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Aging & Worn
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Discussion Starter #1
I never really studied this, (I'll admit it) and I want to learn..........

Would someone please explain to me these two descriptions, as pertains to motorcycle characteristics and impact:

A. Rake
B. Trail

Thanks............

-Soupy
 

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Rake is the severity of the front fork angle from the side relative to 90 degrees from level. Big, crazy custom choppers have a large "rake," like Dennis Hopper's bike in "easy rider." Not sure what trail is, but I'm guessing it has to do with the rear swing arm, and its size/angle
 

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Retired twice: Navy and as a govt contractor
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Rake - the tool you use to clean up your yard in the fall

Trail - The path you take through the woods to Grandmaw's house
 

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Trail is the distance the contact patch of the front tire is located behind the wheel axle. You need both rake and trail in order for the motorcycle to be stable at speed.
 

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Trail is the distance the contact patch of the front tire is located behind the wheel axle. You need both rake and trail in order for the motorcycle to be stable at speed.
I would think the tires contact patch would always be directly under/below the wheel axle? :confused:
 

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On most bicycles the steering axis and the forks point to the same place, on motorcycles they do not, trail is determined by where the steering axis points.

On most motorcycles the forks are parallel to the steering axis but "offset" from the steering axis. You can see the offset on the triple clamp. Trail measurements taken from the forks then need to subtract the offset.

Having the forks parallel to the steering axis is considered the "correct" method, but this is not true for all motorcycles, many bikes with altered fork angles were not done the "correct" way and the fork angle is changed by an angled triple clamp.......the actual rake is still the steering axis angle, but the fork angle is increased. And some bikes come stock with an extended fork angle(angled triple clamp), Yamaha Stryker is one, with a fork angle of 40* and the steering axis angle(rake) at 34*(I think).

Keeping the same wheel, and increasing the steering axis angle, and adding longer fork tubes, you also increase the trail. By increasing the fork angle with angled triple clamps you decrease the trail.

As with a million other characteristics, rake and trail are a part of how the bike handles. With all else equal, more trail means more input is required to make the bike lean.....or its easier to keep straight, less trail means its ready to hit the curves. Rake, all else being equal, rake and wheel base go hand in hand, more rake means less curve for the amount of lean........or you must lean more for the same curve at the same speed.

Since all else is not equal from bike to bike, you can't go by just rake and trail to determine how it will handle.
 

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Discussion Starter #10
Lots of great stuff here. Thanks gang. I've heard these terms many times of course, and realized I really didn't understand what they were/are. I knew they "were" some sort of combined physics type part of the gyroscopic effect of movement, but just wasn't able to put them together in my head (I'm a slow learner I guess).

So, what happens to the effects of rake and trail and their contribution to movement, when you add a side car (let's say) or ride on a bike with TWO front wheels???? Is it nullified? No longer relevant or applicable?

-soupy
 

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...So, what happens to the effects of rake and trail and their contribution to movement, when you add a side car (let's say) or ride on a bike with TWO front wheels???? Is it nullified? No longer relevant or applicable?

-soupy
Rake & trail angles wouldn't be directly affected by the addition of a sidecar, although the bike would handle noticeably differently with the sidecar, mostly because you would no longer be leaning into corners.

2 front wheels (ie trike)? Most designs use automotive style "twin a-arm" suspension, so you can add more confusing geometric terms like camber & toe-in to this conversation :smiley_mornincoffee
 

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Rake & trail angles wouldn't be directly affected by the addition of a sidecar, although the bike would handle noticeably differently with the sidecar....
Rake has a considerable effect with a sidecar. The sidecar introduces drag on that side of the bike and the larger the rake, the less noticeable it is on the steering (less counter-pressure required). Increasing trail also reduces the steering effort with a sidecar.
 

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Motorbike Macgyver
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The way I have always been told and also read from googling to calculate trail is to draw a line from your head tube at whatever angle it sits to the ground. For example just grabbing numbers out of a hat, let's say your head tube sits at a 35* angle, draw a line from your head tube to the ground at a 35* angle. Mark where the line hits the ground. Then draw a line from your axle straight to the ground. The lime from the axle should land behind the line from the head tube. If you have triple clamps, draw a line from the bottom of the fork clamp instead at the appropriate angle. The two lines will form an imaginary triangle. Measure the top angle of that triangle, that's how many degrees of trail you have. From what I understand, the more trail the better it will handle at high speed.
 

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If the head tube, caster angle, steering axis(all the same thing) is 35* then the rake is 35*

"For example just grabbing numbers out of a hat, let's say your head tube sits at a 35* angle, draw a line from your head tube to the ground at a 35* angle. Mark where the line hits the ground. Then draw a line from your axle straight to the ground. The lime from the axle should land behind the line from the head tube."

Correct so far, the distance between the 2 marks on the ground is the trail, measured in inches.
 

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You can see how wheel size will play into the amount of trail. Motorcycles with a 21-inch wheel will steer a bit differently than identical ones with a 19-inch wheel.
 

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I did a comparison of rake and trail between three cruisers, C90T, Valkyrie, VS800, and my old CB450. The rake of all three cruisers ranged from 32 to 33.25 degrees, while the CB is 24.5. The trail of the cruisers, as a percentage of wheel diameter, ranged from 21% to 22%; not surprisingly, allowing for weight and wheelbase differences, the cruisers handle a lot alike. The CB, though, has a trail that is about 16% of wheel diameter; it's not very surprising that it is less stable and a lot more nimble than any of the cruisers, even the VS800, which has a similar weight and 4.5" less wheelbase.
 

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The suspension on your car also has rake and trail which are obviously not needed for balance. On a car you get to add in 2 other parameters, toe and camber. Camber is the easiest to understand because it is simply how much the wheels tilt toward the center of the car. Toe is how much the tires steer toward each other. On a car trail is called caster. It is how far the contact patch is behind the rotation center line.
 
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