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  #1  
Old 30th November 2016
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Default Ride Height Change With Shock Length Change

Quote:
Originally Posted by splattttttt View Post
How much higher did the rear sit with those 13.5"
My wife rides a super low. I believe the stokers are 10.5
So will the rear come up a whοle 3 inches with these installed.
The shocks are at an angle; if you increase the length of shocks by 3", you will raise the back of the bike by more than 3". Before sag is taken into account, that is.
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  #2  
Old 30th November 2016
Brad Brad is offline
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Not to be contrary Folkie, but don't you raise the rear less from vertical because of the angle? If we know the angle, I could calculate "x".


Last edited by Brad; 30th November 2016 at 06:15..
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Old 30th November 2016
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Default

The angle changes, which is entirely the point.

The horizontal distance between the shock studs is about 7":

Code:
     /|
    / |
10 /  |x
  /___|
    7
By Pythagoras:
x² = 10² - 7² = 100 - 49 = 51
∴ x = 7.14
If we increase the shock length by 3":

Code:
     /|
    / |
13 /  |y
  /___|
    7
The horizontal distance is about the same (actually it's slightly less, due to the swing arm dropping).

Using Pythagoras again:
y² = 13² - 7² = 169 - 49 = 120
∴ y = 10.95
The bike is raised by 3.81".
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Old 30th November 2016
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I'll split the last few posts off into a new thread. It'd be a shame to lose them when this ad gets deleted.
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Old 30th November 2016
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Default

The angle begins from the front axle. Bigger vertical change to the rear from shock mount, less toward the front by altering shock length.

Pythagoras didn't ride, but he was a smart dude.
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Quote:
Originally Posted by El Rod View Post
The angle begins from the front axle.
True, but in practice all we need to concern ourselves with, to show that the height of the rear of the bike changes by more than the shock length change, is the right angled triangle between the shock mounts.

The increase in height will be slightly more than the result of that calculation, because:
  1. The length of the base of that right angled triangle will be slightly decreased, as previously mentioned,
    .
  2. The height of the bottom shock mount will be raised slightly.
BTW, that horizontal distance of 7" is only a rough estimate, based on my bike with 11¾" shocks.
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Old 30th November 2016
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I had to go and look at the calculations via an online calculator tool (because it's been too long since I've done that math and I never would have figured it out on my own).

And when I compared some theoretical changes of shock lengths it hit me why this is true seemingly counterintuitive to Brad's example (which is what I was first thinking when I read the OP).

Brad's example, and the one that many of us would probably first assume is true, doesn't recognize that the horizontal distance changes if you set the shock straight up and down. I.E. it's that fixed horizontal distance in the triangle that allows this to be true even though Brad's example is also true. If we stood the shock straight up that vertical distance would change even more, but the vertical distance isn't the shock length in the first place, it's less than the shock length as long as there is any angle.

Thanks Folkie.
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And Brad's example doesn't say anything about changing the shock length, it's just about standing the same length shock straight up.

BTW, I've demonstrated this several times over the years, the first going back to February 2007! Actually, the very first was in a PM to PΟSTAL_ΟNE in June 2006.
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Old 30th November 2016
bgavin bgavin is offline
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Quote:
Originally Posted by Folkie View Post
The angle changes, which is entirely the point.
The Pythagorean theorem only applies to a right triangle.
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It's just as well that I'm only talking about right angled triangles then.

The hypotenuse is the shock, and the two shorter sides are down from the top shock mount, and forward from the bottom shock mount, meeting at a right angle.
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