Why Modifying your Suspension often isn't worth it (Road Cars)

[SV-3]

Interesting YouTube observations from 'Engineering Explained' :

https://allcarvideos.net/2021/04/14/why-modifying-your-suspension-often-isnt-worth-it-road-cars/

(Apologies in advance for the excessive MX-5 use)

[Petrus]

Well, the common ground suspension advice of most died in the wool over here is best refresh stock with an unless very specific use/goals.
Just lowering with stiffer springs is mostly frowned upon for real world roadholding.
So, a nice and welcome confirmation. Thanks for sharing.

[Dev]

I agree with him up to a point and I have followed his videos for years.

It depends on the car and it depends on the kind of suspension and tires  particularly the dampers.

Where I agree is in feel where the car is more fun to drive on the street only if  the damping  does a better job than the stock suspension.  If you add race coil overs then its worse for the street however if you buy a researched set that was made for the street it can be a world of difference over the stock the way it balances the car out.
Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned. There are compromises with every set up.  There is a major difference between stock and something like KW suspension in terms of control and grip particularly camber change that it will definitely have better lateral grip up to a point and then you need better tires to exploit the full benefits.
 
 The story here is primarily about tires. You need to match the tires to the suspension, failing to do so can actually make it worse.   

For a lot of owners that buy the cheap stuff thinking its the same it can be much worse than stock so in order to do it right you need to spend otherwise don't mess with your suspension. The best researched set is what came with the car.

 

[Iain]

The best researched set is what came with the car.

 

This 👆

I even track mine with stock suspension and it goes pretty darn well.

[Petrus]

Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned.

My by far largest disagreement is with his discarding aero.
He even ´explains´ why aero is such a fertile field; the average steer car has aero for fuel consumption and no attention to lift. As such it is a field where humongous gains can be made in traction. And yes, from relatively low speeds. Yes at a price of top speed but hey, who drives at over 100 mph on the public road versus the instances of quick cornering.

[1979scotte]

Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned.

who drives at over 100 mph on the public road versus the instances of quick cornering.

Everyone in the Highlands I've been told.

[Roj]

Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned.

who drives at over 100 mph on the public road versus the instances of quick cornering.

Everyone in the Highlands I've been told.

Not everyone and not all of the time... we need to slow down for the damn motorhomes!

[Roj]

Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned.

My by far largest disagreement is with his discarding aero.
He even ´explains´ why aero is such a fertile field; the average steer car has aero for fuel consumption and no attention to lift. As such it is a field where humongous gains can be made in traction. And yes, from relatively low speeds. Yes at a price of top speed but hey, who drives at over 100 mph on the public road versus the instances of quick cornering.

Have a look at Kyle Engineers on YouTube. AMG F1 aero engineer. Doesn't think much of 'adding' aero on road cars.

[1979scotte]

Where I disagree is there is so much variation in the set up especially for the street that you might not see a net positive result if its not properly tuned.

My by far largest disagreement is with his discarding aero.
He even ´explains´ why aero is such a fertile field; the average steer car has aero for fuel consumption and no attention to lift. As such it is a field where humongous gains can be made in traction. And yes, from relatively low speeds. Yes at a price of top speed but hey, who drives at over 100 mph on the public road versus the instances of quick cornering.

Have a look at Kyle Engineers on YouTube. AMG F1 aero engineer. Doesn't think much of 'adding' aero on road cars.

Yes but you're forgetting something vital Petrus is always right.

[Alex Knight]

Surely this topic is nuanced, and as such there is no 'correct' answer.

I suspect I am more tolerant than most on this forum of a reduction in primary ride quality, in favour of tighter body control that comes with a firmer setup.

What one person wants from a setup is different to another.

At the end of the day, we all want slightly different things from our cars, and different products are available to tailor our cars to those individual targets, no?

[Petrus]

Have a look at Kyle Engineers on YouTube. AMG F1 aero engineer. Doesn't think much of 'adding' aero on road cars.

Do listen to him.
He explains ´road cars´ as being heavy 1800 kgs and up.
He álso explains that is doés make sense with a 1000 kg car. He even gives simulated and measred results quíte worth the effort.
Mine is 880 kg...

But, by all means don´t.
Even cyclist do...

[Petrus]

Yes but you're forgetting something vital Petrus is always right.

She made you sleep on the couch again?!

Beejeezus man; life is too short and too much fun to have such a hang up.

Go enjoy spinning wheels of the V6.

[1979scotte]

Yes but you're forgetting something vital Petrus is always right.

She made you sleep on the couch again?!

That's never happened in almost 15 years.

[Dev]

Surely this topic is nuanced, and as such there is no 'correct' answer.

I suspect I am more tolerant than most on this forum of a reduction in primary ride quality, in favour of tighter body control that comes with a firmer setup.

What one person wants from a setup is different to another.

At the end of the day, we all want slightly different things from our cars, and different products are available to tailor our cars to those individual targets, no?

The tires generally make the biggest difference in terms of grip. I wish the presenter would have explained the obvious to put things into perspective of why we modify the suspension.  Unfortunately most people on car forums modify their suspension for the wrong reasons by copying other peoples bad set ups. The reason for this is cost and that is why its not really a personal thing, its often misguided. Because they made a poor decision they will double down on their bad choices and recommend them to others and deal with the negatives until they go back to stock or something else.

Lets look at two situations without getting into damping quality.

