Spring rate vs linear spring vs progressive spring vs preload MYTH

[Lumikko]

I understand the theory but its when it get pratical that I'm not sure. I feel i can't agree that prelods "only change ride height".

Yes the force taken to push a spring is proportional but adding 5 pounds when the springs is already stocking 30 pounds in enery is tought. Its like a powerlifter, if he lift heavy adding 1 pound is going to feel heavier than before. So there is a progression in what we feel. + 1 pound when you lift 20 pounds doesn't feel the same as if you add 1 pound and lift 300 pounds. The initial force when you turn is huge but after that the spring just want to release the energy stock in it.

The only point i try to make is that "ride height" sounds oversimplified to me. Stiffer springs will have an affect on ride height because its stiffer. How i see preloads is how much force added i need to push the spring first. And like i said before, maybe its the concept of "riding height" that i didnt quite understood. If i understand what u wrote is that the spring will react the same but at different height. I think i get that. For exemple if you put 1/2 inch preloads its gonna be higher standing still but the car will go down higher too.

I tried softer springs with alot of prealoads and it was wierd. I had the right height when the car was standing still but if i put the chassis to the ground, it wont go up.

What i want to achieve is a slightly higher ride height BUT i want the suspension to use all the travel it has.

The thing that i dont understand about ride height is why when i put preloads in the rear it start at somepoint to just spin the wheels. If its only about ride height i should have the same grip but with different ride height ?

The only force compressing the springs is the weight of the vehicle. Because the weight of the vehicle is enough to compress the suspension a little bit, it’s no longer in a preloaded state. The weight of the vehicle is pressing down and the springs are pushing up. The forces are in equilibrium and preload is irrelevant.

This doesn’t mean we can expect the car to handle the same: raising or lowering the chassis affects load transfer in all directions, roll centers, and driveshaft angles. These have a significant impact on handling. But the one thing that remains the same is the spring rate.

When the suspension goes through its travel, the wheels move out and/or in because of the changing A-arm angle. Also, the wheels will have some camber gain especially if you run a high roll center. This causes the tires to scrub sideways and the springs are working to overcome it. There’s also the friction from the suspension linkage and shocks themselves. This is why ride height is measured after drop-rolling the car or just pressing the chassis to the ground and measuring how far it rises. The latter method is more common with touring cars. Off-roaders usually like to drop the car.

Ride height is a dynamic thing even on a smooth track, because putting power through the drive shafts stiffens the CVA joint, any toe-in of the rear wheels pushes them together and resists the wheels from scrubbing out, and anti-squat raises the chassis on power but creates an opposite force (pro-dive) when braking.

However! You are correct when you say it’s oversimplified to say the preload only adjusts ride height and nothing else. Changing the ride height changes the geometry love triangle of the shock mounting holes at each end, and the hinge pin. Raising the ride height makes the angle between the shock and A-arm a little slacker, so forces coming from the wheels and pushing up have a little bit more mechanical advantage for compressing the shocks.

P.S. Different spring rates are not a ride height adjustment. Changing springs always involves setting the preload to get the desired ride height.

If you change spring rates without setting the preload, the amount of preload was incorrect for one of the springs and the comparison is moot. It’s like putting an E string to the lowest spot (G) on a violin, cranking it up to the same tension as before, and wondering why the instrument is out of tune.

 

[cocoune]

The only force compressing the springs is the weight of the vehicle. Because the weight of the vehicle is enough to compress the suspension a little bit, it’s no longer in a preloaded state. The weight of the vehicle is pressing down and the springs are pushing up. The forces are in equilibrium and preload is irrelevant.

This doesn’t mean we can expect the car to handle the same: raising or lowering the chassis affects load transfer in all directions, roll centers, and driveshaft angles. These have a significant impact on handling. But the one thing that remains the same is the spring rate.

When the suspension goes through its travel, the wheels move out and/or in because of the changing A-arm angle. Also, the wheels will have some camber gain especially if you run a high roll center. This causes the tires to scrub sideways and the springs are working to overcome it. There’s also the friction from the suspension linkage and shocks themselves. This is why ride height is measured after drop-rolling the car or just pressing the chassis to the ground and measuring how far it rises. The latter method is more common with touring cars. Off-roaders usually like to drop the car.

