PDA

View Full Version : difference between oil and spring adjustments?



servant
05-31-2001, 06:35 PM
Hello everybody! Thanks in advance for your help. I am brand spankin' new here (2nd post) and it seems like a great BB!

What is the difference between changing the oil weight and changing the spring tension?

WhoKnowsWho
05-31-2001, 07:13 PM
A higher oil weight will slow the damping down, the shock won't move through the piston as quickly. Same effect can be had by using a piston with smaller/less holes. Normally not a good idea on a bumpy track since the shock won't have time to recover for another bump, usually heavier weight is used in touring cars. Springs are use to adjust the weight bias between the front and the rear. Though I can't remember what the effects are off the top of my head, I do know that adjusting the pre-load has no effect on the tension, just the ride height of the vehicle.

ammoace
06-01-2001, 02:14 AM
WKW,
You know that is the first time I heard that about preload clips only adjusting ride height. I am not saying you are wrong but I had in the past thought I was adjusting spring tension by changing the spacers. Hmmm, now I need to rethink this process.
Jerry

ammoace
06-01-2001, 02:24 AM
Sorry but I forgot to add to WKWs answers. If you add stiffer springs in the front the rear will have more bite/traction. Or if you add stiffer springs in the rear the front tires will get more bite. This can be done in oval racing too. If you add a stiffer spring to the left rear the front right will get more bite. The last example is what NASCAR does, I think they call it "adding wedge" to the car. I don't know how much effect having different rate springs on any single corner would have on R/C cars but it does help changing spring rates as a pair front and rear.
A lot of the need for "playing" with different spring rates on your car depends how serious you are into racing and how serious your competition is.
Hope this helps,
Jerry

WhoKnowsWho
06-01-2001, 03:46 AM
Yeah, I used to think moving the spacers down made the spring stiffer, but it doesn't. Just take a spring and squeeze it between your finger and thumb, the pressure you need to apply doesn't change much at all.

nitroracer911
06-01-2001, 10:19 AM
Adding spacers to the shocks does make it a little more stiff. My stadium truck had loose shocks and it was beating the krap out of the bottom of my car. I added some spacers on the shocks and it helped out a bunch. Not to mention when I jumped it.... the landing was less prone to screwing up the bottom of the car....

:p

WhoKnowsWho
06-01-2001, 10:23 AM
Or it just raised the ride height... giving the car more space to bounce and recover from the jump. :)

nitroracer911
06-01-2001, 11:00 AM
i guess we must be talking about something different. When a shock is fully EXTENDED it cannot go any furter. Even when a spacer (U shaped piece of plastic) is added to the shock it does not alter ride height. It simply stiffens the spring. :eek:

So are we talking about something different???? :confused:

StephenB
06-01-2001, 11:10 AM
Guys, the only way to alter spring-rate is to change the spring. The pre-load adjustment clips (also called ride height clips) do nothing but change the ride height. They do NOT stiffen the spring.

A spring has a constant rate of compression unless it's a "progressive spring" which means the more it's compressed, the more resistance it offers. MIP sells progressive springs for 1/8 buggies; unless it's a progressive spring though, the clips will only alter ride height.

Never use the clips to "stiffen" the suspension. That's why AE, Losi, Kyosho, etc all sell springs with different rates (different colors).

servant
06-01-2001, 01:56 PM
okay, so dohickies (I'm sorry fellows, I think "doohicky" is the incorrect spelling :) ) adjust the ride height of the vehicle.

Hey nr911, I think that you are basically talking about the same thing as the others; we have a problem of symantics.

So let's see: you have a single rate spring full uncompressed. For simplicty sake (and because I have no idea how actual spring ratings and lingo work) lets say this spring is a 1lb spring. When you first begin compressing it, it will only require 1lb of force. But as it compresses that force will build to 2lb, 3lb, 4lb, and on up to full compression. Single rate means that the increase in force is consistant throughout the travel. Like say 1lb of force per 1 foot of compression. A progressive rate, on the other hand, might begin 1lb/ft, then half way through change to 2lb/ft, and then finish up with 3lb/ft!

"Another property of springs is that the force increases as the displacement increases. We can express this relation is a formula, known as Hooke's law:" -taken from BSU's web site.

So the tension (rate) doesn't actually change, but the force exhibitted does increase with compression. If you put a bunch of prelaod on the shock, then at its full extension it all ready has more force being exerted by the spring than if there was no preload. Thus the ride height would increase and the suspension would seem "stiffer" when landing.

