[PHeller]

I've recently read a lot of good press about Push's ASC-3 fork coil conversion and one of the things people love is its hydraulic anti-bottoming system.

I know many of proclaimed the same praises of Avalanche's ABS system as well.

Then I noticed the Avalanche Montie (inline coil shock) has got ABS as well.

If this is a good addition to high end coil forks, then does it have lots of value being on a coil rear shock as well?

 

[Adodero]

I think the EXT has it, as well.

 

[tbmaddux]

Hydraulic anti-bottoming is in the Vorsprung Smashpot coil conversion, whereas the PUSH ACS-3 has a small air spring for anti-bottoming. And yes, for rear shocks you can find hydraulic bottom-out control on the EXT Storia and ARMA rear shocks.

 

[PHeller]

Ok, but what's the advantage? More usable travel? No worry of a spikey rebound when bouncing off the rubber bumpers?

 

[digev]

Ok, but what's the advantage? More usable travel? No worry of a spikey rebound when bouncing off the rubber bumpers?

Coils are linear by nature so they rely on the frame's leverage ratio curve to "slow down". But sometimes that’s not enough so delivering a 50% increase in the force required to compress the shock during the last 15% of the travel is a good idea. (That’s what the EXT STORIA v3 does)

 

[minimusprime]

A lot of time and engineering goes into bump stop specification and shape on coil over suspension systems. This is true for cars and motorcycles but also bicycles. Arguably, a properly specified bump stop is going to be a more simple to use and cheaper to implement setup then an HBO setup.

Obviously, the folks at EXT know what they are doing, but so do the folks at push. From the position of needing to fit several frames and shock sizes, it's a safer bet to use a closed cell foam that's specified to add the progressiveness and bottom out resistance characteristics that you want.

It is very inconvenient to utilize this sort of system in a fork, but very convenient to use this sort of system in a shock. This is why you will always see more physical bump stop bumpers then HBO systems in rear shocks.

TLDR, don't under estimate the thought that goes into that little foam puck on your coil shocks. Also, take note that when you buy a DHX, you're getting one choice of bottom out bumper, which is another reason to go with something like the 11/6 over an off the shelf aftermarket shock.

P.S. if learning more about bump stop materials and shapes is interesting to you... there is a ton of information in the motorsports world about this, specifically stock class autocross racing. Many times when you can't change the shocks bodies and springs out, the only mechanic you are left with is internal valving and bump stop bumpers. I spent a ton of my early motorsports career learning what length, shape and density worked best for the ride heights I was running on my stock class miata.

example - Automotive Suspension Experts | Fat Cat Motorsports, Inc. | Bump stop application guide

 

[Dougal]

Consider that virtually all air-shocks rely on a ~2.5mm thick rubber o-ring for a bottom-out stop. Coil shocks are running ~10-20mm thick foam bumpers.

The vast majority of riders do not bottom their shocks out hard with the above bumpers.

You don't want bottom-out control to engage too early or it destroys your mid-stroke response. But you also need a certain amount of stroke for it to fit and work.

In a fork you have a lot of stroke to use, so having the last 20mm or so working in hydraulic bottom-out works quite nicely (20/160 = 12.5% of the stroke) and gives you lots of room to make it engage, then ramp up and go through several stages.

In a shock with ~50-60mm of stroke you're down to 5-7mm. Trying to fit several stages of bleed off into 5-7mm is pretty ugly. Let alone trying to get a nice lead-in and progression into it.

 

[Jesse Hill]

A lot of time and engineering goes into bump stop specification and shape on coil over suspension systems. This is true for cars and motorcycles but also bicycles. Arguably, a properly specified bump stop is going to be a more simple to use and cheaper to implement setup then an HBO setup.

Obviously, the folks at EXT know what they are doing, but so do the folks at push. From the position of needing to fit several frames and shock sizes, it's a safer bet to use a closed cell foam that's specified to add the progressiveness and bottom out resistance characteristics that you want.

It is very inconvenient to utilize this sort of system in a fork, but very convenient to use this sort of system in a shock. This is why you will always see more physical bump stop bumpers then HBO systems in rear shocks.

TLDR, don't under estimate the thought that goes into that little foam puck on your coil shocks. Also, take note that when you buy a DHX, you're getting one choice of bottom out bumper, which is another reason to go with something like the 11/6 over an off the shelf aftermarket shock.

