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Old 06-17-2006, 12:50 AM   #1
kevinthenerd
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Three ideas to improve handling, 2 cheap, 1 expensive

1. Part of the reason why front-wheel-drive cars have poor handling has to do with their weight distribution. If I don't care about acceleration and only care about cornering ability, would it be possible to improve a car's weight distribution by simply filling the trunk with something heavy and cheap? It might seem like a trivial answer: yes, it's possible to get a 50/50 weight split by adding weight to the trunk, but weight in the trunk is also relatively high off the ground. So, MORE IMPORTANTLY, has anyone ever tried this, with or without success?

2. In NASCAR, they sometimes use spacers in the suspension springs to immobilize one coil, making the springs stiffer. Has anyone ever done this successfully with consumer automobiles?

3. I was reading in a Racecar Engineering article where some guy designed and built (from scratch) a fully independent suspension setup for a Saab racecar. I know you can buy lowering springs, sway bars, and the like for most consumer cars, but are there aftermarket mods on the market that totally replace a suspension system with one of a totally different design... like to convert a torsion beam rear suspension to a double-wishbone independent suspsion or something like that?
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Old 06-17-2006, 07:17 AM   #2
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

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Originally Posted by kevinthenerd
would it be possible to improve a car's weight distribution by simply filling the trunk with something heavy and cheap? It might seem like a trivial answer: yes, it's possible to get a 50/50 weight split by adding weight to the trunk, but weight in the trunk is also relatively high off the ground. So, MORE IMPORTANTLY, has anyone ever tried this, with or without success?
It's called 'ballast' and racers often do this.

It's done with the greatest success in race classes where there is a minimum allowable weight for the car and driver.
For example, NASCAR used to have a minumum allowable weight for their car of 3500 lbs, (they might still do, I'm not sure) The race cars were built lighter than this, often by several hundred lbs.

Then metal weights were added to the car in strategic locations to improve handling (their exact location was done in coordination with other factors, such as the track, alignment, stagger, aerodynamics, tires, driver preference, etc ). The added weights help fine tune handling and bring the car up to the allowable minimum weight.

Road going cars are a bit different. One does not want to increase weight, if possible, just move it around. The most simple method is to relocate the battery to the trunk. One can get relocation kits for this; it's very common for drag racers to do.
Finally, there is no harm in just throwing a sandbag in the trunk and seeing how things change. People who drive in snow with RWD do this all the time.

I did this a while back with my Jeep CJ 8 (Scrambler). It has a long wheelbase, for a Jeep and would understeer like crazy. 200 lbs of floor sweep kitty litter in bags in the back made it oversteer significantly in the corners. IMO it did not improve handing, but it sure changed it.

One more point, adding weight in the back changes the polar inertia, that is, it may reduce understeer, but it makes it more difficult for the car to change direction, so it si less agile.

Also, it can move the center of rotation rearwards, If this center is behind the aerodynamic center of pressure, the car becomes less stable at high speeds. (like trying to throw a lawn dart backwards. Soem rear engine cars, (old Beetles, Porsches, Tatras (look them up) had problems in this area.
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Old 06-17-2006, 08:39 AM   #3
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

I guess I'll answer the next two;

2) Yes, there are many things like this at your local parts store.

3) Its common to replace entire front clips and rear suspension on street rods and such, and many are available commercially that you modify for your particular application.
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Old 06-17-2006, 06:20 PM   #4
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

I would try to avoid putting any additional weight into your car. It hurts acceleration. Avoid putting any spacers or anything between the coils of a coil spring. It will stiffen the spring up the same percentage of coils that you immobilize, but it will eventually start cracking the spring and then it will sag or break. Do not use any off the shelf type of suspension conversion kit unless it's absolutely, specifically designed for your car. Your twist beam rear axle will be light-years ahead of a generic IRS suspension that wasn't designed for anything in particular. Lightweight beam type axles aren't glamorous, but they work pretty good anyway. Especially when all they're out there for is to hold the back end of the car up.
What you should try, if possible, is put a bit larger tire on the front than on the back (ala newer FWD Pontiacs).
If you're not lifting the inside rear tire up off the ground in a corner, your rear anti-roll bar is not stiff enough. If you don't have a rear bar, get one. That is your first priority.
Also, things to try when you start running out of ideas--Try a smaller anti-roll bar in the front. Try softer springs in the front. Try removing weight from the front.
So- make life as easy as possible for the front tires and make the back tires do more work.....
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Old 06-17-2006, 07:51 PM   #5
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

