Preface
I have noticed that many cars I see are set up in a way that's at least far from optimal, and often worse than stock. Issues include, but are not limited to...
-wonky front/rear stagger
-insufficient bump or droop travel
-ride height in ranges that compromise suspension geometry
-alignments that compromise handling
-weird weight distributions
-spring/sway combinations that skew the car towards massive understeer or oversteer
-massive levels of preload
The e46 M3 is a nicely set up car, stock-- everything that follows is done, stock, on the e46 M3 as it left the factory. Everything that follows is 100% useful to street cars-- the thought process that "I don't drive on track so this does't apply to me" is misguided... at least if you bought the e46 M3 for what it's actually good at doing.
Everything here can be applied to suspensions at every price point. And, it's equally important at all price points-- a properly set up set of $600 Chinese coilovers likely handles better than a poorly set up set of $6000 coilovers.
That said, there are expenses incurred here. You will need...
-access to corner balancing scales (or pay some else to do it for you)
-adjustable end links
-for people with springs (vs adjustable height coilovers), rear spring pads
Throughout this document I will reference Fat Cats Motorsports' (excellent) e46 M3 setup spreadsheet. You can find it here:
http://www.fatcatmotorsports.com/FCM..._M3_Online.htm
Information that could be useful in making decisions:
-Metal to metal travel of your shocks (the company that makes your suspension should be able to provide this)
-What size springs your shocks use (the company that makes your suspension should be able to provide this-- useful for swapping out springs)
-offsets of your wheels (allows you to calculate vehicle track width of your car front and rear
-corner weights of your car (car does not have to be corner balanced for this)
I'm also not going to get into anything related to aero cars. By aero cars, I mean cars that have too little clearance to be driven on the street or driven onto/off of a trailer without removing your bumper. If you think you may or may not be an aero car... you're almost certainly not.
Spring Rates and Sway Bar Selection
I'm not going to get into Flat Ride, as that is a topic all onto itself (though I will say that I have all my cars set up that way and love it).
Spring rate decisions should be a result of suspension frequency calculations. Suspension frequency is means by which to gauge the stiffness of a setup that factors in motion ratios, corner weights for that specific car/driver, changes from wheel offset changes, unsprung mass, etc. You can easily calculate them using the FCM e46 M3 spreadsheet. To use this spreadsheet effectively, ideally you should get corner weights for your car (you don't need to corner balance it to do this-- just drive onto the scales and record, and then plug those values into the corner weight calculator section of the spreadsheet to see what they'll be once corner balanced).
The basic thought process that should go into front axle spring selection is as follows...
The softer the car is, the more grip it has, all else equal... until you run out of travel, which quickly ramps up the effective spring rate (through the bump stop), rapidly decreasing grip. So, generally...
-the stickier your tires are, the more roll stiffness you need
-the less suspension travel you have, the more stiffness you need
-the higher (stiffer) the frequency is, the less grip you have (for a given tire/setup)
-the stiffer the sways, the less grip you have (for a given tire/setup)
If I were to summarize front spring selection, it would "as little as possible, as much as necessary". As a side perk, this mentality also leads to a car that rides better, as a large portion of ride quality is determined by front axle stiffness.
Additionally, it's important to remember, when picking springs, that shocks have a window of spring rates in which they function well. Often you can have them revalved to accommodate springs outside of their design range, but this adds additional expense.
That said, it's important to remember that the stock springs are only 143 lbs/in. Even spring rates that are generally thought of as crazy soft (e.g. 300 up front) are more than twice as stiff as stock!
Once you've picked out your front springs, it's time to choose the rears. For a flat ride setup the rear frequencies should be 10-20% higher than the fronts. For a more traditional aftermarket setup, the rear frequencies are normally 20-30% lower than the fronts.
In either case, once you've chosen your frequencies it's time to pick out sway bars. Sway bars have two considerations:
1) Primary consideration: set your oversteer/understeer balance. That balance shows up on the spreadsheet as the Front Roll Couple (FRC). The e46 M3 is fairly neutral with an FRC somewhere in the 70-75% range. The spreadsheet has the dimensions of most of the sway bars on the market for this car, so you can pick and choose between them to find a pair that gets the FRC in range for your spring rate selection. FRC is tweaked by the ratio of front bar stiffness to rear bar stiffness.
