Standard Suspension Bump Travel

[bfrank1972]

Originally Posted by Dezoris

This is a good thread for sure!

I just torched my springs, the good thing is you heat them up enough it also shrinks the bump stops and you get a great drop and fix the size of the bump stops without cutting.

What's with the sarcasm? Nobody here's suggesting anything like that.

[Suberman]

Originally Posted by bfrank1972

What's with the sarcasm? Nobody here's suggesting anything like that.

There are idiots everywhere. Trouble with sarcasm is it demands a fairly high level of intelligence to actually use it effectively. In the wrong hands it cuts like a knife, the hands of the guy holding the knife.

This is a truly excellent thread with very valuable information.

Huge thanks to racecompengineering. Anyone contemplating dropping big bucks on coilovers should read and absorb what those guys are telling us. For free I might add.

[86•BRZ]

Originally Posted by Suberman

There are idiots everywhere. Trouble with sarcasm is it demands a fairly high level of intelligence to actually use it effectively. In the wrong hands it cuts like a knife, the hands of the guy holding the knife.

This is a truly excellent thread with very valuable information.

Huge thanks to racecompengineering. Anyone contemplating dropping big bucks on coilovers should read and absorb what those guys are telling us. For free I might add.

I don't start threads often. But when I do I make sure it's a good one!

It's info like this that really brings to light the importance of actual on car testing of springs and "coilover" systems.

So many coilovers are based on specs derived from... well who knows...

Knowing that the bumpstops play such an important part in the suspension tuning of this car is now obviously pretty important.

[DougW]

I agree 100%, the effort we have been putting into the Damptronic Bilstein program has added special camber plates, spring mounts and maybe even a new diff with torsen and clutch pack to solve what I ran into once I lowered a car 2". This left me wondering how others made it work, they don't they load up bumpstops and don't balance full travel spring rates based on full travel of both ends. The entire suspension is a system that everything has to be treated interactively or it just doesn't work together. Track testing, road testing and lots of cad work is the only way to do it right the rest is just good marketing. In almost all professional racing bump stop control is as important as shock valving. Sorry for the rant, to much time with the inlaws I guess
DougW

[7thgear]

Cars have springs and dampers that help them go along their way.
If you are still fuzzy on the hows of springs and dampers, http://www.howstuffworks.com/car-suspension.htm is a good place to start.

The reason I made my comments at the beginning is that none of this should be of any real mystery if one understands the responsibility of springs and dampers in a car.

It is the same as reading a baking recipe that asks for 10 grams of salt for every 100 grams of flour, and then asking how much salt you need if you’re using 200 grams of flour.. the question becomes not one of recipe but of basic math.

But I digress.

A few point notes for assimilation:
- A spring has a rate, this rate determines the speed at which weight transfer occurs, the stiffer the spring, the faster the weight transfer.
- Linear spring rates are a nice thing, they make life predictable.
- Many things can act as a spring… or an energy absorbing device, if you will

Moving on.. all damper/strut systems have some form of bumpstop to prevent the shaft of the damper from punching through the bottom, it would be dangerous to design a mass product without such a consideration (although I’m sure F1 doesn’t have these limits.. but who knows).

The question becomes what to do with that bump stop.

“coilovers” (as we know them), typically have higher spring rates that are linear. If chosen CORRECTLY for the application, then the damper should never bottom out, the springs should never coil-bind, and the bumpstops serves its intended role as a last resort safety mechanism to preserve the damper in the event of an unforeseen shock to the system.. such as hitting a raised curb or running over debris.

The term “being on the bumpstops” is meant to describe those situations where you’ve run out of suspension travel. Your springs were too soft, your damper travel was limited, or both. You are now resting on the bumpstop, and your car is no longer suspended. Any subsequent attempt at absorbing a bump is left with the chassis doing the work and eventual failure of components that overwise would have lasted a long time.

However, on an OEM car, the term need not be understood as it is the racing world. This is because, as demonstrated most often in a macstrut car, the bumpstop also acts a secondary spring with a progressive rate approaching infinity.

This accomplishes a number of things:

1. For minor two and single wheel bumps and dips in the road, your car is utilizing only its springs, this is essentially “the softest setting”
2. when you attack a turn, you engage your bumpstops which increases the effective spring rate, this helps you “set the car” faster and helps fight body roll (not the same as reducing it.. but that’s another topic)

*because they are progressive and soft, you do not feel them engage and there is no jarring "bang" (when you bang that means you've run out of ALL travel.. the bump was too much for your entire spring "system).

3. functions as a safety mechanism for the damper once it is compressed to a maximum point

so as you should see, it is a solution to the everyday problem of mass produced cars and how to make a sports car comfortable during the daily drive.

Now the problem with “lowering” springs is that they “lower” the car on to the bumpstops, which now become engaged ALL the time. So you no longer have a soft spring setting for daily driving, you are now permanently set to a high spring rate mode.

“lowering” the car 2 inches or whatever is downright ludicrous for street driving because you’ve eliminated any real suspension travel and your rates are approaching infinity at this point, so unless you’re driving on glass roads this is a joke.

