Spring seat suspension bouncing - is elastomer better?

[neptronix]

So i have a super cheap suntour NCX seatpost on my hardtail MTB that does about 30mph.
If i hit something gnarly, the seatpost can send me bouncing off the seat like a pogo stick... it's a little unnerving!

I know the right answer is to probably tune the spring harder, but.. i really like a soft setting even if it does rarely bottom out. But anywhere from the soft to medium firmness of the spring provides a pogo stick effect.

I was wondering if elastomer ( Thudbuster LT, etc ) is a bit different this way - IE, it has some degree of damping.

 

[scianiac]

The elastomers seem to not be very bouncy, I have an old thudbuster on my fatbike (which has it's own level of bounce from the tires so hard to tell sometimes), they are actually pretty reasonably priced on ebay but I had to print new elastomers since the ones it came with were way to stiff for my weight. I kinda figured the NCX has some damping inside but guess not. Looking at the NCX though it wouldn't be that hard to add some damping, possibly something as simple as tightly wrapping an old inner tube around the body in the right orientation. That might not do a lot since that rubber doesn't have that much damping properties but you get the idea.

 

[Stealth_Chopper]

Motorcycles went through the whole design progression of hard tail saddle and support designs ~100? years ago.
You must analyse those and then choose one; I imagine because: Suspension.

 

[Chalo]

A lot of the elastomer saddles have a steel coil stuffed into the center of the rubber bumper. I think the main benefit of elastomers vs steel springs is firmer, shorter travel and less resonant bouncing. Almost every saddle in my stable right now has elastomer springs, mainly because the L/XL category of saddles tends to have them.

 

[neptronix]

I've got a nice elastomer/gel seat already. It's the seat post that needs improving.

 

[TheBeastie]

I have had both the suntour NCX seatpost and Thudbuster LT on my Trek DS 8.4, all up I think the Thudbuster LT did provide a slightly more enjoyable ride but there isn't that much difference between them.

I have swapped between both seatposts multiple times on my bike now over the years, and the Thudbuster LT has remained on it for about the last 4 years which should stand for something, but I had both on there for years at a time.

My main bike now is a fat bike (for the last ~year) that I laced a 1000W geared fat motor into which also has a springy fatbike seat. I am now in cushy ride heaven.
I haven't ridden my Trek since.

 

[offGridDownUnder]

Mass-Spring-Damper.

You (plus a bit for the seat/post) are the mass.
The spring or elastomer provides the spring.
What provides the damper?

Without a damper, the spring oscillates until it has dissipated all the energy through friction (which is a damper, but a small one in most metal springs - the ideal spring does not dissipate energy at all).

Too much damper will actually interfere with the spring action by dissipating the energy before the spring moves over it's entire travel. You might want this some times.

Probably what you want is full travel at some reasonable "depth" of bump, and nearly full dissipation on return to "normal" position.

What is the damper in the spring version? The elastomer is the damper in that implementation.

 

[glennb]

I have an NCX I can play with. Might have a quick tinker tomorrow.

They have 50mm total travel. Adjusted for plushness, 20-25mm sag, which contributes nothing to shock absorption, but will contribute rebound energy ... that could be constrained by effectively locking out that portion of travel.

I doubt hard top outs when the post rebounds would problematic in practice, meaning the constraint could be as simple as a thick flexi fine strand cable secured between sadfle rails and lower section of post e.g. 6mm2 power cable.

If the top out proves too clunky though, a slightly elastic lockout would solve it. Easiest to try would be a solid rubber tie down strap secured from rear of saddle or rails to a 27.2mm clamp on the post.

Tuning the strap tension would be via sliding the clamp further down the post, until the saddle is held 20mm below full extension. A slight increase in the post spring's preload would also be required to counteract the strap.

The suspension's progressive rearward travel complicates matters though. And finding appropriately stiff strap will be difficult, but ought to be achievable by some combination of paralleling or looping straps (I.e. doubled, tripled, or even quadruped up) and/or longer lengths secured lower (to the seat tube, as far down as the bottom bracket if need be).

 

[Chalo]

I've got a nice elastomer/gel seat already. It's the seat post that needs improving.

Ah I see. I'm familiar with four basic kinds of suspension seatposts.

The default for comfort bikes is a pretty dumb, sloppy pogo stick whose only damping comes from stiction in the bushing. This kind is basically worthless because it has all the drawbacks of an undefined seat location without putting up any real resistance to big impacts.

Then there is Thudbuster which uses elastomers in a fairly good sized parallelogram. Movement is more controlled, but damping is pretty minimal. The long travel kind seems useful if for whatever reason you can't or don't unweight the saddle to transit bumps. The primary tradeoff is a constantly changing distance and direction between saddle and pedals.

Then there's hydraulic dashpot damped parallelogram posts like SR Suntour NCX. Not a ton of travel there, but the damping and movement control are quite good, and they work for pretty heavy impacts.