2) Sway bars also increase roll stiffness. To some extent (don't want to go overboard with this), you can accommodate stickier tires by increasing roll stiffness though sway bars. Remember, though, that stiffer sway bars also decrease grip-- so it's a balance. Roll stiffness from sways is tweaked by increasing/decreasing the total stiffness of the front/rear bars.
3) I know I said there's two considerations, but here's a non directly handling related third: hollow sways (which the spread sheet allows for) allow for significant increases to stiffness while decreasing the sway bars weight. All else equal, I would go with a hollow sway whenever possible.
Note: It's important to not have your roll stiffness solely depended on the sway bars. Sway bars are springs, too, and thus they're part of the equation for the dampers. If too much of your roll stiffness comes from sway bars, you might be underdamped in roll -- unless you revalve your dampers accordingly, in which case you'll be overdamped in pitch/heave.
Generally it's good to get sway bars that are adjustable, so you can dial in the oversteer/understeer ratio to your exact taste (ass dyno). Handling balance is subjective-- great setup for one driver might be undriveable for someone else. Plus, that way the sways you initially selected are more likely to still be viable as other aspects of your car change or account for any errors from miscalculations on the spreadsheet.
Ride Height
Ride height is an area of car setup where people often go wrong. Generally speaking, for most setups there should be 2 underlying guidelines:
1) Front suspension geometry starts to be compromised below a 13.5" (center of centercap to fender) static ride height, and gets really bad below 13"
2) Front to rear should have a 1/2" stagger, with the rear being 1/2" lower (as measured centercap to fender-- not that this is not actual ride height, just a convenient way to measure)
The gains from a lower CoG are not enough to offset the bump travel and suspension geometry losses that come with it.
(super low race cars you see driving around have taken significant corrective action to fix the suspension geometry)
That said, there are other considerations. Generally speaking, for non aero setups, you want at least (more is better) 50mm of bump travel (distance the spring/shock can compress upwards into the car from static ride height). Depending on your combination of shock/camber plate/spindle, that may not be possible at 13.5" ride height-- in which case you need to go higher.
The easiest way to find out how much bump travel you have is subtraction. Get total shock travel (often called metal to metal travel) from the company that makes your shock, subtract droop travel from total travel (droop travel is how far the suspension sags from static ride height when jacked (with the sway bar disconnected)), and the result is bump travel.
Ride height should be set with one sway bar end link disconnected.
Some setups allow for you to set the bump/drool travel ratio separately from the ride height on the rear. If your setup allows that, I would target a 60:40 split of bump:droop travel, assuming that gives you at least 50mm of bump travel.
Corner Balancing (can be done without coilovers)
It seems like a lot of people skip this step, and as a result it's an area where otherwise very well set up cars tend to miss out. The benefit of corner balancing is that it makes it so the oversteer/understeer ratio is the same when you turn left as when you turn right. This is not something you can do by eyeballing-- small adjustments on the ride heigh adjusters result in large shifts of weight around the car.
Corner balancing can't shift the weight of the car from the frontwards/rearwards or left/right. What it can do is shift weigh to opposite diagonals. As you increase the ride height on a given corner, the weight on that corner and the corner diagonally opposite to it increases. When a car is properly corner balanced, the front left + rear right = front right + rear left. This is called the cross weight. It might help to think of corner balancing as similar to leveling the 4 feet of a table-- it gives the car a stable platform to work from, making it more predictable and consistent.
The general process should be as follows:
1) get the car to the ballpark ride height target and ballpark alignment you'll be running
2) corner balance the car
3) align the car
4) corner balance the car again (as the alignment screwed it up, but you had to do it beforehand to be in the ball park for alignment)
Things to think about while corner balancing
-one sway bar end link must be disconnected on each axle during the corner balancing process!
-the car should be at "target" weight-- for me this means me in the car, and nothing else.
-because the fuel is equally on the left and right side of the car, fuel level is not a factor in corner balancing this car-- any fuel level is equally good.
-when you raise one corner, the opposite corner will lower. Because of this, I like to raise the car in diagonal pairs to keep the ride height changes minimized
-small adjustments make large differences.
-raising any corner increases the weight on the opposite corner. Using this, you can keep the ride heights pretty equal left/right.
