Bilstein Shocks Info

[transio]

I have a good set of stock fronts with 25k miles on them if anyone wants to make me an offer!

[transio]

Originally posted by SlowPro48
Seems like even if you apply a million pounds to the axle at the rate of 1 inch per second for 3 seconds - if the shim stack and oil in the shock only resists with a force of 25 pounds at that rate then that's all that will be transmitted to the frame - 25lbs - no matter what the angle of the shock.

Good point. I hadn't really thought of it that way. But what if your force is less than maximum resistance? What if it's 15 pounds? if lay-down shock takes 15 pound vertical loads as 25 pound axial loads, then it's doing more work. Also, if it travels 18" versus 12", it's doing more work. It may perform better, but I'm pretty convinced that performance increase is at the expense of shock life. That's something that's common in all aspects of racing.

[SlowPro48]

Originally posted by SkidPlate
Actually, I left the old shocks at the garage for them to dispose of. I really don't think they were worth much, if anything, ...

Wonder if they've still got them...


They might not be worth anything but I'd like to get my hands on some that have failed and show them to my suspension guy. Guess I'll just have to wait until I've got my own trashed set!!!

[SlowPro48]

Originally posted by transio
Good point. I hadn't really thought of it that way. But what if your force is less than maximum resistance? What if it's 15 pounds? if lay-down shock takes 15 pound vertical loads as 25 pound axial loads, then it's doing more work. Also, if it travels 18" versus 12", it's doing more work. It may perform better, but I'm pretty convinced that performance increase is at the expense of shock life. That's something that's common in all aspects of racing.

Dude -

1. There is no "vertical load" on the shock.

2. The shock doesn't care if there's 15, 25, or 25,000 pounds pushing on it. It only cares how quickly it's being compressed and extended. It's just two pieces of metal held together by some oil. When moved, it squishes the oil through one set of orifices or another (compression or rebound damping circuits) and the force transmitted depends on the specifics of the damping and the speed with which the two shock halves are being pushed together or pulled apart.

The shock also doesn't care if it's straight up or at a 45 degree angle. It's still got the same oil and same holes to squish it through in order to resist movement. BUT - fortunately smart engineers DO care about shock angle because by tilting the shock they can get more suspension travel without raising the ride height/center of gravity of the vehicle.

Can you imagine a dirt bike with 12" of suspension travel and vertical shocks? The shocks would have to be over 24" long. When you consider the reservoir, mounting eyes, etc. the shock would actually end up being nearly three feet long. Add half a wheel diameter to that and we've got a seat height of at least 4 feet....

It's the same with 4 wheeled stuff. In most cases, low c.g. is the way to go.

I guess theoretically it could reduce the life of the oil in the shock slightly. Since canted shocks travel less, the shaft velocities will be a little higher than if the shock were mounted vertically. The oil might thin a little sooner. If that's the case, I'd say the trade-off is worth it. Not just for high performance applications either. I wouldn't want the bed of my GMC any higher than it is. So I'm glad the shocks are tilted. And they seem to last just fine that way. 300,000 miles and only had to replace the shocks once.

If VX shocks are going bad at 30,000 then there's something else going on besides the fact that they're tilted - especially if they're leaking. Sure would like to get my hands on some and see what the problem is...

OK, Mr. Transio - I've flogged this horse enough. How about you?

[transio]

Originally posted by SlowPro48
OK, Mr. Transio - I've flogged this horse enough. How about you?

Not at all! I'm actually learning something!

Re: "more travel", you're right. After looking at my diagrams a bit, I realized that I put the rotation point of the axle directly beneath the frame mounting point of the shock absorber. By putting it at an infinity, it changed a lot. My bad!

Re: fluid dynamics, you say that all that matters is the speed with which the shock is compressed. What you're missing, though, is that the axial load placed on the shock is specifically what determines the compression rate. Bigger load = faster compression. Internally, the bigger load translates to higher pressure placed on the fluid, which simultaneously increases flow and outward pressure, tending (I guess?) to make the container of the fluid want to burst. If the container is of inferior manufacture, it will rupture?

