shock damping

[lovebunny]

ok. so for bikes the damping on some of the shocks gets pretty complicated. can someone please inform me on how the dampers in car shocks work? i understand theres probly differences between offroad and street. but how do they work? basic grease and plunger? shim stack? or am i waay off? :confused:

[unccpathfinder]

for basic ones the way they were explained in one of my dynamic systems courses if its a fluid based setup it has a variety of holes drilled in a plate to get the desired stiffness and # of oscillations..but that was basic design and i havent cut a shock apart yet to see how it works...but hopefully i'll learn this next sem in road vehicle dynamics...

 

i searched around a lil bit and didnt find nething too helpful

but try searching in topics of road vehicle dynamics and shock absorbers...

 

if your around a college campus that has mechanical engineering you could go to their library (i know u dont have to have an ID to get in ours unless ure checking something out) and look up some dynamics books read/photocopy what your looking for

[88pathoffroad]

Auto shocks use hydraulic oil inside that flows through holes in the inside of the shock's piston. The smaller the holes, the stiffer the shock. They also have some fairly complicated ways of valving shocks so they can be variably stiffer or softer depending on driving situations or external adjustment.

[lovebunny]

oh ok makes sense. we got shocks like that for our bikes. but the most basic ones use a shim stack: a buncha flexible discs that move when oil is forced through them.

[mws]

Higher end auto shocks use various and multiple combinations of pistons, orifices, shim stacks, blowoff valves, bypass circuits, etc etc etc.

But all automotive shocks I am aware of use hydraulic fluid as the energy absorbing media.

Some protoypes have even used variable viscosity fluid!

 

High end Shock design and function is some pretty wild stuff - You can vary damping any way you want - as long as you can afford it!

Velocity dependent, position dependent, whatever.

 

F1 cars develop the new concepts. Other race series exploit it. Motocross shocks have really brought the exotic stuff to the masses.

 

And it's neat to see it FINALLY trickling down to 4x4 trucks and bicycles.

 

Unfortunately, the majority of off road shocks purchased today are primitive piston/orifice designs -which are actually a pretty inferior design. All the shocks I see on the market for the Pathy (save the IAS and RSX) are still piston/orifice dinosaurs.

 

BUT, shim stacks and blowoff valve/bypass designs are showing up on stadium and baja style race trucks, and a few high end private owner trucks. You can spot them easily - when coming off a jump or big bump, the truck lands, the truck squats as it absorbs the energy, and then smoothly rises back up. No bounce, no slam, no kidneys flying out the window.

The Edelbrock IAS and Rancho RSX are the first "consumer" level shocks to start seeing bits and pieces of this theory and technology. But they are barely scratching the potential.

 

As I see it, the big problem is consumer awareness and acceptance. As long as buyers consider a Rancho 5000x or Rough Country to be adequate, the laws of supply and demand mean we'll keep getting primitive tech. Also a significant factor to lack of consumer demand is cost - a well designed and built shock is a very complicated deal with a lot of precise parts and is going to cost over $150. Each. A really nice shock will be at least $300. As long as consumers are more concerned about looks and cheapness, we will still not get the opportunity to buy good ones.

[88pathoffroad]

Yeah...deal is, they ARE more than adequate for 99% of the drivers out there. That and the price point is always going to be an attractor or detractor, depending on who buys the parts.

[jj big shoe]

If you wanna talk high-tech shocks, check this out. Magnetic-rheological shocks. I saw something about a baja team developing a system for their trucks last year -Guess I'll have to save my pennies.

Edited August 4, 2005 by jj big shoe

[Simon]

I saw an article once in the Wheels section of the Toronto Star. It was about a suspension system developed by BOSE (yes, the audio people). It used, basically, large speaker magnets to push/pull the throw of the suspension. It was designed to be an active system. For instance, if your front, driver's side wheel fell into a pothole, this system would, instantly, push the tire down into the pothole, so that corner wouldn't drop, then as soon as it felt the tire coming back up, it would pull it back to proper ride height, so the harsh thud felt while driving through a pothole was almost non existent.

 

Same thing for cornering. They had 2 identical cars (Lexus RWD, can't remember the model), one with brand new factory suspension components, the other with their test system. The stock one would get to the point through the slalom where it would rock back and forth, quite a bit, transferring the weight from side to side (as with any car), thus, causing the driver to need to slow down, or lose control.

 

The Bose equipped test car went through the same slalom, at the same speed, and was actually able to accelerate through it due to the active suspension system keeping the car level and lessening the side to side weight transfer. The tires became the "weak link" in the handling chain.

 

 

Now for the bad part. The system aparently costs about $30,000 CDN, and it's only in test phases, so that's just an estimate. :eek:

 

Cool stuff though. :cool2:

 

Sorry that it's so long, and I hope it makes sense.

[mws]

If you wanna talk high-tech shocks, check this out. Magnetic-rheological shocks. I saw something about a baja team developing a system for their trucks last year -Guess I'll have to save my pennies.

Yup, that would be the variable viscosity approach I mentioned.

If it can be dialed in, it would be much cheaper than using all the various valving.

 

 

And yeah, 99% of consumers believe the existing tech is adequate. As I did. Until I experienced better. Now I consider them "the annoying compromised turds I gotta live with until the aftermarket offers something better at a reasonable price".

 

Riding dirt bikes and feeling what a high tech suspension can do for control, comfort, and safety was just mind blowing to me. Feeling the difference from my damper rod (piston and orifice) damped forks on my old KDX to the rather trick suspenders on my '04 KTM is literally unbelievable.

These things can controllably absorb huge amounts of energy from big impacts, yet are plush as a caddy on small impacts.

 

Imagine that on your truck - no bottoming - even off 2' jumps, yet smooth and plush enough to drink coffee on a wash boarded gravel road at 45 mph. It is possible...

[Guest Repack II]

Another Ridemonkey idiot!!!

 

Didn't bother to read everything but you can also mount the damper on a spring. Orginal RS Boxxers were like that. Enough pressure and the spring is pushed out of the way allowinf for more oil flow. Keeps s* from breaking but don't know if that style has found its way to cars. Seems like most mtb stuff , especially DH, is just an adaptation of automotive/moto technology. Stick with what works.

 

Resevoir shocks work on the principle of volume displacement. If you put a damper on the shaft than the oil speed = shaft speed. With a remote resevoir the oil speed is a function of shock body volume/shaft volume. For example, if there is 150cc of oil in the body, and the shaft has a volume of 50cc, than oil speed through the C damper will be 1/3 of the shaft speed. This saves the compression damper a ton of abuse. There is only a finite amount of force that can be put on a rebound damper, not so with the C.

 

Have you ever seen a Manitou TPC shop display? Manitou technology is a direct copy of automotive tech that has been aournd for years. The Romic Twin Tube system is another adaptation of that. Another reason for a resevoir is that you need to compensate for the displaced oil volume. The air that you put into a 5e or Swinger serves this purpose. On a vehicle there is no pedaling paltform so nitogen is used.

 

Sorry for all the bike-speak.

Edited August 11, 2005 by Repack II