Chop It & Drop It

originally printed @ beginnerbikes.com , August 2003
copyright owned by author


Here we shall look at a topic many of us slept through in school: geometry. Specifically front end geometry concerning motorcycles. For those that have been at the forum for a while, you may have read some of my mumbo jumbo concerning frame geometry and using wierd terms like "rake" and "trail". For those just joining us, and for those of you that have been mulling over motorcycle specifications in magazines or websites and/or simply just wondering what the heck those two terms mean, this article will deal with the subject of rake and trail, and what it means in the real world for your decision on your next motorcycle modification or purchase. So strap on that DOT approved thinking cap and let's get right to the heart of the matter.


Illustration 1: Note the three color coded measurements, yellow for rake, red for trail, blue for offset

First off we'll look at rake. Rake (also known as Castor Angle) is the angle of the steering head --- and consequently the forks as well as on most bikes they are parallel, in relation to a perpendicular line going from the ground through the steering head. See the yellow lines in Illustration 1. A steeper angle yields a shorter wheelbase, a larger angle yields the chopper-esque longer wheelbase. Of course the frame/swingarm design also has a lot to do with the wheelbase, but the angle of the front end will ultimately seal the final figure. Wheelbase will ultimately determine how much lean a motorcycle requires to handle a turn at a given speed. Take two different bikes regardless of weight and power into the same curve at the same speed, the one with the longer wheelbase will have to lean at a greater angle than the shorter wheelbased model in the curve. This means a 250 Rebel with its diminuative 57.1" wheelbase will be able to take "Deadman's Curve" at a speed of 45mph with a 25º lean, a Vulcan Mean Streak with it's massive 67.1" wheelbase would take the same curve at the same speed butwith a sharper lean of 30º (these figures are simply for reference concerning this imaginary situation) This means that the faster both bikes go, the Vulcan will be dragging parts sooner than the Rebel as it will be leaning more to maintain the same speed as the Rebel in the same curves (further proof of the falacy concerning "outgrowing a beginner bike"). This is why sport bikes have shorter wheelbases by design than cruisers, it enables them to take curves at higher speeds.

Next up is trail. Trail is a somewhat confusing concept. The measurement itself is taken by drawing an imaginary line through the steering axis to the ground (angled yellow line in Illustration 1). Next drop a perpendicular line from the front axle to the ground, which in any production motorcycle should fall some distance behind the point where the steering axis line touches down. The distance between these two points is your trail dimension (see the red portion of Illustration 1). Trail ultimately defines the handling characteristics of a motorcycle, how stable it will be at higher speeds, how easy it will flick through S-curves, and how easy it will be to control at sub idle parking lot maneuvers. Bikes with a short trail will be real easy to handle at slow speeds and quite responsive when the road gets occupied with esses, but at higher speeds these bikes will respond more to the road conditions and feel a bit twitchy. On the other side of the coin, bikes with longer trail dimensions may handle like a wheel barrow in the parking lot, require a bit more encouragement to tackle an S curve, but track straight and true like an arrow at freeway speeds, offering little response to the road until the handlebars are activated by the rider. The trick for the motorcycle designer is to find some happy medium for the bike he/she is designing, something that will match the role the bike is intended for.

Do rake and trail go hand in hand with each other? Typically bikes with greater rakes have longer trail dimensions. However, the design of the triple trees is what eventually defines the trail dimension. Offset is measured by drawing an imaginary line from the center of one fork tube to the other, then dropping a perpendicular line from the center of that line to the center of the steering stem. The distance of this perpendicular line is the triple tree offset. What this does is position the front axle to a point where the trail can be made to a suitable position. This means that the closer the forks are to the steering stem the longer the trail can be modified, as the axle is being positioned further back from the steering axis to ground contact point. The farther apart the forks are from the steering stem the shorter the trail.

Now then, with all this in mind let's look at two different motorcycles that are compatible in terms of size and weight, Kawasaki's EN500 Vulcan and Honda's 600cc Shadow VLX. The Vulcan tips the scales at 439 pounds (dry weight), has a 62.7" wheelbase, and sports a 33º rake and 5.9" trail dimension. The Shadow weighs in at 439 pounds dry (or 445 with the chrome Deluxe package), stretches out to 63.2" in wheelbase, and has a 35º rake/6.5" trail dimension.