Car A. factory car with better tires. When worked to the limits it will cause the car to dive and the suspension to wallow but it will have more grip than factory tires up to a point as it runs out of suspension travel creating positive camber as the suspension is compressed and a loss of grip.

Car B. Stiffer suspension with better tires. Because it resists suspension travel better than factory suspension it resists camber change and therefore will have a higher level of grip than the factory suspension on better tires.
Car B. Stiffer suspension with factory tires. Because it has stiffer suspension it will take the factory tires to the edge of traction faster and it will be like driving on a razors edge where you will loose grip early and quickly. This is not ideal and dangerous for the street especially for emergency maneuvers. Therefore tires should be matched to the suspension. 

  When you stiffen the car you have now compromised the comfort but there are ways to offset this problem for an ideal compromise so you have grip and reasonable comfort. 
  Better dampers with enough travel and most of all enough shock oil for good bump travel. The springs on this suspension shouldn't be too stiff and the shock researched for the dynamics of the car. The use of larger swaybars so there resistance to camber change instead of stiffer springs because it only come into play when the suspension is leaning but while driving in a straight line has very little  effect on the bump travel.

A lot of people modify their suspension or tires for the sake of doing it without a clear understanding or distinction between a track set up and one made for the street believing that stiffer is better. It may feel better but it will reduce the handling even if it increases the grip. A reasonably good driver in a factory car will be faster because the suspension is balanced and easier to drive.

[Petrus]

The use of larger swaybars so there resistance to camber change instead of stiffer springs because it only come into play when the suspension is leaning but while driving in a straight line has very little  effect on the bump travel.

Quite.
The bars need to be REAL thick diameter to have effect on the spring rate.
On our MR2 a bit stiffer ARBs is a neat way to get the car more horizontal through corners without changing the OEM geometry or changing the suspension rate.
It is also a simple and easy tool to change the understeer/oversteer balance of the car to your personal style and preference: They do not increase the max overall traction availeble. They cán be set up so the tyres lóóse less by keeping the load on them more evenly spread.

[Dev]

The use of larger swaybars so there resistance to camber change instead of stiffer springs because it only come into play when the suspension is leaning but while driving in a straight line has very little  effect on the bump travel.

Quite.
The bars need to be REAL thick diameter to have effect on the spring rate.
On our MR2 a bit stiffer ARBs is a neat way to get the car more horizontal through corners without changing the OEM geometry or changing the suspension rate.
It is also a simple and easy tool to change the understeer/oversteer balance of the car to your personal style and preference: They do not increase the max overall traction availeble. They cán be set up so the tyres lóóse less by keeping the load on them more evenly spread.

 Static spring rate yes but not dynamic if the car is driven on normal roads where independent suspension matters in regards to stability.
 Sway bars do help with corse correction of the cars behavior at the limits but like anything else you do to your suspension there is a penalty or a negative consequence making the handling worse or exchanging forgiveness for more exploitable grip with sticky tires. If you are not a good driver you can fail and can easily cause an accident.This is why forgiveness is a very important thing with a road car driven near its limits and for accident avoidance in a panic situation.
 
  This is why it is foolish to think that when you upgrade suspension you have increased the safety margin for any kind of quick accident avoidance scenario when what you want is an easy to handle car for your skill level. Often times handling and grip is used in the same sentence but they are very different things.

[Petrus]

I beg to differ, somewhat, about sway bars Dev.
They do not affect the max total grip of the four tyres at all. That is the load and the friction coëfficient.
They cán however deminish the loss of max grip through body roll. Thus in effect giving the driver extra margin.
This is all about the tyre load sensitivity.
If the sway bars can deminish the load increase on the outside front wheel, then the loss of max traction is also smaller.
Quite fun too btw, the theory of sway bar tuning, change relative ratings and see what happens with load shift and traction.

[Dev]

I beg to differ, somewhat, about sway bars Dev.
They do not affect the max total grip of the four tyres at all. That is the load and the friction coëfficient.
They cán however deminish the loss of max grip through body roll. Thus in effect giving the driver extra margin.
This is all about the tyre load sensitivity.
If the sway bars can deminish the load increase on the outside front wheel, then the loss of max traction is also smaller.
Quite fun too btw, the theory of sway bar tuning, change relative ratings and see what happens with load shift and traction.

I never said they cause a max total level of grip of all four tires if tires are a constant. Actually they can do just the opposite on one end vs another when you use a larger sway bar without taking tires into consideration. This is why you need to match the tires to the suspension.  In addition to this roads are not all smooth like a race track, they have imperfections and road irregularities. That is why swaybars can reduce the independent nature of the suspension as a consequence and create a problem with the damping and stability of the car on real roads.
 It is a double edged sword and that is why the whole suspension needs to be considered on how it works together then just changing holes on the sway bar to adjust for behavior at the limit.   
 
 

[Dev]

There is a way to resolve this negative effect with swaybars and independent suspension. That is with active swaybars that are disconnected from both sides and work independently. I have driven a BMW that has the system and it works brilliantly but the motor is prone to break down and worse it adds unnecessary weight and that is why it works best in luxury cars. 

 

[Petrus]

In addition to this roads are not all smooth like a race track, they have imperfections and road irregularities. That is why swaybars can reduce the independent nature of the suspension as a consequence and create a problem with the damping and stability of the car on real roads.

Yes, theoretically they oppose independent wheel movement but again you need réal hefty ones to make a diference in the limited wheel travel of the MR2 on the road.
To add a perspective; even the LandRover Defender grew sway bars Dev...