MegNeg

PB Forum :: SRAM
MegNeg
Author Message
Posted: Jul 26, 2021 at 15:20 Quote
samboa wrote:
vastamyrkky wrote:
Hello everyone. Here are some thoughts of mine about megneg and suspension tuning in general.

Some background with megneg: I just bought megneg for my sons (less than 40kg geared up) Bronson V3. Before the megneg he was on 30% seated sag (who has patience to balance for riding position sag anyway) with 110psi and 3 tokens. Results, bent shock bolt, torn bottom out o-ring and bent bottom out metal plate on top of the inner shaft (btw if you've dropped the travel indicator o-ring from the shock shaft you've probably broken the bottom out o-ring at least on 210x55 super deluxe).

So obviously try megneg. Now with megneg with 132psi, two tokens and two bands 28% seated sag still bottoms out. We tried 145psi and the bottoming out is only on 1.5m drops to flat and I believe it's not harsh anymore. I didn't measure the sag as I was more keen to get rid off the bottoming out and keep the bike from further damage. The rider seems happy but he didn't complain albeit bent the 8mm bolt. So there is more testing to do. I could try less bands and more pressure to get to right sag and not bottom out but will it be too soft on mid travel? Or I could add the 3rd positive air chamber token. But how can a 11y old tell the difference? Once I get my hands on shockwiz I may have more info on how to proceed.

This sure is hard and time consuming way to tune bikes this way. Andrextr has a spreadsheet for air shock force calculation but without air chamber dimensions of megneg its not very accurate (spreadsheet published before megneg). I think rockshox should publish charts or a web page for figuring this out. I mean, why is there a topic with 34 pages about an air can of a rear shock? It shouldn't be this complicated. Maybe we should be talking about rider preferences and correct force curves on shocks rather than absolute values which are dependent of mostly rider weight, rider preference and leverage ratio of the bike.

Just my two cents.

The key is understanding what the MegNeg does, which in the nicest possible way, it seems like you don't..... if you're trying to reduce bottoming out, the MegNeg is not the right tool to focus on. Air pressure and bottom out tokens will do that.

I agree with samboa. Although Megneg does increase resistance at the end of the stroke, if you have used all of the bottom out spacers and a decent amount of air and your son is still bottoming out (which is not bad ocasionally) the rear shock might need some work to get a firmer tune.

Posted: Jul 26, 2021 at 18:53 Quote
samboa wrote:
vastamyrkky wrote:
Hello everyone. Here are some thoughts of mine about megneg and suspension tuning in general.

Some background with megneg: I just bought megneg for my sons (less than 40kg geared up) Bronson V3. Before the megneg he was on 30% seated sag (who has patience to balance for riding position sag anyway) with 110psi and 3 tokens. Results, bent shock bolt, torn bottom out o-ring and bent bottom out metal plate on top of the inner shaft (btw if you've dropped the travel indicator o-ring from the shock shaft you've probably broken the bottom out o-ring at least on 210x55 super deluxe).

So obviously try megneg. Now with megneg with 132psi, two tokens and two bands 28% seated sag still bottoms out. We tried 145psi and the bottoming out is only on 1.5m drops to flat and I believe it's not harsh anymore. I didn't measure the sag as I was more keen to get rid off the bottoming out and keep the bike from further damage. The rider seems happy but he didn't complain albeit bent the 8mm bolt. So there is more testing to do. I could try less bands and more pressure to get to right sag and not bottom out but will it be too soft on mid travel? Or I could add the 3rd positive air chamber token. But how can a 11y old tell the difference? Once I get my hands on shockwiz I may have more info on how to proceed.

This sure is hard and time consuming way to tune bikes this way. Andrextr has a spreadsheet for air shock force calculation but without air chamber dimensions of megneg its not very accurate (spreadsheet published before megneg). I think rockshox should publish charts or a web page for figuring this out. I mean, why is there a topic with 34 pages about an air can of a rear shock? It shouldn't be this complicated. Maybe we should be talking about rider preferences and correct force curves on shocks rather than absolute values which are dependent of mostly rider weight, rider preference and leverage ratio of the bike.

Just my two cents.

The key is understanding what the MegNeg does, which in the nicest possible way, it seems like you don't..... if you're trying to reduce bottoming out, the MegNeg is not the right tool to focus on. Air pressure and bottom out tokens will do that.