Without riding either one, we can presume the following handling characteristics based on what we now know about rake and trail: The Vulcan should be able to negotiate slow speed maneuvers with a bit more ease compared to the VLX thanks to a shorter trail, and at the same time it should be able to handle curves and corners slightly faster than the VLX as it won't lean over as far at any given speed due to its half inch shorter wheelbase. The Vulcan also shouldn't require as much force to negotiate an S-curve. On the freeway leading out of town, take both bikes up to the posted 75mph speed limit and the VLX will handle better as its longer trail dimension offers better stability at higher speeds than the Vulcan. I've ridden both machines and can attest that these theories are in fact true.

As you can see, a motorcycle's handling characteristics are yet one more design that is of a give and take nature. Just like a larger more powerful engine consumes more fuel over a less-peppy smaller engine that conserves fuel, so it is with rake and trail. You just can't have it all.

One trick that is being performed these days is the use of raked triple trees. Some manufacturers are beginning to utilize this design from the early days of choppers to make their bikes easier to handle. Harley Davidson is one example, their new liquid cooled V-Rod sports a most generous 38º rake (the largest OEM rake available currently). Harley was shooting for the dragster look in the V-Rod style wise, and if you've seen pro dragster motorcycles they have some serious rake (and trail) in order to maintain stability at the higher speeds. However, with that greater rake comes a longer wheelbase and a higher trail dimension (depending on the triple tree offset), and Harley wanted this bike to be a decent handler as well as a rocket. The engineers at Harley opted for the raked triple trees. A raked triple tree is designed such that the lower tree sticks out slightly more than the upper tree, thereby creating a greater rake on the forks in relation to the steering head. Harley used a +3º triple tree on the V-Rod, added to their 35º raked frame to get the new 38 degrees of rake. Like a longer offset measurement, the raked triple tree positions the front axle closer to the steering axis to ground contact point, all the while retaining that cool drag/chopper-esque extra rake. In the end, the sub-big bike sized 1130cc V-Rod has a trail dimension that measures a crisp 3.9 inches, very close to most sport bike measurements. Coupled with as much if not more horsepower than the Japanese big bore V2 powered musclebikes that sport 4.5" to 6" trails, and less weight, the V-Rod simply mops the floor with them all around. As Jedi Master Yoda said in the Empire Strikes Back, "Size matters not."


Illustration 2: Note the shorter trail dimension on this diagram (same scale as Illustration 1) with raked trees

Okay I know what may be going through your mind right now. I have a cool cruiser and I want to make it into a cool chopper. So I'll just rush right out and grab up a pair of raked triple trees for it, not only will it give me some of that cool looking extra wheelbase it will also help my handling. Wrong. It just isn't that simple. For starters you need to know what your base rake and trail dimensions are before even contemplating a chopper. Just because something looks good in a magazine doesn't automatically mean that it will work on your particular bike. Those killer showbikes seen in Street Chopper and other magazines have been carefully researched long before the first wrench was turned during assembly. Because if you end up with too short of a trail dimension, you get what is known in the chopper world as a "bar slapper." Meaning as you get going faster and faster, the front wheel becomes more unstable until the point where the handlebars start slapping the tank. Chopper builders add raked trees to their raked frames to shorten the trail. Add raked trees to a stock frame and you guessed it, the trail gets shortened. Chopper builders do it and get away with it because a raked frame already yields a longer trail, making it shorter benefits them. Make a shorter trail even more short and it can cause more harm than good. There is a very fine line amongst frame position, frame rake, triple trees, and fork length that defines how a chopper will handle. If you don't do the research and just start throwing things together from aftermarket catalogs, you could end up with a Franken-bike sporting an unholy handling pact that can bite back.

So with all this in mind, next time you're browsing the spec pages of a given motorcycle and you come across the rake and trail info, you'll begin to get a better idea how said bike will handle without even riding it. And when you do ride it you'll have a better idea of what to expect. Once again to summarize it all: bikes with longer rake and trail dimensions can be expected to be quite stable on the freeway but will feel more sluggish in curves and slow speeds, those with shorter rake and trail will be easier to control at slow speeds and in the curves but will feel more twitchy on the freeway.

That wraps up this portion, and unlike other geometry classes there will be no quiz on this material aside from your experiences and discoveries during the upcoming ride. Keep your knees in the breeze.


When Shadow Shack isn't drawing imaginary lines through his motorcycles, he answers email at an addy that can be found in his forum profile

reprinted from BB.com , May 2004
copyright owned by author

Welcome to the next chapter of Customarily Minded, where the motto here is "Stock bikes can be cool, but it's the customs that make me drool." This month's topic will deal with a personal favorite topic of mine, one that I've applied to several of my bikes. Every now and then I'll get an email on this topic, asking for some information concerning it. If you haven't seen my bikes yet, and you skipped past the title, that topic is none other than the infamous chopper mod. So let's fasten the chin strap of that chrome raked out helmet and cut right into the art of chopping a motorcycle.


