MegNeg

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MegNeg
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Posted: Mar 21, 2021 at 22:02 Quote
R-M-R wrote:

Correct, but I'll clarify that "off the top" refers to the first third of the travel, not just the very first part of the stroke.

Okay thank you. I will start with the configuration you suggested and go from there. Thanks for your help.

Posted: Mar 21, 2021 at 23:06 Quote
Sounds good. These suggestions are just a starting point and it's possible we haven't precisely identified the cause of what you're feeling. You'll probably want to make further adjustments and experiment with negative spring volume, so feel free to check in whenever you want to discuss the strategy.

Posted: Mar 24, 2021 at 0:21 Quote
So looking for some advice on the MegNeg very interesting thread lots of opinions , my MegNeg is in the post I’m looking for a place to start with this I see (RMR) you advice 0 tokens each side as a start , would this apply for my status?

XL Santa Cruz Megatower
Rider weight-80kg geared up.
Fox 36 - no tokens - 5LR 4 HR compression fully open ( took me a while to get here very harsh any other way still not great but manageable)
RSD- standard- 25% sag 5 clicks of rebound - compression fully open.
Riding terrain - north of Scotland torridon ect lots of chatter.

Any help appreciated.

Posted: Mar 24, 2021 at 0:35 Quote
I almost always recommend starting with a fully open negative spring (zero bands) for two reasons:

1. A small negative spring creates a more abrupt increase in force and a soft "hammock" in the mid-stroke. Some situations may benefit from this, but it's more of a workaround than ideal.
2. This is expected to be an iterative process. It's easier to start from wide open.

The motion ratio curve of the Megatower is very progressive. Definitely start with the positive spring wide open (zero tokens) and run as much sag as you can accept. If this prevents you from using full travel, add negative spring reducers (bands) and lower the pressure to keep the sag constant with less force in the mid- and end-stroke.

Posted: Mar 24, 2021 at 5:25 Quote
R-M-R wrote:
I almost always recommend starting with a fully open negative spring (zero bands) for two reasons:

1. A small negative spring creates a more abrupt increase in force and a soft "hammock" in the mid-stroke. Some situations may benefit from this, but it's more of a workaround than ideal.
2. This is expected to be an iterative process. It's easier to start from wide open.

The motion ratio curve of the Megatower is very progressive. Definitely start with the positive spring wide open (zero tokens) and run as much sag as you can accept. If this prevents you from using full travel, add negative spring reducers (bands) and lower the pressure to keep the sag constant with less force in the mid- and end-stroke.

Thanks RMR for the quick response will report back once I find the sweet spot ????

Posted: Mar 25, 2021 at 5:30 Quote
I am lazy when it comes to posting but, this thread has been so helpful and has improved my riding so much that I felt I should mention my story with the MegNeg.

Rider weight fully kited: a bit under 80 Kg
Bike frame: Transition Patrol 2017, aluminium (XL)

When I bought the bike, one thing I immediately noticed was the fact that it was way too easy for me to bottom-out. I would go down a set of stairs with only 4 or 5 steps and the compression at the end would make the shock use full travel. Dropping of a 50 cm curb or even doing an aggressive bunny-hop would have the same effect.
Since suspension was supple with the 33-35% sag recommended by Transition, I focused on progression and eventually ended with 3 tokens in my super-deluxe to avoid the constant bottom-out. This was just partially effective, and I eventually reduced my sag to 28-30%.

I kinda learned to live with less than perfect set-up (modern geometry can compensate bad suspension settings to a certain degree), but as my skills progressed and I got faster/more aggressive, I began to understand that my bike lacked support. Going fast into berms made me bottom-out. Jump lips sucked all of my momentum. I actually felt my set-up was preventing me from riding better. I finally decided to buy the MegNeg.

After installing the megneg, I decided to start with two bands and two tokens, at 30% sag. This was an eye opener. Support was improved, very much so! At my usual speeds, I immediately started overshooting the local jumps (the bike didn't lost as much energy on the lips). There was a problem, however: too much ramp up. When going full speed over roots it was impossible to keep my feet on the pedals.

As RMR suggested, I decided to remove all bands and tokens. Since that lead to a huge increase in the air volume, I assumed bottom-out resistance would increase and I decided to also increase my sag and set it somewhere in the 33-35% interval Transition suggests. What a difference. I felt like I had added 20 mil of travel to the shock. I mean, roots and rocks became almost a non-issue, the bike would just plow over them. The support increased even more with the added psi needed to compensate the removal of the two bands. I did however still bottom out the bike on a couple of ocasions where I felt I shouldn't. I added one token and that has been my setup ever since.

In short: adding and setting the MegNeg transformed my bike and lead to a huge leap in my riding skills. I feel way more confident and composed.


