Zero lift braced front suspension for d21

[seang]

Hello, I have been tossing around this idea for a few hours now, and it would definitely afford less weight, and zero lift capabilities through the removal of the sway bar, bump stops, and torsion bars. Welding in a brace made of plate steel between the lower a arm and bump stop boss, therefore freezing the lower a-arm in its place. The idea here is for autocrossing. The tires would take the shocks, as would your kidneys, but what enthusiast wouldn't mind that in the name of 3 seconds off a lap time. IDK, this is a serious idea for me. Its brutally effective, and simple in theory. I would expect some harshness on bumpy road surfaces, but thats a given. Also, I belive it would still be possible to remove and change the lower ball joint if neccessary if there is still enough room to swing the upper conrol arm upwards a bit. Just imagine sailing over some railroad tracks at speed with no front end swash. What do you think?

Note: I am updating this this many months later to say that it was only an idea, I do not recommend you try this on anything you want to last, or be safe. -SeanG-
Modified by seang at 11:54 PM 2/5/2010

[seang]

Also, one could add bigger bump stops in the stock locations. Bigger upper bump stops would give a "zero lift" during hard cornering. Beefier lower bump stops would limit compression of the already soft stock suspension. The only downside to this setup would be the possible distortion of a-arm bushings under load from being smushed, f*** it, if poly bushings distort, run steel bushings, thats what they do in Fiero's rear suspension to limit bump steer. For now, I haven't tried these things, they are only a theory, so as far as I know, rubber or poly a-arm bushings would already be enough, IDK.

Note: I am updating this this many months later to say that it was only an idea, I do not recommend you try this on anything you want to last, or be safe. -SeanG-


Modified by seang at 11:55 PM 2/5/2010

[PEZi]

i would not mind doing this... but it would have to be after i get my other mods done and thus out it on a trailer...

i'd never ever want to drive this on the street

[seang]

You would really have to watch out for potholes with the first idea, the more I think about that one, the less I really like it, although it does work on go-karts. **** The second one might be more practical for daily duty, as you would still have the torsion bars. This would even complement the soft stock torsion bars because the custom bump stops would be taking alot of the hit, this setup would not even be that harsh on the street, after all bump stops are made of rubber.

[seang]

Here are my lower bump stops I just made yesterday, I had some triangular ones lying around from the rear axle of a 1972 Mazda B1600 that I trimmed the round side off of. They are working good, even with stock blown out shocks and stock soft torsion bars, the fron end does not dip down so far into the road surface like it used to. Keep in mind this was done with spare parts I just had lying around and cost me nothing, although you could get any big beefy ones or just pieces of good rubber, and trim them to fit. The upper ones are still stock, as I would like some extension for off road driving.
Modified by seang at 2:53 PM 8/8/2009

[2kredz3]

what is more important then limiting bump would be limiting extension. by a set of limiting straps and adjust them so you have 1" of downward travel. i bring this to you from BMW tuning, from the factory a bmw usually has around 2" of upward (compression) travel and 10" of extension this is what gives the boat effect on the ride. just by limiting the extension you will gain 10X what even the stiffest sway bar you could find would do it would eliminate your body roll and still give you control over uneven surface.

[2kredz3]

or for that matter you could just extend the upper bump stop as well to limit downward travel, problem there is you can creat a situation where the ball joint pulls apart because all the spring load will be on the ball joint.

[seang]

Good point about the ball joints. I took it for granted that a performance minded individual would want to replace their sloppy ball joints with new ones. New ball joints had better not be able to just pop apart, because the front tires will come off the ground. If they were in that bad of shape, even jacking the front end up would cause them to seperate. Ball joints should not have any up and down movement, or very little.

[Red coupe]

This just sounds like the dumbest idea ever?Have you ever seen ANY race car ever that had no suspension? thats effectively what your doing if you lock the lower control arm...

Sure karts have no suspension, but that is because the chassis is designed for it, and allowed to flex to compensate.

Suspension is there for a reason, stiffer is not only better... It should only be as stiff as need be to control the body, going stiffer is just making the tire skip over bumps and losing grip.

Bump stops should be a safety thing to keep from breaking the shock, but you should not be running on them.

I also wouldn't be too supprised to see a bent control arm if you took out all give from the springs.

[seang]

I think you're kind of right Redcoupe, albiet on the safe side. I think limiting extension/compression by using higher profile bump stops or using limiting straps is probably the only really good idea here. I'm happy with my homemade lower bump stops, (pictured a few posts above), they are almost the same height as stock, (The stock ones rotted/fell off). I want some extension as my truck is a 4x4, so the uppers are gonna stay stock.

