NightShift

I just got a BikeE (my first recumbent). It's a nice bike, but I'd like to try swapping out the front fork/wheel. Suspension would be nice, as would a bigger front wheel (the bike has 16" front, 20" rear), but I don't want to raise the front end any more than I absolutely have to (to get a bigger front wheel). A springer style fork seems like it may be a good idea. The steering is a little twitchy to start with, so I don't think that will be a problem. The only issue I've had making a sharp turn with this bike was on the second ride when I realized the pedal can reach the front wheel.

I did a little reading/Googling to find out about 20" suspension forks, and found complaints about springer forks causing sluggish steering (which I don't think will be an issue for this project, but feel free to tell me I'm wrong) and about the suspension being undampened. So I'm wandering, would there be any issue with using a dampened frame shock for a springer style fork?

Your thoughts?

Doug5150

I'm trying to imagine how you could ever attach a modern frame shock to a springer fork, and I'm just not seeing it since most shocks now are at least six inches long and the springs on the forks you seem to be speaking of are much shorter.... unless you can modify the fork yourself, of course. Cheaper generic shocks (such as off department-store bikes) usually don't have real fluid dampening; all they have is a friction-fit bushing that quickly wears out, and there is no source of replacement parts at all for those shocks.

It might be helpful to provide an image or a link to the forks you are referring to.

FYI: AZUB has a couple recumbent models with telescopic suspension forks and 20" front wheels--- https://www.azub.eu/CZ/models/

NightShift

Ok, maybe I should have been more specific. What I'm considering is a custom fork. That's a big part of why I'm asking in. Alt Bike and not the recumbent forum. I'm aware most department store (and entry level bike shop) suspension forks aren't dampened; that doesn't make me any more interested in going that route.

What I'm visualizing is a 16" bmx fork with a long steerer tube (probably extended and reinforced) with a heavy washer and bushing at the end connecting to a pivot arm, which would connect to the bottom of a 20" fork. The 20" fork would have the steerer cut short and a plate welded to either side (left & right) as a mounting bracket, and a tube over the steer tube of the 16" fork would provide the other bracket. The extremely long neck on the BikeE should make it possible to get a decent angle.

Doug5150

What you seem to be describing is something like the old Monark single-spring fork, but with a modern shock:
https://www.google.com/images?hl=en&s...og&sa=N&tab=wi

First off, the Monark fork has a rear/stationary fork (that fits into the frame's head tube) and a front/moving fork (that rides up-and-down with the wheel's travel). The rear fork is the one that needs to be taller than usual, since it needs room for the wheel to move upwards into.

Secondly, to build this kind of fork you would need to use a bike shock that had a stationary mount at one end, and that type fell out of favor a number of years back.
A solid-mount shock has a screw- or clamp-type base on one end, and a bolt eyelet on the other.
Here is a Yeti frame from 1993 with that type:
https://www.google.com/imgres?imgurl=...:1&um=1&itbs=1

Pretty much all the name-brand rear shocks now have bolt eyelets on both ends.

You can still find solid-mount shocks on eBay, but they are usually generics, they aren't usually oil-damped and you are back to the parts problem I mentioned earlier.
Here is one example, for $11.
https://cgi.ebay.com/Shock-Works-Rear...item3f062a8821
there may be others, that's just the first one I found--but they're likely to be generics of comparable quality also. The name-brand MTB shock companies stopped making them ~10 years ago.

It might be possible to get a coil-over shock that uses a threaded body to adjust the spring preload, and make a threaded mounting arrangement to clamp on the portion of the exposed threaded shock body.

Note also that most name-brand MTB rear shocks cost at least $250 new. Considering the prices, I would just go look around at the prices for already-made 20" suspension forks. The rim brakes won't work for a 16" wheel, but you can switch to using a front disk brake if the fork has mounts for that.

NightShift

I'm hoping to use a 20" wheel.
The Monarch is similar to what I was thinking of, but I was envisioning a longer linkage between the forks.