A huge thank you to everyone in this thread, reading your posts really contributed to a better bike set-up. tup

Posted: Mar 25, 2021 at 18:17 Quote
Hey RMR, question for you as you really seem to have a wealth if information on this topic.

All things being equal, same base psi, no change in positive chamber volume reducers, what impact does removing negative bands have on the mid/end stroke support? If at all?

I'm wondering if the only thing that causes a change in the ramp up is the added base pressure in the positive chamber, or if there is something going on with the negative chamber "pulling" on the system as the chamber is being forced to expand.

I'm having some interesting results as I tune the setup on my v1 Sentinel, and I think I'm missing a piece of the knowledge puzzle!

Posted: Mar 25, 2021 at 20:24 Quote
steveclay wrote:
All things being equal, same base psi, no change in positive chamber volume reducers, what impact does removing negative bands have on the mid/end stroke support? If at all?

None. Once past the equalization port, there is no difference.

The extra mid-stroke support from the MegNeg comes from needing more pressure to hit the same sag. Once you get into the mid-stroke region, it behaves as the standard Debonair positive spring would with the extra pressure, which, obviously, means more support due to the higher pressure.

Posted: Mar 26, 2021 at 23:21 Quote
Bit of a newbie here. I recently built up my first new bike ever.
2020 Kona process 153
Weight 220lbs
Started with 2 positive tokens and was blowing through my travel. 30% sag 240 psi.

Megneg arrived and went with 2 bands in the negative and kept the 2 tokens in the positive. I bumped up the pressure to 270 and was still getting 30% sag. I was not using full travel and found It was a little harsh towards the end of the stroke.

Recently I pulled the negative bands and the positive tokens. bumped the psi to 280 and I am sitting between 30% and 35% sag. this setup was way better for me lots of support midstroke and good bottom out resistance. If I make any changes it will be to add one band to the negative.

My test trail has been new school flow with some 6-8 foot gap jumps. I am going to have to go try some tech to see how this setup works.

I feel that my air pressure is low when compared to what others are running and I am constantly checking my sag.
Thoughts?

Posted: Apr 8, 2021 at 10:39 Quote
Just thought I’d weigh in (ha ha) with my megneg experience as a heavier rider at 105kg

I have a 2019 V3 bronson C S build, and the shock never felt great stock. On the super deluxe R shock I was running ~250 psi, with the three positive token it comes with. Didnt feel playful or poppy, not very progressive, stiff and woody with small bump. Often went through the travel, but had to balance with small bump feel. My biggest desire was a more poppy and supportive shock. Based on everything I had read about megneg thought this was a good solution.

To start I went with 1 neg band and 2 positive tokens, 300 PSI (20% higher PSI)
Small bump - VERY compliant
Mid stroke / pedaling platform - slightly more supportive
Bottom out - Was still using all my travel

With this setup I noticed definitely more playful and poppy feel, good small bump, and I was initially very happy. However, was worried that using all my travel just on my local trails would mean a serious bottom out on a bigger hit.

Reading through this thread I gathered that if the issue was needing MORE bottom out resistance than I did not need to make changes to the negative side, but instead just needed to add PSI. So went up to max ~320-325 PSI, and with that I’m sitting somewhere around 30% Sag. The shock still FEELS good, and there is slightly better bottom out resistance than before but I’m still getting through the travel easier than I’d like. Maybe I am just too heavy of a rider for this and am limited by my max PSI.

Given the current situation at max PSI I have two thoughts:

1) If I am understand this thread correctly, adding more negative bands but keeping same PSI will change the leverage curve, decreasing small bump compliance, but shouldn’t really change my bottom out? However, this seems counterintuitive because more bands = closer to stock shock, and on the stock shock running 325 PSI would have been some serious bottom out resistance.

2) Adding a positive token back in in order to increase bottom out resistance? I dont think Ive ever been able to appreciate “too much” progression in a shock, if I am getting through the travel than more progressive should be better?

I welcome any ideas

Posted: Apr 8, 2021 at 11:03 Quote
vanhuette,

You're close on point 1. There's some "area under the curve" effect on total energy. Below is a chart that shows a slight increase in area under the curve from a fair bit more pressure.



The "maximum" pressure actually refers to the maximum pressure at bottom-out. Bottom-out pressure is higher with reducers (tokens) than without, so you can actually go considerably above "maximum" pressure if you're not using maximum reducers. This is "unofficial" advice, of course; just discussing the physics of it.

If you don't want to do that, your only option is to load it up with reducers or get a firmer high-speed compression damping tune.

Below is a chart for the Monarch because I couldn't quickly find a Deluxe chart.


Posted: Apr 8, 2021 at 11:58 Quote
Much appreciated response RMR, you’ve put a lot of time into this thread!