Ride height is a dynamic thing even on a smooth track, because putting power through the drive shafts stiffens the CVA joint, any toe-in of the rear wheels pushes them together and resists the wheels from scrubbing out, and anti-squat raises the chassis on power but creates an opposite force (pro-dive) when braking.

However! You are correct when you say it’s oversimplified to say the preload only adjusts ride height and nothing else. Changing the ride height changes the geometry love triangle of the shock mounting holes at each end, and the hinge pin. Raising the ride height makes the angle between the shock and A-arm a little slacker, so forces coming from the wheels and pushing up have a little bit more mechanical advantage for compressing the shocks.

P.S. Different spring rates are not a ride height adjustment. Changing springs always involves setting the preload to get the desired ride height.

If you change spring rates without setting the preload, the amount of preload was incorrect for one of the springs and the comparison is moot. It’s like putting an E string to the lowest spot (G) on a violin, cranking it up to the same tension as before, and wondering why the instrument is out of tune.

Wow thanks. It really helped me putting words on what I'm feeling when I'm driving and testing different springs. I understood your exemple with the platform but it was really nice to try with a balance.

So i guess i get more grip with lower ride height because of cog and how the camber change and a arm works. I didnt play alot with oil. I put 40 in front and I'm 30 in rear. It changes things that springs doesn't. I'm 2wd so the weight shift when accelerate is brutal. It was to fast with the 30. Stiffer springs made it incontrolable in fast straight and with softer spring the rear lifted in heavy turn or breaking. Heavier oil slows down the weight shifting a bit and its better.

And i feel that wether its spring stifness or preloads, balancing the front and rear suspension is key. It really works together. Thats my experience from now.

I guess speed is a game changer too. With speed the weight of the car is adding up in turns. I'm only on 14/90 gearing and 2s right now. I guess when i turn at high speed the springs conpress more than at low speed.

The violon is a great exemple. Do you think i absolutely need preloads tho ? Can only the spring be enough ? I would say that the spring rate might be to high.

I tried something yesterday. I put the stiffer springs in the back with preloads to compensate the missing lenght. It was slighly compress and i liked it. Do you think it does the samething as the real rear spring ? They are progressive tho. Since spring rate dosent change I feel that its the same thing if it was linear (unless the smaller spring compress 100%) but not so sure about progressive.

In conclusion i think i just want more suspension travel haha. Longer shocks but mounted a bit higher on the shock tower or closer to the wheels so the a arm can work similar.

If i was racing itnwould be easier. I drive on all terrain so I'm trying to get a good all around suspension so it can't be always perfect everywhere.

Thanks again !

 

[Lumikko]

So i guess i get more grip with lower ride height because of cog and how the camber change and a arm works.

And i feel that wether its spring stifness or preloads, balancing the front and rear suspension is key. It really works together. Thats my experience from now.

I guess speed is a game changer too. With speed the weight of the car is adding up in turns. I'm only on 14/90 gearing and 2s right now. I guess when i turn at high speed the springs conpress more than at low speed.

The violon is a great exemple. Do you think i absolutely need preloads tho ? Can only the spring be enough ? I would say that the spring rate might be to high.

I tried something yesterday. I put the stiffer springs in the back with preloads to compensate the missing lenght. It was slighly compress and i liked it. Do you think it does the samething as the real rear spring ? They are progressive tho. Since spring rate dosent change I feel that its the same thing if it was linear (unless the smaller spring compress 100%) but not so sure about progressive.

Yes, a lower ride height improves grip because it reduces load transfer. Your overall grip is at its highest when each tire carries an equal share of the load. Any change to this (cornering, braking, accelerating, uneven surface) is a disadvantage that we try to minimize. Load transfer takes more grip away from the unloaded tires than it gives the ones with increased load.

You are absolutely on point about the effect of speed on load transfer. Or not so much the speed but rate of acceleration. (When cornering, you are accelerating in the direction you want the car to go and decelerating in relation to the direction you were going in, even if you maintain a constant speed thru the corner. This may be nitpicky or help to understand what’s going on. Ignore if necessary.)

