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Motorcycle Frame Misalignment

Ways You can Check it Yourself
 
 
 
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Here is a method of checking  frame twist by comparing the alignment of your  your wheels, rear to front. . 

 

Steps:

Important....Make sure that 

    1.  The motorcycle wheels are straight and true.

    2.  You use a tape measure from the Swing arm Pivot bolt to rear axel. This will insure the rear wheel is perpendicular to the swing arm pivot.

            (You can not always trust the Manufactures marks for the rear axel position)

    3.  The forks and triple clamp system is straight and true.

    4. There is proper per load on steering head bearings

Place the motorcycle on flat level ground on it's center stand if it has one. If it doesn't, then use a  swing arm pit stand or I've also used 2 automotive safety stands under the foot peg holder.  Be mindful not to use it on a folding foot peg.

 Place transmission in  gear to prevent rear wheel from spinning.

Next, attach one end of the line to a heavy tool like a 2.5 lb hand sledge hammer, or one gallon plastic milk jugs filled with water works well . Now, measure off about 12 ft. or so of line and cut it. Place one heavy object with one end of the line attached to it on the ground a few feet ahead of the front wheel and slightly off to the side. Run the other end of the string along side the motorcycle then around the rear tire. Be careful, the string line should not contact anything other than the rear tire. If it is fouled by the center stand or work stand, then your straight edge is no longer straight. If you are careful in selecting the line's path and use the supplied pictures as examples, you should be able to run the line between the swing arm spring  and the swing arm and not have any fouling to alter the "extended straight edge".


Use a piece of duct tape to secure the string to the rear tire and run the remainder of the string up along the other side of the motorcycle and past the front wheel. Attach another heavy weight to the free end
 

 

 

 

 

 

 

 

 

 


Now, remove any slack the lines have in them on both sides. Go back to the rear wheel and take a look at the string at the widest point of the front portion of the rear tire. Move the strings in front of the bike on both sides until the string is barely touching the rear tire where it passes the front widest portion of the rear tire. What you are doing is creating a "straight edge" and placing it along both sides of the rear tire and extending that line past the front wheel. When you have all of this set up, then the front wheel should be perfectly centered between the two strings passing the front wheel. If if isn't centered, then carefully lift or slide the front wheel to center it between those two strings. With the front wheel centered and pointing straight ahead so the distance is the same on both sides of the front widest portion of the front tire and the rear widest portion of the front tire then go back to the rear wheel and see where the strings touch the rear tire.

  

The distance should be the same on both sides of the front tire at 4 separate points. Right and left front widest portion and right and left rear of front tire widest portion.

 



When the front wheel is centered between the two string lines, the string should be barely touching the widest portion of the front section of the rear tire on both sides of the motorcycle. If it is not, then use the procedure to adjust chain slack or tension. It's quite possible that when you loosen the axle and axle adjustment nuts and bolts, you will disturb the string lines and may have to reset them up. Do not over tighten the chain. Remember, the axle adjuster bolt pushes the axle back on the side it is on. As an example, if there is a gap between the string and tire on the chain side, you will most likely have to move to the other side (brake side) adjuster and loosen it so the axle can be pushed forward on the side opposite of the chain and where the gap exists.

When you are confident you have the chain slack and alignment properly adjusted, recheck all points of your string line prior to and after tightening all nuts and bolts.

When you have aligned the wheels in this method, you should not have to do it again until the rear tire is changed. In addition, when adjusting the chain tension you should only need to loosen the axle nut enough to allow minimal movement. Then turn each axle adjuster bolt the same amount. I use one "flat" or 1/6th of a turn each side. Rarely do I need to turn it more than two flats when I adjust chain slack and this is about every 2000-3000 miles or once, maybe twice between tire changes.

Hopefully, this has been helpful.

Steering Head Rake Angle

You can Check it Yourself
 
 
 
 
Coming soon

F.Y.I.

WHEELBASE:
The distance between the centers of rotation for the front and rear wheels - that is, the distance between the front and rear axle. Typical numbers are 55 to 58 inches for mid-size and larger street sporting motorcycles, 52 to 54 inches for 250 or 500cc Grand Prix bikes and just under 50 inches for 125cc GP bikes. Choppers, as well as the infamous Bohemia motorcycle (a Czech-made, 3-seated behemoth) can easily double these numbers!

 

WHEEL ALIGNMENT:
(1): In the most basic form it means that the front and rear wheel are in-line. That is, they point in the same direction and are not offset from each other. (2): A more constraining definition of the term also requires that both wheels are in the same plane. That is, one wheel is not vertically tilted with respect to the other. On a motorcycle that is not properly set up or has a bent frame, forks or swing arm (1) can be true without (2) being the case. This is illustrated in figure 1.

 

RAKE, Castor Angle, Head Angle
The angle of inclination with respect to the vertical of the axis of rotation about which the front wheel is turned during the steering process. This is usually the angle with respect to the vertical of the steering head of the frame, but not always. For example, if eccentric bearing cups are used in the steering head to alter the angle between the steering head and the steering stem of the triple clamps, than the rake is the inclination with respect to the vertical of the steering stem. The definition of the rake via the axis of rotation is always true and even applies to non-conventional designs. Typical numbers range from about 20 to a little over 30 degrees, the former for GP-racers and dirt bikes, the latter for cruisers and most vintage bikes. Note however that a relatively well-handling motorcycles have been built (most notably by Toni Foale, a 1970s chassis specialist) with much steeper steering head angles (i.e. a much smaller rake angle).

 

TRAIL:
The distance, as measured along the ground, of the point at which the front tire contacts the ground and the axis of rotation (see above) would contact the ground. For a conventional design this means visualizing the continuation of an imaginary line through the center of - and parallel to - the steering head tube that extends to contact the ground a few inches in front of the bike. Then, simply measure the distance between this contact point and the center-point of the tire's contact patch (vertically straight down from the front axle). Note that in an accurate measurements of trail, the wheels need to be aligned as defined above (see figure 2 below).

 

OFFSET:
The perpendicular distance between a line drawn through the centers of the fork tubes and the steering stem center of a triple clamp. The trail is a linear function of the offset of the triple clamps: More offset will yield less trail and vice versa. However, zero offset will not yield zero trail. In that case the trail is a function of the rake and the diameter of the front tire only. The geometry is shown in figure 2.
 
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