Improving high speed stability on Rail 7 - CushCore?

[GrantMeThePower]

Hi all! Been getting more miles on my Rail 7 and really enjoying it! I “upgraded” from a Haibike xduro that was honestly very similar but had the older Bosch motor and I wanted more power and better clearance from the trek. I hit too many rocks and my wife was kicking my butt up hills lol.
After fixing my brake the only issues I’ve had with the rail are:
1. The dropper seat is a little sticky and harder to actuate than my old haibike
2. It does not feel nearly as planted and stable at high speed during descents.
The second is the one I’m posting about today. I’ve so far tried reducing the tire pressures and the air pressure in the shocks. That didn’t seem to make a huge difference. It still feels a bit shaky.
Im thinking it might have to do with the difference in tires-the Haibike was a 27.5 x 2.8 60 tpi with tubes. This is (obviously) 29x 2.6 120 tpi tubeless
Would CushCores or procores make a bug difference? Is there something I’m overlooking on setup? I have the Monolink set to the low position.
I would describe the ride as “skittish” or “shaky” at high speeds.
Perhaps I’m nitpicking and the improvement in clearance and climbs is exactly what I was hoping for. I just didn’t expect to feel less confident at higher speeds.
Thanks I’m advance for any insight or suggestions!!

 

[John B]

how Hard is your rear shock? What setting on the shock are you using? I don’t think a cushcore will make any difference as there for stoping the tyres folding and pinch flats.

 

[GrantMeThePower]

how Hard is your rear shock? What setting on the shock are you using? I don’t think a cushcore will make any difference as there for stoping the tyres folding and pinch flats.

I started by using Trek's calculator at 185 pounds fully loaded (Suspension setup - Trek Bicycle). That has me set the rear shock to 215 PSI and 5 clicks out on the rebound. I lowered the PSI to 195 and moved it two clicks slower rebound. The front suspension started at 98 PSI and I lowered it to 90.

 

[Doug Stampfer]

You need to upgrade your suspension. Cushcores won't do bugger all for stability.
I upgraded my fork damper to the charger RC2 & SKF wipers- absolutely amazing difference, could keep raving for hours on how good the front feels. Even though I thought the yaris were good initially, the upgrade makes heaps of difference to plushness, control & amount of braking needed.
Also replaced my rear shock with a coil. It tracks the ground very well most of the time, once again supplying more control & less braking needed.
The net effect of the upgrades is significantly greater downhill speed. Now if I could just somehow upgrade the 'reaction time' chip in my brain I'd have it nailed.

 

[GrantMeThePower]

You need to upgrade your suspension. Cushcores won't do bugger all for stability.
I upgraded my fork damper to the charger RC2 & SKF wipers- absolutely amazing difference, could keep raving for hours on how good the front feels. Even though I thought the yaris were good initially, the upgrade makes heaps of difference to plushness, control & amount of braking needed.
Also replaced my rear shock with a coil. It tracks the ground very well most of the time, once again supplying more control & less braking needed.
The net effect of the upgrades is significantly greater downhill speed. Now if I could just somehow upgrade the 'reaction time' chip in my brain I'd have it nailed.

hi! Thanks! I’ll research changing the damper. Is it tough to do yourself? Do you mind sharing the cost? Is the wiper part of the same change?

What’s strange to me is that my old Haibike has the same front fork and rear combination. I’ll attach the specs. Why would it be the suspension that’s causing the different feeling if they are the same?

 

[R120]

Sounds to me that you haven't got your suspension set up properly, have you done it?

 

[Gary]

What sort of speed and what sort of trail are we actually talking about here?
A bog standard trek rail is more stable than my Trek Session DH bike.

Contrary to what doug said cushcore in combination with savy tyre choice and pressures can actually add stability to a bike. But I don't think it sounds like that alone would be the solution to your problem.

 

[leftside]

What sort of speed and what sort of trail are we actually talking about here?
A bog standard trek rail is more stable than my Trek Session DH bike.

Contrary to what doug said cushcore in combination with savy tyre choice and pressures can actually add stability to a bike. But I don't think it sounds like that alone would be the solution to your problem.

Agreed. Cushcore definitely felt like a suspension upgrade for me when riding gnarly rocky trails, but this is with suspension that already felt pretty good before I had the cushcore installed. (the tire protection with cushcore is a secondary benefit).

 

[GrantMeThePower]

Sounds to me that you haven't got your suspension set up properly, have you done it?

Hi! I believe I did. If you see my reply to the first comment, I started by using the Trek Suspension calculator and went from there. Other than setting the air pressure and rebound are the additional things to set up? Thanks!