A good fiberglass front clip often weighs less than fakie-looks only carbon fiber front klip stuff, albeit at a similar price. The front fenders are engineered to add stiffness as steel units. You will probably lose some stiffness in your front end, unless the fiberglass fenders are engineered to be stiff (they should use a honeycomb core if you are looking for strenght charachteristics).
On the engineering tip, yea. The rear swingaxle in a FRD-like a VW- is not going to be improved upon in the aftermarket. Anything that would work better than the stock setup would cost way more than it is worth. On a RWD, yes, many systems are available that are far superior to stock. Their benifits lie solely in the fact that they strenghten the rear sub-assembly of the chassis to accomodate more power, so the engineering skill is low to provide a quality piece. (Hence a Ford 9", it's just tried and true, you follow the basic design that has proved sucessfull.
Black Lotus' reply says it all. DO NOT ADD WEIGHT!!!. All this will do is slow the rotation of your vehicle. Relocating your battery is #1 mod. What I have tried but never seen is the relocation of the radiator to the rear. With the appropriate routing and ducting, this puts more weight in the rear (below the trunk) than the battery, and can also be used to add downforce in the rear if ducted correctly (intake in the bottom, exit in the low pressure area of the tail of the car-the reaon for wings in the first place-.
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Old 06-17-2006, 08:03 PM   #6
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

My stock Saturn ION already has its battery in the trunk.

I find my handling changes drastically when I have two bicycles on a bikerack in the back. U-turns become a whole lot easier. That's why I thought of this in the first place.

If you're worried about the polar moment of inertia, then perhaps weight added to the rear passenger seat might be a better idea? It won't help the weight distribution as much as weight right off the back, but it seems to me like what matters here in dynamic cornering (which is anything other than a simple skidpad) is a certain ratio of the car's weight to its moment of inertia. I don't know. I'd have to sit down and figure out the physics, and then I'd have to go see for myself.

When I ask about aftermarket suspension kits, I'm really interested in whether such things exist on the market already because I might be interested in designing application-specific kits myself. I don't know whether it'll be best to devote my time to this or to designing a car from scratch. (I'm a mechanical engineering student interested in starting my own car company. Anyone interested in helping me can email me: kevinthenerd@yahoo.com)

Extra weight will hurt acceleration, but both my handling and acceleration suck so bad that I might be willing to trade one for the other just to have a little fun in one area. It's really just for playing around a bit until I get the time (when I'm out of school) to start working on a real project car: a longitudinal mid-engined tube chassis sleeper based on the Saturn ION body panels.
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Old 06-18-2006, 02:27 AM   #7
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

I've personally never seen a situation where adding weight to achieve 50/50 would improve handling. MagicRat hit that nail on the head; moment of inertia. It might help skidpad numbers by helping balance, but it won't help handling. It takes more force to alter the direction of a heavier car, especially when its located at the poles. So, in short, yes ballast may help in steady state cornering where the change in velocity is constant, but the added weight will probably more than offset any benefits.

The coil spring stops are a fine idea. They're a bit unpredictable since every cycle of a coil spring is a slight bit different. In any given coil might provide different rates to the overall spring, so immobilizing one cycle might have unpredictable results. Not wildly different, but if you're really serious about tuning it for a race, a 10-15# rate difference makes a big deal. You're also limited by how much rate you take out. With the block in, you remove one active coil so you're stuck with whatever rate that provides regardless of whether or not its too much or too little. You might be able to experiment with different methods of wedging the spring. They make ones that adjust against the coils with two bolts which would be rigid, but they also make rubber blocks that fit between the coils. I might experiment with different durometers of rubber, polyurethane, and the bolt-in kind. There are also "helper" springs that bolt on to the shock; probably not an option with FWD struts, but they are infinitely adjustable. You can install them with slack for load carrying, no slack which would add to the rate of your current spring, or under tension. Of course, the right way to do it would be to select the proper rate of spring for the intended useage, but these are some low-buck reversible ideas.

The last question is a matter of how much experience you have. Basically, if you have to ask, then the answer is no Not really, but anything can be done with enough money and engineering. I more or less re-designed my 66 Bonneville's front and rear suspensions, but I didn't have much to change. I wanted to improve a couple things, so I altered control arms, spindles, trailing arms to get the geometry I wanted, but I used the stock mounting points. My changes were a little remedial compared to completely designing a whole system. I suggest you next read should be "race car vehicle dynamics" by Milliken. Its an incredible read but it takes a while to sift through the calculus.
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Old 06-18-2006, 02:35 AM   #8
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Re: Three ideas to improve handling, 2 cheap, 1 expensive

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Originally Posted by curtis73
I suggest you next read should be "race car vehicle dynamics" by Milliken. Its an incredible read but it takes a while to sift through the calculus.
I've heard about that book. I need to read it.
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