Coilover Setup Guide (Your Coilovers Aren't Set Up Right)
CONTENT CREDIT Johnny Pham on Instagram @minifd_mx5
INTRODUCTION:
So you’ve bought and installed a set of two piece coilovers. You expected better and thought you should feel like you're on top of the world yet somehow your fully sick coilovers ride like absolute rubbish. Maybe you do feel like you're on top of the world but you simply don't know better
Are you going ejecto seato instead of gliding over big bumps? Are you experiencing hopping or sudden snap oversteer when cornering hard? Is your car constantly bouncing? Chances are you haven’t set up your coilovers properly and you're hitting bump stops. This write up goes through how to get the most out of your el cheapo coilovers (yes this includes whatever fancy expensive name brand you have as long as it's in two pieces). This is a long one for the geeks so buckle up and enjoy the read
BACKGROUND:
The reason I’m writing this is because there’s a big mix of information out online on how to set up coilovers but I haven’t come across an article that directly addresses considerations like needing to be at street legal height or going even lower than the coilovers will allow out the box
TERMINOLOGY:
-
Two piece coilovers: coilovers with a threaded shock body and lower cup
-
Spring perches: the locking collars right under the spring
-
Stroke: total shock travel from end to end
-
Bump travel: how much the shock can compress from static height. Complementary to droop travel
-
Droop travel: how much the shock can extend from static height. Complementary to bump travel
-
Bottoming out: compressing the shock until it has no more bump travel
-
Motion ratio: ratio of how much the shock travels compared to the wheel. Because the coilover attaches to a spot along the control arm and not to the wheel itself, movement of 1mm at the wheel is 0.68mm at the front shock and 0.77mm at the rear shock
-
‘Preload’: An unhelpful myth. Preload is based on the idea that the spring is pre-compressed and exerting an initial force that needs to be overcome (this state only occurs when the wheel has lifted off the ground). The idea is that the static weight of the car must offset this force before the shock can start compressing. This is unhelpful because: 1. it focuses on weight rather than length measurements which makes it useless for adjustments, and 2. it has no influence on the performance of linear springs once the car is on the ground
-
Resetting the car: lift the whole car up on a hoist and rest it back on the floor. If you don’t have access to a hoist then gently roll the car back and forth a few times. Do not press down over each corner, you will dent the panels, ask me how I know
TESTING CLEARANCES AND SETTING UP A MINIMUM HEIGHT:
Do everything on smooth, level ground. Start by disconnecting front and rear sway bars so that the shocks can move freely. Do the following on a front and rear corner:
1. Disassemble a coilover and reinstall it with the spring and bump stop removed
2. Measuring shock stroke
-
Measure shock stroke: measure by measuring the difference between the length of the shock shaft at full extension and full compression. Jack up the control arm to bottom out the shock. Take note: this is your shock stroke
3. Clearancing and finding minimum height
-
Install your wheel and jack up the control arm until either the shock bottoms out or the wheel contacts something on the car. At the front, turn the wheel to observe any interference
-
Adjust the shock body length by threading the shock into or out of the lower cup so that the shock bottoms out right before the wheel contacts anything
-
*** Take note: this is your absolute minimum functional ride height ***
-
Lock the lower cup in place with the locking collar
4. Matching the setup across each axle
-
Remove the coilover and reinstall it with the spring and bump stop. Set the spring perches so that the spring is barely seated i.e. ‘zero preload’.