 

[R120]

Weel not much if thats all the adjustment you got - you sure everything's done up nice and tight on the bike?

 

[GrantMeThePower]

What sort of speed and what sort of trail are we actually talking about here?
A bog standard trek rail is more stable than my Trek Session DH bike.

Contrary to what doug said cushcore in combination with savy tyre choice and pressures can actually add stability to a bike. But I don't think it sounds like that alone would be the solution to your problem.

I’m in SoCal and the trails im on (in the sections I’m referring to) are usually loose dirt over hard pack. Speeds where I start noticing it are when I get in to the 18-25 mph range-so movin pretty good over fairly rough stuff. I’m not talking about bombing or massive boulders or anything though. It is just more “shaky”. That’s the only way to describe it. More jittery and more vibration.

 

[GrantMeThePower]

Weel not much if thats all the adjustment you got - you sure everything's done up nice and tight on the bike?

Again, I’d like to think so. I’ve gone over the obvious places to check-the stem, derailur, brakes, saddle-they are all tight. If I shake the bike and jump on the pedals stationary I don’t notice anything moving weirdly or seeming loose.

 

[Gary]

I’m in SoCal and the trails im on (in the sections I’m referring to) are usually loose dirt over hard pack. Speeds where I start noticing it are when I get in to the 18-25 mph range-so movin pretty good over fairly rough stuff. I’m not talking about bombing or massive boulders or anything though. It is just more “shaky”. That’s the only way to describe it. More jittery and more vibration.

18-25mph doesn't sound especially fast for a loose over hardpack downhill straight. But your description of the trail could be misleading.
Are you comparing the feeling of lack of stability to another bike at the same speeds?
are you a new rider or experienced?
Not to sound like a dick but mtb descending is shaky. Tyres do make a big difference to trail vibration transmitted through your contact points but you'll probably find the fastest riders on your trails will be on 2.5" tyres and fairly supportive pressures rather than comfy marshmallow 2.8s

 

[Pigin]

I think you need to be more descriptive with the terms shaky and skittish.

Where do you think the vibrations are coming from, front back or general?

What feels shaky?

And in what direction, up down or left to right.

Is it something that happens on turns?

Does it happen on road sections?

Can you ride out of it.

Does moving your body position change it.

What are the numbers for a lottery jackpot win.

 

[Gary]

29 12 18 47 22 03

I'll leave it up to you to decide which week and which lottery to use them on

 

[GrantMeThePower]

18-25mph doesn't sound especially fast for a loose over hardpack downhill straight. But your description of the trail could be misleading.
Are you comparing the feeling of lack of stability to another bike at the same speeds?
are you a new rider or experienced?
Not to sound like a dick but mtb descending is shaky. Tyres do make a big difference to trail vibration transmitted through your contact points but you'll probably find the fastest riders on your trails will be on 2.5" tyres and fairly supportive pressures rather than comfy marshmallow 2.8s

Thanks, Gary. Yes, I'm comparing the "stability" to my old bike at the same speeds. I'll be riding a trail I just recently rode two weeks ago on Sunday and will help with the apples to apples comparison.

I am fairly experienced, but not extremely. I rode MTB fairly regularly (once a week) for a couple of years....15 years ago. About 18 months ago, I got back into it with my first ebike. I ride about the same amount- 1 a week on average. I am certainly not "expert" level, but out of the group of friends I ride with, I'm probably the most advanced. Maybe upper mid level lol.

You definitely don't sound like a dick. I appreciate the input. I agree that it may simply be the difference in tires that I'm feeling-going from the 2.8 27.5" with tubes to the 29" 2.6 tubules. Perhaps the Maxxis DHF II/DHR II fats vs the Bontangers. It is why my initial thinking led me to something like cushcore which I don't have any experience with. I certainly don't feel like the bike is going slower by any means (in fact, it certainly feels capable of going faster) but it is the stability/shaky/vibration that I'm experiencing at the same speeds that is making me feel less confident and requires more effort.

 

[GrantMeThePower]

I think you need to be more descriptive with the terms shaky and skittish.

Where do you think the vibrations are coming from, front back or general?

What feels shaky?

And in what direction, up down or left to right.

Is it something that happens on turns?

Does it happen on road sections?

Can you ride out of it.

Does moving your body position change it.

What are the numbers for a lottery jackpot win.

Great questions. I'll be riding about 30 miles over Sat and Sun this weekend. I'll try to pay more attention to the details and see if I can be more descriptive beyond what I've written.

