knutson@ut-ngp.UUCP (04/26/84)
There are lots of factors at play here. The most important being mass.
To have a car that is driveable, the wheels need to stay on the ground.
That means lots of movement on bumpy roads. To do this, you need as
low a mass as you can get for the suspension parts that move (e.g.
wheels, rims, A arms, etc.). To keep the body from moving with the
wheels, more mass would help but at a disadvantage for maneuverability.
Also, spring rates for the front and rear need to be balanced so you
don't start getting harmonic motion when passing over dips and bumps.
Shocks help dampen this out at the cost of having the motion in the
suspension transfered to the frame. The stiffer the shocks the more
motion that is transferred. Note that there is a difference in the
rates for shock compression and extension. Extension rates are faster
so that when a wheel is picked up, it can be put down on the ground
faster. Overall the whole situation is a compromise with sports
cars getting the performance and rough ride and big luxury
cars getting smooth rides and terrible performance. Most of this comes
from a book called "How to make your car handle" that can be picked
up in most speed shops. I don't remember who wrote it.
--
Jim Knutson
ARPA: knutson@ut-ngp
UUCP: {ihnp4,seismo,kpno,ctvax}!ut-sally!ut-ngp!knutsonseifert@ihuxl.UUCP (D.A. Seifert) (04/26/84)
The trick to having good handling is (a) good suspension geometry,
(b) good sprung to unsprung mass ratio, (c) sticky tires, (d) low
overall mass, (e) low center of gravity, (f) soft springs (surprise!)
(g) misc like good shocks
A good ride requires not (a1) large overall mass, but (a2) good
sprung to unsprung mass ratio,(b) soft springs, (c) misc like good
shocks
Problem is that good suspension geometry is HARD TO GET! Even
Formula 1 race cars have suspensions that are a comprimise(sp)!
Also, a good sprung-to-unsprung mass ratio is a lot cheaper to
get by increasing the sprung mass than it is by decreasing the
unsprung mass (alloy wheels and suspension pieces cost BUCKS)
Independant suspension helps a lot, but requires four additional
constant-velocity joints.
You may be wondering about the soft springs? These help keep
the tires in contact with the road, for better traction.
A tire floating around in mid-air due to stiff spring isn't doing
you any good. Rallye cars sometimes actually have springs *softer*
than stock!! The next question is "don't soft springs allow
lots of body roll?" The answer is yes, but that's what fat anti-roll
bars are for! and these don't hurt the ride like stiff springs do!
So what cars both ride well *and* handle well? Try something from
Europe. The best riding car I've ridden in was a Mercedes 300 Diesel.
(Infinitely better than Caddys or Lincolns!) I've received many
favorable comments on both the ride and handling of my BMW 320i.
A good book with info on both handling and ride is _H_o_w _t_o _M_a_k_e _Y_o_u_r
_C_a_r _H_a_n_d_l_e, I think the author's name is "Puhn".
--
_____
/_____\ That auto-crossing beagle,
/_______\ Snoopy
|___| BMWCCA, Windy City Chapter
____|___|_____ ihnp4!ihuxl!seifertwookie@alice.UUCP (Keith Bauer White Tiger Racing) (04/26/84)
Boy you really opened up a can of worms here!! Suspension design gets into some really heavy stuff (excellent for computer types! Let me know when you get some software for this one!!) There is an excellent book out by Colin Campbell entitled "New Directions in Suspension Design" or something to that effect. Anyway what you basically want is to reduce unsprung weight to the bare minimum ideally zero (I guess I should say unsprung mass). This is done by moving the brakes inboard as on a Jaguar. A nice place to see the ultimate in modern suspension design is on a Formula race car such as a Formula Ford. On the new designs the springs, shocks, brakes etc are all moved inboard leaving only the wheels, spindle and control arms hanging out in the breeze. Thus the unsprung mass is about as minimum as you can get. Also four wheel independent suspension is ideal so that the actions at one wheel will not affect another. To keep the car from rolling in a turn antisway bars are added which takes away from the independent suspension idea since it ties the right and left sides together and stops independent action and so you see suspensions must be a compromise of many things. Things you can do for your car are to reduce the unsprung mass by getting lightweight alloy wheels (real magnesium wheels like Minilites are great ......I can really see the difference in my race car just between the Minilites and aluminum wheels!). If you want more expense brakes parts can be substituted to reduce weight. Adding nice juicy roll bars will help keep the car flat on the turns but you must experiment with front and rear bar sizes to keep the handling as neutral as possible. If you can get some idea of the weight on each wheel and do some heavy calculating you can determine what the spring rates and shock absorber rates should be for your particular application. I can go on and on so if you have further questions we'll give it a try. You noted that a big boat like a Cadillac rides nicely. If you would like to do a comparison go drive a full size Cadillac like the Coupe De Ville (not a Fleetwood) and compare the ride to a Chevrolet Impala. The cars are essentially the same in size and the suspension parts are identical on both cars. The Cadillac however is much heavier and so the Sprung to unsprung weight ratio is much larger on the Cadillac and so it rides better. It won't corner however because of its great mass. So if you can get the same ratio as the Cadillac but at the weight of the Impala you will have a good compromise. This of course applies to small cars as well so look for suspensions with lightweight alloy parts like the new Corvette and inboard brakes like the Jaguar and lightweight like a racecar etc. etc. Unfortunatly these things are usually high tech and so are only on exotic cars but yes they are out there and can be found!! Keith Bauer White Tiger Racing
an@hou2h.UUCP (A.NGUYEN) (04/26/84)
-- Suspension design is always a compromise. You can have soft ride or good handling or li'l bits of each, but not both. It's a matter of what are you willing to put up with: a hard ride up I-91 thru CT, or sparks flying off your door knobs on Old Farms Rd. Au
rogerh@arizona.UUCP (Roger Hayes) (04/26/84)
The answer to "is there a car which will soak up bumps without falling off the road" is yes. Almost any french car is great at exactly this. This is because the french secondary roads are terrible, and the french like to drive fast. My personal experience is with Citroens and Renaults. I had a Citroen D19 for a while -- great, great car. Best suspension system in the world. The absolute standard for comfort in a car, and decent handling in its own dignified way. Unfortunatley, parts and service are totally impossible, so I bought a Renault 5 (aka Le Car). That was much fun to drive, still had a really good ride but felt perky. Sortof like a bumpercar. Underpowered, though. What do you give up? Well, French cars corner on their doorhandles. They stick to the road very well, but they tend to alarm bystanders. Also they are ususually underpowered, especially after federalization. You might check out the AMC Alliance, which is really a Renault built in America. Roger Hayes PS: I drive an MG now. The ride is awful, but it's exciting. I miss my R5 though.