Hey Sambo you are actually wrong. Due to the very nature of the MegNeg it will increase bottom out resistance. You increase the negative chamber which in turn requires more air pressure to equalize the positive and negative at a given sag point example 25%. The negative chamber only effects initial stroke of the shock and once you pass that point it has no effect on assisting you through the travel. Now increasing air pressure increases spring rate which both increase midstroke support and bottom out resistance. This is why Rockshox recommends taking out two bottomless tokens. The key is trial and error. Start at a desired sag ride.. bottom out add tokens try again if you max out on tokens at the desired sag, then add megneg take out two tokens and start with zero bands. If mid stroke is to supportive add band and try again. Keeping identical sag percentage regardless of air pressure. If mid stroke support is good but you bottom out add a token. Its simple just requires a lot of testing and back to back runs. You need to write every change down and feedback notes to help dial it in.

Posted: Jul 27, 2021 at 2:16 Quote
davrob76 wrote:

Hey Sambo you are actually wrong. Due to the very nature of the MegNeg it will increase bottom out resistance. You increase the negative chamber which in turn requires more air pressure to equalize the positive and negative at a given sag point example 25%. The negative chamber only effects initial stroke of the shock and once you pass that point it has no effect on assisting you through the travel. Now increasing air pressure increases spring rate which both increase midstroke support and bottom out resistance. This is why Rockshox recommends taking out two bottomless tokens. The key is trial and error. Start at a desired sag ride.. bottom out add tokens try again if you max out on tokens at the desired sag, then add megneg take out two tokens and start with zero bands. If mid stroke is to supportive add band and try again. Keeping identical sag percentage regardless of air pressure. If mid stroke support is good but you bottom out add a token. Its simple just requires a lot of testing and back to back runs. You need to write every change down and feedback notes to help dial it in.

Hey davrob76, you are almost 100% correct, and I'm super happy you wrote that all out so hopefully Vastamyrkky can find it useful. I say almost 100%, because the nature of the Megneg doesn't increase bottom out resistance, it only (as you correctly said) increases the negative chamber volume. That allows you to run higher pressures, which in turn gives you improved bottom out resistance. Sorry if that sounds pedantic.

For example, pre Megneg, I had my pressures set so I had midstroke support and didn't bottom out. I wanted better small bump, which the Megneg gave me. So from my perspective, it didn't affect bottom out, it made the initial travel softer. I just think it's important to be very clear what the Megneg is doing, which in turn helps people understand.

So I disagree that I am wrong, because ultimately it's adding air pressure that would solve the problem in Vastamyrkky's case. His son is bottoming out, so adding air pressure or bottom out tokens is what he needs. Now if that means his son loses the inital sensitivity of the travel then he should start playing with the Megneg again and fine-tune it.

I appreciate I'm splitting hairs a bit, but this thread is indeed 34 pages long, and it has a tonne of awesome information in it which explains how the Megneg works. If people read it first, a lot of time would be saved on here. Just to be clear, I'm not saying people shouldn't ask questions, it's just helpful if people try and figure things out for themselves first!

Posted: Jul 28, 2021 at 4:15 Quote
ashmtb85 wrote:
IeatRocks wrote:
Just installed my Megneg on a 2020 Mega. Haven't been out for a ride but when cycling the shock I can here a little hiss or squish from the shock right around the 18% stroke mark. Is this just the shock equalizing or do I have something else going on. Browsed the forum and used Google but didn't come up with anything.

Just curious how much do you weigh and how many positive tokens do you have installed? I weigh 150 lb and running like 35% sag with no spacers I still couldn't get full travel. The bike felt harsh and overly progressive/damped so I switched to a coil with a light tune. When I read about people running so little sag with megneg which increases bottom out resistance I find this so surpsining. I have a 2020 mega 275.

I have a megneg on my 2020 Mega 290. I run it at 30% sag with no spacers in positive or negative. I've had it that way for 6 months or so. I would say I've only used full travel once in that time! I weigh 78kg/170 lbs.
I regularly use 90-95% of travel on big impacts and hucks to flat.
I suppose I should add some negative volume reducers but I like how the bike feels so haven't been bothered.

Posted: Jul 28, 2021 at 14:23 Quote
samboa wrote:
davrob76 wrote:

Hey Sambo you are actually wrong. Due to the very nature of the MegNeg it will increase bottom out resistance. You increase the negative chamber which in turn requires more air pressure to equalize the positive and negative at a given sag point example 25%. The negative chamber only effects initial stroke of the shock and once you pass that point it has no effect on assisting you through the travel. Now increasing air pressure increases spring rate which both increase midstroke support and bottom out resistance. This is why Rockshox recommends taking out two bottomless tokens. The key is trial and error. Start at a desired sag ride.. bottom out add tokens try again if you max out on tokens at the desired sag, then add megneg take out two tokens and start with zero bands. If mid stroke is to supportive add band and try again. Keeping identical sag percentage regardless of air pressure. If mid stroke support is good but you bottom out add a token. Its simple just requires a lot of testing and back to back runs. You need to write every change down and feedback notes to help dial it in.