-between each adjustment, bounce the car a couple of times to make sure it settles in at it's new ride height
-the FCM spreadsheet lets you plug in your corner weights and have it calculate your optimal corner weights-- this can make the adjustment process a lot faster
-the corner weighting scales MUST be on level ground to be effective. This isn't something you can do in your driveway (at least without leveling it)
-for cars with multiple alignments (street/track), you should be on your track alignment
Note: you can do an okay corner balance without ride adjustable coilers using BMW's various spring pads from different e46s (the pad that goes between the spring and the control arm). This is what I've done on my M3 wagon (which is on Dinan springs with Koni yellows). Spring pad options are as follows:
5mm # 33 53 1 136 385
7.5mm # 33 53 1 136 386
9mm # 33 53 1 127 224
10mm # 33 53 1 136 387
Sway Bar End Link adjustment
Almost done...
For sway bars to not screw up the handling of the car, they must have almost no preload. Swaybar preload is the result of the ride height of the car being different on one side of the car than the other. To address this you need adjustable end links. The basic premise is that, with the car's (and your) weight on its tires (so not jacked up), the end link should insert into the shock sway mount with zero twist-- just straight in. A slight tweak to this you can add, to keep the end links silent (aka for a car that sees street use), is to add a single turn of preload. This isn't enough to significantly ruin handling, but adds a lot of civility.
No preload also significantly increases the lifespan of your end links and sway bar bushings!
Setting Camber and Tire Pressures
(this part is for track use only)
IMO the best way to set on track camber is to use a pyrometer and set the camber such that the entire tread portion of the tire is the same temperature. If the outside of the tires is hotter than the inside, add more camber. If the inside portion of the tires is hotter than the outside, reduce camber. This uses all parts of the tire equally, resulting in better longevity and tire wear. Obviously being able to do this requires adjustable camber, which on the e46, comes in the forum of camber plates (front) and adjustable rear lower control arms. But, using the setup above, those items pretty quickly pay for themselves in saved tire wear.
... and once you've done this for a couple of events to know where your camber ends up, couldn't hurt to corner balance the car yet again...
Tire pressures are best set by sidewall rollover. Most track tires have an arrow that indicated how much sidewall roll you should optimally get. This keeps you in the useful part of the tires tread. Using a paint pen, you can see how much roll you're getting on a given session (by how close to the arrow the paint wears away). Many people like to tweak their oversteer/understeer by tweaking tire pressures-- I think that's better accomplished by tweak sway settings, and saving tire pressure adjustment to get optimal use out of your tires.
Roll indicator arrow I'm referring to:
I have noticed that many cars I see are set up in a way that's at least far from optimal, and often worse than stock. Issues include, but are not limited to...
-wonky front/rear stagger
-insufficient bump or droop travel
-ride height in ranges that compromise suspension geometry
-alignments that compromise handling
-weird weight distributions
-spring/sway combinations that skew the car towards massive understeer or oversteer
-massive levels of preload
The e46 M3 is a nicely set up car, stock-- everything that follows is done, stock, on the e46 M3 as it left the factory. Everything that follows is 100% useful to street cars-- the thought process that "I don't drive on track so this does't apply to me" is misguided... at least if you bought the e46 M3 for what it's actually good at doing.
Everything here can be applied to suspensions at every price point. And, it's equally important at all price points-- a properly set up set of $600 Chinese coilovers likely handles better than a poorly set up set of $6000 coilovers.
That said, there are expenses incurred here. You will need...
-access to corner balancing scales (or pay some else to do it for you)
-adjustable end links
-for people with springs (vs adjustable height coilovers), rear spring pads
Throughout this document I will reference Fat Cats Motorsports' (excellent) e46 M3 setup spreadsheet. You can find it here:
http://www.fatcatmotorsports.com/FCM..._M3_Online.htm
Information that could be useful in making decisions:
-Metal to metal travel of your shocks (the company that makes your suspension should be able to provide this)
-What size springs your shocks use (the company that makes your suspension should be able to provide this-- useful for swapping out springs)
-offsets of your wheels (allows you to calculate vehicle track width of your car front and rear
-corner weights of your car (car does not have to be corner balanced for this)
I'm also not going to get into anything related to aero cars. By aero cars, I mean cars that have too little clearance to be driven on the street or driven onto/off of a trailer without removing your bumper. If you think you may or may not be an aero car... you're almost certainly not.
Spring Rates and Sway Bar Selection
I'm not going to get into Flat Ride, as that is a topic all onto itself (though I will say that I have all my cars set up that way and love it).
