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.

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.

Additional Variables

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.

 Definitions:

Your front suspension geometry is defined by the following six variables which are defined as:

    • Offset-- Centerline of top of steering neck to centerline of top of fork tubes.
    • Rake-- The angle in degrees of the steering neck from the vertical.
    • Fork Length-- The distance between the top of the fork tubes to the centerline of the axle.
    • Diameter of the front tire.
    • Trail: Distance defined by vertical line from axle to ground and intersect of centerline of steering neck and ground.
    • Raked Triple Trees-- In order to bring trail figures back into line, triple trees with raked steering stems can be used. Expressed in degrees. Usually adjustable in 3, 5, and 7 degrees of rake.
    • Calculations Tire Diameter:
      • Tire Diameter Formula: If you do not know a certain tire diameter use the following formula:
      • Diam Inches = Rim Diam Inches + [ (2 x Aspect Ratio x Section Width) / 25.4]
      • Example: 200/55R18 Tire:
      • 26.7" = 18 + [(2 x 0.55 x 200)/25.4]

Advanced Trail Calculator

Front Tire inches Diameter of front tire. 21" front typically 27.60". 19" front typically 26.10". 16" front typically 25.30". Hayabusa front 120/70x17 23.61".
Rake degrees Steering Neck Rake: Softail 31 to33 deg. FXRS models 29 deg. FXLR 31 deg. Evo Dyna FXD/DX/DXT 28 deg. Evo Dyna FXDL/DWG 32 deg. Evo FLH 26 deg. Sportster 29.6 deg. Choppers 36 deg to 45 deg. FLH series 26 deg. V-Rod 34 deg. Early Hayabusa 24.1 deg.
Triple Clamp Offset inches Distance from center of top of steering neck to centerline of top of fork tubes. Typically in the range of 2.4". V-Rod 2.0". FLH series have a negative offset ( Enter -2.455")
Fork Length inches Length from to top of the fork tubes to the centerline of the axle. Harley forks are in the 30", 32", 34" or longer range. Length will not change trail if the triple trees are not raked. FLH Series 27.75". V-Rod 30". Hayabusa forks are 28.5".
Triple Tree Rake degrees For standard triple trees enter 0 degrees: The FXDWG uses 3 degree trees; V-Rod uses 4 degree trees; FLH series use 5 degree trees. For chassis that have been raked to 40 degrees or more, and too much trail is present, Raked Triple Trees are necessary. Enter the degrees of rake, typically 3, 5, or 7 degrees.
Note: Trail cannot be a negative number as this will adversely affect handling unless you are building a shopping cart. Typical trail figures are between 4 and 6 inches. Various Harley models have the following trail figures: FXR 4.22". Softail 5.0" to 5.8". Dyna Models 4.1" to 5.1". Sportster 4.6". FLH models 6.2". V-Rod 3.87". Early Hayabusa 3.8".
Trail in Inches