I see a lot of discussions on this forum and others about modifying suspension on these cars, but not many that actually take into account some of the very key things that are being affected when you make these changes. Lowering a car, any car, could potentially have an adverse effect on the car's suspension geometry, and in turn, how well or badly that car will ultimately handle or ride. A lot more is going on then just "having less wheel gap" when you lower a car, as well as changing it's spring rates, anti roll bar rates alignment etc.......
I'm hoping this thread will open up a dialogue with other members that have an interest in taking their suspension set up beyond just bolting on various different combinations of parts that are available on the aftermarket, but actually stopping and taking a good look at what we are doing to these cars.
For starters, lets look at and get more familiar with some of they key factors that effect a car when making suspension changes. (This is going to be heavily condensed, as full explanation can literally fill books, and there is already some really great ones out there.) This will be a total "crash course" (no pun intended).
Suspension travel: Will start with this one since it is the easiest to visualize and understand.
Suspension travel is measured in two planes, compression or "bump" travel and "droop" travel. Compression travel is the amount the suspension can travel upward, droop the amount it "hangs down" when unloaded (think of when you jack a car up, and the wheel hangs there). Both springs and damper's limit a cars compression and droop travel.
Having adequate travel in both directions is important, as it directly effects how much "working space" the suspension has to absorb road irregularities, and undulations. For the most part, more working travel is better, as it allows the car to "suck up" larger irregularities without upsetting the chassis, as well as allowing the tire to flow over the road and not deform the contact patch.
When you lower a car, you are lessening it's bump travel. By doing this, you are limiting the amount in which the car can absorb vertical loads into the suspension. A car lowered without anything to compensate, will ride it bumpstops, and bottom out its shocks continuously. Not good for ride quality, not good for the shocks, not good for the tire contact patch as it is constantly getting jarred and deformed as it pounds over the road. This usually comes into play with lowering springs that don't compensate for the amount they lower the car in spring rate, as well as factory shocks not designed to work within the stroke your asking them to. You can trim bumpstops, but if the shock isn't designed to work within the stroke your asking it to, you can forget about them surviving very long, as well as working very well.
The remedy, is properly selected spring rates, as well as dampers designed to work within the travel your asking of them.
Roll center geometry: A cars roll center is the invisiable axis that it's chassis rolls around
Here's another (this one more suited to our cars as it's McStrut design)
When you lower a car, you also lower it's roll center, which isn't too big a deal to an extent. The lower the roll center becomes, the larger the roll couple is as your increasing the distance between the cars CG and roll center. By doing this, you are greatly increasing the cars tendency to want to roll more heavily around it's roll center. Think of it like this, the roll couple is like having an invisible handle that gravity acts on coming out the top of the car. The more you lower that roll center, the longer the handle becomes. The effect is no bueno under heavy cornering, and have absolutely experienced the effect this will have on a car that is overly lowered.
The remedy, on a Mcstrut car like ours, either have longer balljoints made to raise the roll center (you can only go so long on the balljoints as well), or uprights designed to compensate (what you see on race cars). As of writing this, i don't believe either exist for our cars. How much is too much? Well, without doing any real measuring or math for our cars (which I haven't) around the vicinity of 1" is what you usually get before problems really start to rear it's head. The simple remedy, is not lower the car too much. Any gain that you usually see from lowering the cars CG is almost made moot by creating the larger issue of a longer roll couple.
Static Alignment settings: Simply put lowering a car generally creates more negative camber and more positive toe. Both can beneficial to better handling, but also can be detrimental in excessive amounts. For example, while adding more static negative camber in front can be beneficial for front end grip, too much rear camber can mean a car that tough to get to rotate, or too much postive toe one that is too rear happy. Ride height also effects static toe settings. Too much positive or negative toe can have detrimental effects on tire wear and braking stability.
Dynamic camber curve: Simply the amount of camber alignment change you have as the chassis rolls and the suspension moves up and down in it's arc.
A diagram here, again not quite correct as this for double wishbone, but to give you and idea......
