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USING GEOMETRY TO GO FASTER!
Once you have you done your first track day or autocross, you likely have had to get a custom performance alignment to mitigate tire wear and improve handling. Camber, caster, toe - all important adjustments, but the most crucial adjustment you can make (if the car and class allows it) is CAMBER.
When you get serious in motorsports events where you drive your car aggressively on track or in an autocross, some things will become clear. In a modern car, once you start pushing through corners at higher speeds than Mr Magoo, you will likely end up with one of three conditions.
UNDERSTEER (COMMON!)
Understeer is when the tires reach the limit in a corner, and the front loses grip before the rear tires. This is the most common form of handling, and how all OEM manufacturers deliver their cars, to some degree. Why is that? Two reasons - mostly that lawyers hold sway over engineers, as the natural tendency in a car that loses traction is to apply the brakes. That usually leads to a weight transfer to the front, which increases the front tire contact patch, grip (usually) returns, and a driver will hopefully avoid a spin.
But manly men hate understeer, right? Well in reality most cars at a top level are designed with a tough of understeer, just enough to be safe. This is the easiest condition to deal with - it takes fewer "brain cycles" to keep the car at the limit.
OVERSTEER (RARE)
The days of a factory suspensions and alignments that will oversteer (the rear tires lose grip first, which leads to spins) are long over. But in rainy / icy conditions all bets are off, and this can sneak up on you. No racer chasing lap times wants a handling setup that naturally oversteers, unless you are a Drifter. Than that is the setup goal!
NEUTRAL HANDLING (NIRVANA!)
This is the Goldilocks setup, one where the front and rear tires work in balance, and neither end of the car will start to slide before the other. The much vaunted "four wheel drift", which a skilled driver can sustain with some brain power and experience. Most OEM cars will not even have this level of balance, but a handful get pretty close - some Porsches, the 86, maybe a Miata.
In a perfect world both autocross and track drivers will strive for this elusive neutral handling. And with the right suspension changes, roll control, tire selection, and alignment setup most cars can get to this. But some cannot, and end up with some degree of understeer, especially those that are both front weight biased (FWD cars) and those that have a lot of power driving only through the front wheels (FWD). In those cases we will still try all of the tricks in the books to "dial out" that understeer.
STRUT VS OTHER SUSPENSION
The number one cause of the most common form of poor handling and excessive front tire wear (understeer) is adding camber. Sure, there are some other adjustments you can make, but this is by far the biggest fix of that symptom. A handful of sports / sporty cars use a double A-arm front suspensions (or some variation on that), but it is increasingly rare. The C5 Corvette below, like all generations of this chassis, does NOT use a strut suspension.
(https://photos.smugmug.com/Racing-Ev...SC04269-X2.jpg)
Yet as time marches forward, many if not most modern cars DO use a MacPherson Strut front suspension design. We're going to focus on strut cars in this article, because that's my specialty. I've been making camber plates for two decades now and know how they work better than your average bear.
Having MacPherson Struts up front does have its advantages, even if the "techno geeks" talk down this type of front suspension. Compared to other forms of modern suspension, a strut setup: takes up less room, which can allow for more front wheel room; it can be easily adjusted for camber and caster (with aftermarket top mounts) compared to shimming or eccentrics on a Double A-Arm; and they are less costly to produce by the car makers (the real reason they are so prevalent).
REDUCE UNDERSTEER WITH NEGATIVE CAMBER
Now that we have justified our "lower tech" strut front end, let's get to making it better by adding negative camber! There are four ways to add negative camber on MacPherson strut car.
Not all cars can alter all four of these factors, and depending on the racing class rules and factory design, your car might not be allowed to have ANY camber adjustments. It doesn't seem logical to limit camber adjustment in Street classes like SCCA Solo does - but that is the current limit for some cars and classes. Luckily, SCCA Time Trial came out of the dark ages last year and they DO allow camber adjustment for even Street class cars, which saves racers money in needless, premature tire wear. A set of adjustable camber plates can often pay for itself in over the course of just one track day's worth of tire wear savings.
ADJUSTMENT 1 - MOVING THE TOP OF THE STRUT
This is the most common method of camber adjustment - sliding the top of the strut inboard with some form of slotted holes in the tower or within the aftermarket camber plates.