The last kind is something I'm only familiar with because one of my good buddies uses one on his Surly Krampus: a dropper post with suspension travel included by design. It has more and plusher travel than SR Suntour NCX, but I think a less favorable direction of travel than a parallelogram post, and much less free play than a cheap pogo stick post. It seems like an easy choice for someone who wants both a dropper and seat suspension. Here's one example.

Here's the seat suspension I'm reworking right now for my honey: one of my >25 year old Brooks B90/3 saddles with ALL THE SPRINGS.

 

[bananu7]

on my hardtail MTB that does about 30mph.
If i hit something gnarly, the seatpost can send me bouncing off the seat like a pogo stick... it's a little unnerving!
...
I know the right answer is to probably tune the spring harder,

Eh, you won't like my opinion on it. I firmly believe that if you want to both
* ride at 30mph
* hit gnarly stuff at that speed
the vehicle should have full suspension, and likely not a hub drive. Otherwise, you'll either need to slow down or strategize the path through the obstacles better.

Anecdote: on the very first ride when i took my hardtail out, I went on the same route i normally pedalled through unpowered. The road leading to the forest has a couple of sharp-edged concrete slabs. I rode on them numerous times at speeds of around 20km/h without any issue. With motor power, at 40km/h the impact tore the knobs off of the tyre (which was tubeless at the time) and had me walk back in shame. No amount of seat suspension travel would have helped here.

 

[neptronix]

Eh, you won't like my opinion on it. I firmly believe that if you want to both
* ride at 30mph
* hit gnarly stuff at that speed
the vehicle should have full suspension, and likely not a hub drive. Otherwise, you'll either need to slow down or strategize the path through the obstacles better.

I agree, but i'm interested in seeing how far we can take a cheap 29er hardtail. 95% of my riding is street.

I had a Turner O2 ( full suspension with 26" ) and it had 100mm air suspension on both wheels and just floated over everything. It was great. I think 90mm seatpost travel + front 120mm air shock + 29er wheels instead of 29" might come close, let's see

 

[2old]

I've had the Thudbuster, NCX and Kinekt at various times through the years and found the Thudbuster best. I never analyzed why it was superior, just noticed that it enhanced the ride while the others basically suck.

 

[neptronix]

Great comments, all.. thanks for them.

Chalo, i want to like this air seat post, but 40mm of travel is less than the 50mm on my Suntour NCX.. this makes me wonder if someone sells a version with higher travel.. if so, that might be as good as it gets.

I see you are going for 100% seat suspension.. that amount of travel is nuts on that seat, that's awesome!

I have an NCX I can play with. Might have a quick tinker tomorrow.

They have 50mm total travel. Adjusted for plushness, 20-25mm sag, which contributes nothing to shock absorption, but will contribute rebound energy ... that could be constrained by effectively locking out that portion of travel.

I doubt hard top outs when the post rebounds would problematic in practice, meaning the constraint could be as simple as a thick flexi fine strand cable secured between sadfle rails and lower section of post e.g. 6mm2 power cable.

If the top out proves too clunky though, a slightly elastic lockout would solve it. Easiest to try would be a solid rubber tie down strap secured from rear of saddle or rails to a 27.2mm clamp on the post.

This is an interesting idea and may actually work to add some progressiveness. LMK if you experiment with it.

I have had both the suntour NCX seatpost and Thudbuster LT on my Trek DS 8.4, all up I think the Thudbuster LT did provide a slightly more enjoyable ride but there isn't that much difference between them.

I have swapped between both seatposts multiple times on my bike now over the years, and the Thudbuster LT has remained on it for about the last 4 years which should stand for something, but I had both on there for years at a time.

Yeah.. this lines up with what i hear about suspension seatposts.
People who get Thudbuster LT's never report switching to, or finding a better suspension seatpost.

The only possibly 'better' seatposts are the Kinekt and Redshift models that utilize spring and elastomers.. and may have effective damping.. but they only have 35mm of travel.

A quick search on Google shows that elastomer does have damping capabilities.. so the big chunk of elastomer and long travel on the Thudbuster LT looks like the optimal design.. an air suspension of any significant size would be challenging and that's probably why this elastomer design is the best that we can get.


So hey Thundbuster LT owners.. i don't know what the motion of this seatpost looks like but i'm wondering if it travels too far backwards on big hits.. or is it just fine?

Any gotchas? if not, i'll just order one

 

[hillslayer@]

I basically ride a 29er with nxc seatpost most of my 30 mph plus is downhill and if it's looking a little bumpy I am putting most my weight on the pedals.

 

[maiz]

Great comments, all.. thanks for them.

Chalo, i want to like this air seat post, but 40mm of travel is less than the 50mm on my Suntour NCX.. this makes me wonder if someone sells a version with higher travel.. if so, that might be as good as it gets.

