Leaf Spring Front Fork

neicull · #1 10-16-2009, 02:25 PM

Just finished a leaf spring front fork setup. It's pretty stiff. Let me know what you think.

Here's a pic.

dmar836 · #2 10-16-2009, 02:56 PM

I like the simple concept.
Is trail predetermined or experimental?
Are the rockers bushed? Just some things to think about.

I would want more than one bolt on the base of the spring. Despite the wheel axle and spring pivot bolt to tie it all together, the spring could still theoretically walk to one side under heavy breaking.

JMO,
Dave
KC

neicull · #3 10-16-2009, 04:05 PM

The simple concept is definitely what I'm going for.
This is pretty experimental, were going to try different spring resistances, right now it's very stiff.
There's a nylon sleeve inside for the through bolt on the spring end. If I can find something better I will consider using it. It's such a small load on the spring that bushings may be over doing it. I'm trying to keep things affordable at the same time.

The single bolt on the base of the spring hasn't seemed to let the spring walk any, but that's a good point. It's using a 1/2 serrated bolt so I'm confident it won't slip. I may come up with a notch mount or weld on a tab that allows for two bolt holes. Good idea. Thanks for the feedback. I want to keep it as simple as possible, ultimately, for the sake of cost and design. I'll do a little more testing. This hasn't been configured for a front break yet.

dmar836 · #4 10-16-2009, 04:40 PM

As far as the spring rate, you could mount the axle outboard as opposed to inside on the rockers. This will give greater leverage using that stiff spring. This can go only so far as stresses on all parts(especially pivot points) are increased using leverage to overcome a spring that is too stiff. Additionally, you likely have decreased your trail significantly. A spring that settles when mounted will effectively increase the head tube angle and further decrease trail. Big bumps do it more.
I would mount it up and take some measurements for trail. Having rockers extending the axle forward will eat into your trail and you might end up with a bike that is unstable(might even roll backward better than forward). Once you measure it, if it is 2" or less, you could consider turning the fork around then mounting it all back up. This will restore some of the trail. To even begin to do it correctly you have to take the simple trail measurement with the head rake and wheel you plan to use. Experimentation is great but the testing begins with knowing the geometry you have created not just that it "works". Build it, then reverse engineer it to fit safe and proven specs - certainly so if you are selling something.
About the bushings, I meant how are the rockers at the bottom bushed? Without bushings, they will wallow away in no time - especially if you mount the axle outboard to increase the leverage. Either way they must not be just bolt on metal.
Dave

neicull · #5 10-16-2009, 07:05 PM

Thanks for the feedback. I did test ride it, and it worked great. Stiff but it worked nicely. I can do the geometry but ultimately rake and trail is a subjective measurement. I can't afford to engineer a part like Yamaha. I have to use my best judgment. This isn't an unsafe configuration. I have some work left to do with bushings on the rockers. It's still a prototype at this stage. I'll keep you guys posted.

diceman2004 · #6 10-16-2009, 08:43 PM

i like it , i saw a nice custom harley with a front like that , i wanted to make something like that myself , nice job .

Egor · #7 10-16-2009, 09:17 PM

Good job and good thinking. I love all the talent that is out here. You may need to find a lighter metal for your spring but that is cool. I am going to make a springer for that Whizzer, thanks. Have fun, Dave

Kevlarr · #8 10-17-2009, 12:53 AM

You may want to look into a main leaf from a light duty trailer.

**BarelyAWake** · #9 10-17-2009, 06:28 AM

lol if you "engineered it like Yamaha" it'd have about a zillion parts to do the same thing, cost a minimum of $800 and you'd not be allowed to fix it else you'd void yer warranty

dmar836 · #10 10-17-2009, 12:19 PM

However, I have five vintage Yamahas and I have yet to find a design flaw. Gussets are welded correctly, bolt shoulders are the correct length, bushings and spacers are used in the appropriate places, etc. The two cannot be compared. That costs money.
Who can say the same of Chinese products coming into the US? I suspect this is why "all Chinese" cars are not yet here.
But we are on a site where few of the basics are discussed.
JMO
Dave
KC