Well, gentlemen, how does that sound, seeings how I made it up as I went!
:p

At your service (or at least I try!) :cool:

servant
06-01-2001, 02:41 PM
Okay, so that settles the preload issue, now back to the original topic.

Please help me with the differences of oil of spring changes in terms of scenarios: what would be the different effects of the individual adjustments and/or combination there of, on a big jump or a bunch of small whoops.

StephenB
06-01-2001, 03:23 PM
Usually if you're ONLY driving for large jumps (say, a day at a MotoX track) you'd want to install thicker shock oil so the chassis doesn't smack the ground as hard.

Small whoops is the opposite; thinner oil is necessary to "soak up" the bumps and keep the wheels in contact with the ground. Any decent track will have a mixture of both though, so you'll have to compromise both ways and use an oil of middle viscosity.

servant
06-01-2001, 08:29 PM
Okay, so let's say on the large jumps instead of putting heavier oil, we put stiffer springs. How would it handle differently?

Or say on the whoops, instead of lighter oil, we put softer springs?

servant
06-02-2001, 12:17 AM
First of all, let me make sure that we are talking about the same thing:
spring clips, spacers, and preload are all referring to the doohickies that reside between the spring and the top of the shock barrel. Correct?

nitroracer911
06-02-2001, 12:26 AM
i think i am just off my rocker....

the little things I put in my shocks stiffens the whode shock by forcing the spring into a loaded state. (meaning it has more resistance.) These little do-hickies don't make my stadium truck ground clearence any different. The law of physics.... for every action there is an equal and opposite reaction maybe.... i give up.... :mad:

the stupid thing runs and when it hits bumps the shocks work.... I guess that's all i got to say about that :D

Clayton
06-02-2001, 12:57 AM
Stephen is right guys..

The doohickies as they were refered to,
(preload spacer, spring spacers yada yada,) only adjust suspension height.

A spring with a 2.6 rating is consistant through its compression, this is why preloading doesn't change its stiffness, this is also why we have springs known as variable rate springs or progressive springs as Stephen refered to them, they have a differnt coil pattern at one end, the lighter part of the spring compresses to a point, then when the spring gets to the stiffer part the spring of course becomes stiffer.

As for the laws of physics, if a spring has a rate of 2.6, it cannot get stiffer as is compresses..you are still only compressing a 2.6 rate spring.

[ 06-01-2001: Message edited by: Clayton ]

StephenB
06-02-2001, 09:31 AM
Servant, the best way for you to find out is to go to your track & try the adjustments yourself. It'll mean more if you see it work in person than for someone on here to tell you...

WhoKnowsWho
06-02-2001, 10:24 AM
If you think about it all for a sec, you can see it in your mind... a soft spring combined with thick oil, the shock won't rebound fast enough, the oil will slow it down too much. Hard spring with soft oil, the shock will bounce back and forth extremely quickly and most likely bounce the car around with it. Normally, you need some sort of inbetween setting, a medium oil and medium springs. Unless you use progressive springs, and the RPM progressive type pistons. The pistons sound good on paper, they let more oil pass through on short suspension movement, ie. small whoops. And when the shock is compressed more, the holes close and the damping gets thicker, ie. for large jumps. But as StephenB said, the best way to find out the best setting is too experiment and see what needs to be done. And remember, suspension can adjust your steering and traction ability too.

servant
06-02-2001, 01:45 PM
Large jump scenario: say the vehicle is bottoming out all the time. If we were to put thicker oil in, it may stop it from bottoming out but it also may cause the vehicle to recover from the landing too slow. Stiffer springs may cause it to not bottom out, but may cause it to recover too fast (bounce!). Correct?

Whoops scecario: say the vehicle is not soaking them up. Lighter oil would make the shocks respond faster, but would increase the bounciness. Softer springs would allow the shocks to respond faster, but would increase the recovery time. Correct?

Gentlemen, I really appreciate your help in here for a few reasons. First and foremost, it is extremely difficult for me to even get out and drive, let alone getting out to the track. Blind experimentation takes a long time! Secondly, I am just plain one of those types that likes to understand the theory behind things before I jump into them. (once someone was trying to explain to me cords on a piano and I just could not get it. I finally went and spent a half hour with an encyclopedia article on the theory of sound, came back and was able to hear what they were talking about! Kind of weird, huh?) Thirdly, I think that the best structure for being able to help others is a solid foundation of correct knowledge with real experience built on top of it. And being able to help others is very important to me.

