Issue with the rear shock on my Recumbent - new setup

[Peterfr12]

Dear ebikers,

I finally finished my new setup a fully suspended Recumbent powered by a MXUS 3kW hub motor, a 12F nuculear controller and a 20s14p homemade battery (84V 49Ah). Both front and back wheel are motorbike wheel.




I tested my new setup today and yesterday on a flat road for 24 km under the rain, asphalt and then a sandy road. It is great compared to my previous setup with a Mac motor. The MXUS motor did not overheat at all and the temperature was close to 33 C (vs 90 C for a mac motor). This was my main issue with the Mac motor, unable to sustain long trip without reaching 100C quickly. Regen is great since my rear brake does not work – it will require bleeding – and the brake pads are touching the rotor.
Speed on flat : 66 km/h (41 mph) with a 73V battery and 1800-2100 W. 64 km/h without any issue on the sandy road along the canal; it was empty because of the rain so safe. Motorbike tires are a relief. I will add a fairing later to protect me from the rain.


Now the issue I have : when I go over bumps the top of the frame - where will be the topcase -is touching the mudguard of my bike. I am only 145 pounds. I have a rear suspension a DNM DV22AR (I am aware it is a cheap one). I can change the distance between the rear fork and the frame by putting the top part of the suspension to another hole, but it will lift the seat to a position more perpendicular which I want to avoid. Lying in my seat like in a bed is better . I have no technical knowledge on suspension but for me the spring is too soft so how can I harden it? Or how can I change the limit of the damping. The red button is for the rebound force adjustment so I shall not touch it. There is a massive nut on top of the spring, but I cannot unscrew it. I could adjust it in the past but now it is stuck. Or can you let me know what should I purchase as a new rear shock?

Thanks for your help.

Peterfr

 

[Eastwood]

So you say you can’t twist the top part? If so it might already be screwed down all the way. Or you might need to put some type of lubricant on the threads to get it to turn.

If it were me I would just use an air shock, its so much easier to find the right tension with air. Spring shocks are good but sometimes it takes buying a couple of different springs to get the right tension.

 

[MadRhino]

You can screw the preload ring nut further more, I see it still has some thread as it is about on the middle right now. Use some penetrating oil if it is stucked. If you need a stronger spring just buy the next weight up ( the spring weight is stamped on it) of the same size and length.

 

[99t4]

There is a massive nut on top of the spring, but I cannot unscrew it. I could adjust it in the past but now it is stuck.

From your photo it looks like the adjusting nut has rusted to the top of the spring (not sure, it could just be dirt) so yes, try a good rust penetrant over several days, giving frequent light hammer taps to introduce vibrations to increase penetrant uptake into the corrosion.

 

[dogman dan]

Try the preload. Looks like a decent shock actually, I see a rebound knob on it. It won't ride so plush with it screwed down more, but it should at least still absorb some of the worst potholes.

If the bike is steel though, welding on it could modify it enough to take a small motorcycle shock. Like a pit bike shock. If steel, you can also weld on a disc brake mount for the rear.

 

[Peterfr12]

Dear ebikers,

Many thanks for your fast answers. Indeed I thought it was dirt and mud but it was rust. I sprayed some WD40, wait for 50 minutes and then I could tight the big nut hitting gently a screwdriver with a hammer. Thumbs up.

I have a mudguard but the mud is still going easily onto the rear shock when I ride over puddles. My rear shock will get rusty again. How can I protect it? I was thinking to wrap it with something like a 'big condom'. Or spray WD40 very 2 weeks onto it?

Regards,
Peterfr12

 

[MadRhino]

It is basic maintenance to clean, lube and tune suspension components. Hiding them won’t make you more likely to clean and lube.

 

[99t4]

How can I protect it? I was thinking to wrap it with something like a 'big condom'.

You can search on shock boot, they are commonly made of neoprene, fits over the shock with velcro.
You will want to open it up and inspect after wet/muddy rides because, as MadRhino stated above, dirt and moisture may become trapped inside. Depends on the location and fit so might work well or might cause more problems, you'll have to experiment.