Several things can effect a cars dynamic camber curve (SAI, Caster angle, static camber etc...) but, for just the simple look this post is intended for, excessive lowering of a car (especially Mac Strut like ours) can result in a camber curve that is not beneficial to the tires traction patch as the suspension moves through it's arc (excessive camber loss etc.....) which can result in less mechanical grip.
I'm hoping this thread will open up a dialogue with other members that have an interest in taking their suspension set up beyond just bolting on various different combinations of parts that are available on the aftermarket, but actually stopping and taking a good look at what we are doing to these cars.
For starters, lets look at and get more familiar with some of they key factors that effect a car when making suspension changes. (This is going to be heavily condensed, as full explanation can literally fill books, and there is already some really great ones out there.) This will be a total "crash course" (no pun intended).
Suspension travel: Will start with this one since it is the easiest to visualize and understand.
Suspension travel is measured in two planes, compression or "bump" travel and "droop" travel. Compression travel is the amount the suspension can travel upward, droop the amount it "hangs down" when unloaded (think of when you jack a car up, and the wheel hangs there). Both springs and damper's limit a cars compression and droop travel.
Having adequate travel in both directions is important, as it directly effects how much "working space" the suspension has to absorb road irregularities, and undulations. For the most part, more working travel is better, as it allows the car to "suck up" larger irregularities without upsetting the chassis, as well as allowing the tire to flow over the road and not deform the contact patch.
When you lower a car, you are lessening it's bump travel. By doing this, you are limiting the amount in which the car can absorb vertical loads into the suspension. A car lowered without anything to compensate, will ride it bumpstops, and bottom out its shocks continuously. Not good for ride quality, not good for the shocks, not good for the tire contact patch as it is constantly getting jarred and deformed as it pounds over the road. This usually comes into play with lowering springs that don't compensate for the amount they lower the car in spring rate, as well as factory shocks not designed to work within the stroke your asking them to. You can trim bumpstops, but if the shock isn't designed to work within the stroke your asking it to, you can forget about them surviving very long, as well as working very well.
The remedy, is properly selected spring rates, as well as dampers designed to work within the travel your asking of them.
Roll center geometry: A cars roll center is the invisiable axis that it's chassis rolls around
Here's another (this one more suited to our cars as it's McStrut design)
When you lower a car, you also lower it's roll center, which isn't too big a deal to an extent. The lower the roll center becomes, the larger the roll couple is as your increasing the distance between the cars CG and roll center. By doing this, you are greatly increasing the cars tendency to want to roll more heavily around it's roll center. Think of it like this, the roll couple is like having an invisible handle that gravity acts on coming out the top of the car. The more you lower that roll center, the longer the handle becomes. The effect is no bueno under heavy cornering, and have absolutely experienced the effect this will have on a car that is overly lowered.
The remedy, on a Mcstrut car like ours, either have longer balljoints made to raise the roll center (you can only go so long on the balljoints as well), or uprights designed to compensate (what you see on race cars). As of writing this, i don't believe either exist for our cars. How much is too much? Well, without doing any real measuring or math for our cars (which I haven't) around the vicinity of 1" is what you usually get before problems really start to rear it's head. The simple remedy, is not lower the car too much. Any gain that you usually see from lowering the cars CG is almost made moot by creating the larger issue of a longer roll couple.
Static Alignment settings: Simply put lowering a car generally creates more negative camber and more positive toe. Both can beneficial to better handling, but also can be detrimental in excessive amounts. For example, while adding more static negative camber in front can be beneficial for front end grip, too much rear camber can mean a car that tough to get to rotate, or too much postive toe one that is too rear happy. Ride height also effects static toe settings. Too much positive or negative toe can have detrimental effects on tire wear and braking stability.
Dynamic camber curve: Simply the amount of camber alignment change you have as the chassis rolls and the suspension moves up and down in it's arc.
A diagram here, again not quite correct as this for double wishbone, but to give you and idea......
Several things can effect a cars dynamic camber curve (SAI, Caster angle, static camber etc...) but, for just the simple look this post is intended for, excessive lowering of a car (especially Mac Strut like ours) can result in a camber curve that is not beneficial to the tires traction patch as the suspension moves through it's arc (excessive camber loss etc.....) which can result in less mechanical grip.
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