The Anti squat percentage is one of the most talked about numbers in drag racing suspension tuning. It is a useful number, but it is not magic.
- ✅ Anti squat can help you make educated changes from a known starting point. It can help you understand how a 4 link bar change moved the instant center. It can help show whether a change raised or lowered the instant center, shortened or lengthened it, or moved the car toward more or less separation force.
- ✅ But anti squat is only as good as the measurements used to calculate it. It is just a number whereby you can make educated changes. If the car is plotted wrong, the anti squat number is wrong.
- ✅ That is why I do not like looking at anti squat by itself. I want to know the whole picture of the chassis! It is a complete recipe of all the parts working together with the desired chassis reaction.
Anti squat is a tool, not the whole setup
Anti squat percentage is based on where the instant center is located compared to the anti squat line.
That sounds simple, but the anti squat line depends on accurate vehicle measurements. If the wheelbase, center of gravity height, center of gravity length, tire radius, ride height, or bar pickup points are wrong, the anti squat percentage can be misleading.
That does not mean anti squat is useless. It means you need to use it correctly.
Anti squat is best used as a comparison tool on the same car, from a known baseline, using the same measurement process.
For example:
Why anti squat numbers can be misleading
The anti squat number can look very precise, but that does not mean it is perfectly accurate. Small measurement errors can change the plotted instant center and anti squat percentage.
Common issues include:
Instant center length and height still matter
Anti squat is useful, but I always want to look at instant center length and instant center height too.
✅ Instant center length tells you how far forward the projected bar intersection is from the rear axle.
✅ Instant center height tells you how high that intersection is off the ground.
Those two numbers matter because they help describe how the suspension is applying force into the chassis.
A car can have the same anti squat percentage with a different instant center length and height.
That is why I want all three numbers:
Rear spread is a great number to discuss
Rear spread is the vertical distance between the upper and lower bar mounting points at the rear housing bracket.
This is a great number to include when discussing a 4 link setup because it helps describe the geometry at the rear of the car.
Rear spread affects how much separation force and housing rotation influence the chassis. It also helps explain how sensitive a bar change may be.
If two cars both say they have the same anti squat percentage, but one has a very different rear spread, they may not behave the same.
That is why rear spread is worth knowing. It gives more context than anti squat alone.
Front spread is not useful by itself
✅ Front spread is the vertical distance between the upper and lower bar mounting points at the front chassis bracket.
Front spread matters, but it is often misunderstood.
✅ The front spread number by itself is not enough.
Because front spread is affected by the length of the 4 link bars.
A car with shorter bars can have a very different front spread relationship than a car with longer bars, even if the rear spread looks similar.
To understand front spread, you also need to know:
Rear spread is a good number to include in setup discussions. Front spread is only useful when it is discussed with bar lengths, rear spread, and bar angles.
Bar length changes front spread behavior
The length of the 4 link bars changes how the front spread affects the instant center.
✅ Shorter bars create a different rate of change than longer bars.
✅ Longer bars can make the same front bracket spread behave differently because the projected intersection point moves differently as the bar angles change.
That is why you cannot just say:
My front spread is X inches. Is that good?
That question is missing too much information.
The better question is:
My rear spread is X inches, my upper and lower bars are X inches long, my current bar angles are X, my instant center is X inches long and X inches high, and my anti squat is X percent. Does this direction make sense for what the car is doing?
That gives enough context to have a real tuning discussion.
Bar angles help explain the change
Bar angles are another important part of the conversation.
If you move one bar hole, you are not just changing anti squat. You are also changing:
This is why a bar change is not finished when the bolt goes into a different hole.
✅ After a 4 link change, you need to put the car back to race condition and recheck the basics.
✅ That includes ride height, pinion angle, rear end square, scale numbers, shock travel, and anti roll bar condition.
Otherwise, you may think the bar change did something when the real change was ride height, pinion angle, preload, or anti roll bar bind.
✅ Check out the Checklist before and after a bar change!
Use anti squat from a known baseline
The best way to use anti squat is from a known starting point.
Before making a change, follow my CHECKLIST!