Modified by seang at 2:52 PM 8/8/2009
Modified by seang at 2:58 PM 8/8/2009

[seang]

what is more important then limiting bump would be limiting extension. by a set of limiting straps and adjust them so you have 1" of downward travel. i bring this to you from BMW tuning, from the factory a bmw usually has around 2" of upward (compression) travel and 10" of extension this is what gives the boat effect on the ride. just by limiting the extension you will gain 10X what even the stiffest sway bar you could find would do it would eliminate your body roll and still give you control over uneven surface.

Just wanted to promote this^

[Red coupe]

Why would you ever want to limit extension?!Maybe I am wrong here, but you can't compare that to a sway bar...yes a sway bar is some what lifting the inside wheel, but that is the bad part of it, that is what you give up to increase roll stiffness with out increasing spring rate so that the suspension can still absorb bumps instead of bouncing over them....

Body roll is a function of spring rates, wheel base, cg location, roll axis inclination and height and track width. Limiting the extension of the inside wheel will not limit body roll, it will just put less pressure on that wheel giving it less grip.All your doing is helping lift the wheel off the ground, and putting more weight on the outside tire. The force produced by tires is not linear with the weight put on them. Loading a tire with and extra 10 pounds produces less grip then is lost by removing 10 pounds from the load, so there is always more grip when the load is shared as equally as possibly.

Since it would be foolish to trust me alone, let me take the words of a MUCH smarter man, Carroll SmithQuote »We want our springs to have length sufficient so that the spring will not become unloaded with suspension at full droop. The reason for this usually overlooked parameter is that, when the suspension is fully extended, the car is usually flying through the air. When it lands, we want the springs to begin their resistance to compression immediately. If the suspension has to move a finite distance before the spring begins to compress, then a greater amount of suspension travel will be required to absorb the force of landing and we will have to run our ride height higher then we would have to if the springs had be properly designed. Not Good![/quote]Slight variation here, as he is speaking about a spring that is shorter then the stroke of the shock, however while the case of a preloaded spring lifting off the ground is slightly better the principal still applies. the whole car doesn't have to be off the ground if your thinking of each tire individually, and you are still giving the mass of the car a "running start" at compressing the spring.

He continues on the subjectQuote »Another side of the same coin is the fact that we wish to be pushing each of our tires into the track with as much force as we can arrange at all times. If a spring is so short as to uncouple in some combination of droop and roll then that tire is unloaded at a time when the spring could have been loading it This can lead to such things as partial loss of traction at one end of he car and inside wheel spin.[/quote]These were taken from "Engineer to Win - Understanding Race Car Dynamics"

BMW may have less rebound travel then compression... But I think we can agree that not only do you not drive a BMW, you drive a Nissan truck with a different suspension set up and design up front, and an ENTIRELY different suspension set up in the rear.Apples and Oranges.

[seang]

I was only suggesting the Torsion bar front suspension on the HB and Datsun series pickups. I wasn't suggesting anything for the rear leafs here. I can see about coil springs suddenly loading from beyond full extention and creating indesired and possibly unsafe conditions upon re-seating and re-compression, but torsion bars shouldn't unload like a coil spring. For example, a torsion bar extends to the limit, and still has some pre-load.

Note: I am updating this this many months later to say that it was only an idea, I do not recommend you try this on anything you want to last, or be safe. -SeanG-


Modified by seang at 11:57 PM 2/5/2010

[Red coupe]

I was only suggesting the Torsion bar front suspension on the HB and Datsun series pickups. I wasn't suggesting anything for the rear leafs here. I can see about coil springs suddenly loading from beyond full extention and creating indesired and possibly unsafe conditions upon re-seating and re-compression, but torsion bars shouldn't unload like a coil spring. For example, a torsion bar extends to the limit, and still has some pre-load.

Modified by seang at 5:08 AM 8/9/2009

Modified by seang at 5:12 AM 8/9/2009

Slight variation here, as he is speaking about a spring that is shorter then the stroke of the shock, however while the case of a preloaded spring lifting off the ground is slightly better the principal still applies. the whole car doesn't have to be off the ground if your thinking of each tire individually, and you are still giving the mass of the car a "running start" at compressing the spring.

You are still dropping the car back onto the suspension, rather then easing it in. Think of swinging a hammer vs just pushing on something with it.

But much much more importantly then that... Why would you ever want to unload the tire when it could be pushing into the pavement creating grip?

I commend you guys for thinking outside the box... but I can't help but feel you guys need a better understanding of the subject before trying to go so unconventional.