Some factory strut top mounts have slotted holes in the strut tower, and you can maybe eek out maybe a degree of adjustment on these rare setups. Most cars have no factory upper adjustment for camber (or caster) at all, so an solution is required. Camber plates can often work with the OEM diameter springs and not raise or lower the ride height, which is crucial for "Street" classes which allow this adjustment.
Factory and OEM style lowering springs are usually 70-130mm on the inner diameter, which can often limit camber travel inboard just from "spring girth". But on about 90% of strut based cars with OEM diameter springs, there's still enough room to allow worthwhile travel and camber adjustment. We try to shoot for an adjustment range of 2.5 degrees from the stock top mount setting, but even if you can get 1.5 degrees of movement, that's still useful
Once you move to "coilovers" the spring diameter gets much smaller (2.25", 60mm, or 2.5" ID), which almost always unlocks more camber adjustment range. The 2016 Ford Focus RS shown above has relatively large OEM springs inside a small tower. We couldn't slide the top of the strut inboard even 1/4" before the spring hit the tower with those. After we switched to modest Bilstein PSS coilover struts and 60mm ID springs, with camber plates we could then get a full 3/4" of camber travel.
This let us dial in 4.0 deg of static front camber (also at a lowered ride height). That was a game changer for this formerly softly sprung, poorly damped, very camber limited AWD car. The RS went from HEAVY understeer in stock form to only a mild understeer, and dropped 5.7 seconds a lap on a 90 second road course on the exact same tires, with just these suspension changes. Tire wear radically improved as well. With the wider and stickier tires shown above the RS dropped another 2.5 seconds, with no alterations to power or aero.
On some cars, when the geometry of the tower and opening plays nice, we can also afford the room to adjust caster via the aftermarket top mounts. Adding positive caster helps (to a point) with the dynamic camber as you turn the wheels. If your car can get to around +6 to +8 degrees of positive caster, the tires are going to be even happier. We're not going to overemphasize caster here, as the static camber setting is much more crucial.
ADJUSTMENT 2 - TILTING THE STRUT RELATIVE TO THE SPINDLE
This is the second most effective method for altering camber - "kicking" the strut relative to the front spindle and hub. This works on roughly half of all strut equipped car models, if the strut bodies have brackets to attach to the spindle with bolts. If this is what your car has, continue on below. Sadly many German automakers cars have fixated on a clamping style attachment at the spindle (most VWs + BMWs from 1998-up) and do not have any tricks to "kick the strut" for camber.
In the S650 chassis Mustang Darkhorse example shown above, the aftermarket MCS strut housing has a significant slot in the upper bracket hole. Even utilizing the "full sized" factory bolts, you can use the slotted hole to add 0.5 to up to 2 deg of additional negative camber travel. Now these particular Ford strut bolts are splined, so you have to install them loosely to be able to dial in the camber at this spot - once tightened enough to engage the splines, they have to be hammered out of the spindle to allow it to slide. But you don't want these bolts coming loose on track, so the splines are welcomed.
Then there are "crash bolts", which can do the same strut kick, just to smaller degree. Often these are shaped with a "cam" that can be dialed in, other times they are simply smaller diameter bolts than stock. Sometimes the spindle is factory designed (often even as authorized repair or "TSB") to have a larger than necessary upper strut mounting hole, like the 2023 Subaru BRZ front spindle above. The factory upper 16mm hole uses a bolt has a massive shoulder, but replace it with another M14 sized bolt like the bottom hole uses and you just gained a 1/2 degree of additional negative camber.
This is an easy way to gain camber if you cannot get enough at the top with the camber plate (or if the class doesn't allow such a device). Our stock 2023 BRZ shown above went from -1 deg stock to -3.5 deg front camber with camber plates and the M14 upper bolt trick, with stock springs and no ride height changes. This was worth 1.3 seconds a lap on a 90 second track, on the same tires.
There's no free lunch and "kicking the strut" comes with the potential loss of inboard wheel room, at least with very wide fitments using the same offset wheel as before. Kicking the strut often brings the need for a wheel spacer, or wheels with a different offset, but if you can balance this wheel-to-strut relationship correctly this slotted hole adjustment + camber plates can make for two reliable camber adjustments. The slotted bracket trick just takes a bit of time to dial in right, but it needs to be done during the initial suspension install. Normally you dial in the "Gross" camber adjustment on a slotted aftermarket strut housing first, then fine tune the camber setting at the top mount where it is much easier to adjust.
continued below
Once you have you done your first track day or autocross, you likely have had to get a custom performance alignment to mitigate tire wear and improve handling. Camber, caster, toe - all important adjustments, but the most crucial adjustment you can make (if the car and class allows it) is CAMBER.
