suspension on a quad.

[Sparky]

hi all.

i'm about 20 percent into building my streetfighter, and something fun has occured to me. suspension. One of my other hobbies is jeeping and off-roading, so i know a thing or two about suspensions. mostly, the importance of keeping all the wheels on the ground. i suppose this isnt so much of an issue with trikes, but i can see it coming into view with 4 wheels. now, i know this thing will never articulate like a jeep, nor does it need to. (though a 4 wheel drive cycle car is an interesting idea..) But, suspension would smooth out the road, and likely provide more control for steering and braking.

my idea is a transverse leaf spring, like cars used back until the 40's. since this thing effectivly has two solid axles, thats the most sensible. next, though it would be easier to put it on the front, it seems to me that most of your weight would be on the rear. so it would have more use back there. (i think)

ive designed, on paper anyway, how to make it work. my questions to those that have already built and ridden one of these is- is it needed? also, do you think it would adversly affect cornering? how much can you lift one wheel off the ground before another lifts (or, how much torsional twist is there)?

i'll post some pictures of my idea when i get them drawn up.

[AtomicZombie]

I think it would be a fun project to make the mods for suspension.

Here is what I have learned while riding the StreetFighter...

1) A wheel lift is very rare and almost impossible to make happen on purpose. A tire skid will happen before a rollover.

2) Because of the long mono boom and weight mainly over the rear, on very uneven ground the expected frame twist is usually enough to compensate. You get about 2 inches either way on the front wheels.

3) If the ground is so uneven that one front wheel lifts, it has almost no effect on steering or traction.

Check out Richie's quad - it has a pivoting front...

http://www.atomiczombie.com/gallery/richardpeters/trike2.htm

Brad

[Sparky]

i had noticed the bolt in that picture, i was wondering its purpose. it does solve the twisting, but how much it would do for bumpy roads?

i got some badly drawn pictures of my idea. i think yall will get the idea though. of course you could adapt the idea for the front, but i think the rear would be taking more abuse.

http://i14.photobucket.com/albums/a318/sparky96181/StreetFighterrearsusside.jpg

http://i14.photobucket.com/albums/a318/sparky96181/StreetFighterrearsusback-1.jpg

[trikeman]

You guys may find this free out of copyright book quite interesting. You can either view it online or download it as a PDF file.

http://books.google.com/books?id=70mJeb_q19EC&printsec=frontcover&dq=model+t+ford+car&client=firefox-a

Lots of detail on the suspension and construction of the Model T Ford.

[TheKid]

I toyed with the idea of leaf spring suspension. For the rear, due to the nature of bicycle transmissions, axles with universals are necessary to prevent the chain from twisting. On a motor vehicle with solid axles, when the diff tilts in any direction the driveshaft still turns the gears with no adverse effects, because of the u-joints and the design of diff's. On a bicycle, when the solid axle tilts left or right, the rear cogs also tilt, but the chainwheel doesn't, which may put undue stress on the chain and the rear derailler. It would work well on the front, with one minor drawback, which would be most noticeable at high speeds, as is the case with motor vehicles with this type of suspension - when the axle is tilted left or right, if one whell is on level ground and one wheel is higher or lower, the tire on level ground is riding on the inside or outside of the tread. If the terrain is severe, it will ride on the inside or outside sidewall. It also puts strain on the kingpins and the kingpin bearings, although these components would still have a long life unless they're constantly put under severe pressure. As I said, it's a minor drawback, considering the plus side, which is a smoother ride and less stress on the main boom. (Drastic reduction of frame twist)

[Sparky]

oddly, chain twist didnt even occur to me. but it seems that with the length of the chain, it could easily handle it. front suspension would be much easier, but i wonder if it would do anything? all your weight seems to be on the rear.

i recently went from a full suspension mtn bike to a hardtail, and was shocked at how often the back tire bounces off the ground and slips during hard pedaling. it would seem this would be compounded with 4 wheels and a rigid frame. i know this thing aint designed for off-roading, but some bumps are inevitable.

[TheKid]

I had a suspension fork on my Meridian, and there was a noticeable difference over a standard fork, despite having a LWB. On a delta trike or quad, Papa is quite correct about the transverse leaf spring.
While it's true that a long chain can handle some twisting, multi gear chains are designed more for side to side misalignment than twisting. Rear deraillers on the other hand, are less forgiving, and chain twist will not only damage them, but in all probability cause unintended gear shifts. When it comes to rear suspension on deltas and quads, the best way is to go all out with a fixed differential and axles similar to front wheel drive cars, and Mac struts for the suspension. But as Papa says, alignment is critical, as well as insuring that the wheels float perfectly vertical.

[Sparky]

right. i'm inclined to believe you guys. i'll weld the rear up as suggested.

i guess i'll just keep the idea in my head then. i can always add a spring to the front if i decide i need it after the build. its never too late to modify a design. :)

[AtomicZombie]

You could hinge the rear frame assembly and use a bike shock or something as simple as a foam hockey puck. It wouldn't be independant suspension, but the chain would be happy as well as the handling characteristics.

Brad

[TheKid]

I was going to hinge the rear of the DW in the same manner, with a shock on either side to prevent twisting. However, I needed a vehicle to use for carrying loads, and the suspension takes up some of the space I could use for larger loads. (Bear in mind, I wanted to keep the overall length as short as possible.) Besides that, the Streetfox has rear suspension, and I didn't think it made that much of a difference to warrant the extra components, or the time, so I just modded the DW into the Hauler. It's working out really well so far. The DW rear is a great design, and by adding a little tubing to raise the seat, mounting and dismounting are super easy because the main boom is very low and easy to step over, and the seat is high enough to comfortably sit and stand for those of us with disabilities. The chain is also nice and low and doesn't get in the way. All in all, The DW and Streetfighter are modable for almost any application.

[Sparky]

after hurting my brain with ideas of 4 link suspensions and independent wheel suspension and A-arms and struts, i decided that i will leave all that stuff for another day. perhaps AFTER i get the thing built. first things first, right?

ive never ridden a recumbent, and the idea of not being able to stand off the seat when encountering a bump scares me. i have visions of a bruised backside.

on a different note, my pillow blocks and rod ends should be in wednesday, and then i can assemble the rear so i can weld the front so i can put together the whole framework. i know theres still alot to do after that, but at least my neighbor kids will be able to see what the heck i'm building. :D

[AtomicZombie]

Hey, that's "roadie" talk there! Seriously, a bare plywood seat on a recumbent is like heaven compared to even the best upright seat! The only pain you will feel is in your quads after racing!

Brad



ive never ridden a recumbent, and the idea of not being able to stand off the seat when encountering a bump scares me. i have visions of a bruised backside.

[TheKid]

Don't worry about it. You won't feel a thing. Your weight is distributed over several square feet on a recumbent seat compared to less than 1 sq. ft. on an upright. Just visualize the difference.