Moving the rear shock

Well, at least you're not at risk of ruining a good bike in this experiment.
 
Chalo,

You say, " Well, at least you're not at risk of ruining a good bike in this experiment."

Making a shock relocation modification [this was no experiment]the way I have done runs very little risk of ruining either a cheap bike or an expensive one. No holes were drilled into the frame, shock assembly or bell cranks and the bike's OEM shock position/operation can be readily restored -- a reversible modification. The clamp would likely work on a carbon fiber frame.

Yes, defacto, this is a $425 bike from WalMart. Maybe not a good bike for pedal/riding? I have put better brakes and 203 mm rotors on it. Is a good bike high $$ and will this quantity/quality alone lead to a good non pedal assist motorized bike? Bikes are designed for riding/pedaling and not to simply add an e-motor at will. And so we modify them to accommodate motors.

More on experiments: a scientific procedure undertaken to make a discovery, test a hypothesis, or demonstrate a known fact.


The Yamaha ebike has it shock under the top tube.

Thanks Chalo.
 
Hey, no qualms about your modification. Looks like a legit and clever attempt to address the problem you're facing.

But I work on a lot of bikes, and when I see Magna, Next, Kent, Ozone 500, Roadmaster, Genesis, Hyper, Mongoose etc., it usually means it's going to be a long hairy day.

Noted that the $250 Wally World bike now costs $425. It makes sense in the context of everything else.
 
To me, the modifications are ingenious, but possibly impeded by the rear "shock".
 
2old,

You say," To me, the modifications are ingenious, but possibly impeded by the rear "shock"."

"...impeded..." ?

For sure the range of motion possible of the rear axle in compression is greater with the shock unhooked than with the shock in place. Such is the same limiting manner with the 3 Specialized Big Hit downhill frames I have. So yes, any normal rear shock on any of these described bikes would limit full swing motion because shock travel is too short to permit full range -- about 1.5". The Spring Type shocks may have a stiffness of some 650 lbs/in. 3" of travel would be about a 2000 lbs of force -- jarring?

If I like this Hyper Explorer setup for road and towne use I will add

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This Fox Float has no more than 1.5" of travel but for that amount of shock compression the rear axle moves about 6" upward.
 
You sliced a big nut in half, drilled it out for a bearing, then welded that to a ball joint separator? That's some serious Mad Max craftsmanship. :thumb:

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Comrade,

You got it right. Fabricating the bearing containment rings mounted to the pickle fork was the most challenging task of the relocation. Figuring out the bearing alignment mechanism and stabilizing that assembly for welding took some effort as the fork is very slippery plus ordinary clamping doesn't work on the angled faced tangs of the fork.

I did use a Hi-Torque Mini Lathe to face the power hack sawed nuts and make some square precise length spacers.

The fork even with some thoughtful planing may turn out to be a one-off-thing because frames with the "S" curve are not too suitable to bigger motors mounted within the triangle space.
 
The motor has been chosen and is mounted. It turned out the Cyclone 6k was too wide to install with dual-drive for the 175mm Isis BB assembly I had installed so the Cyclone 3k was fitted into the space above the BB shell. The OEM lower shock end mounting tangs were not cut off prematurely as they just missed interfering with the motor sitting as low as possible. In fact they are used in the primary mount.

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The water bottle bungs were also used for additional motor stabilizing.

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A dual drive with both chains on the right side was employed.

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Still to be added: the chain guard
 
DM, sorry I was obtuse. My comment was related to the "shock" being a spring with no damping characteristics (AFAICT), but you took that into account.
 
Kick-in Stationery Idler Pulley for Top Side Chain Run

The motor shaft position which is immediately above and forward of the bottom bracket makes for both a change in the angle of incoming chain to the motor and excessive chain slack during hard acceleration or when encountering large rear suspension travel upward. A spring tensioned idler pulley was added to the power drive chain near the rear sprocket on the bottom chain run to take up this suspension compression generated chain slack. This idler pulley placed here will have no effect on the change of the motors incoming chain angle.

A battery shelf was mounted so it's plane was about 1/2" above the incoming motor chain. During either hard acceleration or bump generated large rear suspension compression the chain would rub on the end of the battery battery shelf. The rubbings were caused by the occasional change in the chain line angle between the rear motor sprocket and the motor drive sprocket.

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During either hard acceleration or big bump compression the generated top side chain slack is not taken up quickly enough by the standard rear derailleur position mounted idler pulley. So there is top side chain slack in these instances which can make for chain derailment. There are two ways to reduce compression generated top side chain slack. The obvious way employs a spring mounted idler pulley on the top chain line. The other way is employing a properly located stationary idler pulley that is in such a location that it starts to fold the chain as the chain angle changes. This fold or deflection occurring in the chain line as the pulley engages makes the chain path longer, hence removing chain slack when the chain angle changes.