When you get serious in motorsports events where you drive your car aggressively on track or in an autocross, some things will become clear. In a modern car, once you start pushing through corners at higher speeds than Mr Magoo, you will likely end up with one of three conditions.
UNDERSTEER (COMMON!)
Understeer is when the tires reach the limit in a corner, and the front loses grip before the rear tires. This is the most common form of handling, and how all OEM manufacturers deliver their cars, to some degree. Why is that? Two reasons - mostly that lawyers hold sway over engineers, as the natural tendency in a car that loses traction is to apply the brakes. That usually leads to a weight transfer to the front, which increases the front tire contact patch, grip (usually) returns, and a driver will hopefully avoid a spin.
But manly men hate understeer, right? Well in reality most cars at a top level are designed with a tough of understeer, just enough to be safe. This is the easiest condition to deal with - it takes fewer "brain cycles" to keep the car at the limit.
OVERSTEER (RARE)
The days of a factory suspensions and alignments that will oversteer (the rear tires lose grip first, which leads to spins) are long over. But in rainy / icy conditions all bets are off, and this can sneak up on you. No racer chasing lap times wants a handling setup that naturally oversteers, unless you are a Drifter. Than that is the setup goal!
NEUTRAL HANDLING (NIRVANA!)
This is the Goldilocks setup, one where the front and rear tires work in balance, and neither end of the car will start to slide before the other. The much vaunted "four wheel drift", which a skilled driver can sustain with some brain power and experience. Most OEM cars will not even have this level of balance, but a handful get pretty close - some Porsches, the 86, maybe a Miata.
In a perfect world both autocross and track drivers will strive for this elusive neutral handling. And with the right suspension changes, roll control, tire selection, and alignment setup most cars can get to this. But some cannot, and end up with some degree of understeer, especially those that are both front weight biased (FWD cars) and those that have a lot of power driving only through the front wheels (FWD). In those cases we will still try all of the tricks in the books to "dial out" that understeer.
STRUT VS OTHER SUSPENSION
The number one cause of the most common form of poor handling and excessive front tire wear (understeer) is adding camber. Sure, there are some other adjustments you can make, but this is by far the biggest fix of that symptom. A handful of sports / sporty cars use a double A-arm front suspensions (or some variation on that), but it is increasingly rare. The C5 Corvette below, like all generations of this chassis, does NOT use a strut suspension.
(https://photos.smugmug.com/Racing-Ev...SC04269-X2.jpg)
Yet as time marches forward, many if not most modern cars DO use a MacPherson Strut front suspension design. We're going to focus on strut cars in this article, because that's my specialty. I've been making camber plates for two decades now and know how they work better than your average bear.
Having MacPherson Struts up front does have its advantages, even if the "techno geeks" talk down this type of front suspension. Compared to other forms of modern suspension, a strut setup: takes up less room, which can allow for more front wheel room; it can be easily adjusted for camber and caster (with aftermarket top mounts) compared to shimming or eccentrics on a Double A-Arm; and they are less costly to produce by the car makers (the real reason they are so prevalent).
REDUCE UNDERSTEER WITH NEGATIVE CAMBER
Now that we have justified our "lower tech" strut front end, let's get to making it better by adding negative camber! There are four ways to add negative camber on MacPherson strut car.
Not all cars can alter all four of these factors, and depending on the racing class rules and factory design, your car might not be allowed to have ANY camber adjustments. It doesn't seem logical to limit camber adjustment in Street classes like SCCA Solo does - but that is the current limit for some cars and classes. Luckily, SCCA Time Trial came out of the dark ages last year and they DO allow camber adjustment for even Street class cars, which saves racers money in needless, premature tire wear. A set of adjustable camber plates can often pay for itself in over the course of just one track day's worth of tire wear savings.
ADJUSTMENT 1 - MOVING THE TOP OF THE STRUT
This is the most common method of camber adjustment - sliding the top of the strut inboard with some form of slotted holes in the tower or within the aftermarket camber plates.