You can “cut” a hard portion of the bumpstop to give yourself more room to travel, but you haven’t solved the problem of utility, you may have made the car bearable in a straight line on city streets, but you’re not stiff enough to avoid resting on the bumpstops during cornering… so whenever you corner hard, you’re relying purely on the grip of your tires and the strength of your shock towers to hold you in place. This is not efficient.

So, that’s that.

[Calum]

Originally Posted by 7thgear

You can “cut” a hard portion of the bumpstop to give yourself more room to travel, but you haven’t solved the problem of utility, you may have made the car bearable in a straight line on city streets, but you’re not stiff enough to avoid resting on the bumpstops during cornering… so whenever you corner hard, you’re relying purely on the grip of your tires and the strength of your shock towers to hold you in place. This is not efficient.

So, that’s that.

First off thanks for the explaination. Can you explain how the bolded section differs from the OEM setup?

[bfrank1972]

Great post, thanks!

Basically I was under the impression that oem cars were like your first "scenario", as in the car should be suspended by springs and never touch bump stops unless some fairly rough pavement is encountered during cornering. I now realize, thanks to the informative posts in this thread, that bump stops in our cars play a major role in how the car behaves at the limit. My confusion is, why do people concern themselves so much with f/r spring rate differences on our cars when in reality the bump stops are playing more of a role at cornering limits? I would think springs and bump stops should be "matched", I.e. stiffer front springs should have somewhat stiffer bump stops - the stops still give progressively but at a steeper rate. Or maybe at that point there is so little travel left it doesn't matter?


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[7thgear]

Originally Posted by Calum

First off thanks for the explaination. Can you explain how the bolded section differs from the OEM setup?

the oem setup still has a progression, when you're doing an offramp at a comuter pace you're not overloading your setup

should you encounter a bump in the road or obstacle, your suspension still has room to compress and absorb as much of that as possible

if you're at the limit, then it's your tire doing all the work, and a serious bump will make you lose traction out-right

[7thgear]

Originally Posted by bfrank1972

My confusion is, why do people concern themselves so much with f/r spring rate differences on our cars when in reality the bump stops are playing more of a role at cornering limits?

spring rate balance is important... if you have it

so a 800lb spring coilover with 2-3" of damper travel can handle 1600-2400lb of force being thrown around...

but if you have NO DAMPER TRAVEL then you are right, spring rate balance is moot because you're at infinity anyway.

so the good turners are the ones that have the entire package worked out

the bad tuners are those that just dump the car and throw up fake gang signs

a top of the line coilover isn't gonna work very well if you slam it to a point where it has no actual motion.

[solidONE]

I've personally cut the small ends of my stock bump stops when I installed my Swift lowering springs. While that affords you more travel before touching the bump stops (about 3/4" ~1" or so on the compression stroke), that would result in a more abrupt change in the rates once the suspension is compressed to the point of touching.

This kind of explains the increased understeer (really not that abrupt) I'm getting at turn in after installing the springs. Although, if I hadn't cut the bumpstops when installing the lowering springs, the bumpstops would have engaged much sooner in the compression stroke... this will theoretically induce understeer even sooner with less cornering force at a more gradual rate vs. a stiffer, cut bumpstop.

Maybe I should have done like dezoris and torched them.

[u/Josh]

How much shorter than stock are the bumpstops that come with RCE yellows?

[DarkSunrise]

Originally Posted by solidONE

I've personally cut the small ends of my stock bump stops when I installed my Swift lowering springs. While that affords you more travel before touching the bump stops (about 3/4" ~1" or so on the compression stroke), that would result in a more abrupt change in the rates once the suspension is compressed to the point of touching.

This kind of explains the increased understeer (really not that abrupt) I'm getting at turn in after installing the springs. Although, if I hadn't cut the bumpstops when installing the lowering springs, the bumpstops would have engaged much sooner in the compression stroke... this will theoretically induce understeer even sooner with less cornering force at a more gradual rate vs. a stiffer, cut bumpstop.

Maybe I should have done like dezoris and torched them.

Interesting. Will you be switching to coilovers?

[Suberman]

Cutting the big end of the bump stop would preserve the effective spring rate better than cutting off the softer, smaller end.

However, the point of this thread is to explain why ideally you need different profile bump stops if you fit different rate springs. You need different profile bump stops, ideally, if you fit shorter springs to lower the car.

A good argument can be made that higher rate springs would benefit from softer rate bump stops, provided the eventual resistance of the bump stop is adequate to provide a progressive rate right up to fully compressed.

If you lower your car without fitting shorter dampers you can bottom the damper unless the bump stop is adequate. Bottoming a damper will break it.

[Racecomp Engineering]

Originally Posted by fatoni

im pretty sure this is why you can buy coilovers with spring rates 5x that of stock and also have a better ride quality.

As long as they're valved well.

Originally Posted by u/Josh

How much shorter than stock are the bumpstops that come with RCE yellows?

20mm

- Andy