I can try to answer a couple:

I would say the vibration feels "general". And sort of if I were to lean in a turn while it was happening I feel like it might slide or I could lose control. Left or right does not matter. As soon as I slow down it feels stable again. "Trail" speeds are fine. Its when I get to some of the fire roads where you pick it up a bit I notice the difference from the old bike.

I have not noticed it on road sections (30mph, for example, on paved roads feels very stable and smooth).

I have not noticed any difference due to body position.

4, 8, 15, 16, 23, 42

 

[Gary]

about your suspension.
Don't quote me on this but If the Yari has followed the trend of the Lyrik the 2021 and the older 2020 models have different air springs.
The new (Lyrik) air spring sits up more in it's travel and isn't nearly as compliant on small bumps than the older spring was. also because the spring curve has changed you can't simply run the same pressure or sag and expect to get the same set-up.
The rear end may have the same shock but the two bikes don't have the same leverage ratio, curve or pedal kickback so again whatever pressures/sag worked best for you on the Haibike are irrelevant to the Trek's set up.
it might not be obvious but you also can't run your rebound at the same position and expect it to perform the same.
it's a new bike so spend some time getting to know it's suspension traits and setting it up to preference. The more experience you have in this the quicker you'll get close to idea from the off.

Take a look at the first post in the suspension set-up sticky I wrote in the general EMTB section of the forum for tips/pointers if you're unsure of what you're doing.

 

[GrantMeThePower]

about your suspension.
Don't quote me on this but If the Yari has followed the trend of the Lyrik the 2021 and the older 2020 models have different air springs.
The new (Lyrik) air spring sits up more in it's travel and isn't nearly as compliant on small bumps than the older spring was. also because the spring curve has changed you can't simply run the same pressure or sag and expect to get the same set-up.
The rear end may have the same shock but the two bikes don't have the same leverage ratio, curve or pedal kickback so again whatever pressures/sag worked best for you on the Haibike are irrelevant to the Trek's set up.
it might not be obvious but you also can't run your rebound at the same position and expect it to perform the same.
it's a new bike so spend some time getting to know it's suspension traits and setting it up to preference. The more experience you have in this the quicker you'll get close to idea from the off.

Take a look at the first post in the suspension set-up sticky I wrote in the general EMTB section of the forum for tips/pointers if you're unsure of what you're doing.

Awesome. I will check out your post and your point makes a lot of sense about the difference in suspension due to geometry changes.

What is news to me is the change in the Yari from the 2020 to the 2021 model. I knew they looked different (the stickers are all black on my new one and were white on the old one). I'm curious why they changed if the new version isn't as compliant on small bumps. That could be exactly the issue I'm experiencing.

If that is the case, what do you think the best option would be to improve the small bump performance? I certainly do not notice any issue on bigger drops, slower moves, etc. Just the rocks and gravel and stability at higher speed.

 

[Gary]

due to geometry changes.

it's not due to geometry changes.
it's due to leverage curve and rate changes.

the reason RS updated the air spring is because folk maoned it sagged into the travel before the fork was loaded and they felt they were being robbed of positive travel. Rockshox adressed this with a change to the physical dimensions of the air spring and now it's simply not so soft off the top. (simplified answer)

improving small bump performance can be achieved in a number of ways. Read the suspension set-up guide and you should understand better what you are working with and how to set it up to your preference.

 

[Forever Wild]

Hi all! Been getting more miles on my Rail 7 and really enjoying it! I “upgraded” from a Haibike xduro that was honestly very similar but had the older Bosch motor and I wanted more power and better clearance from the trek. I hit too many rocks and my wife was kicking my butt up hills lol.
After fixing my brake the only issues I’ve had with the rail are:
1. The dropper seat is a little sticky and harder to actuate than my old haibike
2. It does not feel nearly as planted and stable at high speed during descents.
The second is the one I’m posting about today. I’ve so far tried reducing the tire pressures and the air pressure in the shocks. That didn’t seem to make a huge difference. It still feels a bit shaky.
Im thinking it might have to do with the difference in tires-the Haibike was a 27.5 x 2.8 60 tpi with tubes. This is (obviously) 29x 2.6 120 tpi tubeless
Would CushCores or procores make a bug difference? Is there something I’m overlooking on setup? I have the Monolink set to the low position.
I would describe the ride as “skittish” or “shaky” at high speeds.
Perhaps I’m nitpicking and the improvement in clearance and climbs is exactly what I was hoping for. I just didn’t expect to feel less confident at higher speeds.
Thanks I’m advance for any insight or suggestions!!

What’s your fork offset? How high is your tire pressure? I have cushcore on my trek Powerfly with 27.5 2.8 black diamond butcher tires. I don’t think the cushcores will help. Which fork ? Your fork setup maybe?

