Ricehornet

Umm, yeah.

First off, i dont know if it's the correct term for what im about to ask, i figure, it about the suspension moving, therefore, travel....suspension travel.

I was thinking about what T.O.O said in one of his archieves...he mentioned that Mugen only lowers the car 20mm or so..so from that i was thinking.....why do people slam their cars so low....aside from the looks, doesnt this hurt the car, because it doesnt allow the whole shock to work, nor does it allow the rest of the suspension to move around, before the car bottoms out.....

Like, how low is too low? and what is happening when you lower the car too much? Go into detail if possible, and be technical if need be. Things i would be interested in knowing include, shock stroke (short vs normal), bumpstops, ride height, spring perch settings(koni) and it's effect on shock stroke, spring lenght......and anything else you can think of with suspension travel...or at least, what i think is called suspension travel, please enlighten me if i am wrong.

thanks in advance.

MechE00

I would guess that this might be more germane in the "Tech" forum, but who knows..

anyway the answer as to how low a car should be and how much suspension travel has the same answer that nearly every interesting question has-- "it depends.."

an F1 car will have rather little suspension travel at all, whereas a WRC car will have a whole lot more.. or to compare something with more similar speeds, Touring cars tend to be rather low and stiff compared to baha vehicles, even though top speeds may be in the same ball park.

Essentially a stiffer car responds more quickly in general, while a more softly sprung vehicle can better handle road irregularities while keeping good contact patch. If you threw equivalent tires on your car (wearing stock or near-stock springs) and the RTR Integra (with their _stiff_ springs), and then went out to "race" on some crappy, bumpy road, chances are your car would out-handle the RTR car.. (driver not withstanding).

Some problems with "slamming" a ride would include:
* can't drive on certain driveways, over certain speedbumps, over certain crowns in the road... i.e. insufficient ground clearance for the real world.
* if the suspension is too soft for the height it will allow bottoming out (I assume you know why that's bad for handling) F=k*x if the K is too low, and you can't get enough x, you're in trouble.. (bottoming out may occur in the shock before you get to the bumpstops also.. -- bad news for your shock)
* if the suspension is stiff enough for the height , it may degrade performance on rougher roads (as in the example above)
* tangentially, it's rare for people to match the damping to the spring rates properly, so poor damping may degrade handling

In addition to that, depending on your suspension geometry, you may be altering your wheel alignment and bump behavior into a bad regime (but I am _much_ less than familliar with any specifics.. I'm just extrapolating from my limited work with simple 4-bar mechanisms.. )

I'd much prefer to have pictures/diagrams to explain ride height's effects on bumpstops and shock stroke, and it's relationship to spring perch settings and spring lengths.. but if you just picture the strut assembly in your head and remember F=k*x (this is a simplification of the real formulae involved, but it's instructional), you should be able to figure it out. Since you're an engineering student (unless my memory's gone), see if one of your computer labs has a program called "Working Model".. it's pretty easy to learn how to use, and boy can it be fun..

done right, ride height decisions are a study in trade-offs.. done wrong, it's just expensive and dangerous.

SPiFF

I will leave the real technical details to others since I don't have my pile of reference books here to make me sound smart.

Since this is the competition forum, I will stick to suspension setup for road racing use more then anything. When you lower your car you need to make sure there is enough ride height to allow the suspension to travel its full range of motions. This will depend on how heavy of a spring setup you have and if it is progressive of linear.

In a corner, the cornerling load is transfered though the suspension to the spring .. causing it to compress. As the spring compresses, the damper is also compressing. I donno what all the different parts of the damper are .. but it has a body and a stem I guess. The stem is pushed into the body as the spring compresses. When you "slam" your car using coil over sleeves, cut springs, or wherever you are basically moving the spring down on the shock body pushing the stem down. Now when the spring is loaded up the damper is at its full compression, hits the bump stop, and the spring is not allowed to compress as far as it is needed. What you have now is a car with no suspension. Not good. Looks phat, but doesn't handle well.

Race cars can be lowered a lot and still have a working suspension becuase of 2 main factors. High spring rates and modified racing shocks that have different valving and are much shorter then street going versions.


[Modified by SPiFF, 11:02 AM 6/26/2001]

Ricehornet

Yeah i was going to put it in the tech forum, but i figure who would know more about real world suspension stuff than the competition folk
Yeah, and the answers i was looking for was not just technical explinations but examples from road racing/autoX and such, hence competition folder. since ya'll porbably have some experiences with this
great replies!!
thanks


So, hitting the bumpstop is an indication of suspension wanting to travel more while the actual position of the car does not allow it to because the shock is fully compressed? while the spring wants to be compressed more?
Hence why some of those $$$ shocks are "short stroked" like the neuspeed modified Konis, opposed to the regular ones, which is a reason why to get the shorted ones for coilovers which were ment to handel lower supension?


[Modified by Ricehornet, 3:49 PM 6/26/2001]

MechE00

Well, actually there are two ways of bottoming out.. i.e. 1) hitting the bumpstops 2) the shock bottoming out internally.

#2 can happen if you have your bumpstops trimmed incorrectly or some other installation issue, and is very bad for the shock. In fact, avoiding that is pretty much what the bumpstops are for.

hitting the bumpstop, yes, means basically that the spring rates you have (hypothetically) are insufficient to provide enough force in the stroke length available. And yes, if you shorten the body of the shock (and adjust the internals accordingly), but leave the overall undisplaced length of it the same, you are going to have more room before the bumpstops contact the shock housing.

I have no specific information regarding any Neuspeed modifications of Konis.