-
Measure and adjust the other coilover across each axle to match
ADJUSTING SHOCK TRAVEL AND HEIGHT:
Now for the fun part, setting up bump & droop travel and the height of the car
1. Determine target bump & droop travel
-
If you are unsure of exactly how much bump and droop travel you want, 2/3 bump and 1/3 droop is a good place to start
-
Target droop = 1/3 * stroke; Target bump = 2/3 * stroke
2. Take baseline measurements at front and rear
-
Reset the car
-
With the car on the ground, measure from the bottom of the wheel to the fender. Raise the car and repeat the same measurement
-
*** Take note of the difference between these two measurements ***
3. Adjusting shock travel
-
Measurement above * motion ratio = actual droop travel
-
Stroke - droop travel = actual bump travel
-
Actual droop travel - target droop travel = adjustment needed to be made
-
If actual droop > target droop, raise spring perches by the difference. Knowing the thread pitch of your shock body helps. e.g. one full turn on BC coilovers is 2mm and the spring perches have 8 notches
-
If actual droop < target droop, consider helper springs to lower the shock at static height while keeping the spring seated at all times. Otherwise, if leave it as is if it's acceptable to you
-
Explanation: Increasing droop travel will reduce bump travel. Picture the shock’s position when your car is at static height. As you raise the spring perch, the shock extends. The weight/force on the shock however remains the same and so the spring’s compression stays exactly the same (this is why ‘preload’ is a myth). As you raise the spring perch, you extend the shock and gain more bump travel while losing droop travel.
-
Replicate adjustment across each axle
4. Adjusting ride height
Do the following and measure by the pinch welds
-
Once actual travel = target travel, raise the car to the desired height by unwinding the shock from the lower cup to maintain travel settings. Do not exceed the minimum found above if lowering by the cup after raising it
-
If you're willing to reduce bump travel and gain droop travel, lower the car by the spring perches only. Lowering by the lower cup beyond the set minimum height means the wheel will contact the car before the shock bottoms out, resulting in potential damage and wasted travel (see above). If the car is too tall consider helper springs as above. If the rear is too tall to lower without sacrificing too much travel, consider extended top hats and redoing the process above
5. Reconnect sway bars and get a wheel alignment
Now go set up your suspension properly. This is a living post. Feel free to comment any corrections and I’ll edit them inCoilover Setup Guide (Your Coilovers Aren't Set Up Right)
PREFACE:
There’s a big mix of information out online on how to set up coilovers but there's nothing that directly addresses considerations like bump & droop travel, needing to be at street legal height or going even lower than the coilovers will allow out the box
INTRODUCTION:
So you’ve bought and installed a set of two piece coilovers. You expected better and thought you should feel like you're on top of the world yet somehow your fully sick coilovers ride like absolute rubbish. Maybe you do feel like you're on top of the world and you simply don't know better
Are you going ejecto seato instead of gliding over big bumps? Are you experiencing hopping or sudden snap oversteer when cornering hard? Is your car constantly bouncing? Chances are you haven’t set up your coilovers properly and you're hitting bump stops. This write up goes through how to get the most out of your el cheapo coilovers (yes this includes whatever fancy expensive name brand you have as long as it's in two pieces). This is a long one for the geeks so buckle up and enjoy the read
GLOSSARY:
Two piece coilovers: coilovers with a threaded shock body and lower cup
Spring perches: the locking collars right under the spring
Stroke: total shock travel from end to end
Bump travel: how much the shock can compress from static height. Complementary to droop travel
Droop travel: how much the shock can extend from static height. Complementary to bump travel
Bottoming out: compressing the shock until it has no more bump travel
Motion ratio: ratio of how much the shock travels compared to the wheel. On a double wishbone suspension equipped car, the coilover attaches to a spot along the control arm and not to the wheel itself. Because of this, for every 1mm of movement at the wheel, the shock travels less than 1mm. On an NB MX5, movement of 1mm at the wheel is 0.68mm (0.66mm for NA) at the front shock and 0.77mm at the rear shock
‘Preload’: An unhelpful myth. Preload is based on the idea that the spring is pre-compressed and exerting an initial force that needs to be overcome (this state only occurs when the wheel has lifted off the ground). The idea is that the static weight of the car must offset this force before the shock can start compressing. This is unhelpful because: 1. it focuses on weight rather than length measurements which makes it useless for adjustments, and 2. it has no influence on the performance of linear springs once the car is on the ground
Resetting the car: lift the whole car up on a hoist and rest it back on the floor. If you don’t have access to a hoist then gently roll the car back and forth a few times. Do not press down over each corner, you will dent the panels, ask me how I know
Take note: record/note a measurement
TESTING CLEARANCES AND SETTING UP A MINIMUM HEIGHT:
Do everything on smooth, level ground. Start by disconnecting front and rear sway bars so that the shocks can move freely. Do the following on a front and rear corner:
1. Disassemble a coilover and reinstall it with the spring and bump stop removed
2. Measure shock stroke
Measure shock stroke: measure the difference between the length of the shock shaft at full extension and full compression. Jack up the control arm to bottom out the shock.