Increased rate of acceleration increases load transfer to the rear wheels when going straight, and outer wheels when cornering. Here’s an important fallacy to avoid though: lowering your speed would reduce body roll in a corner because of a lower load transfer. Lowering the ride height also reduces body roll and load transfer. But if you reduce body roll with other means (higher roll center, stiffer springs, thicker sway bars) you are increasing load transfer. Don’t get confused between the two. Simply observing ”more roll / less roll” in a corner or ”more nose-down / nose-up” on braking / acceleration doesn’t necessarily tell you if there’s more load transfer or a faster load transfer going on, or the opposite.

For example: if you put stiffer springs in the rear and this causes the car to jump forward with less squatting when you give it throttle, there’s more load transfer going on even though the body moves less.

Balancing the front and rear is exactly the key. A balanced car will handle better even if you don’t have the shock package optimized for all surfaces.

You don’t necessarily need to preload the springs if the ride height is right. It’s common in race cars for the springs to rattle up and down when the shocks are fully extended.

While we’re on the topic and I feel like rambling, here’s another thing about a load transfer: for a given center of gravity and acceleration, the amount of load transfer will be the same: it’s unavoidable. What we do with suspension geo, springs, sway bars, and shock oils is change how quickly it happens.

Geometric changes can cause the load to transfer instantly and we can set definite stops to how far the body rolls. Springy things transfer the load more gradually and we can set buffered stops to the amount of body roll. Shock oils tune how fast the body moves within the window set with other means. Also, shock oils transfer load more quickly when the movements are rapid.

To say tuning a race car is complex would be an extreme understatement. I have two books in my bookshelf which I reference at the track, and I’ve watched hours and hours of video lectures on Youtube from various sources to get my head around it. At this point, I’m experienced enough to realize that there’s a long road ahead of me before I would dare call myself an expert. Take my advice critically, I’m really just an amateur throwing guesses in the air.

 

[cocoune]

To say tuning a race car is complex would be an extreme understatement. I have two books in my bookshelf which I reference at the track, and I’ve watched hours and hours of video lectures on Youtube from various sources to get my head around it. At this point, I’m experienced enough to realize that there’s a long road ahead of me before I would dare call myself an expert. Take my advice critically, I’m really just an amateur throwing guesses in the air

At least its specific. Right now i just randomly turn and say "oh i like it" lol

I tried to put more preloads recently. I was scared at first but now that i have a better understanding i tried it and liked it. I just try to find the right spring and adjust the height how i like it.

 

[CertifiedMike]