This is a crappy quick sketch, but I was just trying to show the idea.
https://m.flickr.com/photos/60864641@N07/5547723607/

I'm still not clear on why it would need a solid mount. I was thinking flex could be an issue; was that what you are thinking of?
I was thinking maybe beefier pivots would work, like the linkages used for rear suspension (although I was hoping the binder bolts I pulled out of a Mongoose XR200 would do, but I guess I could cut the bb like pivot out of that frame).

I know dampened shocks are expensive, but I've occasionally seen them used for less than $100, and I have the (undampened) shocks off a ProFlex and a Mongoose, so I could use one of those temporarily.

Do you know any 20" suspension forks I should consider? I don't need much travel, but I would like to keep the front end low.

And thanks for the response. The link to the Monarch forks is great.

NightShift

Maybe I can find a cheap 20" full suspension bike and just use the rear end off that. If the toptube is boxy I may be able to cut out the head tube with a section of the down tube attached that I can drill to make the top mount.

If I stay closer to my original idea (which I think would look cooler) maybe, instead of a 16" fork and a long bar to link it, I could go with a taller fork (24" or 26") that I rebend to give it enough rake that I can use a short bar to link the forks.


I added some pictures to my Flickr. A 26" fork which I think I could get a lot of rake with; the holes above the ends are almost big enough for the steel binder bolts I have, just have to be careful to only expand the holes up away from the ends (and not too much). A head tube on a frame with a box down tube, which I could use for the steer side bracket. And a couple pictures of the back of the junked FS Mongoose I have.

To use the back of a FS 20" bike I should be able to remove it from the frame at the pivot and attach it to a box welded to a steer tube. Maybe cut and notch the ends of the head tube/steer side pivot mount and and a couple heavy pinch bolts (seat post clamps)?

NightShift

I think I want the position of the wheel relative to the head tube to be about like this.

https://m.flickr.com/photos/60864641@N07/5552240335/

I think the steering will be ok (if I can avoid lateral flex), and it'd let me run a 20" front wheel with minimal rise compared to the 16".

Doug5150

Those forks steer poorly at low speeds, and are dangerous at high speeds.
Also they do not work well as suspension, because the wheel must move forward as the suspension is compressed--which is the opposite of what you'd want.
Obviously they work, companies make and sell the things,,,, but it's not hardly nearly the best choice on technical grounds.

There's 20" suspension forks out there that have fluid dampening and will work correctly, but they're all rather expensive, over $500.

Alternately you could just try using a Big Apple tire; most 16" tires max out at around 1.75" but the $40 Big Apple in that size is 2" wide.

NightShift

All of this is referring to the type of fork in the picture I used to show the relative position I want for the wheel, right?
I wasn't saying I want that type of fork, just the position.
If I modified the rear of a full suspension bike, assuming I started with a single pivot design, it would probably have the same issue, but as far as I can tell the monarch forks and the design I've been describing would have the wheel move straight up or up and back.
I realize just having the wheel that far forward will seriously affect the handling. I started by saying the steering is twitchy as is, and I thought the change in handling would be ok. I also said you're free to tell me I'm wrong. But please do tell me more than "steer poorly at low speeds and are dangerous at high speeds". If you think the steering issues will be worse than I expect please tell me why. If you're going to say the steering is poor please be descriptive. I've ridden bikes with long forks, and with forks with a lot of rake, but never with a fork this short with this much rake, and this is my first recumbent, so I have some idea of what the issues may be, but I know I'm dealing with issues I'm not familiar with. I really do appreciate any and all input, and I will listen/read attentively. I just ask that whether you like the idea or think it's a bad idea (either specifically for this project or in general) is that you help me understand the basis for your opinion.

Putting on a bigger tire would help both with the small wheel size and the lack of front suspension, but it would make the pedal overlap worse. Also I'm not sure the fork has enough clearance, but I think it does. I'll keep it in mind.