*** Take note: this is your shock stroke ***
3. Check clearance and find minimum height
Install your wheel and jack up the control arm until either the shock bottoms out or the wheel contacts something on the car. At the front, turn the wheel to observe any interference
Two piece coilovers: Adjust the shock body length by threading the shock into or out of the lower cup so that the shock bottoms out right before the wheel contacts anything
One piece coilovers: Add bump stop shims so that the shock bottoms out right before the wheel contacts anything
*** Take note: this is your absolute minimum functional shock body length ***
Lock the lower cup in place with the locking collar
4. Match the setup across each axle
Remove the coilover and reinstall it with the spring and bump stop. Set the spring perches so that the spring is barely seated i.e. ‘zero preload’
Measure and adjust the other coilover across each axle to match
ADJUSTING SHOCK TRAVEL AND HEIGHT:
Now for the fun part, setting up bump & droop travel and the height of the car
1. Determine target bump & droop travel
If you are unsure of exactly how much bump and droop travel you want, 2/3 bump and 1/3 droop is a good place to start
Target droop = 1/3 * stroke; Target bump = 2/3 * stroke
Choosing another target/fine tuning: It doesn't matter how much bump and droop travel you have if you're not bottoming out or topping out. The shock behaves the same whether you have 20mm, 30mm or 40mm of bump or droop travel.
Add bump travel if the shock bottoms out
Add droop travel if the shock tops out
By attaching a small cable tie around the shock piston under the bump stop, you can find out if you've hit the bump stop by seeing if the cable tie has buried itself into the bump stop.
2. Take baseline measurements at front and rear
Reset the car
With the car on the ground, measure from the bottom of the wheel to the fender. Raise the car and repeat the same measurement
*** Take note of the difference between these two measurements ***
3. Adjust shock travel
Measurement above * motion ratio = actual droop travel
Stroke - actual droop travel = actual bump travel
Actual droop travel - target droop travel = adjustment needed to be made
If actual droop > target droop, raise spring perches by the difference. Knowing the thread pitch of your shock body helps. e.g. one full turn on BC coilovers is 2mm and the spring perches have 8 notches
If actual droop < target droop, consider helper springs to lower the shock at static height while keeping the spring seated at all times. Otherwise, leave it as is if it's acceptable to you
Replicate adjustment across each axle
Explanation of why spring perches are used for height adjustment and why 'preload' is a myth:
At static height, the shock is somewhere between the limits of its travel. Imagine a shock that has 100mm of stroke, has a 10kg/mm linear spring installed, and 500kg of force/weight on the corner resulting in 50mm of spring compression. The shock therefore has 50mm of bump travel and 50mm of droop travel.
Raising the spring perch by 5mm extends the overall shock length by moving the shaft 5mm out from the body. The weight/force on the shock remains 500kg and so the spring stays compressed by 50mm but the shock now has 55mm of bump travel and 45mm of droop travel. As the spring perch is raised: the shock is extended, bump travel is gained, droop travel is lost, and spring compression remains unchanged.
At full droop, the shock has no more room to extend via the piston and so the 5mm upward adjustment on the spring perches results in 5mm of spring compression. Importantly, while 'preload' and weight/force on the shock push the piston in opposite directions, they move the spring in the same direction. At full droop, there is an equivalent of 50kg of upward force on the shock. With 500kg on the corner: the first 50kg of force offsets the 'preload'; the remaining 450kg of force compresses the spring by an additional 45mm to a total of 50mm, and pushes the piston 45mm downwards. Once again, the shock has 55mm of shock travel and 45mm of droop travel. Hopefully this explains why 'preload' has no bearing on coilover performance as long as the wheels stay on the ground.