Some factory strut top mounts have slotted holes in the strut tower, and you can maybe eek out maybe a degree of adjustment on these rare setups. Most cars have no factory upper adjustment for camber (or caster) at all, so an solution is required. Camber plates can often work with the OEM diameter springs and not raise or lower the ride height, which is crucial for "Street" classes which allow this adjustment.
Factory and OEM style lowering springs are usually 70-130mm on the inner diameter, which can often limit camber travel inboard just from "spring girth". But on about 90% of strut based cars with OEM diameter springs, there's still enough room to allow worthwhile travel and camber adjustment. We try to shoot for an adjustment range of 2.5 degrees from the stock top mount setting, but even if you can get 1.5 degrees of movement, that's still useful
Once you move to "coilovers" the spring diameter gets much smaller (2.25", 60mm, or 2.5" ID), which almost always unlocks more camber adjustment range. The 2016 Ford Focus RS shown above has relatively large OEM springs inside a small tower. We couldn't slide the top of the strut inboard even 1/4" before the spring hit the tower with those. After we switched to modest Bilstein PSS coilover struts and 60mm ID springs, with camber plates we could then get a full 3/4" of camber travel.
This let us dial in 4.0 deg of static front camber (also at a lowered ride height). That was a game changer for this formerly softly sprung, poorly damped, very camber limited AWD car. The RS went from HEAVY understeer in stock form to only a mild understeer, and dropped 5.7 seconds a lap on a 90 second road course on the exact same tires, with just these suspension changes. Tire wear radically improved as well. With the wider and stickier tires shown above the RS dropped another 2.5 seconds, with no alterations to power or aero.
On some cars, when the geometry of the tower and opening plays nice, we can also afford the room to adjust caster via the aftermarket top mounts. Adding positive caster helps (to a point) with the dynamic camber as you turn the wheels. If your car can get to around +6 to +8 degrees of positive caster, the tires are going to be even happier. We're not going to overemphasize caster here, as the static camber setting is much more crucial.
ADJUSTMENT 2 - TILTING THE STRUT RELATIVE TO THE SPINDLE
This is the second most effective method for altering camber - "kicking" the strut relative to the front spindle and hub. This works on roughly half of all strut equipped car models, if the strut bodies have brackets to attach to the spindle with bolts. If this is what your car has, continue on below. Sadly many German automakers cars have fixated on a clamping style attachment at the spindle (most VWs + BMWs from 1998-up) and do not have any tricks to "kick the strut" for camber.
In the S650 chassis Mustang Darkhorse example shown above, the aftermarket MCS strut housing has a significant slot in the upper bracket hole. Even utilizing the "full sized" factory bolts, you can use the slotted hole to add 0.5 to up to 2 deg of additional negative camber travel. Now these particular Ford strut bolts are splined, so you have to install them loosely to be able to dial in the camber at this spot - once tightened enough to engage the splines, they have to be hammered out of the spindle to allow it to slide. But you don't want these bolts coming loose on track, so the splines are welcomed.
Then there are "crash bolts", which can do the same strut kick, just to smaller degree. Often these are shaped with a "cam" that can be dialed in, other times they are simply smaller diameter bolts than stock. Sometimes the spindle is factory designed (often even as authorized repair or "TSB") to have a larger than necessary upper strut mounting hole, like the 2023 Subaru BRZ front spindle above. The factory upper 16mm hole uses a bolt has a massive shoulder, but replace it with another M14 sized bolt like the bottom hole uses and you just gained a 1/2 degree of additional negative camber.
This is an easy way to gain camber if you cannot get enough at the top with the camber plate (or if the class doesn't allow such a device). Our stock 2023 BRZ shown above went from -1 deg stock to -3.5 deg front camber with camber plates and the M14 upper bolt trick, with stock springs and no ride height changes. This was worth 1.3 seconds a lap on a 90 second track, on the same tires.
There's no free lunch and "kicking the strut" comes with the potential loss of inboard wheel room, at least with very wide fitments using the same offset wheel as before. Kicking the strut often brings the need for a wheel spacer, or wheels with a different offset, but if you can balance this wheel-to-strut relationship correctly this slotted hole adjustment + camber plates can make for two reliable camber adjustments. The slotted bracket trick just takes a bit of time to dial in right, but it needs to be done during the initial suspension install. Normally you dial in the "Gross" camber adjustment on a slotted aftermarket strut housing first, then fine tune the camber setting at the top mount where it is much easier to adjust.
continued below
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