Rudeboy's bone stock 94 Shadow VLX
Let's see what all we can do with one...

There are many methods available to achieve a desirable result, and I will touch on seven of them here along with a pre-chopper history lesson (and don't sweat it, there won't be a test). Please note that these methods will work on any bike, foreign or domestic. Aftermarket parts sources listed are for metric applications, if you have to ask me to explain where to find aftermarket HD accessories, you probably wouldn't understand...pun intended, there's more aftermarket support for Harleys than a dozen people can shake a stick at but the metric market is a bit more limited, hence the resources.

Bobbing
Preceding the chopper era was the reign of the fabulous Bobbers. After the second World War riders were doing what they could to improve the speed of their bikes, and once all the performance mods were exhausted and explored the only venue left was lightening the load. OEM parts were shelved faster than the bikes could whick through the quarter mile, and some items were simply shortened such as the handlebars and fenders. This art of fender shortening became known as bobbing, hence the term "bobber" to describe the bike and "bobbed fender" that describes any short fender. The basic ideal for bobbing a bike is "less is more". That said, things are generally kept simple and clean with few visual complications. Rear ends are often removed (or cut when neccesary), pillion seats are practically a taboo but not unheard of. Flat fenders (or their less expensive counterparts: trailer fenders) often replace OEM units if they aren't cut back, typically mounted to the swingarm rather than the frame as stock fenders were. Front fenders are either shortened or simply removed, and the nubs on the fork lowers can be shaved down and smoothed in the event of fender removal. Drag bars or ape hangers are up to the owner, the bobbers of yesteryear typically sported a narrow bar of some sort but there's no set in stone rule here beyond clean and simple. To that end the true sense of bobbing mandated less weight, so the drag bar tends to be more popular. Black is the most popular color amongst the bobber clan, probably because it's faster. Other colors are optional but typically a single color base with little more than a bit of pinstriping or such detailing is the norm. And with that history lesson and method out of the way, we can leap into the next step in the evolution of choppers, where frames were cut and redesigned to spec...this cutting quickly became known as "chopping".


The Bronx Bomber took a rear-ended 88 VLX and lopped off the damaged portion of the frame to create this fantastic bobber

Chopper Method One: Inch Per Inch Formula

First up is the cheap and easy way, and it doesn't alter the frame so any factory warranties/current retail values on the bike are unaffected. It won't get you the Easyriders "Captain America" look, but for fans of his noble companion "Billy" this will take you far. This first method is one I like to call "the inch per inch formula". What this entails is lowering the rear end while raising the front and nothing more. For every inch you can lower the rear, you can add one inch of fork length up front.

Depending on the design of your bike's swingarm and suspension (and how much of that suspension you wish to retain), you can typically go anywhere from 3 to 6 inches lower in back. Lowering the rear typically involves acquiring a lowering kit (available in the aftermarket for most mid sized and larger cruisers), modifying (shortening) the OEM shock(s), aftermarket shocks, or swapping out the shock(s) for some fabricated solid rear struts. The solid strut can be easily made after the suspension is removed, simply acquire some steel (square tubing for mono-shock bikes, flatter stock for dual shock rear ends), position the swingarm where you want it in relation to the frame, measure your mounting points, and drill holes in said metal and voila: instant hardtail. If you really want to get fancy, remove the shock bushings and drill your holes big enough to accept them as this will help absorb some of the vibes. Granted that rubber bushing will be your only dampning available...but one popular approach to the hardtail mod is to let some air out of the rear tire, some go as low as 15-18psi but I like 20-25 myself. The partially deflated tire acts as a shock absorber, making the ride a little more boingier. That's a technical term, look it up if you don't believe me. One final hardtail method is removing the swingarm and suspension and designing your own rigid rear end, welding it to the OEM frame.

And one word of caution on rigid/hardtail rides, forget what you know about proficient cornering. Curves and corners will need to be taken slowly, as any bumps in the road can send your rear skipping and skating along causing a loss of traction. If you habitually try to beat every yellow light in right turns, this isn't the mod for you. Bumps and potholes can send your tail skywards too, and rough roads can rattle your fillings loose. All in all this is a barhopper's mod, but if you're willing to sacrafice good handling in the name of style, nothing looks cooler than a slammed rear end and a fat tire stuffed up into the fender. Rear lowering kits can be had from numerous manufacturers including Highway Hawk, Scootworks, and Cobra. One good source for modifying OEM shocks is Sons of Thunder Metric Cycles, and SOTMC along with Scootworks carry hardtail struts for some models.

