The Chopper Compendium

gww25 wrote:Here's a little sketch of two bikes having 45-degree rakes showing some the relationship between regular and dropped style rockers.

there looks like there needs to be a rule about the 90* intersection and then an addendum for a rocker set at horizontal 0

With respect to the question of 'negative trail' being okay most of us don't think this is so but there are hundreds of bikes out there running with some rather large amounts of negative trail, mostly girders, but also some springers, and they handle just fine so real world experience tends to also show that trail is not as important to the overall question of steering and handling as generally thought. I personally think negative trail is potentially dangerous but that's just an opinion. The NHTSA found during their studies of modified bikes that positive trail in the range of 2 to 14-inches on bikes raked a maximum of 45-degrees is considered 'safe' but I've never been able to find the raw data for their study. Some extremly high performance road racing bikes are running zero and slightly negative trail but on a smooth track bike handling can't be compared to average road conditions.

Thanx. This makes good pop-corn for thought.

rudog wrote: If, however, you make the statement that minimising trail will make a bike handle better, it still alows for a dropped axle.

I think you mean dropped rocker???????

In the illustration, the axle is the same height in both set ups.

I didn't mean to imply that minimizing trail improves bike handling. It only reduces flop, both at low and high speeds. In reality wheel flop and trail are so closely internected that a lot of designers don't even consider trail and concentrate instead on controlling flop. I have a personal feeling that this was how Sugar Bear came up with his particular rocker patterns and the trail just ended up at whatever it happended to be. I'm from the other school of thought and pretty much ignore flop and worry about trail. Everybody has their own ways of looking at these issues which is why Choppers can be so similar yet so different at the same time.

Thanx for catching that Bob. I was listening to a guy on the radio who had a semi front axle drop on him...yeh!! That was it!!

Gary, the next time your in the Dallas area, I'm buyin' the 1st round. Last time you came thru I had a job. I wish I could have made it.

I'll drop you a line the next time I'm headed that way which might be next month.

you just need to keep heading east to pa and i pick you up at the airport.

What diameter are the SB legs and does he increase the size with longer forks? Also I've read his are solid bar not tubing.

Maxthegardener wrote:

max that video is very informative in the welding jig to keep spacing and the segment on the wheel flop shows exactly what a lot of this thread is all about. watch real close.

joe SB does not change the diameter of the legs. he uses 1.25 solid steel. the fronts are .625 diameter.

I have a question about the sketch.In the pic on right the reference line for point pr runs from the axle through rocker mount of rear leg to reference line for the neck... That makes sence...now the left pic I dont understand why the line from axle to point pr doesnt run through the rear leg as well?

Really good thread this.

I've noticed quite a few trikes over here in the UK running large amounts of negative trail and having spoken to the owners they "Say" they have had no issues with it. Upon talking to them further they usually did not know what trail was or how to measure it?

I'm a fan of the long front end on trikes and build girders for that purpose. Allows me to play with the trail to keep it at around 2-3 ".

Makes the Trike easy to steer even at high speed and low speed and girders have the stiffness to deal with the lateral forces when cornering.

I might have a go a some springers next! Think I'll use seamless tube though.

On the sketch, does the point labeled "PR" stand for "point of rotation"?

I beleive it to be yes...The axis of steering for the wheel.Which is how I would think the dropped rockers cancell flop by keeping the weight of the frontend further from the center of the axis.