 

[jcmonty]

I ride in SoCal (north county San Diego mostly), and definitely am familiar with the type of terrain you are riding.

Going from high volume tires to lower volume (while running appropriate pressures for both) can feel a bit “tougher” over chatter, high speed vibrations. I found 2.8s to be vague and isolating around here honestly, but you could be feeling that difference a bit.

cushcore or other inserts can make a big difference in my experience. I have found it can take the edge off the terrain , muting vibrations some while providing better support at slightly lower pressure. Not to mention the flat protection

Finding a track or trail that exhibits some of the characteristics you believe cause the vibrations or harshness and running laps with “bracketing” changes to spring rate, compression, and rebound can be beneficial as well.

if you have some $ to spend, custom tune of your suspensions can have a big effect as well. Fluid Focus in San Marcos is a great option.

 

[Doug Stampfer]

When I started upgrading my Rail 7 I was having trouble with my wrists & hands & was keen to get better small bump compliance (our local tracks are pretty raw & don't lend themselves to too much speed :-0 )

I started with better tyres- maxxis DHFs -run at lower pressures with cushcores in. That was good - the bontragers are very average compared in every way that's why our local for sale page has plenty taken off new bikes. I was running at around 18 PSI. In hindsight maybe DD tyres without the cushcores would have been cheaper but we'll get to that later.

I then upgraded the airspring to gain the extra 6-10mms of travel Gary was mentioning. - Mmmmm cheap enough - $50 or so- ok it did sit higher but actually maybe more of a PITA for tight cornering while climbing - not that noticeable on the downhills to me.

Bit the bullet & got the RC2 damper for around $650NZ ($480US ish) as well as the SKF seals to bring the yaris up to Lyrik ultimate spec. The damper change over is easy if you follow the various youtube vids. Note the new damper has the oil contained within it - the old motion control (moco) has the oil seperate & will spray out all over your clothes & garage when you take out the lowers if you aren't aware of it. I got the local bike shop to seat the wiper seals as you really need the appropriate tool- cheap easy job for them. Well don't start me raving about how good they feel again It was at this point I realised this should have been my starting point as the small bumps disappeared & the control over rough ground was amazing. However they soon showed up the rear end was definitely lacking in comparison.

I bought a JadeX rear coil after a rocky start with it, the rear end now keeps up with the forks. I feel far more stable, faster & in control with the bike even though I thought it was bloody good to begin with.

I'd recommend you run your local trail on a friends bike with a good fork & shock see if that makes a difference.

 

[GrantMeThePower]

When I started upgrading my Rail 7 I was having trouble with my wrists & hands & was keen to get better small bump compliance (our local tracks are pretty raw & don't lend themselves to too much speed :-0 )

I started with better tyres- maxxis DHFs -run at lower pressures with cushcores in. That was good - the bontragers are very average compared in every way that's why our local for sale page has plenty taken off new bikes. I was running at around 18 PSI. In hindsight maybe DD tyres without the cushcores would have been cheaper but we'll get to that later.

I then upgraded the airspring to gain the extra 6-10mms of travel Gary was mentioning. - Mmmmm cheap enough - $50 or so- ok it did sit higher but actually maybe more of a PITA for tight cornering while climbing - not that noticeable on the downhills to me.

Bit the bullet & got the RC2 damper for around $650NZ ($480US ish) as well as the SKF seals to bring the yaris up to Lyrik ultimate spec. The damper change over is easy if you follow the various youtube vids. Note the new damper has the oil contained within it - the old motion control (moco) has the oil seperate & will spray out all over your clothes & garage when you take out the lowers if you aren't aware of it. I got the local bike shop to seat the wiper seals as you really need the appropriate tool- cheap easy job for them. Well don't start me raving about how good they feel again It was at this point I realised this should have been my starting point as the small bumps disappeared & the control over rough ground was amazing. However they soon showed up the rear end was definitely lacking in comparison.

I bought a JadeX rear coil after a rocky start with it, the rear end now keeps up with the forks. I feel far more stable, faster & in control with the bike even though I thought it was bloody good to begin with.

I'd recommend you run your local trail on a friends bike with a good fork & shock see if that makes a difference.

