How can I change shock position without altering geometry?

[macribs]

Just came across this build
Clever shock mount. Kind of like those Buell S3 motorcycles and a few yamaha's HD etc.

And here is the buell s3.

I've seen more then a few custom cruisers here on ES, and they all seems to be hard tails. Like old harleys. But harley did go for soft tail eventually. Today even custom cruisers motorcycles often uses this horizontal shock setup for added comfort and handling.
It seems at least e-cruisers would benefit from such a shock mount. You could hide the shock and the bike would appear to be hard tail but it would actually have great comfort and handle speed better.
But I think even hooligan city bikes and commuters would benefit from such a design. Such a placment would not take away space for batteries, mid motors or motors mounted on the swing arm. The whole triangle could be filled with batteries. An RV-120 15kw motor on the swing arm.

Are the linkage for those pull shocks very complex in design compared to the traditional setup?
Why has not this type of design caught on? I must be missing something that you engineers seen long time ago?

 

[Grinhill]

This arrangement seems to work well with V-twin motors which can be quite long front-to-rear. Another example is the Britten V1000.

 

[ferret]

The linkage for a pull shock shouldn't be more complex to design.
The pull shockitself however, is much more complex, expansive and hard to set up and maintain.
All pull shocks currently on the market are proprietary while most regular shocks are generic.
I would suggest avoiding the added headache of a pull shock, both for an ebike and a regular mountain bike.

Avner.

 

[macribs]

I see. Did I quick peek at ebay. 1.000 $ for a Buell pull shock.
Well if they are made only in small numbers and only fit one bike it is understandable.

That is really sad. Because a pull shock would be the ultimate design for e-bikes.
And there is no such thing as pull shocks for bikes?


Edited: Wait the Scott Genius LT uses pull shocks. Seen those shocks sold for 300$ and up a few bills.
That ain't to bad. And if you are using the bike for commuting, cruising, or just ride around town I am sure those Equalizer3's would be up for the task. I know the first ones had problems. But it seems they are doing ok from last year tests.

 

[Drunkskunk]

Edited: Wait the Scott Genius uses pull shocks right?

Nope. The pivot for the rear suspension arm is on the seat tube. so when the rear tire moves up, the front of the arm moves down. that polls down on the top of that shock, with a rather convoluted series of arms to keep the shock vertical while it's being compressed.

A pull shock would be cool, but shocks aren't a one size fits all solution.Different bikes need different stroke lengths and valving, not to mention spring size and weight.

If you want an under slung shock, it's better to use a compression shock and build a reverse arm setup that pulls on the shock from the front of the bike. That's a lot of added weight and extra complexity, but sometimes style beats common sense

 

[macribs]

A way more complex linkage seems like the hard way to go. Not sure i need that. And added weight as well.
Anyway I will look some more into pull shocks. One could be lucky and find a used one too. And for a new build it should not really matter what you use as a starting point - so any length pull shock should do really.

Seems the jury is still out on that Equalizer 3 shock

Like the current Genius, the LT’s suspension system is activated by a pull shock.

For me it seems (bottom pic) that when the swing arm pushes upward (compresses) the linkage will pull the shock rather then compress it.

 

[Drunkskunk]

2 big problems with that particular design. 1st, the piston arm is attached to the frame, and the shock body to the suspension arm. That needlessly increases the unsprung weight, and hurts performance. 2nd, the shock is in the line of fire for everything being slung off the tire. Shocks on the other side of the seat tube get shielding from mud, sand, snow, water, blood, entrails, etc. The seals on the shock get dirty and wear out quickly in that position. (I found lots of posts on that when I Googled it)

You might be able to use a shock like that if you had the lower suspension arm pull down on the shock from the front, But I sure wouldn't copy that bike's design.

 

[macribs]

My intentions was not to copy the Scott Genius design. Only to use their shock. Scott has the equalizer vertical - I would place the equalizer horizontal in a frame build from scratch. The only reason to use the scott shock would be price and availability.

I still think the best placement for a shock for e-bikes would be horizontal - mounted under the BB. It would look smooth on a cruiser.
Could easily hide the whole shock so frame appears to be hard tail. A design like that would be suitable for even more bikes then cruisers, would be nice on commuters to allow for max batteries in triangle. City bikes. It could even work for freeride bikes as long as one would ensure enough swing arm travel to deal with the rough stuff.

Look at the placement of the shock in the pick below. Something like would work out great for e-bikes. It will free up space in triangle as well as clean up the swing arm for those tiny lightweight RC motors.

 

[macribs]

I will have to look into this as well. An early specialized Brain technology. Don't make em like that anymore.
Maybe worth making a carbon copy?
It sure frees up the triangle.

Btw I came across this great explanation of suspension and linkage. Notice how the pedals do not move in the first gif and then look at the second.

 

[ferret]

There are mountain bike models which have a horizontal push shock mounted just below the to tube. The designs leave a lot of room free in the front frame triangle.
You might want to consider that approach.

Examples:

 

[sigimem]

@ macribs Sorry but you just can't compare the chain slack of a 300mm travel (guessing) dirt bike with a street bike with a toothed belt thats two different worlds. (1st page)

Hope I can contribute something.

I figured there are only a few reasons for the rather complicated (or varying) designs of bycicle rear suspension.

1. Eliminate/Reduce the squat of the suspension due to chain forces.
2. Eliminate/Reduce the brake torque soaking up the rear suspension.
3. Get a progressive linkage system for the use of a rather linear shock. (KTM used a progressive shock system without linkage for several years called PDS)
4. Optimize the pivot point (/VPP) for best suspension response (don´t know the english term. The rear wheel can move away easily when a force hits it in a special direction)
5. Eliminate the pedal movement due to suspension travel, the chain pulling the pedals. Goes along with 1. and 5.
6. Looks ?

So what is important for an ebike?