The Chopper Compendium

I got really motivated about building my front end after seeing Krymis's write up on cutting trees.I plan a little variation of the original plans(Garys from the old CBH).I mocked up a set of trees for my leafer & got them set up on the bike.I did them in wood first cause I wanted to see if I like how they come out before I do them in steel.I also picked up some cheap pipe so if my design doesnt look good theres not much time or material wasted.Unfortunatly now I'm on hold till my spokes come in from Buchanans.Once I get the wheel built, I can make up the legs to fit.

looks good so far

Nice one Jeff..

I did a real crude mock up of the design for my legs.The axle will be ahead of the pivot point, so I guess it will act more like a springer than a traditional leafer.For some reason the tube looks really beefy, dont know if its just that theyre black.I really want the front to look thin, kinda spindly but not compromise on srength.I'm thinking dropping down a little on diameter of tube or maybe go with solid.Does anyone know about stength vs. tubing size?How much I'll be giving up with something like 3/4" vs. 1". Or is solid a good choice or not?

black will make it look fatter chrome will make it look slimmer on the same size tube

jeff,

first thanks for mentioning me. choppers are truly my life and teaching guys about building them is the next best thing. as for tubing remember that the harman girder was made of 1!"x.065 wall tubing. they were able to make them that thin because of the girder leg construction. The design of the leg has a lot to do with how thin of tubing you can use. solid will have a lot of benefits like not worrying about the weld stress at the trees and the tubing actually sheering int he HAZ. the big draw back is weight. the front will weight about 2.5X as much as if you used tubing. i can say i would be okay with my bike having a regular girder leg leafer at .75" solid stock but then again i have built springers out of .120 wall tubing.

I think I just might see how 3/4 solid looks.The added weight isnt to much of a concern, the front end from top of tree to rocker is only 2ft.

curt wrote:black will make it look fatter chrome will make it look slimmer on the same size tube

Man..youre not kidding.I pulled out an old Springer I have that uses 1" legs & they do look alot thinner than the black tube.

Keep in mind that 1" tubing of 'X' wall thickness is three times stiffer than 3/4" tubing with the same wall thickness so if you want to go down to 3/4" tubing you'll have to increa the wall thickness significantly. For example to match the stiffness of .120 wall 1" tubing you'd have to use 7/8" solid steel bar. solid 3/4" bar is really very weak having a moment of inertia of only 0.012 which is the same as 3/4" tubing with a .120 wall so just because it's solid doesn't mean it's stronger or stiffer than tubing. I personally would not use anything less than 1" tubing on your particular design since there is no 'girder' effect for the lower portion of the leg so even with 1" tubing you'll still need a wall thickness of around .25".
Of course this assumes that I'm seeing your mockup correctly and that the lower segment of the leg is not triangulated.

Yes, you are seeing it correctly.I actually was thinking of adding a peice on the lower portion if I went down in size.Would this be enough to strengthen the legs if I went with 3/4 solid?

It would be well over twice as strong if you extend the rear leg in one piece to the pivot point and then the front leg could be made in two parts forming an elongated 'S' shape as shown in your picture. I think you'll find that 7/8" material looks far better than 3/4". The old Indian forks were made with 7/8" and look well proportioned for a bike about the size of yours. The old rule of thumb is for the fork tube diameters to match the frame tube diameter or perhaps just slightly smaller. There are 'side-loads' on forks as well as compression loads and you can build a very thin fork that handles the compression loads but will flex like mad when you're cornering or hit a bump 'off-center'.

I also just realized that you used 'pipe' for the mockup. Remember that 1" pipe is way bigger than 1" tubing and even 3/4" pipe is slightly larger than 1" tubing.

yeah you know I didnt even think of that when I threw it up.I also think you were right about 3/4 not being a good choice. I did another mock up useing 1"(Aluminum bar).Went with the girder type leg.I think I may make another set of trees with zero offset, so I can give the rear legs a nice gentle bend.

From the looks of things you could still do curved rear legs if you check your trail figures. From the mockup picture it looks like trail will be close to zero as it now sits and you can easily go out to 5" so make a fullsize drawing on cardboard to finalize the geometry.

My intentions are to run the axle ahead of the pivot( have seen this on 1 or 2 other frontends & prefer the look over the trailing link).Of course, never running a leafer I wouldnt know whether the ride is going to be better or worse in this position.Plugging my numbers in to one of the r&t caculators Im coming up with 3.08" for trail.I will do a full scale drawing before I finalize anything.