MegNeg

PB Forum :: SRAM
MegNeg
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flag R-M-R
Posted: Feb 10, 2021 at 2:51 Quote
Any bike will have pop if it has zero damping, so yes, it's always possible.

As you can see from the chart I posted, the difference between the standard Debonair and the MegNeg isn't huge, just a little less spring support in the first third and a little more in the middle. Total energy storage is comparable in the first half or two-thirds of the travel, but less near top-out. I wouldn't say the MegNeg is clearly a pathway to more pop; that has to come from less damping.
flag Zmagas
Posted: Feb 10, 2021 at 4:42 Quote
R-M-R

looking at the chart it seems that coil have more mid-stroke support than air, but air ramps at the end of the travel. So just in theory coil should be better not only for initial sensitivity, but for pumping and active riding as well, just lacking top end ramp up support.
flag R-M-R
Posted: Feb 10, 2021 at 6:45 Quote
Coil has less support, then more, then less again - plus less seal friction, but that's become a minor issue on modern air shocks.
flag Zmagas
Posted: Feb 10, 2021 at 7:56 Quote
R-M-R,

sorry, but I don't understand the statement about coil less support, more support, less support. The graph is linear, so my understanding is that leverage curve/force is consistent, but maybe I'm missing something. It's less than a year that I own full suspension bike, so I'm still learning and trying to understand the concepts of the mtb suspension.

The one thing I noticed with my bike is that breakaway force is pretty high, you need a lot of force to start rear suspension moving. This was another reason to consider MegNeg. It is also interesting, that my Lyrik Ultimate can be quite firm yet very supportive, but still have good small bump compliance, for Super Deluxe its not the case, it's either firm or soft, it cannot be firm and supple, not sure if this is breakaway force or leverage curve in initial stroke
flag R-M-R
Posted: Feb 10, 2021 at 8:39 Quote
I'm comparing a coil to an air spring.

In the first approximately one-third of the travel, the coil offers less support than an air spring. In the "middle" approximately half of the travel, the coil offers more support. In the last approximately sixth of the travel, the coil offers less. These are approximate numbers, of course, and can change a little with how you configure the air spring.

If what you're feeling with your shock is breakaway force, you should get the shock serviced. If you're feeling spring force, there could be something wrong with your negative spring.
flag Zmagas
Posted: Feb 10, 2021 at 9:27 Quote
R-M-R,

ok, understood the part about the coil.

Keep in mind that I don't own the MegNeg yet. I noticed this breakaway force characteristics right from the box, so I don't think it is a matter of servicing, I think maybe this is the behavior of shock / linkage design. This is why I considering NegMeg to get the shock moving more freely increasing sensitivity and slightly enhancing mid-stroke. For me it seems that bike comes alive only after reaching 50% of the travel.
flag R-M-R
Posted: Feb 10, 2021 at 15:36 Quote
When you refer to the breakaway force, do you mean the first millimeter of travel or do you mean the first approximately centimeter of travel?

If your goal is to more easily get into the ~50% range of the travel and to have more support once you reach that zone, then yes, a MegNeg will help (the fewer bands, the better) and a coil will help even more.
flag Zmagas
Posted: Feb 11, 2021 at 2:20 Quote
R-M-R wrote:
When you refer to the breakaway force, do you mean the first millimeter of travel or do you mean the first approximately centimeter of travel?

R-M-R

Both (1mm and 1cm) have high break away point, but it seems that after passing this 1cm it becomes easier for shock to move further.

So I don't know if this is stiction or leverage curve of the shock?

In case this is result of leverage curve then I suppose only MegNeg can help with.
flag R-M-R
Posted: Feb 11, 2021 at 10:51 Quote
1 mm is stiction or a faulty negative spring. Confirm the transfer port is not damaged or blocked.

1 cm is the spring curve.
flag singleandluvinit
Posted: Feb 12, 2021 at 9:59 Quote
Im surprised at how much better it made my Patrol feel vs how little it looks like it changes in terms of actual numbers. Im able to run rebound quite a bit slower and still not get any of that choppiness I was getting with a DPX2. I havent noticed a big difference in bottom out but it made a dramatic difference in repeated hit performance, I can feel it softly absorb each hit on sections that would bounce my feet off the pedals.

Im at 1 negative spacer and 2 positive. I'll probably try 0 negative spacers just to see what its like for bottom out resistance.

What is the difference in feel between less negative spacers vs more positive?
flag R-M-R
Posted: Feb 12, 2021 at 10:43 Quote
singleandluvinit wrote:
What is the difference in feel between less negative spacers vs more positive?

Negative spring volume reducers affect the start of the stroke and positive spring volume reducers affect the end. These changes allow you to alter the base pressure, so we'll explore that. I'll refer to the charts below.

On the first chart, notice the lower spring force of the MegNeg in the early part of the stroke. The more you restrict a negative spring, the more it takes on the S-shape; the less restricted, the more it approaches the straight line of a coil spring.