Do not chase someone else’s anti squat number
One of the biggest mistakes racers make is chasing someone else’s anti squat number.
✅ A car running 120 percent anti squat does not mean your car needs 120 percent.
✅ A radial car, big tire slick car, small tire no prep car, bracket car, and Pro Mod can all want different things.
✅ Even two similar cars may want different setups because of:
It is not a universal target.
A better way to evaluate a 4 link change
When evaluating a 4 link change, I like to look at the complete picture.
Do not just ask:
What is the anti squat?
Ask:
✅ Checkout my Suspension Questionnaire!
The bottom line
Anti squat is a great tool when used correctly.
It helps you understand how a 4 link change moved the instant center compared to the anti squat line. It is very useful for comparing changes from a known baseline.
But anti squat depends heavily on accurate measurements. If the car is plotted wrong, the anti squat number can be wrong.
That is why I also want to know instant center length, instant center height, rear spread, front spread, bar length, and bar angles.
Rear spread is a great number to include in setup discussions.
Front spread can be useful, but not by itself. Front spread is meaningless without bar lengths, rear spread, and bar angles.
Anti squat percentage is based on where the instant center is located compared to the anti squat line.
That sounds simple, but the anti squat line depends on accurate vehicle measurements. If the wheelbase, center of gravity height, center of gravity length, tire radius, ride height, or bar pickup points are wrong, the anti squat percentage can be misleading.
That does not mean anti squat is useless. It means you need to use it correctly.
Anti squat is best used as a comparison tool on the same car, from a known baseline, using the same measurement process.
For example:
- If your car was at 85 percent anti squat and worked well
- Then you moved bars and it went to 105 percent anti squat
- You now have a useful comparison
- You can look at whether the car hit the tire harder, separated faster, carried the front differently, or became more sensitive
Why anti squat numbers can be misleading
The anti squat number can look very precise, but that does not mean it is perfectly accurate. Small measurement errors can change the plotted instant center and anti squat percentage.
Common issues include:
- Ride height was not set correctly before measuring
- Driver weight was not in the car
- Bar hole centers were estimated instead of measured
- Wheelbase was not confirmed
- Center of gravity height was guessed
- Center of gravity length was guessed
- The car was not sitting at race condition
- The rear housing was not square in the car
Instant center length and height still matter
Anti squat is useful, but I always want to look at instant center length and instant center height too.
✅ Instant center length tells you how far forward the projected bar intersection is from the rear axle.
✅ Instant center height tells you how high that intersection is off the ground.
Those two numbers matter because they help describe how the suspension is applying force into the chassis.
- A shorter instant center generally applies force quicker
- A longer instant center generally applies force more gradually
- A higher instant center usually increases the anti squat effect
- A lower instant center usually decreases the anti squat effect
A car can have the same anti squat percentage with a different instant center length and height.
That is why I want all three numbers:
- Anti squat percentage
- Instant center length
- Instant center height
Rear spread is a great number to discuss
Rear spread is the vertical distance between the upper and lower bar mounting points at the rear housing bracket.
This is a great number to include when discussing a 4 link setup because it helps describe the geometry at the rear of the car.
Rear spread affects how much separation force and housing rotation influence the chassis. It also helps explain how sensitive a bar change may be.
If two cars both say they have the same anti squat percentage, but one has a very different rear spread, they may not behave the same.
That is why rear spread is worth knowing. It gives more context than anti squat alone.
Front spread is not useful by itself
✅ Front spread is the vertical distance between the upper and lower bar mounting points at the front chassis bracket.
Front spread matters, but it is often misunderstood.
✅ The front spread number by itself is not enough.
Because front spread is affected by the length of the 4 link bars.
A car with shorter bars can have a very different front spread relationship than a car with longer bars, even if the rear spread looks similar.
To understand front spread, you also need to know:
- Rear spread
- Upper bar length
- Lower bar length
- Upper bar angle
- Lower bar angle
- Instant center length - nice to have
- Instant center height - nice to have
- Anti squat percentage - nice to have
Rear spread is a good number to include in setup discussions. Front spread is only useful when it is discussed with bar lengths, rear spread, and bar angles.