Thanks again and have fun! :)

StephenB
06-02-2001, 10:01 PM
Servant, we're all glad to help. That's what this board is for; but as I'm sure you know there is no replacement for "in the field experience." Learning how and why things work happens most effectively when experience in person ;)

Having said that, I can tell you that you'll never get an offroad vehicle to land a large jump without bottoming out. In fact, the chassis on these vehicles are thick and sturdy for a reason--they're meant to bottom out. There's a difference between *slapping* the ground and breaking parts and bottoming out though. It helps settle the car down and absorbs the impact. Trust me on this one; if you've ever seen a National or Worlds nitro offroad race, you'll know what I'm talking about.

The best way to learn, as I said earlier, is to take your car/truck out to the track and run it with different setups. Bring a large note-pad and a pen, and write down every suspension change you make (do them one at a time!!!) and the result of that change. Pretty soon you'll find patterns for what works well and what doesn't...and then you'll have learned it yourself :D

gubbs3
06-03-2001, 12:38 AM
I like to think of the oil as the "up" or "compression" motion of the shock and the spring as the "rebound" or "down" part. With a heavier weight oil the down motion will be slowed and with a heavier spring the rebound will be faster. Each adjustment works in both directions but this is how I like to think of it just to make my life easier. The best way to find out what each does is just to go out on a track or any surface and test test test. For example: If your car is leaning way too much and making it feel mushy and have a push-loose-push-loose feel as you pump the throttle increasing spring rate won't help the roll much but it will cause the shocks to push up faster once the load is reduced. That could cause the car to become unstable coming out of the corners, having too much motion, when you pour on the power. If you went to heavier oil the car would not lean as much in the quick corners giving the car a smoother feel but it would make the car more responsive because the suspension won't move as fast so all the resistance on the car is transfered mostly to the wheels. However, with the heavier oil the feel of the car will be much more linear, again adding to the smooth feel. What I just said may sound repititious but that's the best I can do to explain it. I know what changes would need to be made to a car to get a certain feel but explaining it requires more skills for writing than I have. To really get a feel for what the changes do, go out with a setup that has very heavy oil and a soft spring and then a setup with light oil and a heavy spring. Go with about 10-15 weight up and 10 down and with springs at least .5 lbs./inch (losi red is 2.5 so go to silver-3.1) difference than your normal setup. If someone wants to clerify what I just said go for it!

HauntedMyst
06-03-2001, 02:44 AM
OK, all this begs the question of why are progessive springs common on touring cars but uncommon on trucks and buggies where to my thinking they would make the most sense given their wider range of motion?

gubbs3
06-03-2001, 04:49 PM
HauntedMyst- I think the reason they are used in touring cars is just for more tuning options. From most of the TC's I've seen, most of them run at full extension and have ride height adjusted by internal limiters. That would mean that by increasing spring preload with a progressive spring you would actually make a minor change to the rate of the spring. I should add that by increasing spring preload you have to put a higher load on the spring before it will start to compress but once it is compressed it will act the same as a spring of the same rate with less preload. That may make it feel stiffer because it takes more force to compress the spring, but only at first.

servant
06-03-2001, 08:18 PM
Thank you everybody for your input! As soon as I get a chance, it is off to the track for me. :)

I also found some awesome info at the following site:
car handling site (http://gallery.uunet.be/heremanss/)

Go check out their info and tell me what you think. Talk about brain racking!

WhoKnowsWho
06-04-2001, 11:17 AM
"download a zipped version (2.5MB)" I think I will save that for later... looks kinda comprehensive! :)

HowieStern
06-04-2001, 01:07 PM
couple things here.....

pre-load spacers do not- change springs rate

but... increasing your pre-load will make the initial movement of the suspension stiffer (but only the first few mm of travel) but will have no effect on mid stroke or botteming resistance... and yes of course it will alter your ride height...

spring rate is not principly used to alter the speed of shaft travel... it is used to handle or shift "weight"... if you run a heavier servo and batteries... you will need heavier springs to get the same drive characteristics as you did with stock springs and a lighter servo and other running gear...

about progressive springs... i'm not so sure they are needed... your car already uses a bit of "progressive" suspension travel... it gets this from the angle of the shocks in relation to the a-arms... you vary the angle, you very the rising rate from nearly a linear curve, to a very aggressive curve... (a very aggressive curve would be very soft at the initial part of travel, and much much firmer near botteming out... a more linear curve would have nearly the same about of firmness the entire way through the stroke)

right now, with nearly all rc shocks, you can not adjust rebound and compression damping seperately... when you change oil or pistions, you are changing both rebound and compression damping.... in most cases, you only need to alter one or the other.... definately not both... but at this point there is no choice... so you increase or decrease one, and you have to deal with the results of the other... hopefully the manufactures will come out with fully adjustable shocks some day.... and make them so you do not need to take them apart to adjust them...

peace out..... :)

DerekB
06-04-2001, 02:21 PM
Howie, nice post!!!! :eek:

The reason it may seem stiffer for the first few mm (or whatever) is because the shock is preloaded (preload spacer, get it) the spring is trying to return to full extension. That's why it may feel stiffer, but in reality it is not. The initial force is up.

