Different layouts for diy front suspension?

[Wheazel]

Lately I have been thinking about front suspensions, and searched some on the internetz about different layouts.
Have also seen at least one example of a homemade suspended front here on the es.

My thoughts are that this might be an intresting area to explore form wise.
I am not expecting to come up with front suspensions that outperform the better dh suspensions,
but for the sake of different design choices, more ways to make a reliable suspended front end would be desireable.
For road commuter bikes, my experience is having a suspension is the big deal. Not so much having a high end one.

Some basic design directions I am thinking of:

Be able to use simple inexpensive shocks as the compressing part(s).
Have the choice to build both "single crown" and "double crown" setups that are stiffer than midrange bike forks. (cant speak for the 40mm high end forks as I haven't tried any)
Low weight is not the highest priority, but unsprung weight should be kept to a minimum.

Some random examples of frontends that differ from the standard fork.

 

[Wheazel]

Another mockup I did. Would something as simple as this work? (pulling shocks/springs)

 

[spinningmagnets]

I asked the curator of a "tank bicycle" website ( http://www.nostalgic.net/site-index ) which style of suspension actually ran the best, He said the JC Higgens and Dayton Twinflex. The Higgens has a trailing link on the front, with a "beehive" tension spring (stretches instead of compresses)

The Dayton Twin-Flex (marketed under license by several companies) had a front and rear suspension that were nearly identical in function. Single beehive compression spring front and rear.

Here's a 1967 DIY that copied an antique motorcycle suspension, when the front wheel goes up, the coil spring is stretched longer (tension spring)

 

[gogo]

^I like the last one, and here is a double crown version:

 

[motomech]

In the late '60's, I had a Zundap that had Earle's forks.
For decades, motorcycle manufacturers have been looking for a new frt. suspension designs, but so far, nothing has proven better than telescopic forks.
I am in constant awe of how well my 13 year old Marzocchi Bombers work. 5 inches of travel absorbs the big hits while never bottoming out, they are light, strong and bullet-proof. The last thing I would want to change on my bike.
Maybe another design for aesthetic reasons, but for any other reason, everything else seems to be a big step backwards.

 

[gogo]

Earles forks are more expensive but are superior for their braking anti-dive and extremely low stiction. Telescopic has several times more seal surface and is prone to binding during use.

For decades, motorcycle manufacturers have been looking for a new frt. suspension designs, but so far, nothing has proven better than telescopic forks.

I've always thought cost was the main reason telescopic have become prevalent. Did your Zundapp seem more compliant over small bumps, and more cushy in general?

 

[E-geezer]

Another mockup I did. Would something as simple as this work? (pulling shocks/springs)

You mean like this?

http://www.laufforks.com/

Unless you're solely focused on style, you can't beat a telescoping fork for performance per $.

 

[Wheazel]

Never seen that one, cool layout!
It looks like the wheel is "loose" and only the fiberglass springs holds it.
The mockup I did was more traditional.

What I feel is the real benefit here apart from form choices, is that suspensionforks for bikes (single crowned) flexes alot in that crown.

 

[IdleMind]

If you have an itch to build your own suspension, then you ought to do it. I've done two and here are some thoughts.

On my recumbent the front end is very light and the non-damped suspension works great.

My cargo bike is an upright bike with 20 inch wheels and also no damping. This gives a good ride but it bounces when when you stand up on the pedals or even pedal hard while seated. This one would be better with damping. But I seldom get over 20 mph and average about 14.5 mph so it works for me.

For a spring rate starting point, I estimate the weight on each wheel and start with that many pounds per inch of suspension travel. For example on my cargo bike I estimated the front end around 90 pounds and the rate for the wheel is about 120 pounds per inch of travel. That rate is not the spring rate but the wheel force after accounting for the linkage leverages.

If you don't know how to calculate spring rates, it's not hard, there are probably internet calculators.

One more thing. The one one actual bike spring shock that I bought had a spring rate spec that was no way near correct. So calculate it out yourself based on wire dia, coil dia and number of active coils.

 

[E-geezer]

Never seen that one, cool layout!
It looks like the wheel is "loose" and only the fiberglass springs holds it.
The mockup I did was more traditional.

What I feel is the real benefit here apart from form choices, is that suspension forks for bikes (single crowned) flexes alot in that crown.

It depends. With older forks and cheap single crowns with quickreleases, they were definitely flexy, both fore and aft and with independent movement in the sliders. These days, not really, there are single crown forks approaching triple crowns in overall stiffness. If you have the budget, I think you would be surprised at the performance of a burlier single crown fork.

That being said, if you are determined to build something new and cool on your own, I'm looking forward to seeing what you come up with. Sourcing the correct spring shouldn't be too hard, it's the damping part of the system that would be tougher. At low speeds, it doesn't matter so much, but as it and also travel increases damping becomes far more important.

Having ridden undamped forks back in the old days, I can remember how lousy they worked. Pogo sticks. That Lauf fork has none, which is the source of the biggest complaints about it.

 

[Wheazel]

These days, not really, there are single crown forks approaching triple crowns in overall stiffness. If you have the budget, I think you would be surprised at the performance of a burlier single crown fork.

What forks are you refering to? The 40mm forks out there? totem and float?

 

[Eteck]

Would something as simple as this work? (pulling shocks/springs)

Similiar.

Found this in another thread:
https://endless-sphere.com/forums/viewtopic.php?f=3&t=64861

 

[Harold in CR]

Wheazel, the fork that you designed is very similar to the Jawa race bike fork used in Speedway racing. You might Google up Jawa and have a look. They are called leading link forks I believe and use rubber bands for the shock and have a damper.