Hi, welcome to the hobby! There's SO much to learn! Go slow, research often! Resist the urge to buy buy buy upgrades! At least for now. You have plenty of time for that once you know better what you need.
Definitions and explainations.
A constant rate spring is a spring that has even spacing between coils. This rate does not change with compression, hence the name.
A progressive rate spring has some coils more close together than others. This spring's rate does increase with compression, progressively.
Spring rate does not change irrellevant of the angle of the shock relative to its mounting points.
The shock rate DOES change relative to that angle.
A shock mounted in a more linear angle will perform more consistantly thru the stroke than a shock mounted at an angle.
A shock using the inner mounting holes of the a arms and the outer holes of the tower will be more consistant SHOCK rate.
There is also the roll bar to be considered here.
The information about the weight transfer and balance are also important and accurate as previously mentioned here.
Ride Height Issue.
It does sound like you may have a pair of springs that is too light for your car. With constant rate springs, this is easy to see because the whole spring crunches up and your car is on the floor.
With progressive rate, it is harder to see the issue because half the spring is crushed and the other half is still good to go. If I read correctly, this was part of your issue?
Stiffer progressive rate spring would cure this issue.
Handling Issues.
If you are experiencing wonky handling, for now, go back to constant rate springs.
Figure out where your roll bar needs to be adjusted to and get your shocks mounted correctly so you have consistent handling and even control. Make sure your car isn't bottoming out super easy and isn't ultra stiff. This is a great starting point.
Start from neutral (middle) settings where adjustments are allowed.
make sure your caster and camber are also set correctly. These will obviously effect your handling.
Make SMALL adjustments and take notes until you know how your adjustments change your handling and if you love or hate it.
Slop.
Tighten loose screws. USE LOCKTITE! I use blue because I bought it 10 years ago and haven't run out yet to try green.
NEVER RED! Its like cement!
While you are fidding around with everything, look for slop in the suspension. you can find it in hinge pins, pillow balls, shock mounts etc. You want ALL that play gone while still allowing for full, smooth suspenion travel. Shim shim shim!!! Replace worn parts and make sure your servo saver is tight enough to not allow your rigs to shoot left or right on a landing.
Whether you are running your buggy or fixing it ALWAYS check for bent, broken and cracked parts hiding about! Junk bearings, improperly fitted wheels etc WILL throw your handling off.
After you have all this set up, if you still don't like your handling, then play with the fancy springs. They may turn out to be the winning tick, but ALL the stuff I just mentioned is free (or cheap cheap) and important, BEFORE you go buying new stuff.
Personally, I enjoy building these things as much as I enjoy running them. IMO, they are about a 50/50 mix of maintaining and upgrading/running, racing or bashing in my case.
There's a LOT that you can do to improve your car with a few washers, some locktite and scraps of lexan (for thin shims)
There's a LOT to tuning. I don't mean to overwhelm.
In my 1:1 truck, I removed the factory progressives in favor of constants. Its a Denali Envoy that drove like my 84 Deville.
Now it drives more in line with how I feel a "performance" vehicle handles. I am very happy with the results. Off road, the truck no longer drives up over a small bump and on the down side feels like we just landed from falling off a cliff.
My 1:1 Focus has H&R progressives and its pretty bouncy even with FRP struts and shocks.
Progressive rate springs belong on the street in my 1:1 opinion at least. They may indeed offer a smoother overall ride but this isn't relevant for an off road rc.
All that said, I've yet to try a progressive spring in r/c as I run offroad, bash 99% of the time. I am toying with the idea of a set to try for a Frankenbuild though.
Good luck!

 

[cocoune]

A shock mounted in a more linear angle will perform more consistantly thru the stroke than a shock mounted at an angle.
A shock using the inner mounting holes of the a arms and the outer holes of the tower will be more consistant SHOCK rate.
There is also the roll bar to be considered here.
The information about the weight transfer and balance are also important and accurate as previously mentioned here.
Ride Height Issue.
It does sound like you may have a pair of springs that is too light for your car. With constant rate springs, this is easy to see because the whole spring crunches up and your car is on the floor.
With progressive rate, it is harder to see the issue because half the spring is crushed and the other half is still good to go. If I read correctly, this was part of your issue?
Stiffer progressive rate spring would cure this issue.
Handling Issues.

Right now my shocks are mounted in the inner holes of the a arm. Sadly the slash 2wd dont have other mounting holes on the shock towers... I like that setting because i have a higher cog. I tried other settings with the stock a arms tho. I might try something new soon.

Its not that i really have an issu but i always feel so close too a sweet spot. And i can't stop changing springs every time i go for a run xd i have a set of 3 hot racing progressive springs. Red, silver and black and i have linear rear traxxas spring (i dont know the rate but it feel abit like the silver ones" today i tried something. Its funky looking and maybe "bad" in theory but it feels great. I put the red ones (softer) in the rear with a poop load of preloads lol and silver in front with no preloads. Silver felt a bit stiff. it needed some preloads too i think.

Yesterday i had the traxxas linear innthe rear with few preloads and the reds hr in the front with few preloads too. I think this set up was the best so far but the red in fronts felt a bit to soft. Tomorrow ill try to wierd looking rear like today with the red in front to see how it balance.

Like i said, today i tried someting funky but since I'm not scared to put preloads anymore it really help me. I like riding high and car handle better on extreme rough terrain. Before i felt that softer springs with preloads was similar to just stiffer springs.

Like you said, linear springs are more easy to understand when drive. Progressive springs is a bit like magic and sometimes the car do unexpected moves.