WhoKnowsWho
06-04-2001, 02:48 PM
Hey Howie, if you did want to change the damping for both seperately, here is how you would do it, http://www.ultimatetraxxas.com/ultimate/review_rpm2stage.asp 2 Stage pistons!

HowieStern
06-04-2001, 04:08 PM
i have heard about, but not used the RPM parts yet... they may be a step in the right direction...
RC shocks could stand to come a long ways... some changes would be really easy....

1. run the shocks upside down.... this puts the heavier oil filled side down, for a lower CG... it simply amazes me why this hasn't been done yet...

2. run much shorter shocks on off-road vehicles... once again this is used to lower CG... but another benefit would be slower shaft speed... the slower the shaft speed, the less heat that is produced, and the less your oil will break down during a long race... the long shocks used today are all the rage, but are too heavy, carry the weight too high, and are simply not needed to acheive the suspension travel they are using....

3. when you change the angle of your shocks, the manufactures should make it so that you don't automatically change the ride height as well.... currently, every off-road rc i have seen will change it's ride height when you do this... you don't want to change two things when you are only trying to make one change....

4. this would be a bit more costly... but external "clickers" for both rebound and compression damping would just make life too sweet.... i can dream can't i??? LOL..

peace out..... :)

servant
06-04-2001, 06:06 PM
Hey Howie,
You make some very good points, especially the observation that changing the relationship between the shock and the arms can result in a progressive-type response.

However, if I understand you correctly, I think that I my differ on a fundamental issue. If you are saying that the force that a spring exerts is constant throughout its compression, then I have to disagree. Hooke's law states that:

"The force it [the spring] exerts is proportional to the movement of one of its ends. Or to put this into a mathematical equation: Force = movement * spring constant."
In other words, the more you compress a spring, the harder it is to further compress it.

Let's apply this. Say we have a spring with 100mm of compression and a rate of 10gF/mm. At 10mm of travel, the spring would exert 100gF; at 60mm = 600gF; at 100mm = 1000gF. Now let's say that this spring is on a shock assembly that allows for 50mm of travel and at its full extension, with no preload, does not compress the spring any, nor extend past the springs length. In other words, for every 1mm that the shock travels, the spring is compressed 1mm; so when the shock assembly is "bottomed out," the spring has traveled 50mm, and thus is exerting 500gF. Now if we add 20mm of preload, at the shocks full extension, the spring is already exerting 200gF. At the "bottomed out" point, the spring will be exerting 700gF.

In short, adding preload does in fact cause the spring to give more resistance throughout the stroke of the shock. It is "stiffer" suspension, and gives virtually the same effect as putting on a stiffer spring, only that effect is at a much, much lesser magnitude.

Boy, let me finish by saying that I, personally, have learned an immense amount from this thread! At you service. :)

DerekB
06-04-2001, 08:37 PM
serv, I think when yuou stated that the spring was constant, that you proved yourself wrong. Springs are constant unless progressive or the coils start hitting each other. I'm gonna have to break out the physics book soon. :)

HowieStern
06-04-2001, 10:51 PM
thats the difference between straight rate, and progressive springs....

progressive actually get firmer when they are compressed... straight rate maintain the same rate until coils hit...

peace out..... :)

WhoKnowsWho
06-04-2001, 11:52 PM
If you say movement, wouldn't that mean the start point, to the end point? So if it moves 20mm, the force applied is the same weather or not it started at it's full extension, or 10mm already compressed.

