, and, if it feels harsh, slightly reduce the low-speed compression damping. This will raise the ride height and still allow you to access full travel.

A coil spring is fully linear - or mildly progressive if you get an MRP progressive spring. You will need to run a lot less sag to have similar bottom-out resistance to your current set-up. 25% may still be too much. You may be a candidate for a firmer compression damper tune, as it sounds like you're relying too heavily on the spring to support you.

Raising the spring rate will help retain the "pop". If you try a firmer compression tune, you may not need much - if any - more spring rate and you'll probably want less rebound damping.

Posted: Nov 14, 2019 at 19:50 Quote
I might be asking a lot, but I appreciate the response and feedback!

Posted: Nov 14, 2019 at 20:43 Quote
dirtnapped wrote:
I might be asking a lot, but I appreciate the response and feedback!

Always happy to help. Keep me posted on how things develop as you experiment with the tuning.

Posted: Nov 18, 2019 at 5:32 Quote
R-M-R wrote:
dirtnapped wrote:
I might be asking a lot, but I appreciate the response and feedback!

Always happy to help. Keep me posted on how things develop as you experiment with the tuning.

Any experience with the dpx2 that comes standard on the evo? I've been playing with mine and am considering the largest volume spacer. I removed the negative spacers and the initial brake away is 10times better but want it to feel plusher without changing where it sits in it's travel. You seem to know your shit so thought it ask ????

Posted: Nov 18, 2019 at 10:28 Quote
doxey91 wrote:
R-M-R wrote:
dirtnapped wrote:
I might be asking a lot, but I appreciate the response and feedback!

Always happy to help. Keep me posted on how things develop as you experiment with the tuning.

Any experience with the dpx2 that comes standard on the evo? I've been playing with mine and am considering the largest volume spacer. I removed the negative spacers and the initial brake away is 10times better but want it to feel plusher without changing where it sits in it's travel. You seem to know your shit so thought it ask ????

Mine (2020) came with the biggest spacer fitted. Felt harsh and couldn't get full travel without lowering pressure, which makes it feel even harsher.

Took the spacer out, and upped the pressure to what specialized recommend on their calculator, now it feels great, plush and poppy, and can get full travel. Haven't touched the negative spacers.

I've since cut out the 5mm travel restrictor, makes the bigger hits that bit more comfortable too.

Posted: Nov 18, 2019 at 10:36 Quote
Suspension calculator:
https://www.specialized.com/us/en/suspension-calculator/app

Posted: Nov 18, 2019 at 16:54 Quote
doxey91 wrote:
Any experience with the dpx2 that comes standard on the evo? I've been playing with mine and am considering the largest volume spacer. I removed the negative spacers and the initial brake away is 10times better but want it to feel plusher without changing where it sits in it's travel. You seem to know your shit so thought it ask ????

The only ways to make it feel softer without changing ride height are to remove positive spring spacers, as moity noted, and/or reduce compression damping.

Maybe a third option: if your rebound damper is set far too slow, speed it up.


 
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