lee@unmvax.UUCP (04/27/84)
Wow. What a question! Here's a couple of reasons:
Unsprung weight
travel
progressive damping (dampening?)
sway control
Anyway, these four things are pretty important when speaking of suspension
systems. Briefly:
Unsprung weight is the weight of the parts that are below the shocks.
Things like, the wheels themselves, brake parts, calipers, etc..
The heavier these are the less responsive the component is. The
faster you go the harder your shocks need to work to dampen the
motion and get the wheel back under control. It is pretty desirable
to have the wheel in good contact with the pavement at all times.
Travel. This is a measure of how far the wheel can pivot before it
strikes some part causing it to stop dead (read HARD jolt friends).
The more of this, the more time those shocks have to get things back under
control. Oh yeah, this is usually movement upwards by the wheels. Cars
don't fly, usually.
Progressive damping. Neat thing to have. When your toodling along
the highway the shock doesn't try to stop the wheel very much at the
start of compression. Makes for a nice ride. The harder you push
the car the further the wheels will travel. the shock gets stiffer
and hence the ride stiffer. Air shocks are great for this. They are
"infinitely" progressive. Air is not easily compressible. Thus, the more
you try to compress it, the harder is resists.
Going around a corner where the body wants to lift on one side is a BIG
problem. The shocks don't like to expand either, so they control this, though
usually well out of proportion to their resistance to compression. Sway bars
help in that they effectively tie (to a degree) the two sides of
the auto together forcing it to try to push the inside into the pavement,
improving traction.
Big cars have alot of mass. 2,000 punds being loaded down on the
suspension takes a LONG time to stop. These cars are usually meant
for fairly slow speed (< 90 MPH) and use softer shocks so that the
wheels take more of the jolt. Push 'em too far and the wheels
can't be kept in contact with the pavement as they flail around.
Go around a corner, hit a bump and LURCH to the outside.
Sports type cars, meant to drive at higher speeds, need stronger shocks,
in proportion to their mass so that when they get going REAL fast
the wheels come under control very quickly should they hit a bump.
Too bad, at low speeds this means a harsh ride as they stop wheel motion
very quickly transferring more of the jolt to the body than the
large beasties.
The automakers try to trade off on ride and handling but they ARE
mass produced.
--
--Lee (Ward)
{ucbvax,convex,gatech,pur-ee}!unmvax!leeseifert@ihuxl.UUCP (D.A. Seifert) (05/01/84)
> Air is not easily compressible. Thus, the more > you try to compress it, the harder is resists. That's quite interesting. Sounds like it would make a nice, inexpensive substitute for brake fluid. Anyone know any good lawyers? "But your Honor, I read it on USENET! It *must* be true!" :-) Sears, et al, must be laughing all the way to the bank selling "air compressors" for that non-compressable air. -sigh- > Going around a corner where the body wants to lift on one side is a BIG > problem. The shocks don't like to expand either, so they control this, though > usually well out of proportion to their resistance to compression. Sway bars > help in that they effectively tie (to a degree) the two sides of > the auto together forcing it to try to push the inside into the pavement, > improving traction. Actually, anti-roll bars do NOT push the inside tires harder to the pavement, they lift them up! The *outside* tires are pressed harder to the pavement. Unfortunately, the outside tires gain less than the inside tires lose (traction, not force! [*] ), so you can end up with *less* cornering power! (surprise) But less roll means less camber and toe changes, so you gain some traction back. And you don't have all that weight slopping back and forth trying to get out of control. (the big win) [*] putting twice the force on a tire does not result in twice the traction :-( > Big cars have alot of mass. 2,000 punds being loaded down on the > suspension takes a LONG time to stop. I guess 1 'pund' must equal 2 pounds? A 2000 pound car is considered fairly light in most circles. (at least if we're discussing *street* cars) A large Detroit land yacht weighs (or used to weigh) 4000-5000 lbs. -- _____ /_____\ That auto-crossing beagle, /_______\ Snoopy |___| BMWCCA, Windy City Chapter ____|___|_____ ihnp4!ihuxl!seifert
roger@felix.UUCP (05/02/84)
[] Sorry, even BMW hasn't figured this one out.