In my case the wider a arms completely change how my suspension is working. I have so much levrage and the wheel can go higher and lower.

What i found is that i really need to set my riding height how i like it and then watch how the car handle. 40 wt oil in front really help too because the weight transfer was too fast.

BEFORE you go buying new stuff.
Personally, I enjoy building these things as much as I enjoy running them. IMO, they are about a 50/50 mix of maintaining and upgrading/running, racing or bashing in my case.
There's a LOT that you can do to improve your car with a few washers, some locktite and scraps of lexan (for thin shims)

Oops i just bought big bores for the rear just "because" hehe. I have a bent (that i unbent) shaft so i was like why not. My lhs responded to alot of my questions and i felt the need to buy something xd i didnt get the gtrs because I'm pretty sure its gonna rub on the camber link in the rear and the shock tower innfront. I like the preloads clips too because its easy to set the exact same height on every shocks. And i already have few springs. Gtrs need bigger springs. I know it wont fit right away on the big bores (my lhs said it will) but its an easy fix.

Thanks for your reply

I'm all with you on the easy and free/not expensive tunning. I'm 50/50 like you and i can't go out without trying something. I put a metal sheet on my rear skid plate instead of buying the rpm and found a cheap way to lift the clipless body.

 

[CertifiedMike]

I'm sure there are lots of ppl who are more familiar with a Slash platform than myself. I have a Jato and a Revo Nitro. Both of them have the GTR shocks. I have always been happy with them.
If you have bent/broken parts... THIS is the time to upgrade! Be sure to look for the CAUSE of the breakage as well as a stronger fix for the broke parts and fix the cause too. That is what I meant by "knowing what parts you NEED"!
If the shocks on the Slash are known crap, go ahead and upgrade! I would bet lots of ppl here can tell you about fit. Maybe some can tell you what color springs they run.
Keeping good ground clearance is important for off roading. Just be sure "stiff" isn't TOO stiff. The car shouldn't be bouncing or struggling to get whole suspension travel.
It sounds like you are well on your way to tinkering out a solution to your own question.
The best part about r/c is that youreally can't do it wrong! Even if you crash and break stuff it will be a learning experience when you repair it and figure out why you crashed. Still a WIN!
Its when I see ppl buying a kit and immediately deck it out with a bunch of aluminum or expensive race parts or whatever that just don't suit the purpose of the build... thats when I feel like this hobby can be a bit "dangerous" to the wallet.
I just bought a few sets of Traxxas springs recently. They were cheap enough that I feel comfortable recommending that you buy a few sets to try just to experiment with.
Generally, if the front is a bit stiffer than the rear, the handling characteristics work well for most ppl.
NEVER be intimidated to do ANY work to your kit. Take pictures or notes during disassembly and get advice like you have here.
I'm sure pretty much everyone here has broken a part, stripped a screw or purchased a part that we didn't actually need. Live and LEARN!

Btw, the RPM brand is in general a GREAT brand! When upgrading/repairing, they would be my first choice over stockers.

Btw, the RPM brand is in general a GREAT brand! When upgrading/repairing, they would be my first choice over stockers.

The body lift is clever as well! You got this!

The body lift is clever as well! You got this!

 

[Lumikko]

Spring rate does not change irrellevant of the angle of the shock relative to its mounting points.
The shock rate DOES change relative to that angle.
A shock mounted in a more linear angle will perform more consistantly thru the stroke than a shock mounted at an angle.
A shock using the inner mounting holes of the a arms and the outer holes of the tower will be more consistant SHOCK rate.

I’m not sure I understand your point as you meant it but this sounds a little odd to me.

In my mind, the shock rate (piston, oil) and spring rate are what they are. It doesn’t matter if the ends are mounted in the inner or outer or upper or lower holes. The shock could be sideways or upside down. Doesn’t matter.

What does matter, and what changes with the mounting points, is the mechanical advantage the lower arm has over the shock.

The suspension – the whole thing, not just the shock – resists compression more when the shock is at a steep angle and this peaks when the lower arm and shock are square at 90 degrees in relation to each other. Another thing that increases resistance to compression is a mounting point closer to the wheel end of the arm i.e. the outer holes.