Dirty Pirate
06-05-2001, 02:42 AM
i am reading that link someone posted earlier in this thread. ive been looking for something like this for some time now., it pretty much covers all the elements of tuning an r/c car.. ground clearance, roll centers, center o' gravity, toe angles castor camber suspension compression etc. all in great immense detail! im very impressed. it tells you wut each change will do,, but it doesnt stop there, it tells you why it does that. which is a great help

*tries to remember his Highschool physics*

servant
06-05-2001, 03:43 PM
Dirty Pirate, that link is awesome, isn't it?! How about that laminar and turbulent flow, or the theorem of Kennedy about 3 objects hinged together having at most 3 poles of movement that are always collinear!!! Great stuff. :)

servant
06-05-2001, 03:48 PM
Now EVERYBODY!!! (except, I think maybe nitroracer911) Before I respond, let me attempt to define and clarify just exactly what it is ya'll are saying (let's forget about, for a moment, progressive springs until we are done with constant rates; also let's forget about such anomalies as coils touching, etc.):

A constant (straight, single, etc.) rate spring exerts the same amount of force through out its movement. IOW, the spring gives no more resistance to movement when it is being fully compressed than when it is being only slightly compressed. IOW, the spring gives the same amount of resistance to movement through out its travel. IOW, it is just as easy to squeeze the spring all the way as it is to squeeze it just a little.

Please read the above carefully. I have said the exact same thing in four slightly different ways. So is this yalls' view of how a constant rate spring works???

serv :)

Grant Tokumi
06-05-2001, 08:45 PM
I'm convinced that it must get harder to push a spring as it gets compressed more. IOW, a constant rate spring gets firmer the more its compressed. I used to think otherwise, but after hearing some explanations, it make sense, or what makes no sense is a constant resistance force throughout a spring travel. If resistance force WAS constant throughout travel, think about it, a spring would compress 0 amount until it reached the force that the spring can't hold it any longer. That already doens't make sense. Then once the force was .0000000001 lbs more than what the spring could hold, the spring would all of a sudden compress 100%.

Thats my thought for the moment anyways, I'm in a rush (gotta go home) right now so I might be missing something, but theres some food for thought. Feel free to hack at my comments.

servant
06-06-2001, 07:09 PM
My dear Grant Tokumi, may I say, quite intuitive, quite intuitive indeed...

WhoKnowsWho
06-07-2001, 10:18 AM
A spring requires force to compress it: Yes
A spring stores force as it is applied to it: Yes
To compress a straight rate spring 10mm from its full extension might take 10 joules.
But to move it another 10mm will take another 10 joules.
That as far as I know is how a straight rate spring works, unless the shock is mounted to create a progressive type effect, to move it 10mm from any starting position (ignoring coils getting closer) will take the same amount of force.

servant
06-07-2001, 03:48 PM
Who, some very good points. Let me draw your attention to your fourth statement, "But to move it another 10mm will take another 10 joules." Key in on the word, "another" (10 joules). In order to move the spring 10mm further, it will require 10 MORE joules, for a total of 20 joules required for 20mm of compression.

That is what is meant when a spring stores the energy. Our 10mm compressed (from full extension) spring is trying to expend that energy, IOW, return to full extension. The more it is compressed, the more energy it has stored, which means it has more force to return itself to full extension. BTW, when energy is stored (the spring is compressed to some degree and staying that way) it is considered potential energy, since the force is there but no actual work is being done.

You see, Who, if it only took 10 joules to compress the spring 10mm from any point of pre-compression (preload) then that would be the opposite of "storing energy." That would be making the energy disappear into thin air. And that, my friend, would be magic!

I hope ya'll are enjoying the brain rackin' as much as I am! -serv :)

DerekB
06-08-2001, 09:10 AM
hey just want to point out that the last post by Serv and and Who pretty much states clearly that a spring has a constant rate throughout it's compression. If it takes 10 joules (whatever unit of work) to move 10mm and another 10j to go an additional 10mm-that means it is constant! Yes, there is potential energy trying to return the spring to equalibrium, but the fact that if you compress the spring 10mm and use 10j and it only requires 10 more joules to go another 10 that means the spring rate is constant throughout it motion...

-Derek :)

Grant Tokumi
06-08-2001, 03:48 PM
Agree.

And to further clarify things, if a spring is not "preloaded" (see my definition of preloaded below) servant's example is correct, i.e. it requires 10j to compress the spring 10mm. However, note that if a spring is already "preloaded" 20mm, it will require 30j to move the spring the same 10mm.

my assumed definition of "preloaded": a spring that is already compressed some amount when the shock is at full extension.

This means that if spacers are added to the shock and no preload results, then spacers DO only change ride height. However, once the addition of spacers create preload, the same shock will become stiffer. Agree? :)

servant
06-09-2001, 12:40 AM
Derek, yes exactly. With a constant rate spring, using the above example numbers: the point is that it takes 10j to move the spring 10mm, and it takes 20j to move it 20mm, 30j for 30mm, and on. Agree? :)