 

[www.recumbents.com]

I second the airshock suggestion. They are adjustable and have much better dampening, so when you hit a bump it doesn't launch you. The air shock is also is safer in the corners.

Warren

 

[MadRhino]

I second the airshock suggestion. They are adjustable and have much better dampening, so when you hit a bump it doesn't launch you. The air shock is also is safer in the corners.

Warren

Easier to tune and light weight, but shorter lifespan and a nightmare to rebuild. They are not safer nor better, only easier to tune properly. For a serious rider, some air forks are doing good but all air shocks are toy grade.

 

[ColinB]

Hi Peter,
I'm not a professional, but I have a few thoughts for you. What type of shock comes with the frame normally? You might want to get that one, or try to match it's specs.

When you go over a big bump and the frame hits the fender, that's called "bottoming out." You can:
- Use a harder spring. Adding pre-load (adjusting the nut) might help a bit, but it's purpose is to change the amount of sag. It won't change the spring rate.
- More damping. You get this several ways. Adjust the shock to add compression damping. (Most don't have this.) Change to heavier oil. Change to smaller holes in shock piston. Change the shock mounting location or angle to make it more progressive. If you change to oil that is too thick, the suspension will feel "dead" and not as plush.

This isn't an air vs coil thing. You just need a shock designed for the frame. To me, better dampening just means the oil weight and internals suit the rider and frame.

Colin

 

[MadRhino]

Agreed with the above. Still, the shock might be short because the rider did mount it on a low position among the mounting holes on the frame, because he feels more comfortable seated low. Then the shock should be set to a shorter travel, and eventually a harder spring.

Even bottoming a spring shock shouldn’t normally make the wheel hit anything that was original equipment of the bike. Only air shocks are falling to full bottom when they fail. Spring shocks can only fall to the fully compressed spring length. To set the tail lower and keep the original suspension travel, either the wheel should be smaller, or the mud guard higher. Otherwise, the shock itself has to be set or replaced for a shorter travel.

 

[Peterfr12]

Dear ebikers,

Many thanks for your comments. I should have been more precise. I purchased a Nazca recumbent steel frame from Holland with the current rear shock adapted to my weight. I added a Mac motor and used it for ~10 000 km. There was no ‘bottoming out’ issue. it was a light setup, but Mac motor suffered from overheating very quickly and the clutch is fragile. My bike tyres get worn after 4000 km and I was using a lot of brake pads. so I decided to go for a big direct drive hub (Mxus) with 3 inch motorbike tyre. In order to accommodate a larger tyre and a disk brake, I had to lengthen the frame of the bike by adding two 20 cm length plates I designed. By changing the geometry of the frame, the light under the bottom of the rack was hitting the top of the middle of the mudguard. See the picture.


I need to decrease the amplitude deltaX to avoid touching the top of the mudguard.
I did a 20 km trip tonight and the setup is fine as I am not touching my mudguard anymore although the suspension is a bit harder. i screw clock wise too much the nut. if I sit onto the rear rack I have over 2 cm left now between the light and the mudguard.

I tried to adjust the disk brake and reached 44 mph with 2400 W on the flat.

When I have time, I will open a new topic on the ebike build thread where I will present my bike as it is rather a rare setup (direct drive recumbent with 82V 50Ah battery).

cheers,
Peterfr12

 

[donn]

My battery is only 52V and I use an ordinary bicycle tire, but you aren't entirely alone - I'm riding a recumbent with rear suspension (Burley Limbo) with a direct drive motor. I'm envious of your rear rack. The Limbo provides no particular means to attach one, and the merest stub of space at the tail of the frame to work with.

 

[MadRhino]

Adding 20 inches to the frame does require a much stronger spring weight, because you had created a powerful lever effect on the suspension. I would add at least 100 lbs to your actual spring weight, meaning if you have a 300 lbs now, it should be replaced with a 400, maybe 450.