Conversely, leaning the shocks in makes the suspension less resistant to compression. So does moving the lower mounting point of the shock inward.

Changes to the upper and lower mounting points may affect ride height, droop, and uptravel, but these are just side-effects. The effect we’re really looking for with shock angles is a geometric progression, if you will. A more upright shock ramps up the stiffness more quickly as it gets closer to 90 degrees. Many drivers describe this as better ”support” against body roll. Leaning the shocks in makes the roll more ”bottomless”, like you compress and compress but the suspension stays relatively soft. Maintaining the angle and moving the shock out makes the suspension a bit harder. Moving it in does the opposite.

The whole shock including the spring is compressed by the lower arm. The lever doesn’t know what it’s up against and it’s frankly impossible for these changes to affect only the damping action (shock rate) of the suspension and not the elastic action (spring rate). Moving the shock around affects both qualities of the suspension.

 

[CertifiedMike]

I think you are correct. I was cutting and pasting some. My proof read sucked!
Let me try again.
The spring rate and oil weight remain constant at any angle the shock is at.
The angle or lever effect will increase the rate of oil trying to flow through the dampers (the holes in the shock dampers) faster at an angle and becomes slower as it straightens in relation to the control arm. This creates a progressive effect on the oil flowing through the damper. The spring rate (provided is a constant rate spring) will remain constant thoughout the stroke, irrelevant of angle.
The location of the shock mount will certainly change the effects it has on itsride height as well as its overall ability to properly suspend the vehicle.
I am sorry if I mispoke. I haven't been back on forums for very long. I should know better than to post while over tired.
I certainly don't claim to know it all. I have not been on a track in a long time and I am rusty.
Thanks for making sure I'm not doing more harm than good!

 

[Lumikko]

The angle or lever effect will increase the rate of oil trying to flow through the dampers (the holes in the shock dampers) faster at an angle and becomes slower as it straightens in relation to the control arm. This creates a progressive effect on the oil flowing through the damper. The spring rate (provided is a constant rate spring) will remain constant thoughout the stroke, irrelevant of angle.

The progressive damping effect you describe affects the suspension rate as well.

The suspension is easier to compress with inclined shocks compared to more upright ones. This is because the mechanical advantage the arm has over the shock changes with the angle.

Another way to put it: when the shock is angled, moving the hub up and down causes a smaller movement of the shock. When the shock is upright, compression of the shock pushes the piston further into the shock. The spring rate is the same but we’re compressing it further -> higher apparent spring rate and damping rate.

 

[CertifiedMike]

This is correct but the rate at which the spring compresses within that apparent change remains constant thoughout its stroke. The lever effect may change the apparent effect of the shock as an assembly.
If I am failing to explain this correctly, I appologize. I am pretty sure I understand what you are saying and i believe it is correct.
I THINK we are splitting hairs as the effect I am refering to is only the spring rate in this case. Thats why I tried to break it down in parts.
Perhaps I have the whole thing wrong but I'm failing to see how any lever pressed against any spring should change the rate of the spring.
I'm really just trying to understand. I will try to research further to see where i could have it wrong.
Again, thanks for helping. I am also here to LEARN!

 

[Lumikko]

We’re definitely in the same boat, learning and trying to convey ideas via text only.

I think I got your point a little better after reading your previous post again: shock angle affects damping rate because it changes the speed of the piston i.e. the piston travels a longer or shorter distance per a given amount of suspension travel.

When the piston moves a longer distance there’s less force behind it. So it also makes the spring appear harder.

The rate of the spring itself or damping rate of the shock remain the same. The angle of the shock in relation to the lower arm changes both of these when looking at the suspension travel, not just shaft movement.

A more angled shock makes it easier to push the chassis to the ground. Upright, it’s harder. It’s a leverage ratio just like there’s a gear ratio: more rpm means less torque and vice versa. More piston speed also means less force pushing the piston.

 

[CertifiedMike]

I think this is all correct as well.
Without a chalkboard and a professor far wiser than myself, we (at least I) may be unable to explain any better!
Again, thanks for making sure WE ALL understand!