R-M-R wrote:
vanhuette,
There's some "area under the curve" effect on total energy. Below is a chart that shows a slight increase in area under the curve from a fair bit more pressure.

I think this is why I’m confused. According to the chart:

Increased negative size + HIGHER PSI to give same sag = more bottom out resistance

But assuming a constant PSI, which would shift the curve lower on the graph, it appears that increased negative size would give the same bottom out resistance (but with less small bump and more mid stroke) and approx. the same area under the curve overall.

Therefore theoretically increasing the number of negative bands in the megneg with constant PSI will decrease the benefits of the larger neg can but give me MORE bottom out resistance?

R-M-R wrote:

So you can actually go considerably above "maximum" pressure if you're not using maximum reducers.

Interesting, Ive never heard this. Do you have any ballpark on how much higher you’re able to go? Anyone else have experience with this?

Posted: Apr 8, 2021 at 12:50 Quote
Maximum pressure: I would have to look up the volumes and do some math. The gist is that you could go over by the same ratio as the change in compression ratio. The maximum pressure at full compression is the only thing that matters; that's the pressure that could damage the can or blow the seals. The shock doesn't care about 300 psi vs. 350 psi, it's the four-figure PSI at full compression that matters, and it's impractical for a manufacturer to give customers a complicated safety chart with maximums that depend on the configuration. They have to assume the worst case scenario (maximum reducers).

Spring support: At constant pressure, the change in the curve due to the MegNeg is primarily in the negative spring region (early part of the travel); there's not much change from the middle onward. At the same pressure, the MegNeg increases sag, decreases mid-stroke support (yes, decreases, because we're talking constant pressure), and creates little change to the bottom-out force. It slightly reduces the total work (energy) required to bottom out the suspension.

When running a MegNeg, the general idea is to increase the pressure, relative to the Debonair with smaller negative spring. If you can't increase the pressure, it complicates the decision of whether the MegNeg is right for you. As I said, I believe it's safe to go a bit over the "maximum" pressure. The amount you can go over depends on how many reducers you plan to use. Just by glancing at the Monarch chart, I'd think 10% over would be fine, assuming zero reducers. My extra-unofficial guess is that it's a lot more than 10%, but that's getting into uncharted territory and I definitely can't recommend that without further research.

Posted: Apr 10, 2021 at 11:28 Quote
R-M-R wrote:
I almost always recommend starting with a fully open negative spring (zero bands) for two reasons:

1. A small negative spring creates a more abrupt increase in force and a soft "hammock" in the mid-stroke. Some situations may benefit from this, but it's more of a workaround than ideal.
2. This is expected to be an iterative process. It's easier to start from wide open.

The motion ratio curve of the Megatower is very progressive. Definitely start with the positive spring wide open (zero tokens) and run as much sag as you can accept. If this prevents you from using full travel, add negative spring reducers (bands) and lower the pressure to keep the sag constant with less force in the mid- and end-stroke.

Hi RMR looking for some help again with Meg neg , currently running 0 positive 2 neg on my megatower it feels okay but is a bit harsh on chatter , I’m 30% sag occasionally using full travel and have 6 from closed on rebound just wondering what I should try next ? All most feels like there’s to much force and not supple of the top every now and then on hits I hear the wheel ding like I have to in weight the back end a bit to much over stuff.

Posted: Apr 10, 2021 at 17:41 Quote
Chassis suspension - forks and linkages - can react only so fast. It takes a while for them to start moving, move a useful amount, stop moving, and return to the neutral position. High-frequency impacts may be too fast for the suspension to keep up.

1. Consider lower tire pressure and/or larger tires. Tires react almost instantly. Also consider an insert, though I recommend avoiding the added mass of an insert, if possible.
2. Ensure your shock is in top condition, including the pivots and internal lubrication.
3. Reduce unsprung mass. The difference between a particularly heavy derailleur, cassette, wheel, and tire, versus a light equivalent in the same category, can be well over 3 lb., even without an insert. Less mass has less inertia and tracks the terrain better.
4. Help the wheel to move more quickly via one or more of the following:
• The MegNeg reduces support (force) in the early part of the stroke, reducing rebound speed. You could eliminate the MegNeg or add negative reducers (bands), but there are better solutions.
• Increase spring pressure. You may want to remove the positive reducers (tokens) to ensure you can still access full travel.
• Reduce rebound damping to help the wheel recover more quickly.
• Reduce low-speed compression damping to reduce the initial force.
• High-speed compression could get interesting. Intuitively, you may think to reduce it, but there can be situations where more HSC helps by reducing the amplitude of the suspension movements. Address the other points first, then experiment with this. Consider a less digressive tune or even a progressive tune (ex. flutter stack). My relevant areas of expertise are kinematics, fit, and chassis dynamics, so you'll want to discuss this with a damper designer.


 
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