There is less spring support with a more linear early stroke, so you would have more sag for the same base air pressure. That's fine, or you can increase base pressure to maintain your sag. If you do the latter, the spring curve will rise beyond the end of the negative spring region (let's call it one-third travel). This would make the mid-stroke and end-stroke force higher than it was before, so you may want to remove a positive spring volume reducer to bring down the end-stroke force. To recap, these changes would lower the spring force curve in the early stroke, raise it in the middle, and lower it in the end. You can see how this makes the spring curve more linear.

In terms of how this would feel, it depends on whether you allow a little more sag or maintain your existing sag. The early stroke can be more supple or the same; the middle can be the same or firmer, and the end can be the same or firmer.

Now let's switch to positive spring volume reducers, shown in the second chart. The effect is significant only near the end of the stroke. If you were to add a positive chamber reducer and not change the negative side, you would exaggerate the S-shape of the curve. You would probably want to reduce the base spring pressure a little to maintain usable end-stroke force. This would make the spring softer everywhere other than the end, which will feel most noticeable as a soft mid-stroke. Some riders would call this "wallowy"; others would call it "plush, yet bottomless".

The spring curve should be considered together with the motion ratio curve of the bike. In the case of the Patrol, the average motion ratio curve is fairly flat (it's actually an S-shape, but let's simplify things). Compared to other bikes, it's less naturally supple off the top and has less bottom-out resistance, but mid-stroke support is high. It's a good candidate for reducers on the positive spring side.


photo
RockShox DebonAir spring curve
flag scottziesman
O+
Posted: Feb 12, 2021 at 11:24 Quote
R-M-R wrote:
singleandluvinit wrote:
What is the difference in feel between less negative spacers vs more positive?

Negative spring volume reducers affect the start of the stroke and positive spring volume reducers affect the end. These changes allow you to alter the base pressure, so we'll explore that. I'll refer to the charts below.

On the first chart, notice the lower spring force of the MegNeg in the early part of the stroke. The more you restrict a negative spring, the more it takes on the S-shape; the less restricted, the more it approaches the straight line of a coil spring.

There is less spring support with a more linear early stroke, so you would have more sag for the same base air pressure. That's fine, or you can increase base pressure to maintain your sag. If you do the latter, the spring curve will rise beyond the end of the negative spring region (let's call it one-third travel). This would make the mid-stroke and end-stroke force higher than it was before, so you may want to remove a positive spring volume reducer to bring down the end-stroke force. To recap, these changes would lower the spring force curve in the early stroke, raise it in the middle, and lower it in the end. You can see how this makes the spring curve more linear.

In terms of how this would feel, it depends on whether you allow a little more sag or maintain your existing sag. The early stroke can be more supple or the same; the middle can be the same or firmer, and the end can be the same or firmer.

Now let's switch to positive spring volume reducers, shown in the second chart. The effect is significant only near the very end of the stroke. If you were to add a positive chamber reducer and not change the negative side, you would exaggerate the S-shape of the curve. You would probably want to reduce the base spring pressure a little to maintain usable end-stroke force. This would make the spring softer everywhere other than the end, which will feel most noticeable as a soft mid-stroke. Some riders would call this "wallowy"; others would call it "plush, yet bottomless".

The spring curve should be considered together with the motion ratio curve of the bike. In the case of the Patrol, the average motion ratio curve is fairly flat (it's actually an S-shape, but let's simplify things). Compared to other bikes, it's less naturally supple off the top and has less bottom-out, but mid-stroke support is high. It's a good candidate for reducers on the positive spring side.


photo
RockShox DebonAir spring curve

I am in awe of your level of bike nerdery!

I decided to try a cascade link on my Sentinel rather than a MegNeg. But I can’t stop coming back to this thread because I feel like I’m learning so much. @R-M-R is this something you do for a living? I very much appreciate you contributions.
flag R-M-R
Posted: Feb 12, 2021 at 11:45 Quote
Thank you; glad it helps. Salute

Yes, this is.
flag ThinkTank45
Posted: Feb 13, 2021 at 8:47 Quote
My new bike is a 2020 Nukeproof Mega 29.
I rode it first without the megneg, with just a touch under 30% sag and two volume reducers. Initial impression was incredibly plush rear suspension but lacking in support when trying to pump on flatter sections.
I installed the megneg and removed both positive volume reducers, so I'm starting out with no bands or tokens and 30% sag.
Only one ride done so far but it feels good. I may need to add back one positive volume reducer but I will do some more riding before deciding. I find it difficult to judge the rebound damping of the shock with the megneg because of the increased mid stroke support. Usually I can balance the rebound front and rear pretty quickly just by bouncing around the car park but it takes longer with the megneg.
flag R-M-R
Posted: Feb 13, 2021 at 9:27 Quote
ThinkTank45,

If you're having trouble balancing the front and rear, you could also consider changing the fork to match the rear, rather than the rear to match the front.

 


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