[SkidPlate]

Originally posted by SlowPro48
Wonder if they've still got them...

Actually, they do have them, it seems that trash doesn't go till Friday. So let me know before then if you still want them, also which ones you want.

One of the fronts is blown and leaking fluid, the other is dry but will not recover from compression by itself. The rears looked ok, the one I compressed by hand was leaking air(?), I could hear it rushing as I worked the shock, could be normal, not sure. I didn't even look at the other rear, but it was dry. One thing for sure, these were all on their way out, large dips on the highway sent me for a little boat ride on the waves, if you get my meaning.

Let me know ASAP, they said they'll save these for me, if you really want them.

-Rob

[transio]

I've got 2 bad rears. They're yours if you want to pay shipping.

[SlowPro48]

Originally posted by transio
..... Re: fluid dynamics, you say that all that matters is the speed with which the shock is compressed. What you're missing, though, is that the axial load placed on the shock is specifically what determines the compression rate....

Haha! Man you're not going to let me slide on outta this discussion are you? Here's the deal - I'm missing a lot of things in life but that little tidbit of info is not one of 'em! I was just using the million pounds to illustrate the point that it doesn't matter how much "force" you apply to one end of the shock body, the other end of the shock will only transmit as much force as the internals will allow (i.e., as much as the damper is resisting the movement of the rod). What YOU'RE missing ;> is that in that example I specified a rate of 1 inch per second - as if the shockwere being compressed by a huge ram or something. It was just for demonstation purposes if you will - another gedanken experiment.

I can see why you might think I was missing something though because I used "pounds" to describe the force - which assumes acceleration due to gravity. I'm not an engineer or physics guy so I talk of force in pounds instead of proper terms like "Pound Force" or "Newton". Sorry. We both know if you put a million pounds on top of an extended VX shock here on earth and let it drop it would (for all practical purposes) fall at 32 ft/sec squared since the resistance generated by the damper would be nil compared to the force of 1 million pounds. But of course while it was falling through the travel of the shock, the bottom of the shock would only be pressing down on the earth the amount the compression damper could resist the shock rod's movement. If you had on steel-toed shoes you could - for an instant - be a hot dog and balance a million ponds on the end of your foot! And about a 30th of a second later - when it reached the end of the travel and the shock bottomed out - well then you'd have a crushed shock and a million pounds on your foot. Ouch!

But the heck with all that outrageous stuff. In the real world our VX shocks only have a thousand pounds or so above them. And practically speaking, that weight doesn't vary much during the typical drive. What determines the shock rod speed is simply the speed of the vehicle and the slope of the obstacle it's rolling over. If you hit a six inch high, four foot wide speed bump and you're doing 30 mph the shock will compress at a speed of about 11 feet/sec (just ignore tire sidewall flex, the car pitching up, etc .) I have no idea how a VX shock plots out on the shock dyno but let me tell you from personal experience - a speed bump like that will give the ol' shims a workout but the VX copes just fine. Haha - I hit that exact speed bump at 30 mph today - was tooling around Duke Univ. Med Center - late for an appt - never been there before - looking for the parking garage - not paying a bit of attention to the road - WHAM I nailed that hump. Fluid dynamics in action...

And to answer the other part of your question - yes, if you have a cheap shock with welded body and the rate of compression is extremely high you can end up in a "hydraulic lock" scenario and the shock body can rupture. This is much more likely with old style damper rod type shocks since they use a fixed orifice. There is a velocity squared relationship between flow and resistance - that is - if rod velocity is doubled you get four times the amount of resistance - quadruple the rod speed and you get 16 times the resistance. It adds up in a hurry and pretty soon you end up in a situation where the fluid won't pass through the damper quickly enough and internal pressure builds and if you've got a weak weld the shock could split. That hardly ever happens though. Most of the time the seal will blow or the shaft will bend before the body will split. With cartridge style dampers like what we've apparently got (don't know for sure since I've never taken one apart but I think someone on this board reported shim stacks) the shims flex away from the piston in response to increased speed thus increasing orifice size and preventing hydraulic lock. Heck they could probably even handle a million pounds without blowing up!!! ;>

[SlowPro48]

Originally posted by SkidPlate
Actually, they do have them, it seems that trash doesn't go till Friday. So let me know before then if you still want them, also which ones you want.