Spring rate decisions should be a result of suspension frequency calculations. Suspension frequency is means by which to gauge the stiffness of a setup that factors in motion ratios, corner weights for that specific car/driver, changes from wheel offset changes, unsprung mass, etc. You can easily calculate them using the FCM e46 M3 spreadsheet. To use this spreadsheet effectively, ideally you should get corner weights for your car (you don't need to corner balance it to do this-- just drive onto the scales and record, and then plug those values into the corner weight calculator section of the spreadsheet to see what they'll be once corner balanced).
The basic thought process that should go into front axle spring selection is as follows...
The softer the car is, the more grip it has, all else equal... until you run out of travel, which quickly ramps up the effective spring rate (through the bump stop), rapidly decreasing grip. So, generally...
-the stickier your tires are, the more roll stiffness you need
-the less suspension travel you have, the more stiffness you need
-the higher (stiffer) the frequency is, the less grip you have (for a given tire/setup)
-the stiffer the sways, the less grip you have (for a given tire/setup)
If I were to summarize front spring selection, it would "as little as possible, as much as necessary". As a side perk, this mentality also leads to a car that rides better, as a large portion of ride quality is determined by front axle stiffness.
Additionally, it's important to remember, when picking springs, that shocks have a window of spring rates in which they function well. Often you can have them revalved to accommodate springs outside of their design range, but this adds additional expense.
That said, it's important to remember that the stock springs are only 143 lbs/in. Even spring rates that are generally thought of as crazy soft (e.g. 300 up front) are more than twice as stiff as stock!
Once you've picked out your front springs, it's time to choose the rears. For a flat ride setup the rear frequencies should be 10-20% higher than the fronts. For a more traditional aftermarket setup, the rear frequencies are normally 20-30% lower than the fronts.
In either case, once you've chosen your frequencies it's time to pick out sway bars. Sway bars have two considerations:
1) Primary consideration: set your oversteer/understeer balance. That balance shows up on the spreadsheet as the Front Roll Couple (FRC). The e46 M3 is fairly neutral with an FRC somewhere in the 70-75% range. The spreadsheet has the dimensions of most of the sway bars on the market for this car, so you can pick and choose between them to find a pair that gets the FRC in range for your spring rate selection. FRC is tweaked by the ratio of front bar stiffness to rear bar stiffness.
2) Sway bars also increase roll stiffness. To some extent (don't want to go overboard with this), you can accommodate stickier tires by increasing roll stiffness though sway bars. Remember, though, that stiffer sway bars also decrease grip-- so it's a balance. Roll stiffness from sways is tweaked by increasing/decreasing the total stiffness of the front/rear bars.
3) I know I said there's two considerations, but here's a non directly handling related third: hollow sways (which the spread sheet allows for) allow for significant increases to stiffness while decreasing the sway bars weight. All else equal, I would go with a hollow sway whenever possible.
Note: It's important to not have your roll stiffness solely depended on the sway bars. Sway bars are springs, too, and thus they're part of the equation for the dampers. If too much of your roll stiffness comes from sway bars, you might be underdamped in roll -- unless you revalve your dampers accordingly, in which case you'll be overdamped in pitch/heave.
Generally it's good to get sway bars that are adjustable, so you can dial in the oversteer/understeer ratio to your exact taste (ass dyno). Handling balance is subjective-- great setup for one driver might be undriveable for someone else. Plus, that way the sways you initially selected are more likely to still be viable as other aspects of your car change or account for any errors from miscalculations on the spreadsheet.
Ride Height
Ride height is an area of car setup where people often go wrong. Generally speaking, for most setups there should be 2 underlying guidelines:
1) Front suspension geometry starts to be compromised below a 13.5" (center of centercap to fender) static ride height, and gets really bad below 13"
2) Front to rear should have a 1/2" stagger, with the rear being 1/2" lower (as measured centercap to fender-- not that this is not actual ride height, just a convenient way to measure)
The gains from a lower CoG are not enough to offset the bump travel and suspension geometry losses that come with it.
(super low race cars you see driving around have taken significant corrective action to fix the suspension geometry)
That said, there are other considerations. Generally speaking, for non aero setups, you want at least (more is better) 50mm of bump travel (distance the spring/shock can compress upwards into the car from static ride height). Depending on your combination of shock/camber plate/spindle, that may not be possible at 13.5" ride height-- in which case you need to go higher.
The easiest way to find out how much bump travel you have is subtraction. Get total shock travel (often called metal to metal travel) from the company that makes your shock, subtract droop travel from total travel (droop travel is how far the suspension sags from static ride height when jacked (with the sway bar disconnected)), and the result is bump travel.
Ride height should be set with one sway bar end link disconnected.