Bar length changes front spread behavior
The length of the 4 link bars changes how the front spread affects the instant center.
✅ Shorter bars create a different rate of change than longer bars.
✅ Longer bars can make the same front bracket spread behave differently because the projected intersection point moves differently as the bar angles change.
That is why you cannot just say:
My front spread is X inches. Is that good?
That question is missing too much information.
The better question is:
My rear spread is X inches, my upper and lower bars are X inches long, my current bar angles are X, my instant center is X inches long and X inches high, and my anti squat is X percent. Does this direction make sense for what the car is doing?
That gives enough context to have a real tuning discussion.
Bar angles help explain the change
Bar angles are another important part of the conversation.
If you move one bar hole, you are not just changing anti squat. You are also changing:
- Upper bar angle
- Lower bar angle
- Instant center length
- Instant center height
- Front spread relationship
- Bar separation relationship
- Pinion angle, if bar length is adjusted or not corrected
- Preload or scale numbers, if the car is not reset after the change
This is why a bar change is not finished when the bolt goes into a different hole.
✅ After a 4 link change, you need to put the car back to race condition and recheck the basics.
✅ That includes ride height, pinion angle, rear end square, scale numbers, shock travel, and anti roll bar condition.
Otherwise, you may think the bar change did something when the real change was ride height, pinion angle, preload, or anti roll bar bind.
✅ Check out the Checklist before and after a bar change!
Use anti squat from a known baseline
The best way to use anti squat is from a known starting point.
Before making a change, follow my CHECKLIST!
- ✅ Then make one change.
- ✅ Then measure again.
- ✅ Now you can compare the new setup against the old setup.
Do not chase someone else’s anti squat number
One of the biggest mistakes racers make is chasing someone else’s anti squat number.
✅ A car running 120 percent anti squat does not mean your car needs 120 percent.
✅ A radial car, big tire slick car, small tire no prep car, bracket car, and Pro Mod can all want different things.
✅ Even two similar cars may want different setups because of:
- Power curve
- Tire type
- Track prep
- Weight bias
- Center of gravity height
- Wheelbase
- Rear shock valving
- Front shock travel
- Spring rate
- Anti roll bar setup
- Converter or clutch behavior
- Gear ratio
- Driver style
It is not a universal target.
A better way to evaluate a 4 link change
When evaluating a 4 link change, I like to look at the complete picture.
Do not just ask:
What is the anti squat?
Ask:
- What was the original instant center length?
- What was the original instant center height?
- What was the original anti squat percentage?
- What is the new instant center length?
- What is the new instant center height?
- What is the new anti squat percentage?
- What is the rear spread?
- What is the front spread?
- How long are the upper and lower bars?
- What are the upper and lower bar angles?
- Did the ride height change?
- Did the pinion angle change?
- Did the scale numbers change?
- Was the anti roll bar neutral?
- Did the car separate faster, slower, more, or less?
- Did the front end rise differently?
- Did the 60 foot improve or get worse?
- Did the car drive straighter or move around?
✅ Checkout my Suspension Questionnaire!
The bottom line
Anti squat is a great tool when used correctly.
It helps you understand how a 4 link change moved the instant center compared to the anti squat line. It is very useful for comparing changes from a known baseline.
But anti squat depends heavily on accurate measurements. If the car is plotted wrong, the anti squat number can be wrong.
That is why I also want to know instant center length, instant center height, rear spread, front spread, bar length, and bar angles.
Rear spread is a great number to include in setup discussions.
Front spread can be useful, but not by itself. Front spread is meaningless without bar lengths, rear spread, and bar angles.
- ✅ Use anti squat to understand the direction of your change.
- ✅ Use the full 4 link geometry to understand why the car reacted the way it did.
Want help with your 4-link, ladder bar, shock settings, or overall suspension baseline?
✅ Start with my Suspension Tuning Questionnaire, then check out Remote and In-Shop tuning.
✅ Start with my Suspension Tuning Questionnaire, then check out Remote and In-Shop tuning.