4. Adjust ride height
Do the following once actual travel = target travel and measure height by the pinch welds
Raise the car to the desired height by unwinding the shock from the lower cup. In this way, the car is raised while maintaining travel settings. Do not exceed the minimum found above if subsequently lowering by the cup after raising it
If the shock is at its minimum functional length, lower the car by the spring perches if you're willing to reduce bump travel and gain droop travel. Lowering by the lower cup beyond the set minimum height means the wheel will contact the car before the shock bottoms out, resulting in potential damage and wasted travel (see above). If the springs become unseated while lowering by the spring perches, consider helper springs as above. If the rear is too tall to lower without sacrificing too much travel, consider extended top hats and redoing the the entire process top to bottom
5. Reconnect sway bars and get a wheel alignment
Now go set up your coilovers properly and enjoy getting the most out of them!
This is a living post. Feel free to comment any corrections and I’ll edit them in
PREFACE:
There’s a big mix of information out online on how to set up coilovers but there's nothing that directly addresses considerations like bump & droop travel, needing to be at street legal height or going even lower than the coilovers will allow out the box
INTRODUCTION:
So you’ve bought and installed a set of two piece coilovers. You expected better and thought you should feel like you're on top of the world yet somehow your fully sick coilovers ride like absolute rubbish. Maybe you do feel like you're on top of the world and you simply don't know better
Are you going ejecto seato instead of gliding over big bumps? Are you experiencing hopping or sudden snap oversteer when cornering hard? Is your car constantly bouncing? Chances are you haven’t set up your coilovers properly and you're hitting bump stops. This write up goes through how to get the most out of your el cheapo coilovers (yes this includes whatever fancy expensive name brand you have as long as it's in two pieces). This is a long one for the geeks so buckle up and enjoy the read
GLOSSARY:
Two piece coilovers: coilovers with a threaded shock body and lower cup
Spring perches: the locking collars right under the spring
Stroke: total shock travel from end to end
Bump travel: how much the shock can compress from static height. Complementary to droop travel
Droop travel: how much the shock can extend from static height. Complementary to bump travel
Bottoming out: compressing the shock until it has no more bump travel
Motion ratio: ratio of how much the shock travels compared to the wheel. On a double wishbone suspension equipped car, the coilover attaches to a spot along the control arm and not to the wheel itself. Because of this, for every 1mm of movement at the wheel, the shock travels less than 1mm. On an NB MX5, movement of 1mm at the wheel is 0.68mm (0.66mm for NA) at the front shock and 0.77mm at the rear shock
‘Preload’: An unhelpful myth. Preload is based on the idea that the spring is pre-compressed and exerting an initial force that needs to be overcome (this state only occurs when the wheel has lifted off the ground). The idea is that the static weight of the car must offset this force before the shock can start compressing. This is unhelpful because: 1. it focuses on weight rather than length measurements which makes it useless for adjustments, and 2. it has no influence on the performance of linear springs once the car is on the ground
Resetting the car: lift the whole car up on a hoist and rest it back on the floor. If you don’t have access to a hoist then gently roll the car back and forth a few times. Do not press down over each corner, you will dent the panels, ask me how I know
Take note: record/note a measurement
TESTING CLEARANCES AND SETTING UP A MINIMUM HEIGHT:
Do everything on smooth, level ground. Start by disconnecting front and rear sway bars so that the shocks can move freely. Do the following on a front and rear corner:
1. Disassemble a coilover and reinstall it with the spring and bump stop removed
2. Measure shock stroke
Measure shock stroke: measure the difference between the length of the shock shaft at full extension and full compression. Jack up the control arm to bottom out the shock.