Thanks, Doug! Lol...sounds like you’re gonna convince me to spend a bunch more money Haha jk.

do you have the part number for the damper? I went on rockshox and saw a couple different ones:

Charger 2 Damper Upgrade Kit - FS-UPK-CH2-A1 - RockShox

Charger 2 Damper Upgrade Kit, FS-UPK-CH2-A1, RockShox. To achieve maximum suspension performance, proper setup and tuning is essential. Go to www.rockshox.com/app for suggested air spring pressure and rebo...

www.sram.com

Charger 2.1 Damper Upgrade Kit - FS-UPK-CH21-A1 - RockShox

Charger 2.1 Damper Upgrade Kit, FS-UPK-CH21-A1, RockShox. The new Charger 2.1 damper upgrade kit allows the fork to ride higher in the travel on compression while keeping the tires planted to the ground for u...

www.sram.com

I’m guessing it’s the second as it is “2.1” and the other is “2” but I’m not sure since you said “RC2”. I’m not sure what the difference is.

Did you do the install yourself on the damper and then take the washer kit to your lbs for install, or do they have to be done together?
Thanks for your response and help on these. It sounds like the cushcore may be cool but the damper is where the real difference would come from.

 

[GrantMeThePower]

Is this the right one? I see ones that are $250 that seem like the same and then this one:

RockShox Damper Upgrade Kit - Charger2.1 RC2 Crown Adjust, Lyrik/Yari (A1+/2016+) / Pike 29+ (B1+/2017+)

Wonder why the RockShox Charger2.1 Damper Upgrade Kit is a mountain biker favorite in the Damper, Compression collection? Part #00.4020.170.000. The Charger 2.1 damper upgrade kit allows the fork to ride higher in the travel on compression while keeping the tires planted to the ground for...

www.worldwidecyclery.com

 

[Gary]

Set up the fork you have properly first.
Why have you suddenly jumped to the conclusion it's your damper at fault?
I have 2 lyriks but have ridden Yari's on other bikes on big local rides with long rough EWS Enduro stages and even with their more basic damper the Yari's were fine.

 

[GrantMeThePower]

Set up the fork you have properly first.
Why have you suddenly jumped to the conclusion it's your damper at fault?
I have 2 lyriks but have ridden Yari's on other bikes on big local rides with long rough EWS Enduro stages and even with their more basic damper the Yari's were fine.

Hi Gary,

I did read the full PDF and watched the two videos you had posted. Everything mentioned there has been done correctly, just as I had previously done on the Haibike. All of that information was really applicable to all full suspension bikes and I had done it previously. It is always great to learn as much as possible. Thank you for pointing me towards those resources.

EDIT- Also, as you mention, the setup is fine. I'm not trying to imply it is "broken"- It simply isn't as planted and stable feeling as my last bike which had, though a year older version, the same shock and fork. This was really me trying to understand why it would be that way and what steps I could take to enhance the ride quality to match what I had experienced on that. Thanks again!

 

[Doug Stampfer]

Set up the fork you have properly first.
Why have you suddenly jumped to the conclusion it's your damper at fault?
I have 2 lyriks but have ridden Yari's on other bikes on big local rides with long rough EWS Enduro stages and even with their more basic damper the Yari's were fine.

I wasn't implying his (or my damper) was at fault. I also thought the yaris were good until I upgraded. I spent a lot of time setting mine up with the basic adjustments there were to get it as best I could. I even used a shockwiz that told me it though the yari was fine except for a bit of HSC. My point was really to try the same tracks on a Rail with better suspension before spending money on anything else like cushcores really to see if there is much difference.
I guess I've kind of veered off from the original query why the bikes felt different though & that I find interesting. I would have assumed the Rail would be all over the Haibike as it has won many shootouts & comparisons due to its downhill performance. I find the Rail incredibly nimble in tight stuff & stable downhill so I'm wondering if the Haibike was maybe just a bit sluggish?

 

[Doug Stampfer]

Is this the right one? I see ones that are $250 that seem like the same and then this one:

RockShox Damper Upgrade Kit - Charger2.1 RC2 Crown Adjust, Lyrik/Yari (A1+/2016+) / Pike 29+ (B1+/2017+)

Wonder why the RockShox Charger2.1 Damper Upgrade Kit is a mountain biker favorite in the Damper, Compression collection? Part #00.4020.170.000. The Charger 2.1 damper upgrade kit allows the fork to ride higher in the travel on compression while keeping the tires planted to the ground for...

www.worldwidecyclery.com

Yes I got that one because it has low & high speed compression adjustment. You may not require the HSC but it gives you more tunability

 

[GrantMeThePower]

Yes I got that one because it has low & high speed compression adjustment. You may not require the HSC but it gives you more tunability

Awesome. Thanks, Doug! I’ll ride a couple more months before going this way but it’s good to know what options there are. The cushcores seemed like a cheaper way to add some small bump compliance but maybe it’s better to just wait and go this route.