Dave Armstrong

I have a Linear recumbent. It's a little different than a bike E, it has under the seat steering, but it also has 20" rear wheel and 16" front wheel. Because of the position your sitting on a recumbent most of your weight is towards the back of the bike. It might help more to set up rear suspension and leave the fork as is. Looking at the angle of the front fork I think suspension will create some handling issues. I think they did make a rear suspension for one model of the Bike E. I like the challenge of making something work that it wasn't really made to fit but I think there could be some unforseen difficulties since rear suspension on recumbents are very common but front suspension on a recumbent is kind of rare.

Doug5150

The exact issue is the front wheel's trail. The front tire's contact patch is normally about two inches behind where the steering axis would hit the ground. Building a fork like you say would put the contact patch a couple inches in front of the steering axis.

https://en.wikipedia.org/wiki/Bicycle...namics#Balance

If you want it, go and build it (-or just go buy some bent lowrider forks, if you want to try it faster).
Every commercially-made bicycle in probably at least the last 75 years as a couple inches of positive trail, and you're going to be doing it the opposite direction.
Lots of people don't like their feet hitting the front tire, but nobody does what you are describing, because it screws up the bike's handling.

If you fit a 20" tire at all, that alone will add a lot of stability, plus lift the front of the bike only a bit more than two inches. If you get a Big Apple in 20", they come in a 2.35" width (if the fork will take it) and will lift the bike's front another half inch or so.


Also We Note: if you use fenders, mounting fenders can be a problem with the Big Apples.

NightShift

Ok. For this project I will probably stick with something more traditional and just use a 20" wheel and a fork that will give trail similar to the stock fork, which will probably be enough to keep the wheel away from the crank and will ease my mind about potholes and similar obstacles.

I'm still interested in making a Monarch type fork with a frame shock. Completely apart from recumbents I'd like to hear thoughts on this.

Before I completely abandon the strange and unusual for this bike, how about compound steering? I'm thinking something like a SwingBike frame, but very short. Probably with a damper of some sort to stiffen the steering at the first pivot/existing head tube.
I've never ridden a SwingBike, and I've never seen one with a damper, and I have absolutely no clue what the issues may be. Naturally this makes the idea much more interesting.
I'm guessing I would want a steeper angle for the front/new head tube.

NightShift

Resurrecting an old thread.

Just ran across the Birdy and the fork looks very much like what I was visualizing.
Anyone know where I could get the fork by itself?

turbo1889

I also have been interested in building something along these lines as well (front suspension fork that uses rear suspension MTB shock strut) but for different reason. Specifically "over the front wheel" cargo bike that uses a smaller wheel on the front then normal with a big cargo rack mounted solid to the front of the frame over the smaller front wheel (often done with old steel 26" wheel MTB using a 20" heavy duty BMX wheel up front).

Such cargo bikes are well capable of hauling 200+lbs of cargo that is easily balanced being right over the front wheel down low due to the smaller size front wheel and mounted solid to the frame and not turning with the front wheel and 100-lbs or so is a normal no sweat (unless climbing hills !!!) no problem cargo load for such bikes and as an extra bonus they are one of the few kinds of cargo bikes that if you make the front cargo rack fold up narrow will fit on a standard public transit bike rack.

The main problem with them is that if you hit a chuck-hole with a full cargo load you usually wreck your front wheel because they are almost all front rigid (heavy duty) fork designs since most front suspension forks aren't going to take that kind of loading. I've often thought of trying to figure out how to build a front fork for such a cargo bike using a rear MTB suspension shock strut which are far stronger with a whole lot more pre-load then most front suspension forks such that when unloaded it would just handle like a rigid fork but when you hit a chuck hole while carrying a heavy cargo load there would be enough give in the front fork suspension to keep from beating up and killing front wheels.

I enjoyed reading this thread and the ideas in it very much and thank you for resurrecting it and bumping it up to the top otherwise I would have never found it otherwise.

These are the kind of cargo bikes I'm talking about, and I think you can see how they could benefit from a seriously heavy duty custom front suspension fork built using a MTB rear suspension shock strut: