Improving high speed stability on Rail 7 - CushCore?

[>moto<]

There are a couple of things that spring to mind reading your post @GrantMeThePower. Is there a big difference in bike weight? A heavier bike will feel more stable at speed (everything else being equal).

Tyres will play a big part too and for a couple of reasons. Firstly the wider tyres you had will add to the suppleness of the ride. Changing to a bigger and better tyre like the Maxxis Minion DHF will add weight, which adds rotating mass, which adds stability. It's also a way better tyre than the Bontrager.

I see you have mentioned that you adjusted the rebound a few clicks, but it sounds like it was just a couple of clicks and probably at the same time as you adjusted the air pressure. I would set the sag (air pressure) where it should be and then adjust the rebound. Slowing down your rebound will make the bike track the ground worse, especially at speed. Try speeding the rebound up until it feels shit and then back it off a few clicks.

The probelm with rebound is the effect of too much or too little is similar in that both instaces will lead to the feeling of 'jitteryness' and instability.

 

[GrantMeThePower]

There are a couple of things that spring to mind reading your post @GrantMeThePower. Is there a big difference in bike weight? A heavier bike will feel more stable at speed (everything else being equal).

Tyres will play a big part too and for a couple of reasons. Firstly the wider tyres you had will add to the suppleness of the ride. Changing to a bigger and better tyre like the Maxxis Minion DHF will add weight, which adds rotating mass, which adds stability. It's also a way better tyre than the Bontrager.

I see you have mentioned that you adjusted the rebound a few clicks, but it sounds like it was just a couple of clicks and probably at the same time as you adjusted the air pressure. I would set the sag (air pressure) where it should be and then adjust the rebound. Slowing down your rebound will make the bike track the ground worse, especially at speed. Try speeding the rebound up until it feels shit and then back it off a few clicks.

The probelm with rebound is the effect of too much or too little is similar in that both instaces will lead to the feeling of 'jitteryness' and instability.

Hi Moto- thanks for your reply! There is a weight difference. It’s roughly 5 pounds heavier. As I mentioned it also runs on 2.8” tires and 27.5” wheels. It also have a more compact riding position. I’m sure all of those things contribute to it. I am greedy I guess haha. I want it all!

I don’t think that the 2.8” Maxxis tires will fit on the stock 29mm wheels.

Your point about too much rebound feeling the same as too little is very interesting and you were right I did adjust that and the air pressure at the same time. I’ll reset the sag and make more gradual changes this weekend over my couple of rides. Thanks for that tip-I was definitely thinking I needed less and less.

 

[Gary]

too much rebound feeling the same as too little

too much rebound does not feel the same as too little. and that's not what >MOTO< was saying.
too little and the rear end will want buck your weight forwards on the return stroke too much and the rear will pack down and not recover quickly enough becoming harsh and tracking the ground less.
Both can be detrimental to stability but in different ways and for different reasons.

 

[Pigin]

Planted and stable seems different to your initial description so I’ll have a go.

The reason that the head angle gets mentioned so often is that it affects the castor angle of a bike front wheel. If you were to stand side on and look at your forks, draw an imaginary line down the line of the forks to the floor and you will notice that it’s ahead of where the tyre contacts the floor. The angle is created by drawing an upright from the contact patch, down the imaginary line and along the floor. As the head angle changes so does the distance between the contact patch and that imaginary line.

The effect of varying this is that the wheel is more or less likely to want to turn back on itself. Think of how a shopping trolley wheel always wants to align itself.

Combine the above with different tensions on the headstock and thereby increasing or decreasing the friction needed to turn the wheel left to right and you have got yourself a whole array of variance on how bikes handle.

If you think about the above you can also see how rear sag can influence that angle.

My guess is that you are sensing the differences in the set ups.

 

[Yoak]

I think a new set of tyres would make the biggest differences for the least money spent. I’ve had (and ride) lots of different Trek bikes over the 2 last years. I find the Bontragers that comes with these bikes are not very confidence inspiring at all.

 

[Stray cat]

Sure. I swapped front tyre for a Maxxis Assegai and it was a huge improvement.