I see you are going for 100% seat suspension.. that amount of travel is nuts on that seat, that's awesome!



This is an interesting idea and may actually work to add some progressiveness. LMK if you experiment with it.



Yeah.. this lines up with what i hear about suspension seatposts.
People who get Thudbuster LT's never report switching to, or finding a better suspension seatpost.

The only possibly 'better' seatposts are the Kinekt and Redshift models that utilize spring and elastomers.. and may have effective damping.. but they only have 35mm of travel.

A quick search on Google shows that elastomer does have damping capabilities.. so the big chunk of elastomer and long travel on the Thudbuster LT looks like the optimal design.. an air suspension of any significant size would be challenging and that's probably why this elastomer design is the best that we can get.


So hey Thundbuster LT owners.. i don't know what the motion of this seatpost looks like but i'm wondering if it travels too far backwards on big hits.. or is it just fine?

Any gotchas? if not, i'll just order one

Wild card:

Home - Air Seat - The Best Bike Suspension

Air Seat bike suspension offers a unique advantage by combining seat stability with a full 360-degree range of motion for superior shock absorption.

airseatliyida.com

 

[neptronix]

^-- i looked at that and it seems to have a very small amount of travel.. they don't even mention the travel amount.. and it's seen bottoming out on what doesn't look like extreme terrain.

The design is interesting though, it probably rides very well on crappy roads but can't handle significant bumps.. i deal with both!

I basically ride a 29er with nxc seatpost most of my 30 mph plus is downhill and if it's looking a little bumpy I am putting most my weight on the pedals.

Ah, i do that right now.. and with a 60psi rear tire... it actually works out well.. i just need to stop being launched off the seat after hitting big bumps, lol.. so this requires a form of damping.

 

[hillslayer@]

Other options is Walmart makes an Ozark trail full suspension, 120 mm travel on the rear it's a 29er with good reviews on sale for 450.00 .

 

[hillslayer@]

Other options is Walmart makes an Ozark trail full suspension, 120 mm travel on the rear it's a 29er with good reviews on sale for 450.00 .

Forgot to mention it's a tru axle rear frame so kind of limits it to one expensive hub motor.

 

[neptronix]

Switching out the frame is not an option, i'm interested in maximizing what can be done with a cheap hardtail.

 

[bananu7]

Switching out the frame is not an option, i'm interested in maximizing what can be done with a cheap hardtail.

What's the widest rear tyre you can fit?

 

[lnanek]

Wild card:

Home - Air Seat - The Best Bike Suspension

Air Seat bike suspension offers a unique advantage by combining seat stability with a full 360-degree range of motion for superior shock absorption.

airseatliyida.com

I have the Air Seat, amusingly. My first attempt at adding seat cushioning was a cheap Satori spring seat post:

https://a.co/d/hrMm0nM

It's still on there, but I didn't like how much it compressed when I sat on it. Makes mounting tougher.

I didn't want to give up my seat which is one of the few I could find that wrap around the butt:

https://a.co/d/5VhEu0Z

So Air Seat was basically just a way to add a bunch of springs to a seat I liked, kind of like how Chalo is pumping up the springs in the seat he's working on.

The only other seat I like is this one I had previously that was stolen:

Extra Wide Comfort Seat #6911V

Extra Wide Comfort Seat #6911V - The Worksman Cycles Factory Direct Store, America's Oldest Cycle Manufacturer, Industrial Bicycles and Tricycles, since 1898

www.worksmancycles.com

So if your only goal is to add extra springs to a fixed seat selection, I kind of like the Air Seat concept.

 

[neptronix]

What's the widest rear tyre you can fit?

Yeah i don't want to go the tire route, you trade improvements in NVH for range.
I want a bike that's smooth with narrow tires on high pressure, and unfortunately we can't buy 750D rims yet.

So if your only goal is to add extra springs to a fixed seat selection, I kind of like the Air Seat concept.

Makes sense.. based on the problem i currently have with a 50mm Suntour NCX, and a gel seat with elastomer.. i'd like less springs actually.. lol

 

[fechter]

I have a thudbuster and love it. Most of my riding is on very bumpy fire roads. It seems to have enough damping to avoid bouncing.
Also there’s this stuff called damping grease you might try on your existing seat post. It’s the stuff they use on slow motion toilet seats, camera lenses, etc. It comes in different viscosities.

 

[neptronix]

Oh interesting! the suntour does have a ton of pivot points which could be lubricated and i think this wouldn't create too much stiction since the existing amount feels like zero.

Many different options indeed, thanks for this idea!



I think i should just get a thudbuster LT for the 30mph hardtail and let my lady inherit this seat post since hers only does 20mph and see if a grease change improves the feel or not.

 

[fechter]

You probably want one of the runnier flavors for that application. The really thick stuff, like on the toilet seat, would probably be like glue and stop the travel altogether.