Rake & Trail Calculator
Sine, Cosine, Hike!
We know you were day dreaming about sex when the triangles were floating about the blackboard, or for those of you who were already warped, you were doodling motorcycles while the teacher droned on about sines, cosines, tangents. Now all these years later when you finally got the money to build your dream bike by ripping off some other poor fool in the stock market, all you can do is thumb through pictures of other people's projects, searching for that "look", blissfully unaware of what all that trigonometry was for.
We're going to make it easy for you to do the calculations and we're going to present some data for you to study. The decisions are up to you. It might explain why shopping carts weren't meant to go 200mph.
Advanced Rake and Trail Calculator
Extended front ends, raked frames, Easy Rider... Peter Fonda and Dennis Hopper with Jack Nicholson in tow "looking for adventure"...Panheads forever!.. Low speed "floppers"...cruising for 50 miles with no hands on the ape-hangers. Things get complicated in the land of rake and trail. Trying to make these art forms work, people resort to putting a different rake in the triple clamps than is in the steering head in an attempt to bring the trail back into line. We aren't going to make any suggestions in this area as we like to go 200mph, stomp on the brakes and slide through the turns.
Old School Word of Advice
Extended Bagger Big Wheel Mania has spawned an industry of 30" billet wheels and kits to "chop" your frame. We have no idea how you can cut and weld up a frame without a dedicated frame jig. We get calls from people who have installed these "kits" whose bikes have handling issues like weaving at speed. Without a frame jig not only can there be misalignment but there can be twist in the neck. Weldments are under tension and will move when cut. Be aware.
We made road race frames way over 3 decades ago and have been welding for almost four decades. No fixtures is complete insanity.
Here Bryan Stock of Bryan's Customs
is doing an "up and out 6" rake" on his frame jig. Bryan has done these
for 40 plus years and will tell you even factory frames can be off
before he modifies them. He has had customers bring him "bagger neck
kits" and he has wrestled with them calling them true POS.
Old School Up and Out. Not the 30" wheel slammed bagger routine.
Sugar Bear Springers
Sugar Bear builds springers that have different, but effective, rake and trail figures...this was Sugar Bear's daily beater for years. The neck and tree are parallel and the front wheel suspension pivots provide easy wheel movement and no "flopping". This is one of the shorter springers that Sugar Bear makes. You can contact Sugar Bear at (310) 768-4158. You can't run the calc's on these...they end up with zero trail. Sugar bear has a new long bike that he takes his traditional "Sunday ride" on...it's black this time.
Reputable custom builders like Big Dog Motorcycles or any one of a dozen other frame builders are your best source of advice on this subject. Firms like these can supply you with complete motorcycles or frames that have specialized triple clamps and front ends. Harley-Davidson motorcyles can be raked and turned into the most radical choppers. Use this calculator to see what the chassis, rake, forks and triple clamps have to do with your magical "trail" figure.
Pictured is a Big Dog K9 which has 39 degrees of rake, 3 degree raked trees, and 12" over forks. The result is 4.35" of Trail.
A word to the wise: If you want to extend your stock Harley's front end by using a set of raked triple trees...DONT! Raked triple trees are really used where the bike has a raked neck of 40 degrees or more. In these cases the raked trees bring the trail back to a shorter, more manageable, distance. Using raked trees on a stock steering stem will shorten the trail too much and lead to instability as the speed increases. Picture a high speed shopping cart. Consider, instead, a set of raked cups that keep the pivot and the fork tubes parallel to each other but "kick out" the front end....or rake your chassis by cutting your neck and positioning it for longer tubes, chopper style.
In some cases where the builder is going for a raked look and chooses not to cut his steering neck, custom raked triple clamps with less offset can be designed. Combined with longer fork tubes to keep the neck at a reasonable height, less offset in the triple trees will increase the trail to reasonable levels (4 to 6 inches). Less offset will move the fork tubes closer to the gas tank on full lock....so check this in advance.
If you want to enter other things like wheelbase and alternate fork lengths and find out how your rake and trail changes as well as the height of the forks etc. you might want to use our Professional Rake and Trail Calculator.
Your front suspension geometry is defined by the following six variables which are defined as:
Advanced Trail Calculator