 

[GrantMeThePower]

Ok so, some thoughts from my ride today:

I readjusted the sag after resetting my tire pressures (tire pressures- front 20, rear 24). I found I was a little high in air in the front and a little low in the back. Set the sag to 30% rear and about 18% in front.

I tried to really focus on what I was feeling while I was riding (for better or worse. It makes a ride really unfun when you're hyper focused on the bad parts lol). I think it is mostly the tires. A lot of the small bump downhill things felt better with the adjusted pressures all around, but I lost the bike twice in some shitty falls due to bad traction. It was really dry and loose today and I think it is just that uneasiness on the tires that I'm constantly aware of as not feeling right.

I decided to take the bike to my local trek shop to have them check out the dropper that was also acting up and I got in a convo with the head of their service and told him my feelings and he asked if he could keep it for a few days and really go over the whole thing and make sure its set up as well as it could be a do a proper fitting in the middle of the week. I said no prob-i really want it to feel great.

Unfortunately, I think that 2.6" is the widest I can go on these wheels so I can't get the same tires I was used to but maybe there are some options for improvement from stock in the 2.6" size range. I'd like to feel that cornering isn't risking losing the bike on anything loose and to not feel like it is constantly a battle to get the wheel traction on the steep technical stuff. The back wheel wouldn't even get traction in the walk mode when I was trying to push it up a tough spot. It would just spin.

 

[Rosemount]

The stock Bontrager tyres are crap .
I ride with a guy who has a Trek . He has complained about the tyres a lot ...

 

[Gary]

@GrantMeThePower Dude. How tall are you? And what size is your Rail?
Just seen your seatpost thread and it might just be the video but in it you look like a really big guy on a pretty small frame.

 

[GrantMeThePower]

@GrantMeThePower Dude. How tall are you? And what size is your Rail?
Just seen your seatpost thread and it might just be the video but in it you look like a really big guy on a pretty small frame.

hi Gary...funny you say that because 1) I thought my quarantine bod looked a little big in that too lol and 2) I was actually wondering if I got too big of a rail lol. I think it’s the right size.

I’m 5’10”, 183. I have a lot of muscle, though, so I look big for my frame (weight lifting is my primary exercise). I could use to lose about 10 pounds around the mid section though lol. The rail is a size large. According to trek’s page that’s the right size for me. I did think a medium might fit better with the stand over height but it would not be as good for the riding.

 

[Gary]

At 5'10 you could ride M, L or XL (at 445mm, 465mm or 495mm reach) depending on what you wanted from the bike.
The M would be a lot more playful (but the less stable)
The XL would be a lot less nimble but a lot more stable and you'd be resticted with how long a dropper you could use.
There seems to be very little difference in standover between them as the top tube remains low throughout and the seat mast increases per size.

I'm taller than you and hated how difficult the XL rail I rode felt to raise the front wheel on and bunnyhop. But I'm kinda old skool and still ride dirtjump bikes, M Enduro and DH bikes and a small 27.5 Emtb so kinda the opposite end of the spectrum from you and look for maneuverability and playfulness in a bike at the detriment of stability.

 

[GrantMeThePower]

At 5'10 you could ride M, L or XL (at 445mm, 465mm or 495mm reach) depending on what you wanted from the bike.
The M would be a lot more playful (but the less stable)
The XL would be a lot less nimble but a lot more stable and you'd be resticted with how long a dropper you could use.
There seems to be very little difference in standover between them as the top tube remains low throughout and the seat mast increases per size.

I'm taller than you and hated how difficult the XL rail I rode felt to raise the front wheel on and bunnyhop. But I'm kinda old skool and still ride dirtjump bikes, M Enduro and DH bikes and a small 27.5 Emtb so kinda the opposite end of the spectrum from you and look for maneuverability and playfulness in a bike at the detriment of stability.

Yeah I couldn’t see handling a bigger bike. So did you end up with a medium rail at the end?

 

[Gary]

Nah. I don't have a rail at all.

 

[Philly G]

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.

Good to know the upgrades made such a big difference! I also am searching for the Brendog/Pilgrim skills upgrade software for my brain ?