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I call this idler pulley arrangement a kick-in idler pulley because it spins or folds the chain line only during rear suspension compression when the chain angle changes.

A straight line is the shortest distance between two points.

This top side idler pulley has ended compression slack chain derailment and chain rubbing on the battery plate.
 
The Fox Has Been Deployed

It was time to get rid of the OEM spring only shock and install a rear air-shock that could be adjusted. The adjustment for the low end of the OEM spring shock setting began at a very stiff setting. With the air pressure adjustable Fox 🦊 shock I can say the OEM shock stiffness compared to a Fox shock air pressure setting of 220psi but with without damping. The current air pressure test setting is 160 psi.

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The fit of the extension shaft had to be very tight allowing no pivotal action about the connection. The extension shaft has to act as a rigid extension of the end of the Fox shock.

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No irreversible modifications were made to the Fox but the decal is now reversed.

Note. Adding the Fox does not make this "Mountain Bike" very much more suitable for bumpy trail riding but it has made hitting road potholes less jarring. The build was intended for a Townee.
 
Creating anti-sag for rear suspension frame response to motor acceleration

With anti-sag you feel the seat rise, not sag, when going to WOT quickly. Single chain motor drives like done here before adding fixed chain rollers will likely produce seat sag upon acceleration. To make an anti-sag response the chain deflection pulley(s) will have to be positioned such that the necessary chain perimeter gets longer as the RSS ( rear suspension system) goes into compression. If the rear axle is fastened to the lower stay [as on the Hyper Explorer] the change in necessary chain length [for suspension movement] approaches zero as the deflection pulley’s fixed position is placed closer to the lower stay’s pivot bolt. Specialized Big Hit suspension fastens the rear axle to the upper stay so the deflection pulleys placement on the lower stays rotation pivot will not produce zero chain length change for suspension compressions.

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Another stationery deflection pulley has been added to the Hyper Explorer frame but because the bike has 2 chain drives on one side moving the bottom deflection pulley down below the BB shell is more tasky than if there was only one chain. The system response is getting closer to anti sag after adding the lower deflection pulley shown in the photo below.

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Placement of a deflection pulley below the BB shell for the lower chain run creates an increase in chain perimeter for compression — hence some anti-sag for this single reduction Big Hit bike shown below..

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The anti-sag feature that some MT bikes have is designed with the chain going around the BB axle. So to preserve the anti-sag feature on an Ebike build from a bike with anti-sag, the final chain drive going to the rear hub must also go around on the BB shaft. No jack shafts.

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This bike has a not visible stationery deflection pulley below the BB axel to keep the chain from rubbing on the lower stay. Since a deflection pulley on the lower chain run placed below the BB but placed inside the chain loop, the chain perimeter will still need more chain length for suspension compression. Here the original anti-sag features are preserved/enhanced.
 
Fitting the Rear Fox Float X2 shock

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The Fox Float X2 rear shock does not have a big steel spring, just air and oil to allow it to out perform the older heavy steal spring versions on downhill installations. It does come with two spacial costs. The high volume cylinder is big and the side oil can needs lateral clearance. Not all bike rear shock placement spaces even with mild modifications can accommodate this air-oil shock.

By mild modifications (2 types)

1. Drilling a new set(s) of anchoring holes on one or both frame fastening ends

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A flat bar bell crank like on the Thumper can easily be drilled to make for additional shock mount locations. But some bell cranks are not suited to making other mounts.

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2. Sometimes the frame structure supporting the seat tube is over designed and some surgical grinding of it metal to fit the oil can’s needed space can be done while still leaving plenty of seat support strength. Some grinding on the Broadie frame for the oil can clearance could be done and still leave adequate seat post strength.

There are some machine design programs that can be set up to do the kinematic analysis of the various shock assemble bars and projections of them to determine what set of drill holes will have clearance for the shock’s motions. One can do this graphically by hand.

Whatever mount holes you choose to use (existing or added) a new shock location will likely change the mechanical advantage [MA] of the lever that connects the shock to the upper stays. If you increase the MA you will need more air pressure to get the same initial loading sag [ suggested for Fox X2 20% - 30% of total shock travel].

My scenario: MA location giving shock clearance = 126% over lowest OEM holes’ MA. I chose an air pressure based on the rider weight plus all add-ons (motor, controller, batteries etc) = 210 lbs. The Fox tuning guide suggests an initial air pressure of 1 psi per pound of rider weight. To get 30% sag the pressure needed was 250 psi or about 1.26 x 200 = 252 psi. To get only 20% sag the shock air pressure needed was 300psi which is the shocks max suggested air pressure. So if you weight over 160 lbs you may have to settle for more than 20% sag, or find a shock mount that has a lower MA. The lower MA will convert your suspension to less wheel travel for a given shock travel.
 
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