P.S. if learning more about bump stop materials and shapes is interesting to you... there is a ton of information in the motorsports world about this, specifically stock class autocross racing. Many times when you can't change the shocks bodies and springs out, the only mechanic you are left with is internal valving and bump stop bumpers. I spent a ton of my early motorsports career learning what length, shape and density worked best for the ride heights I was running on my stock class miata.

example - Automotive Suspension Experts | Fat Cat Motorsports, Inc. | Bump stop application guide

Is this actually Fat Cat or are you just using them for reference?

 

[JohnnyC7]

example - Automotive Suspension Experts | Fat Cat Motorsports, Inc. | Bump stop application guide

Haven't encountered FCM before, some good videos on his youtube channel!

 

[Jayem]

Hydraulic ABS has saved my a$$ more than once when I landed on my front wheel or nearly lost control in a section, the fact that it dampens is significant IMO.

 

[minimusprime]

Is this actually Fat Cat or are you just using them for reference?

No, but I know Shaikh quite well. I was quite involved in the miata track racing and autoX scene for many years. I was sponsored and supported by Blackbird Fabworx and we utilized FCM suspension setups for a time... ultimately switching to Penske because we had some loftier goals.

I grew up building and racing cars and motorcycles. I fancied myself quite good at setting up a car... that is, until I bought/built a miata. That was my car setup and building masters degree.

There is no more true statement in life then, the more I learn, the more I learn I don't know. Suspension and aerodynamics are two areas that are humbling to say the least. Trying to adapt what I've learned on cars/motorcycles to bicycles is a mixed bag. The wheels fall off the bus when the majority of the mass is dynamic, and shaft speeds are a factor of 4-10x what a vehicle sees.

 

[mike156]

Trying to adapt what I've learned on cars/motorcycles to bicycles is a mixed bag. The wheels fall off the bus when the majority of the mass is dynamic, and shaft speeds are a factor of 4-10x what a vehicle sees.

Amen
Seems like none of the knowledge I picked up from cars works on bikes.

I will say though, the MTB community is way more open to talking about the specifics of damping behavior than the auto community. I don't think I've ever come across auto guys talking about how different pistons behave. Mostly just what your damping ratios should be and where the digressive knee should happen when it comes to specifics on dampers. I was never in the Miata stuff though so maybe they did. I'll give them credit though, they did more with 130hp then I could with 400. lol.

 

[Nurse Ben]

I had the same question as the OP.

Thanks Dougal for making sense of it.

Consider that virtually all air-shocks rely on a ~2.5mm thick rubber o-ring for a bottom-out stop. Coil shocks are running ~10-20mm thick foam bumpers.

The vast majority of riders do not bottom their shocks out hard with the above bumpers.

You don't want bottom-out control to engage too early or it destroys your mid-stroke response. But you also need a certain amount of stroke for it to fit and work.

In a fork you have a lot of stroke to use, so having the last 20mm or so working in hydraulic bottom-out works quite nicely (20/160 = 12.5% of the stroke) and gives you lots of room to make it engage, then ramp up and go through several stages.

In a shock with ~50-60mm of stroke you're down to 5-7mm. Trying to fit several stages of bleed off into 5-7mm is pretty ugly. Let alone trying to get a nice lead-in and progression into it.

 

[digev]

Just a thought. Can changing the bottom out bumper make the shock feel more «bottomless»?!

When I bottom out my CCIL Coil I can definitely feel it.

FYI: http://www.avalanchedownhillracing.com/Shape Factor Bumper.htm

 

[ghostbiker]

Just a thought. Can changing the bottom out bumper make the shock feel more «bottomless»?!

Yes they can, but something like shape factor bumper cannot be safely used on shocks with very thin shafts like DHX2 or CC stuff because it could actually snap it.

 

[digev]

Yes they can, but something like shape factor bumper cannot be safely used on shocks with very thin shafts like DHX2 or CC stuff because it could actually snap it.

Oh Ok. So an 8mm shaft is too thin?

Thanks for replying

 

[ghostbiker]

Oh Ok. So an 8mm shaft is too thin?

Thanks for replying

If 9mm one on dhx is I would say so, unless DHX is alu and CC is steel, but I don´t think that is the case.

 

[CaveGiant]

Well I've got a 8mm solid steel shaft on my db coil. It's bottoms like a & *-*4. I'm 95 kg....

Is there any aftermarket bumper solution?

 

[minimusprime]

Yes they can, but something like shape factor bumper cannot be safely used on shocks with very thin shafts like DHX2 or CC stuff because it could actually snap it.

source?

 

[ghostbiker]

source?

Avalanche