Now that we have the rear end covered on the inch per inch formula, it's time to tackle the front. To add fork length you can order fork extensions for some bikes. Fork extensions are simply top caps with a little extra length to them, they replace the top cap with a 2 to 6 inch long piece of sealed matching fork tube. But for maximum integrity, actual longer fork tubes is your best bet. Forking by Frank has been supplying longer OEM fork tube replacements since the dawn of the chopper age way back when, and you can order any length of fork tube (up to 10" over stock length) for just about any motorcycle in production or not. And one final option to raising the front is going up to a larger front wheel, if you graduate from a 19" rim to a 21 incher this can add another inch to the equation, and few things look better on a chopper than a 21 inch front wheel.

One final word on the inch per inch method, by making these modifications you will be tilting your frame rearwards so your frame rake increases the more extreme you go, thereby increasing trail. Slow speed handling will suffer but freeway rides will be straight and true, your center of gravity is also moved further rearward. As an added bonus straight line stops will be more controlled since the front end won't dive as hard.


Kaholo went for the full tilt 4" hardtail slam out back and added 4" fork extensions to his 600 Shadow, with the turn signals covering the seam

Chopper Method Two: Raked Trees

The next method to chopping up a perfectly good bike without altering the frame is by swapping out the OEM triple trees with a set of raked trees. In addition to looking great, raked trees add a few extra degrees of slant to the forks. The downside to this is trail reduction, and if you don't have much trail to begin with raked trees can make a bike very dangerous. Raked trees are typically available in a +3 to +7 degree range, although I've seen some that add as much as 12º of rake. Raked trees by themselves will place the bike into a leaned forward stance, and if you read that Lowering editorial you know that this unbalances the bike in the wrong way. Hence, depending on what the original rake was before the raked trees were added, and how much extra rake the trees provide,you are going to have to make an "inch per inch" modification to the bike in the form of either lowering the rear or raising the front, one to three inches on either end being the typical mod here. Please do the research before slapping a set of raked trees onto your bike, there are several online rake/trail calcualtors. I like the ones at RB Racing and Perse Performance.


On my 92 VLX I went with +6º trees, 4" over forks, and a modified rear shock


Chopper Method Three: Frame Modification

Next up on the chopping block is modifying the frame. Please check with your dealership about warranty and retail price values before tackling this mod, as it can serve to void or affect both. This mod will also affect your insurance premiums...remember when you were getting your quote they asked if any modifications were done to the motor or frame? There ya go. Anyways, this is the old school way of making a chopper (and consequently this is how the name "chopper" came to be)and is still in use today. Kennedy's Choppers shows one painless method of adding some rake, but most folks like to extend the downtubes and backbone of a frame when attempting frame mods. What this incurs is cutting the frame tubes, stretching them apart, and inserting a sleeve in between that is welded and reinforced. This sleeve is usually comprised of a similar diameter tube section with smaller tubes welded inside, these smaller portions are then inserted into the frame. But some welders prefer to reinfoce these extended frame tubes externally, by welding a smaller length of support material along the entire length of the modified frame tube. The end result is the steering head is now positioned in a new angle, thereby increasing rake (and trail). This is where the aforementioned raked trees really work, since the modified frame already boasts a high trail figure the raked trees serve to bring this dimension back down into a more user freindly neighborhood. And they also give a little more slope to the already slanted forks. Triple tree design becomes a very important factor with a modified frame.


Steve went hardtail and stretched the frame downtubes a few inches on his 88 VT600 Shadow

Chopper Method Four: Mix And Match

Now that the three major methods have been covered, the fourth option is to mix and match those processes, which is inevitable...The most extreme choppers out there do just that, the frames are modified for more rake, raked trees are added for both more forking fun as well as making the bike more manageable, and the rear is often nice and squatty to boot, and bobbing can become part of the equation as well. Obviously this isn't an approach that you do in steps, unless you have a thick wallet to continually replace parts along the way each time you make a change. Nay, a lot of planning and research goes into each of the previously mentioned methods, so it stands to reason that by combining them that said research increases exponentially. So plan accordingly.

For example, by using the inch per inch formula, you can lower the rear two inches and add two inches of fork length up front. By adding raked trees to the inch per inch formula, you can stick with the 2" over forks and have the front return to a lower position for the "ground pounder" look or go with 4" over forks to retain the inch per inch stance and more rake/wheelbase. Modifying the frame inevitably demands raked trees to retain a decent trail dimension, and longer forks is also mandated.


