reversed suspension, pull suspension, is it a thing?

jimmyhackers

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just wondering. as most rear shocks for bikes are compression/squash.

are there shocks that work in expansion/stretch? if so, is there a proper name for them?
 
I've seen a couple. Its a great option to know about if you are designing a frame. I don't know where you would find the part number or the company that makes the "pull" shock absorbers. You can use a linkage to compress an off-the-shelf shock, like the ebike below

In the cruiser below, the rear swingarm has the pivot at the center/front, and the bottom has a linkage

https://endless-sphere.com/forums/viewtopic.php?t=70448

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Zlatko's CBM

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The shock is called 'snipped motorcycle inner tube' :)
There are quite a few DIY projects featuring those. No sticktion, some damping, nice progression, infinitely fine-tuneable by varying 'preload' and number of 'rings'.

You do need some sort of stop in suspension to keep the o-rings from falling off and applying preload.
 
ah so they do exsist. little bit pricey :S

do you think it would be possible to make one from a single or dual chamber air shock? those cheapish a5 ones?

be either applying a vaccum to a single chamber shock? (i know a vaccum is a lot more succeptable to leaks)
or swapping the pressues round in a dual chamber shock? (im not sure exactly if that'll work)
 
jimmyhackers said:
ah so they do exsist. little bit pricey :S

do you think it would be possible to make one from a single or dual chamber air shock? those cheapish a5 ones?

be either applying a vaccum to a single chamber shock? (i know a vaccum is a lot more succeptable to leaks)
or swapping the pressues round in a dual chamber shock? (im not sure exactly if that'll work)

grant peterson, of rivendell, once floated an idea of a pull suspension design centered on a football-shaped air bladder. ride characteristics could be tweaked with a simple air pump. I don't know if he ever moved to the prototype stage but you might be able to find mention of it on the internets. or call him, he would likely chat with you about it.
 
jimmyhackers said:
ah so they do exsist. little bit pricey :S

do you think it would be possible to make one from a single or dual chamber air shock? those cheapish a5 ones?

be either applying a vaccum to a single chamber shock? (i know a vaccum is a lot more succeptable to leaks)
or swapping the pressues round in a dual chamber shock? (im not sure exactly if that'll work)

What exactly are you try to accomplish by using a pull shock?
Are you building a custom frame?

Personally I wouldn't want a bike frame designed for pull shocks because it would be "married" to a proprietary shock that is hard to maintain or replace, compared to standard shocks which are standardized and available from several manufacturers.
I am not aware of and performance advantages to pull shock to justify preferring them to standard shocks.

Almost everything is possible with enough effort/time/money, and it will take a lot of these to design and convert/build a custom shock with equivalent performance to off the shelf shocks.

Avner.
 
Again, a pull suspension makes a ton of sense if you want to use rubber bands as suspension element.
Cheap, easy, somewhat tuneable, actually works fine - you only need some topout bumper.
Otherwise, why reinvent the wheel?
 
Now that we've established that its rare, you will likely be the only person posting about your efforts in this area.

Discussion is likely to focus on speculation, but I think it could be a fun exercise. If you make any experiments on this, please post the results.
 
it will be a custom frame.....im going for a recumbant akira (kaneda bike) look/style.

more so the low seating position than all the fancy cowlings.

i tried having the suspension above the rear arm before but it really compromised how low that seating position could be.

i have a general idea of what a custom shock would look/work like. see my terrible paint picture. red bits would be seals and the blue bits air valves.... i figure it should work without air valves, but if i wanted to get fancy it should be easy enough to adapt/fit them.
 

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Maybe just make the swing arm slightly longer (so the pivot point is more inside the frame) with a downward facing L around the pivot point and then use a compression shock placed where it is on your drawing but rotated 90deg. Very similar size package but no custom shock and no complex linkages.

I'm more curious how you're going to do the fork, linkage fork of some sort?
 
Interesting, though I can't help think the need for a 'pull' shock could be offset be more favorable design geometry. In your paint sketch, it seems like that stubby tab sticking out below the shock is going to need to be incredibly beefy. Just eyeballing the lever arm ratio looks like 10:1, so if your cycle weighs a couple hundred pounds, half of that on the rear, 10:1 ratio, then that little stub needs to support about 1000 pounds force. ...and really needs to support a 1-time load several thousand pounds more than that so fatigue fracture doesn't come into play.

If you could somehow get the shock in compression on the top side (sort of the standard geometry), then at least all that force could be distributed back into the core of the frame which is generally the strongest part.
 
Check out the " Fox Pull Shock"

https://www.google.com/search?client=firefox-b-1-d&q=fox+pull+shock
 
i would like to go fox shocks....but they usually cost about as much as my whole bike. :s

seeing as i mainly do on-road and light offroad (trails n mud, no big jumps) with my bikes, ive never been able to justify getting some. (im not sam pilgrim)

ive added a pic of the MK1 which no longer exsists, this was made mainly to see if the excesive steering angle and longer frame (wheelbase) would work.
it looked terrible, but handled great.

the design of the rear swing arm would mean if i did do a pull shock. it would be mostly under/inside/between the two arms.
 

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Very plush, good for long travel application..
Probably the earliest pull shock application that I know of, early 90's, with off-road legend Mert Lawwill:

https://www.pinkbike.com/news/now-that-was-a-bike-yeti-lawwill-dh6.html

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Stuck around to late 90's:

http://www.vintagemtbworkshop.com/1998-yeti-dh-8.html

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