One of the fronts is blown and leaking fluid, the other is dry but will not recover from compression by itself. The rears looked ok, the one I compressed by hand was leaking air(?), I could hear it rushing as I worked the shock, could be normal, not sure. I didn't even look at the other rear, but it was dry. One thing for sure, these were all on their way out, large dips on the highway sent me for a little boat ride on the waves, if you get my meaning.

Let me know ASAP, they said they'll save these for me, if you really want them.

-Rob

Great googly moogly man those things sound completely trashed!!! They're dry? What in the world is going on here?! How many miles on them?

I'll gladly pay shipping if you're sure you don't want them. It sounds like you're pretty sure if you left them at the shop but if you ship them down here just know it's going to be like the French Revolution and my suspension guy's Port-a-Band is the guillotine!!!

[transio]

Originally posted by SlowPro48
Haha! Man you're not going to let me slide on outta this discussion are you?

Just trying to learn, man

With cartridge style dampers like what we've apparently got (don't know for sure since I've never taken one apart but I think someone on this board reported shim stacks) the shims flex away from the piston in response to increased speed thus increasing orifice size and preventing hydraulic lock. Heck they could probably even handle a million pounds without blowing up!!! ;>

Gotcha. That kind of blows my theory.

PS - iirc, even engineers and physicists use pounds as a measure of force. A pound of force can exist independant of gravity. It's when pounds are used as an identifier of mass that they become gravity-dependant.

PPS - thx for taking the time to explain everything

[t2p]

Can you imagine a dirt bike with 12" of suspension travel and vertical shocks? The shocks would have to be over 24" long. When you consider the reservoir, mounting eyes, etc. the shock would actually end up being nearly three feet long. Add half a wheel diameter to that and we've got a seat height of at least 4 feet....

.
I basically stated this (in this thread or another similar thread) a month or two ago. Oh well.
.
For the historians ....... Suzuki put a spotlight on this around 30 years ago when they introduced the 1975 RM125 with the long travel rear with canted shock absorbers.

[SkidPlate]

Originally posted by SlowPro48
Great googly moogly man those things sound completely trashed!!! They're dry? What in the world is going on here?! How many miles on them?

I'll gladly pay shipping if you're sure you don't want them. It sounds like you're pretty sure if you left them at the shop but if you ship them down here just know it's going to be like the French Revolution and my suspension guy's Port-a-Band is the guillotine!!!

Hehe, yeah, they are in rough shape, which is probably why I like the Bilsteins so much. There is only about 50k miles on them, but the freakin potholes around here just tore them all to h3ll. Im actually glad to hear that your tearing them apart, I wouldn't want to see anyone try and put them back on. I do expect a full report of what you find once the guillotine hits them.

I'll call the shop today and tell them to hold these shocks for me. I probably won't make it over there to get them till the weekend, hopefully your not in a hurry. I'll send you an email to work out the shipping details.

Actually, I see your from Winston-Salem... I'm going to be on Cape Hatteras for a week starting 8/28, want to stop and pick them up?

-Rob

[VR4-Quest]

OK, stupid question....so the H1's are stiffer, so why do they list them for the Rodeo and Amigo, and the H2's for the heavier Trooper?

[transio]

VR4, I was wondering the same thing. I got the info from the people at Bilstein, though.

[transio]

Just to get this thread back on topic:

Originally posted by SkidPlate
I had the H1's installed this weekend and I have to say I am impressed. They are VERY close to stock performance... I would highly recommend these to anyone looking for a reasonably priced shock replacement with damn near stock performance. Once again, the model numbers are:
Bilstein
F: B46-1738-H1
R: B46-1739-H1

That's two of us who concur! Who's next?