Originally posted by transio


<<<snip>>> #1
That means that whatever happens inside doesn't matter.

<<<snip>>> #2
The shocks are in compression, with a pin joint at either end. The vertical force gets translated along the axis of the shock absorber, which then pushes back with a vertical AND horizontal load. The horizontal load gets absorbed by the wheel's mounting bracket (and whatever assembly that is attached to). Because the shock absorber is at an angle, it has to handle not only the vertical load applied by the road, but the horizontal loads created by the fact that it's angled. Essentially, it makes the shock work harder than it would in a vertical mounting position.

<<<snip>>> #3
Additionally, it's not making the shock travel less. That's a misconception. The shock actually has to travel MORE for the same amount of wheel travel.

<<<snip>>> #4
I don't see one benefit to having the shocks mounted this way.

Well I just logged on here to ask a stupid engine question but now I've seen this so it looks like I'll have to run my mouth some more. Please forgive me - I'm not trying to start an argument - but it seems to me that some of your logic is 100% backwards from the way I see things! What up with that???

Here are my responses to your points as quoted above:

1. Actually, whatever happens inside is the ONLY thing that matters as far as force transmitted by the shock. The force vector diagrams you provided apply to solid rods, etc. But our shocks are not solid.

Just forget all that vector stuff and do this little gedanken experiment. Envision a shock in which there is no oil - say it's brand new and comes with a couple different weights of oil and you just haven't decided which viscosity to use therefore you haven't filled it yet - so there is NO damping. And the pistons, rod, seals, etc are all made of Unobtanium, a new alloy that is completely frictionless. You're holding this trick $5000 shock in your hot little hands - just marvelling at how easily it slides in and out. How much force does this take? Practically none! There's no damping and no friction so all your hands feel is a wee bit of inertia as you accelerate the mass of the shock body.

If you mount the shocks on the VX like this how much force will they transmit from the axle to the frame when you whack that big speedbump at the mall? NONE!!! There's nothing going on in that shock. It's all spring and no shock, baby! The VX soaks that bump right up - but then it proceeds to pogo your ***** into the next lane and you almost sideswipe a bluehair in a Fleetwood Brougham. You decide you better put some oil in those babies. You take them off and fill them to the proper level with the lightest oil. You're compressing and expanding the shock - working the bubbles out - you feel the damping now and you notice when you push as hard as you can it takes about 4 seconds to completely collapse the shock. This pectoral workout reminds you of when you were a kid and got hold of your sister's Mark Eden Bust Developer. Then you discovered the instruction booklet with those pictures of June Wilkinson......

Whoa! Major derailment there! Get that thought train back on the tracks. On with the gedanken! So - you slap the shocks back on, hit the same speedbump and notice it still soaks the bump up pretty good but there's also still a lot of bouncing afterwards. Rides kind of like that Fleetwood you almost hit. So you decide to use the thicker oil to slow down the rebound. It'll stiffen up the compression damping too. This time when you're working the bubbles out it kind of reminds you of your dad's Bullworker. You're pushing as hard as you can and it takes a good 10 seconds to collapse the shock. You're thinking man this is going to be a stiff ride. When I hit the bump this time the shock is going to put up a fight. There's going to be some major damping going on. It's not going to collapse easily. It's going to transmit a lot of force from the axle to the frame.

Do you get where I'm going with this? What goes on inside the shock DOES matter. If you don't get it then take the gedanken one step further. Say you're still thinking about June Wilkinson when it comes time to change the shock oil. You're distracted and you fill them with 90W gear oil so they hardly move - no better yet - you're so distracted you fill them with some epoxy resin you had mixed up and set aside for another project. It sets up and by the time you get the shocks installed on the VX they are basically solid rods. ***In other words, they are what you depict in your vector diagram!***

NOW what happens when you hit that speed bump? No spring action at all! The shocks transmit ALL the force. Depending on how fast you hit and the slope of the speedbump, that force approaches infinity and either the axle, the frame or the shocks will yield as they try to accelerate the 4000lb VX against gravity at an impossible rate. Get it? As far as force transmitted by the shock, what happens inside is the ONLY thing that matters.

2. The shock is compressed in one plane and, as you noted, is mounted on pins at both ends. The pins are perpendicular to the plane of motion - like a bicycle wheel and axle. The shock body halves are therefore free to rotate as the shock is compressed and so the shock doesn't see a vertical or horizontal component per se. The shock just feels squished along its axis and that's all it knows.

3. Nope. Shock at an angle will travel less. Do another thought experiment. Think of a dirt bike swingarm with shock straight up and down, mounted at the axle. One inch of wheel travel compresses the shock 1 inch. Now lay it over as far as it will go - that's right - parallel with the swingarm! Hey! The wheel's moving up and down but the shock's not being compressed at all!!!

4. Uh, let's see.... I've got it! A real world demonstration! Show up at the Swamp Fox enduro (1/16/05, Charleston, SC) and I will locate a vintage bike like maybe a 1966 Maico with straight up and down shocks for you to ride. After 70 miles of sand whoops with 4" of suspension travel I bet you will see the benefit to lay-down shocks....