Big Mike didn't leave many OEM parts untampered on his 2002 VLX

Chopper Method Five: Chopper Conversion Kit

Approach number five is a new one that hit the market recently, a chopper conversion kit. These kits serve to give that combination style with zero mods to the frame, and is actually reversible if for some strange reason you would ever wish to revert back to a stock ride. These conversion kits include a meticulously designed set of triple trees that artificially recreates a new steering axis as well as a new rake, along with a set of longer fork tubes. All is made to spec for each particular model so the end result is that radical raked and stretched out chopper look and feel. These kits are well designed with safety and quality in mind and they sport superior craftsmanship. That means they aren't cheap, but you could easily sink the same amount of cash into the combination approach yet all the mathmatics are figured out for you, and it doesn't take as long to get it all together and go for that first ride. Check out Seeger Cycle Accessories for info on such kits, they have them available for both Harleys and Metrics.


Dragula went with the Seeger kit and 8" over forks along with a ton of chrome on his 89 VLX

Chopper Method Six: "Ground-Up" Custom Build

Method number six is an educational experience and will cost a pretty penny too. This is the ground-up custom build route, where you go to the aftermarket catalogs for everything. Frames, swingarms, front ends, wheels, tanks and fenders, engines, you name it it's out there waiting for you to slap it all together to your desires. But this direction requires as much research as it does funding and construction time, as you don't want the wrong combination of parts. Just because this set of trees looked good in that magazine and that frame looked good in another magazime doesn't mean it will work together on your creation. And the final result is a real chore to register, so keep any and all reciepts/bills of sale. If you can score someone's half-built project that they gave up on you can jump in where he left off and save a bundle of time and money. A slightly different route would be the kit bikes, or "bike in a box". Check out the various HR3 kit bikes in the Custom Chrome catalog, you can get a complete kit that works right and looks good starting at $13,000 and up, and oftentimes that's less than the asking price of a used stock Hog. Getting a title on a kit bike is easier than a custom build, but not as quick and painless as it would be with a factory production model.


VLXer KGOR shelled out a lot of 20's to complete this ride


Chopper Method Seven: "Just Go Out and Buy One"

And of course the last way to get a chopper is to buy one that is already built. There are numerous factory designed/constructed bikes out there, with names like American Ironhorse, Bourget, Big Dog, OCC, and West Coast Choppers to name a few. Since these are factory built designs, they come with a VIN and it's no different than buying a Harley or Honda when it comes to registration time. Or you could even pick up someone else's ground-up custom build and finish it yourself, assuming the builder already registered it then it comes with a title. Or perhaps you could pick up someone's unfinished project and pick up where he left off with method six...but in either case you're also trusting his design and construction abilities too, unlike the factory jobs that are professionally done you stand a chance at acquiring someone's haphazardly thrown together "frankenbike".


Jesse James' "El Diablo" serial#002 as seen at Southern Nevada HD, asking price: $70K

In closing there are a few things I'd like to point out about the chopper mod. Do the research before buying your first part(s). Lots of it. Especially concerning rake and trail. Make sure you have everything you'll need for the transformation before turning that first wrench, after all you don't want to have the major stuff done and then find out you need a longer brake and speedo line. This means you'll be forced to drool all over an unrideable bike while those parts are awaiting delivery somewhere in Podunkville. Having a second bike to ride is always beneficial, I have no qualms about the "one to ride and one for show" principle. Also of noteworthy mention, aftermarket parts designed to spec doesn't neccessarily translate into quick and easy bolt-on simplicity. Expect to run into snags along the way, one company I went with (Rizoma) was so far off in every respect with my Shadow I think I would have had an easier time adapting Harley parts. Aftermarket parts compatibility isn't the only issue to contend with, in some cases your kickstand ends up being too long or too short and the bike will be parked in a near upright or waaaaay leaned over stance, so be prepared to modifiy or exchange that too. If you can, purchase the most expensive parts first as they won't get any cheaper in the next year or two thanks to inflation. Finally, while this kind of modification can be easily performed on a beginner bike, it is not a beginner mod. A chopper is to the new cruiser rider as a 600+cc supersport is to the new sport rider. They handle much differently. They brake much differently. They corner much differently. In other words, get some good saddle time in on your first bike before considering a chopper. Besides, with a long wheelbase you'll never pass the DMV riding portion of the license test when it comes time for the slalom through the cones. And leave early for work, because while the front wheel may be on time you'll be five minutes late.

Keep those raked knees in the breeze.


When Shadow Shack isn't filming the latest episode of Japanese Chopper, he can be reached on the forum or via his profile

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Head out on the highway
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And whatever comes our way "

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Fire all of the guns at once and
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