Some setups allow for you to set the bump/drool travel ratio separately from the ride height on the rear. If your setup allows that, I would target a 60:40 split of bump:droop travel, assuming that gives you at least 50mm of bump travel.
Corner Balancing (can be done without coilovers)
It seems like a lot of people skip this step, and as a result it's an area where otherwise very well set up cars tend to miss out. The benefit of corner balancing is that it makes it so the oversteer/understeer ratio is the same when you turn left as when you turn right. This is not something you can do by eyeballing-- small adjustments on the ride heigh adjusters result in large shifts of weight around the car.
Corner balancing can't shift the weight of the car from the frontwards/rearwards or left/right. What it can do is shift weigh to opposite diagonals. As you increase the ride height on a given corner, the weight on that corner and the corner diagonally opposite to it increases. When a car is properly corner balanced, the front left + rear right = front right + rear left. This is called the cross weight. It might help to think of corner balancing as similar to leveling the 4 feet of a table-- it gives the car a stable platform to work from, making it more predictable and consistent.
The general process should be as follows:
1) get the car to the ballpark ride height target and ballpark alignment you'll be running
2) corner balance the car
3) align the car
4) corner balance the car again (as the alignment screwed it up, but you had to do it beforehand to be in the ball park for alignment)
Things to think about while corner balancing
-one sway bar end link must be disconnected on each axle during the corner balancing process!
-the car should be at "target" weight-- for me this means me in the car, and nothing else.
-because the fuel is equally on the left and right side of the car, fuel level is not a factor in corner balancing this car-- any fuel level is equally good.
-when you raise one corner, the opposite corner will lower. Because of this, I like to raise the car in diagonal pairs to keep the ride height changes minimized
-small adjustments make large differences.
-raising any corner increases the weight on the opposite corner. Using this, you can keep the ride heights pretty equal left/right.
-between each adjustment, bounce the car a couple of times to make sure it settles in at it's new ride height
-the FCM spreadsheet lets you plug in your corner weights and have it calculate your optimal corner weights-- this can make the adjustment process a lot faster
-the corner weighting scales MUST be on level ground to be effective. This isn't something you can do in your driveway (at least without leveling it)
-for cars with multiple alignments (street/track), you should be on your track alignment
Note: you can do an okay corner balance without ride adjustable coilers using BMW's various spring pads from different e46s (the pad that goes between the spring and the control arm). This is what I've done on my M3 wagon (which is on Dinan springs with Koni yellows). Spring pad options are as follows:
5mm # 33 53 1 136 385
7.5mm # 33 53 1 136 386
9mm # 33 53 1 127 224
10mm # 33 53 1 136 387
Sway Bar End Link adjustment
Almost done...
For sway bars to not screw up the handling of the car, they must have almost no preload. Swaybar preload is the result of the ride height of the car being different on one side of the car than the other. To address this you need adjustable end links. The basic premise is that, with the car's (and your) weight on its tires (so not jacked up), the end link should insert into the shock sway mount with zero twist-- just straight in. A slight tweak to this you can add, to keep the end links silent (aka for a car that sees street use), is to add a single turn of preload. This isn't enough to significantly ruin handling, but adds a lot of civility.
No preload also significantly increases the lifespan of your end links and sway bar bushings!
Setting Camber and Tire Pressures
(this part is for track use only)
IMO the best way to set on track camber is to use a pyrometer and set the camber such that the entire tread portion of the tire is the same temperature. If the outside of the tires is hotter than the inside, add more camber. If the inside portion of the tires is hotter than the outside, reduce camber. This uses all parts of the tire equally, resulting in better longevity and tire wear. Obviously being able to do this requires adjustable camber, which on the e46, comes in the forum of camber plates (front) and adjustable rear lower control arms. But, using the setup above, those items pretty quickly pay for themselves in saved tire wear.
... and once you've done this for a couple of events to know where your camber ends up, couldn't hurt to corner balance the car yet again...
Tire pressures are best set by sidewall rollover. Most track tires have an arrow that indicated how much sidewall roll you should optimally get. This keeps you in the useful part of the tires tread. Using a paint pen, you can see how much roll you're getting on a given session (by how close to the arrow the paint wears away). Many people like to tweak their oversteer/understeer by tweaking tire pressures-- I think that's better accomplished by tweak sway settings, and saving tire pressure adjustment to get optimal use out of your tires.
Roll indicator arrow I'm referring to:
Comment