This article does a decent job of summarizing how suspension design and vehicle weight affect ride quality and handling characteristics. While not an academic paper or a textbook, it does correctly explain those details that are otherwise 500 pages long.
https://www.rqriley.com/suspensn.htm
Here is an interesting perspective from this article: that weight reduction has significant implications on the ride quality and handling of a vehicle. Now, one of the common complaints about new Lexus vehicles (and TNGA vehicles in general) is their excessive weight compared to the size. What's more, Toyota/Lexus engineers intentionally design their new vehicles to be heavy: they are not incompetent at weight reduction, the Prius Prime (and to some extent the Camry Hybrid) is the best example.
From the article, vehicle weight affects ride quality and handling in following ways:
>>A heavier vehicle has a lower payload-to-vehicle weight ratio. This means the addition of extra occupants has lower impact on the ride frequency and damping coefficient. A lighter car, on the other hand, has a narrower "sweet spot"; more occupants will cause the ride to be too soft while too few will make it too hard.
>>A lighter car is more vulnerable to longitudinal disturbances, which humans are most sensitive too. As a result acceleration and deceleration can cause a 'jerkier' ride. This is exacerbated when there's luggage in the trunk causing the vehicle to pitch up.
>>Going back to payload-to-vehicle mass ratio. Payload will cause a vehicle to sit lower because it compresses the springs; this will cause the center of gravity to shift downwards. A heavier vehicle lowers less than a lighter one. Therefore the heavier vehicle can be engineered to have a lower center of gravity. This is exactly what TNGA aims for.
The Toyota 86, a super light sports car, has a very low center of gravity. But this is at the cost of having very stiff suspension. The natural ride frequency of the 86 is over 2 Hz (like a race car), and prolonged driving will cause pain and even injuries. The similarly light Miata opted for softer suspensions (causing a significant roll) to make the car more practical to drive.
>>As modern cars keep getting bigger tyres and wheels, more powerful brakes, and fancier suspension items, unsprung weight also keeps growing. A lower sprung-to-unsprung weight ratio makes the ride harsher when there are bumps and potholes. Adding weight to the body (more sprung weight) keeps the tires more firmly attached to the road since the springs have more compressive force. In this case the car not only has a smoother ride, but also has more grip.
Lighter cars will always perform better on well-paved tracks, but on actual roads (especially pothole-ridden roads in USA) they may have worse mechanical grip and arguably harsher ride.
I think this is a well-thought argument for Lexus/Toyota's intentional engineering choice when it comes to vehicle weight, not to mention the body rigidity and safety bonuses. Do I think it's the right way to go? Not necessarily, because as electrification kicks in, weight reduction will again be very important since batteries and hydrogen tanks are heavy. But it's a good argument regardless, backed by real world experiences.
I think forum member @spwolf mentioned multiple times that the C-HR, a 1,500 kg subcompact SUV (which is 100-150 kg overweight compared to competion), has the best in-class ride quality and handling and by a wide margin. Recent Lexus sports vehicles also behave very well on tracks and roads alike, despite their weight disadvantage. A more extreme example would be the R35 GT-R, which made competitors wonder for a decade how such a heavy beast just kept beating their stripped-out feather-weight track machines.
https://www.rqriley.com/suspensn.htm
Here is an interesting perspective from this article: that weight reduction has significant implications on the ride quality and handling of a vehicle. Now, one of the common complaints about new Lexus vehicles (and TNGA vehicles in general) is their excessive weight compared to the size. What's more, Toyota/Lexus engineers intentionally design their new vehicles to be heavy: they are not incompetent at weight reduction, the Prius Prime (and to some extent the Camry Hybrid) is the best example.
From the article, vehicle weight affects ride quality and handling in following ways:
>>A heavier vehicle has a lower payload-to-vehicle weight ratio. This means the addition of extra occupants has lower impact on the ride frequency and damping coefficient. A lighter car, on the other hand, has a narrower "sweet spot"; more occupants will cause the ride to be too soft while too few will make it too hard.
>>A lighter car is more vulnerable to longitudinal disturbances, which humans are most sensitive too. As a result acceleration and deceleration can cause a 'jerkier' ride. This is exacerbated when there's luggage in the trunk causing the vehicle to pitch up.
>>Going back to payload-to-vehicle mass ratio. Payload will cause a vehicle to sit lower because it compresses the springs; this will cause the center of gravity to shift downwards. A heavier vehicle lowers less than a lighter one. Therefore the heavier vehicle can be engineered to have a lower center of gravity. This is exactly what TNGA aims for.
The Toyota 86, a super light sports car, has a very low center of gravity. But this is at the cost of having very stiff suspension. The natural ride frequency of the 86 is over 2 Hz (like a race car), and prolonged driving will cause pain and even injuries. The similarly light Miata opted for softer suspensions (causing a significant roll) to make the car more practical to drive.
>>As modern cars keep getting bigger tyres and wheels, more powerful brakes, and fancier suspension items, unsprung weight also keeps growing. A lower sprung-to-unsprung weight ratio makes the ride harsher when there are bumps and potholes. Adding weight to the body (more sprung weight) keeps the tires more firmly attached to the road since the springs have more compressive force. In this case the car not only has a smoother ride, but also has more grip.
Lighter cars will always perform better on well-paved tracks, but on actual roads (especially pothole-ridden roads in USA) they may have worse mechanical grip and arguably harsher ride.
I think this is a well-thought argument for Lexus/Toyota's intentional engineering choice when it comes to vehicle weight, not to mention the body rigidity and safety bonuses. Do I think it's the right way to go? Not necessarily, because as electrification kicks in, weight reduction will again be very important since batteries and hydrogen tanks are heavy. But it's a good argument regardless, backed by real world experiences.
I think forum member @spwolf mentioned multiple times that the C-HR, a 1,500 kg subcompact SUV (which is 100-150 kg overweight compared to competion), has the best in-class ride quality and handling and by a wide margin. Recent Lexus sports vehicles also behave very well on tracks and roads alike, despite their weight disadvantage. A more extreme example would be the R35 GT-R, which made competitors wonder for a decade how such a heavy beast just kept beating their stripped-out feather-weight track machines.
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