Hey davrob76, you are almost 100% correct, and I'm super happy you wrote that all out so hopefully Vastamyrkky can find it useful. I say almost 100%, because the nature of the Megneg doesn't increase bottom out resistance, it only (as you correctly said) increases the negative chamber volume. That allows you to run higher pressures, which in turn gives you improved bottom out resistance. Sorry if that sounds pedantic.

For example, pre Megneg, I had my pressures set so I had midstroke support and didn't bottom out. I wanted better small bump, which the Megneg gave me. So from my perspective, it didn't affect bottom out, it made the initial travel softer. I just think it's important to be very clear what the Megneg is doing, which in turn helps people understand.

So I disagree that I am wrong, because ultimately it's adding air pressure that would solve the problem in Vastamyrkky's case. His son is bottoming out, so adding air pressure or bottom out tokens is what he needs. Now if that means his son loses the inital sensitivity of the travel then he should start playing with the Megneg again and fine-tune it.

I appreciate I'm splitting hairs a bit, but this thread is indeed 34 pages long, and it has a tonne of awesome information in it which explains how the Megneg works. If people read it first, a lot of time would be saved on here. Just to be clear, I'm not saying people shouldn't ask questions, it's just helpful if people try and figure things out for themselves first!

Oh yea Samboa i was just saying that with the megneg you can increase spring rate enough to prevent bottom out without sacrificing small bump. Thats all i was saying if you went through all the other steps then move on to megneg. With megneg you arent simply tuning bottom out you are increasing spring rate to help with bottom out

Posted: Aug 4, 2021 at 8:27 Quote
If you were to put a megneg on your bike and pack the neg chamber full of bands and no spacers in the positive chamber would this make the bike less progressive since the ratio of positive/negative goes up? Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?

Posted: Aug 4, 2021 at 8:30 Quote
Not sure if this is allowed, but i have a megneg for sale if anyone wants to try it. it's brand new, didn't end up using it.

230/205x57.5-65mm stroke, brand new in the box. could save someone a few bucks - pinkbike.com/buysell/3120980/

Posted: Aug 4, 2021 at 12:53 Quote
ashmtb85 wrote:
If you were to put a megneg on your bike and pack the neg chamber full of bands and no spacers in the positive chamber would this make the bike less progressive since the ratio of positive/negative goes up? Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?

I think with the megneg full of negative bands, the negative chamber is still 60% larger than on a standard super deluxe.

Posted: Aug 4, 2021 at 14:23 Quote
ThinkTank45 wrote:
ashmtb85 wrote:
If you were to put a megneg on your bike and pack the neg chamber full of bands and no spacers in the positive chamber would this make the bike less progressive since the ratio of positive/negative goes up? Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?

I think with the megneg full of negative bands, the negative chamber is still 60% larger than on a standard super deluxe.

How about in terms of positive/negative ratio? My question is if this is some sort of a hack to make the rear end of a bike less progressive

Posted: Aug 4, 2021 at 18:23 Quote
ashmtb85 wrote:
ThinkTank45 wrote:
ashmtb85 wrote:
If you were to put a megneg on your bike and pack the neg chamber full of bands and no spacers in the positive chamber would this make the bike less progressive since the ratio of positive/negative goes up? Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?

I think with the megneg full of negative bands, the negative chamber is still 60% larger than on a standard super deluxe.

How about in terms of positive/negative ratio? My question is if this is some sort of a hack to make the rear end of a bike less progressive
How do you define progressive?
Adding negative spacers won't change progression in the bottom half of travel.
Is the air can volume without spacers really too small?

Posted: Aug 5, 2021 at 2:44 Quote
ashmtb85 wrote:
ThinkTank45 wrote:
ashmtb85 wrote:
If you were to put a megneg on your bike and pack the neg chamber full of bands and no spacers in the positive chamber would this make the bike less progressive since the ratio of positive/negative goes up? Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?

I think with the megneg full of negative bands, the negative chamber is still 60% larger than on a standard super deluxe.

