The Chopper Compendium

I have changed the way i build frontends drastically. I have started using a base trail # of 2" and adding the result of the wheel equation to it to get my adjusted trail #. for my 250 rear 90/90 front i get a 1.778" adjustment that needs added to the 2". So I have an adjusted trail of 3.778" to build with for girders and hydraulic frontends. For anything with a rocker system I get close to a zero trail number and apply 90* rule or horizontal rule. I build the spring leg hole at half the angle of rake from a horizontal zero...i.e. if my rake is 37* i will move off horizontal 18.5* to place my rocker hole for the spring leg. last pic attached is of the cad drawing for my rockerC springer.

measuring for custom made rockers

it starts out with a 90/90/19 avon tire and 19" rim


I set my rocker up with a .125" trail
I set mine up with 1" offset trees so there is automatically a 1" line paralleled to the steering axis


located the rigid leg mounting hole using the 90* rule


locating the sprung leg hole by intersection of arc and 1/2 the rake angle


my rocker design is subtle compared to sugar bear's, however it is geared towards a more aggressive ride. Sugar bear rockers look good but lack the ground clearance to lean into a road in my area as they turn on an incline and i may scrape the rocker bottom, negating the need for steering and wishing for a surfboard.

this helps greatly thanks

here is an example of the same bike with .125" trail and 2" trail

A big thanks for posting all this.

It's hard to imagine the depth of rocker design until you read this.

NP remember this only works with suspension systems that have a rocker at the axle. girders, and hydraulic forks need trail to operate properly.

When sugarbear uses the #1 rocker with a 30* rake and an avon 90/90/21 his trail is 0.630" and has a wheel flop factor of about 0.125". The #1 rocker has to have the axle hole and the rigid leg hole on horizontal zero and the sprung leg hole should be 8* above horizontal zero.

Attached is the wheel flop chart in excel. Wheel flop is seen as a drop in the neck when the wheel is turned from side to side. I figure a 40* rotation of the handlebars per side. The formula if you wanted to figure out your own flop factor is Flop=(((trail)*(sine of rake)*(cosine of rake))/90)*40 . So sugarbear's wheel flop for a trail of 0.630 and rake of 30* would be 0.1212. Less than an 1/8" of movement at the neck when turning the bars from side to side.

you really make me see how much I suck at math .

awesome information you've posted up, Krymis. it is MUCH appreciated!

-dan

dan i just have to give back to the guys that helped me get the knowledge to build this stuff. that and its kinda nice to post something i have been working on since old chopperbuilders forum was up and now people appreciate it. Makes the time i traveled away from my family and hours in front of mock ups well worth it. I got in contact with Jaxon on Friday and we talked for an hour. I had not heard from him in maybe 5 years.

This excellent information, thank you for posting it

So been absent for a while...I have been experimenting. I recently bought a west coast choppers CFL. The stock front end was 6 over with 6* trees on a 4up 2 out frame. I retained a 90/90/21 metzler tire with a 2.15" width rim and wide glide hubs, 8" tall risers, 26" wide drag bars. What i experienced was the wider the trees were the better handling feel. I would attribute the perceived feel to is the fact that there must a levered force on the turn of the axle and around neck. The wider the trees/ legs the better it handled. This may seem very small in comparison to other ideas but this really does make a big difference in feel of the steering. So what you now have is the fact that you get a good compromise from a 6" wide rigid leg hole to rigid leg hole and use a wishbone style bend on both sets of legs to get a wide glide width. With this setup you get very little over or understeer. You get very good performance from the 90* rule and the mid glide tree width.

The orientation of the rockers affects the way the front end responds to the sweep of the front wheel and the tree/leg width affect the perceived feel of that response

I have built mine to the chopper handbook plans and only been able to push it around the shop from what I can tell it is one of the best frontends I have ever had cant wait to put some cash together so I can run it at speed . I do thank you for the info it has been a great help

here is a CAD drawing of my new skinny wide springer. It has a full blind top tree, risers mount in the same mount area as the rigid leg tubes. The risers actually help keep the upper tree from moving. One down fall is the choice of bars and where the knurling is placed will have to be custom with the springer. At the end of the day I could not place the legs close enough to get the regular harley riser spacing without sacrificing tube diameter on the rear leg.



the spring perch has a full spring retainer system for top and bottom of all 4 springs, hidden neck mounting, and the spring rod sides through the perch on a delrin spacer rather than a bronze bushing...i took that and many other things from dick allen, sugarbear, century, and gary weishaupt. any questions or suggestions let me know please.
By the way it will have a dog leg bend on both front and rear tubes 6" above the tire to accommodate the mid and wide glide hubs.