*** Take note: this is your shock stroke ***
3. Check clearance and find minimum height
Install your wheel and jack up the control arm until either the shock bottoms out or the wheel contacts something on the car. At the front, turn the wheel to observe any interference
Two piece coilovers: Adjust the shock body length by threading the shock into or out of the lower cup so that the shock bottoms out right before the wheel contacts anything
One piece coilovers: Add bump stop shims so that the shock bottoms out right before the wheel contacts anything
*** Take note: this is your absolute minimum functional shock body length ***
Lock the lower cup in place with the locking collar
4. Match the setup across each axle
Remove the coilover and reinstall it with the spring and bump stop. Set the spring perches so that the spring is barely seated i.e. ‘zero preload’
Measure and adjust the other coilover across each axle to match
ADJUSTING SHOCK TRAVEL AND HEIGHT:
Now for the fun part, setting up bump & droop travel and the height of the car
1. Determine target bump & droop travel
If you are unsure of exactly how much bump and droop travel you want, 2/3 bump and 1/3 droop is a good place to start
Target droop = 1/3 * stroke; Target bump = 2/3 * stroke
Choosing another target/fine tuning: It doesn't matter how much bump and droop travel you have if you're not bottoming out or topping out. The shock behaves the same whether you have 20mm, 30mm or 40mm of bump or droop travel.
Add bump travel if the shock bottoms out
Add droop travel if the shock tops out
By attaching a small cable tie around the shock piston under the bump stop, you can find out if you've hit the bump stop by seeing if the cable tie has buried itself into the bump stop.
2. Take baseline measurements at front and rear
Reset the car
With the car on the ground, measure from the bottom of the wheel to the fender. Raise the car and repeat the same measurement
*** Take note of the difference between these two measurements ***
3. Adjust shock travel
Measurement above * motion ratio = actual droop travel
Stroke - actual droop travel = actual bump travel
Actual droop travel - target droop travel = adjustment needed to be made
If actual droop > target droop, raise spring perches by the difference. Knowing the thread pitch of your shock body helps. e.g. one full turn on BC coilovers is 2mm and the spring perches have 8 notches
If actual droop < target droop, consider helper springs to lower the shock at static height while keeping the spring seated at all times. Otherwise, leave it as is if it's acceptable to you
Replicate adjustment across each axle
Explanation of why spring perches are used for height adjustment and why 'preload' is a myth:
At static height, the shock is somewhere between the limits of its travel. Imagine a shock that has 100mm of stroke, has a 10kg/mm linear spring installed, and 500kg of force/weight on the corner resulting in 50mm of spring compression. The shock therefore has 50mm of bump travel and 50mm of droop travel.
Raising the spring perch by 5mm extends the overall shock length by moving the shaft 5mm out from the body. The weight/force on the shock remains 500kg and so the spring stays compressed by 50mm but the shock now has 55mm of bump travel and 45mm of droop travel. As the spring perch is raised: the shock is extended, bump travel is gained, droop travel is lost, and spring compression remains unchanged.
At full droop, the shock has no more room to extend via the piston and so the 5mm upward adjustment on the spring perches results in 5mm of spring compression. Importantly, while 'preload' and weight/force on the shock push the piston in opposite directions, they move the spring in the same direction. At full droop, there is an equivalent of 50kg of upward force on the shock. With 500kg on the corner: the first 50kg of force offsets the 'preload'; the remaining 450kg of force compresses the spring by an additional 45mm to a total of 50mm, and pushes the piston 45mm downwards. Once again, the shock has 55mm of shock travel and 45mm of droop travel. Hopefully this explains why 'preload' has no bearing on coilover performance as long as the wheels stay on the ground.
4. Adjust ride height
Do the following once actual travel = target travel and measure height by the pinch welds
Raise the car to the desired height by unwinding the shock from the lower cup. In this way, the car is raised while maintaining travel settings. Do not exceed the minimum found above if subsequently lowering by the cup after raising it
If the shock is at its minimum functional length, lower the car by the spring perches if you're willing to reduce bump travel and gain droop travel. Lowering by the lower cup beyond the set minimum height means the wheel will contact the car before the shock bottoms out, resulting in potential damage and wasted travel (see above). If the springs become unseated while lowering by the spring perches, consider helper springs as above. If the rear is too tall to lower without sacrificing too much travel, consider extended top hats and redoing the the entire process top to bottom
5. Reconnect sway bars and get a wheel alignment
Now go set up your coilovers properly and enjoy getting the most out of them!
This is a living post. Feel free to comment any corrections and I’ll edit them in