How about in terms of positive/negative ratio? My question is if this is some sort of a hack to make the rear end of a bike less progressive

Well, the positive chamber size doesn't change when you add a megneg to a super deluxe. So you have the same positive chamber and a negative chamber that's 60% larger than stock.

In answer to 'Would this setup be less progressive than a setup with similar sag and no spacers in the stock air can?'
...Almost certainly not.
You would have to run much higher air pressure in the megneg equipped shock to achieve the same sag. This would mean that the force required to use full travel would be higher.

Posted: Aug 8, 2021 at 3:12 Quote
luckyguy19 wrote:
...
My stock shock is starting to making air noises when cycling through the stroke like it has air in the dampening oil. I've had this happen before and a rebuild of the shock cured it. It will be a week or so till I get the oil and check ball to fix the stock shock so I'd like to play around with the Super Deluxe.
...

I did have the exact same issue with my stock thru shaft RT3 on a 2019 Slash 8.
A full service and rebleed fixed the issue. At the same time I've also installed the Megneg.
Currently I'm running 2 neg. bands, 0 tokens at 220psi (weight approx. 80kgs/176lbs).

But now the issue with the knocking sound and air noises starts to reappear. It just happens in the first few cycles and goes away then. But it starts to happen again once the bike is not ridden and the shock without use for some minutes.

It seems that the dummy shaft definitely leaks oil from the damper with time and use.
I could imagine the reason is either due to bottoming out every now and then or due to overheating of the shock, which leads to oil being force out of the dummy shafts seals.
It's funny that it wasn't an issue for several months riding on my more mellow home trails, but the shock obviously doesn't like riding bike parks all day long ...

Did you identified the issue in more detail?
Is there something one can do other than completely rebuilding the shock?

Thanks!

Posted: Aug 16, 2021 at 0:07 Quote
I have been reading this thread for the last two hours and there is some great information and recommendations on here. However, I could not find any information about running a MegNeg on a Yeti SB150. Does anyone have any experience running the MegNeg on the this bike?

I've been running the MegNeg on my Super Deluxe Ultimate for about 6 weeks. I just went with the Rock Shox recommendation of removing 1 positive token and adding two negative bands. This for the most part has been ok, but I am looking for the Goldilocks set-up.

I am considering the following alternative set-ups

0 positive & 0 negative
0 Positive & 1 negative
0 Positive & 2 negative

I have not changed anything but the sag since initial set-up. I started running at about 35% sag, but was bottoming out too often. I am now at 30% and have not achieved full travel. The bike is fairly linear, so I'm thinking the MegNeg should work well with 30% sag. For reference, my rider weight is approximately 215 lbs.

Any thoughts or recommendations would be greatly appreciated...thanks!

Posted: Aug 19, 2021 at 10:38 Quote
dadbod72 wrote:

I am considering the following alternative set-ups

0 positive & 0 negative
0 Positive & 1 negative
0 Positive & 2 negative

I have not changed anything but the sag since initial set-up. I started running at about 35% sag, but was bottoming out too often. I am now at 30% and have not achieved full travel. The bike is fairly linear, so I'm thinking the MegNeg should work well with 30% sag. For reference, my rider weight is approximately 215 lbs.

Any thoughts or recommendations would be greatly appreciated...thanks!

need more info on what you want to achieve, but I'm feeling helpful today so I'll take a stab at it...

-start with recommend sag for bike. Keep sag constant while you do initial set up. That will require more or less air depending on bands/tokens used.

-Assuming correct sag and not bottoming? then remove another positive token and change air to achieve same sag.

-Dont have any positive tokens to remove? then start filling up the negative air chamber and effectively you reduce the increased air volume of the megneg. Adding negative bands will make initial stroke relatively stiffer than less bands, but also reduce mid stroke support and ultimately bottom out (less total air for a given sag point).

-Now, if you add enough negative bands and start bottoming too much...now what?!! Depends on how you want the bike to feel. You could remove a band = increase airspring midstroke/bottom suport and create softer initial stroke (stronger negative spring) OR add a token if you like the midstroke and starting stroke but just don't want to bottom as much.

Anyway, I could be explaining this wrong, but that's how I worked through setup on my bike. Hope it helps!!

Posted: Sep 2, 2021 at 10:35 Quote
Anybody know if RS makes a service kit for the Megneg, and what the part number might be? I did a basic air can service a few weeks back and notices the last big/fat O-ring that goes on the outside was a little stretched and isn't giving me the tightest seal all the way around. A googling comes up empty.


 
Copyright © 2000 - 2021. Pinkbike.com. All rights reserved.
dv42 0.006372
Mobile Version of Website